2nd September 2009, 12:32
| #16 | ||||
| BANNED Join Date: Jun 2007 Location: Bengalooru
Posts: 1,480
Thanked: 17 Times
| Quote:
IMO, it doesn't belong here. Other OT posts: Quote:
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2nd September 2009, 15:56
| #17 | |
| BHPian  Join Date: Sep 2006 Location: Bangalore
Posts: 939
Thanked: 29 Times
| Quote:
though i am not an expert on the SIP side, but with my experience on other circuit switched protocols , let me see if i can clarify on your questions. Q1. I am not sure of the meaning as to why it isnt part of the same transaction. Ofcourse it is part of the same transaction and this i am saying from the state machine point of view that will be maitained at both the sender and the receiver end for a particular transaction, unless the ACK is not mandatory. Q2. The invite is basically a handshake before the actual media/voice path can be established between the two ends. the 180 rining is more of alerting and is similar to when you phone rings (during which the RBT is fed back to the caller )when someone is making a call to you and 200 ok comes only when you answer the call/recieve the call. The same is the case with other protocols such as SS7 where you have IAM then the ACM and you recieve an ANM only when someone picks the call. I dont think if this can be achieved in request-response/two message. There are series of handshakes that take place during call initiation which cannot be achieved using a simple request/response. | |
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2nd September 2009, 17:28
| #18 | ||
| BHPian  | Sip - Rfc 3261 Quote:
"In the case of a transaction where the request was an INVITE (known as an INVITE transaction), the transaction also includes the ACK only if the final response was not a 2xx response. If the response was a 2xx, the ACK is not considered part of the transaction. The reason for this separation is rooted in the importance of delivering all 200 (OK) responses to an INVITE to the UAC. To deliver them all to the UAC, the UAS alone takes responsibility for retransmitting them (see Section 13.3.1.4), and the UAC alone takes responsibility for acknowledging them with ACK (see Section 13.2.2.4). Since this ACK is retransmitted only by the UAC, it is effectively considered its own transaction". Quote:
Last edited by im_srini : 2nd September 2009 at 17:35. | ||
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3rd September 2009, 12:28
| #19 |
| Senior - BHPian  | |
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23rd September 2009, 00:15
| #20 | |
| Team-BHP Support   | Quote:
SIP is way more flexible than traditional telephony, so you need more flexible protocol. For example, consider John who lives in Bangalore, wants to talk to George in Chennai. The call made by John first goes to the telephone exchange he is connected in Bangalore, travel through the telephony cloud and reaches the telephone exchange connected to George's phone and then sends a ring to George's phone. By this time, the TDM channel for the entire conversation is already allocated. When George picks the phone, they start talking on that TDM channel. But VOIP doesn't work that way. SIP (signalling) and RTP(payload) may or may not use the same path. For example, SIP proxies only setup the call, they don't deal with payload or RTP. SIP Example 1: John calls George, both are using SIP phones, call is made directly. John -----INVITE -------->George John<---------RINGING---George George picks up John<-----------200 OK----George Now talk... John<-------RTP---------->George John hangs up John------BYE------------->George John<-----------OK------George SIP Example 1: John calls George, both are using SIP phones, call is made via SIP proxy. John -----INVITE ----Proxy---INVITE---->George John<----RINGING----Proxy---RINGING---George George picks up John<-----200 OK-----Proxy---200 OK--George Now proxy gives the direct IP address of John to George (SDP contains the direct IP) Proxy-------ACK------>George Now talk... John<-------RTP---------->George John hangs up John------BYE---Proxy-----BYE--->George John<------OK---Proxy----OK---George Basically ACK is used to give the redirection info for RTP path. The SIP proxy handles only SIP and not RTP. This is my understanding after doing some programming in SIP. Remember I am no expert on SIP. I am not sure whether ACK is initiated by the proxy or the endpoint (John). What happens if there is no direct access between John & George, that too I am not sure. Different SIP PBX and proxies have different behaviors. | |
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1st March 2019, 18:06
| #21 |
| BHPian  Join Date: Dec 2006 Location: KL-01/KL-08
Posts: 326
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