INTERNET-DRAFT L. Coene(Ed) Internet Engineering Task Force Siemens Issued: November 2002 J. Pastor Expires: May 2003 Ericsson Telephony Signalling Transport over SCTP applicability statement draft-ietf-sigtran-signalling-over-sctp-applic-06.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1ID-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This document describes the applicability of the new protocols developed under the signalling transport framework[RFC2719]. A description of the main issues regarding the use of the Stream Control Transmission Protocol (SCTP)[RFC2960] and each adaptation layer for transport of telephony signalling information over IP infrastructure is explained. Coene & Pastor [Page 1] Draft Telephony Signalling AS October 2002 Table of contents Telephony signalling over SCTP Applicability statement ......... ii Chapter 1: Introduction ........................................ 2 Chapter 1.1: Scope ..... ....................................... 3 Chapter 1.2: Terminology ....................................... 3 Chapter 1.3: Contributors ...................................... 3 Chapter 2: SIGTRAN architecture ................................ 4 Chapter 2.1: Overview ......................................... 4 Chapter 3: Issues for transporting Telephony signalling information over SCTP .......................................... 6 Chapter 3.1: Congestion control ................................ 6 Chapter 3.2: Detection of failures ............................. 6 Chapter 3.2.1: Retransmission TimeOut (RTO) calculation ........ 7 Chapter 3.2.2: Heartbeat ....................................... 7 Chapter 3.2.3: Maximum Number of retransmissions ............... 7 Chapter 3.3: Shorten end-to-end message delay ................. 7 Chapter 3.4: Bundling considerations ........................... 8 Chapter 3.5: Stream Usage ...................................... 8 Chapter 4: User Adaptation Layers............................... 8 Chapter 4.1: Access Signalling.................................. 11 Chapter 4.1.1: IUA (ISDN Q.921 User Adaptation) ................ 11 Chapter 4.1.2: V5UA (V5.2-User Adaptation) Layer ............... 12 Chapter 4.1.3: DUA (DPNSS/DASS User adaptation) Layer .......... 13 Chapter 4.2: Network Signalling ................................ 13 Chapter 4.2.1: MTP lvl3 over IP ................................ 14 Chapter 4.2.1.1: M2UA (SS7 MTP2-User Adaptation) Layer ......... 14 Chapter 4.2.1.2: M2PA (SS7 MTP2-User Peer-to-Peer Adaptation) .. 15 Chapter 4.2.1.3: Main difference between M2PA and M2UA ......... 16 Chapter 4.2.2: M3UA (SS7 MTP3 User Adaptation) Layer ........... 17 Chapter 4.2.3: SUA (SS7 SCCP User Adaptation) Layer ............ 18 Chapter 5: Security considerations ............................. 20 Chapter 6: References and related work ......................... 20 Chapter 7: Acknowledgments ..................................... 21 Chapter 8: Author's address .................................... 22 1 INTRODUCTION Coene & Pastor [Page 2] Draft Telephony Signalling AS October 2002 This document intends to inform how to transport telephony signalling protocols, used in classic telephony systems, over IP networks. The whole architecture is called SIGTRAN (Signalling Transport) as described in RFC2719 and is composed of a transport protocol(SCTP) and several User Adaptation layers(UAL). The transport protocol SCTP has been been developed to fulfill the stringent requirements that telephony signalling networks have. The set of User Adaptation layers have also been introduced to make it possible that different signalling protocols can use the SCTP layer. 