Internet Engineering Task Force INTERNET-DRAFT Authors Transport Working Group Lyndon Ong Category: Informational Nortel Networks November 1998 Expires: June 1999 Architectural Framework for Signaling Transport < draft-ong-sigtran-framework-arch-00.txt > Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." To view the entire list of current Internet-Drafts, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast). Abstract This document defines an architecture framework for transporting PSTN signaling information over IP. It defines an architectural model, and identifies functional requirements and performance requirements for signaling transport. PSTN signaling must be encapsulated and identified for transport over IP networks, and signaling performance requirements for message loss, delay, etc. must be supported by protocol mechanisms. Ong Informational [Page 1] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt Table of Contents 1. Introduction ....................................................3 1.1 Overview ........................................................3 1.2 Terminology .....................................................3 1.3 Requirements ....................................................3 1.4 Comparisons with Other Efforts ..................................4 2. Signaling Transport Architectural Model ..........................4 2.1 Signaling for Media Gateway Interface ..........................4 2.2 Signaling for Database Access ..................................7 3. Functional Requirements for Signaling Transport .................8 3.1 Protocol encapsulation and identification .......................8 3.2 Path and node management ........................................8 3.3 Packet loss recovery and resequencing ...........................8 3.4 Flow control ....................................................8 4. Performance Requirements ........................................8 5. Management Considerations .......................................9 5.1 SS7 interface MIBs ..............................................9 5.2 protocol MIBs ...................................................9 6. Security ........................................................9 6.1 Security architecture ...........................................9 6.2 interface security needs ........................................9 7. Acknowledgements .................................................9 8. References .......................................................9 Authors' Addresses ..................................................9 Ong Informational [Page 2] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt 1. Introduction 1.1 Overview This document identifies an architecture and set of requirements for signaling transport over IP networks. 1.2 Terminology The following terms have been identified in related work [1,2]. Media Gateway (MG): A MG terminates PSTN facilities (trunks, loops), packetizes the media stream for IP, if it is not already packetized, and delivers packetized traffic to the IP network. Examples of MGs are NAS (Network Access Servers) and VoIP gateways. Media Gateway Controller (MC): A MC provides the call control "intelligence" as well as resource management of the media gateways. The MC determines call handling based on service logic and resource availability at the MG. The MC sends commands to the MG to, e.g., terminate a call from PSTN and deliver voice packets to an IP destination. Service Control Point (SCP): This is a node in an SS7 network that provides centralized service logic and data, such as call routing information. Signal Transfer Point (STP): This is a node in an SS7 network that routes signaling messages based on their destination address in the SS7 network Signaling Gateway (SG): An SG is an entity that receives/sends PSTN 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 may also transport (back-haul) Q.931 signaling to an MC. Backhaul: Backhaul refers to the transport of signaling from the point of interface for the associated data stream (i.e., the MG) back to the point of call processing (i.e., the MC), if this is not local. 1.3 Requirements Requirements for signaling transport include the following: - Protocol encapsulation and identification - Path and node management - Packet loss recovery and resequencing - Flow control Ong Informational [Page 3] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt 1.4 Comparisons with Other Efforts Signaling transport focuses on transparent transport of PSTN-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 such as differentiated services to support the functional and performance requirements for signaling. Since the focus is on transport, the following items will be outside the scope of the signaling transport work: - definition of the call control protocols themselves - definition of protocol conversion for call control, such as conversion from Channel Associated Signaling (CAS) to message signaling protocols. The signaling transport will, however, be defined in such a way as to support encapsulation and carriage of a variety of call control protocols. 