draft-ietf-sigtran-framework-arch-00.txt   draft-ietf-sigtran-framework-arch-01.txt 
Internet Engineering Task Force Internet Engineering Task Force
INTERNET-DRAFT Authors INTERNET-DRAFT Authors
Transport Working Group Lyndon Ong Transport Working Group Lyndon Ong, Nortel Networks
Category: Informational Nortel Networks Category: Informational Ian Rytina, Miguel Garcia, Ericsson
February 1999 Ian Rytina April 1999 HannsJuergen Schwarzbauer, Lode Coene, Siemens
Expires: September 1999 Ericsson Expires: November 1999 Huai-an Paul Lin, Telcordia
Imre Juhasz, Telia
Matt Holdrege, Ascend
Chip Sharp, Cisco Systems
Architectural Framework for Signaling Transport Architectural Framework for Signaling Transport
< draft-ietf-sigtran-framework-arch-00.txt > < draft-ietf-sigtran-framework-arch-01.txt >
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026. Internet-Drafts are working with all provisions of Section 10 of RFC2026. Internet-Drafts are
documents of the Internet Engineering Task Force (IETF), its areas, and working documents of the Internet Engineering Task Force (IETF), its
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Abstract Abstract
This document defines an architecture framework and functional requirements This document defines an architecture framework and functional
for transport of signaling information over IP. The framework describes requirements for transport of signaling information over IP. The
relationships between functional and physical entities exchanging signaling framework describes relationships between functional and physical
information, such as Signaling Gateways and Media Gateway Controllers, and entities exchanging signaling information, such as Signaling Gateways
identifies where signaling transport may be used. and Media Gateway Controllers. It identifies interfaces where
signaling transport may be used and the functional and performance
requirements that apply from existing Switched Circuit Network (SCN)
signaling protocols.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [2]
Table of Contents Table of Contents
1. Introduction..............................................3 1. Introduction..............................................2
1.1 Overview.................................................3 1.1 Overview.................................................2
1.2 Terminology..............................................3 1.2 Terminology..............................................2
1.3 Scope...................................................4 1.3 Scope...................................................4
2. Signaling Transport Architecture.........................5 2. Signaling Transport Architecture.........................5
2.1 Gateway Component Functions.............................5 2.1 Gateway Component Functions.............................5
2.2 SS7 Interworking for Connection Control.................5 2.2 SS7 Interworking for Connection Control.................5
2.3 ISDN Interworking for Connection Control................7 2.3 ISDN Interworking for Connection Control................6
2.4 CAS Backhaul............................................7 2.4 CAS Backhaul............................................7
2.5 Architecture for Database Access........................8 2.5 Architecture for Database Access........................8
3. Protocol Architecture.....................................8 3. Protocol Architecture.....................................9
3.1. SS7 access for Media Gateway Control....................8 3.1. SS7 access for Media Gateway Control....................9
3.2. Q.931 Access to MGC.....................................9 3.2. Q.931 Access to MGC....................................10
3.3. SS7 Access to IP/SCP...................................10 3.3. SS7 Access to IP/SCP...................................10
3.4. SG to SG...............................................10 3.4. SG to SG...............................................11
4. Functional Requirements..................................11 4. Functional Requirements..................................13
5. Management...............................................12 5. Management...............................................16
6. Security.................................................12 6. Security.................................................17
7. Acknowledgements.........................................12 7. Abbreviations............................................17
8. References...............................................12 8. Acknowledgements.........................................18
Authors' Addresses..........................................12 9. References...............................................18
Authors' Contact Information................................19
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
1. Introduction 1. Introduction
1.1 Overview 1.1 Overview
This document defines an architecture framework for transport of signaling This document defines an architecture framework for transport of
information over IP. The framework describes relationships between functional message-based signaling protocols over IP networks. The scope of
and physical entities used for control of Media Gateways and identifies where this work includes definition of encapsulation methods, end-to-end
signaling transport may be required. The architecture is based on [1]. protocol mechanisms and use of existing IP capabilities to support
the functional and performance requirements for signaling transport.
The framework portion describes the relationships between functional
and physical entities used in signaling transport, including the
framework for control of Media Gateways, and other scenarios where
signaling transport may be required.
The requirements portion describes functional and performance
requirements for signaling transport such as flow control, in-sequence
delivery and other functions that may be required for specific SCN
signaling protocols.
1.2 Terminology 1.2 Terminology
The following are general terms are used in this document: The following are general terms are used in this document:
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [3]
Backhaul: Backhaul:
Backhaul refers to the transport of signaling from the point of interface Backhaul refers to the transport of signaling from the point of interface for
for the associated data stream (i.e., the MGU) back to the point of call the associated data stream (i.e., the MGU) back to the
processing (i.e., the MGCU), if this is not local. point of call processing (i.e., the MGCU), if this is not local.
Common Transport Protocol (CTP):
CTP is the transport layer protocol, which provides the interface
for signaling transport across and within IP networks. CTP refers
to both the transport function and the adaptation function (required
to provide the SCN protocols with the same interface that exists
towards the lower layers today).
Switched Circuit Network (SCN): Switched Circuit Network (SCN):
The term SCN is used to refer to a network that carries traffic within The term SCN is used to refer to a network that carries traffic within
channelized bearers of pre-defined sizes. Examples include Public Switched channelized bearers of pre-defined sizes. Examples include Public
Telephone Networks (PSTNs) and Public Land Mobile Networks (PLMNs). Examples Switched Telephone Networks (PSTNs) and Public Land Mobile Networks
of signaling protocols used in SCN include Q.931, Signaling System 7 (SS7) (PLMNs). Examples of signaling protocols used in SCN include Q.931,
ISDN User Part (ISUP) and Global System for Mobile Communication (GSM). SS7 MTP Level 3 and SS7 Application/User parts.
The following are terms for functional entities relating to signaling The following are terms for functional entities relating to signaling
transport in a distributed gateway model. transport in a distributed gateway model.
