draft-ietf-sigtran-signalling-over-sctp-applic-03.txt   draft-ietf-sigtran-signalling-over-sctp-applic-04.txt 
INTERNET-DRAFT L. Coene(Ed) INTERNET-DRAFT L. Coene(Ed)
Internet Engineering Task Force Siemens Internet Engineering Task Force Siemens
Issued: January 2002 Issued: February 2002 J. Pastor
Expires: July 2002 Expires: August 2002 Ericsson
Telephony Signalling Transport over SCTP applicability statement Telephony Signalling Transport over SCTP applicability statement
<draft-ietf-sigtran-signalling-over-sctp-applic-03.txt> <draft-ietf-sigtran-signalling-over-sctp-applic-04.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working all provisions of Section 10 of RFC2026. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
skipping to change at page 2, line 5 skipping to change at page 2, line 5
http://www.ietf.org/shadow.html http://www.ietf.org/shadow.html
Abstract Abstract
This document describes the applicability of the Stream Control This document describes the applicability of the Stream Control
Transmission Protocol (SCTP)[RFC2960] for transport of telephony Transmission Protocol (SCTP)[RFC2960] for transport of telephony
signalling information over IP infrastructure. Special signalling information over IP infrastructure. Special
considerations for using SCTP to meet the requirements of considerations for using SCTP to meet the requirements of
transporting telephony signalling [RFC2719] are discussed. transporting telephony signalling [RFC2719] are discussed.
Draft SCTP & Telephony signalling January 2002 Draft Telephony UAL AS March 2002
Table of contents Table of contents
Telephony signalling over SCTP Applicability statement ......... ii Telephony signalling over SCTP Applicability statement ......... ii
Chapter 1: Introduction ........................................ 2 Chapter 1: Introduction ........................................ 2
Chapter 1.1: Terminology ....................................... 2 Chapter 1.1: Terminology ....................................... 2
Chapter 1.2: Contributors ...................................... 3 Chapter 1.2: Contributors ...................................... 3
Chapter 1.3: Overview ......................................... 3 Chapter 1.3: Overview ......................................... 3
Chapter 2: Applicability of telephony signalling transport Chapter 2: Applicability of telephony signalling transport
using SCTP ..................................................... 4 using SCTP ..................................................... 4
Chapter 3: Issues for transporting Telephony signalling Chapter 3: Issues for transporting Telephony signalling
information over SCTP .......................................... 4 information over SCTP .......................................... 4
Chapter 3.1: Congestion control ................................ 4 Chapter 3.1: Congestion control ................................ 4
Chapter 3.2: Detection of failures ............................. 5 Chapter 3.2: Detection of failures ............................. 5
Chapter 3.2.1: Retransmission TimeOut (RTO) calculation ........ 5 Chapter 3.2.1: Retransmission TimeOut (RTO) calculation ........ 5
Chapter 3.2.2: Heartbeat ....................................... 5 Chapter 3.2.2: Heartbeat ....................................... 5
Chapter 3.2.3: Maximum Number of retransmissions ............... 5 Chapter 3.2.3: Maximum Number of retransmissions ............... 5
Chapter 3.3: Shorten end-to-end message delay ................. 6 Chapter 3.3: Shorten end-to-end message delay ................. 6
Chapter 3.4: Bundling considerations ........................... 6 Chapter 3.4: Bundling considerations ........................... 6
Chapter 3.5: Stream Usage ...................................... 6 Chapter 3.5: Stream Usage ...................................... 6
Chapter 4: Security considerations ............................. 6 Chapter 4: User Adaptation Layers............................... 6
Chapter 5: References and related work ......................... 7 Chapter 4.1: IUA (ISDN Q.921 User Adaptation). ................. 7
Chapter 6: Acknowledgments ..................................... 7 Chapter 4.2: V5UA (V5.2-User Adaptation) Layer.................. 8
Chapter 7: Author's address .................................... 7 Chapter 4.3: M2UA (SS7 MTP2 User Adaptation) Layer.............. 8
Chapter 4.4: M2PA (SS7 MTP2-User Peer-to-Peer Adaptation) Layer. 9
Chapter 4.5: M3UA (SS7 MTP3 User Adaptation) Layer.............. 11
Chapter 4.6: SUA (SS7 SCCP User Adaptation) Layer............... 11
Chapter 5: Security considerations ............................. 12
Chapter 6: References and related work ......................... 13
Chapter 7: Acknowledgments ..................................... 13
Chapter 8: Author's address .................................... 14
1 INTRODUCTION 1 INTRODUCTION
Transport of telephony signalling requires special Transport of telephony signalling requires special
considerations. In order to use SCTP, special care must be taken to considerations. In order to use SCTP, special care must be taken to
meet the performance, timing and failure management requirements. meet the performance, timing and failure management requirements.
