draft-ietf-pint-pre-implement-02.txt   rfc2458.txt 
PINT Working Group H. Lu (Editor) Netowrk Working Group H. Lu
Internet Draft M. Krishnaswamy Request for Comments: 2458 Editor
Lucent Technologies Category: Informational M. Krishnaswamy
L. Conroy Lucent Technologies
Roke Manor Research L. Conroy
S. Bellovin Roke Manor Research
F. Burg S. Bellovin
A. DeSimone F. Burg
K. T. Tewani A. DeSimone
AT&T Labs K. Tewani
P. Davidson AT&T Labs
Nortel P. Davidson
H. Schulzrinne Nortel
Columbia University H. Schulzrinne
K. Vishwanathan Columbia University
Isochrome K. Vishwanathan
Isochrome
Expires in Six Months August 1998 November 1998
Toward the PSTN/Internet Inter-Networking Toward the PSTN/Internet Inter-Networking
--Pre-PINT Implementations --Pre-PINT Implementations
<draft-IETF-pint-pre-implement-02.txt>
Status of this Memo Status of this Memo
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This memo provides information for the Internet community. This memo Copyright (C) The Internet Society (1998). All Rights Reserved.
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Abstract Abstract
This document contains the information relevant to the development of This document contains the information relevant to the development of
the inter-networking interfaces underway in the Public Switched the inter-networking interfaces underway in the Public Switched
Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working
Toward PSTN/Internet Inter-Networking May 1998
Group. It addresses technologies, architectures, and several (but by Group. It addresses technologies, architectures, and several (but by
no means all) existing pre-PINT implementations of the arrangements no means all) existing pre-PINT implementations of the arrangements
through which Internet applications can request and enrich PSTN through which Internet applications can request and enrich PSTN
telecommunications services. The common denominator of the enriched telecommunications services. The common denominator of the enriched
services (a.k.a. PINT services) is that they combine the Internet and services (a.k.a. PINT services) is that they combine the Internet and
PSTN services in such a way that the Internet is used for non-voice PSTN services in such a way that the Internet is used for non-voice
interactions, while the voice (and fax) are carried entirely over the interactions, while the voice (and fax) are carried entirely over the
PSTN. One key observation is that the pre-PINT implementations, being PSTN. One key observation is that the pre-PINT implementations, being
developed independently, do not inter-operate. It is a task of the developed independently, do not inter-operate. It is a task of the
PINT Working Group to define the inter-networking interfaces that PINT Working Group to define the inter-networking interfaces that
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services. services.
Table of Contents Table of Contents
1. Introduction ....................................... 3 1. Introduction ....................................... 3
2. Terminology ....................................... 3 2. Terminology ....................................... 3
3. PINT Services ....................................... 4 3. PINT Services ....................................... 4
4. Architectural Overview ............................... 5 4. Architectural Overview ............................... 5
4.1 Public Switched Telephone Network ............... 5 4.1 Public Switched Telephone Network ............... 5
4.2 Pre-PINT Systems ............................... 9 4.2 Pre-PINT Systems ............................... 9
5. IN-Based Solutions ............................... 18 5. IN-Based Solutions ............................... 20
5.1 The Lucent System ............................... 18 5.1 The Lucent System ............................... 20
5.1.1 Roles of the Web Server, Service Node, and SMS ....... 19 5.1.1 Roles of the Web Server, Service Node, and SMS ....... 20
5.1.2 A Click-to-Dial-Back Service Scenario ............... 20 5.1.2 A Click-to-Dial-Back Service Scenario ............... 21
5.1.3 Web Server-Service Node Interface ............... 21 5.1.3 Web Server-Service Node Interface ............... 22
5.1.4 Web Server-SMS Interface and SNMP MIB ............... 23 5.1.4 Web Server-SMS Interface and SNMP MIB ............... 24
5.1.5 Security Considerations ........................... 24 5.1.5 Security Considerations ........................... 26
5.2 Siemens Web Call Center ........................... 25 5.2 Siemens Web Call Center ........................... 27
5.2.1 Service Description ............................... 25 5.2.1 Service Description ............................... 27
5.2.2 Implementation ................................... 27 5.2.2 Implementation ................................... 29
5.2.3 Derived Requirements/Lessons ..................... 32 5.2.3 Derived Requirements/Lessons ..................... 35
6. Alternative Solutions ............................... 34 6. Alternative Solutions ............................... 37
6.1 The AT&T System ..................................... 34 6.1 The AT&T System ..................................... 37
6.1.1 High Level Architecture ............................ 34 6.1.1 High Level Architecture ............................ 38
6.1.2 IP Client to CallBroker Interface .................. 36 6.1.2 IP Client to CallBroker Interface .................. 39
6.1.3 Protocol ........................................... 36 6.1.3 Protocol ........................................... 40
6.1.4 APIs Exposed to the IP Client ..................... 37 6.1.4 APIs Exposed to the IP Client ..................... 41
6.1.5 Voice-Bridge Control API ........................ 37 6.1.5 Voice-Bridge Control API ........................ 41
6.2 Simple Computer Telephony Protocol ............... 37 6.2 Simple Computer Telephony Protocol ............... 41
6.2.1 Overview ........................................... 37 6.2.1 Overview ........................................... 41
6.2.2 How SCTP Fits in with the Reference PINT Services .. 38 6.2.2 How SCTP Fits in with the Reference PINT Services .. 42
7. Session Initiation Protocol--An Emerging Standard .. 39 7. Session Initiation Protocol--An Emerging Standard .. 43
7.1 Overview ....................................... 39 7.1 Overview ....................................... 43
7.2 SIP Protocol ....................................... 40 7.2 SIP Protocol ....................................... 44
7.3 SIP Entities ....................................... 41 7.3 SIP Entities ....................................... 45
7.4 Providing Call Control Functionality ............... 41 7.4 Providing Call Control Functionality ............... 46
8. Overall Security Considerations ..................... 43 8. Overall Security Considerations ..................... 47
9. Conclusion ....................................... 44 9. Conclusion ....................................... 48
10. Acknowledgments ................................... 44 10. Acknowledgments ................................... 48
11. Appendix ....................................... 44 11. Appendix ....................................... 49
11.1 PSTN/IN 101 ....................................... 44 11.1 PSTN/IN 101 ....................................... 49
11.1.1 Public Switched Telephone Network ............... 44 11.1.1 Public Switched Telephone Network ............... 49
11.1.2 Intelligent Network ............................... 46 11.1.2 Intelligent Network ............................... 51
11.2 Call Center Features ............................. 54
Toward PSTN/Internet Inter-Networking May 1998 12. References ....................................... 56
Authors' Addresses ......................................... 57
11.2 Call Center Features ............................. 49 Full Copyright Statement .................................. 60
12. References ....................................... 50
1. Introduction 1. Introduction
This document contains the information relevant to the development of This document contains the information relevant to the development of
the inter-networking interfaces underway in the Public Switched the inter-networking interfaces underway in the Public Switched
Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working Telephone Network (PSTN)/Internet Inter-Networking (PINT) Working
Group. It addresses technologies, architectures, and several (but by Group. It addresses technologies, architectures, and several (but by
no means all) existing pre-PINT implementations of the arrangements no means all) existing pre-PINT implementations of the arrangements
through which Internet applications can request and enrich PSTN through which Internet applications can request and enrich PSTN
telecommunications services. The common denominator of the enriched telecommunications services. The common denominator of the enriched
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right to perform certain activities. right to perform certain activities.
PINT Gateway -- the PSTN node that interacts with the Internet. PINT Gateway -- the PSTN node that interacts with the Internet.
User or Customer -- the person who asks for a service request to be User or Customer -- the person who asks for a service request to be
issued. In the context of PINT Services, this person will use an issued. In the context of PINT Services, this person will use an
Internet host to make his or her request. The term "user" is also Internet host to make his or her request. The term "user" is also
used to describe a host originating the PINT service request on used to describe a host originating the PINT service request on
behalf of this person. behalf of this person.
Toward PSTN/Internet Inter-Networking May 1998
3. PINT Services 3. PINT Services
This document addresses four services initially identified by the This document addresses four services initially identified by the
PINT Working Group and presently supported by pre-PINT PINT Working Group and presently supported by pre-PINT
implementations. These services are: click-to-dial-back, click-to- implementations. These services are: click-to-dial-back, click-to-
fax, click-to-fax-back and voice-access-to-content. fax, click-to-fax-back and voice-access-to-content.
Note that the word "click" should not be taken literally. It is Note that the word "click" should not be taken literally. It is
rather used to point out that initiation of the related services rather used to point out that initiation of the related services
takes place on the Internet, where point and click are the most takes place on the Internet, where point and click are the most
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PSTN could route the call depending on the time of day, day of week, PSTN could route the call depending on the time of day, day of week,
availability of agents in different locations, and so on. availability of agents in different locations, and so on.
Click-to-Fax Click-to-Fax
With this service, a user at an IP host requests that a fax be sent With this service, a user at an IP host requests that a fax be sent
to a particular fax number. In particular this service is especially to a particular fax number. In particular this service is especially
meaningful when the fax is to be sent to someone who has only a fax meaningful when the fax is to be sent to someone who has only a fax
machine (but no access to the Internet). Consider, as an example, a machine (but no access to the Internet). Consider, as an example, a
service scenario in which a Web user makes a reservation for a hotel service scenario in which a Web user makes a reservation for a hotel
Toward PSTN/Internet Inter-Networking May 1998
room in Beijing from a travel service page containing hotel room in Beijing from a travel service page containing hotel
information of major cities around the world. Suppose a specific information of major cities around the world. Suppose a specific
Beijing hotel chosen by the user does not have Internet connection Beijing hotel chosen by the user does not have Internet connection
but has a fax machine. The user fills out the hotel reservation form but has a fax machine. The user fills out the hotel reservation form
and then clicks a button sending out the form to the travel service and then clicks a button sending out the form to the travel service
provider, which in turn generates a fax request and sends it together provider, which in turn generates a fax request and sends it together
with the hotel reservation form to the PSTN. Upon receiving the with the hotel reservation form to the PSTN. Upon receiving the
request and the associated data, the PSTN translates the data into request and the associated data, the PSTN translates the data into
the proper facsimile format and delivers it to the Beijing hotel as the proper facsimile format and delivers it to the Beijing hotel as
specified in the fax request. specified in the fax request.
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With this service, a user at an IP host requests that certain With this service, a user at an IP host requests that certain
information on the Internet be accessed (and delivered) in an audio information on the Internet be accessed (and delivered) in an audio
form over the PSTN, using the telephone as an informational form over the PSTN, using the telephone as an informational
appliance. One application of this service is to provide Web access appliance. One application of this service is to provide Web access
to the blind. (This may require special resources--available in the to the blind. (This may require special resources--available in the
PSTN--to convert the Web data into speech.) PSTN--to convert the Web data into speech.)
4. Architectural Overview 4. Architectural Overview
4.1 Public Switched Telephone Network 4.1 Public Switched Telephone Network
From an application perspective, Internet nodes are interconnected From an application perspective, Internet nodes are interconnected
directly, as shown in Figure 1. When two machines are to communicate, directly, as shown in Figure 1. When two machines are to communicate,
they will have the address of the destination end system, and will they will have the address of the destination end system, and will
send network level datagrams, assuming that the underlying send network level datagrams, assuming that the underlying
infrastructure will deliver them as required. infrastructure will deliver them as required.
_____ _____
__ _____/ \_____ __ _____/ \_____
[__] / \ [__] / \
[----]-.-.-.-. Internet .-. [----]-.-.-.-. Internet .-.
\_____ _______/ | \_____ _______/ |
__ \__./ __ . __ \__./ __ .
[__] / [__] | [__] / [__] |
[----]-. [----]-. [----]-. [----]-.
Key: .-.-. Internet Access Link
Figure 1 Key: .-.-. Internet Access Link
Toward PSTN/Internet Inter-Networking May 1998 Figure 1
Where all nodes are on the same (broadcast) network, there is no need Where all nodes are on the same (broadcast) network, there is no need
for intervening routers; they can send and deliver packets to one for intervening routers; they can send and deliver packets to one
another directly. The Internet nodes are responsible for their own another directly. The Internet nodes are responsible for their own
communications requests, and act as peers in the communication communications requests, and act as peers in the communication
sessions that result. sessions that result.
This contrasts with the situation in the PSTN. There, the end systems This contrasts with the situation in the PSTN. There, the end systems
are configured as shown in Figure 2. The end systems tend to be are configured as shown in Figure 2. The end systems tend to be
specific to a particular type of traffic, so that, for example, the specific to a particular type of traffic, so that, for example, the
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__ \ [-!-] [-!-] ! ()/\() __ \ [-!-] [-!-] ! ()/\()
\ \ \__[CO ]=========[CO ]==\\ ! ___/__\ \ \ \__[CO ]=========[CO ]==\\ ! ___/__\
[Fax]________[---] [---] \\ [-!-] / __ [Fax]________[---] [---] \\ [-!-] / __
\\=======[CO ]____/ \ \ \\=======[CO ]____/ \ \
[---]________[Fax] [---]________[Fax]
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
CO Central Office (Telephone Exchange) CO Central Office (Telephone Exchange)
Figure 2 Figure 2
Communications between the terminals are all "circuit switched", so a Communications between the terminals are all "circuit switched", so a
dedicated synchronous data path (or circuit) needs to be placed dedicated synchronous data path (or circuit) needs to be placed
between the end terminals for carrying all communications. Arranging between the end terminals for carrying all communications. Arranging
for such a circuit to be made or removed (cleared) is the for such a circuit to be made or removed (cleared) is the
responsibility of the Central Offices in the network. A user makes a responsibility of the Central Offices in the network. A user makes a
request via his or her terminal, and this request is passed on to the request via his or her terminal, and this request is passed on to the
"local" Central Office. The relationship between the terminals and "local" Central Office. The relationship between the terminals and
the local Central Offices to which they are connected is strictly the local Central Offices to which they are connected is strictly
Client/Server. Client/Server.
skipping to change at page 7, line 4 skipping to change at page 7, line 27
the above figure) and is used to carry the data traffic generated by the above figure) and is used to carry the data traffic generated by
the terminals. The other connection acts as part of a separate the terminals. The other connection acts as part of a separate
network (and is shown as a dotted line in the above figure). This is network (and is shown as a dotted line in the above figure). This is
the signaling network, and is used by the Central Offices to request the signaling network, and is used by the Central Offices to request
a connection to be made between themselves and the destination of the a connection to be made between themselves and the destination of the
required circuit. This will be carried across the trunk link to the required circuit. This will be carried across the trunk link to the
"next" Central Office in the path. The path, once in place through "next" Central Office in the path. The path, once in place through
the PSTN, always takes the same route. This contrasts with the the PSTN, always takes the same route. This contrasts with the
Internet, where the underlying datagram nature of the infrastructure Internet, where the underlying datagram nature of the infrastructure
means that data packets are carried over different routes, depending means that data packets are carried over different routes, depending
Toward PSTN/Internet Inter-Networking May 1998
on the combined traffic flows through the network at the time. on the combined traffic flows through the network at the time.
The call set up process can be viewed as having two parts: one in The call set up process can be viewed as having two parts: one in
which a request for connection is made, and the other in which the which a request for connection is made, and the other in which the
circuit is made across the PSTN and call data flows between the circuit is made across the PSTN and call data flows between the
communicating parties. This is shown in the next pair of figures (3a communicating parties. This is shown in the next pair of figures (3a
and 3b). and 3b).
/--\ /--\
() () () ()
--____ --____
/++\ \ /++\ \
/----\ \ /----\ \
A \ [-!-] A \ [-!-]
\->[CO ] \->[CO ]
[---] [---]
Time = 13:55 Time = 13:55
Figure 3a Figure 3a
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
CO Central Office (Telephone Exchange) CO Central Office (Telephone Exchange)
/--\ /--\
() () () ()
-- ................................. -- .................................
/ \<--- ^ ! ! /--\ / \<--- ^ ! ! /--\
/----\ \ ! v ! () () /----\ \ ! v ! () ()
A' \ [-!-] [-!-] ! -- A' \ [-!-] [-!-] ! --
\__[CO ]=========[CO ]==\\ v ->-/ \ \__[CO ]=========[CO ]==\\ v ->-/ \
[---] [---] \\ [-!-] / /----\ [---] [---] \\ [-!-] / /----\
\\=======[CO ]____/ B' \\=======[CO ]____/ B'
Time = 14:00 [---] Time = 14:00 [---]
Figure 3b Figure 3b
Figure 3 shows a particular kind of service that can be provided; Figure 3 shows a particular kind of service that can be provided;
call booking. With this service, a request is sent for a connection call booking. With this service, a request is sent for a connection
to be made between the A and B telephones at a specified time. The to be made between the A and B telephones at a specified time. The
telephone is then replaced (the request phase is terminated). At the telephone is then replaced (the request phase is terminated). At the
specified time, the CO will make a connection across the network in specified time, the CO will make a connection across the network in
the normal way, but will, first, ring the "local" or A' telephone to the normal way, but will, first, ring the "local" or A' telephone to
inform the user that his or her call is now about to be made. inform the user that his or her call is now about to be made.