Media Gateway (MG): Media Gateway (MG):
A MG terminates terminates SCN media streams, packetizes the media data,, if it A MG terminates SCN media streams, packetizes the media data,, if it
is not already packetized, and delivers packetized traffic to the packet network. is not already packetized, and delivers packetized traffic to the
It performs these functions in reverse order for media streams flowing from the packet network. It performs these functions in reverse order for media
packet network to the SCN. streams flowing from the packet network to the SCN.
Media Gateway Controller (MGC): Media Gateway Controller (MGC):
An MGC handles the registration and management of resources at the MG. An MGC handles the registration and management of resources at the MG.
The MGC may have the ability to authorize resource usage based on local policy. The MGC may have the ability to authorize resource usage based on local
policy. For signaling transport purposes, the MGC serves as a possible
termination and origination point for SCN application protocols, such
as SS7 ISDN User Part and Q.931/DSS1.
Signaling Gateway (SG): Signaling Gateway (SG):
An SG is a signaling agent [1,4] that receives/sends SCN native signaling at the edge An SG is a signaling agent that receives/sends SCN native signaling at
of the IP network. The SG function may relay, translate or terminate SS7 the edge of the IP network. The SG function may relay, translate or
signaling in an SS7-Internet Gateway. The SG function may also be co-resident terminate SS7 signaling in an SS7-Internet Gateway. The SG function may
with the MG function to process SCN signaling associated with line or trunk also be co-resident with the MG function to process SCN signaling associated
terminations controlled by the MG. with line or trunk terminations controlled by the MG (e.g., signaling backhaul).
Signaling Transport Gateway (STG):
An SG which transports upper layer signaling information over a
different underlying network; for example, ISUP over IP instead
of ISUP over lower SS7 layers. In this document, SG should be interpreted
as performing STG functions unless otherwise noted.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
Signaling Interworking Gateway (SIG):
An SG which interworks both upper and lower layer signaling information,
for example, interworking of ISUP/MTP and H.225/IP.
The following are terms for physical entities relating to signaling The following are terms for physical entities relating to signaling
transport in a distributed gateway model: transport in a distributed gateway model:
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [4]
Media Gateway Unit (MGU) Media Gateway Unit (MGU)
An MG-Unit is a physical entity that contains the MG function. It may An MG-Unit is a physical entity that contains the MG function. It may
contain other functions, esp. an SG function for handling facility- contain other functions, esp. an SG function for handling facility-
associated signaling. associated signaling.
Media Gateway Control Unit (MGCU) Media Gateway Control Unit (MGCU)
An MGC-Unit is a physical entity containing the MGC function. An MGC-Unit is a physical entity containing the MGC function.
Signaling Gateway Unit (SGU) Signaling Gateway Unit (SGU)
An SG-Unit is a physical entity containing the SG function. An SG-Unit is a physical entity containing the SG function.
Signaling End Point (SEP): Signaling End Point (SEP):
This is a node in an SS7 network that originates or terminates signaling This is a node in an SS7 network that originates or terminates signaling
messages. Examples include a database or central office. messages. One example is a central office switch.
Signal Transfer Point (STP): Signal Transfer Point (STP):
This is a node in an SS7 network that routes signaling messages based on This is a node in an SS7 network that routes signaling messages based on
their destination address in the SS7 network their destination point code in the SS7 network
1.3 Scope 1.3 Scope
Signaling transport focuses on transparent transport of message-based signaling Signaling transport provides transparent transport of message-based
protocols over IP networks. The scope of this work includes definition of signaling protocols over IP networks. The scope of this work includes
encapsulation methods, end-to-end protocol mechanisms and use of IP capabilities definition of encapsulation methods, end-to-end protocol mechanisms and
such as differentiated services to support the functional and performance use of IP capabilities to support the functional and performance
requirements for signaling. requirements for signaling.
There are several cases where signaling transport may be useful, as described Signaling transport shall be used for transporting SCN signaling
in greater detail in following sections. One example is transport of SCN between a Signaling Gateway Unit and Media Gateway Controller Unit.
signaling between a Signaling Gateway Unit and Media Gateway Controller Unit. Signaling transport may also be used for transport of message-based
Other examples include transport of facility-associated SCN signaling between signaling between a Media Gateway Unit and Media Gateway Controller
a Media Gateway Unit and Media Gateway Controller Unit, and transport of Unit, between dispersed Media Gateway Controller Units, and between two
signaling between two Signaling Gateway Units connection signaling endpoints Signaling Gateway Units connecting signaling endpoints in the SCN.
in the SCN.
Since the focus is on transport, the following items will be outside the scope Signaling transport will be defined in such a way as to support
of the signaling transport work: encapsulation and carriage of a variety of SCN protocols. It
- definition of the call control protocols themselves is defined in such a way as to be independent of any protocol
- definition of protocol conversion for call control, such as conversion from translation functions taking place within the Signaling Gateway Unit or
Channel Associated Signaling (CAS) to message signaling protocols Media Gateway Unit, since its function is limited to the transport of
- specification of the functions taking place within the SGU or MGU - in the protocol.
particular, this work does not address whether the SGU provides STG or
SIG functions, as this is transparent to the transport function.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt Since the function being provided is transparent transport, the following
areas are considered outside the scope of the signaling transport work:
The signaling transport will be defined in such a way as to support INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [5]
encapsulation and carriage of a variety of call control protocols. It
is defined in such a way as to be independent of any protocol translation - definition of the SCN protocols themselves
functions taking place within the Signaling Gateway Unit or Media Gateway - signaling interworking such as conversion from Channel Associated
Unit, since its function is limited to the transport of the protocol. Signaling (CAS) to message signaling protocols
- specification of the functions taking place within the SGU or MGU - in
particular, this work does not address whether the SGU provides
mediation/interworking, as this is transparent to the transport
function.