Draft Telephony UAL AS March 2002
1.1 Terminology 1.1 Terminology
The following terms are commonly identified in related work: The following terms are commonly identified in related work:
Association: SCTP connection between two endpoints. Association: SCTP connection between two endpoints.
Stream: A uni-directional logical channel established within an Stream: A uni-directional logical channel established within an
association, within which all user messages are delivered in association, within which all user messages are delivered in
sequence except for those submitted to the unordered delivery sequence except for those submitted to the unordered delivery
service. service.
Draft SCTP & Telephony signalling January 2002
1.2 Contributors 1.2 Contributors
The following people contributed to the document: L. Coene(Editor), The following people contributed to the document: L. Coene(Editor),
M. Tuexen, G. Verwimp, J. Loughney, R.R. Stewart, Qiaobing Xie, M. Tuexen, G. Verwimp, J. Loughney, R.R. Stewart, Qiaobing Xie,
M. Holdrege, M.C. Belinchon, A. Jungmaier, and L. Ong. M. Holdrege, M.C. Belinchon, A. Jungmaier, J. Pastor and L. Ong.
1.3 Overview 1.3 Overview
SCTP provides a general purpose, reliable transport between two SCTP provides a general purpose, reliable transport between two
endpoints. endpoints.
The following functions are provided by SCTP: The following functions are provided by SCTP:
- Reliable Data Transfer - Reliable Data Transfer
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- Graceful termination of association - Graceful termination of association
- Support of multi-homing for added reliability - Support of multi-homing for added reliability
- Protection against blind denial-of-service attacks - Protection against blind denial-of-service attacks
- Protection against blind masquerade attacks - Protection against blind masquerade attacks
Telephony Signalling transport over IP normally uses the following Telephony Signalling transport over IP normally uses the following
Draft Telephony UAL AS March 2002
architecture: architecture:
Telephony Application Telephony Application
| |
+------------------------------------+ +------------------------------------+
| Signalling Adaptation module | | Signalling Adaptation module |
+------------------------------------+ +------------------------------------+
| |
+------------------------------------+ +------------------------------------+
|Stream Control Transmission Protocol| |Stream Control Transmission Protocol|
| (SCTP) | | (SCTP) |
+------------------------------------+ +------------------------------------+
| |
Internet Protocol (IPv4/IPv6) Internet Protocol (IPv4/IPv6)
Figure 1.1: Telephony signalling transport protocol stack Figure 1.1: Telephony signalling transport protocol stack
Draft SCTP & Telephony signalling January 2002
The components of the protocol stack are : The components of the protocol stack are :
(1) Adaptation modules are used when the telephony application needs (1) Adaptation modules are used when the telephony application needs
to preserve an existing primitive interface. (e.g. management to preserve an existing primitive interface. (e.g. management
indications, data operation primitives, ... for a particular indications, data operation primitives, ... for a particular
user/application protocol). user/application protocol).
(2) SCTP, specially configured to meet the telephony application (2) SCTP, specially configured to meet the telephony application
performance requirements. performance requirements.
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transport layer and below. Telephony applications needing this level transport layer and below. Telephony applications needing this level
of fault tolerance can make use of SCTP's multi-homing support. of fault tolerance can make use of SCTP's multi-homing support.
SCTP can be used for telephony applications where head-of-line SCTP can be used for telephony applications where head-of-line
blocking is a concern. Such an application should use multiple blocking is a concern. Such an application should use multiple
streams to provide independent ordering of telephony signalling streams to provide independent ordering of telephony signalling
messages. messages.
3 Issues for transporting telephony signalling over SCTP 3 Issues for transporting telephony signalling over SCTP
Draft Telephony UAL AS March 2002
3.1 Congestion Control 3.1 Congestion Control
The basic mechanism of congestion control in SCTP have been The basic mechanism of congestion control in SCTP have been
described in [RFC2960]. SCTP congestion control sometimes conflicts described in [RFC2960]. SCTP congestion control sometimes conflicts
with the timing requirements of telephony signalling transport. with the timing requirements of telephony signalling transport.
