Media Gateway Control Protocol (MEGACO/H.248.1)
MEGACO/H.248 is used to control Media Gateways in a Multimedia systems. MEGACO can be Text or Binary (ASN.1) encoded. Sometimes it's also referred as GCP (Gateway Control Protocol).
A MediaGateway (MGw) as its name says is a system used as a Gateway for Media. Current uses are in telephony (Internet, Mobile and Wireline) and Video Broad and NarrowCasting. A MediaGateway is usually placed at the edge of two or more different Tranport Mediums (like: ATM (AAL1,AAL2,AAL5), IP, TDM, even two wire PSTN) and its main duty is to convert media (voice/video) between these domains. MediaGateways are often capable of playing and listening to DTMFs, playing tones (like busy tones), handling voice/video messaging and other similar tasks.
Regardless of the original intention to allow interoperability between systems. It has become an over-standarized protocol so that interoperability between machinery of different vendors (and even between different machines from the SAME vendor) it's almost impossible.
H.248 over SCTP decoded by Ronnie Sahlberg's decoder in the 0.10.9-SVN-13213 build.
The MEGACO dissector works for TEXT encoding of the protocol if EOL is used as SEParator. Dissection of binary encoding has recently been added (2004-10-25) as a separate dissector, it now handles binary H248 ower M3UA and SCTP.
If TCP is used there may be issues with desegmentation; such traces would be valuable.
- You can change the ports on which MEGACO is dissected for UDP/TCP
- You can specify whether the raw text of MEGACO packets is to be displayed
- You can specify whether a detailed dissection of MEGACO packets is to be displayed
Example capture file
XXX - Add a simple example capture file to the SampleCaptures page and link from here. Keep it short, it's also a good idea to gzip it to make it even smaller, as Wireshark can open gzipped files automatically.
A complete list of MEGACO display filter fields can be found in the display filter reference
A complete list of H.248 display filter fields can be found in the display filter reference
- Show only the MEGACO based traffic:
megacoShow only the H.248 based traffic:
RFC3015 Megaco Protocol Version 1.0
RFC3525 Gateway Control Protocol Version 1 (MEGACO version 2)
ITU-T Recs. H.248.1 -> H.248.59 (the datum is from Sep-2007, you can bet that by the time you read this there'll be many more!)
ITU-T H.248.1 Gateway control protocol: Version 3
Given the fact that everyone extends the standard to make its implementation un-interoperable, was the standardization process really necessary???