Module: sip-router Branch: 4.1 Commit: b6c109a38f8fca82005166ed73d370a2f974a3db URL: http://git.sip-router.org/cgi-bin/gitweb.cgi/sip-router/?a=commit;h=b6c109a… Author: Daniel-Constantin Mierla <miconda(a)gmail.com> Committer: Daniel-Constantin Mierla <miconda(a)gmail.com> Date: Thu Nov 21 20:24:20 2013 +0100 sl: README updated --- modules/sl/README | 102 ++++++++++++++++++++++++++--------------------------- 1 files changed, 50 insertions(+), 52 deletions(-) diff --git a/modules/sl/README b/modules/sl/README index 447f700..5d7723d 100644 --- a/modules/sl/README +++ b/modules/sl/README @@ -1,4 +1,3 @@ - The SL Module - Statless request handling Bogdan Iancu @@ -10,7 +9,7 @@ Daniel-Constantin Mierla asipto.com Copyright � 2003 FhG FOKUS - _________________________________________________________________ + __________________________________________________________________ Table of Contents @@ -25,10 +24,10 @@ Daniel-Constantin Mierla 3. Functions - 3.1. sl_send_reply(code, reason) - 3.2. send_reply(code, reason) - 3.3. sl_reply_error() - 3.4. sl_forward _reply([ code, [ reason ] ]) + 3.1. sl_send_reply(code, reason) + 3.2. send_reply(code, reason) + 3.3. sl_reply_error() + 3.4. sl_forward _reply([ code, [ reason ] ]) 4. Statistics @@ -80,10 +79,10 @@ Chapter 1. Admin Guide 3. Functions - 3.1. sl_send_reply(code, reason) - 3.2. send_reply(code, reason) - 3.3. sl_reply_error() - 3.4. sl_forward _reply([ code, [ reason ] ]) + 3.1. sl_send_reply(code, reason) + 3.2. send_reply(code, reason) + 3.3. sl_reply_error() + 3.4. sl_forward _reply([ code, [ reason ] ]) 4. Statistics @@ -114,31 +113,30 @@ Chapter 1. Admin Guide 1. Overview - The SL module allows the SIP server to act as a stateless UA server - and generate replies to SIP requests without keeping state. That is + The SL module allows the SIP server to act as a stateless UA server and + generate replies to SIP requests without keeping state. That is beneficial in many scenarios, in which you wish not to burden server's memory and scale well. - The SL module needs to filter ACKs sent after a local stateless reply + The SL module needs to filter ACKs sent after a local stateless reply to an INVITE was generated. To recognize such ACKs, ser adds a special "signature" in to-tags. This signature is sought for in incoming ACKs, and if included, the ACKs are absorbed. - To speed up the filtering process, the module uses a timeout - mechanism. When a reply is sent, a timer us set. As long as the timer - is valid, the incoming ACK requests will be checked using TO tag - value. Once the timer expires, all the ACK messages are let through - - a long time passed till it sent a reply, so it does not expect any ACK - that have to be blocked. - - The ACK filtering may fail in some rare cases. If you think these - matter to you, better use stateful processing (TM module) for INVITE - processing. Particularly, the problem happens when a UA sends an - INVITE which already has a to-tag in it (e.g., a re-INVITE) and the - server want to reply to it. Then, it will keep the current to-tag, - which will be mirrored in ACK. SER will not see its signature and - forward the ACK downstream. Caused harm is not bad--just a useless ACK - is forwarded. + To speed up the filtering process, the module uses a timeout mechanism. + When a reply is sent, a timer us set. As long as the timer is valid, + the incoming ACK requests will be checked using TO tag value. Once the + timer expires, all the ACK messages are let through - a long time + passed till it sent a reply, so it does not expect any ACK that have to + be blocked. + + The ACK filtering may fail in some rare cases. If you think these + matter to you, better use stateful processing (TM module) for INVITE + processing. Particularly, the problem happens when a UA sends an INVITE + which already has a to-tag in it (e.g., a re-INVITE) and the server + want to reply to it. Then, it will keep the current to-tag, which will + be mirrored in ACK. SER will not see its signature and forward the ACK + downstream. Caused harm is not bad--just a useless ACK is forwarded. 2. Parameters @@ -170,7 +168,7 @@ modparam("sl", "default_reason", "Server Error") 2.3. bind_tm (int) - Controls if SL module should attempt to bind to TM module in order to + Controls if SL module should attempt to bind to TM module in order to send stateful reply when the transaction is created. Default value is 1 (enabled). @@ -182,17 +180,16 @@ modparam("sl", "bind_tm", 0) # feature disabled 3. Functions - 3.1. sl_send_reply(code, reason) - 3.2. send_reply(code, reason) - 3.3. sl_reply_error() - 3.4. sl_forward _reply([ code, [ reason ] ]) + 3.1. sl_send_reply(code, reason) + 3.2. send_reply(code, reason) + 3.3. sl_reply_error() + 3.4. sl_forward _reply([ code, [ reason ] ]) -3.1. sl_send_reply(code, reason) +3.1. sl_send_reply(code, reason) - For the current request, a reply is sent back having the given code - and text reason. The reply is sent stateless, totally independent of - the Transaction module and with no retransmission for the INVITE's - replies. + For the current request, a reply is sent back having the given code and + text reason. The reply is sent stateless, totally independent of the + Transaction module and with no retransmission for the INVITE's replies. Meaning of the parameters is as follows: * code - Return code. @@ -203,19 +200,20 @@ modparam("sl", "bind_tm", 0) # feature disabled sl_send_reply("404", "Not found"); ... -3.2. send_reply(code, reason) +3.2. send_reply(code, reason) - For the current request, a reply is sent back having the given code - and text reason. The reply is sent stateful or stateless, depending of - the TM module: if a transaction exists for the current request, then - the reply is sent statefully, otherwise stateless. + For the current request, a reply is sent back having the given code and + text reason. The reply is sent stateful or stateless, depending of the + TM module: if a transaction exists for the current request, then the + reply is sent statefully, otherwise stateless. Meaning of the parameters is as follows: * code - Return code. * reason - Reason phrase. - This function can be used from REQUEST_ROUTE, FAILURE_ROUTE, - BRANCH_ROUTE. + This function can be used from REQUEST_ROUTE and FAILURE_ROUTE. It can + be used on ONREPLY_ROUTE executed by tm module (upon a t_on_reply() + callback). Example 1.5. send_reply usage ... @@ -224,10 +222,10 @@ send_reply("404", "Not found"); send_reply("403", "Invalid user - $fU"); ... -3.3. sl_reply_error() +3.3. sl_reply_error() - Sends back an error reply describing the nature of the last internal - error. Usually this function should be used after a script function + Sends back an error reply describing the nature of the last internal + error. Usually this function should be used after a script function that returned an error code. Example 1.6. sl_reply_error usage @@ -235,11 +233,11 @@ send_reply("403", "Invalid user - $fU"); sl_reply_error(); ... -3.4. sl_forward _reply([ code, [ reason ] ]) +3.4. sl_forward _reply([ code, [ reason ] ]) - Forward statelessy the current received SIP reply, with the option to - change the status code and reason text. The new code has to be in the - same class. The received reply is forwarded as well by core when the + Forward statelessy the current received SIP reply, with the option to + change the status code and reason text. The new code has to be in the + same class. The received reply is forwarded as well by core when the config execution ended, unless it is dropped from config. Meaning of the parameters is as follows: