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INTERNET DRAFT                                               Taruni Seth

Internet Engineering Task Force                          Albert Broscius

February 26, 1999                                      Christian Huitema

Expires August 26, 1999                                   Huai-An P. Lin

<draft-ietf-sigtran-tcap-perf-req-00.txt>                       Bellcore

   Performance Requirements for TCAP Signaling in Internet Telephony

              T. Seth, A. Broscius, C. Huitema, H. P. Lin

Status of this document

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as "work in progress."

To view the entire list of current Internet-Drafts, please check the "
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This document is an Internet-Draft.  Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and its
working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.


To allow interoperability between the existing telephone network and
Internet Telephony (IT) it is necessary for the signaling performance to
be comparable to that of the current standards to avoid introducing
degradation in the service. In this Internet Draft, we discuss the

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

performance requirements for TCAP signaling across an IP network. We
also highlight the dependency on the SCP database location and thus
problems related in providing high-quality service for TCAP based appli-

Table of Contents

1. Introduction

2. Context
   .............................................. 4

3. Overview of TCAP
   .............................................. 5

3.1 TCAP in a Nutshell
   .............................................. 5

3.2 Signaling Connection Control Part
   .............................................. 6

3.3 Global Title Translation
   .............................................. 6

3.4 Service Control Point (SCP)
   .............................................. 7

3.5 TCAP Transaction Flow Diagram
   .............................................. 7

4. Performance Requirements
   .............................................. 9

4.1 Query Response Time
   .............................................. 9

4.2 SSP Response Time
   .............................................. 10

4.3 SCP Response Time
   .............................................. 10

4.3.1 SCP Handling Time
   .............................................. 11

4.3.2 Disk Lookup Time
   .............................................. 11

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

4.3.3 Link Output Delay
   .............................................. 11

4.3.4 Total SCP Response Time
   .............................................. 12

4.4 Message Transfer Time
   .............................................  12

4.5 Other General Parameters
   .............................................. 13

4.5.1 maxResponseTime
   .............................................. 13

4.5.2 maxPendingTime
   .............................................. 13

5. Implications to VoIP
   .............................................. 13

6. References
   .............................................. 15

7. Authors' Addresses
   .............................................. 15

Full Copyright Statement
   .............................................. 16

1.  Introduction

A public switched telephone network (PSTN) based telephone call involves
the delivery of voice over a dedicated circuit-switched network (CSN)
and the delivery of call processing signaling messages over a separate
packet switched network called the Common Channel Signaling (CCS) net-
work. PSTN call processing involves two types of signaling messages: the
ISUP (ISDN User Part) [2] messages which are responsible for the basic
setup, management and teardown of a telephone call and the Transaction
Capabilities User Part (TCAP) [3] messages, which are used for non-
circuit related messages used in advanced call setup features, and those
requiring access to network databases, such as the database of valid
calling card PIN numbers. To interwork with PSTN, Internet Telephony
must process these ISUP and TCAP messages. Both of these protocols have
specific performance requirements. Requirements for ISUP messages were
discussed in [1]. This Internet Draft focuses mainly on some of the

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

issues related to the performance requirement of the TCAP messages.

2.  Context

A commonly envisioned Internet Telephony system architecture includes an
IP network as the core communication infrastructure. Both reliable and
unreliable data is transported over the IP infrastructure through the
use of a variety of upper layer protocols. In the IP network, generally,
all the traffic competes against each other in a single flow. Segmenting
signaling, data and voice traffic flows on the network allows the per-
formance guarantees of the different traffic components to be set
independently, since they differ in their loss and delay tolerance

Signalling quality requirements could be expressed by simply stating
that call set-up time, and generally signalling delays, should be simi-
lar to those observed in classic telephony networks. When analyzing the
requirements, we will distinguish between absolute requirements, which
are mandated for proper interaction with the classic telephone network,
and quality objectives, which are mostly desirable goals based on user

The mandatory requirements of telephony systems are specified in several
"General Requirement" documents published by Bellcore and ITU-T. We need
to derive loss and delay bounds from the existing telephony standards
for inter working of Internet Telephony and the PSTN. Both loss and
latency affect the perceived user quality when establishing telephone
calls across the Internet Telephony infrastructure. Excessive delay may
cause call setup failure through end-switch time-outs, requiring the
user to re-dial.  TCAP loss may also cause call setup failures through
timeouts that may leave resources in the network held in an active state
after a call teardown message is lost.