2. Signaling Transport Architecture 2. Signaling Transport Architecture
2.1 Gateway Component Functions 2.1 Gateway Component Functions
Figure 1 defines a commonly defined functional model for the VoIP Gateway Figure 1 defines a commonly defined functional model
that separates out the functions of SG, MGC and MG. This model may be that separates out the functions of SG, MGC and MG. This model may be
implemented in a number of ways, with functions implemented in separate implemented in a number of ways, with functions implemented in separate
devices or combined in single physical units. devices or combined in single physical units.
Where physical separation exists between functional entities, Signaling Where physical separation exists between functional entities, Signaling
Transport can be applied to ensure that SCN signaling information is Transport can be applied to ensure that SCN signaling information is
transported between entities with the required functionality and transported between entities with the required functionality and
performance. performance.
Signaling gateway Signaling gateway (opt)
+---------------+ +--------------+ +---------------+ +--------------+
| | SG-SG transport | | | | | |
SCN<-------->[SG] <--+---------O------------+--> [SG] <------> SCN SCN<-------->[SG] <--+---------O------------+--> [SG] <------> SCN
signal | | | | | | signal signal | | | | | | signal
+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
| | Signaling|gateway Signaling|gateway (opt)
O O O O
| | | |
+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
| | | MGC-MGC signaling | | | | | | | | |
| [MGC] <--+--------O-------------+--> [MGC] | | [MGC] <--+--------O-------------+--> [MGC] |
| | | | | | | | | | | |
| | | | | | | | | | | |
+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
Gateway | controller Gateway | Controller (opt) Gateway | controller Gateway | controller (opt)
O O O O
| | | |
+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
| | | | | | Media | | | | | | Media
<-IMT--+---->[MG] <---+-----RTP stream-------+-> [MG] <----+-IMT-----> <------+---->[MG] <---+-----RTP stream-------+-> [MG] <----+-------->
| | | | stream| | | | stream
+---------------+ +--------------+ +---------------+ +--------------+
Media gateway Media gateway Media gateway Media gateway
Notes: Figure 1: Sigtran Functional Model
- IMT stands for Inter-Machine Trunk
Figure 1: Gateway Functional Model INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [6]
As discussed above, the interfaces pertaining to signaling transport
include SG to MGC, SG to SG and may potentially include MGC to MGC or
MG to MGC as well.
2.2 SS7 Interworking for Connection Control 2.2 SS7 Interworking for Connection Control
Figure 2 below shows some example implementations of these functions in Figure 2 below shows some example implementations of these functions in
physical entities as used for interworking of SS7 and IP networks for Voice physical entities as used for interworking of SS7 and IP networks for
over IP. No recommendation is made as to functional distribution Voice over IP, Voice over ATM, Network Access Servers, etc. No
and other implementations are possible. recommendation is made as to functional distribution and other
implementations are possible.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
For interworking with SS7-controlled SCN networks, the SG terminates the For interworking with SS7-controlled SCN networks, the SG terminates the
SS7 link and transfers the signaling information to the MGC using signaling SS7 link and transfers the signaling information to the MGC using
transport. The MG terminates the intermachine trunk and controls the trunk signaling transport. The MG terminates the interswitch trunk and
based on the control signaling it receives from the MGC. Depending on controls the trunk based on the control signaling it receives from the
implementation, the SG and MGC may be in separate devices or co-located. MGC. As shown below in case (a), the SG, MGC and MG
may be implemented in separate physical units, or as in case (b), the
MGC and MG may be implemented in a single physical unit.
An alternative case (c) is the SS7 F-link, where the signaling link is In alternative case (c), a facility-associated SS7 link is terminated
facility-associated, and is terminated by the same device (i.e., the MG) by the same device (i.e., the MGU) that terminates the interswitch trunk.
that terminates the intermachine trunk. In this case, the SG function is In this case, the SG function is co-located with the MG function, as shown
co-located with the MG function, as shown in Figure 2. below, and signaling transport is used to "backhaul" control signaling to
the MGCU.
In the latter case, the signaling messages are "backhauled" to the MGC for Note: SS7 links may also be terminated directly on the MGCU by
call processing, using signaling transport functionality. cross-connecting at the physical level before or at the MGU.
SGU SGU
+--------+ +--------+
SS7<------>[SG] | SS7<------>[SG] |
(ISUP) | | | (ISUP) | | |
+---|----+ +---|----+
ST | SGU MGCU ST | SGU MGCU
+---|----+ +--------+ +--------+ +---|----+ +--------+ +--------+
| [MGC] | SS7---->[SG] | | [MGC] | | [MGC] | SS7---->[SG] | | [MGC] |
| | | | | | | | | | | | | | | | | | | |
+---|----+ +---|----+ +--|-|---+ +---|----+ +---|----+ +--|-|---+
MGCU | ST | | | MGCU | ST | | |
| | ST | | | | ST | |
+---|----+ +---|----+ +--|-|---+ Media +---|----+ Media +---|----+ +--|-|---+
IMT------->[MG] | IMT-->[MG/MGC]| SS7 F-link-->[SG]| | ------->[MG] | ----->[MG/MGC]| SS7 link-->[SG]| |
| | | | IMT ------> [MG] | stream | | stream | | Media------> [MG] |
+--------+ +--------+ +--------+ +--------+ +--------+ stream +--------+
MGU MGU MGU MGU MGU MGU
(a) (b) (c) (a) (b) (c)
Notes: ST = Signaling Transport used to carry SCN signaling Notes: ST = Signaling Transport used to carry SCN signaling
Figure 2: Example Implementations Figure 2: Example Implementations
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [7]
In some implementations, the function of the SG may be divided into In some implementations, the function of the SG may be divided into
multiple physical entities to support scaling and addressing concerns. multiple physical entities to support scaling and addressing concerns.
Signaling Transport can be used between SGs as well as from SG to MGC. Thus, Signaling Transport can be used between SGs as well as from SG
This is shown in Figure 3 below. to MGC. This is shown in Figure 3 below.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
SGU MGCU SGU MGCU
+---------+ +---------+ +---------+ +---------+
| |ST| | | |ST| |
| [SG 2]------>[MGC] | | [SG2]------------------------------>[MGC] |
| ^ | | | | | ^ ^ | | |
+----|----+ +----|----+ +---|-|---+ +---------+
| | | |
ST | | | | ST
ST| +--------------------------------+
| | | |
SS7 +----|------------|--+ | |
-----------> [SG 1] | | SS7 +---|----------+ SS7 +----|---------+
| | | -----------> [SG1] | -----------> [SG1] |
------------------------->[MG] | media | | media | |
+--------------------+ ------------------->[MG] | ------------------->[MG] |
MGU stream +--------------+ stream +--------------+
MGU MGU
Figure 3: Multiple SG Case Figure 3: Multiple SG Case
In this configuration, there may be more than one MGU handling
facility associated signaling (i.e. more than one containing it's
own SG function), and only a single SGU. It will therefore be
possible to transport one SS7 layer between SG1 and SG2, and
another SS7 layer between SG2 and MGC. For example, SG1 could
transport MTP3 to SG2, and SG2 could transport ISUP to MGC.
2.3 ISDN Interworking for Connection Control 2.3 ISDN Interworking for Connection Control
In ISDN access signaling, the signaling channel is carried along with data In ISDN access signaling, the signaling channel is carried along with
channels, so that the SG function for handling Q.931 signaling data channels, so that the SG function for handling Q.931 signaling
is co-located with the MG function for handling the data stream. Where is co-located with the MG function for handling the data stream. Where
Q.931 is then transported to the MGC for call processing, signaling transport Q.931 is then transported to the MGC for call processing, signaling
would be used between the SG function and MGC. This is shown in Figure 3 below. transport would be used between the SG function and MGC. This is shown
in Figure 3 below.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [8]
MGCU MGCU
+-------------+ +-------------+
| [MGC] | | [MGC] |
| | | | | | | |
+-----|-|-----+ +-----|-|-----+
| | | |
| O device control | O device control
| | | |
Q.931/ST O | Q.931/ST O |
| | | |
+-----|-|-----+ +-----|-|-----+
| | | | | | | |
Q.931-->[SG]| | Q.931---->[SG]| |
D-Chan| | | signals| | |
| | | | | |
B-Chan---->[MG] | Media---->[MG] |
| | stream | |
+-------------+ +-------------+
MGU MGU
Figure 3: Q.931 transport model Figure 4: Q.931 transport model
2.4 CAS Backhaul
In the case of Channel Associated Signaling (CAS), the signaling is
carried coupled with the data stream, and as in the Q.931 case, the
SCN signaling gateway function (SG) is co-located with the media gateway
function (MG). It is assumed here that the CAS is converted to a packet-
based SCN signaling protocol and backhauled to the MGC using signaling
transport capabilities. (Need for this tbd with megaco group).
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt 2.4 Architecture for Database Access
2.5 Architecture for Database Access Transaction Capabilities (TCAP) is the application part within SS7
that is used for non-circuit-related signaling.
Transaction Capabilities (TCAP or TC) is the application part within SS7 TCAP signaling within IP networks may be used for cross-access between
that is used for non-circuit-related signaling such as database access.
TCAP/TC signaling within IP networks may be used for cross-access between
entities in the SS7 domain and the IP domain, such as: entities in the SS7 domain and the IP domain, such as:
- access from an SS7 network to an IP network database - access from an SS7 network to a Service Control Point (SCP) in IP
- access from an SS7 network to an MGC - access from an SS7 network to an MGC
- access from an MGC to an SS7 network element - access from an MGC to an SS7 network element
- access from an IP Signaling End Point (ISEP) to an SS7 network element - access from an IP SCP to an SS7 network element
A basic functional model for TCAP/TC over IP is shown in Figure 4. INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [9]
A basic functional model for TCAP over IP is shown in Figure 4.
+--------------+ +--------------+
| ISEP/Database| | IP SCP |
+--|----|------+ +--|----|------+
| | | |
SGU | | SGU SGU | | SGU
+--------------+ | | +--------------+ +--------------+ | | +--------------+
| | / / | | | | | | | |
SS7<--------->[SG] -------/ / | [SG]<---------> SS7 SS7<--------->[SG] ---------+ | | [SG]<---------> SS7
(TCAP) | | | / | | | (TCAP) | | | | | | |
+------|-------+ / +------|-------+ +------|-------+ | +------|-------+
| ____/ | | | |
O / O O +------------+ O
MGCU | / | MGCU MGCU | | | MGCU
+-------|-----/-+ +-----|--------+ +-------|----|--+ +-----|--------+
| | / | | | | | | | | | | |
| [MGC] | | [MGC] | | [MGC] | | [MGC] |
| | | | | | | | | | | |
+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
| | | |
+-------|----------+ +-----|------+ +-------|-------+ +-----|------+
| | | | | | Media | | | | | | Media
<-IMT-------->[MG]<---------RTP stream----->[MG]<--------IMT--> <------+---->[MG] <---+--RTP stream---+--> [MG] <-+-------->
| | | | stream| | | | stream
+------------------+ +------------+ +---------------+ +------------+
MGU MGU MGU MGU
Notes: IMT is Inter-Machine Trunk Figure 5: TCAP Signaling over IP
Figure 4: TCAP Signaling over IP
3. Protocol Architecture 3. Protocol Architecture
This section provides a series of examples of protocol architecture
for the use of Signaling Transport Common Transport Protocol (CTP).
