RFC 4166
Telephony Signalling Transport over Stream Control Transmission Protocol (SCTP) Applicability Statement
RFC 4166: Telephony Signalling Transport over SCTP Applicability Statement 🎀
Okay bestie, RFC 4166 is giving informational 💅. It came out of the Network Working Group in February 2006, written by L. Coene (Siemens) and J. Pastor-Balbas (Ericsson). It's Category: Informational, so it's sharing guidance rather than setting an Internet standard. Its header doesn't list anything it Obsoletes or Updates, so it's not replacing or changing any other RFC 🦋.
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 (2006).
Abstract 💜
This doc explains where the different protocols from the signalling transport framework fit. It walks through the main issues with using SCTP (the Stream Control Transmission Protocol) and explains each adaptation layer used to carry telephony signalling over IP infrastructure 🌈.
Table of Contents 📋
1. Introduction ....................................................2
1.1. Scope ......................................................2
1.2. Terminology ................................................3
1.3. Contributors ...............................................3
2. SIGTRAN Architecture ............................................3
3. Issues for Transporting Telephony Signalling over SCTP ..........5
3.1. Congestion Control .........................................5
3.2. Detection of Failures ......................................6
3.2.1. Retransmission TimeOut (RTO) Calculation ............6
3.2.2. Heartbeat ...........................................7
3.2.3. Maximum Number of Retransmissions ...................7
3.3. Shorten End-to-End Message Delay ...........................7
3.4. Bundling Considerations ....................................7
3.5. Stream Usage ...............................................7
4. User Adaptation Layers ..........................................7
4.1. Access Signalling .........................................10
4.1.1. IUA (ISDN Q.921 User Adaptation) ...................10
4.1.2. V5UA (V5.2-User Adaptation) Layer ..................12
4.1.3. DUA (DPNSS/DASS User adaptation) Layer .............13
4.2. Network Signalling ........................................13
4.2.1. MTP lvl3 over IP ...................................14
4.2.2. M3UA (SS7 MTP3 User Adaptation) Layer ..............17
4.2.3. SUA (SS7 SCCP User Adaptation) Layer ...............18
5. Security Considerations ........................................20
6. Informative References .........................................201. Introduction 🌸
This doc is all about how to carry the telephony signalling protocols used in classic telephony systems over IP networks. As [RFC2719] describes, the whole setup is called SIGTRAN (Signalling Transport). It's made up of a transport protocol (SCTP) plus several User Adaptation Layers (UALs). SCTP was built to meet the strict requirements of telephony signalling networks [RFC3257], and the UALs exist so that different signalling protocols can use the SCTP layer 🧚.
1.1. Scope 💖
This doc covers the SIGTRAN user adaptation layers and SCTP, and how they're used to carry telephony signalling information over IP networks.
1.2. Terminology 📖
These are the terms that keep popping up in related work:
Association: an SCTP connection between two endpoints.Stream: a uni-directional logical channel set up within an association. Within it, all user messages get delivered in sequence, except for the ones sent using the unordered delivery service.SPU: the signalling protocol user, which is the application sitting on top of the User adaptation layer.CTSP: Classical Telephony Signalling Protocol. Examples include MTP level 2, MTP level 3, and SCCP.UAL: User Adaptation Layer, the protocol that wraps the upper-layer telephony signalling protocols so they can be carried over SCTP/IP.ISEP: IP Signalling Endpoint, an IP node that implements SCTP and a User adaptation layer.SP: Signalling Point.
1.3. Contributors 🫶
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. Iconic squad 👑.
2. SIGTRAN Architecture 🏗️
The SIGTRAN architecture is all about carrying signalling information over IP infrastructure. Telephony signalling over IP usually follows this stack:
Telephony Signalling Protocol
|
+------------------------------------+
| User Adaptation Layers |
+------------------------------------+
|
+------------------------------------+
|Stream Control Transmission Protocol|
| (SCTP) |
+------------------------------------+
|
Internet Protocol (IPv4/IPv6)Figure 1: Telephony SIGnalling TRANsport Protocol Stack
The components of that stack are:
- Adaptation layers, used when the telephony application needs to keep an existing primitive interface (for example, management indications or data operation primitives for a particular user/application protocol).
