oSIP协议桟浅析

oSIP协议栈浅析

1. oSIP介绍 ...................................................................................................................................... 1 2. oSIP结构分析 .............................................................................................................................. 1

2.1 oSIP结构 ............................................................................................................................ 1 2.2 状态机(Finite State Machines)模块 .................................................................................. 2

2.2.1 概述 ......................................................................................................................... 2 2.2.2 ICT状态机 .............................................................................................................. 3 2.2.3 NICT状态机 ........................................................................................................... 4 2.2.4 IST状态机 ............................................................................................................... 5 2.2.5 NIST状态机 ............................................................................................................ 6 2.3 解析器(Parsers)模块 ......................................................................................................... 7

2.3.1 SIP Parser ................................................................................................................. 7 2.3.2 SDP Parser ............................................................................................................... 9 2.3.3 URL Parser ............................................................................................................. 10 2.4 工具(Facilities)模块 ........................................................................................................ 11

2.4.1 SDP negotiator ....................................................................................................... 11 2.4.2 Dialog management ............................................................................................... 11

3. oSIP特点 .................................................................................................................................... 11

3.1 oSIP的优点 ...................................................................................................................... 11 3.2 oSIP的缺点 ...................................................................................................................... 12 4. oSIP应用结构图 ........................................................................................................................ 12 5. oSIP使用概述 ............................................................................................................................ 13

5.1 初始化oSIP ..................................................................................................................... 13 5.2 注册CALL BACK函数 ................................................................................................. 13 5.3 Transaction操作 ............................................................................................................... 15 6. 参考............................................................................................................................................ 15

oSIP协议栈浅析

1. oSIP介绍

oSIP是按照RFC3261(SIP)和RFC2327(SDP)标准，并使用标准c编写的一个SIP协议栈。它是一个公开源码的免费协议栈。oSIP协议栈结构简单而小巧，它并不提供高层的SIP会话控制的API，它主要提供一些解析SIP/SDP消息的API和事务处理的状态机。

oSIP支持线程安全，既可以用于多线程的编程模式，也可以用于单线程的编程模式；oSIP可以用来开发User Agent，IP soft-phone和SIP Proxy等等。

oSIP目前最后版本为V 0.9.7，不久oSIP版本将升级至oSIP2（V 1.99.7）。oSIP2主要调整了一些函数和结构名称，以及一些头文件的名称、内容结构的调整，整体的构架和功能不变。

本文以下描述都基于oSIP V0.9.6版本。

2. oSIP结构分析

2.1 oSIP结构

oSIP主要包括三大部分的内容：状态机模块、解析器模块和工具模块。 状态机模块的功能：

完成对某个事务（注册过程，呼叫过程等等）状态记录，并在特定状态下触发相应的事件或回调函数。

解析器模块的功能：

该模块主要完成对SIP消息结构剖析、SDP消息的结构剖析以及URI结

构的剖析；

工具模块的功能：

该模块提供一些SDP等处理的一些工具。

oSIP的模块结构图如下(图2-1)：

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oSIP协议栈浅析

Application 解析器模块 SIP parser URL parser SDP parser Finite State Machines 状态机模块 工具模块(可选项) Dialogue Facilities SDP negotiation Facilities oSIP模块 图2-1 oSIP结构

2.2 状态机(Finite State Machines)模块

2.2.1 概述

oSIP状态机(Finite State Machines)主要分为四类，分别为： ? ICT ? NICT ? IST ? NIST

-- Invite Client (outgoing) Transaction -- Non-Invite Client (outgoing) Transaction -- Invite Server (incoming) Transaction -- Non-Invite Server (incoming) Transaction

