The Message Transfer Part (MTP) is part of the

Signaling System 7 Signalling System No. 7 (SS7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down telephone calls in most parts of the world-wide public switched telephone network (PSTN). The protocol also perform ...

(SS7) used for communication in

Public Switched Telephone Network The public switched telephone network (PSTN) provides Communications infrastructure, infrastructure and services for public Telecommunications, telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that ...

s. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners. MTP is formally defined primarily in

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

recommendation
Q.701Q.702Q.703Q.704
an
Q.705
Tests for the MTP are specified in the

recommendation
Q.781
for MTP2 and i
Q.782
for MTP3. These tests are used to validate the correct implementation of the MTP protocol. Different countries use different variants of the MTP protocols. In North America, the formal standard followed is

ANSI The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

T1.111. In Europe, national MTP protocols are based on

ETSI The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...

br>EN 300-0088-1

Functional levels

The SS7 stack can be separated into four functional levels: Level 1 through Level 3 comprise the ''MTP'', and Level 4 the ''MTP user''. ''MTP Level 3'' is sometimes abbreviated ''MTP3''; ''MTP Level 2'', ''MTP2''. MTP and SCCP are together referred to as the ''Network Service Part (NSP)''. There is no one-to-one mapping of MTP Levels 1 through 3 onto the

OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...

. Instead, MTP provides the functionality of layers 1, 2 and part of

layer 3 In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate routers. Functions The network layer provides the means of transfe ...

in the

. The part of layer 3 of the

that MTP does not provide, is provided by SCCP or other Level 4 parts (MTP users).ITU-T Recommendation Q.1400 (03/1993)
Clause 2.2, ''OSI layering and SS No. 7'', p. 4.ITU-T Recommendation Q.1400 (03/1993)
Figure 1/Q.1400, ''Relationship between SS No. 7 Functional Levels and OSI Layering'', p. 5.

Signalling Data Link Functional Level

''MTP Level 1'' is described i
ITU-T Recommendation Q.702
and provides the ''Signalling Data Link'' functional level for narrowband signalling links. For broadband signalling links
ITU-T Recommendation Q.2110
o
Q.2111
describe the signalling data link function. MTP1 represents the physical layer. That is, the layer that is responsible for the connection of SS7 Signaling Points into the transmission network over which they communicate with each other. Primarily, this involves the conversion of messaging into electrical signal and the maintenance of the physical links through which these pass. In this way, it is analogous to the Layer 1 of ISDN or other, perhaps more familiar, protocols. MTP1 normally uses a timeslot in an

E-carrier The E-carrier is a member of the series of carrier systems developed for digital transmission of many simultaneous telephone calls by time-division multiplexing. The European Conference of Postal and Telecommunications Administrations (CEPT) orig ...

T-carrier The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell System ...

. The Physical interfaces defined include E-1 (2048 kbit/s; 32 64 kbit/s channels), DS-1 (1544 kbit/s; 24 64kbit/s channels), V.35 (64 kbit/s), DS-0 (64 kbit/s), and DS-0A (56 kbit/s).

Signalling Link Functional Level

''MTP Level 2'' is described i
ITU-T Recommendation Q.703
and provides the ''Signalling Link'' functional level for narrowband signalling links. For broadband signalling links
ITU-T Recommendation Q.2140
an
Q.2210
describe the signalling link function referred to as ''MTP3b''. The signalling link functional level may also be provided using the

SIGTRAN SIGTRAN is the name, derived from ''signaling transport'', of the former Internet Task Force (I) working group that produced specifications for a family of protocols that provide reliable datagram service and user layer adaptations for Signaling ...

protocol M2PA described in RFC 4165. ''MTP Level 2'' ensures accurate end-to-end transmission of a message across a signaling link. MTP2 provides flow control, error detection and sequence checking, and retransmits unacknowledged messages. MTP2 uses packets called ''signal units'' to transmit SS7 messages. There are three types of signal units:

Fill-in Signal Unit Fill-in can refer to: * A puzzle, see Fill-In (puzzle) * In numerical analysis, the entries of a matrix which change from zero to a non-zero value in the execution of an algorithm; see Sparse matrix#Reducing fill-in * An issue of a comic book pro ...

(FISU), Link Status Signal Unit (LSSU),

Message Signal Unit A message is a discrete unit of communication intended by the source for consumption by some recipient or group of recipients. A message may be delivered by various means, including courier, telegraphy, carrier pigeon and electronic bus. A ...

(MSU). Access to the signalling link functional level's service interface can be provided over

SCTP The Stream Control Transmission Protocol (SCTP) is a computer networking communications protocol in the transport layer of the Internet protocol suite. Originally intended for Signaling System 7 (SS7) message transport in telecommunication, the p ...

by the

protocol

M2UA M, or m, is the thirteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''em'' (pronounced ), plural ''ems''. History Th ...

, described in RFC 3331. MTP Level 2 is tested using the protocol tester and test specifications described i
Q.755Q.755.1Q.780
an
Q.781

Q.2150.3
. ''MTP Level 3'' functions can also be provided by using the

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and a ...