3.1. SS7 access for Media Gateway Control 3.1. SS7 access for Media Gateway Control
This section provides a protocol architecture for signaling transport This section provides a protocol architecture for signaling transport
supporting SS7 access for Media Gateway Control. supporting SS7 access for Media Gateway Control.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
****** SS7 ******* SS7 ****** IP ******* ****** SS7 ******* SS7 ****** IP *******
*SEP *--------* STP *------* SG *------------* MGC * *SEP *--------* STP *------* SG *------------* MGC *
****** ******* ****** ******* ****** ******* ****** *******
+----+ +-----+ +----+ +-----+
|ISUP| | ISUP| |ISUP| | ISUP|
+----+ +-----+ +---------+ +-----+ +----+ +-----+ +---------+ +-----+
|MTP | |MTP | |MTP | CTP| | CTP | |MTP | |MTP | |MTP | CTP| | CTP |
+ + + + + +----+ +-----+ + + + + + +----+ +-----+
| | | | | | UDP| | UDP |
| | | | | | TCP| | TCP |
+ + + + + +----+ +-----+
| | | | | | IP | | IP | | | | | | | IP | | IP |
+----+ +-----+ +---------+ +-----+ +----+ +-----+ +---------+ +-----+
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [10]
CO - Telco Central Office STP - Signal Transfer Point SEP - Signaling End Point
STP - Signal Transfer Point SG - Signaling Gateway CTP - Common Transport Protocol
SG - Signaling Gateway
MGC - Media Gateway Controller MGC - Media Gateway Controller
CTP - Common Transport Protocol
Note: Choice of UDP vs. TCP not yet decided. Figure 6: SS7 Access to MGC
3.2. Q.931 Access to MGC 3.2. Q.931 Access to MGC
This section provides a protocol architecture for signaling transport This section provides a protocol architecture for signaling transport
supporting ISDN access (Q.931) for Media Gateway Control. supporting ISDN point-to-point access (Q.931) for Media Gateway Control.
****** ISDN ********* IP ******* ****** ISDN ********* IP *******
* SP *--------------* MG/SG *------------* MGC * * EP *--------------* SG/MG *------------* MGC *
****** ********* ******* ****** ********* *******
+----+ +-----+ +----+ +-----+
|Q931| | Q931| |Q931| | Q931|
+----+ +---------+ +-----+ +----+ +---------+ +-----+
|Q921| |Q921| CTP| | CTP | |Q921| |Q921| CTP| | CTP |
+ + + +----+ +-----+ + + + +----+ +-----+
| | | | UDP| | UDP |
| | | | TCP| | TCP |
+ + + +----+ +-----+
| | | | IP | | IP | | | | | IP | | IP |
+----+ +---------+ +-----+ +----+ +---------+ +-----+
MG/SG - Media Gateway with SG function for backhaul MG/SG - Media Gateway with SG function for backhaul
SP - ISDN Signaling Point EP - ISDN End Point
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt Figure 7: ISDN Access
3.3. SS7 Access to IP/SCP 3.3. SS7 Access to IP/SCP
This section identifies a protocol architecture for signaling This section provides a protocol architecture for database
between an SS7 SEP and an IP domain SEP (ISEP). access, for example providing signaling between two IN
nodes or two mobile network nodes. There are a number of
scenarios for the protocol stacks and the functionality
contained in the CTP, depending on the SS7 application.
In the diagrams, SS7 Application Part (S7AP) is used for
generality to cover all Application Parts (e.g. MAP, IS-41,
INAP, etc). Depending on the protocol being transported, S7AP may or
may not include TCAP. The interface to the SS7 layer below
S7AP can be either the TC-user interface or the SCCP-user
interface.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [11]
Figure 8a shows the scenario where SCCP is the signaling
protocol being transported between the SG and an IP Signaling
Endpoint (ISEP), that is, an IP destination supporting some
SS7 application protocols.
****** SS7 ******* SS7 ****** IP ******* ****** SS7 ******* SS7 ****** IP *******
*SEP *--------* STP *------* SG *-------------* ISEP* *SEP *--------* STP *------* SG *-------------* ISEP*
****** ******* ****** ******* ****** ******* ****** *******
+-----+ +-----+ +-----+ +-----+
|S7AP | |S7AP | |S7AP | |S7AP |
+-----+ +-----+ +---------+ +-----+ +-----+ +-----+
|SCCP*| |SCCP*| | SCCP* | |SCCP*| |SCCP | |SCCP |
+-----+ +-----+ +---------+ +-----+ +-----+ +-----+ +---------+ +-----+
|MTP | |MTP | |MTP | CTP| |CTP | |MTP | |MTP | |MTP | CTP| |CTP |
+ + + + + +----+ +-----+ + + + + + +----+ +-----+
| | | | | | UDP| |UDP |
| | | | | | TCP| |TCP |
+ + + + + +----+ +-----+
| | | | | | IP | |IP | | | | | | | IP | |IP |
+-----+ +-----+ +---------+ +-----+ +-----+ +-----+ +---------+ +-----+
*Note: may or may not be present depending on application Figure 8a: SS7 Access to IP node - SCCP being transported
SS7 Application Part (S7AP) is used for generality. Figure 8b shows the scenario where S7AP is the signaling
protocol being transported between SG and ISEP. Depending on
the usage case, S7AP may or may not include TCAP, which implies
that CTP must be able to support both the TC-user and the
SCCP-user interfaces.
****** SS7 ******* SS7 ****** IP *******
*SEP *--------* STP *------* SG *-------------* ISEP*
****** ******* ****** *******
+-----+ +-----+
|S7AP | |S7AP |
+-----+ +----+----+ +-----+
|SCCP | |SCCP| | | |
+-----+ +-----+ +----|CTP | |CTP |
|MTP | |MTP | |MTP | | | |
+ + + + + +----+ +-----+
| | | | | |IP | |IP |
+-----+ +-----+ +---------+ +-----+
Figure 8b: SS7 Access to IP node - S7AP being transported
3.4. SG to SG 3.4. SG to SG
This section identifies a protocol architecture for support of This section identifies a protocol architecture for support of
signaling between two endpoints in an SCN signaling signaling between two endpoints in an SCN signaling
network, using signaling transport directly between two SGs. network, using signaling transport directly between two SGs.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [12]
The following figure describes protocol architecture for a The following figure describes protocol architecture for a
scenario with two SGs providing different levels of function scenario with two SGs providing different levels of function
for interworking of SS7 and IP. This corresponds to the scenario for interworking of SS7 and IP. This corresponds to the scenario
given in Figure 3 above. given in Figure 3.