In an engineered network (e.g. a private intranet), in which network In an engineered network (e.g. a private intranet), in which network
capacity and maximum traffic is very well understood, some telephony capacity and maximum traffic is very well understood, some telephony
signalling applications may choose to relax the congestion control signalling applications may choose to relax the congestion control
rules in order to satisfy the timing requirements. But this should rules in order to satisfy the timing requirements. But this should
be done without destabilising the network, otherwise this would lead be done without destabilising the network, otherwise this would lead
to potential congestion collapse of the network. to potential congestion collapse of the network.
Some telephony signalling applications may have their own congestion Some telephony signalling applications may have their own congestion
Draft SCTP & Telephony signalling January 2002
control and flow control techniques. These techniques may interact control and flow control techniques. These techniques may interact
with the congestion control procedures in SCTP. Additionally, with the congestion control procedures in SCTP. Additionally,
telephony applications may use SCTP stream based flow control telephony applications may use SCTP stream based flow control
[SCTPFLOW]. [SCTPFLOW].
3.2 Detection of failures 3.2 Detection of failures
Telephony systems often must achieve high availability in operation. Telephony systems often must achieve high availability in operation.
For example, they are often required to be able to preserve stable For example, they are often required to be able to preserve stable
calls during a component failure. Therefore error situations at the calls during a component failure. Therefore error situations at the
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network behaviour [ALLMAN99]. network behaviour [ALLMAN99].
In some rare cases, telephony applications might not want to use the In some rare cases, telephony applications might not want to use the
exponential timer back-off concept in RTO calculation in order to exponential timer back-off concept in RTO calculation in order to
speed up failure detection. The danger of doing this is that, when speed up failure detection. The danger of doing this is that, when
network congestion occurs, not backing off the timer may worsen the network congestion occurs, not backing off the timer may worsen the
congestion situation. Therefore, this strategy should never be used congestion situation. Therefore, this strategy should never be used
in public Internet. in public Internet.
It should be noted that not using delayed SACK will also help faster It should be noted that not using delayed SACK will also help faster
Draft Telephony UAL AS March 2002
failure detection. failure detection.
3.2.2 Heartbeat 3.2.2 Heartbeat
For faster detection of (un)availability of idle paths, the For faster detection of (un)availability of idle paths, the
telephony application may consider lowering the SCTP parameter telephony application may consider lowering the SCTP parameter
HB.interval. It should be noted this will result in a higher traffic HB.interval. It should be noted this will result in a higher traffic
load. load.
3.2.3 Maximum number of retransmissions 3.2.3 Maximum number of retransmissions
Setting Path.Max.Retrans and Association.Max.Retrans SCTP parameters Setting Path.Max.Retrans and Association.Max.Retrans SCTP parameters
to lower values will speed up both destination address and peer to lower values will speed up both destination address and peer
Draft SCTP & Telephony signalling January 2002
failure detection. However, if these values are set too low, the failure detection. However, if these values are set too low, the
probability of false detections will increase. probability of false detections will increase.
3.3 Shorten end-to-end message delay 3.3 Shorten end-to-end message delay
Telephony applications often require short end-to-end message Telephony applications often require short end-to-end message
delays. The methods described in section 3.2.1 on lowering RTO and delays. The methods described in section 3.2.1 on lowering RTO and
not using delayed SACK may be considered. not using delayed SACK may be considered.
3.4 Bundling considerations 3.4 Bundling considerations
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3.5 Stream Usage 3.5 Stream Usage
Telephony signalling traffic is often composed of multiple, Telephony signalling traffic is often composed of multiple,
independent message sequences. It is highly desirable to transfer independent message sequences. It is highly desirable to transfer
those independent message sequences in separate SCTP streams. This those independent message sequences in separate SCTP streams. This
reduces the probability of head-of-line blocking in which the reduces the probability of head-of-line blocking in which the
retransmission of a lost message affects the delivery of other retransmission of a lost message affects the delivery of other
messages not belonging to the same message sequence. messages not belonging to the same message sequence.
4 Security considerations 4 User Adaptation Layers
Draft Telephony UAL AS March 2002
Users Adaptation Layers are defined to substitute the telephony
signaling protocol that is below of the telephony signaling protocol
to be relayed.
There are UALs for both access signaling (DSS1) and trunk signaling
(SS7). A brief description of the standardized UALs follows in the
next sub-sections.