For more complex services, the requesting telephone is often For more complex services, the requesting telephone is often
connected via its "local" CO to a Service Node (SN), where the user connected via its "local" CO to a Service Node (SN), where the user
can be played prompts and can specify the parameters of his or her can be played prompts and can specify the parameters of his or her
request in a more flexible manner. This is shown below, in Figures request in a more flexible manner. This is shown below, in Figures
Toward PSTN/Internet Inter-Networking May 1998
4a and 4b. For more details of the operation of the Service Node (and 4a and 4b. For more details of the operation of the Service Node (and
other Intelligent Network units), see the Appendix. other Intelligent Network units), see the Appendix.
When the SN is involved in the request and in the call setup process, When the SN is involved in the request and in the call setup process,
it appears, to the CO, to be another PSTN terminal. As such, the it appears, to the CO, to be another PSTN terminal. As such, the
initial request is routed to the Service Node, which, as an end initial request is routed to the Service Node, which, as an end
system, then makes two independent calls "out" to A' and B'. system, then makes two independent calls "out" to A' and B'.
/--\ [---] /--\ [---]
() () [SN ] () () [SN ]
--___ [|--] --___ [|--]
/++\ \ | /++\ \ |
/----\ \ | /----\ \ |
\ | \ |
A \ [|-!] A \ [|-!]
\->[CO ] \->[CO ]
[---] [---]
Time = 13:55 Time = 13:55
Figure 4a Figure 4a
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
CO Central Office (Telephone Exchange) CO Central Office (Telephone Exchange)
SN Service Node SN Service Node
/--\ [---] /--\ [---]
() () [SN ] () () [SN ]
-- [|--] /--\ -- [|--] /--\
/ \<-- | ............................... () () / \<-- | ............................... () ()
/----\ \ | ^ ! ! -- /----\ \ | ^ ! ! --
\ | / v v / \ \ | / v v / \
A' \ [|-!] [-!-] [-!-] ->-/----\ A' \ [|-!] [-!-] [-!-] ->-/----\
\--[CO ] [CO ] [CO ] / \--[CO ] [CO ] [CO ] /
[---] [---] [---]___/ B' [---] [---] [---]___/ B'
Time = 14:00 Time = 14:00
Figure 4b Figure 4b
Note that in both cases as shown in Figures 3 and 4 a similar service Note that in both cases as shown in Figures 3 and 4 a similar service
can be provided in which the B' telephone is replaced by an can be provided in which the B' telephone is replaced by an
Intelligent Peripheral (or an Special Resource Functional entity Intelligent Peripheral (or an Special Resource Functional entity
within a Service Node), playing an announcement. This allows a "wake within a Service Node), playing an announcement. This allows a "wake
up" call to be requested, with the Intelligent Peripheral or Service up" call to be requested, with the Intelligent Peripheral or Service
Node Special Resource playing a suitable message to telephone A' at Node Special Resource playing a suitable message to telephone A' at
the specified time. Again, for more details of the operation of the the specified time. Again, for more details of the operation of the
Special Resources (and other Intelligent Network units), see the Special Resources (and other Intelligent Network units), see the
Appendix. Appendix.
Toward PSTN/Internet Inter-Networking May 1998 4.2 Pre-PINT Systems
4.2 Pre-PINT Systems
Although the pre-PINT systems reported here (i.e., those developed by Although the pre-PINT systems reported here (i.e., those developed by
AT&T, Lucent, Siemens and Nortel) vary in the details of their AT&T, Lucent, Siemens and Nortel) vary in the details of their
operation, they exhibit similarities in the architecture. This operation, they exhibit similarities in the architecture. This
section highlights the common features. Specific descriptions of section highlights the common features. Specific descriptions of
these systems will follow. these systems will follow.
All of the systems can be seen as being quite similar to that shown All of the systems can be seen as being quite similar to that shown
in the following diagram. In each case, the service is separated into in the following diagram. In each case, the service is separated into
two parts; one for the request and another for execution of the two parts; one for the request and another for execution of the
service. Figure 5 summarizes the process. service. Figure 5 summarizes the process.
_____ _____
__ _____/ \_____ __ _____/ \_____
[__] / \ [__] / \
[-++-]-.-.>.-. Internet .-.- [-++-]-.-.>.-. Internet .-.-
\_____ _______/ . \_____ _______/ .
\___/ v \___/ v
[----] . [----] .
[PINT]-.- [PINT]-.-
[----] [----]
% %
v v
[---] [---]
[SN ] [SN ]
[|--] [|--]
Figure 5a Figure 5a
Key: CO Central Office (Telephone Exchange) Key: CO Central Office (Telephone Exchange)
SN Service Node SN Service Node
PINT PSTN/Internet Gateway PINT PSTN/Internet Gateway
.-.-. Internet Access Link .-.-. Internet Access Link
%%% Gateway/Service Node Link %%% Gateway/Service Node Link
___ PSTN Access Lines ___ PSTN Access Lines
=== PSTN Trunk Links (inter-CO user data links) === PSTN Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
Toward PSTN/Internet Inter-Networking May 1998
_____ _____
__ _____/ \_____ __ _____/ \_____
[__] / \ [__] / \
[----]-.-.-.-. Internet .-.- [----]-.-.-.-. Internet .-.-
\_____ _______/ . \_____ _______/ .
\___/ | \___/ |
[----] . [----] .
[PINT]-.- [PINT]-.-
[-%--] [-%--]
% %
skipping to change at page 10, line 28 skipping to change at page 10, line 52
/--\ [-%-] /--\ [-%-]
() () [SN ] () () [SN ]
-- [|--] /--\ -- [|--] /--\
/ \<-- | .................... () () / \<-- | .................... () ()
/----\ \ | ^ ! ! -- /----\ \ | ^ ! ! --
\ | / v v / \ \ | / v v / \
A' \ [|-!] [-!-] [-!-] ->-/----\ A' \ [|-!] [-!-] [-!-] ->-/----\
\--[CO ]=======[CO ]======[CO ] / \--[CO ]=======[CO ]======[CO ] /
[---] [---] [---]__/ B' [---] [---] [---]__/ B'
Figure 5b Figure 5b
Comparing Figure 4a with Figure 5a, the differences lie in the way Comparing Figure 4a with Figure 5a, the differences lie in the way
that the information specifying the request is delivered to the that the information specifying the request is delivered to the
Service Node. In the PSTN/IN method shown in the earlier diagram, the Service Node. In the PSTN/IN method shown in the earlier diagram, the
user connects to the SN from the telephone labeled A, with the user connects to the SN from the telephone labeled A, with the
connection being routed via the CO. In the latter case, the request connection being routed via the CO. In the latter case, the request
is delivered from an Internet node, via the PINT gateway, and thence is delivered from an Internet node, via the PINT gateway, and thence
to the Service Node over a "private" link. The effect is identical, to the Service Node over a "private" link. The effect is identical,
in that the request for service is specified (although the actual in that the request for service is specified (although the actual
parameters used to specify the service required may differ somewhat). parameters used to specify the service required may differ somewhat).
skipping to change at page 11, line 4 skipping to change at page 11, line 35
the commands are couched at a "lower level", specifying the call the commands are couched at a "lower level", specifying the call
states required for the intended service connection rather than the states required for the intended service connection rather than the
service identifier and the addresses involved (leaving the service identifier and the addresses involved (leaving the
Intelligent Network components to coordinate the details of the Intelligent Network components to coordinate the details of the
service call on the gateway's behalf). In this way the vocabulary of service call on the gateway's behalf). In this way the vocabulary of
the commands is closer to that used to control Central Offices. The the commands is closer to that used to control Central Offices. The
difference really lies in the language used for the services difference really lies in the language used for the services
specification, and all systems can use the overall architecture specification, and all systems can use the overall architecture
depicted in Figure 5; the only question remains whether the depicted in Figure 5; the only question remains whether the
Intelligent Network components are actually needed in these other Intelligent Network components are actually needed in these other
Toward PSTN/Internet Inter-Networking May 1998
approaches. approaches.
The following diagram (Figure 6) shows the interface architecture The following diagram (Figure 6) shows the interface architecture
involved in providing the kind of service mentioned above. involved in providing the kind of service mentioned above.
Internet __ __ Internet __ __
Server [__] _______ [__] Server [__] _______ [__]
[W3S-]-. ___/ .-.-.-[W3C-] Internet [W3S-]-. ___/ .-.-.-[W3C-] Internet
_________________|/.-.-.-.-. \ Terminal _________________|/.-.-.-.-. \ Terminal
/ .. . \ / .. . \
skipping to change at page 11, line 42 skipping to change at page 12, line 38
[---] [---] \|/ [---] [---] [---] \|/ [---]
/--\ | |____| | /--\ /--\ | |____| | /--\
()/\() | | ()/\() ()/\() | | ()/\()
/--\___| 1 |___/--\ /--\___| 1 |___/--\
Fixed PSTN Terminal [] Fixed PSTN Terminal Fixed PSTN Terminal [] Fixed PSTN Terminal
Mobile Terminal Mobile Terminal
Key: W3S HTTP (Web) Server Key: W3S HTTP (Web) Server
W3C HTTP (Web) Client/Browser W3C HTTP (Web) Client/Browser
CO Central Office (Telephone Exchange) CO Central Office (Telephone Exchange)
MSC Mobile Switching Center (Mobile Network Telephone Exchange) MSC Mobile Switching Center (Mobile Network Telephone
Exchange)
SN Service Node SN Service Node
SSP Service Switching Point SSP Service Switching Point
SCP Service Control Point SCP Service Control Point
SMS Service Management System SMS Service Management System
.-.-. Internet relationship .-.-. Internet relationship
___ PSTN Access relationship ___ PSTN Access relationship
... PSTN "core" signaling relationship ... PSTN "core" signaling relationship
Figure 6 Figure 6
The interfaces are: The interfaces are:
A The interface over which Internet requests for service are delivered A The interface over which Internet requests for service are
to the Service Node delivered to the Service Node
B The interface over which Service Management requests are sent B The interface over which Service Management requests are sent
from the Internet to the Service Management System from the Internet to the Service Management System
C The interface over which the Service Node sends call control
Toward PSTN/Internet Inter-Networking May 1998 requests to a connected Central Office
D The interface over which the Service Management System manages
C The interface over which the Service Node sends call control requests the Service Node
to a connected Central Office E The interface over which Internet requests for service are
D The interface over which the Service Management System manages the delivered to the Service Control Point
Service Node F The interface over which the Service Control Point sends service
E The interface over which Internet requests for service are delivered call control requests to the Mobile Switching Center
to the Service Control Point
F The interface over which the Service Control Point sends service call
control requests to the Mobile Switching Center
G The interface over which the Service Control Point sends service G The interface over which the Service Control Point sends service
control requests to the Service Switching Point control requests to the Service Switching Point
H The interface over which the Service Management System manages the H The interface over which the Service Management System manages
Service Control Point the Service Control Point
I The interface over which the Service Node sends service call control I The interface over which the Service Node sends service call
requests to the Mobile Switching Center control requests to the Mobile Switching Center
In practice, a number of the interfaces have very similar purposes to In practice, a number of the interfaces have very similar purposes to
one another. The means by which these purposes are achieved differ, one another. The means by which these purposes are achieved differ,
in that some of the interfaces (C and I) reflect access arrangements, in that some of the interfaces (C and I) reflect access arrangements,
whilst others (F and G) imply a "core" signaling relationship. whilst others (F and G) imply a "core" signaling relationship.
However, it is possible to categorize them in terms of the "intent" However, it is possible to categorize them in terms of the "intent"
of messages sent across the interfaces. of messages sent across the interfaces.
For example, Interfaces A and E are similar; one of the main aims of For example, Interfaces A and E are similar; one of the main aims of
PINT work is to ensure that they are the same. Similarly, Interfaces PINT work is to ensure that they are the same. Similarly, Interfaces
skipping to change at page 13, line 5 skipping to change at page 14, line 5
Protocols. All of the others use existing protocols in the PSTN/IN. Protocols. All of the others use existing protocols in the PSTN/IN.
Traditionally, these have been codified by different groups, and this Traditionally, these have been codified by different groups, and this
is likely to be the case in the PINT work. is likely to be the case in the PINT work.
The general arrangements for the different systems are shown below The general arrangements for the different systems are shown below
(Figures 7, 8, 9, and 10). They differ in the details of their (Figures 7, 8, 9, and 10). They differ in the details of their
configurations, but the main tasks they perform are very similar, and configurations, but the main tasks they perform are very similar, and
so the overall operation is similar to the generic architecture shown so the overall operation is similar to the generic architecture shown
in Figures 5 and 6. in Figures 5 and 6.
Toward PSTN/Internet Inter-Networking May 1998
Key for following diagrams: Key for following diagrams:
Components: Components:
W3C World Wide Web Client W3C World Wide Web Client
W3S World Wide Web Server W3S World Wide Web Server
WSA Web Server "Back End Program" Interface (CGI or Servlet interface) WSA Web Server "Back End Program" Interface (CGI or Servlet
interface)
Srvlt Servlet "back end" program/objects Srvlt Servlet "back end" program/objects
FS Finger Server FS Finger Server
SCTPC Simple Computer Telephony Protocol Client SCTPC Simple Computer Telephony Protocol Client
SCTPS Simple Computer Telephony Protocol Server SCTPS Simple Computer Telephony Protocol Server
CBC CallBroker Client CBC CallBroker Client
CBS CallBroker Server CBS CallBroker Server
SSTPC Service Support Transport Protocol Client SSTPC Service Support Transport Protocol Client
SSF Service Switching Function SSF Service Switching Function
SCF Service Control Function SCF Service Control Function
SRF Special Resource Function SRF Special Resource Function
CO Central Office/ Public Telephone Exchange CO Central Office/ Public Telephone Exchange
SSP Service Switching Point SSP Service Switching Point
SCP Service Control Point SCP Service Control Point
SR/I.IP Special Resource/ "Internet" Intelligent Peripheral SR/I.IP Special Resource/ "Internet" Intelligent Peripheral
SMS Service Management System SMS Service Management System
INAPAd Intelligent Network Application Part Adaptor INAPAd Intelligent Network Application Part Adaptor
PktFlt Packet Filter (Firewall) PktFlt Packet Filter (Firewall)
SNMPAg Simple Network Management Protocol Agent SNMPAg Simple Network Management Protocol Agent
Protocols: Protocols:
P0 HyperText Transfer Protocol
P1 HTTP Server <-> "Back End Program" internal protocol
P2 CallBroker Client <-> CallBroker Server protocol (AT&T system),
or SCTP Client <-> Server protocol (Nortel system)
P3 PINT User Agent <-> PINT Gateway protocol
P4 Intra-Intelligent Network protocol (e.g., INAP)
P5 Proprietary (INAP-based) Gateway-> I.IP protocol
P6 Finger protocol
P7 Digital Subscriber Signaling 1 protocol
P8 Simple Network Management Protocol
P9 SMS <-> Service Control Point/Service Node protocol
Toward PSTN/Internet Inter-Networking May 1998
_____ _______ _____ P0 HyperText Transfer Protocol
|[W3C]|----(p0)-->| [W3S] |<--(p0)----|[W3C]| P1 HTTP Server <-> "Back End Program" internal protocol
|[---]| | [WSA] | |[FS.]| P2 CallBroker Client <-> CallBroker Server protocol (AT&T system),
|-----| | ! | |[-!-]| or SCTP Client <-> Server protocol (Nortel system)
| (p1) | |--\--| P3 PINT User Agent <-> PINT Gateway protocol
| ! | ^ P4 Intra-Intelligent Network protocol (e.g., INAP)
| ! | (p6) P5 Proprietary (INAP-based) Gateway-> I.IP protocol
| ! | \ P6 Finger protocol
| (p1) | \ P7 Digital Subscriber Signaling 1 protocol
| ! | \ P8 Simple Network Management Protocol
|[Srvlt]| \ P9 SMS <-> Service Control Point/Service Node protocol
|___!___| \ _____ _______ _____
! \ |[W3C]|----(p0)-->| [W3S] |<--(p0)----|[W3C]|
(p3) \ |[---]| | [WSA] | |[FS.]|
Internet ! ! |-----| | ! | |[-!-]|
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.!.+.+.+.+.+.+.+. | (p1) | |--\--|
PSTN/IN _______________!_________________ ____!_____ __________ | ! | ^
|I [PktFlt] I| |[PktFlt]| |[PktFlt]| | ! | (p6)
|N Gateway N| | ! | | ! | | ! | \
|A ___________________________ A| | ! | | ! | | (p1) | \
|P | | P| | ! | |[SNMPAg]| | ! | \
-(p4)-- |A | <-(p4)-> [SCP] <-(p4)-> | A|-(p5)->|[SR/IIP]| | [SMS] | |[Srvlt]| \
\ |d | [-^-] | d| |[------]| | [-^-] | |___!___| \
\ |__| ! |__| |________| |___!____| ! \
\ ! ! (p3) \
[-v-] !-----------------(p9)---------------------! Internet ! !
[SSP] .+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.!.+.+.+.+.+.
[---] PSTN/IN _______________!_________________ ____!_____ __________
___| |______ |I [PktFlt] I| |[PktFlt]| |[PktFlt]|
| | |N Gateway N| | ! | | ! |
| /--\ | /--\ |A ___________________________ A| | ! | | ! |
| ()/\() | ()/\() |P | | P| | ! | |[SNMPAg]|
|__/__\ |____/__\ -(p4)-- |A | <-(p4)-> [SCP] <-(p4)-> | A|-(p5)->|[SR/IIP]| | [SMS] |
\ |d | [-^-] | d| |[------]| | [-^-] |
Figure 7: The Siemens Web Call Center \ |__| ! |__| |________| |___!____|
\ ! !