The SS7 User Part (S7UP) shown is an SS7 protocol using MTP directly
for transport within the SS7 network, for example, ISUP.
In this scenario, there are two different usage cases of CTP,
one which transports MTP3 signaling, the other which transports
ISUP signaling.
****** SS7 ****** IP ****** IP ****** ****** SS7 ****** IP ****** IP ******
*SEP *-------* SG1*----------* SG2*-------*MGC * *SEP *-------* SG1*----------* SG2*-------*MGC *
****** ****** ****** ****** ****** ****** ****** ******
+----+ +----+ +----+ +----+
|S7UP| |S7UP| |S7UP| |S7UP|
+----+ +----+----+ +----+ +----+ +----+----+ +----+
|MTP3| |MTP3|CTP | |CTP | |MTP3| |MTP3| | | |
+----+ +---------+ +---------| +----+ +----+ +---------+ +----+ CTP| |CTP |
|MTP2| |MTP2| CTP| |CTP | | | | |MTP2| |MTP2| CTP| |CTP | | | |
+ + + +----+ +----+ | | | ----+ +---------+ +----+ <span class="insert">CTP| |CTP |</span>
| | | | UDP| |UDP |UDP | |UDP | + + + +----+ +----+----+ +----+
| | | | TCP| |TCP |TCP | |TCP | | | | | IP | | IP | | IP |
| | | |----| |----|----| |----|
| | | | IP | | IP | IP | | IP |
+----+ +----+----+ +----+----+ +----+ +----+ +----+----+ +----+----+ +----+
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt S7UP - SS7 User Part
Figure 9: SG to SG Case 1
The following figure describes a more generic use of The following figure describes a more generic use of
SS7-IP interworking for transport of SS7 upper layer SS7-IP interworking for transport of SS7 upper layer
signaling across an IP network, where the endpoints are signaling across an IP network, where the endpoints are
both SS7 SEPs. both SS7 SEPs.
****** SS7 ****** IP ****** SS7 ****** ****** SS7 ****** IP ****** SS7 ******
*SEP *--------* SG *-----------* SG *--------*SEP * *SEP *--------* SG *-----------* SG *--------*SEP *
****** ****** ****** ****** ****** ****** ****** ******
+----+ +-----+ +----+ +-----+
|S7UP| | S7UP| |S7UP| | S7UP|
+----+ +-----+ +----+ +-----+
|MTP3| | MTP3| |MTP3| | MTP3|
+----+ +---------+ +---------+ +-----+ +----+ +---------+ +---------+ +-----+
|MTP2| |MTP2| CTP| |CTP |MTP2| | MTP2| |MTP2| |MTP2| CTP| |CTP |MTP2| | MTP2|
+ + + +----+ +----+ + + + + + + +----+ +----+ + + +
| | | | UDP| |UDP | | | |
| | | | TCP| |TCP | | | |
| | | |----| |----| | | |
| | | | IP | | IP | | | | | | | | IP | | IP | | | |
+----+ +----+----+ +----+----+ +-----+ +----+ +----+----+ +----+----+ +-----+
Figure 10: SG to SG Case 2
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [13]
4. Functional Requirements 4. Functional Requirements
Signaling transport provides for the transport of native SCN protocol Signaling transport provides for the transport of native SCN protocol
messages over a packet switched network. messages over a packet switched network.
Signaling transport shall: Signaling transport shall:
1) Transport of a variety of SCN protocol types, such as the application 1) Transport of a variety of SCN protocol types, such as the application
and user parts of SS7 (including ISUP, SCCP, TCAP, MAP, INAP, IS-41, etc.) and user parts of SS7 (including MTP Level 3, ISUP, SCCP, TCAP, MAP, INAP,
and layer 3 of the DSS1/PSS1 protocols (i.e. Q.931 and QSIG). IS-41, etc.) and layer 3 of the DSS1/PSS1 protocols (i.e. Q.931 and QSIG).
2) Provide an identifier for the particular SCN protocol being transported. 2) Provide a means to identify the particular SCN protocol being
transported.
3) Provide a common base protocol defining header formats, security 3) Provide a common base protocol defining header formats, security
extensions and generic requirements for signaling transport, and support extensions and procedures for signaling transport, and support
extensions as necessary to add individual SCN protocols if and when required. extensions as necessary to add individual SCN protocols if and when
required.
4) In conjunction with the underlying network protocol (IP) and transport 4) In conjunction with the underlying network protocol (IP) and transport
protocol (TCP, UDP or other), provide the relevant functionality as defined protocol (CTP), provide the relevant functionality as defined
by the appropriate SCN lower layer. by the appropriate SCN lower layer.
Relevant functionality may include (according to the protocol being Relevant functionality may include (according to the protocol being
transported): transported):
- flow control - flow control
- in sequence delivery of signaling messages (tbd. if this is supported - in sequence delivery of signaling messages within a control stream
across multiple SCN signaling sessions)
- logical identification of the entities on which the signaling messages - logical identification of the entities on which the signaling messages
in sequence delivery of signaling messages <span class="insert">within a control stream</span>
originate or terminate originate or terminate
- logical identification of the physical interface controlled by the - logical identification of the physical interface controlled by the
signaling message signaling message
- load sharing over multiple signaling transport sessions - error detection
- retransmission - recovery from failure of components in the transit path
- information on unavailability of peer entities. - retransmission and other error correcting methods
- detection of unavailability of peer entities.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-00.txt
<span class="insert">detection of</span> unavailability of peer entities.