- SCTP, specially configured to meet the performance requirements of telephony applications.
- The standard Internet Protocol.
The telephony signalling protocols that can be transported are:
- [RFC3332] SS7 MTP3 users: SCCP, ISUP, TUP...
- [RFC3331] SS7 MTP2 users: MTP3
- [RFC3868] SS7 SCCP users: RANAP, MAP(+TCAP), INAP(+TCAP)...
- [RFC3057] ISDN Q.921 users: Q.931
- [RFC3807] V5.2 / DSS1
- ....
The user adaptation layers (UALs) are a set of protocols that wrap a specific signalling protocol so it can be carried over SCTP. The trick is that the upper signalling protocols being relayed stay totally unaware that the lower layers have changed from the original telephony ones 🕵️♀️. So the upper interface of a UAL has to look exactly like the upper layer's interface to its original lower layer. If an MTP user is being relayed over the IP network, the related UAL that carries it has the same upper interface MTP has.
SCTP was designed to meet the strict transport requirements that classical signalling protocols have, which is why it's the recommended transport protocol for this job 💅.
SCTP provides these functions:
- 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 for 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 the transport protocol for telephony signalling applications. It preserves message boundaries during data transport, so each UAL can define its own message structure within the SCTP user data. That user data can be delivered in the order it was sent within a stream (in sequence delivery), or unordered ✨.
SCTP can also give redundancy at the transport layer and below. Telephony applications that need that level of redundancy can use 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 🚦
Transporting telephony signalling needs special consideration. To use SCTP, an implementation must take special care to meet the performance, timing, and failure management requirements 😤.
3.1. Congestion Control 🌊
The basic congestion control mechanism in SCTP is described in [RFC2960]. Unfortunately, SCTP congestion control sometimes clashes with the timing requirements of the telephony signalling application messages it carries. During congestion, SCTP may delay messages, which can break the timing requirements of those telephony applications 😭.
In an engineered network (for example, a private intranet) where network capacity and maximum traffic are very well controlled, some telephony signalling applications may choose to relax SCTP's congestion control rules to meet their timing requirements. To do that, they should bring their own congestion control mechanisms. This must be done without destabilizing the network, otherwise it could lead to potential congestion collapse of the network 💀.
Some telephony signalling applications may already 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, based on the classical signalling layers it's replacing. Those requirements may be specific to each UAL.
For example, telephony systems are often required to keep stable calls during a component failure. So error situations at the transport layer and below must be detected quickly, so the UAL can take appropriate steps to recover and preserve the calls. This puts special requirements on SCTP to discover when a destination address or a peer can't be reached 📡.
3.2.1. Retransmission TimeOut (RTO) Calculation ⏱️
The SCTP protocol parameter RTO.Min has a direct impact on how the RTO itself is calculated. Some telephony applications want to lower RTO.Min to less than 1 second. That lets the message sender hit the maximum number-of-retransmission threshold faster when there are network failures. The catch is that 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 the RTO calculation, so they can speed up failure detection. The danger is that when network congestion occurs, not backing off the timer may make the congestion worse. Therefore, this strategy should never be used on the public Internet 🚫.
It should be noted that not using delayed SACK will also increase the speed of failure detection ⚡.
3.2.2. Heartbeat ✨
okay so, for faster detection of when idle paths are up or down 👀, the telephony app may consider lowering the SCTP parameter HB.interval. just know this might mean more traffic on the wire 🚦 (so it's a tradeoff, bestie!)
