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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):
SIP parser
|
URL parser
|
SDP parser
|
Finite
State
Machines
|
Dialogue Facilities
|
SDP negotiation
Facilities
|
Application
|
状态机模块
|
解析器模块
|
工具模块(可选项)
|
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:
Ø
ICT -- Invite Client (outgoing) Transaction
Ø
NICT -- Non-Invite Client (outgoing) Transaction
Ø
IST -- Invite Server (incoming) Transaction
Ø
NIST -- Non-Invite Server (incoming) Transaction
2.2.2 ICT状态机
ICT_PRE_CALLING
|
ICT_COMPLETED
|
ICT_PROCEEDING
|
ICT_TERMINATED
|
Transaction initialization
|
ICT_CALLING
|
cb_ict_transport_error
|
cb_ict_invite_sent
|
cb_ict_invite_sent2
|
cb_ict_transport_error
|
图 2-2: ICT State Machine
|
cb_ict_kill_transaction
|
cb_ict_transport_error
|
cb_ict_1xx_received
|
cb_ict_2xx_received
|
cb_ict_transport_error
|
cb_ict_1xx_received
|
cb_ict_Nxx_received
|
cb_ict_Nxx_received
|
cb_ict_3456xx_received2
cb_ict_ack_sent2
|
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
2.2.3 NICT状态机
NICT_PRE_TRYING
|
NICT_COMPLETED
|
NICT_PROCEEDING
|
NICT_TERMINATED
|
Transaction initialization
|
NICT_TRYING
|
cb_nict_transport_error
|
cb_nict_XXX_sent
|
cb_nict_request_sent2
|
cb_nict_1xx_received
|
图2-3: NICT State Machine
|
cb_nict_Nxx_received
|
cb_nict_kill_transaction
|
cb_nict_transport_error
|
cb_nict_request_sent2
|
cb_nict_1xx_received
|
cb_nict_Nxx_received
|
cb_nict_transport_error
|
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
3 -- cb_nict_3xx_received
4 -- cb_nict_4xx_received
5 -- cb_nict_5xx_received
6 -- cb_nict_6xx_received
2.2.4 IST状态机
IST_PRE_PROCEEDING
|
IST_CONFIRMED
|
IST_COMPLETED
|
IST_TERMINATED
|
Transaction initialization
|
IST_PROCEEDING
|
cb_ist_invite_received
|
cb_ist_Nxx_sent
|
图2-4: IST State Machine
|
cb_ist_ack_received
|
cb_ist_1xx_sent
|
cb_ist_transport_error
|
cb_ist_2xx_sent
|
cb_ist_ack_received2
|
cb_ist_3456xx_sent2
|
cb_ist_invite_received2
|
cb_ist_kill_transaction
|
cb_ist_transport_error
|
cb_ist_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_ist_Nxx_sent:其中N表示一下几个值,
3
-- cb_ist_3xx_sent
4
-- cb_ist_4xx_sent
5
-- cb_ist_5xx_sent
6
-- cb_ist_6xx_sent
2.2.5 NIST状态机
NIST_PRE_TRYING
|
NIST_COMPLETED
|
NIST_PROCEEDING
|
NIST_TERMINATED
|
Transaction initialization
|
NIST_TRYING
|
cb_nist_XXX_ received
|
cb_nist_1xx_sent
|
图2-5: NIST State Machine
|
cb_nist_Nxx_sent
|
cb_nist_kill_transaction
|
cb_nist_transport_error
|
cb_nist_1xx_sent
|
cb_nist_Nxx_sent
|
cb_nist_transport_error
|
cb_nist_request_received2
|
cb_nist_request_received2
|
cb_nist_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_nist_XXX_ received:其中XXX表示一下几种消息类型,
register --
cb_nist_register_received
bye
-- cb_nist_bye_received
options --
cb_nist_options_received
info
-- cb_nist_info_received
cancel
-- cb_nist_cancel_received
notify
-- cb_nist_notify_received
subscribe
-- cb_nist_subscribe_received
unknown
-- cb_nist_unknown_received
cb_nist_Nxx_ sent:其中N表示一下几个值
2 -- cb_nist_2xx_sent
3 -- cb_nist_3xx_sent
4 -- cb_nist_4xx_sent
5 -- cb_nist_5xx_sent
6 -- cb_nist_6xx_sent
2.3 解析器(Parsers)模块
oSIP的SIP Parser处理的SIP头域(SIP Header fields)及其相应的操作功能列表如下:
SIP Header(头域)
|
Functions(函数名称—简写)
|
|
Accept
|
set(),get()
|
☆
|
Accept-Encoding
|
set(),get(),init(),parse(),2char(),free(),clone()
Getelement(),setelement()
|
☆
|
Accept-Language
|
set(),get()
|
☆
|
Alert-Info
|
set(),get()
|
☆
|
Allow
|
set(),get()
|
☆
|
Authentication-Info
|
|
|
Authorization
|
Init(),set(),parse(),get(),getauth_type(),setauth_type(),
Getusername(),setusername(),getrealm(),setrealm(),
Getnonce(),setnonce(),geturi(),seturi(),getresponse(),
Setresponse(),getdigest(),setdigest(),getalgorithm(),
Setalgorithm(),getcnonce(),setcnonce(),getopaque(),
Setopaque(),getmessage_qop(),setmessage_qop(),
getnonce_count(),setnonce_count(),2char(),free(),
clone()
|
☆
|
Call-ID
|
set(),get(),parse(),2char(),free(),clone(),getnumber(),
setnumber(),gethost(),sethost()
|
☆
|
Call-Info
|
set(),get(),init(),parse(),2char(),free(),clone(),
geturi(),seturi()
|
☆
|
Contact
|
set(),get(),init(),parse(),2char(),free(),clone()
|
☆
|
Content-Disposition
|
set(),get(),parse()
|
☆
|
Content-Encoding
|
set(),get()
|
☆
|
Content-Language
|
|
|
Content-Length
|
set(),get(),init(),parse(),2char(),free(),clone()
|
☆
|
Content-Type
|