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oSIP协议栈浅析

2.2.2 ICT状态机

cb_ict_kill_transaction Transaction initialization ICT_PRE_CALLING cb_ict_transport_error cb_ict_invite_sent cb_ict_transport_error cb_ict_invite_sent2 ICT_CALLING ICT_TERMINATED cb_ict_2xx_received cb_ict_transport_error cb_ict_1xx_received cb_ict_Nxx_received cb_ict_transport_error cb_ict_3456xx_received2 cb_ict_1xx_received ICT_COMPLETED ICT_PROCEEDING cb_ict_ack_sent2 cb_ict_Nxx_received

图 2-2: ICT State Machine

注：

cb_ict_xxx_xxxx 表示从一种状态转换到另一种状态时将调用该回调函数

表示从一种状态转换到另一种状态时不调用任何回调函数

cb_ict_Nxx_received：其中N表示一下几个值 3 -- cb_ict_3xx_received 4 -- cb_ict_4xx_received 5 -- cb_ict_5xx_received 6 -- cb_ict_6xx_received

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oSIP协议栈浅析

2.2.3 NICT状态机

cb_nict_kill_transaction Transaction initialization NICT_PRE_TRYING cb_nict_transport_error cb_nict_XXX_sent cb_nict_transport_error cb_nict_request_sent2 NICT_TRYING NICT_TERMINATED cb_nict_transport_error cb_nict_1xx_received cb_nict_Nxx_received cb_nict_request_sent2 NICT_COMPLETED NICT_PROCEEDING cb_nict_1xx_received cb_nict_Nxx_received 图2-3: NICT State Machine 注：

cb_nict_xxx_xxxx 表示从一种状态转换到另一种状态时将调用该回调函数

表示从一种状态转换到另一种状态时不调用任何回调函数

cb_nict_XXX_sent：其中XXX表示一下几种消息类型，

register -- cb_nict_register_sent bye -- cb_nict_bye_sent options -- cb_nict_options_sent info -- cb_nict_info_sent cancel -- cb_nict_cancel_sent notify -- cb_nict_notify_sent subscribe -- cb_nict_subscribe_sent unknown -- cb_nict_unknown_sent

cb_nict_Nxx_received：其中N表示一下几个值 2 -- cb_nict_2xx_received

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oSIP协议栈浅析

c connection_add(),connection_get(),nettype_get(), addrtype_get(),addr_get(),addr_multicast_ttl_get(), addr_multicast_int_get() bandwidth_add(),bwtype_get(),bandwidth_get() time_descr_add(),start_time_get(),stop_time_get() repeat_add(),repeat_get() adjustments_set(),adjustments_get() key_set(),keytype_get(),keydata_get() attribute_add(),att_field_get(),att_value_get() media_add(),media_get(),port_get(),number_of_port_get(), proto_get(),payload_add(),payload_get(), b t r z k a m

另外，oSIP还包含对SDP包的一些基本操作[set(), get(), init(), parse(), 2char(), free(), clone()],及对各类type的init()和free()操作

2.3.3 URL Parser

这里的URL是指SIP中的URI，URI有很多参数格式，在RFC3261中列举了一些比较例子：

The URIs within each of the following sets are equivalent: sip:alice@atlanta.com;transport=TCP sip:alice@AtLanTa.CoM;Transport=tcp

sip:carol@chicago.com

sip:carol@chicago.com;newparam=5 sip:carol@chicago.com;security=on

sip:biloxi.com;transport=tcp;method=REGISTER?to=sip:bob@biloxi.com sip:biloxi.com;method=REGISTER;transport=tcp?to=sip:bob@biloxi.com

sip:alice@atlanta.com?subject=project x&priority=urgent sip:alice@atlanta.com?priority=urgent&subject=project x

The URIs within each of the following sets are not equivalent:

SIP:ALICE@AtLanTa.CoM;Transport=udp (different usernames) sip:alice@AtLanTa.CoM;Transport=UDP

sip:bob@biloxi.com (can resolve to different ports) sip:bob@biloxi.com:5060

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sip:bob@biloxi.com (can resolve to different transports) sip:bob@biloxi.com;transport=udp

sip:bob@biloxi.com (can resolve to different port and transports) sip:bob@biloxi.com:6000;transport=tcp

sip:carol@chicago.com (different header component) sip:carol@chicago.com?Subject=next meeting

sip:bob@phone21.boxesbybob.com (even though that's what

sip:bob@192.0.2.4 phone21.boxesbybob.com resolves to)