Earlier work specified the requirements for ISUP Signaling over IP based
on the PSTN specifications[1]. ISUP messages are used for basic call
control and setup, whereas TCAP messages are particular to each specific
application and do not have generic performance requirements. However,
there are some specifications for the network elements involved in a
TCAP transaction, which allow us to estimate some other measures. Here
we will try and establish a similar set of parameters for TCAP messag-
ing, based on signalling performance metrics such as the query-response

In this Internet draft, we focus on the performance requirements for
TCAP applications. We discuss mandatory requirements as established by
the timers in PSTN network elements, which determine the tolerance of
these applications to delays and losses. We will also discuss the user
expectations and values of these requirements as available from current

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

PSTN implementations. We summarize the implications of these in a VoIP
framework and discuss merits of existing  technologies to enhance these
performance requirements in the IP networks.

3.  Overview of TCAP

3.1.    TCAP in a Nutshell

TCAP messages are designed for accessing databases or other switches to
retrieve information or invoke features. TCAP enables the deployment of
advanced intelligent network services by supporting non-circuit related
information exchange between signaling points using the signaling con-
nection control part (SCCP) connectionless service for message tran-
sport. This is a fundamental difference between ISUP and TCAP protocols.
ISUP messages follow a particular path used to establish a circuit con-
nection and use the Message Transfer Part (MTP) to route its messages,
whereas TCAP information is not related to any one circuit and must be
transferred through the network using end-to-end signaling, which is
achieved by the SCCP protocol above MTP. The term "Transaction Capabili-
ties" refers to the application layer protocol, called TCAP, plus the
supporting Presentation, Session, and Transport layers, called the
Application Services Part (ASP). A common example of TCAP usage is in
dialing a 800, 888, or 900 number. An SSP uses TCAP to query an SCP to
determine the routing number(s) associated with the dialed digits. The
SCP uses TCAP to return a response containing the routing number(s) (or
an error) back to the SSP.

TCAP messages consist of two portions: a Transaction Portion composed
entirely of protocol control information, and a Component Portion which
contains protocol-related information as well as data concerning the
application process.

The transaction portion of the TCAP message identifies whether the tran-
saction between two nodes is expected to consist of a single message
(i.e. one way communication) or multiple messages (i.e. interactive com-
munication). There are five types of TCAP messages, called Package Type:
Query, Response, Conversation, Unidirectional, and Abort. The transac-
tion portion provides the information necessary for the signaling point
to route the component information to its destination. It contains the
Transaction ID and the package type identifier. The Transaction ID is a
reference to correlate messages within the same transaction and associ-
ate the TCAP transaction with a specific application at the originating
and destination signaling points.

In a single transaction, one or more operations may occur. For each
operation, one or more components may be involved. Components provide
the information that request an action, invoke an operation or provide
the reaction to a previous request. Component types include Invoke,

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

Return Result, Return Error, and Reject. Components include parameters
which contain application-specific data carried unexamined by TCAP.

3.2.    Signaling Connection    Control Part

The SCCP provides connectionless and connection-oriented network ser-
vices above MTP Level 3. SCCP provides two major functions that are
lacking in the MTP. The first of these is the capability to address
applications within a signaling point. The MTP can only receive and
deliver messages from a node "as a whole"; it does not deal with
software applications within a node. While MTP Level 3 provides point
codes to allow messages to be addressed to specific signaling points,
SCCP provides subsystem numbers to allow messages to be addressed to
specific applications (called subsystems) at these signaling points.
SCCP is used as the transport layer for TCAP-based services such as toll
free (800) phone, calling card, and wireless services. The SCCP controls
provide efficient routing of TCAP like messages that are independent of
voice network connections.  Their routing information may contain the
Link Selection information besides the Originating and Destination Point
Codes, if necessary.

3.3.    Global Title    Translation

SCCP also provides the means by which a Signal Transfer Point (STP) can
perform global title translation (GTT), a procedure by which the desti-
nation signaling point and subsystem number (SSN) is determined from
digits (i.e., the global title) present in the signaling message. The
global title digits may be the dialed 800/888 number, calling card
number, or mobile subscriber identification number depending on the ser-
vice requested. Since an STP provides global title translation, ori-
ginating signaling points do not need to know the destination point code
or subsystem number of every potential destination to which they might
have to route a message for the associated service. Only the STPs need
to maintain a database of destination point codes and subsystem numbers
associated with specific services and possible destinations. The STP
examines the message, and determines where the message should be routed.