3.2.3. Maximum Number of Retransmissions 💅
setting Path.Max.Retrans and Association.Max.Retrans to lower values will speed up both destination address failure detection and peer failure detection 🏃♀️💨. BUT if you set them too low, the chance of false fault detections might go up 😭. it's giving "fast but risky" energy, so pick your values wisely 🫶
3.3. Shorten End-to-End Message Delay 🎀
telephony apps often need really short end-to-end message delays 🫣. the method from Section 3.2.1 for lowering RTO may be considered here. different paths inside one association will have different RTOs 🛤️, so using the path with the lowest RTO will lead to a shorter end-to-end message delay for the app running on top of the UALs. main character path selection 👑
3.4. Bundling Considerations 🧺
bundling small telephony signalling messages at transmission helps improve bandwidth usage efficiency on the network 📶. the catch? bundling can add some extra delay to certain messages 🐢. so if end-to-end delay is a concern for you, definitely factor this in 🙈
3.5. Stream Usage 🌊
telephony signalling traffic is often made up of multiple, independent message sequences 🧵. it's highly desirable to send each of those independent sequences over its own separate SCTP stream ✨. why? because it lowers the chance of head-of-line blocking, which is when retransmitting one lost message holds up delivery of other messages that aren't even part of the same sequence 😤. not on my watch!! 💜
4. User Adaptation Layers 🧚
Users Adaptation Layers (UALs) exist to encapsulate different signalling protocols so they can be transported over SCTP/IP 🦋.
there are UALs for both access signalling (DSS1) and trunk signalling (SS7) 📞. a quick rundown of the standardized UALs is coming up in the next sub-sections 👇.
the delivery mechanism in several UALs supports:
- Seamless operation of UALs user peers over an IP network connection.
- The interface boundary that the UAL user had with the traditional lower layer.
- Management of SCTP transport associations and traffic between SGs and ISEPs or two ISEPs
- Asynchronous reporting of status changes to management.
Signalling User Adaptation Layers have been developed for both Access and Trunk Telephony Signalling 💖. here's how they break down:
Access Signalling: this is the signalling needed between an access device and an exchange in the core network, so you can establish, manage, or release the voice or data call paths 📱. several protocols have been developed for this purpose.
Trunk Signalling: this is the signalling used between exchanges inside the core network to establish, manage, or release the voice or data call paths 🏢. the most common protocols for this are known as the SS7 system, which belongs to the Common Channel Signalling (CCS) philosophy 🧠. the SS7 protocol stack looks like this:
+------+-----+-------+- -+-------+------+-----+------+
| | | | | | MAP | CAP | INAP |
+ | + RANAP |...| BSSAP +-------------------+
| ISUP | TUP | | | | TCAP |
+ | +---------------------------------------+
| | | SCCP |
+----------------------------------------------------+
| MTP3 |
+----------------------------------------------------+
| MTP2 |
+----------------------------------------------------+
| MTP1 |
+----------------------------------------------------+
Figure 2: SS7 Protocol Stackthe telephony signalling protocols that will be transported with the already designed UALS are:
- ISDN Q.921 Users: Q.931
- V5.2/DSS1
- DPNSS/DASS2 [RFC4129]
- SS7 MTP3 Users: SCCP, ISUP, TUP
- SS7 MTP2 Users: MTP3
- SS7 SCCP Users: TCAP, RANAP, BSSAP, ...
there are two main scenarios for using the different UALS for IP Signalling Transport 🗺️:
- 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
TTSP - Traditional Telephony Signalling Protocol
UAL - User Adaptation Layer
SCTP - Stream Control Transport Protocol
Figure 3: General Architecture of SS7-IP Interworkingthis is also referred to as SG-to-AS communication 🤝. AS is the name that UAL usually gives to the ISEP nodes, and it stands for Application Server 💻.
- Communication inside the IP network.
