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The Message Transfer Part (MTP) is part of the Signaling System 7 (SS7) used for communication in Public Switched Telephone Networks. MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners. MTP is formally defined primarily in ITU-T recommendations (Q.701 ), (Q.702 ), (Q.703 ), (Q.704 ) and (Q.705 ). Tests for the MTP are specified in the ITU-T recommendations (Q.781 ) for MTP2 and in (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 T1.111. In Europe, national MTP protocols are based on ETSI (EN 300-008-1 ). ==Functional levels== The SS7 stack can be separated into four functional levels:〔(ITU-T Recommendation Q.700 ), Figure 3/Q.700, ''SS No. 7 functional levels'', p. 8.〕 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''.〔See for example, RFC 3331 and RFC 3332 for the usage ''MTP2'' and ''MTP3''.〕 MTP and SCCP are together referred to as the ''Network Service Part (NSP)''.〔(ITU-T Recommendation Q.711 (03/2001) ), Figure 1/Q.711, ''Functional diagram for the SCCP in Signalling System No. 7'', p. 2.〕 There is no one-to-one mapping of MTP Levels 1 through 3 onto the OSI model.〔(ITU-T Recommendation Q.700 (03/1993) ), Clause 4, ''OSI layering and SS No. 7'', p. 9.〕 Instead, MTP provides the functionality of layers 1, 2 and part of layer 3 in the OSI model.〔(ITU-T Recommendation Q.700 (03/1993) ), Figure 2/Q.700, ''Architecture of SS No. 7'', p. 7.〕 The part of layer 3 of the OSI model 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.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Message Transfer Part」の詳細全文を読む スポンサード リンク
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