Message Transfer Part

The Message Transfer Part (MTP ) is a part of the SS7 signaling, and describes how signaling information is transmitted. It is used for communication on the public telephone network (PSTN). MTP is responsible for the transport of SS7 messages between the communication partners.

A distinction is made between three MTP levels, which can be incorporated into the OSI model. MTP Level 1, the Physical layer, MTP Level 2 of the data layer and the MTP Level 3, the network layer.

• MTP Level 1 defines the physical, electrical and functional parameters for a signaling link. These include specifications such as clock speed, voltages, coding procedures, and size and shape of the connectors. Are usual interfaces, V.35 or G.703 comply with the recommendations. Level 1 represents the physical layer for a signaling link, which typically consists of a digital network of a 64-kbit/s-Kanal. But it can also analogue channels, which are operated with a modem, can be used.
• MTP Level 2 defines the process for error- free exchange of messages over a signaling link. These include functions to enable the communications link or stop to check for errors and to correct them if necessary. The messages are separated by flags. Level 2 is similar in structure to the commonly used procedure HDLC, however, a number of functions.
• MTP Level 3 defines the interaction of several individual signaling links. All aspects that are at the logical level for the exchange of messages between two signaling points across multiple signaling links of time together, are regulated. For this purpose the transmission of the incoming message is part of the desired signaling link. The separation of these functions in a separate Level 3 also serves the management of the signaling network: signaling links can be added, or it can be switched in the event of an error on a substitute, without the configuration to higher, more abstract levels must be changed.