Telephony
Signalling
********* over IP *********
* ISEP *------------------* ISEP *
********* *********
+-------+ +-------+
|SigProt| |SigProt|
+-------+ +-------+
| UAL | | UAL |
+-------+ +-------+
| SCTP | | SCTP |
+-------+ +-------+
| IP | | IP |
+-------+ +-------+
Figure 4: General Architecture of Intra-IP Communicationthis is also referred to as IPSP communication 🌈. IPSP stands for IP Signalling Point, and it describes the role the UAL plays on an IP-based node.
the first scenario applies to 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 has developed UALs to transport the following Access Signalling protocols:
- ISDN Q.931
- V5.2
- DPNSS/DASS2
4.1.1. IUA (ISDN Q.921 User Adaptation) 🌸
UAL: IUA (ISDN Q.921 User Adaptation)
this document supports both ISDN Primary Rate Access (PRA) and Basic Rate Access (BRA), including both point-to-point and point-to-multipoint modes of communication 🔥. that 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 is for the SG to take on the server role 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 are Q.931 and QSIG 📦.
the main scenario this UAL supports is the SG-to-ISP communication, where the ISEP role is typically played by a node called an MGC, as defined in [RFC2719] 🎯.
****** ISDN ****** IP *******
*PBX *---------------* SG *--------------* MGC *
****** ****** *******
+-----+ +-----+
|Q.931| (NIF) |Q.931|
+-----+ +----------+ +-----+
| | | | IUA| | IUA |
| | | +----+ +-----+
|Q.921| |Q.921|SCTP| |SCTP |
| | | +----+ +-----+
| | | | IP | | IP |
+-----+ +-----+----+ +-----+
NIF - Nodal Interworking Function
PBX - Private Branch Exchange
SCTP - Stream Control Transmission Protocol
IUA - ISDN User Adaptation Layer Protocol
Figure 5: ISDN-IP Interworking using IUAthe SCTP (and UDP/TCP) Registered User Port Number Assignment for IUA is 9900 🎀.
the value IANA assigned for the Payload Protocol Identifier in the SCTP Payload Data chunk is "1" 🧾.
4.1.2. V5UA (V5.2-User Adaptation) Layer 🍓
UAL: V5UA (V5.2-User Adaptation)
V5UA is an extension of 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's typically 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 - Access Network
NIF - Nodal Interworking Function
LAPV5 - Link Access Protocol for the V5 channel
SCTP - Stream Control Transmission Protocol
Figure 6: V5.2-IP Interworking using V5UAthe SCTP (and UDP/TCP) Registered User Port Number Assignment for V5UA is 5675 🌟.
the value IANA assigned for the Payload Protocol Identifier in the SCTP Payload Data chunk is "6" 💜.
4.1.3. DUA (DPNSS/DASS User adaptation) Layer 💖
UAL: DUA (DPNSS/DASS2 User Adaptation)
okay so the DUA is built on top of IUA 🧚 and it adds the extra bits IUA needs for a DPNSS/DASS2 transport 💅. DPNSS is the Digital Private Network Signalling System and DASS2 is the Digital Access Signalling System 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
Figure 7: DPNSS-IP Interworking using DUAThe value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is "10". .
4.2. Network Signalling 🌸
The SIGTRAN WG has 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 🎀
UALs:
4.2.1.1. M2UA (SS7 MTP2-User Adaptation) Layer 🔥
M2UA is typically used between a Signalling Gateway (SG) and a Media Gateway Controller (MGC) 💖. The SG terminates up to MTP Level 2, and the MGC terminates MTP Level 3 and above. In other words, the SG carries MTP Level 3 messages over an IP network to an MGC 🫶.
MTP3 and MTP3b are the only SS7 MTP2 User protocols that are transported by this UAL.
The SG provides an interworking of transport functions with the IP transport, so it can move MTP2-User signalling messages to an Application Server (e.g., MGC) where the peer MTP2-User lives ✨.
