draft-ietf-sigtran-framework-arch-02.txt   draft-ietf-sigtran-framework-arch-03.txt 
Internet Engineering Task Force Internet Engineering Task Force
INTERNET-DRAFT Authors INTERNET-DRAFT Authors
Transport Working Group Lyndon Ong, Nortel Networks Transport Working Group Lyndon Ong, Nortel Networks
Category: Informational Ian Rytina, Miguel Garcia, Ericsson Category: Informational Ian Rytina, Miguel Garcia, Ericsson
June 1999 HannsJuergen Schwarzbauer, Lode Coene, Siemens June 1999 HannsJuergen Schwarzbauer, Lode Coene, Siemens
Expires: January 2000 Huai-an Paul Lin, Telcordia Expires: January 2000 Huai-an Paul Lin, Telcordia
Imre Juhasz, Telia Imre Juhasz, Telia
Matt Holdrege, Ascend Matt Holdrege, Ascend
Chip Sharp, Cisco Systems Chip Sharp, Cisco Systems
Architectural Framework for Signaling Transport Framework Architecture for Signaling Transport
< draft-ietf-sigtran-framework-arch-02.txt > < draft-ietf-sigtran-framework-arch-03.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 with all provisions of Section 10 of RFC2026. Internet-Drafts are
working documents of the Internet Engineering Task Force (IETF), its working documents of the Internet Engineering Task Force (IETF), its
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Abstract Abstract
This document defines an architecture framework and functional This document defines an architecture framework and functional
requirements for transport of signaling information over IP. The requirements for transport of signaling information over IP. The
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The following are general terms are used in this document: The following are general terms are used in this document:
Backhaul: Backhaul:
Backhaul refers to the transport of signaling from the point of interface for 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 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. point of call processing (i.e., the MGCU), if this is not local.
Signaling Transport (SIG): Signaling Transport (SIG):
SIG refers to signaling transport, which provides the interface SIG refers to a protocol stack for transport of SCN signaling protocols
for signaling transport across and within IP networks. SIG includes over an IP network. It will support standard primitives to interface
a set of functions supplementing a standard IP transport with an unmodified SCN signaling application being transported, and
protocol to provide the SCN protocol being transported with the same supplements a standard IP transport protocol underneath with functions
service interface that is provided by its SCN lower layer. designed to meet transport requirements for SCN signaling.
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 channelized bearers of pre-defined sizes. Examples include Public
Switched Telephone Networks (PSTNs) and Public Land Mobile Networks Switched Telephone Networks (PSTNs) and Public Land Mobile Networks
(PLMNs). Examples of signaling protocols used in SCN include Q.931, (PLMNs). Examples of signaling protocols used in SCN include Q.931,
SS7 MTP Level 3 and SS7 Application/User parts. 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
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+-------|-------+ +-----|--------+ +-------|-------+ +-----|--------+
Media | | | | | | Media Media | | | | | | Media
<------+---->[MG] <---+-----RTP stream-------+-> [MG] <----+--------> <------+---->[MG] <---+-----RTP stream-------+-> [MG] <----+-------->
stream| | | | stream stream| | | | stream
+---------------+ +--------------+ +---------------+ +--------------+
Media gateway Media gateway Media gateway Media gateway
Figure 1: Sigtran Functional Model Figure 1: Sigtran Functional Model
As discussed above, the interfaces pertaining to signaling transport As discussed above, the interfaces pertaining to signaling transport
include SG to MGC, SG to SG and may potentially include MGC to MGC or include SG to MGC, SG to SG. Signaling transport may potentially be
MG to MGC as well. 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 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 physical entities as used for interworking of SS7 and IP networks for
Voice over IP, Voice over ATM, Network Access Servers, etc. No Voice over IP, Voice over ATM, Network Access Servers, etc. No
recommendation is made as to functional distribution and other recommendation is made as to functional distribution and many other
implementations are possible. examples are possible but are not shown to be concise. The use of
signaling transport is independent of the implementation.
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 SS7 link and transfers the signaling information to the MGC using
signaling transport. The MG terminates the interswitch trunk and signaling transport. The MG terminates the interswitch trunk and
controls the trunk based on the control signaling it receives from the controls the trunk based on the control signaling it receives from the
MGC. As shown below in case (a), the SG, MGC and MG 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 may be implemented in separate physical units, or as in case (b), the
MGC and MG may be implemented in a single physical unit. MGC and MG may be implemented in a single physical unit.
In alternative case (c), a facility-associated SS7 link is terminated In alternative case (c), a facility-associated SS7 link is terminated
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MGU MGU
Figure 4: Q.931 transport model Figure 4: Q.931 transport model
2.4 Architecture for Database Access 2.4 Architecture for Database Access
Transaction Capabilities (TCAP) is the application part within SS7 Transaction Capabilities (TCAP) is the application part within SS7
that is used for non-circuit-related signaling. that is used for non-circuit-related signaling.
