Dialogic 6.2 manual Interpreting the Message Header, Bits Byte, General I Frame, November 105

BSMI Debugging

Bits

8	7	6	5	4	3	2	1		Byte
0	1	1	1	1	1	1	0		1
			SAPI				C/R	0	2
			TEI					1	3
			N(s)					0	4
			N(r)					P/F	5
			Message						-
	- - - - - - - - - - - -			FCS - - - - - - - - - - - - -					n - 2
									n - 1
0	1	1	1	1	1	1	0		n

			Bits					Example
8	7	6	5	4	3	2	1	-
		Not Shown in Trace
								00
0	0	0	0	0	0	0	0
								C1
1	1	0	0	0	0	0	1
								00
0	0	0	0	0	0	0	0
								00
0	0	0	0	0	0	0	0

See Figure 7

Not Shown in Trace

Not Shown in Trace

General I Frame Example SETUP I Frame

Figure 6. I Frame Formats

Interpreting the Message Header

The Message header starts at byte offset 5 of the hexadecimal string. For Q.931 call control messages, this header identifies the D-channel message and references the call for which the message applies.

03 278D Xmit 00 60 0 Setup 00 00 0 0018

00C10000 08010105040288901801812C0735353532303030

Message

Header

Figure 7 compares the general structure for a Message header against the example SETUP message header, and illustrates the following points:

„The Protocol Discriminator value is 0x08 for all Q.931 call control messages.

„Modules assign 1-byte call reference values for Q.931 messages, so the call reference length is always 0x01 and the third byte in the Message header contains the call reference value (0x0001 in the example).

November 2009 105