全文下載連接(不保證永久有效):http://u.sohu.com/download?fileid=11702529523807282
oSIP協議棧淺析
1. oSIP介紹
oSIP是按照RFC3261(SIP)和RFC2327(SDP)標準，並使用標準c編寫的一個SIP協議棧。它是一個公開源碼的免費協議棧。oSIP協議棧結構簡單而小巧，它並不提供高層的SIP會話控制的API，它主要提供一些解析SIP/SDP消息的API和事務處理的狀態機。
oSIP支持線程安全，既可以用於多線程的編程模式，也可以用於單線程的編程模式；oSIP可以用來開發User Agent，IP soft-phone和SIP Proxy等等。
oSIP目前最後版本爲V 0.9.7，不久oSIP版本將升級至oSIP2（V 1.99.7）。oSIP2主要調整了一些函數和結構名稱，以及一些頭文件的名稱、內容結構的調整，整體的構架和功能不變。
本文以下描述都基於oSIP V0.9.6版本。
2. oSIP結構分析
2.1 oSIP結構
oSIP主要包括三大部分的內容：狀態機模塊、解析器模塊和工具模塊。
狀態機模塊的功能：
完成對某個事務（註冊過程，呼叫過程等等）狀態記錄，並在特定狀態下觸發相應的事件或回調函數。
解析器模塊的功能：
該模塊主要完成對SIP消息結構剖析、SDP消息的結構剖析以及URI結構的剖析；
工具模塊的功能：
該模塊提供一些SDP等處理的一些工具。
oSIP的模塊結構圖如下(圖2-1)：
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SIP parser
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URL parser
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SDP parser
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Finite
State
Machines
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Dialogue Facilities
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SDP negotiation
Facilities
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Application
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狀態機模塊
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解析器模塊
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工具模塊(可選項)
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oSIP模塊
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圖2-1 oSIP結構
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2.2.1 概述
oSIP狀態機(Finite State Machines)主要分爲四類，分別爲：
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狀態機
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ICT_PRE_CALLING
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ICT_COMPLETED
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ICT_PROCEEDING
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ICT_TERMINATED
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Transaction initialization
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ICT_CALLING
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cb_ict_transport_error
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cb_ict_invite_sent
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cb_ict_invite_sent2
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cb_ict_transport_error
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圖 2-2: ICT State Machine
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cb_ict_kill_transaction
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cb_ict_transport_error
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cb_ict_1xx_received
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cb_ict_2xx_received
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cb_ict_transport_error
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cb_ict_1xx_received
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cb_ict_Nxx_received
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cb_ict_Nxx_received
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cb_ict_3456xx_received2
cb_ict_ack_sent2
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cb_ict_xxx_xxxx
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表示從一種狀態轉換到另一種狀態時將調用該回調函數
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表示從一種狀態轉換到另一種狀態時不調用任何回調函數
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cb_ict_Nxx_received：其中N表示一下幾個值
3 -- cb_ict_3xx_received
4 -- cb_ict_4xx_received
5 -- cb_ict_5xx_received
6 -- cb_ict_6xx_received
2.2.3 NICT狀態機
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NICT_PRE_TRYING
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NICT_COMPLETED
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NICT_PROCEEDING
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NICT_TERMINATED
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Transaction initialization
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NICT_TRYING
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cb_nict_transport_error
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cb_nict_XXX_sent
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cb_nict_request_sent2
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cb_nict_1xx_received
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圖2-3: NICT State Machine
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cb_nict_Nxx_received
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cb_nict_kill_transaction
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cb_nict_transport_error
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cb_nict_request_sent2
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cb_nict_1xx_received
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cb_nict_Nxx_received
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cb_nict_transport_error
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cb_nict_xxx_xxxx
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表示從一種狀態轉換到另一種狀態時將調用該回調函數
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表示從一種狀態轉換到另一種狀態時不調用任何回調函數
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cb_nict_XXX_sent：其中XXX表示一下幾種消息類型，
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表示一下幾個值
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狀態機
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IST_PRE_PROCEEDING
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IST_CONFIRMED
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IST_COMPLETED
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IST_TERMINATED
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Transaction initialization
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IST_PROCEEDING
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cb_ist_invite_received
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cb_ist_Nxx_sent
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圖2-4: IST State Machine
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cb_ist_ack_received
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cb_ist_1xx_sent
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cb_ist_transport_error
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cb_ist_2xx_sent
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cb_ist_ack_received2
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cb_ist_3456xx_sent2
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cb_ist_invite_received2
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cb_ist_kill_transaction
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cb_ist_transport_error
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cb_ist_xxx_xxxx
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表示從一種狀態轉換到另一種狀態時將調用該回調函數
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表示從一種狀態轉換到另一種狀態時不調用任何回調函數
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cb_ist_Nxx_sent：其中N表示一下幾個值，
3 -- cb_ist_3xx_sent
4 -- cb_ist_4xx_sent
5 -- cb_ist_5xx_sent
6 -- cb_ist_6xx_sent
2.2.5 NIST狀態機
