Overview

The Message Transfer Part (MTP) Level is known as the signaling data link. It is equivalent to the OSI model Physical Layer (Layer 1). Figure 2.1 displays the physical, electrical, and functional characteristics of the signaling links connecting SS7 components.

Figure 2.1: MTP Level 1 in the SS7 Layers

A signaling data link is a bi-directional transmission path that allows for the transfer of signaling messages. The transfer of signaling messages over a communication link must transfer at the same data rate in either direction. SS7 signaling data links are capable of operation over terrestrial and satellite transmission links. The signaling terminal at each end of the signaling data link contains the MTP Level 2 functionality for transmitting and receiving SS7 messages.

Digital Signaling Link

A digital signaling link is composed of a digital transmission channel connecting two digital switches or network nodes that provide an interface to the signaling terminals.

Figure 2.2 shows how a SS7 system uses a digital signaling link to transfer messages. To transfer data messages on a digital line, data communications equipment (DCE) are attached at the end of each digital switch to convert the messages from digital form unique to the switching system to the SS7 form. The DCE buffers and converts messages between the signaling link and the switching system s signaling terminal.

Figure 2.2: Digital Signaling Data Link

Digital signaling links are often used on newer switching systems. Because signaling messages are relatively small in content size, the common data...