2. Signaling Transport Architectural Model 2.1 Signaling for Media Gateway Interface 2.1.1 Gateway Component Functions Figure 1 defines a commonly defined functional model for the VoIP Gateway that separates out the functions of SG, MC and MG. This model may be implemented in a number of ways, with functions implemented in separate devices or combined in single devices. Where physical separation exists between functional entities, Signaling Transport can be applied to ensure that PSTN signaling information is transported between entities with the required functionality and performance. Ong Informational [Page 4] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt Signaling gateway Signaling gateway (opt) +---------------+ +--------------+ | | SG-SG transport | | PSTN<-------->[SG] <--+---------O------------+--> [SG] | signal | | | | | | +-------|-------+ +-----|--------+ | | O O | | +-------|-------+ +-----|--------+ | | | MC-MC signaling | | | | [SA] <---+--------O-------------+--> [SA] | | [MC] | | [MC] | | | | | | | +-------|-------+ +-----|--------+ Gateway | controller Gateway | Controller (opt) O O | | +-------|-------+ +-----|--------+ | | | | | | <-IMT--+---->[MG] <---+-----RTP stream-------+-> [MG] <----+-IMT-----> | | | | +---------------+ +--------------+ Media gateway Media gateway Notes: - IMT stands for Inter-Machine Trunk Figure 1: Gateway Functional Model Ong Informational [Page 5] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt SS7 gateway +--------------+ | | SS7<--------->[SG] | (ISUP) | | | | | | +------|-------+ ST | O Controller | SS7 gateway Controller +------|-------+ +--------------+ +-------------+ | | | | | | | | [MC] | SS7------->[SG] | | [MC] | | | | | | | | | | | | | | | | | | | | | +------|-------+ +-------|------+ +-----|-|-----+ | | | | O ST O | O | | ST O | | | | | +-------|-------+ +-------|------+ +-----|-|-----+ | | | | | | | | | | | | | | | | SS7----->[SG]| | IMT------->[MG] | IMT------>[MG/MC] | F-link| | | | | | | | | | | | | | IMT-------->[MG] | | | | | | | +---------------+ +--------------+ +-------------+ VoIP gateway VoIP gateway VoIP gateway (a) (b) (c) Notes: - ST stands for Signaling Transport used to carry PSTN signaling Figure 2: Example Implementations 2.1.2 SS7 Interworking For interworking with SS7-controlled PSTN networks, the SG terminates the SS7 link and transfers the signaling information to the MC using signaling transport. The MG terminates the intermachine trunk and controls the trunk based on the control signaling it receives from the MC. Depending on implementation, the SG and MC may be in separate devices or co-located. An alternative case (c) is the SS7 F-link, where the signaling link is facility-associated, and is terminated by the same device (i.e., the MG) that terminates the intermachine trunk. In this case, the SG function is co-located with the MG function, as shown in Figure 2. In the latter case, the signaling messages are "backhauled" to the MC for call processing, using signaling transport functionality. Note: exactly what layers of SS7 are terminated above is ffs. Ong Informational [Page 6] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt 2.1.3 ISDN Interworking 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 MC for call processing, signaling transport would be used between the SG function and MC. This is shown in Figure 3 below. Controller +-------------+ | | | [MC] | | | | | | | | | +-----|-|-----+ | | | O device control | | Q.931/ST O | | | +-----|-|-----+ | | | | Q.931---->[SG]| | D-Chan| | | | | | B-Chan------>[MG] | | | +-------------+ VoIP gateway Figure 3: Q.931 transport model 2.1.4 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 PSTN 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 PSTN signaling protocol and backhauled to the MC using signaling transport capabilities. (Need for this tbd with navdec group). 2.2 Signaling for Database Access Transaction Capabilities (TCAP or TC) is the application part within SS7 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: - access from an SS7 network to an IP network database - access from an SS7 network to an MC - access from an MC to an SS7 network element - access from an IP database to an SS7 network element A basic functional model for TCAP/TC over IP is shown in Figure 4. Ong Informational [Page 7] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt +--------------+ | OS-Database | +--|----|------+ TCAP| | SS7 gateway IP | | SS7 gateway +--------------+ | | +--------------+ | v | / / | | SS7<---------->[SG] ------/ / | [SG]<---------> SS7 (TCAP) | | | / | | | | | | / | | | +------|-------+ / +------|-------+ | / | TCAP/IP | / | O TCAP/ O Originating | IP / | Terminating Controller | / | Controller +-------|------/+ +-----|--------+ | | / | | | | | [SA] / | | [SA] | | [MC] |<------------->| [MC] | | | | | | | +-------|-------+ +-----|--------+ O O | | +-------|----------+ +----------|------+ | | | | | | | | | | | | <-IMT-------->[MG]<---------RTP stream----->[MG]<--------IMT--> | | | | | | | | | | | | +------------------+ +-----------------+ originating VoIP gateway terminating VoIP gateway Notes: - IMT is Inter-Machine Trunk Figure 4: TCAP Signaling over IP 3. Functional Requirements for Signaling Transport 3.1 Protocol encapsulation and identification 3.2 Path and node management 3.3 Packet loss recovery and resequencing 3.4 Flow control 4. Performance Requirements tbd. Ong Informational [Page 8] INTERNET-DRAFT draft-ong-sigtran-framework-arch-00.txt 5. Management Considerations 5.1 SS7 interface MIBs 5.2 protocol MIBs 6. Security 6.1 Security architecture 6.2 interface security needs tbd, e.g., key management, inter-domain management 7. Acknowledgements The author would like to thank K. Chong, I. Elliott, M. Holdrege, C. Sharp and G. Sidebottom for their comments and suggestions. 8. References [1] F. Cuervo, N. Greene, et al, "SS7-Internet Interworking - Architectural Framework" , July 1998, work in progress. [2] F. Cuervo, G. Gibbs, "Media Gateway Architecture", , November 1998, work in progress. Authors' Addresses Lyndon Ong Nortel Networks 4401 Great America Parkway Santa Clara, CA 95054 long@baynetworks.com Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Ong Informational [Page 9]