Number o Bite Used

The new MSU fields are defined as follows:

• The SIO identifies the protocol type, such as SCCP, ISUP, TUP, and TCAP, present in the MSU. It also identifies the version of the SS7 protocol. The SIO is an 8-bit (1-octet) value that is broken into two parts: a 4-bit subservice field and a 4-bit service indicator field.

The 4-bit subservice field identifies the protocol version (national or international) and the MSU priority. The MSU priority bits have four possible options, ranging from a lowest-priority value of 0 to a highest-priority value of 3.

The 4-bit service indicator specifies the MTP3 user or L4 protocol, as indicated in Table 4-1.

Table 4-1. Service Indicator

MTP User

Service Indicator Value

Signaling Network Management (SNM) Message

0

Maintenance (MTN) Regular Message

1

Maintenance Special (MTNS) Message

2

SCCP

3

TUP

4

ISUP

5

Data User Part (DUP)—circuit-based messages

6

DUP—facility messages

7

• The Service Information Field (SIF) contains the routing label and control information from upper-level protocols (that is, SCCP, ISUP, TUP, TCAP, or network management). It has a maximum length of 272 octets. Routing labels route the MSU through the network to its final destination and are discussed in the next section. The remaining part of the SIF carries the user message or control data of the higher-level protocols.

0 0

Post a comment