The delivery mechanism in the several UALs
- Support seamless operation of UALs user peers over an IP network
connection.
- Support the interface boundary that the UAL user had with the
traditional lower layer.
- Support management of SCTP transport associations and traffic
between SGs and ISEPs or two ISEPs
- Support asynchronous reporting of status changes to management.
Two main scenarios have been developed for Signaling Transport:
- Intercommunication of traditional Signaling transport nodes and IP
based nodes.
Traditional Telephony
Telephony Signaling
******* Signaling ********** over IP ********
* SEP *----------------* SG *--------------* ISEP *
******* ********** ********
+-----+ +------+
| SP | | SP |
+-----+ +----+----+ +------+
| | | |UAL | | UAL |
| | | +----+ +------+
|TTST | |TTST|SCTP| | SCTP |
| | | +----+ +------+
| | | | IP | | IP |
+-----+ +---------+ +------+
SEP: Signaling Endpoint
SG: Signaling Gateway
ISEP: IP Signaling Endpoint
SP: Signaling Protocol
TTST: Traditional Telephony Signaling Transport
UAL: User Adaptation Layer
SCTP: Stream Control Transport Protocol
Draft Telephony UAL AS March 2002
It is also referred as SG to AS communication. AS I the name that
UAL usually gives to the ISEP nodes. It stands for Application
Server.
- Communication inside the IP networks.
Telephony
Signaling
******** over IP ********
* ISEP *------------------* ISEP *
******** ********
+------+ +------+
| SP | | SP |
+------+ +------+
| UAL | | UAL |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
It is also referred as IPSP communication. IPSP is the name of the
role that an IP-based node plays UAL usually gives to the ISEP
nodes. It stands for IP Signaling Point.
4.1 IUA (ISDN Q.921 User Adaptation)
This document supports both ISDN Primary Rate Access (PRA) as well as
Basic Rate Access (BRA) including the support for both point-to-point
and point-to-multipoint modes of communication. This support
includes Facility Associated Signaling (FAS), Non-Facility Associated
Signaling (NFAS) and NFAS with backup D channel.
It implements the client/server architecture. The default orientation
would be for the SG to take on the role of server while the ISEP is
the client. The SCTP (and UDP/TCP) Registered User Port Number
Assignment for IUA is 9900.
Examples of the upper layers to be transported would be Q.931 and
QSIG.
The main scenario supported by this UAL is the SG to ISEP
communication where the ISEP role is typically played by a node
called MGC defined in [RFC2719].
Draft Telephony UAL AS March 2002
****** ISDN ****** IP *******
* EP *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|Q.931| (NIF) |Q.931|
+-----+ +----------+ +-----+
| | | | IUA| | IUA |
| | | +----+ +-----+
|Q.921| |Q.921|SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP | | IP |
+-----+ +-----+----+ +-----+
NIF - Nodal Interworking Function
EP - ISDN End Point
SCTP - Stream Control Transmission Protocol
IUA - ISDN User Adaptation Layer Protocol
The SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA
is 9900.
The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is 1
4.2 V5UA (V5.2-User Adaptation) Layer
It is an extension from the IUA layer with the modifications needed
to support the differences between Q.921 / Q.931, and V5.2 layer 2 /
layer 3. It supports analog telephone access, ISDN basic rate access
and ISDN primary rate access over a V5.2 interface. It is basically
implemented in an interworking scenario with SG.
****** V5.2 ****** IP *******
* AN *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|V5.2 | (NIF) |V5.2 |
+-----+ +----------+ +-----+
| | | |V5UA| |V5UA |
| | | +----+ +-----+
|LAPV5| |LAPV5|SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP + | IP |
+-----+ +-----+----+ +-----+
Draft Telephony UAL AS March 2002
AN Access Network
NIF Nodal Interworking Function
LAPV5 Link Access Protocol for the V5 channel
SCTP - Stream Control Transmission Protocol
The SCTP (and UDP/TCP) Registered User Port Number Assignment for
V5UA is 5675.