1.1 Scope The scope of this document is to explain the way that user adaptation layers and SCTP protocols have to be used to transport Telephony signalling information over IP. 1.2 Terminology The following terms are commonly identified in related work: Association: SCTP connection between two endpoints. Stream: A uni-directional logical channel established within an association, within which all user messages are delivered in sequence except for those submitted to the unordered delivery service. SPU: Signalling protocol user, the application on top of the User adaptation layer. CTSP: Classical Telephony Signalling protocol(examples: MTP level2, MTP level 3, SCCP....). UAL: User adaptation layer: the protocol that encapsulate the upper layer telephony signalling protocols that are to be transported over SCTP/IP. ISEP: IP signalling endpoint: a IP node that implements SCTP and a User adapatation layer. SP: signalling point 1.3 Contributors Coene & Pastor [Page 3] Draft Telephony Signalling AS October 2002 The following people contributed to the document: L. Coene(Editor), M. Tuexen, G. Verwimp, J. Loughney, R.R. Stewart, Qiaobing Xie, M. Holdrege, M.C. Belinchon, A. Jungmaier, J. Pastor and L. Ong. 2 SIGTRAN architecture The SIGTRAN architecture describes the transport of signalling information over IP infrastructure. Telephony Signalling transport over IP normally uses the following architecture: Telephony Signalling Application | +------------------------------------+ | Signalling Adaptation Layers | +------------------------------------+ | +------------------------------------+ |Stream Control Transmission Protocol| | (SCTP) | +------------------------------------+ | Internet Protocol (IPv4/IPv6) Figure 1.1: Telephony signalling transport protocol stack The components of the protocol stack are : (1) Adaptation modules are used when the telephony application needs to preserve an existing primitive interface. (e.g. management indications, data operation primitives, ... for a particular user/application protocol). (2) SCTP, specially configured to meet the telephony application performance requirements. (3) The standard Internet Protocol. The telephony signalling protocols to be transported can be: - SS7 MTP3 users: SCCP, ISUP, TUP... - SS7 MTP2 users: MTP3 - SS7 SCCP users: RANAP, MAP(+TCAP), INAP(+TCAP)... Coene & Pastor [Page 4] Draft Telephony Signalling AS October 2002 - ISDN Q.921 users: Q.931 - V5.2/DSS1 - .... Every classic telephony protocol can have a corresponding UAL developed. The user adaptation layers(UALs) are a set of protocols that encapsulate a specific signalling protocol to be transported over SCTP. The adapation is done in a way that the upper signalling protocols that are relayed remain unaware that the lower layers are different to the originail lower telephony signalling layers. In that sense, the upper interface of the user adapatation layers need to be the same as the upper layer interface to its original lower layer. If a MTP user is being relayed over the IP network, the related UAL used to transport the MTP user will have the same upper interface as MTP has. The Stream Control Transmission protocol was designed to fulfill the stringent transport requirements that classical signalling protocols have and is therefore the recommended transport protocol to use for this purpose. The following functions are provided by SCTP: - Reliable Data Transfer - Multiple streams to help avoid head-of-line blocking - Ordered and unordered data delivery on a per-stream basis - Bundling and fragmentation of user data - Congestion and flow control - Support continuous monitoring of reachability - Graceful termination of association - Support of multi-homing for added reliability - Protection against blind denial-of-service attacks - Protection against blind masquerade attacks SCTP is used as the transport protocol for telephony signalling applications. Message boundaries are preserved during data transport by SCTP and so each UAL can specify its own message structure withing the SCTP user data. The SCTP user data can be delivered by the order of transmission within a stream(in sequence delivery) or unordered. Coene & Pastor [Page 5] Draft Telephony Signalling AS October 2002 SCTP can be used to provide redundancy at the transport layer and below. Telephony applications needing this level of redundancy can make use of SCTP's multi-homing support. SCTP can be used for telephony applications where head-of-line blocking is a concern. Such an application should use multiple streams to provide independent ordering of telephony signalling messages. 