TCAP signaling within IP networks may be used for cross-access between TCAP 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, for example:
- access from an SS7 network to a Service Control Point (SCP) in IP - 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 SCP 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. A basic functional model for TCAP over IP is shown in Figure 5.
+--------------+ +--------------+
| IP SCP | | IP SCP |
+--|----|------+ +--|----|------+
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3.1 Signaling Transport Components 3.1 Signaling Transport Components
Signaling Transport in the protocol architecture figures below is Signaling Transport in the protocol architecture figures below is
assumed to consist of three components (see Figure 6): assumed to consist of three components (see Figure 6):
1) an adaptation sub-layer that supports specific primitives, e.g., 1) an adaptation sub-layer that supports specific primitives, e.g.,
management indications, required by a particular SCN signaling management indications, required by a particular SCN signaling
application protocol. application protocol.
2) a Common Signaling Transport Protocol that supports a common set 2) a Common Signaling Transport Protocol that supports a common set
of reliable transport functions for signaling transport. of reliable transport functions for signaling transport.
3) a standard IP transport protocol provided by the operating system. 3) a standard, unmodified IP transport protocol.
+-- +--------------------------------+ +-- +--------------------------------+
| | SCN adaptation module | | | SCN adaptation module |
| +--------------------------------+ | +--------------------------------+
| | | |
S | +--------------------------------+ S | +--------------------------------+
I | | Common Signaling Transport | I | | Common Signaling Transport |
G | +--------------------------------+ G | +--------------------------------+
| | | |
| +--------------------------------+ | +--------------------------------+
| | standard IP transport (UDP) | | | standard IP transport |
+-- +--------------------------------+ +-- +--------------------------------+
Figure 6: Signaling Transport Components Figure 6: Signaling Transport Components
3.2. SS7 access for Media Gateway Control 3.2. 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.
****** SS7 ******* SS7 ****** IP ******* ****** SS7 ******* SS7 ****** IP *******
*SEP *--------* STP *------* SG *------------* MGC * *SEP *--------* STP *------* SG *------------* MGC *
****** ******* ****** ******* ****** ******* ****** *******
+----+ +-----+ +----+ +-----+
|ISUP| | ISUP| |ISUP| | ISUP|
+----+ +-----+ +---------+ +-----+ +----+ +-----+ +---------+ +-----+
|MTP | |MTP | |MTP | SIG| | SIG | |MTP | |MTP | |MTP | SIG| | SIG |
+ + + + + +----+ +-----+ |L1-3| |L1-3 | |L1-3+----+ +-----+
| | | | | | IP | | IP | | | | | | | IP | | IP |
+----+ +-----+ +---------+ +-----+ +----+ +-----+ +---------+ +-----+
STP - Signal Transfer Point SEP - Signaling End Point STP - Signal Transfer Point SEP - Signaling End Point
SG - Signaling Gateway SIG - Signaling Transport SG - Signaling Gateway SIG - Signaling Transport
MGC - Media Gateway Controller MGC - Media Gateway Controller
Figure 7: SS7 Access to MGC Figure 7: SS7 Access to MGC
3.3. Q.931 Access to MGC 3.3. Q.931 Access to MGC
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MGCU Media Gateway Controller Unit MGCU Media Gateway Controller Unit
MTP Signaling System 7 Message Transfer Part MTP Signaling System 7 Message Transfer Part
PLMN Public Land Mobile Network PLMN Public Land Mobile Network
PSTN Public Switched Telephone Network PSTN Public Switched Telephone Network
S7AP SS7 Application Part S7AP SS7 Application Part
S7UP SS7 User Part S7UP SS7 User Part
SCCP SS7 Signaling Connection Control Part SCCP SS7 Signaling Connection Control Part
SCN Switched Circuit Network SCN Switched Circuit Network
SEP Signaling End Point SEP Signaling End Point
SG Signaling Gateway SG Signaling Gateway
SIG Signaling Transport SIG Signaling Transport protocol stack
SS7 Signaling System No. 7 SS7 Signaling System No. 7
TCAP Signaling System 7 Transaction Capabilities Part TCAP Signaling System 7 Transaction Capabilities Part
8. Acknowledgements 8. Acknowledgements
The authors would like to thank K. Chong, I. Elliott, Ian Spiers, The authors would like to thank K. Chong, I. Elliott, Ian Spiers,
Al Varney, Goutam Shaw, C. Huitema, Mike McGrew and Greg Sidebottom Al Varney, Goutam Shaw, C. Huitema, Mike McGrew and Greg Sidebottom
for their valuable comments and suggestions. for their valuable comments and suggestions.
9. References 9. References
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