Subject: Re: [Megaco] Megaco Digest, Vol 54, Issue 2

From: Rajiv Ginotra <[email-masked]>
Date: Sun, 12 Oct 2008 13:30:14 +0530

Hi All,

Just to add what Priyanka said, Even when u send the modify with local
descriptor containing codec other than in remote descriptor then you send
the "Codec Negotiation Failure" as the intersection between the New local
and the existing remote is empty.

Regards
Rajiv

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Sent: Friday, October 10, 2008 11:52 AM
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Subject: Megaco Digest, Vol 54, Issue 2

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Today's Topics:

   1. Codec Negotiation Question (Ramesh Babu Kuppili)
   2. Re: Codec Negotiation Question (Deepak Bissa)
   3. Re: Codec Negotiation Question (Priyanka Yadav)

----------------------------------------------------------------------

Message: 1
Date: Fri, 10 Oct 2008 10:27:09 +0530
From: Ramesh Babu Kuppili <[email-masked]>
Subject: [Megaco] Codec Negotiation Question
To: [email-masked]
Cc: Murugesh Govindaraju <[email-masked]>
Message-ID: <[email-masked]>
Content-Type: text/plain; charset="us-ascii"

Gurus,
 
I have a question about Codec Negotiation in Megaco.
 
Lets says the switch initially sends us local and remote codec list.  We
take a intersection of the both local and remote and respond to the request.
 
Then at a later stage lets says the switch sends another modify with only
local codec list.  And this time the local codec does not intersect with the
remote codec list that was received previously.
 
My question is, "How should the gateway behave to the the codec list in the
modify?".
 
1. Should it assume the the remote will also support all the codecs in the
list of Modify and respond to the modify with all supported codecs.
2. Should it send a "codec negotiation failure" as response for Modify since
the codec list in the modify does not intersect with the remote codec list
previously sent.
 
- ramesh
 
~~~~~~~~~~~~~~~~~~Example messages~~~~~~~~~~~~~~~~~~~ Request with both
local and remote:
    MEGACO/1    [172.16.43.151]    Transaction = 58738{Context = 3{Modify =
Eag26/ep2{Media{Stream = 1{LocalControl{Mode = SendReceive , ReservedValue =
off , ReservedGroup = off , tdmc/ec = on} , Local{v=0    c=IN IP4 $
m=audio $ RTP/AVP 18    a=ptime:40    v=0    c=IN IP4 $    m=audio $ RTP/AVP
101    a=rtpmap:101 telephone-event/8000    a=ptime:40    } , Remote{v=0
c=IN IP4 172.16.43.155    m=audio 6024 RTP/AVP 18    a=ptime:40    v=0
c=IN IP4 172.16.43.155    m=audio 6024 RTP/AVP 101    a=rtpmap:101
telephone-event/8000    a=ptime:40    }}}}}}
Request with local only:
    MEGACO/1    [172.16.43.151]    Transaction = 58741{Context = 3{Modify =
AG26{Media{Stream = 1{LocalControl{Mode = SendReceive , tdmc/ec = off}} ,
TerminationState{Buffer = off , fax/faxstate = Negotiating}} , Events =
16777230{fax/faxconnchange , al/on , al/fl}} , Modif    c=IN IP4 $
m=audio $ RTP/AVP 8    a=ptime:20    }} , TerminationState{Buffer = off ,
ipfax/faxstate = Negotiating , ctyp/calltyp = FAX}}}}}
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Message: 2
Date: Fri, 10 Oct 2008 11:06:57 +0530
From: Deepak Bissa <[email-masked]>
Subject: Re: [Megaco] Codec Negotiation Question
To: Ramesh Babu Kuppili <[email-masked]>, "[email-masked]"
	<[email-masked]>
Cc: Murugesh Govindaraju <[email-masked]>
Message-ID:
	
<[email-masked]>
	
Content-Type: text/plain; charset="us-ascii"

As per section 7.1.1 of H.248.1 (v3)
"If a required descriptor other than the Audit Descriptor is unspecified
(i.e. entirely absent) from a command, the previous values set in that
descriptor for that termination, if any, are retained."

Thus, in case when only local codec is sent by MGC and remote is absent then
previous remote descriptor will be retained.
In such scenario, if the local codec does not intersect with remote codec
and MG does not asymmetric codec then it should reply with an error "515
Unsupported Media Type".
If asymmetric codec is supported by MG then codec negotiation will be
successful.

With regards,
Deepak Bissa
________________________________
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Ramesh Babu Kuppili
Sent: Friday, October 10, 2008 10:27 AM
To: [email-masked]
Cc: Murugesh Govindaraju
Subject: [Megaco] Codec Negotiation Question

Gurus,

I have a question about Codec Negotiation in Megaco.

Lets says the switch initially sends us local and remote codec list.  We
take a intersection of the both local and remote and respond to the request.

Then at a later stage lets says the switch sends another modify with only
local codec list.  And this time the local codec does not intersect with the
remote codec list that was received previously.

My question is, "How should the gateway behave to the the codec list in the
modify?".

1. Should it assume the the remote will also support all the codecs in the
list of Modify and respond to the modify with all supported codecs.
2. Should it send a "codec negotiation failure" as response for Modify since
the codec list in the modify does not intersect with the remote codec list
previously sent.

- ramesh