3 Issues for transporting telephony signalling over SCTP Transport of telephony signalling requires special considerations. In order to use SCTP, special care must be taken to meet the performance, timing and failure management requirements. 3.1 Congestion Control The basic mechanism of congestion control in SCTP have been described in [RFC2960]. SCTP congestion control sometimes conflicts with the timing requirements of telephony signalling application messages which are transported by SCTP. During congestion, messages may be delayed by SCTP, thus sometimes violating the timing requirements of those telephony applications. In an engineered network (e.g. a private intranet), in which network capacity and maximum traffic are very well understood, some telephony signalling applications may choose to relax the congestion control rules of SCTP in order to satisfy the timing requirements. In order to do this, they should employ their own congestion control mechanisms. But this should be done without destabilising the network, otherwise this would lead to potential congestion collapse of the network. Some telephony signalling applications may have their own congestion control and flow control techniques. These techniques may interact with the congestion control procedures in SCTP. 3.2 Detection of failures Telephony systems often must have no single point of failure in operation. The UAL must meet certain service availability and performance requirements according to the classical signalling layers they are Coene & Pastor [Page 6] Draft Telephony Signalling AS October 2002 replacing. Those requirements may be specific for each UAL. For example, telephony systems are often required to be able to preserve stable calls during a component failure. Therefore error situations at the transport layer and below must be detected quickly so that the UAL can take approriate steps to recover and preserve the calls. This poses special requirements on SCTP to discover unreachablility of a destination address or a peer. 3.2.1 Retransmission TimeOut (RTO) calculation The SCTP protocol parameter RTO.Min value has a direct impact on the calculation of the RTO itself. Some telephony applications want to lower the value of the RTO.Min to less than 1 second. This would allow the message sender to reach the maximum number-of-retransmission threshold faster in the case of network failures. However, lowering RTO.Min may have a negative impact on network behaviour [ALLMAN99]. In some rare cases, telephony applications might not want to use the exponential timer back-off concept in RTO calculation in order to speed up failure detection. The danger of doing this is that, when network congestion occurs, not backing off the timer may worsen the congestion situation. Therefore, this strategy should never be used in public Internet. It should be noted that not using delayed SACK will also help faster failure detection. 3.2.2 Heartbeat For faster detection of (un)availability of idle paths, the telephony application may consider lowering the SCTP parameter HB.interval. It should be noted this might result in a higher traffic load. 3.2.3 Maximum number of retransmissions Setting Path.Max.Retrans and Association.Max.Retrans SCTP parameters to lower values will speed up both destination address and peer failure detection. However, if these values are set too low, the probability of false fault detections might increase. Coene & Pastor [Page 7] Draft Telephony Signalling AS October 2002 3.3 Shorten end-to-end message delay Telephony applications often require short end-to-end message delays. The method described in section 3.2.1 on lowering RTO may be considered. The different paths within a single association will have a different RTO, so using the path with the lowest RTO will lead to a shorter end-to-end message delay for the application running on top of the UAL's. 3.4 Bundling considerations Bundling small telephony signalling messages at transmission helps improve the bandwidth usage efficiency of the network. On the downside, bundling may introduce additional delay to some of the messages. This should be taken into consideration when end-to-end delay is a concern. 