Hi buddies,
A small introduction of myself:
I'm working as a Testing Engineer in a MNC company. I'm involved in Telecom & Voip testing. I'm interested in Networking domain too.
I'm creating this blog to share my experience and improve knowledge in voip protocols like SIP, H323 etc and telecom protocols like SS7, V5.2 etc. And i sure, this blog will help for all the telecom & SIP beginners to learn and improve.
Many Thanks to all of you.
Sunday, December 12, 2010
SIP Tutorial for Begineers
1. What is SIP?
SIP - Session Initiation protocol. It's a signaling protocol which is used to establish, modify & terminate multimedia sessions (Carries voice, data & video) in an IP network. It's one of the protocol from the VOIP family. It's an application layer protocol.
2. What are the elements of SIP?
Proxy server, Registrar server, Location server, Redirect server, User Agents are the elements of the SIP.
3. What is the RFC for SIP?
To start, RFC 3261 is best choice.
4. What is the stateful & stateless proxy?
stateful proxy maintain its state for all the transaction. It uses TCP and forking is happening on stateful proxy.
5. What is transaction in sip?
A transaction is a sequence of SIP messages exchanged between SIP network elements. A transaction consists of one request and all responses to that request. That includes zero or more provisional responses and one or more final responses.
If a transaction was initiated by an INVITE request then the same transaction also includes ACK, but only if the final response was not a 2xx response. If the final response was a 2xx response then the ACK is not considered part of the transaction.
Transaction is identified by Branch id, To header, From header and C-sequence
6.What is a dialog in sip?
We have shown what transactions are, that one transaction includes INVITE and it's responses and another transaction includes BYE and it responses when a session is being torn down. But we feel that those two transactions should be somehow related--both of them belong to the same dialog. A dialog represents a peer-to-peer SIP relationship between two user agents. A dialog persists for some time and it is very important concept for user agents.
Dialogs are identified using Call-ID, From tag, and To tag. Messages that have these three identifiers same belong to the same dialog.
7. When c-seq id will be incremented?
CSeq header field is used to order messages, in fact it is used to order messages within a dialog. The number must be monotonically increased for each message sent within a dialog otherwise the peer will handle it as out of order request or retransmission. In fact, the CSeq number identifies a transaction within a dialog because we have said that requests and associated responses are called transaction. This means that only one transaction in each direction can be active within a dialog. One could also say that a dialog is a sequence of transactions.
SIP - Session Initiation protocol. It's a signaling protocol which is used to establish, modify & terminate multimedia sessions (Carries voice, data & video) in an IP network. It's one of the protocol from the VOIP family. It's an application layer protocol.
2. What are the elements of SIP?
Proxy server, Registrar server, Location server, Redirect server, User Agents are the elements of the SIP.
3. What is the RFC for SIP?
To start, RFC 3261 is best choice.
4. What is the stateful & stateless proxy?
stateful proxy maintain its state for all the transaction. It uses TCP and forking is happening on stateful proxy.
5. What is transaction in sip?
A transaction is a sequence of SIP messages exchanged between SIP network elements. A transaction consists of one request and all responses to that request. That includes zero or more provisional responses and one or more final responses.
If a transaction was initiated by an INVITE request then the same transaction also includes ACK, but only if the final response was not a 2xx response. If the final response was a 2xx response then the ACK is not considered part of the transaction.
Transaction is identified by Branch id, To header, From header and C-sequence
6.What is a dialog in sip?
We have shown what transactions are, that one transaction includes INVITE and it's responses and another transaction includes BYE and it responses when a session is being torn down. But we feel that those two transactions should be somehow related--both of them belong to the same dialog. A dialog represents a peer-to-peer SIP relationship between two user agents. A dialog persists for some time and it is very important concept for user agents.
Dialogs are identified using Call-ID, From tag, and To tag. Messages that have these three identifiers same belong to the same dialog.
7. When c-seq id will be incremented?
CSeq header field is used to order messages, in fact it is used to order messages within a dialog. The number must be monotonically increased for each message sent within a dialog otherwise the peer will handle it as out of order request or retransmission. In fact, the CSeq number identifies a transaction within a dialog because we have said that requests and associated responses are called transaction. This means that only one transaction in each direction can be active within a dialog. One could also say that a dialog is a sequence of transactions.
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