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# Message Transfer Part Level 3 (MTP3)
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MTP3 is part of the [SS7](/SS7) stack. It is NOT part of the [SIGTRAN](/SIGTRAN) family of protocols. The purpose of the [SIGTRAN](/SIGTRAN) family of protocols is to carry [SS7](/SS7) traffic over IP networks.
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The hardware and software functions of the [SS7](/SS7) protocols are divided into functional abstractions called "levels". These levels map loosely to the Open Systems Interconnect (OSI) 7-layer model defined by the International Standards Organization ([ISO](/ISO)).
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Different MTP3 flavors exist:
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- [ANSI](/ANSI) T1.111.4-1996
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- [ITU-T](/ITU-T) Q.704 7/1996
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- GF 001-9001 (Chinese ITU variant)
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## History
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XXX - add a brief description of MTP3 history
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## Protocol dependencies
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The Message Transfer Part (MTP) is divided into three levels.
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1. MTP Level 1 is equivalent to the OSI Physical Layer. It defines the physical, electrical, and functional characteristics of the digital signaling link. Physical interfaces defined include:
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- E-1 (2048 kb/s: 32 64 kb/s channels)
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- DS-1 (1544 kb/s: 24 64kb/s channels)
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- V.35 (64 kb/s)
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- DS-0 (64 kb/s)
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- DS-0A (56 kb/s)
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2. MTP Level 2 ([MTP2](/MTP2)) is equivalent to the OSI Data Link Layer. It ensures accurate end-to-end transmission of a message across a signaling link. Level 2 implements flow control, message sequence validation, and error checking. When an error occurs on a signaling link, the message (or set of messages) is retransmitted.
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3. MTP Level 3 is equivalent to the OSI Network Layer. It provides message routing between signaling points in the SS7 network. MTP Level 3 re-routes traffic away from failed links (usually without losing any messages and always without re-ordering messages) and controls traffic when congestion occurs or a signaling point fails.
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In IP networks
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- MTP3 is frequently carried on [M2PA](/M2PA) or [M2UA](/M2UA) (both of which logically replace MTP2 and below)
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- [M3UA](/M3UA) is used to transport MTP3 payloads across IP networks (it logically replaces MTP3 in a [SIGTRAN](/SIGTRAN) network). Early versions (Internet Drafts) of M3UA simply transported the entire MTP3 message across IP but the RFC3332 version of M3UA does not.
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MTP3 is sometimes carried over [SSCF-NNI](/SSCF-NNI) over [SSCOP](/SSCOP) over [ATM](/ATM). Then it is usually referred to as MTP3-b (for "broadband").
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MTP3 is commonly used to carry [ISUP](/ISUP) and [SCCP](/SCCP) messages. Other SS7 protocols above MTP3 include [TUP](/TUP) (a predecessor to ISUP which is only still used in some parts of China) and [IUP](/IUP) (used in England).
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## Example traffic
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XXX - Add example traffic here (as plain text or Wireshark screenshot).
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## Wireshark
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The MTP3 dissector is fully functional. It supports standard ITU MTP3 as well as the ANSI, Chinese, and Japanese variants (the variant selection is a Preference of the dissector). Some national options (such as congestion levels) are supported via preference settings.
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Wireshark also contains an "MTP3MG" ("MTP3 Management") dissector for MTP3 control messages. These are messages exchanged between the MTP3 layer management at each endpoint.
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## Preference Settings
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The most important preference setting for [SS7](/SS7) and [SIGTRAN](/SIGTRAN) dissection in Wireshark is the MTP3 variant. All of the SS7-related dissectors (except [TCAP](/TCAP)) follow MTP3's preference setting.
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## Example capture file
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- [SampleCaptures/isup.cap](uploads/__moin_import__/attachments/SampleCaptures/isup.cap) a single call's signalling sequence using ISUP/MTP3/M3UA/SCTP/IP
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## Display Filter
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A complete list of MTP3 display filter fields can be found in the [display filter reference](http://www.wireshark.org/docs/dfref/m/mtp3.html)
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Show only the MTP3 based traffic:
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```
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mtp3
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```
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## Capture Filter
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You cannot directly filter MTP3 protocols while capturing.
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## External links
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- The ITU specifications of MTP3 are available for free on the web:
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- [Q.701](http://www.itu.int/rec/T-REC-Q.701/en) gives an introduction to MTP (layers 1, 2, and 3)
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- [Q.704](http://www.itu.int/rec/T-REC-Q.704/en) describes MTP3
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- Wikipedia's [Message\_Transfer\_Part](http://en.wikipedia.org/wiki/Message_Transfer_Part) page has more info.
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## Discussion
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It might be a good idea to have a page with the SS7 family and "only" refer to it from here. Or is MTP3 the family (sorry, telephonie neebie)? - *[UlfLamping](/UlfLamping)*
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I think SS7 would be thought of as the family; MTP3 is just a member of the family, at the network layer (with MTP2 at the logical link layer). - *Guy Harris*
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---
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Imported from https://wiki.wireshark.org/MTP3 on 2020-08-11 23:17:01 UTC |