3.5 Stream Usage Telephony signalling traffic is often composed of multiple, independent message sequences. It is highly desirable to transfer those independent message sequences in separate SCTP streams. This reduces the probability of head-of-line blocking in which the retransmission of a lost message affects the delivery of other messages not belonging to the same message sequence. 4. User Adaptation Layers Users Adaptation Layers (UALs) are defined to encapsulate different signalling protocols in order to transport them over SCTP/IP There are UALs for both access signalling (DSS1) and trunk signalling (SS7). A brief description of the standardized UALs follows in the next sub-sections. The delivery mechanism in the several UALs - Supports seamless operation of UALs user peers over an IP network connection. - Supports the interface boundary that the UAL user had with the traditional lower layer. Coene & Pastor [Page 8] Draft Telephony Signalling AS October 2002 - Supports management of SCTP transport associations and traffic between SGs and ISEPs or two ISEPs - Supports asynchronous reporting of status changes to management. Signalling User Adaptation Layers have been developed for both: Access and Trunk Telephony Signalling. They are defined as follows. Access Signalling: This is the signalling that is needed between and access device and an exchange in the core network in order to establish, manage or release the voice or data call paths. There are several protocols that have been developed for this purpose. Trunk Signalling: This is the signalling that is used between the exchanges inside the core network in order to establish, manage or release the voice or data call paths. The most common protocols used for this purpose are known as the SS7 system that belongs to the Common Channel Signalling (CCS) philosophy. The SS7 protocol stack is depicted below: +------+-----+-------+- -+-------+------+-----+------+ | | | | | | MAP | CAP | INAP | + | + RANAP |...| BSSAP +-------------------+ | ISUP | TUP | | | | TCAP | + | +---------------------------------------+ | | | SCCP | +----------------------------------------------------+ | MTP3 | +----------------------------------------------------+ | MTP2 | +----------------------------------------------------+ | MTP1 | +----------------------------------------------------+ The Telephony Signalling Protocols to be transported with the already designed UALS are: - ISDN Q.921 Users: Q.931 - V5.2/DSS1 - DPNSS/DASS2 - SS7 MTP3 Users: SCCP, ISUP, TUP - SS7 MTP2 Users: MTP3 - SS7 SCCP Users: TCAP, RANAP, BSSAP, ... Two main scenarios have been developed to use the different UALS for IP Signalling Transport: Coene & Pastor [Page 9] Draft Telephony Signalling AS October 2002 (1) Intercommunication of traditional Signalling transport nodes and IP based nodes. Traditional Telephony Telephony Signalling ********* Signalling ********** over IP ******** * SEP *----------------* SG *--------------* ISEP * ********* ********** ******** +-------+ +-------+ |SigProt| |SigProt| +-------+ +----+----+ +-------+ | | | |UAL | | UAL | | | | +----+ +-------+ | TTST | |TTST|SCTP| | SCTP | | | | +----+ +-------+ | | | | IP | | IP | +-------+ +---------+ +-------+ SEP - Signalling Endpoint SG - Signalling Gateway ISEP - IP Signalling Endpoint SigProt - Signalling Protocol TTST - Traditional Telephony Signalling Transport UAL - User Adaptation Layer SCTP - Stream