Switches can generate queries addressed to their local STPs, which,
using global title translation, select the correct destination to which
the message should be routed. STPs must maintain a database that enables
them to determine to where a query should be routed. Global title trans-
lation effectively centralizes the problem and places it in a node (the
STP) that has been designed to perform this function. Further, an STP
can perform "intermediate global title translation," in which it uses
its tables to find another STP further along the route to the destina-
tion. Intermediate global title translation minimizes the need for STPs
to maintain extensive information about nodes which are far removed from
them. Global Title Translation is also used at the STP to share load

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

among mated Service Control Point (SCP) databases in both normal and
failure scenarios. It can select an SCP on either a priority basis
(referred to as primary -- backup) or to allow load sharing across all
available SCPs.

3.4.    Service Control Point (SCP)

An SCP site refers to the hardware and node software needed to support
applications. An SCP is a network system that supports the execution of
service logic in response to queries from switching systems. These ser-
vices are implemented as features of switching systems and network data-
bases. The SCP node serves as a network host to each application and
provides common functions as distributing incoming messages to the
appropriate application, assigning external signaling links, SCP mainte-
nance and controlling SCP overload procedures.  The SCP applications
consist of application-specific software and data that can be accessed
by other nodes on the signaling network, such as a switching system or
an Operator Services System (OSS). Each application may provide many
individual services, and these are transparent to the SCP node. In
return, this application formulates the parameters of a response mes-
sage, which the node formats and routes to the appropriate network

3.5.    TCAP Transaction        Flow Diagram

In the VoIP framework, TCAP messages must be supported not only in order
to interoperate with the PSTN, but to allow development of new services.
In the IP network, there exist the Media Gateway Controllers (MGC),
which are the counterparts to the switches in the PSTN network.  These
MGCs contain the Call Controller, which provides signaling functionality
for call setup. The TCAP signaling may be envisioned within IP networks
between the MGC and/or a SG and an IP-based SCP (IP-SCP) (Figure 1).
Further, as shown in the architecture document [4], the TCAP signaling
may also be used for cross-access between entities in the SS7 domain and
the IP domain, such as:  - access from an SS7 network to an IP-SCP -
access from an SS7 network to an MGC - access from an MGC to an SS7 net-
work element (SCP) - access from an IP-SCP to an SS7 network element

In this minimal scenario of a TCAP call query (Figure 1), the signal may
be an  incoming TCAP query to the ingress signaling gateway (SG) or may
originate at the MGC. It is accordingly processed and sent to the IP-SCP
which will then process it and return an appropriate response.

Call Related TCAP Transaction/Message Flow Diagram [5]

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

                 | SG/MGC|                             | IP-SCP|
                 |       |                             |       |
                 |       |                             |       |
                 | Query |                             |       |
                 | ------|-------------------------------->    |
                 |       |                             |       |
                 |       |                             |       |
                 |       |                       Conversation  |
                 |     <-|--------------------------------     |
                 |       |                             |       |
                 |       |                             |       |
                 | Conversation                        |       |
                 |   ----|-------------------------------->    |
                 |       |                             |       |
                 |       |                             |       |
                 |       |                            Response |
                 |    <--|-----------------------------|--     |

        Figure 1: simplified scenario of a TCAP query and response

The sequence of messages that must complete successfully before the TCAP
transaction query is satisfied is as follows:

*    Query message processing by the SG or MGC

*    Query message transport to the IP database (IP-SCP),

*    Query message processing by the IP-SCP,

*    Conversation message processing by the IP-SCP,

*    Conversation message transport from the IP-SCP to the SG or MGC,

*    Conversation message processing by the SG/MGC,

*    Conversation message transport from the SG/MGC to the IP-SCP,

*    Conversation message processing by the IP-SCP,

*    Response message processing by the IP-SCP,

*    Response message transport from the IP-SCP to the SG/MGC,

*    Response message processing by the SG/MGC,

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

4.  Performance Requirements

The end-to-end AIN performance is a function of the performance of each
AIN network element (e.g., an SSP, STP) and each network system (e.g., a
SCP) and their interfaces. Thus to ensure overall network performance,
the performance objectives and requirements must be defined for each
component. We described the requirements for STPs in our earlier docu-
ment [1], and here we discuss them for SSPs and SCPs. The SSP generally
originates a query to the SCP and awaits its response. The performance
of the TCAP applications relies on the Query Response Time. The SCP per-
formance depends not only on its several components and interfaces but
also on the application process(es) involved. Thus its conformance test-
ing depends on the use of standard application processes called bench-
mark transactions, that emulate the potential AIN service on a SCP.

