6/2/2016
`
`https://www.ietf.org/rfc/rfc2719.txt
`
`Network Working Group L. Ong
`Request for Comments: 2719 Nortel Networks
`Category: Informational I. Rytina
` M. Garcia
` Ericsson
` H. Schwarzbauer
` L. Coene
` Siemens
` H. Lin
` Telcordia
` I. Juhasz
` Telia
` M. Holdrege
` Lucent
` C. Sharp
` Cisco Systems
` October 1999
`
` Framework Architecture for Signaling Transport
`
`Status of this Memo
`
` This memo provides information for the Internet community. It does
` not specify an Internet standard of any kind. Distribution of this
` memo is unlimited.
`
`Copyright Notice
`
` Copyright (C) The Internet Society (1999). All Rights Reserved.
`
`Abstract
`
` This document defines an architecture framework and functional
` requirements for transport of signaling information over IP. The
` framework describes relationships between functional and physical
` entities exchanging signaling information, such as Signaling Gateways
` 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.
`
`Ong, et al. Informational [Page 1]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
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`Table of Contents
`
` 1. Introduction..................................................2
` 1.1 Overview.....................................................2
` 1.2 Terminology..................................................3
` 1.3 Scope.......................................................5
` 2. Signaling Transport Architecture.............................5
` 2.1 Gateway Component Functions.................................5
` 2.2 SS7 Interworking for Connection Control.....................6
` 2.3 ISDN Interworking for Connection Control....................8
` 2.4 Architecture for Database Access............................9
` 3. Protocol Architecture........................................10
` 3.1 Signaling Transport Components..............................10
` 3.2 SS7 access for Media Gateway Control........................11
` 3.3 Q.931 Access to MGC.........................................12
` 3.4 SS7 Access to IP/SCP........................................12
` 3.5 SG to SG....................................................14
` 4. Functional Requirements......................................15
` 4.1 Transport of SCN Signaling Protocols........................15
` 4.2 Performance of SCN Signaling Protocols......................17
` 4.2.1 SS7 MTP Requirements......................................17
` 4.2.2 SS7 MTP Level 3 Requirements..............................17
` 4.2.3 SS7 User Part Requirements................................18
` 4.2.4 ISDN Signaling Requirements...............................18
` 5. Management...................................................19
` 6. Security Considerations......................................19
` 6.1 Security Requirements.......................................19
` 6.2 Security Mechanisms Currently Available in IP Networks......20
` 7. Abbreviations................................................21
` 8. Acknowledgements.............................................21
` 9. References...................................................21
` Authors' Addresses..............................................22
` Full Copyright Statement........................................24
`
`1. Introduction
`
`1.1 Overview
`
` This document defines an architecture framework for transport of
` message-based signaling protocols over IP networks. The scope of
` this work includes definition of encapsulation methods, end-to-end
` 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.
`
`Ong, et al. Informational [Page 2]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
`
` 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
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` specific SCN signaling protocols.
`
`1.2 Terminology
`
` The following are general terms are used in this document:
`
` Backhaul:
`
` Backhaul refers to the transport of signaling from the point of
` interface for the associated data stream (i.e., SG function in the
` MGU) back to the point of call processing (i.e., the MGCU), if this
` is not local.
`
` Signaling Transport (SIG):
`
` SIG refers to a protocol stack for transport of SCN signaling
` protocols over an IP network. It will support standard primitives to
` interface with an unmodified SCN signaling application being
` transported, and supplements a standard IP transport protocol
` underneath with functions designed to meet transport requirements for
` SCN signaling.
`
` Switched Circuit Network (SCN):
`
` The term SCN is used to refer to a network that carries traffic
` within channelized bearers of pre-defined sizes. Examples include
` Public Switched Telephone Networks (PSTNs) and Public Land Mobile
` Networks (PLMNs). Examples of signaling protocols used in SCN
` include Q.931, SS7 MTP Level 3 and SS7 Application/User parts.
`
` The following are terms for functional entities relating to signaling
` transport in a distributed gateway model.
`
` Media Gateway (MG):
`
` A MG terminates SCN media streams, packetizes the media data,, if it
` is not already packetized, and delivers packetized traffic to the
` packet network. It performs these functions in reverse order for
` media streams flowing from the packet network to the SCN.
`
`Ong, et al. Informational [Page 3]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
`
` Media Gateway Controller (MGC):
`
` 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. 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.
`
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` Signaling Gateway (SG):
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`https://www.ietf.org/rfc/rfc2719.txt
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` An SG is a signaling agent that receives/sends SCN native signaling
` at the edge of the IP network. The SG function may relay, translate
` or terminate SS7 signaling in an SS7-Internet Gateway. The SG
` function may also be co-resident with the MG function to process SCN
` signaling associated with line or trunk terminations controlled by
` the MG (e.g., signaling backhaul).
`
` The following are terms for physical entities relating to signaling
` transport in a distributed gateway model:
`
` Media Gateway Unit (MGU)
`
` An MG-Unit is a physical entity that contains the MG function. It
` may contain other functions, esp. an SG function for handling
` facility-associated signaling.
`
` Media Gateway Control Unit (MGCU)
`
` An MGC-Unit is a physical entity containing the MGC function.
`
` Signaling Gateway Unit (SGU)
`
` An SG-Unit is a physical entity containing the SG function.
`
` Signaling End Point (SEP):
`
` This is a node in an SS7 network that originates or terminates
` signaling messages. One example is a central office switch.
`
` Signal Transfer Point (STP):
`
` This is a node in an SS7 network that routes signaling messages based
` on their destination point code in the SS7 network.
`
`Ong, et al. Informational [Page 4]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
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`1.3 Scope
`
` Signaling transport provides transparent transport of message-based
` signaling protocols over IP networks. The scope of this work
` includes definition of encapsulation methods, end-to-end protocol
` mechanisms and use of IP capabilities to support the functional and
` performance requirements for signaling.
`
` Signaling transport shall be used for transporting SCN signaling
` between a Signaling Gateway Unit and Media Gateway Controller Unit.
` Signaling transport may also be used for transport of message-based
` signaling between a Media Gateway Unit and Media Gateway Controller
` Unit, between dispersed Media Gateway Controller Units, and between
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` two Signaling Gateway Units connecting signaling endpoints or signal
` transfer points in the SCN.
`
` Signaling transport will be defined in such a way as to support
` encapsulation and carriage of a variety of SCN protocols. It is
` defined in such a way as to be independent of any SCN protocol
` translation functions taking place at the endpoints of the signaling
` transport, since its function is limited to the transport of the SCN
` protocol.
`
` Since the function being provided is transparent transport, the
` following areas are considered outside the scope of the signaling
` transport work:
`
` - definition of the SCN protocols themselves.
` - signaling interworking such as conversion from Channel Associated
` 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.
` - similarly, some management and addressing functions taking place
` within the SGU or MGU are also considered out of scope, such as
` determination of the destination IP address for signaling, or
` specific procedures for assessing the performance of the transport
` session (i.e., testing and proving functions).
`
`2. Signaling Transport Architecture
`
`2.1 Gateway Component Functions
`
` Figure 1 defines a commonly defined functional model 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 devices
` or combined in single physical units.
`
`Ong, et al. Informational [Page 5]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
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` Where physical separation exists between functional entities,
` Signaling Transport can be applied to ensure that SCN signaling
` information is transported between entities with the required
` functionality and performance.
`
` +---------------+ +--------------+
` | | | |
` SCN<-------->[SG] <--+---------O------------+--> [SG] <------> SCN
` signal | | | | | | signal
` +-------|-------+ +-----|--------+
` Signaling|gateway Signaling|gateway (opt)
` O O
` | |
` +-------|-------+ +-----|--------+
` | | | | | |
` | [MGC] <--+--------O-------------+--> [MGC] |
` | | | | | |
` | | | | | |
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` +-------|-------+ +-----|--------+
` Gateway | controller Gateway | controller (opt)
` O O
` | |
` +-------|-------+ +-----|--------+
` Media | | | | | | Media
` <------+---->[MG] <---+-----RTP stream-------+-> [MG] <----+-------->
` stream| | | | stream
` +---------------+ +--------------+
` Media gateway Media gateway
`
` Figure 1: Sigtran Functional Model
`
` As discussed above, the interfaces pertaining to signaling transport
` include SG to MGC, SG to SG. Signaling transport may potentially be
` applied to the MGC to MGC or MG to MGC interfaces as well, depending
` on requirements for transport of the associated signaling protocol.
`
`2.2 SS7 Interworking for Connection Control
`
` Figure 2 below shows some example implementations of these functions
` in physical entities as used for interworking of SS7 and IP networks
` for Voice over IP, Voice over ATM, Network Access Servers, etc. No
` recommendation is made as to functional distribution and many other
` examples are possible but are not shown to be concise. The use of
` signaling transport is independent of the implementation.
`
`Ong, et al. Informational [Page 6]
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
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` For interworking with SS7-controlled SCN networks, the SG terminates
` the SS7 link and transfers the signaling information to the MGC using
` signaling transport. The MG terminates the interswitch trunk and
` controls the trunk based on the control signaling it receives from
` the 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.
`
` In alternative case (c), a facility-associated SS7 link is terminated
` by the same device (i.e., the MGU) that terminates the interswitch
` trunk. In this case, the SG function is co-located with the MG
` function, as shown below, and signaling transport is used to
` "backhaul" control signaling to the MGCU.