****** SS7 ****** IP *******
*SEP *-----------* SG *-------------* MGC *
****** ****** *******
+----+ +----+
|S7UP| |S7UP|
+----+ +----+
|MTP3| |MTP3|
| | (NIF) | |
+----+ +----+----+ +----+
| | | |M2UA| |M2UA|
| | | +----+ +----+
|MTP2| |MTP2|SCTP| |SCTP|
| | | +----+ +----+
| | | |IP | |IP |
+----+ +---------+ +----+
MGC - Media Gateway Controller
SG - Signalling Gateway
SEP - SS7 Signalling Endpoint
NIF - Nodal Interworking Function
IP - Internet Protocol
SCTP - Stream Control Transmission Protocol
Figure 8: SS7-IP Interworking using M2UAThe SCTP (and UDP/TCP) Registered User Port Number Assignment for M2UA is 2904 🌈.
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) 🦋
M2PA is used between SS7 Signalling Points that run the MTP Level 3 protocol 💅. The SS7 Signalling Points can also use standard SS7 links with SS7 MTP Level 2 to carry MTP Level 3 signalling messages 🧚.
Both configurations are possible: SS7 and IP talking to each other through an SG, and ISEPs talking to each other 💜.
Connection of SS7 and IP nodes:
******** SS7 *************** IP ********
* SEP *--------* SG *--------* IPSP *
******** *************** ********
+------+ +------+
| TCAP | | TCAP |
+------+ +------+
| SCCP | | SCCP |
+------+ +-------------+ +------+
| MTP3 | | MTP3 | | MTP3 |
+------+ +------+------+ +------+
| | | | M2PA | | M2PA |
| | | +------+ +------+
| MTP2 | | MTP2 | SCTP | | SCTP |
| | | +------+ +------+
| | | | IP | | IP |
+------+ +------+------+ +------+
SEP - SS7 Signalling Endpoint
Figure 9: SS7-IP Interworking with M2PACommunication 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
Figure 10: Intra-IP Communication using M2PAThese figures are only examples, and other configurations are possible 🌸. For instance, IPSPs without traditional SS7 links could use the protocol layers MTP3/M2PA/SCTP/IP to route SS7 messages in a network made entirely of IP links 💖.
Another example is two SGs connected over an IP network to form an SG mated pair, a lot like how STPs get provisioned in traditional SS7 networks 👑.
The SCTP (and UDP/TCP) Registered User Port Number Assignment for M2PA is 3565 🫶.
The value assigned by IANA for the Payload Protocol Identifier in the SCTP Payload Data chunk is "5".
4.2.1.3. Main Differences between M2PA and M2UA 💅
- 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.
- 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.
4.2.2. M3UA (SS7 MTP3 User Adaptation) Layer 👑
UAL: M3UA (SS7 MTP3 User Adaptation)
M3UA 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
Figure 11: SS7-IP Interworking using M3UACommunication between two IP nodes:
******** IP ********
* IPSP *----------* IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
Figure 12: Intra-IP Communication using M3UAM3UA uses a client-server architecture 🦋. It is recommended that the ISEP acts as the client and initiates the SCTP associations with the SG. The port reserved by IANA is 2905, and this is the port upon which the SG should listen for possible client connections 💜.
The assigned payload protocol identifier for the SCTP DATA chunks is "3". slay, bestie 🌈💅✨
4.2.3. SUA (SS7 SCCP User Adaptation) Layer ✨
UAL: SUA (SS7 SCCP User Adaptation)
Okay so SUA is giving main character energy 💅 It carries any SS7 SCCP-User signalling over IP, stuff like MAP, INAP, SMS, BSSAP, or RANAP, and it uses SCTP to do it 🦋 Every one of those applications has its own timing requirements, and you'll find those in their own standards documents 🫶
Here are the configurations, bestie 🌸
- Interconnection of SS7 and IP:
******** *************** ********
* SEP * SS7 * * 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
Figure 13: SS7-IP Interworking using SUA- IP Node to IP Node communication:
******** ********
* * IP * *
* IPSP *--------* IPSP *
* * * *
******** ********
+------+ +------+
| SUAP | | SUAP |
+------+ +------+
| SUA | | SUA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
Figure 14: Intra-IP Communication using SUANow the port stuff 🎀 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" 🍓
5. Security Considerations 🔐
Ngl this section is where things get serious 😭 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. Although some security needs overlap, any security solution should fulfill all the different parties' needs. See specific Security Considerations in each UAL Technical specification for details (for general security principles of SIGTRAN, see [RFC3788]).