4.1.    Query Response Time

Query Response Time is defined as the time it takes to send a query to a
database host and for the database to process the query and return data
to the querying entity (e.g. SSP, STP). The Query response time for the
Network User Identifier (NUI) database host and the NUI database to pro-
cess a Public Packet Switched Network (PPSN) query and return the data
to the querying entity is given as [6]:

*    Mean value                       0.25 to 0.5 seconds

The common user expectation for most simple TCAP query-response applica-
tions appears to be on the order of 0.5sec.  However, the actual PSTN
working data shows that these are in the range of 250-350ms.

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

                                                Query  Response Time
                                      |                                       |
                                SCP Response Time               Message Transfer Time
                        |             |              |
                        |             |              |
                SCP Handling    Disk LookUp    Link Output
                      Time          Time         Delay
                        |             |                 |
                        |             |                 |
                  +----------+  Number of       +-------------+
                  |          |   LookUps        |             |
                  |          |                  |             |
                  |          |                  |             |
          SCP Platform   SCP Application   Msg. Queueing   Msg. Emission
        Processing Time  Processing Time        Delay         Delay

        Figure 2: Time components in a TCAP query

4.2.    SSP Response    Time

The SSP uses a timer T1 to establish the time for a message from the SCP
in response to a message sent by the SSP to the SCP. Each instance of
this timer T1 is associated with a particular TCAP transaction, and only
one timer is set for a given transaction. The allowable range for timer
T1, is from 0.1 to 30.0 seconds, with 0.1 second increments, and a
default value is 3.0 seconds [7].

The SSP starts this T1 timer after it sends a Query (or Conversation
Package) to the SCP and then awaits an SCP call-related response (or
Conversation Package) for the particular TCAP transaction. The SSP can-
cels the timer on receipt of this response, closes the particular TCAP
transaction, and continues call processing.

4.3.    SCP Response    Time

The SCP response time is calculated as a sum of the SCP Handling Time,
Disk Lookup Time and Link Output Delay. It is defined as the interval
that begins when the last bit of a Call Related message enters the SCP,
and ends when the last bit of a Call Related message leaves the SCP.

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

4.3.1.  SCP Handling Time

It is defined as the interval that begins when the last bit of a Call
Related message enters the SCP, and ends when the last bit of a Call
Related message is placed at the outgoing signaling link buffer, exclud-
ing time taken for a disk lookup. It is further subdivided into the SCP
Platform Processing Time and the SCP Application Processing Time.

SCP Platform Processing Time: This has three time contributions. The
first begins when the last bit of a Call Related message enters the SCP,
and ends when the TCAP message is made available to the application pro-
cess. Second involves execution time of any application support process-
ing functions needed by the SCP application, and the third begins when
the platform receives the outgoing message from the application process
and ends when the last bit of a Call Related message is placed at the
outgoing signaling link buffer. The mean and 95th percentile SCP Plat-
form Processing Time in processing a Call Related message which does not
involve a disk look up [7], (but does involve processing of critical
operations, administration, and maintenance functions) is

*    Mean value                          <= 100 ms

*    0.95 prob. of not exceeding         <= 120 ms

SCP Application Processing Time: It is the difference between the SCP
Handling Time and the SCP Platform Processing Time. It is a function of
desired overall service delay, network architecture, deployment etc. and
is negotiated and tailored to each application's need.

4.3.2.  Disk Lookup Time

Certain applications require access to data on the disk, and some mes-
sages may even require multiple disk lookups. The Disk Lookup Time
required in determining a SCP response message, must be

*                         <= 30 ms for each Lookup.