`
` Note: SS7 links may also be terminated directly on the MGCU by
` cross-connecting at the physical level before or at the MGU.
`
` SGU
` +--------+
` SS7<------>[SG] |
` (ISUP) | | |
` +---|----+
` ST | SGU MGCU
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` +---|----+ +--------+ +--------+
` | [MGC] | SS7---->[SG] | | [MGC] |
` | | | | | | | | | |
` +---|----+ +---|----+ +--|-|---+
` MGCU | ST | | |
` | | ST | |
` Media +---|----+ Media +---|----+ +--|-|---+
` ------->[MG] | ----->[MG/MGC]| SS7 link-->[SG]| |
` stream | | stream | | Media------> [MG] |
` +--------+ +--------+ stream +--------+
` MGU MGU MGU
`
` (a) (b) (c)
`
` Notes: ST = Signaling Transport used to carry SCN signaling
`
` Figure 2: Example Implementations
`
`Ong, et al. Informational [Page 7]
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`
` In some implementations, the function of the SG may be divided into
` multiple physical entities to support scaling, signaling network
` management and addressing concerns. Thus, Signaling Transport can be
` used between SGs as well as from SG to MGC. This is shown in Figure 3
` below.
`
` SGU MGCU
` +---------+ +---------+
` | | ST | |
` | [SG2]------------------------------>[MGC] |
` | ^ ^ | | |
` +---|-|---+ +---------+
` | |
` | | ST
` ST| +--------------------------------+
` | |
` | |
` SS7 +---|----------+ SS7 +----|---------+
` -----------> [SG1] | -----------> [SG1] |
` media | | media | |
` ------------------->[MG] | ------------------->[MG] |
` stream +--------------+ stream +--------------+
` MGU MGU
`
` Figure 3: Multiple SG Case
`
` In this configuration, there may be more than one MGU handling
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` 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
`
` In ISDN access signaling, the signaling channel is carried along with
` 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 Q.931 is then transported to the MGC for call processing,
` signaling transport would be used between the SG function and MGC.
` This is shown in Figure 3 below.
`
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` MGCU
` +-------------+
` | [MGC] |
` | | | |
` +-----|-|-----+
` | |
` | O device control
` | |
` Q.931/ST O |
` | |
` +-----|-|-----+
` | | | |
` Q.931---->[SG]| |
` signals| | |
` | | |
` Media---->[MG] |
` stream | |
` +-------------+
` MGU
`
` Figure 4: Q.931 transport model
`
`2.4 Architecture for Database Access
`
` Transaction Capabilities (TCAP) is the application part within SS7
` that is used for non-circuit-related signaling.
`
` TCAP signaling within IP networks may be used for cross-access
` between entities in the SS7 domain and the IP domain, such as, for
` example:
`
` - access from an SS7 network to a Service Control Point (SCP) in IP.
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` - access from an SS7 network to an MGC.
` - access from an MGC to an SS7 network element.
` - access from an IP SCP to an SS7 network element.
`
` A basic functional model for TCAP over IP is shown in Figure 5.
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` +--------------+
` | IP SCP |
` +--|----|------+
` | |
` SGU | | SGU
` +--------------+ | | +--------------+
` | | | | | |
` SS7<--------->[SG] ---------+ | | [SG]<---------> SS7
` (TCAP) | | | | | | |
` +------|-------+ | +------|-------+
` | | |
` O +------------+ O
` MGCU | | | MGCU
` +-------|----|--+ +-----|--------+
` | | | | | | |
` | [MGC] | | [MGC] |
` | | | | | |
` +-------|-------+ +-----|--------+
` | |
` +-------|-------+ +-----|------+
` Media | | | | | | Media
` <------+---->[MG] <---+--RTP stream---+--> [MG] <-+-------->
` stream| | | | stream
` +---------------+ +------------+
` MGU MGU
`
` Figure 5: TCAP Signaling over IP
`
`3. Protocol Architecture
`
` This section provides a series of examples of protocol architecture
` for the use of Signaling Transport (SIG).
`
`3.1 Signaling Transport Components
`
` Signaling Transport in the protocol architecture figures below is
` assumed to consist of three components (see Figure 6):
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` 1) an adaptation sub-layer that supports specific primitives, e.g.,
` management indications, required by a particular SCN signaling
` application protocol.
` 2) a Common Signaling Transport Protocol that supports a common set
` of reliable transport functions for signaling transport.
` 3) a standard, unmodified IP transport protocol.