For example: For example:
- if the native SCN protocol is ISUP or SCCP, the relevant functionality - if the native SCN protocol is ISUP or SCCP, the relevant functionality
provided by MTP2/3 shall be provided. provided by MTP2/3 shall be provided.
- if the native SCN protocol is TCAP, the relevant functionality provided - if the native SCN protocol is TCAP, the relevant functionality
by SCCP and MTP 2/3 shall be provided. provided by SCCP and MTP 2/3 shall be supported.
- if the native SCN protocol is Q.931, the relevant functionality provided - if the native SCN protocol is Q.931, the relevant functionality
by Q.921 shall be provided. provided by Q.921 shall be supported.
- if the native SCN protocol is MTP3, the relevant functionality of MTP2 - if the native SCN protocol is MTP3, the relevant functionality of MTP2
shall be provided. shall be supported.
5) Support the ability to multiplex several higher layer SCN sessions on 5) Support the ability to multiplex several higher layer SCN sessions on
one underlying signaling transport session. This allows, for example, the one underlying signaling transport session. This allows, for example,
output of several DSS1 D-Channel sessions to be carried in one signaling several DSS1 D-Channel sessions to be carried in one signaling
transport session. transport session.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [14]
In general, in-sequence delivery is required for signaling messages
within a single control stream, but is not necessarily required
for messages that belong to different control streams. The protocol
should if possible take advantage of this property to avoid blocking
delivery of messages in one control stream due to sequence error within
another control stream. However, the SG will not be required to process
the SCN application protocol in order to identify control streams.
6) Be able to transport complete messages of greater length than the 6) Be able to transport complete messages of greater length than the
underlying SCN segmentation/reassembly limitations. For example, signaling underlying SCN segmentation/reassembly limitations. For example,
transport should not be constrained by the length limitations defined for signaling transport should not be constrained by the length limitations
SS7 lower layer protocol (e.g. 272 bytes in the case of narrowband SS7) but defined for SS7 lower layer protocol (e.g. 272 bytes in the case of
should be capable of carrying longer messages without requiring segmentation. narrowband SS7) but should be capable of carrying longer messages
without requiring segmentation.
7) Allow for a range of suitably robust security schemes to protect signaling 7) Allow for a range of suitably robust security schemes to protect
information being carried across networks. For example, signaling information being carried across networks. For example,
signaling transport shall be able to operate over proxyable sessions, signaling transport shall be able to operate over proxyable sessions,
and be able to be transported through firewalls. and be able to be transported through firewalls.
8) Provide for congestion avoidance on the Internet, by supporting 8) Provide for congestion avoidance on the Internet, by supporting
appropriate controls on signaling traffic generation (including signaling appropriate controls on signaling traffic generation (including
generated in SCN) and reaction to network congestion. signaling generated in SCN) and reaction to network congestion.
4.2 Performance of SCN Signaling Protocols
This section provides basic values regarding performance requirements
of key SCN protocols to be transported. Currently only messaged based
SCN protocols are considered. Failure to meet these requirements
is likely to result in adverse and undesirable signaling and call
behavior.
4.2.1 SS7 MTP requirements
The performance requirements below have been specified for
transport of MTP Level 3 network management messages. The requirements
given here are only applicable if all MTP Level 3 messages are to be
transported over the IP network.
- Message Delay
- MTP Level 3 peer-to-peer procedures require response within
500 to 1200 ms when terrestrial signaling links are used. This
value includes round trip time and processing at the remote end.
Failure to meet this limitation will result in the initiation of
error procedures for specific timers, e.g., timer T4 of ITU-T
Recommendation Q.704.
4.2.2 SS7 MTP Level 3 requirements
The performance requirements below have been specified for transport of
MTP Level 3 user part messages as part of ITU-T SS7 Recommendations [SS7].
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [15]
- Message Loss
- no more than 1 in 10E+7 messages will be lost due to transport
failure
- Sequence Error
- no more than 1 in 10E+10 messages will be delivered out-of-sequence
(including duplicated messages) due to transport failure
- Message Errors
- no more than 1 in 10E+10 messages will contain an error that is
undetected by the transport protocol (requirement is 10E+9 for
ANSI specifications)
- Availability
- availability of any signaling route set is 99.9998% or better,
i.e., downtime 10 min/year or less. A signaling route set is
the complete set of allowed signaling paths from a given
signaling point towards a specific destination.
- Message length (payload accepted from SS7 user parts)
- 272 bytes for narrowband SS7, 4091 bytes for broadband SS7
4.2.3 SS7 User Part Requirements
ISUP Message Delay - Protocol Timer Requirements
- to be provided.
ISUP Message Delay - End-to-End Requirements
- to be provided.
TCAP Requirements - End-to-End Requirements
- to be provided.
4.2.4 ISDN Signaling Requirements
Q.931 Message Delay
- round-trip delay should not exceed 4 seconds.
A timer of this length is used for a number of procedures, esp.
RELEASE/RELEASE COMPLETE and CONNECT/CONNECT ACK where
excessive delay may result in management action on the
channel, or release of a call being set up. Note: while this
value is indicated by protocol timer specifications, faster
response time is normally expected by the user.
- 12 sec. timer (T309) is used to maintain an active call
in case of loss of the data link, pending re-establishment.
The related ETSI documents specify a maximum value of 4 seconds
while ANSI specifications [T1.607] default to 90 seconds.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [16]
5. Management 5. Management
Tbd. Operations, Administration & Management (OA&M) of IP networks or SCN
networks is outside the scope of SIGTRAN. Examples of OA&M include
legacy telephony management systems or IETF SNMP managers. OA&M
implementors and users should be aware of the functional interactions
of the SG, MGC and MG and the physical units they occupy.
