In the following sample of dectrace output text, the arrow after the board number shows if the message was received (<--) or sent (-->).
43.61
protocol discriminator = Q.931 Call Control
call reference = 01 00 flag = 0
00000101 message type = SETUP board 00 nai 00 group 00 -->
00000100 IE bearer capability
00000011 length = 0x03
octet 3
1------- extension bit
-00----- coding standard = CCITT
---00000 information transfer capability = speech
octet 4
1------- extension bit
-00----- transfer mode = circuit mode
---10000 information transfer rate = 64 Kbit/s
octet 5
1------- extension bit
-01----- layer 1 id = layer 1 id
---00010 user info layer 1 = mu law
00011000 IE channel identification
00000011 length = 0x03
octet 3
1------- extension bit
-0------ interface identifier = implicitly identified
--1----- interface type = PRI
---0---- spare bits = spare bits
----1--- pref/excl = exclusive
-----0-- D-channel ind = not
------01 info channel selection = B1 channel
octet 3.2
1------- extension bit
-00----- coding standard = CCITT
---0---- number/map = number
----0011 channel type = B channel
octet 3.3
1------- extension bit
-0000001 channel number = 0x01
01110000 IE called party number
00000100 length = 0x04
octet 3
1------- extension bit
-000---- type of number = unknown
----0000 numbering plan = unknown
octet 4 etc
number = 12.
channel number = 0x01
43.67
protocol discriminator = Q.931 Call Control
call reference = 01 00 flag = 1
00000010 message type = CALL_PROCEEDING board 00 nai 00 group 00 <--
00011000 IE channel identification
00000011 length = 0x03
octet 3
1------- extension bit
-0------ interface identifier = implicitly identified
--1----- interface type = PRI
---0---- spare bits = spare bits
----1--- pref/excl = exclusive
-----0-- D-channel ind = not
------01 info channel selection = B1 channel
octet 3.2
1------- extension bit
-00----- coding standard = CCITT
---0---- number/map = number
----0011 channel type = B channel
octet 3.3
1------- extension bit
-0000001 channel number = 0x01
45.84
protocol discriminator = Q.931 Call Control
call reference = 01 00 flag = 1
00000001 message type = ALERTING board 00 nai 00 group 00 <--