Control Transport Protocol It is also referred as SG to AS communication. AS I the name that UAL usually gives to the ISEP nodes. It stands for Application Server. (2) Communication inside the IP network. Telephony Signalling ********* over IP ********* * ISEP *------------------* ISEP * ********* ********* +-------+ +-------+ |SigProt| |SigProt| +-------+ +-------+ | UAL | | UAL | +-------+ +-------+ | SCTP | | SCTP | +-------+ +-------+ | IP | | IP | +-------+ +-------+ This is also referred to as IPSP communication. IPSP is the name Coene & Pastor [Page 10] Draft Telephony Signalling AS October 2002 of the role that an UAL plays on an IP-based node. It stands for IP Signalling Point. The first scenario is applied for both types of signalling (access and trunk signalling). On the other hand the peer to peer basis can only be used for trunk signalling. 4.1 Access Signalling The SIGTRAN WG have developed UALs to transport the following Access Signalling protocols: - ISDN Q.931 - V5.2 - DPNSS/DASS2 4.1.1 ISDN Q.931 over IP UAL: IUA (ISDN Q.921 User Adaptation) This document supports both ISDN Primary Rate Access (PRA) as well as Basic Rate Access (BRA) including the support for both point-to-point and point-to-multipoint modes of communication. This support includes Facility Associated Signalling (FAS), Non-Facility Associated Signalling (NFAS) and NFAS with backup D channel. It implements the client/server architecture. The default orientation would be for the SG to take on the role of server while the ISEP is the client. The SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA is 9900. Examples of the upper layers to be transported would be Q.931 and QSIG. The main scenario supported by this UAL is the SG to ISEP communication where the ISEP role is typically played by a node called MGC defined in [RFC2719]. ****** ISDN ****** IP ******* *PBX *---------------* SG *--------------* MGC * ****** ****** ******* +-----+ +-----+ |Q.931| (NIF) |Q.931| +-----+ +----------+ +-----+ | | | | IUA| | IUA | | | | +----+ +-----+ |Q.921| |Q.921|SCTP| |SCTP | | | | +----+ +-----+ | | | | IP | | IP | +-----+ +-----+----+ +-----+ Coene & Pastor [Page 11] Draft Telephony Signalling AS October 2002 NIF - Nodal Interworking Function PBX - Private Branch Exchange SCTP - Stream Control Transmission Protocol IUA - ISDN User Adaptation Layer Protocol The SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA is 9900. The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is ô1ö 4.1.2 V5UA over IP UAL: V5UA (V5.2-User Adaptation) It is an extension from the IUA layer with the modifications needed to support the differences between Q.921 / Q.931, and V5.2 layer 2 / layer 3. It supports analog telephone access, ISDN basic rate access and ISDN primary rate access over a V5.2 interface. It is basically implemented in an interworking scenario with SG. ****** V5.2 ****** IP ******* * AN *---------------* SG *--------------* MGC * ****** ****** ******* +-----+ +-----+ |V5.2 | (NIF) |V5.2 | +-----+ +----------+ +-----+ | | | |V5UA| |V5UA | | | | +----+ +-----+ |LAPV5| |LAPV5|SCTP| |SCTP | | | | +----+ +-----+ | | | | IP + | IP | +-----+ +-----+----+ +-----+ AN û Access Network NIF û Nodal Interworking Function LAPV5 û Link Access Protocol for the V5 channel SCTP - Stream Control Transmission Protocol The SCTP (and UDP/TCP) Registered User Port Number Assignment for V5UA is 5675. Coene & Pastor [Page 12] Draft Telephony Signalling AS October 2002 The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is "6". 4.1.3 DPNSS/DASS2 over IP UAL: DUA (DPNSS/DASS2 User Adaptation) The DUA is built on top of IUA defining the necessary extensions to IUA for a DPNSS/DASS2 transport. DPNSS stands for Digital Private Network Signalling System and DASS2 for Digital Access Signalling System No 2 ****** DPNSS ****** IP ******* *PBX *---------------* SG *--------------* MGC * ****** ****** ******* +-----+ +-----+ |DPNSS| (NIF) |DPNSS| | L3 | | L3 | +-----+ +-----+----+ +-----+ | | | | DUA| | DUA | |DPNSS| |DPNSS+----+ +-----+ | L2 | | L2 |SCTP| |SCTP | | | | +----+ +-----+ | | | | IP + | IP | +-----+ +-----+----+ +-----+ PBX - Private Branch eXchange NIF - Nodal Interworking function SCTP - Stream Control Transmission Protocol DUA - DPNSS User Adaptation Layer Protocol The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is "TBD". 