Feature #3334

use proper sdp in libosmo-mgcp-client

Added by dexter 9 days ago. Updated 2 days ago.

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libosmo-mgcp-client currently uses hardcoded SDP with fixed values. It also uses a payload type 255, which is illegal.

- Add new struct members to allow setting of ptime, payload type and rtpmap if needed.
- Generate proper SDP and use it when communicating to the MGW
- Decode the SDP responses from osmo-mgw.
- Update both, the normal mgcp_client and mgcp_client_fsm


#1 Updated by dexter 9 days ago

  • Status changed from New to In Progress
  • % Done changed from 0 to 50

Status update: The usage of payload type 255 in libosmo-mgcp-client is now removed. The client now generates proper SDP. We can set ptime, fixed payload types and we can define dynamic payload types using rtpmap.

We can not yet decode the SDP that is received from osmo-mgw. I am currently working on this. However, there is an open question about the API. I would suggest the following:

Lets have an enum with fixed codec configurations from which the user can choose. It will be a limited number of configurations. Depending on the value from that enum that is passed on to the SDP generator, the generator will check if the desired codec can be described using a fixed payload type, or if a dynamic payload type has to be generated. The paser would work the other way around. The parsing result would be just a value from the enum we have defined. The great advantage here is that there is an easy interface. Otherwise we will have to keep Codec string, payload type and rate and we would have to extrapolate on parsing. Lets quickly discuss this tomorrow.

#2 Updated by dexter 2 days ago

  • % Done changed from 50 to 90

I have added functionality to generate and perse SDP on the client side. We can now parse and set the ptime, the codec configuration and optionally we can also influence the payload type. But at least for the BSS side we will use only the IANA/3gpp payload types, which are used by default.

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