M3UA M3UA is a communication protocol of the SIGTRAN family, used in telephone networks to carry signaling over Internet Protocol (IP). M3UA enables the SS7 protocol's User Parts (e.g. ISUP, SCCP and TUP) to run over virtually any network technol ...

protocol, described in RFC 4666, in IPSP mode. MTP3 provides routing functionality to transport signaling messages through the SS7 network to the requested endpoint. Each network element in the SS7 network has a unique address, the Point Code (PC). Message routing is performed according to this address. A distinction is made between a

Signaling Transfer Point A Signal Transfer Point (STP) is a node in an SS7 network that routes signaling messages based on their destination point code in the SS7 network. It works as a router that relays SS7 messages between ''signaling end-points'' (SEPs) and other s ...

(STP) which only performs MTP message routing functionalities and a Signaling End Point (SEP) which uses MTP to communicate with other SEPs (that is, telecom switches). MTP3 is also responsible for network management; when the availability of MTP2 data links changes. MTP3 establishes alternative links and re-routes traffic away from failed links and signaling points and propagates information about route availability through the network. Also controls traffic when congestion occurs. Access to the signalling network functional level's service interface (as described i
Q.701
can be provided over

by the

protocol

, described in RFC 4666. MTP Level 3 is tested using the protocol tester and test specifications described i
Q.755Q.755.1Q.780
an
Q.782

MTP Users

''Level 4'' consists of ''MTP Users''. The remaining components of the SS7 stack are all directly, or indirectly, ''MTP Users''. Some examples of parts at ''Level 4'' are SCCP, ISUP, TUP, and, in the UK, IUP. The services provided to ''MTP Level 4'' by the ''MTP'' (that is, MTP to MTP Users) is described i
ITU-T Recommendation Q.701
775148760

References

{{Reflist ; ITU-T recommendations
ITU-T Recommendation Q.700
''Introduction to CCITT Signalling System No. 7''.
ITU-T Recommendation Q.701
''Functional description of the message transfer part (MTP) of Signalling System No. 7''.
ITU-T Recommendation Q.702
''Signalling data link''.
ITU-T Recommendation Q.703
''Signalling link''.
ITU-T Recommendation Q.704
''Signalling network functions and messages''.
ITU-T Recommendation Q.705
''Signalling network structure''.
ITU-T Recommendation Q.706
''Message transfer part signalling performance''.
ITU-T Recommendation Q.707
''Testing and maintenance''.
ITU-T Recommendation Q.708
''Assignment procedures for international signalling point codes''.
ITU-T Recommendation Q.709
''Hypothetical signalling reference connection''.
ITU-T Recommendation Q.710
''Simplified MTP version for small systems''.
ITU-T Recommendation Q.750
''Overview of Signalling System No. 7 management''.
ITU-T Recommendation Q.751.1
''Network element management information model for the Message Transfer Part (MTP)''.
ITU-T Recommendation Q.751.3
''Network element information model for MTP accounting''.
ITU-T Recommendation Q.752
''Monitoring and measurements for Signalling System No. 7 networks''.
ITU-T Recommendation Q.755
''Signalling System No. 7 protocol tests''.
ITU-T Recommendation Q.755.1
''MTP Protocol Tester''.
ITU-T Recommendation Q.780
''Signalling System No. 7 test specification — General description''.
ITU-T Recommendation Q.781
''MTP Level 2 test specification''.
ITU-T Recommendation Q.782
''MTP Level 3 test specification''.
ITU-T Recommendation Q.1400
''Architecture framework for the development of signalling and OA&M protocols using OSI concepts''.
ITU-T Recommendation Q.2110
''B-ISDN ATM adaptation layer — Service specific connection oriented protocol (SSCOP)''.
ITU-T Recommendation Q.2111
''B-ISDN ATM adaptation layer — Service specific connection oriented protocol in a multilink and connectionless environment (SSCOPMCE)''.
ITU-T Recommendation Q.2140
''B-ISDN ATM adaptation layer — Service specific coordination function for signalling at the network node interface (SSCF at NNI)''.
ITU-T Recommendation Q.2150.0
''Generic signalling transport service''.
ITU-T Recommendation Q.2150.1
''Signalling transport converter on MTP3 and MTP3b''.
ITU-T Recommendation Q.2150.2
''Signalling transport converter on SSCOP and SSCOPMCE''.
ITU-T Recommendation Q.2150.3
''Signalling transport converter on SCTP''.
ITU-T Recommendation Q.2210
''Message transfer part level 3 functions and messages using the services of ITU-T Recommendation Q.2140''. ; IETF RFCs * RFC 2719, ''Framework Architecture for Signaling Transport''. * RFC 4165, ''Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) — User Peer-to-Peer Adaptation Layer (M2PA)''. * RFC 3331, ''Signaling System 7 (SS7) Message Transfer Part 2 (MTP2) — User Adaptation Layer (M2UA)'' * RFC 4666, ''Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) — User Adaptation Layer (M3UA)''

External links