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NIST_PRE_TRYING
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NIST_COMPLETED
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NIST_PROCEEDING
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NIST_TERMINATED
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Transaction initialization
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NIST_TRYING
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cb_nist_XXX_ received
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cb_nist_1xx_sent
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圖2-5: NIST State Machine
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cb_nist_Nxx_sent
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cb_nist_kill_transaction
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cb_nist_transport_error
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cb_nist_1xx_sent
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cb_nist_Nxx_sent
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cb_nist_transport_error
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cb_nist_request_received2
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cb_nist_request_received2
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cb_nist_xxx_xxxx
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表示從一種狀態轉換到另一種狀態時將調用該回調函數
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表示從一種狀態轉換到另一種狀態時不調用任何回調函數
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cb_nist_XXX_ received：其中XXX表示一下幾種消息類型，
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表示一下幾個值
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
oSIP的SIP Parser處理的SIP頭域(SIP Header fields)及其相應的操作功能列表如下：
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SIP Header(頭域)
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Functions(函數名稱—簡寫)
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Accept
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set(),get()
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☆
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Accept-Encoding
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set(),get(),init(),parse(),2char(),free(),clone()
Getelement(),setelement()
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☆
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Accept-Language
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set(),get()
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☆
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Alert-Info
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set(),get()
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☆
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Allow
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set(),get()
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☆
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Authentication-Info
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Authorization
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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()
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☆
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Call-ID
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set(),get(),parse(),2char(),free(),clone(),getnumber(),
setnumber(),gethost(),sethost()
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☆
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Call-Info
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set(),get(),init(),parse(),2char(),free(),clone(),
geturi(),seturi()
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☆
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Contact
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set(),get(),init(),parse(),2char(),free(),clone()
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☆
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Content-Disposition
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set(),get(),parse()
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☆
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Content-Encoding
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set(),get()
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☆
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Content-Language
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Content-Length
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set(),get(),init(),parse(),2char(),free(),clone()
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☆
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Content-Type
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set(),get(),init(),parse(),2char(),free(),clone()
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☆
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CSeq
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set(),get(),init(),parse(),2char(),free(),clone(),
getnumber(),setnumber(),getmethod(),setmethod()
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☆
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Date
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Error-Info
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set(),get()
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☆
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Expires
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From
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set(),get(),init(),parse(),2char(),free(),clone(),
getdisplayname(),setdisplayname(),geturl(),seturl(),
param_get(),param_parseall(),param_setvalue(),
param_getvalue(),param_getname(),param_setname(),
compare()
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☆
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In-Reply-To
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Max-Forwards
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Min-Expires
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MIME-Version
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set(),get()
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☆
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Organization
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Priority
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Proxy-Authenticate
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set(),get()
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☆
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Proxy-Authorization
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set(),get()
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☆
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Proxy-Require
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Record-Route
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set(),get(),init(),parse(),2char(),free()
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☆
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Reply-To
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Require