The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is 6
4.3 DUA (DPNSS/DASS 2 User Adaptation) Layer
The DUA is built on top of IUA defining the necessary extensions to
IUA for a DPNSS/DASS2 transport. DPNSS stands for Digital Private
Network Signaling System and DASS2 for Digital Access Signaling
System No 2
****** DPNSS ****** IP *******
*PBX *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|DPNSS| (NIF) |DPNSS|
| L3 | | L3 |
+-----+ +----------+ +-----+
| | | | DUA| | DUA |
|DPNSS| |DPNSS+----+ +-----+
| L2 | | L2 |SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP + | IP |
+-----+ +-----+----+ +-----+
PBX - Private Branch eXchange
NIF - Nodal Interworking function
SCTP - Stream Control Transmission Protocol
DUA - DPNSS User Adaptation Layer Protocol
The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is TBD.
4.4 M2UA (SS7 MTP2 User Adaptation) Layer
This protocol would be mainly used between a Signaling Gateway (SG)
Draft Telephony UAL AS March 2002
and Media Gateway Controler (MGC). The SG will terminate up to MTP
Level 2 and the MGC will terminate MTP Level 3 and above. In other
words, the SG will transport MTP Level 3 messages over an IP network
to a MGC.
The only SS7 MTP2 User is MTP3 that is the protocol transported by
this UAL.
The SG provides a interworking of transport functions with the IP
transport, in order to transfer the MTP2-User signaling messages to
and from an Application Server (e.g. MGC) where the peer MTP2-
User protocol layer exists.
****** SS7 ****** IP *******
*SEP *-----------* SG *-------------* MGC *
****** ****** *******
+----+ +----+
|S7UP| |S7UP|
+----+ +----+
|MTP + |MTP |
| L3 | (NIF) |L3 |
+----+ +----+----+ +----+
|MTP | |MTP |M2UA| |M2UA|
| | | +----+ +----+
| L2 | | L2 |SCTP| |SCTP|
| L1 | | L1 +----+ +----+
| | | |IP | |IP |
+----+ +---------+ +----+
MGC - Media Gateway Controler
SG - Signaling Gateway
SEP - SS7 Signaling Endpoint
NIF - Nodal Interworking Function
IP - Internet Protocol
SCTP - Stream Control Transmission Protocol
The SCTP (and UDP/TCP) Registered User Port Number Assignment for
M2UA is 2904.
The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is 2
4.5 M2PA (SS7 MTP2-User Peer-to-Peer Adaptation) Layer
This protocol is used between SS7 Signaling Points employing the MTP
Level 3 protocol. The SS7 Signaling Points may also employ standard
SS7 links using the SS7 MTP Layer 2 to provide transport of MTP Layer
Draft Telephony UAL AS March 2002
3 signaling messages.
Both configurations: intercommunication of SS7 and IP with SG and
communication between ISEPs are possible.
******** IP ********
* IPSP *--------* IPSP *
******** ********
+------+ +------+
| TCAP | | TCAP |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| MTP3 | | MTP3 |
+------+ +------+
| M2PA | | M2PA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
IP - Internet Protocol
IPSP - IP Signaling Point
SCTP - Stream Control Transmission Protocol
******** SS7 *************** IP ********
* SEP *--------* SG *--------* IPSP *
******** *************** ********
+------+ +------+
| TCAP | | TCAP |
+------+ +------+
| SCCP | | SCCP |
+------+ +-------------+ +------+
| MTP3 | | MTP3 | | MTP3 |
+------+ +------+------+ +------+
| MTP2 | | MTP2 | M2PA | | M2PA |
+------+ +------+------+ +------+
| MTP1 | | MTP1 | SCTP | | SCTP |
| | | +------+ +------+
| | | | IP | | IP |
+------+ +------+------+ +------+
SEP - SS7 Signaling Endpoint
Draft Telephony UAL AS March 2002
These figures are only an example. Other configurations are possible.
For example, IPSPs without traditional SS7 links could use the
protocol layers MTP3/M2PA/SCTP/IP to route SS7 messages in a network
with all IP links.
Another example is that two SGs could be connected over an IP network
to form an SG mated pair similar to the way STPs are provisioned in
traditional SS7 networks.
The SCTP (and UDP/TCP) Registered User Port Number Assignment for
M2PA is TBD.
The value assigned by IANA for the Payload Protocol Identifier in the
SCTP Payload Data chunk is TBD
Differences between M2PA and M2UA include:
a. M2PA: IPSP processes MTP3/MTP2 primitives.
M2UA: MGC transports MTP3/MTP2 primitives between the SG's MTP2
and the MGC's MTP3 (via the NIF) for processing.
b. M2PA: SG-IPSP connection is an SS7 link.
M2UA: SG-MGC connection is not an SS7 link. It is an
extension of MTP to a remote entity.
c. M2PA: SG is an SS7 node with a point code.
M2UA: SG is not an SS7 node and has no point code.
d. M2PA: SG can have upper SS7 layers, e.g., SCCP.
M2UA: SG does not have upper SS7 layers since it has no MTP3.
e. M2PA: relies on MTP3 for management procedures.
M2UA: uses M2UA management procedures.
4.6 M3UA (SS7 MTP3 User Adaptation) Layer
This adaptation layer supports the transport of any SS7 MTP3-User
signaling such as TUP, ISUP and SCCP over IP using the services of
SCTP.
This protocol allows both:
- Interconnection of SS7 and IP nodes
- Communication between two IP nodes
Draft Telephony UAL AS March 2002
******** SS7 ***************** IP ********
* SEP *---------* SGP *--------* ASP *
******** ***************** ********
+------+ +---------------+ +------+
| ISUP | | (NIF) | | ISUP |
+------+ +------+ +------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+-+------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
SEP - SS7 Signaling End Point
SCTP - Stream Control Transmission Protocol
NIF - Nodal Interworking Function
******** IP ********
* IPSP *----------* IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
It works using the client-server philosophy. ISEP is recommended to
be client when talking with a SG. The reserved port by IANA is 2905
to listen to possible client connections.
The assigned payload protocol identifier for the SCTP DATA chunks is
3.
4.7 SUA (SS7 SCCP User Adaptation) Layer
This adaptation layer supports the transport of any SS7 SCCP-User
signaling such as MAP, INAP, SMS, BSSAP, RANAP over IP using the
services of SCTP. SUA can support only non-call related signaling.
Draft Telephony UAL AS March 2002
SUA does not pose stringent timing constraints on SCTP due to the
fact that SUA applications have broad timing requirement (from 10 of
seconds to hours) which the applications guard themselves and the
timing supervision of the application is end-to-end, not hop-by-
hop(as with ISUP).
Possible configurations showed in the pictures below:
- Interconnection of SS7 and IP
- IP Node to IP Node communication
******** SS7 *************** IP ********
* SEP *---------* *--------* *
* or * * SG * * ASP *
* STP * * * * *
******** *************** ********
+------ +------+
| SUAP | | SUAP |
+------+ +------+------+ +------+
| SCCP | | SCCP | SUA | | SUA |
+------+ +------+------+ +------+
| MTP3 | | MTP3 | | | |
+------+ +------+ SCTP | | SCTP |
| MTP2 | | MTP2 | | | |
+------+ +------+------+ +------+
| L1 | | L1 | IP | | IP |
+------+ +------+------+ +------+
SUAP - SCCP/SUA User Protocol (TCAP, for example)
STP - SS7 Signaling Transfer Point
******** IP ********
* *--------* *
* IPSP * * IPSP *
* * * *
******** ********
+------+ +------+
| SUAP | | SUAP |
+------+ +------+
| SUA | | SUA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
Draft Telephony UAL AS March 2002
IANA has registered SCTP Port Number 14001 for SUA. It is
recommended that SGs use this SCTP port number for listening for new
connections. The payload protocol identifier for the SCTP DATA chunks
is 4.
5 Security considerations
UALs are designated to carry signaling messages for telephony
services. As such, UALs must involve the security needs of several
parties: the end users of the services; the network providers and
the applications involved. Additional requirements may come from
local regulation. While having some overlapping security needs, any
security solution should fulfill all of the different parties'
needs. See specific Security considerations in each UAL technical
specification.
SCTP only tries to increase the availability of a network. SCTP does SCTP only tries to increase the availability of a network. SCTP does
not contain any protocol mechanisms which are directly related to not contain any protocol mechanisms which are directly related to
user message authentication, integrity and confidentiality user message authentication, integrity and confidentiality
functions. For such features, it depends on the IPSEC protocols and functions. For such features, it depends on the IPSEC protocols and
architecture and/or on security features of its user protocols. architecture and/or on security features of its user protocols.
Mechanisms for reducing the risk of blind denial-of-service attacks Mechanisms for reducing the risk of blind denial-of-service attacks
and masquerade attacks are built into SCTP protocol. See RFC2960, and masquerade attacks are built into SCTP protocol. See RFC2960,
section 11 for detailed information. section 11 for detailed information.
Currently the IPSEC working group is investigating the support of Currently the IPSEC working group is investigating the support of
multihoming by IPSEC protocols. At the present time to use IPSEC, multihoming by IPSEC protocols. At the present time to use IPSEC,
one must use 2 * N * M security associations if one endpoint uses N one must use 2 * N * M security associations if one endpoint uses N
addresses and the other M addresses. addresses and the other M addresses.
Draft SCTP & Telephony signalling January 2002 6 References and related work
5 References and related work
[RFC2960] Stewart, R. R., Xie, Q., Morneault, K., Sharp, C. , , [RFC2960] Stewart, R. R., Xie, Q., Morneault, K., Sharp, C. , ,
Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, M., Zhang, Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, M., Zhang,
L. and Paxson, V, "Stream Control Transmission Protocol", RFC2960, L. and Paxson, V, "Stream Control Transmission Protocol", RFC2960,
October 2000. October 2000.
[RFCOENE] Coene, L., Tuexen, M., Verwimp, G., Loughney, J., Stewart, [RFCOENE] Coene, L., Tuexen, M., Verwimp, G., Loughney, J., Stewart,
R. R., Xie, Q., Holdrege, M., Belinchon, M.C., and Jungmayer, A., R. R., Xie, Q., Holdrege, M., Belinchon, M.C., and Jungmayer, A.,
"Stream Control Transmission Protocol Applicability statement", "Stream Control Transmission Protocol Applicability statement",
<draft-ietf-sigtran-sctp-applicability-03.txt>, December 2000. Work <draft-ietf-sigtran-sctp-applicability-03.txt>, December 2000. Work
Draft Telephony UAL AS March 2002
In Progress. In Progress.
[RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, [RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene,
L., Lin, H., Juhasz, I., Holdrege, M., Sharp, C., "Framework L., Lin, H., Juhasz, I., Holdrege, M., Sharp, C., "Framework
Architecture for Signalling Transport", RFC2719, October 1999 Architecture for Signalling Transport", RFC2719, October 1999
[SCTPFLOW] Stewart, R., Ramalho, M., Xie, Q., Conrad, P. and Rose, [SCTPFLOW] Stewart, R., Ramalho, M., Xie, Q., Conrad, P. and Rose,
M., "SCTP Stream based flow control", September 2000, Work in M., "SCTP Stream based flow control", September 2000, Work in
Progress. Progress.
[ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End
Network Path Properties", Proc. SIGCOMM'99, 1999. Network Path Properties", Proc. SIGCOMM'99, 1999.
6 Acknowledgments 7 Acknowledgments
This document was initially developed by a design team consisting of This document was initially developed by a design team consisting of
Lode Coene, John Loughney, Michel Tuexen, Randall R. Stewart, Lode Coene, John Loughney, Michel Tuexen, Randall R. Stewart,
Qiaobing Xie, Matt Holdrege, Maria-Carmen Belinchon, Andreas Qiaobing Xie, Matt Holdrege, Maria-Carmen Belinchon, Andreas
Jungmaier, Gery Verwimp and Lyndon Ong. Jungmaier, Gery Verwimp and Lyndon Ong.
The authors wish to thank Renee Revis, H.J. Schwarzbauer, T. Taylor, The authors wish to thank Renee Revis, H.J. Schwarzbauer, T. Taylor,
G. Sidebottom, K. Morneault, T. George, M. Stillman and many others G. Sidebottom, K. Morneault, T. George, M. Stillman and many others
for their invaluable comments. for their invaluable comments.
7 Author's Address 8 Author's Address
Lode Coene Phone: +32-14-252081 Lode Coene Phone: +32-14-252081
Siemens Atea EMail: lode.coene@siemens.atea.be Siemens Atea EMail: lode.coene@siemens.atea.be
Atealaan 34 Atealaan 34
B-2200 Herentals B-2200 Herentals
Belgium Belgium
Draft SCTP & Telephony signalling January 2002 Javier Pastor-Balbas Phone:
Ericsson Email: javier.pastor-balbas@ece.ericsson.se
Expires: July 2002 Spain
Expires: August 2002
Draft Telephony UAL AS March 2002
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved. Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise to others, and derivative works that comment on or otherwise
explain it or assist in its implementation may be prepared, explain it or assist in its implementation may be prepared,
copied, published and distributed, in whole or in part, without copied, published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice restriction of any kind, provided that the above copyright notice
 End of changes. 

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