Toward PSTN/Internet Inter-Networking May 1998 [-v-] !-----------------(p9)-----------------!
[SSP]
_____ _______ [---]
|[W3C]|----(p0)-->| [W3S] | ___| |______
|[---]| | [WSA] | | |
|-----| | ! | | /--\ | /--\
| (p1) | | ()/\() | ()/\()
| ! | |__/__\ |____/__\
| ! |
| ! |
| (p1) |
| ! |
|[SSTPC]|-<--------------------------------------
|___!___| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[-v-] (p7) !-----------------(p9)---------------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 8: The Lucent System Figure 7: The Siemens Web Call Center
Toward PSTN/Internet Inter-Networking May 1998 _____ _______
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
| ! |
| ! |
| (p1) |
| ! |
|[SSTPC]|-<----------------------------------
|___!___| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[-v-] (p7) !-----------------(p9)-----------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
_____ ________ Figure 8: The Lucent System
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
|[WS/CBS]|
|[Adaptr]|
|___!____|
^
(p2)
_____ ___v____
|[CBC]| | [CBS] |
|[---]|<---(p2)-->| [---] |-<-------------------------------------
|-----| |___!____| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[---] (p7) !-----------------(p9)---------------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Figure 9: The AT&T System _____ ________
|[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] |
|-----| | ! |
| (p1) |
| ! |
|[WS/CBS]|
|[Adaptr]|
|___!____|
^
(p2)
_____ ___v____
|[CBC]| | [CBS] |
|[---]|<---(p2)-->| [---] |-<---------------------------------
|-----| |___!____| !
! (p8)
(p3) !
Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+
PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! |
| [SCF Adaptor] | | ! |
| ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____|
| ! !
[---] (p7) !-----------------(p9)-----------------!
[CO.]____|
[---]
___| |_______
| |
| /--\ | /--\
| ()/\() | ()/\()
|__/__\ |____/__\
Toward PSTN/Internet Inter-Networking May 1998 Figure 9: The AT&T System
_____ ________ _____ ________
|[W3C]|----(p0)-->| [W3S] | |[W3C]|----(p0)-->| [W3S] |
|[---]| | [WSA] | |[---]| | [WSA] |
|-----| | ! | |-----| | ! |
| (p1) | | (p1) |
| ! | | ! |
|[WS/ ]| |[WS/ ]|
|[ SCTPS]| |[ SCTPS]|
|[Adaptr]| |[Adaptr]|
|___!____| |___!____|
^ ^
(p2) (p2)
_______ ___v___ _______ ___v___
|[SCTPC]| |[SCTPS]| |[SCTPC]| |[SCTPS]|
|[-----]| <-(p2)--> |[-----]|-<-------------------------------------- |[-----]| <-(p2)--> |[-----]|-<----------------------------------
|-------| |___!___| ! |-------| |___!___| !
! (p8) ! (p8)
(p3) ! (p3) !
Internet ! v Internet ! v
.+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+. .+.+.+.+.+.+.+.+.+.+.+. v .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+. ! .+.+.
PSTN/IN _______________!__________________________________ ____!_____ PSTN/IN _______________!__________________________________ ____!_____
| [PktFlt] Service [PktFlt]| |[PktFlt]| | [PktFlt] Service [PktFlt]| |[PktFlt]|
| ! Node | | ! | | ! Node | | ! |
| [SCF Adaptor] | | ! | | [SCF Adaptor] | | ! |
| ! | |[SNMPAg]| | ! | |[SNMPAg]|
|[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] | |[SSF]<-(p4)->[SCF] <-------(p4)--------> [SRF] | | [SMS] |
|[|--] [-^-] [---] | | [-^-] | |[|--] [-^-] [---] | | [-^-] |
|_|_____________!________________________________| |___!____| |_|_____________!________________________________| |___!____|
| ! ! | ! !
[---] (p7) !-----------------(p9)---------------------! [---] (p7) !-----------------(p9)-----------------!
[CO.]____| [CO.]____|
[---] [---]
___| |_______ ___| |_______
| | | |
| /--\ | /--\ | /--\ | /--\
| ()/\() | ()/\() | ()/\() | ()/\()
|__/__\ |____/__\ |__/__\ |____/__\
Figure 10: The Nortel System Figure 10: The Nortel System
As these are independent systems developed by different groups, the As these are independent systems developed by different groups, the
names of the components, unsurprisingly, don't match. Some features names of the components, unsurprisingly, don't match. Some features
are offered by one of the systems, while they aren't by others. are offered by one of the systems, while they aren't by others.
However, there are a number of common features. All of the systems However, there are a number of common features. All of the systems
provide a Web-based interface (at least as an option), using "back provide a Web-based interface (at least as an option), using "back
end" programs to construct protocols to pass onwards to the end" programs to construct protocols to pass onwards to the
Intelligent Network system. Intelligent Network system.
Several Intelligent Network Functional Entities are combined into a Several Intelligent Network Functional Entities are combined into a
Service Node in the Lucent, AT&T , and Nortel systems, while in the Service Node in the Lucent, AT&T , and Nortel systems, while in the
Siemens scheme they are separate units. However, this is not Siemens scheme they are separate units. However, this is not
particularly important for the provision of the services they offer. particularly important for the provision of the services they offer.
Toward PSTN/Internet Inter-Networking May 1998
The main difference lies in whether or not the SCF is "aware" of the The main difference lies in whether or not the SCF is "aware" of the
Internet interface and has been modified to be "complicit" in Internet interface and has been modified to be "complicit" in
supporting these Internet requests. The Siemens approach was to re- supporting these Internet requests. The Siemens approach was to re-
use an existing SCP, providing a gateway function to translate as use an existing SCP, providing a gateway function to translate as
needed. The Lucent system used a "lighter weight" SCF adapter to needed. The Lucent system used a "lighter weight" SCF adapter to
terminate the Internet protocols, as the SCF was modified to support terminate the Internet protocols, as the SCF was modified to support
the Internet interface directly. the Internet interface directly.
The AT&T CallBroker and Nortel SCTP Servers introduce an intermediate The AT&T CallBroker and Nortel SCTP Servers introduce an intermediate
protocol (labeled p2) that allows an alternative to the Web based protocol (labeled p2) that allows an alternative to the Web based
skipping to change at page 18, line 53 skipping to change at page 20, line 7
its support for Call Center agent notification. Equivalent its support for Call Center agent notification. Equivalent
functionality would be provided in the AT&T and Nortel systems as functionality would be provided in the AT&T and Nortel systems as
mentioned above, and this would in turn be associated with event mentioned above, and this would in turn be associated with event
notifications being sent as part of their (p3) Internet/IN protocol. notifications being sent as part of their (p3) Internet/IN protocol.
These differences reflect the different emphases in the products as These differences reflect the different emphases in the products as
they were developed; again, future work will have to ensure that they were developed; again, future work will have to ensure that
common protocols can be used to support the chosen services fully. common protocols can be used to support the chosen services fully.
5. IN-Based Solutions 5. IN-Based Solutions
5.1 The Lucent System 5.1 The Lucent System
Figure 11 depicts the overall interconnection architecture of the Figure 11 depicts the overall interconnection architecture of the
Lucent prototype in support of the four PINT services. The IN-based Lucent prototype in support of the four PINT services. The IN-based
architecture utilizes the Service Node and Service Management System architecture utilizes the Service Node and Service Management System
in addition to the Web server, which enables Web-based access to the in addition to the Web server, which enables Web-based access to the
PINT services. This section summarizes the roles of these elements PINT services. This section summarizes the roles of these elements
Toward PSTN/Internet Inter-Networking May 1998
(complemented by a click-to-dial-back service scenario), outlines the (complemented by a click-to-dial-back service scenario), outlines the
interfaces of Web Server-Service Node and Web Server-Service interfaces of Web Server-Service Node and Web Server-Service
Management System (i.e., the interfaces A & B), and addresses the Management System (i.e., the interfaces A & B), and addresses the
common security concerns. common security concerns.
5.1.1 Roles of the Web Server, Service Node, and Service Management 5.1.1 Roles of the Web Server, Service Node, and Service Management
System System
Web Server Web Server
The Web Server stores the profiles of content providers as well as The Web Server stores the profiles of content providers as well as
pre-registered users. The content provider profile contains pre-registered users. The content provider profile contains
information such as content provider ID, telephone number, and fax information such as content provider ID, telephone number, and fax
number. In addition, the profile may also include service logic that number. In addition, the profile may also include service logic that
specifies, for example, the telephone (or fax) number to be reached specifies, for example, the telephone (or fax) number to be reached
based on time of the day, day of the week, or geographical location based on time of the day, day of the week, or geographical location
of the user, and the conditions to accept the charge of the calls. of the user, and the conditions to accept the charge of the calls.
skipping to change at page 20, line 5 skipping to change at page 21, line 5
specialized functions (like playing announcements, voice recognition specialized functions (like playing announcements, voice recognition
and text-to-speech conversion). and text-to-speech conversion).
Service Management System Service Management System
The SMS performs administration and management of service logic and The SMS performs administration and management of service logic and
customer-related data on the SN. It is responsible for the customer-related data on the SN. It is responsible for the
replication of content provider profiles and provision of these data replication of content provider profiles and provision of these data
on the SN. These functions are non-real time. on the SN. These functions are non-real time.
Toward PSTN/Internet Inter-Networking May 1998 Web Users
____________
Web Users O -------------------------- | Internet |-------------------
____________ ------------ |
O -------------------------- | Internet |------------------------ |
------------ | |
| ---------------- -------------- ------------
| | Service Node | D | Service | B |Web Server|
---------------- -------------- --------------- | (SN) |------------| Management |---------------| |
| Service Node | D | Service | B | Web Server | | | |System (SMS)| | |
| (SN) |------------| Management |------------------| | | | A -------------- | |
| | |System (SMS)| | | | |-----------------------------------------| |
| | A -------------- | | ---------------- ------------
| |--------------------------------------------| | | |
---------------- --------------- | I | C
| | | |
| I | C ----------- ---------
| | |Mobile | |Central|
----------- --------- |Switching| |Office |
|Mobile | |Central| | Center | ---------
|Switching| |Office | ----------- |
| Center | --------- | |
----------- | | |
| | O O
| |
O O
Mobile Wireline PSTN Mobile Wireline PSTN
Users Users Users Users
Figure 11: Overall Interconnection Architecture of the Lucent System Figure 11: Overall Interconnection Architecture of the Lucent System
5.1.2 A Click-to-Dial-Back Service Scenario 5.1.2 A Click-to-Dial-Back Service Scenario
A Web user, who has simultaneous access to the Web and telephone A Web user, who has simultaneous access to the Web and telephone
services (this can be achieved, for example, by having an ISDN services (this can be achieved, for example, by having an ISDN
connection), is browsing through a sales catalogue and deciding to connection), is browsing through a sales catalogue and deciding to
speak to a sales representative. speak to a sales representative.
When the Web user clicks a button inviting a telephone call from the When the Web user clicks a button inviting a telephone call from the
sales office, the Web Server sends a message to the SN over the A sales office, the Web Server sends a message to the SN over the A
interface, thus crossing the Internet-to-PSTN boundary. By matching interface, thus crossing the Internet-to-PSTN boundary. By matching
the information received from the Web Server with the content the information received from the Web Server with the content
skipping to change at page 20, line 55 skipping to change at page 22, line 4
sales office, the Web Server sends a message to the SN over the A sales office, the Web Server sends a message to the SN over the A
interface, thus crossing the Internet-to-PSTN boundary. By matching interface, thus crossing the Internet-to-PSTN boundary. By matching
the information received from the Web Server with the content the information received from the Web Server with the content
provider profile that had been previously loaded and activated by the provider profile that had been previously loaded and activated by the
SMS over the D interface, the SN recognizes the signal. SMS over the D interface, the SN recognizes the signal.
At this point, the SN calls the Web user. The user answers the call, At this point, the SN calls the Web user. The user answers the call,
hears an announcement, e.g., "Please wait, while we are connecting hears an announcement, e.g., "Please wait, while we are connecting
you to the sale agent", and is waiting to be connected to the sale you to the sale agent", and is waiting to be connected to the sale
agent. Then the SN invokes service logic as indicated in the profile. agent. Then the SN invokes service logic as indicated in the profile.
The execution of this logic selects an appropriate sales agent to The execution of this logic selects an appropriate sales agent to
call based on the time of the day. It is 8 P.M. in New York where call based on the time of the day. It is 8 P.M. in New York where
the Web user is located, and the New York sales office has closed. the Web user is located, and the New York sales office has closed.
The San Francisco office, however, is still open, and so the SN makes The San Francisco office, however, is still open, and so the SN makes
Toward PSTN/Internet Inter-Networking May 1998
a call to an agent in that office. Finally, the SN bridges the two a call to an agent in that office. Finally, the SN bridges the two
calls and establishes a two-party call between the sales agent and calls and establishes a two-party call between the sales agent and
the Web user. the Web user.
5.1.3 Web Server-Service Node Interface 5.1.3 Web Server-Service Node Interface
Lucent developed the Service Support Transfer Protocol (SSTP) for Lucent developed the Service Support Transfer Protocol (SSTP) for
communications between the SN and Web Server. SSTP is of a communications between the SN and Web Server. SSTP is of a
request/response type running on top of a reliable transport layer, request/response type running on top of a reliable transport layer,
such as TCP. The Web Server sends a request to the SN to invoke a such as TCP. The Web Server sends a request to the SN to invoke a
service and the SN responds with a message indicating either success service and the SN responds with a message indicating either success
or failure. Note that SSTP engages only the service control function or failure. Note that SSTP engages only the service control function
[1, 2, 3] of the SN. [1, 2, 3] of the SN.
5.1.3.1 Web Server to Service Node 5.1.3.1 Web Server to Service Node
In this direction, three kinds of messages may be sent: the In this direction, three kinds of messages may be sent: the
Transaction Initiator message, the Data Message, and the End of Data Transaction Initiator message, the Data Message, and the End of Data
message. message.
The latter two messages are needed if the service to be invoked The latter two messages are needed if the service to be invoked
involves data (such as the case in click-to-fax, click-to-fax-back involves data (such as the case in click-to-fax, click-to-fax-back
and voice-access-to-content). This was so designed to handle the and voice-access-to-content). This was so designed to handle the
varying size of data and to ensure that the size of each stream is varying size of data and to ensure that the size of each stream is
within the allowable size of the underlying transport packet data within the allowable size of the underlying transport packet data
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+ Content Provider ID, which uniquely represents the content + Content Provider ID, which uniquely represents the content
provider. This information is the key to accessing the content provider. This information is the key to accessing the content
provider's service logic and data on the SN. provider's service logic and data on the SN.
+ Content Provider Directory Number, which is the telephone or fax + Content Provider Directory Number, which is the telephone or fax
number of the content provider to be called through the PSTN. number of the content provider to be called through the PSTN.
+ User Directory Number, which is the telephone or fax number of the + User Directory Number, which is the telephone or fax number of the
user requesting the service. user requesting the service.
Toward PSTN/Internet Inter-Networking May 1998
+ Billed Party, which specifies the party (either the user or content + Billed Party, which specifies the party (either the user or content
provider), to be billed. provider), to be billed.
In addition, optional parameters may be sent from the Web Server to In addition, optional parameters may be sent from the Web Server to
the SN. For example, a retry parameter may be sent to specify the the SN. For example, a retry parameter may be sent to specify the
number of times the SN will attempt to complete a service request number of times the SN will attempt to complete a service request
upon failure before the transport connection times out. upon failure before the transport connection times out.
b. Data Message b. Data Message
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transaction ID and a data segment. The transaction ID must be the transaction ID and a data segment. The transaction ID must be the
same as that of the transaction initiator part first invoking the same as that of the transaction initiator part first invoking the
service. service.
c. End of Data Message c. End of Data Message
This message contains the transaction ID and the end of data This message contains the transaction ID and the end of data
delimiter. The transaction ID is the same as that of the relevant delimiter. The transaction ID is the same as that of the relevant
transaction initiator message. transaction initiator message.
B. Service Node to Web Server 5.1.3.2 Service Node to Web Server
The SN must respond to a service request from the Web Server. The The SN must respond to a service request from the Web Server. The
response message consists of the information elements: response message consists of the information elements:
transaction ID, service type, result, time, and error code. transaction ID, service type, result, time, and error code.
+ Transaction ID, which is the same as that of the original service + Transaction ID, which is the same as that of the original service
request. request.
+ Service Type, which is the same as that of the original service + Service Type, which is the same as that of the original service
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+ Result, which is either success or failure. + Result, which is either success or failure.
+ Time, which indicates the time of the day completing the request. + Time, which indicates the time of the day completing the request.
+ Error Code, which gives the reason for failure. Possible reasons + Error Code, which gives the reason for failure. Possible reasons
for failure are content provider telephone (or fax) busy, content for failure are content provider telephone (or fax) busy, content
provider telephone (or fax) no answer, user telephone busy, user provider telephone (or fax) no answer, user telephone busy, user
refusal to complete, user no answer, nuisance control limit reached, refusal to complete, user no answer, nuisance control limit reached,
and content provider telephone (or fax) not in the SN database. and content provider telephone (or fax) not in the SN database.
