Link Access Procedure, Channel D (LAPD)

Link Access Procedures on the D channel (LAPD), specified in ITU-T Q.920 and ITU-T Q.921, is the second layer protocol on the ISDN protocol stack in the D channel.

It is heavily based on HDLC.

History

History of HDLC and LAP

Protocol dependencies

• ISDN: Typically, LAPD uses ISDN as its transport mechanism.

• RTP: Wireshark also supports decoding LAPD frames transported via RTP payload

Example traffic

Wireshark

The LAPD dissector is fully functional.

Preference Settings

• Use GSM SAPI values. Default OFF.
• RTP payload type for embedded LAPD. Default 0, that means LAPD dissection in RTP packets is disabled.

Example capture file

• SampleCaptures/toshiba.general.gz

Display Filter

A complete list of LAPD display filter fields can be found in the display filter reference

Show only the LAPD based traffic:

 lapd

Capture Filter

You cannot directly filter LAPD protocols while capturing. XXX - is this true?

External links

• http://www.cisco.com/en/US/docs/internetworking/technology/handbook/ISDN.html

• http://www.itu.int/rec/T-REC-Q.921/en

• http://en.wikipedia.org/wiki/Link_Access_Procedures%2C_D_channel

Discussion

Imported from https://wiki.wireshark.org/LAPD on 2020-08-11 23:15:55 UTC