ISDN Q931 Message

[mohitgrover89@live.com]

Guys, we all know about debug isdn q931 output message, I've 4 doubts in that. (which are in highlighted form in the attached snapshot)

• What is meaning & use of Channel ID [which is i = 0xA9839F in our case] (Line 30) ?
• What is pd & what does that mean  (Line 31) ?
• What does this mean i = 0x0081 (Line 10) (I thing I know about this that this value is in hexadecimal, after that 0081 represent what ?)

        & i = 0x80 (Line 12)

Please check the attached snapshot for your reference.

Thank you in advance.

[Nishant Savalia]

Hi Mohit,

Below is the required information:-

1). channel id is composed of Bearer capability and the channel (i.e. slot occupied for the call)

     for e.g in your case Bearer Capability is = 0x8090A3 and channel is 31 which int turns into 0xA9839F

Here, A398 value is interchanged from the bearer capability and 9F (80+1F) is the hex value of channel no 31 (hex=1F)

2). pd stands for protocol discriminator which means that value is used to distinguish messages for user-network call control from other messages.

for e.g

pd=8 for Q.931 user-network call control messages

pd=9 for Q.2931 user-network call control messages

3). Progress Ind i = 80 means it indicates that tones and announcements are available for that particular call.

     various other progress indicaiton is as below:-

• PI=0 No progress indicator is included. Message type: Setup
• PI=1 Call is not end-to-end ISDN; further call progress information may be available in-band. Message type: Alert, setup, progress, connect
• PI=2 Destination address is non-ISDN Message type: Alert, progress, connect
• PI=3 Origination address is non-ISDN Message type: Setup
• PI=8 In-band information or appropriate pattern is now available Message type: Alert, progress, connect

4). calling party & called party information is as below:

· 80 the router

· 81 the private network near the local user (possibly a local private branch exchange [PBX])

· 82 the public network near the local user (local telco switch)

· 83 the transit network (in the ISDN cloud)

· 84 the public network near the remote user (remote telco switch)

· 85 the private the network near the remote user (possibly a remote PBX)

· 87 the international network

· 8A a network beyond the internetworking point

[mohitgrover89@live.com]

Hi Nishant, thanks for your quick response.

Channel ID is composed of Bearer capability + Channel

Bearer Cap -> 0x8090A3 represents Voice/Speech call (G711 - A-law)

For e.g. In our case Bearer Capability is = 0x8090A3 (which represent that G711 A Law codec is being used) and channel is 31 which int turns into 0xA9839F (how it got turn into this value 0xA9839F, is that a hexa. addition or sort of something)

A398 value is interchanged from the bearer capability and 9F (80+1F) is the hex value of channel no 31 (hex=1F) ?

[paolo bevilacqua]

Decoding these values require understanding of Q.931:

https://www.itu.int/rec/T-REC-Q.931/recommendation.asp?lang=en&parent=T-REC-Q.931-199805-I

[mohitgrover89@live.com]

That is really helpful Paolo, Thanks

[paolo bevilacqua]

Thank you for the nice rating and good luck!