4.3.3.  Link Output Delay

It is the interval that begins when last bit of a SCP Response message
is placed at the outgoing signaling link buffer, and ends when the last
bit of the Call Related message leaves the SCP on the outgoing signaling
link. The two components of the Link Output Delay are the message queu-
ing delay and the message emission delay. Queuing delay is a function of
link occupancy and the message length distribution. Emission delay is a
function of the signaling link speed and the message length distribu-
tion. Under normal conditions, messages are expected to be shorter than
279 octets. The Link Output Delay [7] calculated using the M/G/1 queuing

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

formula for messages of length 279 octets and at a Link load of 0.4
erlang should be

*                                      56 Kb/s           64Kb/s

*    Mean value                        <= 55 ms          <= 47 ms

*    0.95 prob. of not exceeding       <=102 ms          <= 89 ms

4.3.4.  Total SCP Response Time

The industry requirement for SCP response times for a simple TCAP tran-
saction (one query, one response, for data retrieval from a LIDB for an
operator system) can be summarized as follows [6]:

*                          Daily Peak                Yearly Peak
                      (aka Reference Load A)    (aka Reference Load B)

*    Mean value              <= 250 ms                <= 400 ms

*    0.95 prob. not exceed      300 ms                   600 ms

4.4.    Message Transfer        Time

The maximum signalling delay is a function of several parameters, such
as the propagation time on the signalling links (which is variable of
distance), number of SSPs, STPs, (or SG/MGC) and SCPs involved in each
connection as well as the processing time, emission and queuing delays
within each of these network elements. Delay allocation rules, in most
standards, apply to processing time only, as the propagation time por-
tion is determined by the distance and speed of the signal in the
transmission facility. However it is possible to estimate the upper
bound for the time available for message transfers from the maximum
query response time and a sum of the times required by the various com-
ponents of the network involved in the query.

Consider a mean time of 350ms for a simple TCAP query-response applica-
tion, which uses a single disk lookup, a 25ms average SCP Application
Processing Time and a 64Kbps link. Then, the transmission time available
between the querying agent and the database is of the order of 150 ms
for a query and its response.

Mean Values

*    SCP Platform Processing Time                                 100 ms

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

*    Disk Lookup (Assuming one)                                    30 ms

*    SCP Application Processing Time (Assumed)                     25 ms

*    Link Output Delay (64 kbps link)                              47 ms

*    SCP Response Time                                            202 ms

*    Average Query Response                                       350 ms

*    Implied Message Transfer Time                                148 ms

Thus, if the SCP Response Time is independent of the network technology
(other than the Link Output Delay), we have roughly a 150 ms budget for
TCAP message transfer--round trip, or 75 ms one way, to achieve a
response time comparable to the PSTN.

4.5.    Other General Parameters

Certain parameters such as maxResponseTime and maxPendingTime are also
defined as general performance measures over the CCS network.

4.5.1.  maxResponseTime

It is the maximum time the SCP allows itself to respond to a message
received over the CCS network. It takes into account the time it will
take for the SCP reply to reach the sending node i.e. the SSP. It is an
administrable value with a default set to 2.0 seconds [6].

4.5.2.  maxPendingTime

It is the maximum time the SCP will wait for a reply to a Conversation
or Query Package Type. This value is meant to be a "catch all" in case
of an error. Applications that need to monitor the time or depend on the
timing of the reply to the message sent set separate timers. It is an
administrable value with a default set to 15.0 minutes [6].

5.  Implications to VoIP

Telephony applications can be described as relatively intolerant to
packet losses and network delay. The quality of service delivered by an
IP transport mechanisms depends on the quality of the underlying IP net-
work service. Statistical measurements and analysis by Guy Almes [8] and
also Sanghi et. al. [9], show that the losses in the Internet today are
in the range of 2-10%. Losses have a direct correlation with delay. A
tentative conclusion from this is that the basic Internet quality,
today, would not really allow the transmission of toll quality voice,

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

except on some "lucky" subsets.

We may expect that Internet Telephony traffic will often be transported
over dedicated IP networks, and that prioritization and access control
will be used to minimize loss and delay (to signaling traffic), via
QoS-based differentiated services mechanisms.  This will guarantee a
level of service that is compatible with quality expectation of PSTN
users. In IP routing, the use of differentiated services via traffic
schedulers such as Weighted Fair Queuing (WFQ), and Priority Queuing,
allows traffic flows to be distinguished and prioritized. This enables
allocation of QoS parameters to different flows.  However, preliminary
laboratory tests of commercial routers supporting differentiated ser-
vices indicate that there are some overhead delays associated with
implementing these mechanisms and may lead to some unexpected complica-
tions. These delays are probably processing delays of the WFQ scheduling
algorithm and some additional queuing delays. The average shift in the
delay comprises of:

1.   A one-time overhead of 10ms delay associated with tagging the
     incoming signaling packets with the required precedence bits at the
     ingress router.