SCTP only tries to increase the availability of a network. SCTP does not contain any protocol mechanisms directly related to communication security, i.e., user message authentication, integrity, or confidentiality functions. For such features, SCTP depends on security protocols. In the field of system security, SCTP includes mechanisms for reducing the risk of blind denial-of-service attacks as described in Section 11 of [RFC2960].
This document does not add any new components to the protocols included in the discussion. For secure use of the SIGTRAN protocols, readers should go through the "Security Considerations for SIGTRAN Protocols" [RFC3788]). According to that document, the use of the IPsec is the main requirement to secure SIGTRAN protocols in the Internet, but Transport Layer Security (TLS) is also considered a perfectly valid option for use in certain scenarios (see [RFC3436] for more information on using TLS with SCTP). Recommendations of usage are also included. 🔥
6. Informative References 📚
- [ALLMAN99] Allman, M. and V. Paxson, "On Estimating End-to-End Network Path Properties", Proc. SIGCOMM'99, 1999.
- [RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V. Paxson, "Stream Control Transmission Protocol", RFC 2960, October 2000.
- [RFC3257] Coene, L., "Stream Control Transmission Protocol Applicability Statement", RFC 3257, April 2002.
- [RFC2719] Ong, L., Rytina, I., Garcia, M., Schwarzbauer, H., Coene, L., Lin, H., Juhasz, I., Holdrege, M., and C. Sharp, "Framework Architecture for Signaling Transport", RFC 2719, October 1999.
- [RFC3057] Morneault, K., Rengasami, S., Kalla, M., and G. Sidebottom, "ISDN Q.921-User Adaptation Layer", RFC 3057, February 2001.
- [RFC3331] Morneault, K., Dantu, R., Sidebottom, G., Bidulock, B., and J. Heitz, "Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) - User Adaptation Layer", RFC 3331, September 2002.
- [RFC3332] Sidebottom, G., Morneault, K., and J. Pastor-Balbas, "Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User Adaptation Layer (M3UA)", RFC 3332, September 2002.
- [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport Layer Security over Stream Control Transmission Protocol", RFC 3436, December 2002.
- [RFC3868] Loughney, J., Sidebottom, G., Coene, L., Verwimp, G., Keller, J., and B. Bidulock, "Signalling Connection Control Part User Adaptation Layer (SUA)", RFC 3868, October 2004.
- [RFC4165] George, T., Dantu, R., Kalla, M., Schwarzbauer, H.J., Sidebottom, G., Morneault, K.,"SS7 MTP2-User Peer-to-Peer Adaptation Layer", RFC 4165, September 2005.
- [RFC3807] Weilandt, E., Khanchandani, N., and S. Rao, "V5.2-User Adaptation Layer (V5UA)", RFC 3807, June 2004.
- [RFC4129] Mukundan, R., Morneault, K., and N. Mangalpally, "Digital Private Network Signaling System (DPNSS)/Digital Access Signaling System 2 (DASS 2) Extensions to the IUA Protocol", RFC 4129, September 2005.
- [RFC3788] Loughney, J., Tuexen, M., and J. Pastor-Balbas, "Security Considerations for Signaling Transport (SIGTRAN) Protocols", RFC 3788, June 2004.
Authors' Addresses 🌷
Lode Coene Siemens Atealaan 34 Herentals B-2200 Belgium
Phone: +32-14-252081 EMail: lode.coene@siemens.com
Javier Pastor-Balbas Ericsson Via de los Poblados 13 Madrid 28033 Spain
Phone: +34 91 339 1397 EMail: J.Javier.Pastor@ericsson.com
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📦 where this page comes from
- ietf: rfc4166 2006-02
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms