Now I understand. If both legs use the same codec, the codec ("fake") will be used in a pass-through way, so no additional transcoding is applied, as in PROXY PASS-THROUGH condition. So let me reason in a default media scenario (no proxy-media). Now, as I explained in the first mail, sofia build "ep_codec_string" (SWITCH_ ORIGINATOR_CODEC_VARIABLE) as the intersection between the codec list received in SDP offer and the codec loaded in the core. So if the offered SDP codec list is NOT a subset of the loaded core codecs the other legs will miss some codecs proposed by the calling endpoint. That said, if I want to be sure every codecs my endpoint support won't be filtered I have to register a "fake" pass-through codec for each one. ... you did not answer to my last question :). I haven't found any other endpoint module the can interwork in PROXY mode with sofia (even h323 doesn't support this). My question: is there a standard/ recommended way to exchange capability between endpoint of different nature in FS proxy mode? Maybe using SDP o/a as done in sofia sip? Thank you again for you help. Giovanni -----Original Message----- From: freeswitch-dev-bounces@lists.freeswitch.org on behalf of Anthony Minessale Sent: Sat 10/22/2011 4:48 PM To: freeswitch-dev@lists.freeswitch.org Subject: Re: [Freeswitch-dev] Strange behaviour in SOFIA SIP that's what I was trying to explain. PROXY mode does not let you manipulate anything, it's pure pass-through negotiation between the endpoints. All the stuff with ep_codec_string are relevant only when you are not trying to use proxy mode. This is a common mistake people make assuming not using proxy mode means somehow doing more work but it's not the case, any time both legs of a call use the same codec it's equally efficient to what you end up with in proxy mode. proxy mode simply means take the inbound SDP and offer it AS IS to the far end and vice-versa and use a fake codec in the middle that is agnostic. On Fri, Oct 21, 2011 at 10:36 AM, Visciano Giovanni <Giovanni.Visciano@italtel.it> wrote:
Hello Anthony. Maybe I want not so clear, let me explain.
I do not want to apply any codec manipulation, I'm working on a prototype endpoint module that has "proxy media capabilty" and wants to interoperate with other endpoints. What I saw is that in a sofia vs sofia call (proxy mode+late negotiation) they exchange through FS calling/called endpoint capability looking at SDP session carried by channel variables, so internally they use SDP O/A scheme. I thought that "ep_codec_string"->SWITCH_ORIGINATOR_CODEC_VARIABLE could be used to exchange capability without using a protocol specific format (SDP). If this is not the case, what's the right way to negotiate capability between endpoints in proxy mode?
Than you. Giovanni
PS: I did not find any existing endpoint except sofia that support this. Am I right?
-----Original Message----- From: freeswitch-dev-bounces@lists.freeswitch.org on behalf of Anthony Minessale Sent: Fri 10/21/2011 5:06 PM To: freeswitch-dev@lists.freeswitch.org Subject: Re: [Freeswitch-dev] Strange behaviour in SOFIA SIP
any codec manipulation techniques and proxy media mode are not compatible. Proxy media mode means stay completely out of the codec negotiation process.
On Thu, Oct 20, 2011 at 3:11 PM, Visciano Giovanni <Giovanni.Visciano@italtel.it> wrote:
Preconditions on sip profile ---------------------------- inbound-codec-prefs NOT set outbound-codec-prefs NOT set inbound-proxy-media=TRUE inbound-bypass-media=FALSE inbound-late-negotiation=TRUE + inherit_codec=TRUE
TEST scenario ------------- SIP phone send INVITE with SDP to FS
INVITE SDP[codelist=PCMA, PCMU, G722, G729] --> FS
FS has just the CORE_PC_MODULE [PCMA, PCMU, PASS-THR, VIDEO-PASS-THR, L16]
The "ep_codec_string" channel variable is loaded with [PCMA, PCMU]
EXPECTED -------- In "proxy-media + late-negotiation" scenario: ep_codec_string=[PCMA,PCMU,G722,G729]
PROBLEM ------- According to the documentation (http://wiki.freeswitch.org/wiki/Codec_negotiation):
"ep_codec_string: This variable is only available if late negotiation is enabled on the profile. It's a readable string containing all the codecs proposed by the calling endpoint." and "inherit_codec=true (only applicable when late-negotiation is enabled) will take the codec negotiated when the B leg answers and pass it to the A leg so it also uses the same codec (if the A leg supports it); otherwise, it will use whatever it can from its own list"
The variable ep_codec_string doesn't contain ALL the codecs proposed by the calling endpoint. It contains the intersection between the codecs proposed by the calling and the codecs loaded in FS. In proxy-media / no-media configuration the called endpoint doesn't have the calling codec list so he can't negotiate using all the capabilities available. (I'm working on a test endpoint module that should work in proxy and no-media configuration ... mod_sofia vs mod_sofia works because they look at the remote sdp variable)
Source reference - sofia_glue.c->sofia_glue_set_r_sdp_codec_string()
Regards, Giovanni
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