2.   A 10ms per-node (router) delay arising from applying the WFQ algo-
     rithm to the different traffic flows.

The delays associated with the implementation of WFQ will probably
increase linearly with the number of routers in the transmission path.
The network designer would have to very carefully decide if they can
justify the use of QoS to guarantee reliability, if use of differen-
tiated services imposes unacceptable delays on the transmission of TCAP
signaling messages. For example, if one-way transmission time is about
75ms and there are 3 routers in the path between the querying entity and
the IP-SCP, then applying ToS based WFQ to the signaling packets would
reduce available transmission time to roughly 35ms (10ms for tagging and
30ms for WFQ at the 3 routers). It may be argued that these delays are
vendor specific and can be improved over time and that packets may be
tagged at source. However, tagging at ingress routers across different
network domains as a security measure may still be an issue.

In the IT architecture the IP-SCP is still an ambiguous network element.
It would allow the SG or the MGC to directly access the database to
satisfy the TCAP queries. Since the IP network is not as robust as the
existing PSTN, the high loss probability of messages will impose strict
restrictions on the location of the IP-SCP within the IP network. More-
over, if the TCAP query originates in the IP network and needs to access
an PSTN based SCP, it would involve complex message processing and
transmission. The estimate of the message transfer time in Section 4.4,

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Internet draft   SIGTRAN, TCAP Performance Requirement February 26, 1999

would imply that there is little scope for retransmission in the event
of network losses. At this stage, we can only conclude that these delays
need to be investigated more thoroughly before deciding the effective-
ness of using Differentiated Services to prioritize signaling traffic.

6.  References

[1]  T. Seth, et al, "Performance Requirements for Signaling in Internet
     Telephony" <draft-seth-sigtran-req-00.txt>, Nov. 1998.

[2]  American National Standard Institute (ANSI), "Signaling System No.
          7 (SS7) - Integrated Services Digital  (ISDN) User Part," ANSI
          standard T1.113, January 3, 1995.

[3]  Bellcore, "AIN Switch - Service Control Point(SCP)/ Adjunct Inter-
          face Generic Requirements", GR-1299-CORE, Issue 2, Dec. 1994,
          tion 2-TCAP.
      .IP [4] L. Ong, " Architectural Framework for Signaling Transport"
     <draft-sigtran-framework-arch-01.txt>,  Feb. 1999.

[5]  Bellcore, "Advanced Intelligent Network Generic Requirements
     (AINGR): Switch - Service Control Point(SCP)/ Adjunct Interface, ",
     GR-1299-CORE, Issue 4, Sept. 1997.

[6]  Bellcore, "Service Control Point Node, Generic Requirements", TR-
     NWT-000029, Issue 1, Sept. 1990.

[7]  Bellcore, "Advanced Intelligent Network (AIN) Service Control
     Point(SCP), Generic Requirements", GR-1280-CORE, Issue 1, Aug.

[8]  Guy Almes, "Loss and Delay Measurement Plots", http://ippm-
          db.advanced.org/plots, Advanced Network & Services, Inc.

[9]  D. Sanghi et.al., "Experimental Assessment of End-to-End Behavior
          on Internet", Proc. IEEE  INFOCOM '93, March 1993, pp 867-874.

7.  Authors' Addresses

        Taruni U Seth
        445 South Street, MCC-1G209R
        Morristown, NJ 07960-6438
        Phone: 973 829-4046

        Email: tseth@notes.cc.bellcore.com

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        445 South Street, MCC-1A264B
        Morristown, NJ 07960-6438
        Phone: 973 829-4781

        Email: broscius@bellcore.com

        Christian Huitema
        445 South Street, MCC-1J244B
        Morristown, NJ 07960-6438
        Phone: 973 829-4266

        Email: huitema@bellcore.com

        Huai-An P. Lin
        445 South Street, MCC-1A216R
        Morristown, NJ 07960-6438
        Phone: 973 829-2412

        Email: hlin@bellcore.com

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