Mtp1

MTP1 operates at Layer 1 of the SS7 protocol stack and has equivalent functions to that of OSI's physical layer. It is responsible for the physical and electrical characteristics of the line, which include providing a bearer path for the signaling link. MTP1 can be served on a terrestrial TDM circuit or on a satellite link.

Think about what type of physical medium you're using for the signaling link. Most times, signaling is transferred over a DS0 on a T1 within the U.S. and Japan, over an E1 internationally, or on a DS0 over a V.35 interface. In Japan, remember that 48-kbps signaling links are also available. The requirements for the setup of a signaling data link are as follows:

• The signaling data link must be reserved for SS7 traffic only.

• Echo cancellers, digital pads, and A-Law converters must be removed from the link to ensure a full duplex link between signaling points.

• The standard signaling data link should be 64 kbps, but you can use links as low as 4.8 kbps as long as you adhere to the user part requirements.

The preceding list comes from ITU-T Q.702, "Specification of the Signaling Data Link," 3/93.

On an international note, SS7 signaling data links are required to be 64 kbps and transmitted on TS16 of an E1 circuit. This requirement can be modified if both parties involved agree to a specific timeslot and configure accordingly, but deviation from this timeslot is not likely.

Specifications for a T1-based signaling data link are based on the use of alternate mark inversion (AMI) encoding (for more on T1 or E1 technology, refer to Chapter 5, "T1 Technology" and Chapter 6, "E1, R2, and Japanese Carrier Technology"). Because AMI steals the least significant bit, thus allowing only 56 kbps of data on each timeslot, the standard signaling link speed in the U.S. is 56 kbps. This is the most common speed in the United States, but 64-kbps links do exist. This depends on the provider that you are receiving the signaling link from.

SS7 signaling links can also be deployed over analog facilities, although it is certainly not common. In the case of an analog facility, the link must be at least 4.8 kbps and you must use either V.27 or V.27 bis.

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