~~~~~~~~~~~~~~~~~~Example messages~~~~~~~~~~~~~~~~~~~ Request with both
local and remote:
    MEGACO/1
    [172.16.43.151]
    Transaction = 58738{Context = 3{Modify = Eag26/ep2{Media{Stream =
1{LocalControl{Mode = SendReceive , ReservedValue = off , ReservedGroup =
off , tdmc/ec = on} , Local{v=0
    c=IN IP4 $
    m=audio $ RTP/AVP 18
    a=ptime:40
    v=0
    c=IN IP4 $
    m=audio $ RTP/AVP 101
    a=rtpmap:101 telephone-event/8000
    a=ptime:40
    } , Remote{v=0
    c=IN IP4 172.16.43.155
    m=audio 6024 RTP/AVP 18
    a=ptime:40
    v=0
    c=IN IP4 172.16.43.155
    m=audio 6024 RTP/AVP 101
    a=rtpmap:101 telephone-event/8000
    a=ptime:40
    }}}}}}
Request with local only:
    MEGACO/1
    [172.16.43.151]
    Transaction = 58741{Context = 3{Modify = AG26{Media{Stream =
1{LocalControl{Mode = SendReceive , tdmc/ec = off}} ,
TerminationState{Buffer = off , fax/faxstate = Negotiating}} , Events =
16777230{fax/faxconnchange , al/on , al/fl}} , Modif
    c=IN IP4 $
    m=audio $ RTP/AVP 8
    a=ptime:20
    }} , TerminationState{Buffer = off , ipfax/faxstate = Negotiating ,
ctyp/calltyp = FAX}}}}}

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Message: 3
Date: Fri, 10 Oct 2008 11:52:56 +0530
From: "Priyanka Yadav" <[email-masked]>
Subject: Re: [Megaco] Codec Negotiation Question
To: "'Ramesh Babu Kuppili'" <[email-masked]>, <[email-masked]>
Cc: 'Murugesh Govindaraju' <[email-masked]>
Message-ID: <005901c92aa0$a48603f0$83a44e0a@priyadavwxp01>
Content-Type: text/plain; charset="us-ascii"

Hi Ramesh
I think you should send a "codec negotiation faliure" as response of Modify
since the codec list in modify doesnot intersect with the remote codec list
previously sent.
If you go by approach one and in your example case One gateway will move
from codec 18 to 8.
But the other gateway will not have any information about this codec change.
So, I think second approach is better.
 
Thanks
Priyanka

  _____  

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Ramesh Babu Kuppili
Sent: Friday, October 10, 2008 10:27 AM
To: [email-masked]
Cc: Murugesh Govindaraju
Subject: [Megaco] Codec Negotiation Question

Gurus,
 
I have a question about Codec Negotiation in Megaco.
 
Lets says the switch initially sends us local and remote codec list.  We
take a intersection of the both local and remote and respond to the request.
 
Then at a later stage lets says the switch sends another modify with only
local codec list.  And this time the local codec does not intersect with the
remote codec list that was received previously.
 
My question is, "How should the gateway behave to the the codec list in the
modify?".
 
1. Should it assume the the remote will also support all the codecs in the
list of Modify and respond to the modify with all supported codecs.
2. Should it send a "codec negotiation failure" as response for Modify since
the codec list in the modify does not intersect with the remote codec list
previously sent.
 
- ramesh
 
~~~~~~~~~~~~~~~~~~Example messages~~~~~~~~~~~~~~~~~~~ Request with both
local and remote:
    MEGACO/1
    [172.16.43.151]
    Transaction = 58738{Context = 3{Modify = Eag26/ep2{Media{Stream =
1{LocalControl{Mode = SendReceive , ReservedValue = off , ReservedGroup =
off , tdmc/ec = on} , Local{v=0
    c=IN IP4 $
    m=audio $ RTP/AVP 18
    a=ptime:40
    v=0
    c=IN IP4 $
    m=audio $ RTP/AVP 101
    a=rtpmap:101 telephone-event/8000
    a=ptime:40
    } , Remote{v=0
    c=IN IP4 172.16.43.155
    m=audio 6024 RTP/AVP 18
    a=ptime:40
    v=0
    c=IN IP4 172.16.43.155
    m=audio 6024 RTP/AVP 101
    a=rtpmap:101 telephone-event/8000
    a=ptime:40
    }}}}}}

Request with local only:
    MEGACO/1
    [172.16.43.151]
    Transaction = 58741{Context = 3{Modify = AG26{Media{Stream =
1{LocalControl{Mode = SendReceive , tdmc/ec = off}} ,
TerminationState{Buffer = off , fax/faxstate = Negotiating}} , Events =
16777230{fax/faxconnchange , al/on , al/fl}} , Modif
    c=IN IP4 $
    m=audio $ RTP/AVP 8
    a=ptime:20
    }} , TerminationState{Buffer = off , ipfax/faxstate = Negotiating ,
ctyp/calltyp = FAX}}}}}

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