Differences between revisions 17 and 18
Revision 17 as of 2005-02-21 12:53:03
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Editor: LuisOntanon
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Revision 18 as of 2005-04-02 00:15:38
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Comment: Canonicalize RFC link style, fix display filter.
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H.248 over SCTP [attachment:H.248decoded.gif decoded] by Ronnie Sahlbergs decoder in the 0.10.9-SVN-13213 build. H.248 over SCTP [attachment:H.248decoded.gif decoded] by Ronnie Sahlberg's decoder in the 0.10.9-SVN-13213 build.
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 MEGACO }}}  megaco }}}
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 * add link to MEGACO specification and where to find additional info on the web about MEGACO
 * [http://www.ietf.org/rfc/rfc3015.txt?number=3015 RFC3015]: MEGACO version 1
 * [http://www.ietf.org/rfc/rfc3525.txt?number=3525 RFC3525]: MEGACO version 2
 * [http://www.iana.org/assignments/megaco-h248 IANA Megaco assignments]:
 * [http://www.ietf.org/rfc/rfc3015.txt RFC3015] ''Megaco Protocol Version 1.0''
 * [http://www.ietf.org/rfc/rfc3525.txt RFC3525] ''Gateway Control Protocol Version 1'' (MEGACO version 2)
 * [http://www.iana.org/assignments/megaco-h248 IANA Megaco assignments]

Media Gateway Control Protocol (MEGACO/H.248.1)

MEGACO is used to control a Media Gateway in a VoIP system. MEGACO can be Text or Binary (ASN.1) encoded.

History

Protocol dependencies

  • ["MTP3"]: MEGACO can use ["MTP3"] as its transport protocol; MEGACO is indicated in MTP3 by the service indicator 14.
  • ["SCTP"]: Typically(?) MEGACO uses ["SCTP"] as its transport protocol; MEGACO is indicated in SCTP by a payload protocol ID of 7.
  • ["TCP"]: MEGACO can use ["TCP"] as its transport protocol. The well known TCP port for MEGACO traffic is 2944; if TCP is used, a TPKT header must be included.
  • ["UDP"]: MEGACO can use ["UDP"] as its transport protocol. The well known UDP port for MEGACO traffic is 2944

Example traffic

H.248 over SCTP [attachment:H.248decoded.gif decoded] by Ronnie Sahlberg's decoder in the 0.10.9-SVN-13213 build.

Ethereal

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 in case of SCTP "decode as" may have to be used as the TEXT encoding dissector may take precedence.

If TCP is used there may be issues with desegmentation; such traces would be valuable.

Preference Settings

  • 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 Ethereal can open gzipped files automatically.

Display Filter

A complete list of MEGACO display filter fields can be found in the [http://www.ethereal.com/docs/dfref/MEGACO/MEGACO.html display filter reference]

  • Show only the MEGACO based traffic:

     megaco 

Capture Filter

You cannot directly filter MEGACO protocols while capturing. However, if you know the ["TCP"] or ["SCTP"] port used (see above), you can filter on that one.

Discussion

H248/MEGACO (last edited 2010-05-24 19:34:29 by BillMeier)