C. Usage Scenarios: Click-to-Fax and Click-to-Fax-Back 5.1.3.3 Usage Scenarios: Click-to-Fax and Click-to-Fax-Back
For the click-to-fax and click-to-fax-back services, the Lucent For the click-to-fax and click-to-fax-back services, the Lucent
system implemented only the case where the data to be sent as system implemented only the case where the data to be sent as
facsimile reside in the Web server. There are at least three messages facsimile reside in the Web server. There are at least three messages
that need to be sent from the Web server to the Service Node for that need to be sent from the Web server to the Service Node for
these services. these services.
Toward PSTN/Internet Inter-Networking May 1998
The first message is the Transaction Initiator that identifies the The first message is the Transaction Initiator that identifies the
service type as well as a unique Transaction ID. It also includes the service type as well as a unique Transaction ID. It also includes the
sender/receiver fax number. sender/receiver fax number.
The next is one or more messages of the data to be faxed. Each The next is one or more messages of the data to be faxed. Each
message carries the same unique Transaction ID as the above. message carries the same unique Transaction ID as the above.
Last comes the end of message. It consists of the Transaction ID Last comes the end of message. It consists of the Transaction ID
(again, the same as that of the messages preceding it) and the end of (again, the same as that of the messages preceding it) and the end of
data delimiter. data delimiter.
Upon receiving these messages, the Service Node, equipped with the Upon receiving these messages, the Service Node, equipped with the
special resource of a fax card, converts the data into the G3 format, special resource of a fax card, converts the data into the G3 format,
calls the receiver fax, and sends back the result to the Web server calls the receiver fax, and sends back the result to the Web server
immediately. Note that the receiver fax busy or no answer is immediately. Note that the receiver fax busy or no answer is
interpreted as failure. Further, while the receiver fax answering the interpreted as failure. Further, while the receiver fax answering the
call is interpreted as success, it does not necessarily mean that the call is interpreted as success, it does not necessarily mean that the
fax would go through successfully. fax would go through successfully.
5.1.4 Web Server-SMS Interface and SNMP MIB 5.1.4 Web Server-SMS Interface and SNMP MIB
This interface is responsible for uploading the content provider This interface is responsible for uploading the content provider
profile from the Web Server to the SMS and for managing the profile from the Web Server to the SMS and for managing the
information against any possible corruption. The SN verifies the information against any possible corruption. The SN verifies the
Content Provider ID and the Content Provider Directory Number sent by Content Provider ID and the Content Provider Directory Number sent by
the Web Server with the content provider profile pre-loaded from the the Web Server with the content provider profile pre-loaded from the
SMS. SMS.
The content provider profile was based on ASN.1 [4] structure and The content provider profile was based on ASN.1 [4] structure and
SNMP [5] was used to set/get the object identifiers in the SMS SNMP [5] was used to set/get the object identifiers in the SMS
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MAX-ACCESS not-accessible MAX-ACCESS not-accessible
STATUS current STATUS current
DESCRIPTION DESCRIPTION
" A conceptual row of the inweb. Each row " A conceptual row of the inweb. Each row
contains profile of one Content Provider" contains profile of one Content Provider"
INDEX { inwebSmsNumber } INDEX { inwebSmsNumber }
:= { inwebContProviderTable 1 } := { inwebContProviderTable 1 }
InwebContProviderEntry := SEQUENCE { InwebContProviderEntry := SEQUENCE {
inwebSmsNumber Integer32, inwebSmsNumber Integer32,
Toward PSTN/Internet Inter-Networking May 1998
inwebContentProviderId Integer32, inwebContentProviderId Integer32,
inwebContentProviderPhoneNumber Integer32, inwebContentProviderPhoneNumber Integer32,
inwebContentProviderFaxNumber Integer32 inwebContentProviderFaxNumber Integer32
} }
inwebSmsNumber OBJECT-TYPE inwebSmsNumber OBJECT-TYPE
SYNTAX Integer32 SYNTAX Integer32
MAX-ACCESS read-only MAX-ACCESS read-only
STATUS current STATUS current
DESCRIPTION DESCRIPTION
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:= { inwebContProviderEntry 3 } := { inwebContProviderEntry 3 }
inwebContentProviderFaxNumber OBJECT-TYPE inwebContentProviderFaxNumber OBJECT-TYPE
SYNTAX Integer32 SYNTAX Integer32
MAX-ACCESS read-create MAX-ACCESS read-create
STATUS current STATUS current
DESCRIPTION DESCRIPTION
" Content Provider's Fax Number " " Content Provider's Fax Number "
:= { inwebContProviderEntry 4 } := { inwebContProviderEntry 4 }
5.1.5 Security Considerations 5.1.5 Security Considerations
The Lucent prototype addressed the security issues concerning the The Lucent prototype addressed the security issues concerning the
interface between the Web Server and the SN. Those concerning the interface between the Web Server and the SN. Those concerning the
interface between the Web Server and SMS, which was based in SNMP, interface between the Web Server and SMS, which was based in SNMP,
were handled by the built-in security features of SNMP. were handled by the built-in security features of SNMP.
+ Secure Communication Links + Secure Communication Links
If the Network Operator (PSTN provider) is also the Web Service If the Network Operator (PSTN provider) is also the Web Service
provider, the Web Server and SN/SMS will communicate over a corporate provider, the Web Server and SN/SMS will communicate over a corporate
intranet. This network is almost always protected by the intranet. This network is almost always protected by the
corporation's firewall and so can be deemed secure. This was the case corporation's firewall and so can be deemed secure. This was the case
handled by the Lucent prototype. handled by the Lucent prototype.
Nevertheless, if different corporations serve as the Network Operator Nevertheless, if different corporations serve as the Network Operator
Toward PSTN/Internet Inter-Networking May 1998
and the Web Service Provider, then it is likely that there may not and the Web Service Provider, then it is likely that there may not
exist a dedicated secure communication link between the Web Server exist a dedicated secure communication link between the Web Server
and SN/SMS. This raises serious security considerations. One possible and SN/SMS. This raises serious security considerations. One possible
solution is to use Virtual Private Networks (VPN). VPN features solution is to use Virtual Private Networks (VPN). VPN features
support authentication of the calling and called parties and support authentication of the calling and called parties and
encryption of the messages sent over insecure links (such as those on encryption of the messages sent over insecure links (such as those on
the Internet). the Internet).
+ Non-Repudiation + Non-Repudiation
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NCL has two parameters: one defining the number of requests from a NCL has two parameters: one defining the number of requests from a
user and the other the period over which these requests takes place. user and the other the period over which these requests takes place.
A user may also attempt to request a call from a directory number A user may also attempt to request a call from a directory number
other than that of a content provider. This scenario was handled by other than that of a content provider. This scenario was handled by
verifying the directory number (and the content provider ID) against verifying the directory number (and the content provider ID) against
the database on the SN containing all the content provider the database on the SN containing all the content provider
information. If the directory number (or the content provider ID) was information. If the directory number (or the content provider ID) was
not in the database, the request would be rejected. not in the database, the request would be rejected.
5.2 Siemens Web Call Center 5.2 Siemens Web Call Center
5.2.1 Service Description 5.2.1 Service Description
The Web Call Center is an Intelligent Network System that accepts The Web Call Center is an Intelligent Network System that accepts
requests from Internet nodes for services to be provided on the PSTN. requests from Internet nodes for services to be provided on the PSTN.
As the name suggests, it was designed to support a cluster of As the name suggests, it was designed to support a cluster of
services that, taken together, provide a subset of the features of a services that, taken together, provide a subset of the features of a
Call Center, with almost all user interactions provided via World Call Center, with almost all user interactions provided via World
Wide Web requests and responses. See the appendix for a background Wide Web requests and responses. See the appendix for a background
description of Call Center Features. description of Call Center Features.
From an Intelligent Network perspective, there are a number of From an Intelligent Network perspective, there are a number of
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customer makes a request to be called back by an agent at a time of customer makes a request to be called back by an agent at a time of
the customer's choosing to discuss an item of interest to him or her. the customer's choosing to discuss an item of interest to him or her.
The agent will be selected based on his or her availability and The agent will be selected based on his or her availability and
expertise in this topic; the agent will be told whom he or she is expertise in this topic; the agent will be told whom he or she is
calling and the topic of interest, and then the agent will be calling and the topic of interest, and then the agent will be
connected to the customer. connected to the customer.
In addition, the individual services that were deployed to support In addition, the individual services that were deployed to support
this scenario provided support for management of the list of this scenario provided support for management of the list of
available agents as well. This involved allowing the agent to "log available agents as well. This involved allowing the agent to "log
Toward PSTN/Internet Inter-Networking May 1998
into" and "out of" the system and to indicate whether the agent was into" and "out of" the system and to indicate whether the agent was
then ready to handle calls to the customer. The list of services, as then ready to handle calls to the customer. The list of services, as
seen from a user perspective, follows. seen from a user perspective, follows.
The services support: The services support:
i) Customer Request service - the customer explores a corporate Web i) Customer Request service - the customer explores a corporate Web
site, selects a link that offers to request an agent to call the site, selects a link that offers to request an agent to call the
customer back and then is redirected to the Web Call Center server. customer back and then is redirected to the Web Call Center server.
This presents customer with a form asking for name, the telephone This presents customer with a form asking for name, the telephone
number at which he or she wishes to be called, and the time at which number at which he or she wishes to be called, and the time at which
the call is to be made. Note will also be made of the page to which the call is to be made. Note will also be made of the page to which
the customer was referred to when he or she was redirected. Once the the customer was referred to when he or she was redirected. Once the
form has been returned, the customer receives an acknowledgment page form has been returned, the customer receives an acknowledgment page
listing the parameters he or she has entered. listing the parameters he or she has entered.
ii) Agent Registration/Logon - An agent requests a "login" page on ii) Agent Registration/Logon - An agent requests a "login" page on
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identifier will be checked against a list of known identities. If identifier will be checked against a list of known identities. If
found, the password will be checked, and if this matches the record found, the password will be checked, and if this matches the record
held by the service then a new session record is made of this held by the service then a new session record is made of this
identity and the Internet node from which the call has been made. identity and the Internet node from which the call has been made.
NB: This is very similar to the Universal Personal Telecommunications NB: This is very similar to the Universal Personal Telecommunications
(UPT) service feature "register for incoming calls". It implies that (UPT) service feature "register for incoming calls". It implies that
the identified person has exclusive use of the Internet node from the identified person has exclusive use of the Internet node from
that point onwards, so messages for them can be directed there. that point onwards, so messages for them can be directed there.
iii) Agent Ready - an agent who has already logged on can indicate iii) Agent Ready - an agent who has already logged on can indicate
that he or she is ready by requesting an appropriate "ready" page on that he or she is ready by requesting an appropriate "ready" page on
the Web Call Center Server. The service will match the agent by the the Web Call Center Server. The service will match the agent by the
Internet node Identifier and Agent Identity passed along with the Web Internet node Identifier and Agent Identity passed along with the Web
request against its list of "active" agents. It will mark them as request against its list of "active" agents. It will mark them as
being ready to handle calls in its list of available agents (with being ready to handle calls in its list of available agents (with
their pre-defined skill set). their pre-defined skill set).
iv) Agent Not Ready - an agent can request an appropriate "ready" iv) Agent Not Ready - an agent can request an appropriate "ready"
page on the Web Call Center Server to indicate that he or she is page on the Web Call Center Server to indicate that he or she is
temporarily not ready to handle calls. temporarily not ready to handle calls.
v) Agent Logoff - an agent can request an appropriate "Logout" page v) Agent Logoff - an agent can request an appropriate "Logout" page
on the Web Call Center Server to indicate that he or she is no longer on the Web Call Center Server to indicate that he or she is no longer
associated with a particular Internet node. The service will match associated with a particular Internet node. The service will match
the agent by the Internet Node Identifier and Agent Identity passed the agent by the Internet Node Identifier and Agent Identity passed
along with the Web request against its list of "active" agents. Once along with the Web request against its list of "active" agents. Once
found, the session record for that agent is removed and the caller is found, the session record for that agent is removed and the caller is
notified of this with an acknowledgment page. notified of this with an acknowledgment page.
NB: This is very similar to the UPT "unregister" service feature. NB: This is very similar to the UPT "unregister" service feature.
Toward PSTN/Internet Inter-Networking May 1998
vi) Call Center Agent Selection and Notification - When the time vi) Call Center Agent Selection and Notification - When the time
that the customer selected has arrived and an available agent with that the customer selected has arrived and an available agent with
the right skills has been selected from the appropriate list, this the right skills has been selected from the appropriate list, this
service will send a notification to the Internet node associated with service will send a notification to the Internet node associated with
that agent. A dedicated server is assumed to be running on the that agent. A dedicated server is assumed to be running on the
agent's machine that, on receiving the notification, triggers the agent's machine that, on receiving the notification, triggers the
agent's browser into requesting a "Agent Call In" page from the Web agent's browser into requesting a "Agent Call In" page from the Web
Call Center Server. Once the agent's machine has made this request, Call Center Server. Once the agent's machine has made this request,
he or she will be told that there is a customer to call. he or she will be told that there is a customer to call.
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ix) Agent/Customer Telephony Callback - the agent will make a ix) Agent/Customer Telephony Callback - the agent will make a
request of a "dial-back" page on the Web Call Center Server. The request of a "dial-back" page on the Web Call Center Server. The
Internet node Identifier and Agent Identity he or she uses will be Internet node Identifier and Agent Identity he or she uses will be
matched against a list of agents expected to handle calls, and, when matched against a list of agents expected to handle calls, and, when
the appropriate records have been found, the service will make the the appropriate records have been found, the service will make the
telephone call through to the customer and then connect the agent to telephone call through to the customer and then connect the agent to
this telephone call (using the telephone number registered in the this telephone call (using the telephone number registered in the
respective Call Center service record). respective Call Center service record).
5.2.2 Implementation 5.2.2 Implementation
5.2.2.1 Introduction 5.2.2.1 Introduction
The Siemens Web Call Center used an existing IN system and service The Siemens Web Call Center used an existing IN system and service
logic that supported Call Center features. The scenario it supports logic that supported Call Center features. The scenario it supports
is very similar to the Siemens IN-based Call Center on which it was is very similar to the Siemens IN-based Call Center on which it was
based; one of the goals was to minimize changes to the service based; one of the goals was to minimize changes to the service
offered. It is also virtually identical to the service "Internet offered. It is also virtually identical to the service "Internet
Requested Telephony Dial-back" provided by the Lucent system. Requested Telephony Dial-back" provided by the Lucent system.
As provided via the Internet, the services involved are mostly the As provided via the Internet, the services involved are mostly the
same as those provided via the PSTN and IN alone. The main same as those provided via the PSTN and IN alone. The main
differences lie in the use of the World Wide Web as an interface to differences lie in the use of the World Wide Web as an interface to
Toward PSTN/Internet Inter-Networking May 1998
the services rather than a telephone, SSP, and Intelligent the services rather than a telephone, SSP, and Intelligent
Peripheral. Also, the feature by which a telephone call is made Peripheral. Also, the feature by which a telephone call is made
between the agent and the customer is implemented within the IN between the agent and the customer is implemented within the IN
system in a different way; this is the only element in which the PSTN system in a different way; this is the only element in which the PSTN
is involved. is involved.
5.2.2.2 Web Call Center Configuration 5.2.2.2 Web Call Center Configuration
The general arrangement for the Web Call Center system is shown in The general arrangement for the Web Call Center system is shown in
Figure 7. The components that were added to an existing IN system to Figure 7. The components that were added to an existing IN system to
deal with the Internet interface are described next. deal with the Internet interface are described next.
In addition to the SCP, SSP and SMS that were part of the original In addition to the SCP, SSP and SMS that were part of the original
IN-based system, another unit was included to send notification IN-based system, another unit was included to send notification
messages to agents; in the IN system the agents were sent "wake up" messages to agents; in the IN system the agents were sent "wake up"
telephone calls when they were required to handle their next telephone calls when they were required to handle their next
customers' call back. This unit is called the "Internet Intelligent customers' call back. This unit is called the "Internet Intelligent
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Network Application Protocol) messages into the SCP, making it think Network Application Protocol) messages into the SCP, making it think
that it had received an Initial DP trigger from an SSP. It also that it had received an Initial DP trigger from an SSP. It also
intercepted the "Connect To Resource" and "Prompt and Collect" INAP intercepted the "Connect To Resource" and "Prompt and Collect" INAP
messages sent from the SCP, acting on these to return the parameters messages sent from the SCP, acting on these to return the parameters
generated by the Internet users when they filled in the forms that generated by the Internet users when they filled in the forms that
triggered the service transaction. It also translated the "Play triggered the service transaction. It also translated the "Play
Announcement" message sent to the Intelligent Peripheral into a form Announcement" message sent to the Intelligent Peripheral into a form
that it could use. Finally, it passed on the INAP message used by that it could use. Finally, it passed on the INAP message used by
the SCP to trigger SSP into making the telephone call back. the SCP to trigger SSP into making the telephone call back.