在oSIP中处理SIP URI有比较多的操作函数提供，主要有对

host,port,username,password, scheme的get()和set()，以及对参数的初始化设置和剖析处理。详细函数名称请参考源代码中的url.h。

2.4 工具(Facilities)模块

2.4.1 SDP negotiator

SDP协商工具(SDP negotiator)帮助end point提供协商codec等功能

2.4.2 Dialog management

对话管理工具(Dialog management)是oSIP提供的一个比较强大的辅助工具，主要用于有能力应答呼叫的end point。

对话管理工具(Dialog management)能够帮助记录请求和响应消息，利用这

个工具使end point能够快速准确的作出应答。

3. oSIP特点

3.1 oSIP的优点

? Osip没有给开发者限定在特定的某个执行模式下，能够使开发者选定一

个比较适合自己的模式。

? Osip的各个模块是相对清晰、独立的，因而去掉某个模块时也比较容易。

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? Osip的解析器提供了较为完善的API，包含了消息的构造、修改和产生

等。

3.2 oSIP的缺点

?

oSIP目前版本源代码结构、定义比较混乱，并且缺乏文档，阅读比较困难；该问题将在oSIP2中得到改善。

?

oSIP不提供任何快速产生请求消息和响应消息的方法，所有请求消息和响应消息的形成必须调用一组sip message api来手动组装完成，关于这方面的缺陷，osip作者可能在以后会开发一个eXoSIP的API来完成。

?

由于oSIP结构简单，外围相关模块需要用户自己开发，如SIP消息的接收和发送，RTP/RTCP的语音数据的处理等。

4. oSIP应用结构图

Receive/Send SIP Messages Receive/Send RTP/RTCP ⑦ B Main thread Application ② Transaction Context 解析器模块 SIP parser URL parser SDP parser ⑤ A ④ Finite State Machines 状态机模块 ⑥ ③ ① oSIP Instance 工具模块(可选项) Dialogue Facilities SDP negotiation Facilities oSIP模块 图4-1 oSIP应用

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oSIP协议栈浅析

其中： ①：初始化oSIP和注册CALL BACK函数； ②：添加事件A; ③：执行事务 ④：取消事件A ⑤：解析消息 ⑥：触发CALL BACK函数 ⑦：接收/发送消息 A：保存状态 B：接收/发送语音包

5. oSIP使用概述

5.1 初始化oSIP

在使用oSIP前必须先初始化oSIP，主要调用函数osip_global_init()和osip_init()，具体操作代码如下：

osip_t *osip;

// initialise internal element first

if (0!=osip_global_init())

return -1;

// allocate a global osip element.

if (0!=osip_init(&osip))

return -1;

5.2 注册CALL BACK函数

需要注册的call back函数主要包含发送消息、结束事务、发送失败、4个状态机(ICT、NICT、IST、NIST)相关函数。 注册发送消息的CALL BACK函数：

osip_setcb_send_message(osip, &application_cb_snd_message); 注册结束事务的CALL BACK函数：

osip_setcb_ict_kill_transaction(osip,&application_cb_ict_kill_transaction);

osip_setcb_ist_kill_transaction(osip,&application_cb_ist_kill_transaction);

osip_setcb_nict_kill_transaction(osip,&application_cb_nict_kill_transaction);

osip_setcb_nist_kill_transaction(osip,&application_cb_nist_kill_transaction);

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注册发送失败的CALL BACK函数：

osip_setcb_ict_transport_error(osip,&application_cb_transport_error); osip_setcb_ist_transport_error(osip,&application_cb_transport_error); osip_setcb_nict_transport_error(osip,&application_cb_transport_error); osip_setcb_nist_transport_error(osip,&application_cb_transport_error);

