Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services

Signaling System No. 7

By Lee Dryburgh and Jeff Hewett

ITU Protocol Message Contents

The definition of each message type indicates a set of fields that comprise the message. While some fields are mandatory, others are optional. As specified by Q.773, the standard set of ITU messages includes:

  • Unidirectional
  • Begin
  • End
  • Continue
  • Abort

The following sections describe these messages, the fields that are included in each one, and indicate which fields are mandatory or optional.

Unidirectional Message

The Unidirectional Message is sent when no reply is expected. Table 10-9 lists the message contents.

Table 10-9. Unidirectional Message Fields

Unidirectional Message Fields

Mandatory/Optional

Message Type

Total Message Length

Mandatory

Dialogue Portion

Optional

Component Portion Tag

Component Portion Length

Mandatory

One or More Componnts

Mandatory

Begin Message

The Begin Message is sent to initiate a transaction. Table 10-10 lists the message contents.

Table 10-10. Begin Message Fields

Begin Message Fields

Mandatory/Optional

Message Type

Total Message Length

Mandatory

Originating Transaction ID Tag

Transaction ID Length

Transaction ID

Mandatory

Dialogue Portion

Optional

Component Portion Tag

Component Portion Length

Optional [*]

One or More Components

Optional

EndMessage

The End Message is sent to end a transaction. Table 10-11 lists the message contents.

Table 10-11. End Message Fields

End Message Fields

Mandatory/Optional

Message Type

Total Message Length

Mandatory

Destination Transaction ID Tag

Transaction ID Length

Transaction ID

Mandator

Dialogue Portion

Optional

Component Portion Tag

Component Portion Length

Optional [*]

One or More Components

Optional

Continue Message

The Continue Message is sent when a transaction has previously been established and additional information needs to be sent without ending the transaction. Table 10-12 lists the message contents.

Table 10-12. Continue Message Fields

Continue Message Fields

Mandatory/Optional

Message Type

Total Message Length

Mandatory

Originating Transaction ID Tag

Transaction ID Length

Transaction ID

Mandatory

Destination Transaction ID Tag

Transaction ID Length

Transaction ID

Mandatory

Dialogue Portion

Optional

Component Portion Tag

Component Portion Length

Optional [*]

One or More Components

Optional

Abort Message

The Abort Message is sent to terminate a previously established transaction. Table 10-13 lists the message contents.

Table 10-13. Abort Message Fields

Abort Message Fields

Mandatory/Optional

Message Type

Total Message Length

Mandatory

Destination Transaction ID Tag

Transaction ID Length

Transaction ID

Mandatory

P-Abort Cause Tag

P-Abort Cause Length

P-Abort Cause

Optional [*]

Dialogue Portion

Optional

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