5.2.2.3 User Interaction 5.2.2.3 User Interaction
In the IN/PSTN-based system, the services have contact with the In the IN/PSTN-based system, the services have contact with the
customers and agents via their telephones, SSPs, and Intelligent customers and agents via their telephones, SSPs, and Intelligent
Peripherals programmed to play announcements to them and to capture Peripherals programmed to play announcements to them and to capture
their responses. These responses are indicated by DTMF tones sent by their responses. These responses are indicated by DTMF tones sent by
pressing keys on the telephones. pressing keys on the telephones.
In this case, almost all interactions are provided via World Wide Web In this case, almost all interactions are provided via World Wide Web
requests and responses. The sequence of announcements and responses requests and responses. The sequence of announcements and responses
for each service are "collapsed" into individual form filling for each service are "collapsed" into individual form filling
transactions, and the requests are not limited to digits (or "star" transactions, and the requests are not limited to digits (or "star"
and "hash"). The implications of the use of forms on service and "hash"). The implications of the use of forms on service
operation are covered in more detail later (under HTTP/IN Service operation are covered in more detail later (under HTTP/IN Service
mapping). mapping).
5.2.2.4 Service/Caller Identifiers 5.2.2.4 Service/Caller Identifiers
When provided via the IN/PSTN-based system, the services are passed When provided via the IN/PSTN-based system, the services are passed
the Calling Line Identity (CLI) of the caller and the number the the Calling Line Identity (CLI) of the caller and the number the
caller dials (the DN). The CLI value is used extensively to identify caller dials (the DN). The CLI value is used extensively to identify
Toward PSTN/Internet Inter-Networking May 1998
the caller and (in the case of the agent) to index into service data the caller and (in the case of the agent) to index into service data
tables to decide what to do next. While an equivalent value to the tables to decide what to do next. While an equivalent value to the
DN is passed to the Web-based transactions as the requested Universal DN is passed to the Web-based transactions as the requested Universal
Resource Locator (URL), the CLI cannot be given reliably. The nearest Resource Locator (URL), the CLI cannot be given reliably. The nearest
equivalent caller identifier is the IP Address of the customer or equivalent caller identifier is the IP Address of the customer or
agent's machine. However, the use of HTTP proxies means that this agent's machine. However, the use of HTTP proxies means that this
"original" Internet node Address may not be available; if a proxy is "original" Internet node Address may not be available; if a proxy is
used then its IP Address will be associated with the request. used then its IP Address will be associated with the request.
In providing these Call Center features the customer only has one In providing these Call Center features the customer only has one
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used by call center agents as a service management (pre-service) used by call center agents as a service management (pre-service)
task. The cookie value is unique to the machine and is used to index task. The cookie value is unique to the machine and is used to index
into a list of machine IP addresses that is stored as part of the into a list of machine IP addresses that is stored as part of the
service data. service data.
Also, a session cookie is stored onto the agent's machine when the Also, a session cookie is stored onto the agent's machine when the
agent registers, and is cleared when he or she de-registers. This is agent registers, and is cleared when he or she de-registers. This is
used to identify the agent and so the IP address of the node with used to identify the agent and so the IP address of the node with
which the agent is associated (and from which the agent's subsequent which the agent is associated (and from which the agent's subsequent
requests should originate). The services that interact with Call requests should originate). The services that interact with Call
Toward PSTN/Internet Inter-Networking May 1998
Center agents use the agent session cookie value as an identifier; in Center agents use the agent session cookie value as an identifier; in
principle this is unnecessary but it does simplify the session data principle this is unnecessary but it does simplify the session data
lookup procedure. The rest of the services use the persistent machine lookup procedure. The rest of the services use the persistent machine
identifier in place of the CLI, indexing into their service data identifier in place of the CLI, indexing into their service data
using it. Both cookies are sent with each agent request; if they are using it. Both cookies are sent with each agent request; if they are
not present, then the request is redirected to other services (for not present, then the request is redirected to other services (for
example to the agent Logon service). example to the agent Logon service).
5.2.2.5 Mapping from HTTP Transactions to IN-Based Service Features 5.2.2.5 Mapping from HTTP Transactions to IN-Based Service Features
All of the client-initiated services require user interaction. With All of the client-initiated services require user interaction. With
the IN/PSTN-based system, the majority of the services are typified the IN/PSTN-based system, the majority of the services are typified
by the callers being connected to an announcement unit that plays by the callers being connected to an announcement unit that plays
them a list of choices and captures their selection. The caller can them a list of choices and captures their selection. The caller can
pre-dial the digits needed; in this case the prompts are not needed pre-dial the digits needed; in this case the prompts are not needed
and are not made. and are not made.
The pattern of operation is somewhat different in the Internet case, The pattern of operation is somewhat different in the Internet case,
as the initial HTTP request returns a response, after which the Web as the initial HTTP request returns a response, after which the Web
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handled by a "normal" Web Server. In both cases the service logic is handled by a "normal" Web Server. In both cases the service logic is
only triggered when the form is submitted; this means that, again, only triggered when the form is submitted; this means that, again,
each of the services can be treated as a single IN feature. each of the services can be treated as a single IN feature.
The IN service logic that deals with these requests has a general The IN service logic that deals with these requests has a general
pattern of action. An HTTP request is received, and this triggers the pattern of action. An HTTP request is received, and this triggers the
IN service logic into action. The service logic "sees" this as an IN service logic into action. The service logic "sees" this as an
Initial DP message and starts its processing as if it had been sent Initial DP message and starts its processing as if it had been sent
from an SSF. The SCF uses what appears to it to be an Intelligent from an SSF. The SCF uses what appears to it to be an Intelligent
Peripheral to collect the parameters of the request, and then to send Peripheral to collect the parameters of the request, and then to send
Toward PSTN/Internet Inter-Networking May 1998
back final announcements to the requesting entity. back final announcements to the requesting entity.
The main difference, from the perspective of the IN service logic The main difference, from the perspective of the IN service logic
running on the SCF, is that the service does not need to instruct the running on the SCF, is that the service does not need to instruct the
SSF to make a temporary connection to the Intelligent Peripheral. It SSF to make a temporary connection to the Intelligent Peripheral. It
is as if this connection had already been made. Similarly, there is is as if this connection had already been made. Similarly, there is
no need to close the service transaction by sending an explicit no need to close the service transaction by sending an explicit
"Continue Execution" message to the SSF. "Continue Execution" message to the SSF.
The sequence of "prompt/collect" instructions used to collect service The sequence of "prompt/collect" instructions used to collect service
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Peripheral to which it sends normal "Request Report Prompt & Collect" Peripheral to which it sends normal "Request Report Prompt & Collect"
messages, and from which it receives data values in response. messages, and from which it receives data values in response.
All services have to fit in with the underlying HTTP interaction All services have to fit in with the underlying HTTP interaction
pattern, and so will be expected to send a final "Announce" pattern, and so will be expected to send a final "Announce"
instruction to the Intelligent Peripheral at the end of the service; instruction to the Intelligent Peripheral at the end of the service;
this is done in many IN services anyway and in all of the service this is done in many IN services anyway and in all of the service
features described here. These announcements form the content features described here. These announcements form the content
returned to the Web Client. returned to the Web Client.
5.2.2.6 Non-World Wide Web Interactions 5.2.2.6 Non-World Wide Web Interactions
There are two exceptions to the sole use of the World Wide Web for There are two exceptions to the sole use of the World Wide Web for
interaction. The first one occurs in the "Message Waiting"/"Wake Up interaction. The first one occurs in the "Message Waiting"/"Wake Up
Call" service by which the selected agent is informed of a callback Call" service by which the selected agent is informed of a callback
request. World Wide Web transactions are very simple; the client request. World Wide Web transactions are very simple; the client
browser makes a request for content associated with a particular HTTP browser makes a request for content associated with a particular HTTP
URL, and the server sends a response, marking the end of the URL, and the server sends a response, marking the end of the
transaction. The server cannot make a spontaneous association with a transaction. The server cannot make a spontaneous association with a
client; it must be initiated by the client request. client; it must be initiated by the client request.
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making a further HTTP request of the server. In this way the "Agent making a further HTTP request of the server. In this way the "Agent
Instruction" transaction is started automatically, while still Instruction" transaction is started automatically, while still
allowing it to use a normal HTTP request/response pattern. allowing it to use a normal HTTP request/response pattern.
The second exception occurs in the final "Agent/Customer Telephony The second exception occurs in the final "Agent/Customer Telephony
Callback" service. While this transaction is initiated by the agent Callback" service. While this transaction is initiated by the agent
selecting a link on the "call instructions page" returned to them, selecting a link on the "call instructions page" returned to them,
and includes a "confirmation" page being sent back to them in an HTTP and includes a "confirmation" page being sent back to them in an HTTP
response, the purpose of this service is to make a telephone response, the purpose of this service is to make a telephone
connection via the PSTN between the agent's telephone and the connection via the PSTN between the agent's telephone and the
Toward PSTN/Internet Inter-Networking May 1998
customer's telephone. It is the only service element that involves customer's telephone. It is the only service element that involves
the PSTN directly. From an IN/PSTN perspective, the resulting the PSTN directly. From an IN/PSTN perspective, the resulting
telephone connection is different from that provided in the scheme telephone connection is different from that provided in the scheme
using the IN and PSTN alone. In this case, a PSTN call is made out to using the IN and PSTN alone. In this case, a PSTN call is made out to
the agent's telephone, another call is made out to the customer's the agent's telephone, another call is made out to the customer's
telephone, and these calls are bridged. This differs from the earlier telephone, and these calls are bridged. This differs from the earlier
scheme, in which the agent originated a call to the voice mail replay scheme, in which the agent originated a call to the voice mail replay
system, and this call was redirected to a new destination (the system, and this call was redirected to a new destination (the
customer's telephone). As this feature differs in purpose from the customer's telephone). As this feature differs in purpose from the
other services, and it requires a different implementation within the other services, and it requires a different implementation within the
IN and PSTN system, it was organized as a separate service in this IN and PSTN system, it was organized as a separate service in this
case. case.
5.2.2.7 Security Considerations 5.2.2.7 Security Considerations
In the case of this system, assumptions were made that the interface In the case of this system, assumptions were made that the interface
presented to requesting agents and customers was provided via a fire presented to requesting agents and customers was provided via a fire
wall to deal with most attacks on the IN components. The interface wall to deal with most attacks on the IN components. The interface
appeared as a Web Server, and there was no direct access to the HTTP appeared as a Web Server, and there was no direct access to the HTTP
documents served, nor to the servlets providing the service logic. documents served, nor to the servlets providing the service logic.
The Callback service was deemed to have simpler security requirements The Callback service was deemed to have simpler security requirements
than other IN services as it was akin to a free phone "1-800" service than other IN services as it was akin to a free phone "1-800" service
access number; the agents work for the service subscriber and are not access number; the agents work for the service subscriber and are not
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running the agent services could be charged directly to them. As such running the agent services could be charged directly to them. As such
the authorization for service is defined by the contract between the the authorization for service is defined by the contract between the
service subscriber and the service provider. service subscriber and the service provider.
Authentication of agents was seen as a problem. As an interim Authentication of agents was seen as a problem. As an interim
measure, cookies were used, but this scheme delivers the cookie data measure, cookies were used, but this scheme delivers the cookie data
as a plain text item (a header of the Web request). Secure Socket as a plain text item (a header of the Web request). Secure Socket
Layer connections were required for communication with the agent Layer connections were required for communication with the agent
services, and this had an impact on the performance of the IN system. services, and this had an impact on the performance of the IN system.
5.2.3 Derived Requirements/Lessons 5.2.3 Derived Requirements/Lessons
Security is seen as a major issue. A firewall was used to control Security is seen as a major issue. A firewall was used to control
access to the IN Components. Similarly, SSL was used for access to the IN Components. Similarly, SSL was used for
communication with the Agents, so as to protect the cookie values communication with the Agents, so as to protect the cookie values
that they were sending with their requests. that they were sending with their requests.
For other services, it is likely that the entity from which requests For other services, it is likely that the entity from which requests
appear to originate will be charged for the service to be rendered. appear to originate will be charged for the service to be rendered.
This has implications in terms of authentication and authorization of This has implications in terms of authentication and authorization of
service provision at the time of the request. It is necessary for the service provision at the time of the request. It is necessary for the
service to be authorized in such a way that non-repudiation is service to be authorized in such a way that non-repudiation is
ensured; this is likely to mean that a certificate of identity be ensured; this is likely to mean that a certificate of identity be
provided from the person making the request, and that this can be provided from the person making the request, and that this can be
tied in with a financial account that that person has with the tied in with a financial account that that person has with the
service provider. The certificate can then be stored as part of the service provider. The certificate can then be stored as part of the
Toward PSTN/Internet Inter-Networking May 1998
billing record. While the process of electronic commerce is outside billing record. While the process of electronic commerce is outside
of the scope of this work, the mechanism by which a request for of the scope of this work, the mechanism by which a request for
confirmation of identity is passed out to the requesting user and is confirmation of identity is passed out to the requesting user and is
delivered back to the service logic must be considered. delivered back to the service logic must be considered.
When changing from a "pure" IN/PSTN system to one supporting requests When changing from a "pure" IN/PSTN system to one supporting requests
via the Internet, the differences in the way that clients interacted via the Internet, the differences in the way that clients interacted
with the services meant that the service logic had to be redesigned. with the services meant that the service logic had to be redesigned.
It was realized that maintaining the state of a service during its It was realized that maintaining the state of a service during its
processing was going to be a problem; this problem was sidestepped by processing was going to be a problem; this problem was side-stepped
re-engineering the services as form processors, allowing them to deal by re-engineering the services as form processors, allowing them to
with fully specified requests as a single (Web) transaction. In deal with fully specified requests as a single (Web) transaction. In
addition, a "normal" Web Server was used to deliver the forms to the addition, a "normal" Web Server was used to deliver the forms to the
users. This is a change from the IN system, where the equivalent of users. This is a change from the IN system, where the equivalent of
the form (the prompts) were sent in sequence as part of the same the form (the prompts) were sent in sequence as part of the same
service process. service process.
The Call Center features provided suited this change. However, this The Call Center features provided suited this change. However, this
may not be the case for other IN services. It is quite common for may not be the case for other IN services. It is quite common for
services to be designed such that the user is prompted for a services to be designed such that the user is prompted for a
response, and the service continues dependent on this response. The response, and the service continues dependent on this response. The
Web form presents all of the options at once, so this kind of variant Web form presents all of the options at once, so this kind of variant
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as it did to make the changes to the service logic. as it did to make the changes to the service logic.
In the Siemens Web Call Center, the "Internet Intelligent Peripheral" In the Siemens Web Call Center, the "Internet Intelligent Peripheral"
with which the service logic communicated was running as a separate with which the service logic communicated was running as a separate
program on the same node. Where more complex behavior is required of program on the same node. Where more complex behavior is required of
it (such as conversion of text to speech data and interface with the it (such as conversion of text to speech data and interface with the
PSTN) then it would almost certainly be on a separate node. If data PSTN) then it would almost certainly be on a separate node. If data
is transferred from the Internet in such a scheme, any intermediate is transferred from the Internet in such a scheme, any intermediate
gateway would be involved in relaying the data to this node. gateway would be involved in relaying the data to this node.
Toward PSTN/Internet Inter-Networking May 1998
6. Alternative Solutions 6. Alternative Solutions
6.1 The AT&T System 6.1 The AT&T System
AT&T developed a framework for controlling voice and voice-band data AT&T developed a framework for controlling voice and voice-band data
(e.g., fax) and for providing PINT services. Key to the framework is (e.g., fax) and for providing PINT services. Key to the framework is
CallBroker, a logical entity that acts on behalf of a user to set up CallBroker, a logical entity that acts on behalf of a user to set up
sessions and make requests for PSTN resources. The sessions typically sessions and make requests for PSTN resources. The sessions typically
include initiation of calls between two or more end points specified include initiation of calls between two or more end points specified
by the user. In addition to its interactions with the PSTN for call by the user. In addition to its interactions with the PSTN for call
setup, the CallBroker is responsible for other functions, when setup, the CallBroker is responsible for other functions, when
necessary, such as authentication and usage recording. necessary, such as authentication and usage recording.
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service providers to extend the architecture defined here to serve as service providers to extend the architecture defined here to serve as
a platform for other advanced/value-added services (to be identified a platform for other advanced/value-added services (to be identified
later). In addition, the view taken here is that the IP client is later). In addition, the view taken here is that the IP client is
more general, and implements a protocol for communication with the more general, and implements a protocol for communication with the
CallBroker that allows full two-way communications. For example, this CallBroker that allows full two-way communications. For example, this
is required for the cases where a called party hangs up and an is required for the cases where a called party hangs up and an
indication may be necessary to be given to the IP Client about this indication may be necessary to be given to the IP Client about this
status/progress. This is also necessary when conferencing to give an status/progress. This is also necessary when conferencing to give an
indication/status of various parties joining the call. indication/status of various parties joining the call.
6.1.1 High Level Architecture 6.1.1 High Level Architecture
A high level architecture depicting various logical entities and the A high level architecture depicting various logical entities and the
Interfaces among these logical Entities and the IP Client is shown in Interfaces among these logical Entities and the IP Client is shown in
Figure 12. Figure 12.