注册ICT、NICT、IST、NIST CALL BACK函数

osip_setcb_ict_2xx_received2(osip,&application_cb_rcvresp_retransmission); osip_setcb_ict_3456xx_received2(osip,&application_cb_rcvresp_retransmission); osip_setcb_ict_invite_sent2(osip,&application_cb_sndreq_retransmission); osip_setcb_ist_2xx_sent2(osip,&application_cb_sndresp_retransmission); osip_setcb_ist_3456xx_sent2(osip,&application_cb_sndresp_retransmission); osip_setcb_ist_invite_received2(osip,&application_cb_rcvreq_retransmission); osip_setcb_nict_2xx_received2(osip,&application_cb_rcvresp_retransmission); osip_setcb_nict_3456xx_received2(osip,&application_cb_rcvresp_retransmission); osip_setcb_nict_request_sent2(osip,&application_cb_sndreq_retransmission); osip_setcb_nist_2xx_sent2(osip,&application_cb_sndresp_retransmission); osip_setcb_nist_3456xx_sent2(osip,&application_cb_sndresp_retransmission); osip_setcb_nist_request_received2(osip,&application_cb_rcvreq_retransmission); osip_setcb_ict_invite_sent (osip,&application_cb_sndinvite); osip_setcb_ict_ack_sent (osip,&application_cb_sndack); osip_setcb_nict_register_sent(osip,&application_cb_sndregister); osip_setcb_nict_bye_sent (osip,&application_cb_sndbye); osip_setcb_nict_cancel_sent (osip,&application_cb_sndcancel); osip_setcb_nict_info_sent (osip,&application_cb_sndinfo); osip_setcb_nict_options_sent (osip,&application_cb_sndoptions); osip_setcb_nict_subscribe_sent (osip,&application_cb_sndoptions); osip_setcb_nict_notify_sent (osip,&application_cb_sndoptions);

osip_setcb_nict_unknown_sent(osip,&application_cb_sndunkrequest); osip_setcb_ict_1xx_received(osip,&application_cb_rcv1xx); osip_setcb_ict_2xx_received(osip,&application_cb_rcv2xx); osip_setcb_ict_3xx_received(osip,&application_cb_rcv3xx); osip_setcb_ict_4xx_received(osip,&application_cb_rcv4xx); osip_setcb_ict_5xx_received(osip,&application_cb_rcv5xx); osip_setcb_ict_6xx_received(osip,&application_cb_rcv6xx); osip_setcb_ist_1xx_sent(osip,&application_cb_snd1xx); osip_setcb_ist_2xx_sent(osip,&application_cb_snd2xx); osip_setcb_ist_3xx_sent(osip,&application_cb_snd3xx); osip_setcb_ist_4xx_sent(osip,&application_cb_snd4xx); osip_setcb_ist_5xx_sent(osip,&application_cb_snd5xx);

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osip_setcb_ist_6xx_sent(osip,&application_cb_snd6xx);

osip_setcb_nict_1xx_received(osip,&application_cb_rcv1xx); osip_setcb_nict_2xx_received(osip,&application_cb_rcv2xx); osip_setcb_nict_3xx_received(osip,&application_cb_rcv3xx); osip_setcb_nict_4xx_received(osip,&application_cb_rcv4xx); osip_setcb_nict_5xx_received(osip,&application_cb_rcv5xx); osip_setcb_nict_6xx_received(osip,&application_cb_rcv6xx); osip_setcb_nist_1xx_sent(osip,&application_cb_snd1xx); osip_setcb_nist_2xx_sent(osip,&application_cb_snd2xx); osip_setcb_nist_3xx_sent(osip,&application_cb_snd3xx); osip_setcb_nist_4xx_sent(osip,&application_cb_snd4xx); osip_setcb_nist_5xx_sent(osip,&application_cb_snd5xx); osip_setcb_nist_6xx_sent(osip,&application_cb_snd6xx);