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`Ong, et al. Informational [Page 10]
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` +-- +--------------------------------+
` | | SCN adaptation module |
` | +--------------------------------+
` | |
` S | +--------------------------------+
` I | | Common Signaling Transport |
` G | +--------------------------------+
` | |
` | +--------------------------------+
` | | standard IP transport |
` +-- +--------------------------------+
`
` Figure 6: Signaling Transport Components
`
`3.2. SS7 access for Media Gateway Control
`
` This section provides a protocol architecture for signaling transport
` supporting SS7 access for Media Gateway Control.
`
` ****** SS7 ******* SS7 ****** IP *******
` *SEP *--------* STP *------* SG *------------* MGC *
` ****** ******* ****** *******
`
` +----+ +-----+
` |ISUP| | ISUP|
` +----+ +-----+ +---------+ +-----+
` |MTP | |MTP | |MTP | SIG| | SIG |
` |L1-3| |L1-3 | |L1-3+----+ +-----+
` | | | | | | IP | | IP |
` +----+ +-----+ +---------+ +-----+
`
` STP - Signal Transfer Point SEP - Signaling End Point
` SG - Signaling Gateway SIG - Signaling Transport
` MGC - Media Gateway Controller
`
` Figure 7: SS7 Access to MGC
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`3.3. Q.931 Access to MGC
`
` This section provides a protocol architecture for signaling transport
` supporting ISDN point-to-point access (Q.931) for Media Gateway
` Control.
`
` ****** ISDN ********* IP *******
` * EP *--------------* SG/MG *------------* MGC *
` ****** ********* *******
`
` +----+ +-----+
` |Q931| | Q931|
` +----+ +---------+ +-----+
` |Q921| |Q921| SIG| | SIG |
` + + + +----+ +-----+
` | | | | IP | | IP |
` +----+ +---------+ +-----+
`
` MG/SG - Media Gateway with SG function for backhaul
` EP - ISDN End Point
`
` Figure 8: ISDN Access
`
`3.4. SS7 Access to IP/SCP
`
` This section provides a protocol architecture for database 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 SIG, 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.
`
` Figure 9a 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.
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` ****** SS7 ******* SS7 ****** IP *******
` *SEP *--------* STP *------* SG *-------------* ISEP*
` ****** ******* ****** *******
`
` +-----+ +-----+
` |S7AP | |S7AP |
` +-----+ +-----+
` |SCCP | |SCCP |
` +-----+ +-----+ +---------+ +-----+
` |MTP | |MTP | |MTP |SIG | |SIG |
` + + + + + +----+ +-----+
` | | | | | | IP | |IP |
` +-----+ +-----+ +---------+ +-----+
`
` Figure 9a: SS7 Access to IP node - SCCP being transported
`
` Figure 9b shows the scenario where S7AP is the signaling protocol
` being transported between SG and ISEP. Depending on the protocol
` being transported, S7AP may or may not include TCAP, which implies
` that SIG 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| | | |
` +-----+ +-----+ +----|SIG | |SIG |
` |MTP | |MTP | |MTP | | | |
` + + + + + +----+ +-----+
` | | | | | |IP | |IP |
` +-----+ +-----+ +---------+ +-----+
`
` Figure 9b: SS7 Access to IP node - S7AP being transported
`
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`RFC 2719 Framework Architecture for Signaling Transport October 1999
`
`3.5. SG to SG
`
` This section identifies a protocol architecture for support of
` signaling between two endpoints in an SCN signaling network, using
` signaling transport directly between two SGs.
`
` The following figure describes protocol architecture for a scenario
` with two SGs providing different levels of function for interworking
` of SS7 and IP. This corresponds to the scenario 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 SIG, one
` which transports MTP3 signaling, the other which transports ISUP
` signaling.
`
` ****** SS7 ****** IP ****** IP ******
` *SEP *-------* SG1*----------* SG2*-------*MGC *
` ****** ****** ****** ******
`
` +----+ +----+
` |S7UP| |S7UP|
` +----+ +----+----+ +----+
` |MTP3| |MTP3| | | |
` +----+ +---------+ +----+ SIG| |SIG |
` |MTP2| |MTP2|SIG | |SIG | | | |
` + + + +----+ +----+----+ +----+
` | | | | IP | | IP | | IP |
` +----+ +----+----+ +----+----+ +----+
`
` S7UP - SS7 User Part
`
` Figure 10: SG to SG Case 1
`
` The following figure describes a more generic use of SS7-IP
` interworking for transport of SS7 upper layer signaling across an IP
` network, where the endpoints are both SS7 SEPs.
`
`Ong, et al. Informational [Page 14]
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` ****** SS7 ****** IP ****** SS7 ******
` *SEP *--------* SG *-----------* SG *--------*SEP *
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`https://www.ietf.org/rfc/rfc2719.txt
`6/2/2016
` ****** ****** ****** ******
`
` +----+ +-----+
` |S7UP| | S7UP|
`