4.2 Network Signalling The SIGTRAN WG have developed UALs to transport the following SS7 protocols: - MTP2 Users: MTP3 - MTP3 Users: ISUP, TUP, SCCP - SCCP Users: TCAP, RNSAP, RANAP, BSSAP, ... 4.2.1 MTP lvl3 over IP Coene & Pastor [Page 13] Draft Telephony Signalling AS October 2002 UALs: - M2UA (SS7 MTP2 User Adaptation) - M2PA (SS7 MTP2-User Peer-to-Peer Adaptation) 4.2.1.1 M2UA (SS7 MTP2 User Adaptation) M2UA protocol is mainly used between a Signalling Gateway (SG) and Media Gateway Controller (MGC). The SG will terminate up to MTP Level 2 and the MGC will terminate MTP Level 3 and above. In other words, the SG will transport MTP Level 3 messages over an IP network to a MGC. The only SS7 MTP2 User is MTP3 that is the protocol transported by this UAL. The SG provides a interworking of transport functions with the IP transport, in order to transfer the MTP2-User signalling messages to and from an Application Server (e.g. MGC) where the peer MTP2- User protocol layer exists. ****** SS7 ****** IP ******* *SEP *-----------* SG *-------------* MGC * ****** ****** ******* +----+ +----+ |S7UP| |S7UP| +----+ +----+ |MTP3| |MTP3| | | (NIF) | | +----+ +----+----+ +----+ | | | |M2UA| |M2UA| | | | +----+ +----+ |MTP2| |MTP2|SCTP| |SCTP| | | | +----+ +----+ | | | |IP | |IP | +----+ +---------+ +----+ MGC - Media Gateway Controler SG - Signalling Gateway SEP - SS7 Signalling Endpoint NIF - Nodal Interworking Function IP - Internet Protocol SCTP - Stream Control Transmission Protocol The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2UA is 2904. Coene & Pastor [Page 14] Draft Telephony Signalling AS October 2002 The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is "2" 4.2.1.2 M2PA (SS7 MTP2-User Peer-to-Peer Adaptation) Layer M2PA protocol is used between SS7 Signalling Points employing the MTP Level 3 protocol. The SS7 Signalling Points may also employ standard SS7 links using the SS7 MTP Layer 2 to provide transport of MTP Layer 3 signalling messages. Both configurations: intercommunication of SS7 and IP with SG and communication between ISEPs are possible. Communication between two IP nodes: ******** IP ******** * IPSP *--------* IPSP * ******** ******** +------+ +------+ | TCAP | | TCAP | +------+ +------+ | SCCP | | SCCP | +------+ +------+ | MTP3 | | MTP3 | +------+ +------+ | M2PA | | M2PA | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ IP - Internet Protocol IPSP - IP Signalling Point SCTP - Stream Control Transmission Protocol Interconnection of SS7 and IP nodes: Coene & Pastor [Page 15] Draft Telephony Signalling AS October 2002 ******** SS7 *************** IP ******** * SEP *--------* SG *--------* IPSP * ******** *************** ******** +------+ +------+ | TCAP | | TCAP | +------+ +------+ | SCCP | | SCCP | +------+ +-------------+ +------+ | MTP3 | | MTP3 | | MTP3 | +------+ +------+------+ +------+ | | | | M2PA | | M2PA | | | | +------+ +------+ | MTP2 | | MTP2 | SCTP | | SCTP | | | | +------+ +------+ | | | | IP | | IP | +------+ +------+------+ +------+ SEP - SS7 Signalling Endpoint These figures are only an example. Other configurations are possible. For example, IPSPs without traditional SS7 links could use the protocol layers MTP3/M2PA/SCTP/IP to route SS7 messages in a network with all IP links. Another example is that two SGs could be connected over an IP network to form an SG mated pair similar to the way STPs are provisioned in traditional SS7 networks. The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA is TBD. The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is TBD 4.2.1.3 Main differences