osip_setcb_ist_invite_received (osip,&application_cb_rcvinvite); osip_setcb_ist_ack_received (osip,&application_cb_rcvack); osip_setcb_ist_ack_received2 (osip,&application_cb_rcvack2); osip_setcb_nist_register_received(osip,&application_cb_rcvregister); osip_setcb_nist_bye_received (osip,&application_cb_rcvbye); osip_setcb_nist_cancel_received (osip,&application_cb_rcvcancel); osip_setcb_nist_info_received (osip,&application_cb_rcvinfo); osip_setcb_nist_options_received (osip,&application_cb_rcvoptions); osip_setcb_nist_subscribe_received(osip,&application_cb_rcvoptions); osip_setcb_nist_notify_received (osip,&application_cb_rcvoptions);

osip_setcb_nist_unknown_received (osip,&application_cb_rcvunkrequest);

5.3 Transaction操作

在注册完CALL BACK函数后，应用程序可以建立Transaction来调用oSIP的解析器和状态机模块的操作，来实现不同应用程序的需求。

6. 参考

[1] SIP -- RFC3261

(http://www.ietf.org)

[2] SDP -- RFC2327(http://www.ieft.org) [3] oSIP Library

-- http://www.gnu.org/software/osip/

[4] oSIP mailing list -- http://www.atosc.org/pipermail/public/osip/

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osip_setcb_ist_6xx_sent(osip,&application_cb_snd6xx);

osip_setcb_nict_1xx_received(osip,&application_cb_rcv1xx); osip_setcb_nict_2xx_received(osip,&application_cb_rcv2xx); osip_setcb_nict_3xx_received(osip,&application_cb_rcv3xx); osip_setcb_nict_4xx_received(osip,&application_cb_rcv4xx); osip_setcb_nict_5xx_received(osip,&application_cb_rcv5xx); osip_setcb_nict_6xx_received(osip,&application_cb_rcv6xx); osip_setcb_nist_1xx_sent(osip,&application_cb_snd1xx); osip_setcb_nist_2xx_sent(osip,&application_cb_snd2xx); osip_setcb_nist_3xx_sent(osip,&application_cb_snd3xx); osip_setcb_nist_4xx_sent(osip,&application_cb_snd4xx); osip_setcb_nist_5xx_sent(osip,&application_cb_snd5xx); osip_setcb_nist_6xx_sent(osip,&application_cb_snd6xx);

osip_setcb_ist_invite_received (osip,&application_cb_rcvinvite); osip_setcb_ist_ack_received (osip,&application_cb_rcvack); osip_setcb_ist_ack_received2 (osip,&application_cb_rcvack2); osip_setcb_nist_register_received(osip,&application_cb_rcvregister); osip_setcb_nist_bye_received (osip,&application_cb_rcvbye); osip_setcb_nist_cancel_received (osip,&application_cb_rcvcancel); osip_setcb_nist_info_received (osip,&application_cb_rcvinfo); osip_setcb_nist_options_received (osip,&application_cb_rcvoptions); osip_setcb_nist_subscribe_received(osip,&application_cb_rcvoptions); osip_setcb_nist_notify_received (osip,&application_cb_rcvoptions);

osip_setcb_nist_unknown_received (osip,&application_cb_rcvunkrequest);

5.3 Transaction操作

在注册完CALL BACK函数后，应用程序可以建立Transaction来调用oSIP的解析器和状态机模块的操作，来实现不同应用程序的需求。

6. 参考

[1] SIP -- RFC3261

(http://www.ietf.org)

[2] SDP -- RFC2327(http://www.ieft.org) [3] oSIP Library

-- http://www.gnu.org/software/osip/

[4] oSIP mailing list -- http://www.atosc.org/pipermail/public/osip/

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