Message Transfer Part Level 3 (MTP3)

MTP3 is part of the SS7 stack. It is NOT part of the SIGTRAN family of protocols. The purpose of the SIGTRAN family of protocols is to carry SS7 traffic over IP networks.

The hardware and software functions of the 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).

Different MTP3 flavors exist:

History

XXX - add a brief description of MTP3 history

Protocol dependencies

The Message Transfer Part (MTP) is divided into three levels.

  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:
    • E-1 (2048 kb/s: 32 64 kb/s channels)
    • DS-1 (1544 kb/s: 24 64kb/s channels)
    • V.35 (64 kb/s)
    • DS-0 (64 kb/s)
    • DS-0A (56 kb/s)
  2. MTP Level 2 (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.

  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.

In IP networks

MTP3 is sometimes carried over SSCF-NNI over SSCOP over ATM. Then it is usually referred to as MTP3-b (for "broadband").

MTP3 is commonly used to carry ISUP and SCCP messages. Other SS7 protocols above MTP3 include TUP (a predecessor to ISUP which is only still used in some parts of China) and IUP (used in England).

Example traffic

XXX - Add example traffic here (as plain text or Wireshark screenshot).

Wireshark

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.

Wireshark also contains an "MTP3MG" ("MTP3 Management") dissector for MTP3 control messages. These are messages exchanged between the MTP3 layer management at each endpoint.

Preference Settings

The most important preference setting for SS7 and SIGTRAN dissection in Wireshark is the MTP3 variant. All of the SS7-related dissectors (except TCAP) follow MTP3's preference setting.

Example capture file

Display Filter

A complete list of MTP3 display filter fields can be found in the display filter reference

Capture Filter

You cannot directly filter MTP3 protocols while capturing.

Discussion

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

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

MTP3 (last edited 2009-04-11 14:08:10 by JeffMorriss)