________________ ________________
/ /
1 _____ / 2 _____ 1 _____ / 2 _____
/|________________| |________| | PSTN /|________________| |________| | PSTN
|____| \ |____| |____| \ |____|
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\_____________ \_____________
/ \ / \
/ \ / \
/ \ / \
__ __ __ __
/\ /\ /\ /\
Calling Participant Calling Participant
Party (Called Party) Party (Called Party)
Figure 12: The CallBroker Architecture Figure 12: The CallBroker Architecture
Toward PSTN/Internet Inter-Networking May 1998
The CallBroker, in addition to the initiation and control of calls on The CallBroker, in addition to the initiation and control of calls on
behalf of the user, performs additional functions. These functions behalf of the user, performs additional functions. These functions
include authenticating the IP Client, usage recording, and management include authenticating the IP Client, usage recording, and management
of the session for the IP Client for the telephony call. The notion of the session for the IP Client for the telephony call. The notion
of the session requires that a client state machine be maintained in of the session requires that a client state machine be maintained in
the CallBroker. This also helps in notifying the IP Client about the the CallBroker. This also helps in notifying the IP Client about the
status/progress of the requests generated from the IP Client. status/progress of the requests generated from the IP Client.
From the perspective of the IP Client, the logical entities needed From the perspective of the IP Client, the logical entities needed
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llllllllllllllll llllllllllllllll
x x
x Interface 2c x Interface 2c
x x
_______ _______
| | | |
|_____| |_____|
Bridge Bridge
Figure 13: Functional Entities in the Call Broker Figure 13: Functional Entities in the Call Broker
Various interfaces (i.e., 2a, 2b, 2c in Figure 13) between different Various interfaces (i.e., 2a, 2b, 2c in Figure 13) between different
functional entities in the CallBroker may also be standardized. The functional entities in the CallBroker may also be standardized. The
Session State Management Function may be physically realized as part Session State Management Function may be physically realized as part
of the CallBroker Server. of the CallBroker Server.
Toward PSTN/Internet Inter-Networking May 1998 6.1.2 IP Client to CallBroker Interface
6.1.2 IP Client to CallBroker Interface
Communication on the IP Client to CallBroker Interface (Interface 1 Communication on the IP Client to CallBroker Interface (Interface 1
in Figure 12) is a simple ASCII based protocol running directly on in Figure 12) is a simple ASCII based protocol running directly on
TCP. The messages on this interface are primarily requests from the TCP. The messages on this interface are primarily requests from the
client to the CallBroker, responses from the CallBroker to the IP client to the CallBroker, responses from the CallBroker to the IP
client responding to the requests and unsolicited events from the client responding to the requests and unsolicited events from the
CallBroker to the IP client. Since the communication is not strictly CallBroker to the IP client. Since the communication is not strictly
transaction oriented, traditional encapsulation protocols like HTTP transaction oriented, traditional encapsulation protocols like HTTP
cannot be used. There has been some ongoing work attempting to use cannot be used. There has been some ongoing work attempting to use
multiple concurrent HTTP POST requests to support event delivery but, multiple concurrent HTTP POST requests to support event delivery but,
without too much difficulty, the ASCII protocol specified here can without too much difficulty, the ASCII protocol specified here can
easily be mapped to the POST payload of the HTTP protocol. easily be mapped to the POST payload of the HTTP protocol.
6.1.3 Protocol 6.1.3 Protocol
Basic Format Basic Format
The basic format of the protocol is as follows: The basic format of the protocol is as follows:
[header]<<LF> [header]<<LF>
<<LF> <<LF>
[body]<<LF> [body]<<LF>
<<LF> <<LF>
<<LF> <<LF>
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Message-id represents the operation of the message. Message-id represents the operation of the message.
Version-info contains optional version information of the protocol. Version-info contains optional version information of the protocol.
This is to aid possible version mismatch detection and graceful error This is to aid possible version mismatch detection and graceful error
recovery. recovery.
Body Body
The body of the protocol messages consists of name value pairs. These The body of the protocol messages consists of name value pairs. These
Toward PSTN/Internet Inter-Networking May 1998
name-value pairs are interpreted with reference to the message-id name-value pairs are interpreted with reference to the message-id
which signifies the operation to be performed by the CallBroker. which signifies the operation to be performed by the CallBroker.
6.1.4 APIs Exposed to the IP Client 6.1.4 APIs Exposed to the IP Client
The APIs of the CallBroker exposed to the IP client are distinct and The APIs of the CallBroker exposed to the IP client are distinct and
different from the APIs that the CallBroker uses from the different different from the APIs that the CallBroker uses from the different
supporting subsystems including the authentication subsystem and the supporting subsystems including the authentication subsystem and the
usage recording subsystem. The IP client APIs enable clients to usage recording subsystem. The IP client APIs enable clients to
effectively control voice conferencing. effectively control voice conferencing.
6.1.5 Voice-Bridge Control API 6.1.5 Voice-Bridge Control API
The Voice Bridge Control API is used by CallBroker applications to The Voice Bridge Control API is used by CallBroker applications to
access voice bridging functionality. The API distinguishes between access voice bridging functionality. The API distinguishes between
sessions and calls. Calls represent actual voice calls placed from/to sessions and calls. Calls represent actual voice calls placed from/to
the voice bridge. These calls can be grouped together in sessions. the voice bridge. These calls can be grouped together in sessions.
All the calls that belong to a session are bridged. Calls have a All the calls that belong to a session are bridged. Calls have a
significance outside the scope of sessions. Every call can be significance outside the scope of sessions. Every call can be
associated with multiple sessions with different weights at the same associated with multiple sessions with different weights at the same
time. The advantage of this approach is the ability to support time. The advantage of this approach is the ability to support
concepts like whispering in a conference call. Calls can also be concepts like whispering in a conference call. Calls can also be
dropped from a conference session and bridged together in a new dropped from a conference session and bridged together in a new
session to give the notion of a sub-conference. These calls can later session to give the notion of a sub-conference. These calls can later
be re-added to the main conference session. be re-added to the main conference session.
6.2 Simple Computer Telephony Protocol 6.2 Simple Computer Telephony Protocol
6.2.1 Overview 6.2.1 Overview
The Simple Computer Telephony Protocol (SCTP) is a third party call The Simple Computer Telephony Protocol (SCTP) is a third party call
control protocol and as such does not comply with the PINT charter. control protocol and as such does not comply with the PINT charter.
SCTP is described in this section to show how PINT services could be SCTP is described in this section to show how PINT services could be
implemented using SCTP, and where SCTP fits into the PINT implemented using SCTP, and where SCTP fits into the PINT
architecture. architecture.
In addition to third party call control, SCTP also provides In addition to third party call control, SCTP also provides
subscriber (i.e., user) feature management (e.g., allows a user to subscriber (i.e., user) feature management (e.g., allows a user to
set do not disturb, call forwarding parameters), and subscriber set do not disturb, call forwarding parameters), and subscriber
monitoring of terminal, line and address status. SCTP is strictly monitoring of terminal, line and address status. SCTP is strictly
client/server-based. It has no provisions for peer to peer client/server-based. It has no provisions for peer to peer
communications. SCTP runs as a TCP application protocol. It is communications. SCTP runs as a TCP application protocol. It is
ASCII-based and uses sockets. The SCTP Server is usually connected to ASCII-based and uses sockets. The SCTP Server is usually connected to
a switch via a CTI (Computer-Telephony Integration) connection. a switch via a CTI (Computer-Telephony Integration) connection.
Because of this, feature interactions are limited to those within the Because of this, feature interactions are limited to those within the
context of a single call, and not between PSTN services. The SCTP context of a single call, and not between PSTN services. The SCTP
Server within a PINT Gateway could also be connected to an SN, or an Server within a PINT Gateway could also be connected to an SN, or an
SCP. See figures below. SCTP does NOT carry media. SCP. See figures below. SCTP does NOT carry media.
Toward PSTN/Internet Inter-Networking May 1998 6.2.2 How SCTP Fits in with the Reference PINT Services
6.2.2 How SCTP Fits in with the Reference PINT Services
SCTP Client as Part of a Web Server SCTP Client as Part of a Web Server
+------+ +--------+ +--------+ +------+ +------+ +--------+ +--------+ +------+
| | | | SCTP | | | | | | | | SCTP | | | |
| |----| |-------| |----| | | |----| |-------| |----| |
| | | | | | | | | | | | | | | |
+------+ +--------+ +--------+ +------+ +------+ +--------+ +--------+ +------+
User's PC Web Server/ PINT Gateway SN/SCP/Switch User's PC Web Server/ PINT Gateway SN/SCP/Switch
CGI CGI
Figure 14: SCTP Client as Part of a Web Server Figure 14: SCTP Client as Part of a Web Server
In this architecture, the SCTP Client is embedded in the Web Server. In this architecture, the SCTP Client is embedded in the Web Server.
It is there for the specific purpose of initiating calls to the PSTN It is there for the specific purpose of initiating calls to the PSTN
based on user requests. The SCTP Server is within the PINT Gateway. based on user requests. The SCTP Server is within the PINT Gateway.
We go through the classic PINT examples: We go through the classic PINT examples:
Click-to-dial-back: The SCTP Client issues an SCTP MakeCall to the Click-to-dial-back: The SCTP Client issues an SCTP MakeCall to the
SCTP Server with the calling number supplied by Web page, and called SCTP Server with the calling number supplied by Web page, and called
number supplied by the user. number supplied by the user.
skipping to change at page 39, line 5 skipping to change at page 43, line 5
to Web Server and treatment set to a URI for the file of the to Web Server and treatment set to a URI for the file of the
particular Web page to be read to the called number. The SCTP Server particular Web page to be read to the called number. The SCTP Server
takes care of the file to voice conversion and this is fed into the takes care of the file to voice conversion and this is fed into the
call as if it were voice. call as if it were voice.
In all of the above cases, the SCTP Client can generate a variety of In all of the above cases, the SCTP Client can generate a variety of
different Web pages to send to the Web Server via CGI (Common Gateway different Web pages to send to the Web Server via CGI (Common Gateway
Interface). The content of these pages is based on the call Interface). The content of these pages is based on the call
completion status of the CallMake SCTP action. completion status of the CallMake SCTP action.
Toward PSTN/Internet Inter-Networking May 1998
SCTP Client Running on the User's PC SCTP Client Running on the User's PC
+------+ +------+
HTML | | INTERNET HTML | | INTERNET
+-----+ /--------------| | +-----+ /--------------| |
| |---/ +------+ | |---/ +------+
| | Web Server | | Web Server
| |---\ | |---\
+-----+ \ +-----+ \
User's PC \ SCTP +------+ +------+ User's PC \ SCTP +------+ +------+
\------------| |-------| | PSTN \------------| |-------| | PSTN
| | | | | | | |
+------+ +------+ +------+ +------+
PINT Gateway SN/SCP/Switch PINT Gateway SN/SCP/Switch
Figure 15: SCTP Client Running on the User's PC Figure 15: SCTP Client Running on the User's PC
In this architecture, the user has an SCTP Client co-located with it. In this architecture, the user has an SCTP Client co-located with it.
If the user is using the telephone line for connection to a Web If the user is using the telephone line for connection to a Web
Server and there is an incoming call, then the SCTP Server in the Server and there is an incoming call, then the SCTP Server in the
PINT Gateway will post this event to the SCTP Client. A window will PINT Gateway will post this event to the SCTP Client. A window will
pop up on the user's screen with options available to the user for pop up on the user's screen with options available to the user for
handling of the incoming call. The user can choose to take the call, handling of the incoming call. The user can choose to take the call,
send it to voice mail, or send it to another number. send it to voice mail, or send it to another number.
For the Fax back service, for example, if the user had a separate fax For the Fax back service, for example, if the user had a separate fax
machine from his or her PC, then the SCTP Server would tell the SCTP machine from his or her PC, then the SCTP Server would tell the SCTP
Client there is an incoming fax. The user would end or suspend his or Client there is an incoming fax. The user would end or suspend his or
her Internet connection, the fax would come in, and the user could her Internet connection, the fax would come in, and the user could
then resume the Internet connection. then resume the Internet connection.
7. Session Initiation Protocol--An Emerging Standard 7. Session Initiation Protocol--An Emerging Standard
7.1 Overview 7.1 Overview
SIP, the Session Initiation Protocol, is a simple signaling protocol SIP, the Session Initiation Protocol, is a simple signaling protocol
for Internet conferencing and telephony. It is currently under for Internet conferencing and telephony. It is currently under
development within the IETF MMUSIC (Multiparty Multimedia Session development within the IETF MMUSIC (Multiparty Multimedia Session
Control) Working Group. Control) Working Group.
SIP provides the necessary mechanisms to support the following SIP provides the necessary mechanisms to support the following
services: services:
- call forwarding, including the equivalent of 700-, 800- and 900- - call forwarding, including the equivalent of 700-, 800- and 900-
type calls; type calls;
- call-forwarding no answer; - call-forwarding no answer;
- call-forwarding busy; - call-forwarding busy;
- call-forwarding unconditional; - call-forwarding unconditional;
- other address-translation services; - other address-translation services;
- callee and calling "numbers" delivery, where the numbers can be of - callee and calling "numbers" delivery, where the numbers can be of
Toward PSTN/Internet Inter-Networking May 1998
any (preferably unique) naming scheme; any (preferably unique) naming scheme;
- personal mobility, i.e., the ability to reach a called party under - personal mobility, i.e., the ability to reach a called party under
a single, location-independent address, even when the user changes a single, location-independent address, even when the user changes
terminals; terminals;
- terminal-type negotiation and selection: a caller can be given a - terminal-type negotiation and selection: a caller can be given a
choice of how to reach a party, e.g., via Internet telephony, choice of how to reach a party, e.g., via Internet telephony,
mobile, phone, and an answering service; mobile, phone, and an answering service;
- caller and callee authentication; - caller and callee authentication;
- blind and supervised call transfer; - blind and supervised call transfer;
- user location; and - user location; and
- invitation to multicast conferences. - invitation to multicast conferences.
Extensions of SIP to allow third-party signaling (e.g., for click- Extensions of SIP to allow third-party signaling (e.g., for click-
to-dial-back services, fully meshed conferences and connections to to-dial-back services, fully meshed conferences and connections to
Multipoint Control Units (MCUs), as well as mixed modes and the Multipoint Control Units (MCUs), as well as mixed modes and the
transition between those) have been specified. transition between those) have been specified.
SIP addresses users by an email-like address and re-uses some of the SIP addresses (URLs) can be embedded in Web pages. SIP is
infrastructure of electronic mail delivery such as DNS MX records or addressing-neutral, with addresses expressed as URLs of various types
using SMTP EXPN for address expansion. SIP addresses (URLs) can also such as SIP, H.323 or telephone (E.164). A purely representational
be embedded in Web pages. SIP is addressing-neutral, with addresses example of a SIP URL might be sip:+12125551212@foo.example.com, where
expressed as URLs of various types such as SIP, H.323 or telephone foo.example.com is the host serving as a gateway into the PSTN.
(E.164). A purely representational example of a SIP URL might be
sip:12125551212@foo.example.com, where foo.example.com is the host
serving as a gateway into the PSTN.
SIP is independent of the packet layer and only requires an SIP is independent of the packet layer and only requires an
unreliable datagram service, as it provides its own reliability unreliable datagram service, as it provides its own reliability
mechanism. While SIP typically is used over UDP or TCP, it could, mechanism. While SIP typically is used over UDP or TCP, it could,
without technical changes, be run over IPX, or carrier pigeons, ATM without technical changes, be run over IPX, or carrier pigeons, ATM
AAL5 or X.25, in rough order of desirability. AAL5 or X.25, in rough order of desirability.
SIP can set up calls "out-of-band". For example, while the SIP SIP can set up calls "out-of-band". For example, while the SIP
protocol exchanges use IP, plus UDP or TCP, the actual data transport protocol exchanges use IP, plus UDP or TCP, the actual data transport
can take place via the PSTN. This feature makes it possible to use can take place via the PSTN. This feature makes it possible to use
SIP to control a PBX or send requests to a Service Control Point. The SIP to control a PBX or send requests to a Service Control Point. The
PINT services make use of this flexibility. PINT services make use of this flexibility.
7.2 SIP Protocol 7.2 SIP Protocol
SIP is a textual client-server protocol, similar in syntax to HTTP SIP is a textual client-server protocol, similar in syntax to HTTP
and RTSP. Requests consist of a method (INVITE, BYE, ACK, or and RTSP. Requests consist of a method (INVITE, BYE, ACK, or
REGISTER), a list of parameter-value pairs describing the request and REGISTER), a list of parameter-value pairs describing the request and
an optional request body. Parameters include the origin and an optional request body. Parameters include the origin and
destination of the call and a unique call identifier. They may destination of the call and a unique call identifier. They may
indicate the caller's organization as well as the call's subject and indicate the caller's organization as well as the call's subject and
priority. The request body contains a description of the call to be priority. The request body contains a description of the call to be
established or the conference to be joined. The description format is established or the conference to be joined. The description format is
not prescribed by SIP; SDP is one possibility being standardized not prescribed by SIP; SDP is one possibility being standardized
within the IETF. For the purposes of providing PINT services, an within the IETF. For the purposes of providing PINT services, an
additional phone number address format is to be added to SDP. additional phone number address format is to be added to SDP.
Responses indicate whether a request is still being processed, was Responses indicate whether a request is still being processed, was
successful, can possibly be satisfied by another node or failed. When successful, can possibly be satisfied by another node or failed. When
Toward PSTN/Internet Inter-Networking May 1998
a call is redirected, the response indicates the name of the node to a call is redirected, the response indicates the name of the node to
be tried. Unsuccessful calls may also return a better time to try be tried. Unsuccessful calls may also return a better time to try
again. again.
In a typical successful call, the caller sends an INVITE request to In a typical successful call, the caller sends an INVITE request to
the callee. The callee accepts the call by returning a response code the callee. The callee accepts the call by returning a response code
to the callee, which then confirms the receipt of that acceptance to the callee, which then confirms the receipt of that acceptance
with an ACK request. Either side can terminate the call by sending a with an ACK request. Either side can terminate the call by sending a
BYE request. BYE request.
Requests can be authenticated using standard HTTP password and Requests can be authenticated using standard HTTP password and
challenge-response mechanisms. Requests and responses may also be challenge-response mechanisms. Requests and responses may also be
signed and encrypted. signed and encrypted.
7.3 SIP entities 7.3 SIP entities
SIP distinguishes three kinds of entities: SIP distinguishes three kinds of entities:
User agents receive and initiate calls and may forward the call. User agents receive and initiate calls and may forward the call.
A proxy server is an intermediary program that acts as both a server A proxy server is an intermediary program that acts as both a server
and a client for the purpose of making requests on behalf of other and a client for the purpose of making requests on behalf of other
clients. Requests are serviced internally or by passing them on, clients. Requests are serviced internally or by passing them on,
possibly after translation, to other servers. A proxy must interpret, possibly after translation, to other servers. A proxy must interpret,
and, if necessary, rewrite a request message before forwarding it. A and, if necessary, rewrite a request message before forwarding it. A
skipping to change at page 41, line 52 skipping to change at page 46, line 8
A PSTN gateway initiates phone calls between two parties. This may be A PSTN gateway initiates phone calls between two parties. This may be
a server that sends requests to an SCP in an IN environment or it may a server that sends requests to an SCP in an IN environment or it may
be a CTI-controlled PBX. be a CTI-controlled PBX.
A SIP call may traverse one or more proxy servers. A SIP call may traverse one or more proxy servers.
The servers that control a PBX or an SCP act as user agents. A Web The servers that control a PBX or an SCP act as user agents. A Web
server may also act as a SIP user agent. server may also act as a SIP user agent.
7.4 Providing Call Control Functionality 7.4 Providing Call Control Functionality
The SIP for PINT specification provides details on how to use SIP to The SIP for PINT specification provides details on how to use SIP to
initiate phone calls between two PSTN end points. (SIP can also initiate phone calls between two PSTN end points. (SIP can also
initiate calls between Internet end points and between an Internet initiate calls between Internet end points and between an Internet
and PSTN end point, but this is beyond the scope of this document.) and PSTN end point, but this is beyond the scope of this document.)
It should be noted that the SIP client for initiating such phone It should be noted that the SIP client for initiating such phone
calls can be either at the user's location (his/her workstation) or calls can be either at the user's location (his/her workstation) or
Toward PSTN/Internet Inter-Networking May 1998
can be a Web server that calls up a SIP client via a CGI program. can be a Web server that calls up a SIP client via a CGI program.
There is no difference in operation or functionality, except that the There is no difference in operation or functionality, except that the
owner of the Web server may be legally responsible for the calls owner of the Web server may be legally responsible for the calls
made. made.
A SIP client needs to convey two addresses to the PSTN gateway: the A SIP client needs to convey two addresses to the PSTN gateway: the
party making the call and the party to be called. (The party to be party making the call and the party to be called. (The party to be
billed also needs to be identified; this can either be done by a SIP billed also needs to be identified; this can either be done by a SIP
header or by having the server look up the appropriate party based on header or by having the server look up the appropriate party based on
the two parties. This aspect is for further study.) the two parties. This aspect is for further study.)
Described below are three ways these addresses can be conveyed in Described below are three ways these addresses can be conveyed in
SIP. In the example, the address of party A is +1-212-555-1234 and SIP. In the example, the address of party A is +1-212-555-1234 and
that of party B is +1-415-555-1200. (The URL types in this and other that of party B is +1-415-555-1200. (The URL types in this and other
examples are representational; they may but do not have to exist.) examples are representational; they may but do not have to exist.)
(1) The two PSTN addresses are contained in the To header (and (1) The two PSTN addresses are contained in the To header (and
request-URI) and an Also header. For example: request-URI) and an Also header. For example:
INVITE sip:1-212-555-1234@pbx.example.com INVITE sip:+1-212-555-1234@pbx.example.com SIP/2.0
To: phone:1-212-555-1234 To: phone:1-212-555-1234
From: sip:j.doe@example.com From: sip:j.doe@example.com
Content-type: application/sdp Content-type: application/sdp
Call-ID: 19970721T135107.25.181@foo.bar.com Call-ID: 19970721T135107.25.181@foo.bar.com
Also: phone:+1-415-555-1200 Also: phone:+1-415-555-1200
v=0 v=0
o=user1 53655765 2353687637 IN IP4 128.3.4.5 o=user1 53655765 2353687637 IN IP4 128.3.4.5
c=PSTN E.164 +1-415-555-1200 c=PSTN E.164 +1-415-555-1200
t=0 0 t=0 0
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In that case, the gateway first connects to party A and then party B, In that case, the gateway first connects to party A and then party B,
but without waiting for A to accept the call before calling B. but without waiting for A to accept the call before calling B.
(2) Parties A and B are indicated by separate invitations. This (2) Parties A and B are indicated by separate invitations. This
allows the gateway to make sure that party A is indeed available allows the gateway to make sure that party A is indeed available
before calling party B. After calling party A, the gateway could before calling party B. After calling party A, the gateway could
play an announcement indicating that the call is being connected play an announcement indicating that the call is being connected
using, for example, RTSP with appropriate Conference header using, for example, RTSP with appropriate Conference header
indicating the call. indicating the call.
INVITE sip:1-212-555-1234@pbx.example.com INVITE sip:+1-212-555-1234@pbx.example.com SIP/2.0
To: phone:1-212-555-1234 To: phone:1-212-555-1234
From: sip:j.doe@example.com From: sip:j.doe@example.com
Content-type: application/sdp Content-type: application/sdp
Call-ID: 19970721T135107.25.181@foo.bar.com Call-ID: 19970721T135107.25.181@foo.bar.com
... ...
INVITE sip:1-415-555-1200@pbx.example.com INVITE sip:+1-415-555-1200@pbx.example.com SIP/2.0
To: phone:+1-415-555-1200 To: phone:+1-415-555-1200
From: sip:j.doe@example.com From: sip:j.doe@example.com
Content-type: application/sdp Content-type: application/sdp
Call-ID: 19970721T135107.25.181@foo.bar.com Call-ID: 19970721T135107.25.181@foo.bar.com
Toward PSTN/Internet Inter-Networking May 1998
... ...
(3) The two PSTN addresses are conveyed in the To header of the SIP (3) The two PSTN addresses are conveyed in the To header of the SIP
request and the address in the SDP media description. Thus, a request request and the address in the SDP media description. Thus, a request
may look as follows: may look as follows:
INVITE sip:1-212-555-1234@pbx.example.com INVITE sip:+1-212-555-1234@pbx.example.com SIP/2.0
To: phone:1-212-555-1234 To: phone:1-212-555-1234
From: sip:j.doe@example.com From: sip:j.doe@example.com
Content-type: application/sdp Content-type: application/sdp
Call-ID: 19970721T135107.25.181@foo.bar.com Call-ID: 19970721T135107.25.181@foo.bar.com
v=0 v=0
o=user1 53655765 2353687637 IN IP4 128.3.4.5 o=user1 53655765 2353687637 IN IP4 128.3.4.5
c=PSTN E.164 +1-415-555-1200 c=PSTN E.164 +1-415-555-1200
t=0 0 t=0 0
m=audio 0 RTP/AVP 0 m=audio 0 RTP/AVP 0
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(e.g., the requesting IP-host) is allowed to use a network resource (e.g., the requesting IP-host) is allowed to use a network resource
(e.g., requesting services from the PINT gateway). (e.g., requesting services from the PINT gateway).
+Non-repudiation to account for all operations in case of doubt or +Non-repudiation to account for all operations in case of doubt or
dispute. dispute.
+Confidentiality to avoid disclosure of information (e.g., the end +Confidentiality to avoid disclosure of information (e.g., the end
user profile information and data) without the permission of its user profile information and data) without the permission of its
owner. owner.
Toward PSTN/Internet Inter-Networking May 1998
In the course of the PINT interface development, additional In the course of the PINT interface development, additional
requirements are likely to arise. It is imperative that the resultant requirements are likely to arise. It is imperative that the resultant
interfaces include specific means to meet all the security interfaces include specific means to meet all the security
requirements. requirements.
9. Conclusion 9. Conclusion
This document has provided the information relevant to the This document has provided the information relevant to the
development of inter-networking interfaces between the PSTN and development of inter-networking interfaces between the PSTN and
Internet for supporting PINT services. Specifically, it addressed Internet for supporting PINT services. Specifically, it addressed
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10. Acknowledgments 10. Acknowledgments
The authors would like to acknowledge Scott Bradner, Igor Faynberg, The authors would like to acknowledge Scott Bradner, Igor Faynberg,
Dave Oran, Scott Petrack, Allyn Romanow for their insightful comments Dave Oran, Scott Petrack, Allyn Romanow for their insightful comments
presented to the discussions in the PINT Working Group that lead to presented to the discussions in the PINT Working Group that lead to
the creation of this document. the creation of this document.
11. Appendix 11. Appendix
11.1 PSTN/IN 101 11.1 PSTN/IN 101
11.1.1 Public Switched Telephone Network 11.1.1 Public Switched Telephone Network
What is normally considered as "the Telephone Network" consists of a What is normally considered as "the Telephone Network" consists of a
set of interconnected networks. Potentially, each of these networks set of interconnected networks. Potentially, each of these networks
could be owned by a different Network Operator. The official name for could be owned by a different Network Operator. The official name for
such a network is Public Switched Telecommunications Network (PSTN). such a network is Public Switched Telecommunications Network (PSTN).
A simple PSTN consists of a set of Switches (called Central Offices A simple PSTN consists of a set of Switches (called Central Offices
or Telephone Exchanges) with links interconnecting them to make up or Telephone Exchanges) with links interconnecting them to make up
the network, along with a set of access connections by which the network, along with a set of access connections by which
terminals are attached. The PSTN is used to deliver calls between terminals are attached. The PSTN is used to deliver calls between
terminals connected to itself or to other PSTNs with which it is terminals connected to itself or to other PSTNs with which it is
interconnected. Calls on the PSTN are circuit switched; that is, a interconnected. Calls on the PSTN are circuit switched; that is, a
bi-directional connection is made between the calling and called bi-directional connection is made between the calling and called
terminals for the duration of the call. In PSTNs the connection is terminals for the duration of the call. In PSTNs the connection is
usually carried through the network in digital format occupying a usually carried through the network in digital format occupying a
fixed bandwidth; this is usually 56 or 64 Kbps. The overall fixed bandwidth; this is usually 56 or 64 Kbps. The overall
configuration of the PSTN is shown in Figure 16. configuration of the PSTN is shown in Figure 16.
Toward PSTN/Internet Inter-Networking May 1998
/--\ /--\
()/\()__ ()/\()__
/__\ \ ................................. /__\ \ .................................
\ ! ! ! /--\ \ ! ! ! /--\
__ \ [-!-] [-!-] ! ()/\() __ \ [-!-] [-!-] ! ()/\()
\ \ \__[CO ]=========[CO ]==\\ ! ___/__\ \ \ \__[CO ]=========[CO ]==\\ ! ___/__\
[Fax]________[---] [---] \\ [-!-] / __ [Fax]________[---] [---] \\ [-!-] / __
\\=======[CO ]____/ \ \ \\=======[CO ]____/ \ \
[---]________[Fax] [---]________[Fax]
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
Figure 16 Figure 16
Messages are sent between the Switches to make and dissolve Messages are sent between the Switches to make and dissolve
connections through the network on demand and to indicate the status connections through the network on demand and to indicate the status
of terminals involved in a call; these "signaling" messages are of terminals involved in a call; these "signaling" messages are
carried over a separate (resilient) data network dedicated to this carried over a separate (resilient) data network dedicated to this
purpose. This signaling network is also known as the Common Channel purpose. This signaling network is also known as the Common Channel
Signaling (CCS) or Signaling System Number 7 (or SS7) network after Signaling (CCS) or Signaling System Number 7 (or SS7) network after
the names of the signaling protocol suite used. the names of the signaling protocol suite used.
As yet, the majority of access connections to a PSTN carry analogue As yet, the majority of access connections to a PSTN carry analogue
skipping to change at page 46, line 5 skipping to change at page 50, line 29
each of the potential connections, together with a separate channel each of the potential connections, together with a separate channel
dedicated to sending and receiving call request and call alert data dedicated to sending and receiving call request and call alert data
as well as carrying packet switched user data. These call request and as well as carrying packet switched user data. These call request and
call alert messages act as the equivalent of the pulses or tones that call alert messages act as the equivalent of the pulses or tones that
are sent when dialing, and the ringing signal that is sent to a are sent when dialing, and the ringing signal that is sent to a
telephone when a call is being made to it. telephone when a call is being made to it.
The operation of the call request is fairly simple in most cases and The operation of the call request is fairly simple in most cases and
is shown in Figure 17. is shown in Figure 17.
Toward PSTN/Internet Inter-Networking May 1998
/--\ /--\
() () () ()
--____ --____
/++\ \ ................................. /--\ /++\ \ ................................. /--\
/----\ \ ^ v ! () () /----\ \ ^ v ! () ()
A \ [-!-] [-!-] ! -- A \ [-!-] [-!-] ! --
\->[CO ]=========[CO ]==\\ v ->-/ \ \->[CO ]=========[CO ]==\\ v ->-/ \
[---] [---] \\ [-!-] / /----\ [---] [---] \\ [-!-] / /----\
\\=======[CO ]____/ B \\=======[CO ]____/ B
[---] [---]
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
CO Central Office (Telephone Exchange) CO Central Office (Telephone Exchange)
Figure 17 Figure 17
The user presses a sequence of numbers on a telephone handset The user presses a sequence of numbers on a telephone handset
(labeled A), and the telephone passes a sequence of digits (either as (labeled A), and the telephone passes a sequence of digits (either as
pulses or tone pairs) to the Central Office via the access line. The pulses or tone pairs) to the Central Office via the access line. The
Central Office contains a processor that will be notified that the Central Office contains a processor that will be notified that the
user has made a request and the digit string that is the sole user has made a request and the digit string that is the sole
parameter of the request. This digit string is taken to be the unique parameter of the request. This digit string is taken to be the unique
address of an access line connected either to itself or to another address of an access line connected either to itself or to another
Central Office. There is a hierarchical addressing scheme, so that Central Office. There is a hierarchical addressing scheme, so that
the digit string can be parsed easily. A call request to a terminal the digit string can be parsed easily. A call request to a terminal
(labeled B) connected to a remote Central Office can be routed by (labeled B) connected to a remote Central Office can be routed by
examining the digit string passed; the Central Office will extract examining the digit string passed; the Central Office will extract
the part of the passed address that corresponds to the remote Central the part of the passed address that corresponds to the remote Central
Office in question, and can route the request onward, forming an Office in question, and can route the request onward, forming an
inter-Switch call request and passing it via the signaling network. inter-Switch call request and passing it via the signaling network.
At the same time it will allocate one of its available transmission At the same time it will allocate one of its available transmission
channels towards the remote Central Office. channels towards the remote Central Office.
11.1.2 Intelligent Network 11.1.2 Intelligent Network
This scheme has been used since the 1950s, and suffices for the This scheme has been used since the 1950s, and suffices for the
majority of calls. However, there are a range of other services that majority of calls. However, there are a range of other services that
can be (and have been) provided, enhancing this basic call can be (and have been) provided, enhancing this basic call
processing. Freephone or Premium Rate services (1-800 or 1-900 processing. Freephone or Premium Rate services (1-800 or 1-900
services) are good examples of the supplementary services that have services) are good examples of the supplementary services that have
been introduced. Apart from the important feature that the cost of been introduced. Apart from the important feature that the cost of
these calls is varied so that the caller does not pay for a free- these calls is varied so that the caller does not pay for a free-
phone call, or pays an extra charge for a premium rate call, they phone call, or pays an extra charge for a premium rate call, they
have the similarity that the number dialed must be translated to have the similarity that the number dialed must be translated to
arrive at the "real" address of the destination terminal. They are arrive at the "real" address of the destination terminal. They are
known as number translation services, and make up the bulk of all known as number translation services, and make up the bulk of all
supplementary services delivered today. supplementary services delivered today.