between M2PA and M2UA: a. M2PA: IPSP processes MTP3/MTP2 primitives. M2UA: MGC transports MTP3/MTP2 primitives between the SG's MTP2 and the MGC's MTP3 (via the NIF) for processing. b. M2PA: SG-IPSP connection is an SS7 link. M2UA: SG-MGC connection is not an SS7 link. It is an extension of MTP to a remote entity. c. M2PA: SG is an SS7 node with a point code. M2UA: SG is not an SS7 node and has no point code. d. M2PA: SG can have upper SS7 layers, e.g., SCCP. M2UA: SG does not have upper SS7 layers since it has no MTP3. Coene & Pastor [Page 16] Draft Telephony Signalling AS October 2002 e. M2PA: relies on MTP3 for management procedures. M2UA: uses M2UA management procedures. 4.3 MTP lvl3-Users (ISUP, TUP, SCCP) over IP UAL: M3UA (SS7 MTP3 User Adaptation) M3UA protocol supports the transport of any SS7 MTP3-User signalling such as TUP, ISUP and SCCP over IP using the services of SCTP. Interconnection of SS7 and IP nodes: ******** SS7 ***************** IP ******** * SEP *---------* SGP *--------* ASP * ******** ***************** ******** +------+ +---------------+ +------+ | ISUP | | (NIF) | | ISUP | +------+ +------+ +------+ +------+ | MTP3 | | MTP3 | | M3UA | | M3UA | +------| +------+-+------+ +------+ | MTP2 | | MTP2 | | SCTP | | SCTP | +------+ +------+ +------+ +------+ | L1 | | L1 | | IP | | IP | +------+ +------+ +------+ +------+ SEP - SS7 Signalling End Point SCTP - Stream Control Transmission Protocol NIF - Nodal Interworking Function Communication between two IP nodes: Coene & Pastor [Page 17] Draft Telephony Signalling AS October 2002 ******** IP ******** * IPSP *----------* IPSP * ******** ******** +------+ +------+ |SCCP- | |SCCP- | | User | | User | +------+ +------+ | SCCP | | SCCP | +------+ +------+ | M3UA | | M3UA | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ It works using the client-server philosophy. ISEP is recommended to be client when talking with a SG. The reserved port by IANA is 2905 to listen to possible client connections. The assigned payload protocol identifier for the SCTP DATA chunks is ô3ö. 4.4 SCCP-Users over IP UAL: SUA (SS7 SCCP User Adaptation) SUA protocol supports the transport of any SS7 SCCP-User signalling such as MAP, INAP, SMS, BSSAP, RANAP over IP using the services of SCTP. SUA can support only non-call related signalling. SUA does not pose stringent timing constraints on SCTP due to the fact that SUA applications have broad timing requirement (from 10 of seconds to hours) which the applications guard themselves and the timing supervision of the application is end-to-end, not hop-by- hop(as with ISUP). Possible configurations are showed in the pictures below. - Interconnection of SS7 and IP: Coene & Pastor [Page 18] Draft Telephony Signalling AS October 2002 ******** *************** ******** * SEP * IP * * IP * * * or *---------* SG *--------* ASP * * STP * * * * * ******** *************** ******** +------ +------+ | SUAP | | SUAP | +------+ +------+------+ +------+ | SCCP | | SCCP | SUA | | SUA | +------+ +------+------+ +------+ | | | | | | | | MTP3 | | MTP3 | SCTP | | SCTP | | | | | | | | +------+ +------+------+ +------+ | MTP2 | | MTP2 | IP | | IP | +------+ +------+------+ +------+ SUAP - SCCP/SUA User Protocol (TCAP, for example) STP - SS7 Signalling Transfer Point - IP Node to IP Node communication: ******** ******** * * IP * * * IPSP *--------* IPSP * * * * * ******** ******** +------+ +------+ | SUAP | | SUAP | +------+ +------+ | SUA | | SUA | +------+ +------+ | SCTP | | SCTP | +------+ +------+ | IP | | IP | +------+ +------+ IANA has registered SCTP Port Number 14001 for SUA. It is recommended that SGs use this SCTP port number for listening for new connections. The payload protocol identifier for the SCTP DATA chunks is "4". Coene & Pastor [Page 19] Draft Telephony Signalling AS October 2002 5 Security considerations UALs are designated to carry signalling messages for telephony services. As such, UALs must involve the security needs of