set(),get(),init(),parse(),2char(),free(),clone()
|
☆
|
CSeq
|
set(),get(),init(),parse(),2char(),free(),clone(),
getnumber(),setnumber(),getmethod(),setmethod()
|
☆
|
Date
|
|
|
Error-Info
|
set(),get()
|
☆
|
Expires
|
|
|
From
|
set(),get(),init(),parse(),2char(),free(),clone(),
getdisplayname(),setdisplayname(),geturl(),seturl(),
param_get(),param_parseall(),param_setvalue(),
param_getvalue(),param_getname(),param_setname(),
compare()
|
☆
|
In-Reply-To
|
|
|
Max-Forwards
|
|
|
Min-Expires
|
|
|
MIME-Version
|
set(),get()
|
☆
|
Organization
|
|
|
Priority
|
|
|
Proxy-Authenticate
|
set(),get()
|
☆
|
Proxy-Authorization
|
set(),get()
|
☆
|
Proxy-Require
|
|
|
Record-Route
|
set(),get(),init(),parse(),2char(),free()
|
☆
|
Reply-To
|
|
|
Require
|
|
|
Retry-After
|
|
|
Route
|
set(),get(),init(),parse(),2char(),free()
|
☆
|
Server
|
|
|
Subject
|
|
|
Supported
|
|
|
Timestamp
|
|
|
To
|
set(),get(),init(),parse(),2char(),free(),clone()
|
☆
|
Unsupported
|
|
|
User-Agent
|
|
|
Via
|
set(),append(),get(),init(),free(),parse(),2char(),
setversion(),getversion(),setprotocol(),getprotocol(),
sethost(),gethost(),setport(),getport(),setcomment(),
getcomment(),clone()
|
☆
|
Warning
|
|
|
WWW-Authenticate
|
Init(),set(),quoted_string_set(),token_set(),parse(),
get(),getauth_type(),setauth_type(),getrealm(),setrealm(),
getdomain(),setdomain(),getnonce(),setnonce(),getstale(),
setstale(),getopaque(),setopaque(),getalgorithm(),
setalgorithm(),getqop_options(),setqop_options(),2char(),
free(),clone()
|
☆
|
注:标示“☆”表示oSIP支持该头域(SIP Header fields)解析处理,未注的表示目前还没有解析处理(这些被保存在字符串中,可自行处理分析),可能会在后续版本中逐步补充。
SDP的格式一般为:
<type>=<value>
type通常为一个英文字母,其取值如下(按照RFC2327,带“*”的表示为可选条目):
Session description
v= (protocol version)
o= (owner/creator and session identifier).
s= (session name)
i=* (session information)
u=* (URI of description)
e=* (email address)
p=* (phone number)
c=* (connection information - not required if included in all media)
b=* (bandwidth information)
One or more time descriptions (see below)
z=* (time zone adjustments)
k=* (encryption key)
a=* (zero or more session attribute lines)
Zero or more media descriptions (see below)
Time description
t= (time the session is active)
r=* (zero or more repeat times)
Media description
m= (media name and transport address)
i=* (media title)
c=* (connection information - optional if included at session-level)
b=* (bandwidth information)
k=* (encryption key)
a=* (zero or more media attribute lines)
在oSIP中处理的type和相应操作功能如下:
type(类型)
|
Functions(函数名称—简写)
|
v
|
version_set(),version_get()
|
o
|
origin_set(),username_get(),sess_id_get(),
sess_version_get(),nettype_get(),addrtype_get(),
addr_get()
|
s
|
name_set(),name_get()
|
i
|
info_set(),info_get()
|
u
|
uri_set(),uri_get()
|
e
|
email_add(),email_get()
|
p
|
phone_add(),phone_get()
|
c
|
connection_add(),connection_get(),nettype_get(),
addrtype_get(),addr_get(),addr_multicast_ttl_get(),
addr_multicast_int_get()
|
b
|
bandwidth_add(),bwtype_get(),bandwidth_get()
|
t
|
time_descr_add(),start_time_get(),stop_time_get()
|
r
|
repeat_add(),repeat_get()
|
z
|
adjustments_set(),adjustments_get()
|
k
|
key_set(),keytype_get(),keydata_get()
|
a
|
attribute_add(),att_field_get(),att_value_get()
|
m
|
media_add(),media_get(),port_get(),number_of_port_get(),
proto_get(),payload_add(),payload_get(),
|
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
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
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%20meeting
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
SDP
协商工具
(SDP negotiator)
帮助
end point提供协商codec等功能
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
n
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。
n
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。
n
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
|
SIP parser
|
URL parser
|
SDP parser
|
Finite
State
Machines
|
Dialogue Facilities
|
SDP negotiation
Facilities
|
Main thread
|
状态机模块
|
解析器模块
|
工具模块(可选项)
|
oSIP
模块
|
图4-1 oSIP应用
|
Receive/Send
RTP/RTCP
|
oSIP
Instance
|
Transaction
Context
|
①
|
②
|
③
|
⑥
|
④
|
⑤
|
⑦
|
B
|
A
|
Application
|
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);
|
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);
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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/