6. Security 6. Security
Tbd. 6.1 Security requirements
7. Acknowledgements When SCN related signaling is transported over an IP network
two possible network scenarios can be distinguished:
The author would like to thank K. Chong, I. Elliott, M. Holdrege, C. Sharp, - Signaling transported only within an Intranet;
C. Huitema, I. Rytina and G. Sidebottom for their comments and suggestions. Security measures are applied at the discretion of the network
owner.
8. References - Signaling transported, at least to some extent, in the public
Internet;
The public Internet should be regarded generally as an "insecure"
network and usage of security measures is required.
[1] F. Cuervo, N. Greene, et al, "SS7-Internet Interworking - Architectural Generally security comprises several aspects
Framework" <draft-greene-ss7-arch-frame-01.txt>, July 1998, work in progress.
Authors' Addresses - Authentication:
It is required to ensure that the information is sent to/from a known
and trusted partner.
- Integrity:
It is required to ensure that the information hasn't been modified
while in transit.
- Confidentiality:
It might be sometimes required to ensure that the transported
information is encrypted to avoid illegal use.
- Availability:
It is required that the communicating endpoints remain in
service for authorized use even if under attack.
6.2 Security mechanisms currently available in IP networks
Several security mechanisms are currently available for use in IP networks.
- IPSEC ([RFC2401]):
IPSEC provides security services at the IP layer that address the above
mentioned requirements. It defines the two protocols AH and ESP
respectively that
essentially provide data integrity and data
confidentiality services.
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [17]
The ESP mechanism can be used in two different modes:
- Transport mode;
- Tunnel mode.
In Transport mode IPSEC protects the higher layer protocol data
portion of an IP packet, while in Tunnel mode a complete IP packet
is encapsulated in a secure IP tunnel.
If the CTP embeds any IP addresses outside of the SA/DA in the IP
header, passage through a NAT function will cause problems. The same
is true for using IPsec in general, unless an IPsec ready RSIP
function is used as described in draft-ietf-nat-terminology-02.txt.
The use of IPSEC does not hamper the use of TCP or UDP as the
underlying basis of CTP. If automated distribution of keys is
required the IKE protocol (RFC[2409]) can be applied.
- SSL, TLS ([RFC2246]):
SSL and TLS also provide appropriate security services but operate on
top of TCP/IP only.
It is not required to define new security mechanisms in CTP, as the
use of currently available mechanisms is sufficient to provide the
necessary security. It is recommended that IPSEC or some equivalent
method be used, especially when transporting SCN signaling over
public Internet.
7. Abbreviations
CAS Channel-Associated Signaling
CTP Common Transport Protocol
DSS1 Digital Subscriber Signaling
INAP Intelligent Network Application Part
ISEP IP Signaling End Point
ISUP Signaling System 7 ISDN User Part
MAP Mobile Application Part
MG Media Gateway
MGU Media Gateway Unit
MGC Media Gateway Controller
MGCU Media Gateway Controller Unit
MTP Signaling System 7 Message Transfer Part
PLMN Public Land Mobile Network
PSTN Public Switched Telephone Network
S7AP SS7 Application Part
S7UP SS7 User Part
SCCP SS7 Signaling Connection Control Part
SCN Switched Circuit Network
SEP Signaling End Point
SG Signaling Gateway
SS7 Signaling System No. 7
TCAP Signaling System 7 Transaction Capabilities Part
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01.txt [18]
8. Acknowledgements
The authors would like to thank K. Chong, I. Elliott, Ian Spiers,
Al Varney, Goutam Shaw, C. Huitema, Mike McGrew and Greg Sidebottom
for their valuable comments and suggestions.
9. References
[NAT] IP Network Address Translator (NAT) Terminology and Considerations
<draft-ietf-nat-terminology-02.txt>, P. Srisurech and M. Holdrege, April
1999, work in progress.
[PSS1/QSIG] ECMA Standard ECMA-143 -Inter-Exchange Signalling Procedures
and Protocol (QSIG-BC)
[Q.931/DSS1] ITU-T Recommendation Q.931, ISDN user-network interface layer 3
specification (5/98)
[SS7] ITU-T Recommendations Q.700-775, Signalling System No. 7
[SS7 MTP] ITU-T Recommendations Q.701-6, Message Transfer Part of SS7
[T1.607] ANSI T1.607-1998, Digital Subscriber Signaling System Number 1 (DSS1)
- Layer 3 Signaling Specification for Circuit-Switched Bearer Services
Authors' Contact Information
Lyndon Ong Ian Rytina Lyndon Ong Ian Rytina
Nortel Networks Ericsson Australia Nortel Networks Ericsson Australia
4401 Great America Parkway 37/360 Elizabeth Street 4401 Great America Parkway 37/360 Elizabeth Street
Santa Clara, CA 95054 Melbourne, Victoria 3000, Australia Santa Clara, CA 95054, USA Melbourne, Victoria 3000, Australia
long@nortelnetworks.com ian.rytina@ericsson.com long@nortelnetworks.com ian.rytina@ericsson.com
Matt Holdrege Lode Coene
Ascend Communications Siemens Atea
1701 Harbor Bay Parkway Atealaan 34
Alameda, CA 94502 USA Herentals, Belgium
matt@ascend.com lode.coene@ntnet.atea.be
Miguel-Angel Garcia Chip Sharp
Ericsson Espana Cisco Systems
Retama 7 7025 Kit Creek Road
28005 Madrid, Spain Res Triangle Pk, NC 27709, USA
Miguel.A.Garcia@ericsson.com chsharp@cisco.com
Imre Juhasz Haui-an Paul Lin
Telia Telcordia Technologies
Sweden Piscataway, NJ, USA
imre.i.juhasz@telia.se hlin@research.telcordia.com
Hanns Juergen Schwarzbauer
Siemens AG
Munich, Germany
HannsJuergen.Schwarzbauer@ICN.SIEMENS.DE
INTERNET-DRAFT draft-ietf-sigtran-framework-arch-01. txt [19]
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