several parties: the end users of the services; the network providers and the applications involved. Additional requirements may come from local regulation. While having some overlapping security needs, any security solution should fulfill all of the different parties' needs. See specific Security considerations in each UAL technical specification. SCTP only tries to increase the availability of a network. SCTP does not contain any protocol mechanisms which are directly related to user message authentication, integrity and confidentiality functions. For such features, it depends on the IPSEC protocols and architecture and/or on security features of its user protocols. Mechanisms for reducing the risk of blind denial-of-service attacks and masquerade attacks are built into SCTP protocol. See RFC2960, section 11 for detailed information. Currently the IPSEC working group is investigating the support of multihoming by IPSEC protocols. At the present time to use IPSEC, one must use 2 * N * M security associations if one endpoint uses N addresses and the other M addresses. 6 References and related work [RFC2960] Stewart, R. R., Xie, Q., Morneault, K., Sharp, C. , , Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and Paxson, V, "Stream Control Transmission Protocol", RFC2960, October 2000. [RF3257] Coene, L., Tuexen, M., Verwimp, G., Loughney, J., Stewart, R. R., Xie, Q., Holdrege, M., Belinchon, M.C., and Jungmayer, A., "Stream Control Transmission Protocol Applicability statement", RFC3257, April 2002. [RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L., Lin, H., Juhasz, I., Holdrege, M., Sharp, C., "Framework Architecture for Signalling Transport", RFC2719, October 1999. [RFC3057] Morneault, K., Rengasami, S., Kalla, M., Sidebottom, G., Coene & Pastor [Page 20] Draft Telephony Signalling AS October 2002 "ISDN Q.921-User Adaptation Layer", RFC3057, February 2001. [RFC3331] Morneault, K., Dantu, R., Sidebottom, G., George, T., Bidulock, B., Heitz , J., "Signaling System 7 (SS7) Message Transfer Part (MTP) 2 - User Adaptation Layer", RFC3331, September 2002. [RFC3332] Sidebottom, G., Pastor-Balbas, J., Rytina, I., Mousseau, G., Ong, L., Schwarzbauer, H.J., Gradischnig, K., Morneault, K., Kalla, M., Glaude, N., Bidulock, B., Loughney, J., "SS7 MTP3-User Adaptation Layer (M3UA)", RFC3332, September 2002. [RFCzzzz] Loughney, J., Sidebottom, G., Mousseau, G., Lorusso, S., Coene, L., Verwimp, G., Keller, J., Escobar, F., Sully, W., Furniss, S., Bidulock, B.,"SS7 SCCP-User Adaptation Layer (SUA)", RFCzzzz, May 2002. [RFCwwww] George, T., Dantu, R., Kalla, M., Schwarzbauer, H.J., Sidebottom, G., Morneault, K.,"SS7 MTP2-User Peer-to-Peer Adaptation Layer", RFCwwww, June 2002. [RFCqqqq] Weilandt, E., Khanchandani, N., Rao, S.,"V5.2-User Adaptation Layer (V5UA)", RFCqqqq, June 2002 [RFCtttt] Vydyam, A., Mukundan, R., Mangalpally, N., Morneault, K.,"DPNSS/DASS 2 extensions to the IUA protocol", RFCtttt, August 2002. [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End Network Path Properties", Proc. SIGCOMM'99, 1999. 7 Acknowledgments This document was initially developed by a design team consisting of Lode Coene, John Loughney, Michel Tuexen, Randall R. Stewart, Qiaobing Xie, Matt Holdrege, Maria-Carmen Belinchon, Andreas Jungmaier, Gery Verwimp and Lyndon Ong. The authors wish to thank Renee Revis, H.J. Schwarzbauer, T. Taylor, G. Sidebottom, K. Morneault, T. George, M. Stillman and many others for their invaluable comments. 8 Author's Address Coene & Pastor [Page 21] Draft Telephony Signalling AS October 2002 Lode Coene Phone: +32-14-252081 Siemens Atea EMail: lode.coene@siemens.atea.be Atealaan 34 B-2200 Herentals Belgium Javier Pastor-Balbas Phone: Ericsson Espana S.A. Email: j.javier.pastor@ericsson.com C/ Retama 1 28045 Madrid Spain Expires: August 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). 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. 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