These were originally programmed into each Central Office, but the These were originally programmed into each Central Office, but the
complexity of maintaining the data tables on each processor grew complexity of maintaining the data tables on each processor grew
cumbersome, so a more general solution was sought. After a cumbersome, so a more general solution was sought. After a
considerable gestation period, the eventual solution was the considerable gestation period, the eventual solution was the
Toward PSTN/Internet Inter-Networking May 1998
Intelligent Network. This takes the separation of Central Offices and Intelligent Network. This takes the separation of Central Offices and
the network links interconnecting them a stage further. the network links interconnecting them a stage further.
The Central Offices are considered to provide the Call Control The Central Offices are considered to provide the Call Control
Function (CCF). In addition, the Service Switching Function (SSF) is Function (CCF). In addition, the Service Switching Function (SSF) is
provided to "enhance" the operation of these Switches by detecting provided to "enhance" the operation of these Switches by detecting
when a particular request has been made (such as by dialing 1-800). when a particular request has been made (such as by dialing 1-800).
If this pattern is detected, the equipment implementing the SSF will If this pattern is detected, the equipment implementing the SSF will
send a specialized request message over the signaling network to a send a specialized request message over the signaling network to a
separate computer that implements the Service Control Function (SCF). separate computer that implements the Service Control Function (SCF).
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\ || / ! ! /--\ \ || / ! ! /--\
__ \ [|-!] [-!-] ! ()/\() __ \ [|-!] [-!-] ! ()/\()
\ \ \__[SSF] [CCF] ! ___/__\ \ \ \__[SSF] [CCF] ! ___/__\
[Fax]________[CCF]=========[---]==\\ [!--] / __ [Fax]________[CCF]=========[---]==\\ [!--] / __
\\========[CCF]__/ \ \ \\========[CCF]__/ \ \
[---]_______[Fax] [---]_______[Fax]
Key: ___ access relationship Key: ___ access relationship
=== trunk relationship === trunk relationship
... signaling relationship ... signaling relationship
Figure 18 Figure 18
The advantage is that there can be a much smaller number of physical The advantage is that there can be a much smaller number of physical
units dedicated to the SCF, and as they are connected to the units dedicated to the SCF, and as they are connected to the
signaling network they can be contacted by, and can send instructions signaling network they can be contacted by, and can send instructions
back to, all of the units providing the SSF and thus the CCF. back to, all of the units providing the SSF and thus the CCF.
In another enhancement, a separate entity called the Special Resource In another enhancement, a separate entity called the Special Resource
Function (SRF) was defined. Equipment implementing this function Function (SRF) was defined. Equipment implementing this function
includes announcement units to play recorded messages (for example, includes announcement units to play recorded messages (for example,
prompts to enter digits) to callers. It will also include the tone prompts to enter digits) to callers. It will also include the tone
decoders needed to capture any digits pressed by the caller in decoders needed to capture any digits pressed by the caller in
response to the prompts. It is connected to the rest of the PSTN response to the prompts. It is connected to the rest of the PSTN
usually via trunk data links. It will also include a signaling usually via trunk data links. It will also include a signaling
connection (directly or indirectly) back to the SCF, via the PSTN's connection (directly or indirectly) back to the SCF, via the PSTN's
core signaling network. core signaling network.
As an example of the way that these different functional entities As an example of the way that these different functional entities
interact, the SCF can ask an SSF handling a call to route the caller interact, the SCF can ask an SSF handling a call to route the caller
temporarily through to an SRF. In response to instructions sent to it temporarily through to an SRF. In response to instructions sent to it
Toward PSTN/Internet Inter-Networking May 1998
from the SCF over the signaling network, the SRF can play from the SCF over the signaling network, the SRF can play
announcements and can collect digits that the user presses on their announcements and can collect digits that the user presses on their
terminal in response to prompts they are played. Once these digits terminal in response to prompts they are played. Once these digits
have been collected they can be passed on to the SCF via a signaling have been collected they can be passed on to the SCF via a signaling
message for further processing. In normal operation, the SCF would message for further processing. In normal operation, the SCF would
then ask the SSF to dissolve the temporary connection between the then ask the SSF to dissolve the temporary connection between the
user's terminal and the SRF. This allows the collection of account user's terminal and the SRF. This allows the collection of account
numbers or passwords (or PINs) and forms the heart of many "Calling numbers or passwords (or PINs) and forms the heart of many "Calling
Card" services. Card" services.
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\ || / ! \ | /--\ \ || / ! \ | /--\
__ \ [|-!] [-!-] \ | ()/\() __ \ [|-!] [-!-] \ | ()/\()
\ \ \__[SSP]=========[CO ]==\\ \ | ___/__\ \ \ \__[SSP]=========[CO ]==\\ \ | ___/__\
[Fax]________[---] [---] \\ [!-|] / __ [Fax]________[---] [---] \\ [!-|] / __
\\=======[CO ]__/ \ \ \\=======[CO ]__/ \ \
[---]_______[Fax] [---]_______[Fax]
Key: ___ Access Lines Key: ___ Access Lines
=== Trunk Links (inter-CO user data links) === Trunk Links (inter-CO user data links)
... Inter-CO signaling network links ... Inter-CO signaling network links
SSP Service Switching Point - a unit that implements the Service SSP Service Switching Point - a unit that implements the
Switching Function Service Switching Function
CCP Call Control Point - a unit that performs call control CCP Call Control Point - a unit that performs call control
functions. functions.
This is normally a kind of Central Office (shown as CO above) This is normally a kind of Central Office (shown as CO
SCP Service Control Point - a unit implementing the Service Control above)
Function. NOTE that this is connected to the SS7 Network and SCP Service Control Point - a unit implementing the Service
uses this connection for all of its communications. Control Function. NOTE that this is connected to the SS7
Network and uses this connection for all of its
communications.
I.P Intelligent Peripheral - a unit that contains specialized I.P Intelligent Peripheral - a unit that contains specialized
resources (like announcement units, tone decoders). resources (like announcement units, tone decoders).
In effect, it implements Special Resource Functions. In effect, it implements Special Resource Functions.
SN Service Node SN Service Node
Figure 19 Figure 19
This diagram also shows a unit called a Service Node, or SN. This This diagram also shows a unit called a Service Node, or SN. This
contains components that realize all of the operational Intelligent contains components that realize all of the operational Intelligent
Network functions (SSF, SCF, SDF, and SRF). It is sometimes more Network functions (SSF, SCF, SDF, and SRF). It is sometimes more
Toward PSTN/Internet Inter-Networking May 1998
convenient to have all of these elements in one node (for example, convenient to have all of these elements in one node (for example,
for operations and maintenance reasons), particularly within smaller for operations and maintenance reasons), particularly within smaller
PSTNs or where there is a relatively low level of requests for PSTNs or where there is a relatively low level of requests for
particular services. Another difference is that, as they are all co- particular services. Another difference is that, as they are all co-
located, proprietary protocols can be used for internal located, proprietary protocols can be used for internal
communication, rather than the full Intelligent Network Application communication, rather than the full Intelligent Network Application
Part (INAP) protocol used over the core signaling network between Part (INAP) protocol used over the core signaling network between
discrete units. It also differs from the "unbundled" approach in that discrete units. It also differs from the "unbundled" approach in that
it is connected to the COs within a PSTN as a peripheral, having only it is connected to the COs within a PSTN as a peripheral, having only
an access connection to a Central Office; there is no connection to an access connection to a Central Office; there is no connection to
the core signaling network. Other than this, it operates in a similar the core signaling network. Other than this, it operates in a similar
way, and can provide the same kinds of services. Information on the way, and can provide the same kinds of services. Information on the
specification of the Intelligent Network can be found in the ITU specification of the Intelligent Network can be found in the ITU
recommendations [1], while two books ([2] and [3]) describe the recommendations [1], while two books ([2] and [3]) describe the
system, its history, operation, and the philosophy behind it. system, its history, operation, and the philosophy behind it.
11.2 Call Center Features 11.2 Call Center Features
A Call Center is a system that allows a company to be organized with A Call Center is a system that allows a company to be organized with
a group of similar individuals (agents), all of whom can either make a group of similar individuals (agents), all of whom can either make
calls to, or take calls from, customers. The system distributes calls to, or take calls from, customers. The system distributes
incoming calls to the agents based on their availability and incoming calls to the agents based on their availability and
automates the placement of outgoing calls, selecting an agent to automates the placement of outgoing calls, selecting an agent to
handle the call and routing the call to them only once the call handle the call and routing the call to them only once the call
request has been made of the PSTN. request has been made of the PSTN.
The incoming call distribution feature ("automatic call The incoming call distribution feature ("automatic call
skipping to change at page 50, line 4 skipping to change at page 55, line 7
the job of company telephone receptionist in routing incoming calls. the job of company telephone receptionist in routing incoming calls.
Where possible, the information gleaned from the customer can be Where possible, the information gleaned from the customer can be
provided to the selected agent, usually via a separate networked provided to the selected agent, usually via a separate networked
computer connection. Similarly, if an outgoing call is being made to computer connection. Similarly, if an outgoing call is being made to
one of a list of customers, information on the customer and the one of a list of customers, information on the customer and the
purpose of the call can be provided to the agent selected to handle purpose of the call can be provided to the agent selected to handle
the call. Such configurations are generally called "Computer the call. Such configurations are generally called "Computer
Telephony Integration" or CTI systems. Strictly, a CTI system can be Telephony Integration" or CTI systems. Strictly, a CTI system can be
arranged to handle routing of incoming calls and automation of arranged to handle routing of incoming calls and automation of
Toward PSTN/Internet Inter-Networking May 1998
outgoing calls only (also known as computer integrated telephony outgoing calls only (also known as computer integrated telephony
features), without the agents having access to a network of features), without the agents having access to a network of
computers. However, the business case for combining the telephony computers. However, the business case for combining the telephony
functions of the call center with provision to the agents of functions of the call center with provision to the agents of
computers with customer information can be compelling. computers with customer information can be compelling.
This is often further combined with a company's order and service This is often further combined with a company's order and service
processing computer system. In this case, a call is treated as part processing computer system. In this case, a call is treated as part
of a business transaction, with the information to be exchanged of a business transaction, with the information to be exchanged
captured as fields of a computer form. While such a computer system captured as fields of a computer form. While such a computer system
skipping to change at page 50, line 55 skipping to change at page 56, line 10
Center could be configured centrally while still allowing agents to Center could be configured centrally while still allowing agents to
be located anywhere within the telephone network. It also means that be located anywhere within the telephone network. It also means that
the supported company can pay for the Call Center features "as they the supported company can pay for the Call Center features "as they
go" rather than having a high "up front" cost. go" rather than having a high "up front" cost.
12. References 12. References
[1] ITU-T Q.12xx Recommendation Series, Geneva, 1995. [1] ITU-T Q.12xx Recommendation Series, Geneva, 1995.
[2] I. Faynberg, L. R. Gabuzda, M. P. Kaplan, and N. J. Shah, "The [2] I. Faynberg, L. R. Gabuzda, M. P. Kaplan, and N. J. Shah, "The
Intelligent Network Standards, their Application to Services", Intelligent Network Standards, their Application to Services",
McGraw-Hill, 1996. McGraw-Hill, 1996.
[3] T. Magedanz and R. Popesku-Zeletin, "Intelligent Networks: Basic [3] T. Magedanz and R. Popesku-Zeletin, "Intelligent Networks: Basic
Technology, Standards and Evolution", Intl. Thomson Computer Press, Technology, Standards and Evolution", Intl. Thomson Computer
Press, 1996.
Toward PSTN/Internet Inter-Networking May 1998
1996.
[4] Information processing systems - Open Systems Interconnection - [4] Information processing systems - Open Systems Interconnection -
Specification of Abstract Syntax Notation One (ASN.1), International Specification of Abstract Syntax Notation One (ASN.1),
Organization for Standardization, International Standard 8824, International Organization for Standardization, International
December, 1987. Standard 8824, December, 1987.
[5] McCloghrie, K., Editor, "Structure of Management Information for [5] McCloghrie, K., Editor, "Structure of Management Information for
Version 2 of the Simple Network Management Protocol (SNMPv2)", Version 2 of the Simple Network Management Protocol (SNMPv2)",
RFC1902, January 1996. RFC 1902, January 1996.
[6] D. Kristol and L. Montulli, RFC2109, "HTTP State Management [6] Kristol, D. and L. Montulli, "HTTP State Management Mechanism",
Mechanism", February, 1997. RFC 2109, February 1997.
[7] D. Zimmerman, RFC1288, "The Finger User Information Protocol", [7] Zimmerman, D., "The Finger User Information Protocol", RFC 1288
December, 1991. December 1991.
Author's Addresses Authors' Addresses
Steve Bellovin Steve Bellovin
AT&T Labs AT&T Labs
Room B135 Room E-215
180 Park Ave. Bldg. 103 180 Park Ave. Bldg. 103
Florham Park, NJ 07932-0000 Florham Park, NJ 07932-0000
USA USA
E-Mail: smb@research.att.com
Telephone: +1 973 360 8656 Phone: +1 973 360 8656
Fax: +1 973 360 8077 Fax: +1 973 360 8077
EMail: smb@research.att.com
Fred M. Burg Fred M. Burg
AT&T Labs AT&T Labs
Room 1N-117 Room 1N-117
307 Middletown Lincroft Road 307 Middletown Lincroft Road
Lincroft, NJ 07738 Lincroft, NJ 07738
USA USA
E-Mail: fburg@hogpb.att.com
Telephone: +1 732 576 4322 Phone: +1 732 576 4322
Fax: +1 732 576 4317 Fax: +1 732 576 4317
EMail: fburg@hogpb.att.com
Lawrence Conroy Lawrence Conroy
Roke Manor Research Limited Roke Manor Research Limited
IT&N-INIA Group IT&N-INIA Group
Roke Manor, Old Salisbury Lane, Roke Manor, Old Salisbury Lane,
Romsey, Hampshire SO51 0ZN Romsey, Hampshire SO51 0ZN
U.K. U.K.
E-mail: lwc@roke.co.uk
Telephone: +44 1794 833666 Phone: +44 1794 833666
Fax: +44 1794 833434 Fax: +44 1794 833434
EMail: lwc@roke.co.uk
Paul Davidson Paul Davidson
Nortel Nortel
P.O.Box 3511 Station "C" P.O.Box 3511 Station "C"
Mail Stop 242 Mail Stop 242
Toward PSTN/Internet Inter-Networking May 1998
Ottawa, Ontario, Canada K1Y 4H7 Ottawa, Ontario, Canada K1Y 4H7
E-Mail: pauldav@nortel.ca
Telephone: +1 613 763 4234
Phone: +1 613 763 4234
EMail: pauldav@nortel.ca
A. DeSimone A. DeSimone
AT&T Labs Lucent Technologies
Room 1N-113 Room 6H510
307 Middletown Lincroft Road 600-700 Mountain Avenue
Lincroft, NJ 07738 Murray Hill, NJ 07974-0636
USA USA
E-Mail: tds@att.com
Telephone: +1 732 576 5655 Phone: +1 908 582 2382
Fax: +1 732 576 4317 Fax: +1 908 582 1086
E-Mail:tds@lucent.com
Murali Krishnaswamy Murali Krishnaswamy
Bell Laboratories Bell Laboratories
Lucent Technologies Lucent Technologies
Room 2G-527a Room 2G-527a
101 Crawfords Corner Road 101 Crawfords Corner Road
Holmdel, NJ 07733-3030 Holmdel, NJ 07733-3030
USA USA
E-mail: murali@bell-labs.com
Telephone: +1 732 949 3611 Phone: +1 732 949 3611
Fax: +1 732 949 3210 Fax: +1 732 949 3210
EMail: murali@bell-labs.com
Hui-Lan Lu Hui-Lan Lu
Bell Laboratories Bell Laboratories
Lucent Technologies Lucent Technologies
Room 4K-309 Room 4K-309
101 Crawfords Corner Road 101 Crawfords Corner Road
Holmdel, NJ 07733-3030 Holmdel, NJ 07733-3030
USA USA
E-mail: hui-lan.lu@bell-labs.com
Telephone: +1 732 949 0321 Phone: +1 732 949 0321
Fax: +1 732 949 1196 Fax: +1 732 949 1196
EMail: hui-lan.lu@bell-labs.com
Henning Schulzrinne Henning Schulzrinne
Dept. of Computer Science Dept. of Computer Science
Columbia University Columbia University
New York, NY 10027 New York, NY 10027
USA USA
E-Mail: schulzrinne@cs.columbia.edu
Telephone: +1 212 939 7042 (@Bell Labs: 732 949 8344)
Fax: +1 212 666 0140
Phone: +1 212 939 7042 (@Bell Labs: 732 949 8344)
Fax: +1 212 666 0140
EMail: schulzrinne@cs.columbia.edu
Kamlesh T. Tewani Kamlesh T. Tewani
AT&T Labs AT&T Labs
Room 1K-334 Room 1K-334
101, Crawfords Corner Rd. 101, Crawfords Corner Rd.
Holmdel, NJ 07733 Holmdel, NJ 07733
USA USA
E-Mail: tewani@att.com
Telephone: +1 732 949 5369
Fax: +1 732 949 8569
Toward PSTN/Internet Inter-Networking May 1998 Phone: +1 732 949 5369
Fax: +1 732 949 8569
EMail: tewani@att.com
Kumar Vishwanathan Kumar Vishwanathan
Isochrone Isochrone
E-Mail: kumar@isochrone.com EMail: kumar@isochrone.com
Full Copyright Statement
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