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Retry-After
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Route
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set(),get(),init(),parse(),2char(),free()
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☆
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Server
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Subject
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Supported
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Timestamp
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To
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set(),get(),init(),parse(),2char(),free(),clone()
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☆
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Unsupported
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User-Agent
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Via
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set(),append(),get(),init(),free(),parse(),2char(),
setversion(),getversion(),setprotocol(),getprotocol(),
sethost(),gethost(),setport(),getport(),setcomment(),
getcomment(),clone()
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☆
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Warning
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WWW-Authenticate
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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()
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☆
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注：標示“☆”表示oSIP支持該頭域(SIP Header fields)解析處理，未注的表示目前還沒有解析處理（這些被保存在字符串中，可自行處理分析），可能會在後續版本中逐步補充。
SDP的格式一般爲：
<type>=<value>
type通常爲一個英文字母，其取值如下（按照RFC2327,帶“*”的表示爲可選條目）：
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中處理的type和相應操作功能如下：
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type(類型)
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Functions(函數名稱—簡寫)
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v
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version_set(),version_get()
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o
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origin_set(),username_get(),sess_id_get(),
sess_version_get(),nettype_get(),addrtype_get(),
addr_get()
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s
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name_set(),name_get()
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i
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info_set(),info_get()
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u
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uri_set(),uri_get()
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e
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email_add(),email_get()
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p
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phone_add(),phone_get()
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c
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connection_add(),connection_get(),nettype_get(),
addrtype_get(),addr_get(),addr_multicast_ttl_get(),
addr_multicast_int_get()
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b
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bandwidth_add(),bwtype_get(),bandwidth_get()
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t
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time_descr_add(),start_time_get(),stop_time_get()
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r
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repeat_add(),repeat_get()
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z
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adjustments_set(),adjustments_get()
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k
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key_set(),keytype_get(),keydata_get()
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a
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attribute_add(),att_field_get(),att_value_get()
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m
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media_add(),media_get(),port_get(),number_of_port_get(),
proto_get(),payload_add(),payload_get(),
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另外，oSIP還包含對SDP包的一些基本操作[set(), get(), init(), parse(), 2char(), free(), clone()],及對各類type的init()和free()操作
這裏的URL是指SIP中的URI，URI有很多參數格式，在RFC3261中列舉了一些比較例子：
The URIs within each of the following sets are equivalent:
sip:[email protected];transport=TCP
sip:[email protected];Transport=tcp
sip:[email protected];newparam=5
sip:[email protected];security=on
sip:biloxi.com;transport=tcp;method=REGISTER?to=sip:[email protected]
sip:biloxi.com;method=REGISTER;transport=tcp?to=sip:[email protected]
sip:[email protected]?subject=project x&priority=urgent
sip:[email protected]?priority=urgent&subject=project x
The URIs within each of the following sets are not equivalent:
SIP:[email protected];Transport=udp (different usernames)
sip:[email protected];Transport=UDP
sip:[email protected] (can resolve to different ports)
sip:[email protected]:5060
sip:[email protected] (can resolve to different transports)
sip:[email protected];transport=udp
sip:[email protected] (can resolve to different port and transports)
sip:[email protected]:6000;transport=tcp
sip:[email protected] (different header component)
sip:[email protected]?Subject=next%20meeting
sip:[email protected] (even though that's what
sip:[email protected] phone21.boxesbybob.com resolves to)
在oSIP中處理SIP URI有比較多的操作函數提供，主要有對host,port,username,password, scheme的get()和set()，以及對參數的初始化設置和剖析處理。詳細函數名稱請參考源代碼中的url.h。
SDP協商工具(SDP negotiator)幫助end point提供協商codec等功能
對話管理工具(Dialog management)是oSIP提供的一個比較強大的輔助工具，主要用於有能力應答呼叫的end point。
對話管理工具(Dialog management)能夠幫助記錄請求和響應消息，利用這個工具使end point能夠快速準確的作出應答。
3. oSIP特點
3.1 oSIP的優點
n Osip沒有給開發者限定在特定的某個執行模式下，能夠使開發者選定一個比較適合自己的模式。
n Osip的各個模塊是相對清晰、獨立的，因而去掉某個模塊時也比較容易。
n Osip的解析器提供了較爲完善的API，包含了消息的構造、修改和產生等。
3.2 oSIP的缺點
¨ oSIP目前版本源代碼結構、定義比較混亂，並且缺乏文檔，閱讀比較困難；該問題將在oSIP2中得到改善。
¨ oSIP不提供任何快速產生請求消息和響應消息的方法，所有請求消息和響應消息的形成必須調用一組sip message api來手動組裝完成，關於這方面的缺陷，osip作者可能在以後會開發一個eXoSIP的API來完成。
¨ 由於oSIP結構簡單，外圍相關模塊需要用戶自己開發，如SIP消息的接收和發送，RTP/RTCP的語音數據的處理等。
4. oSIP應用結構圖
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Receive/Send
SIP Messages
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SIP parser
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URL parser
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SDP parser
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Finite
State
Machines
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Dialogue Facilities
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SDP negotiation
Facilities
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Main thread
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狀態機模塊
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解析器模塊
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工具模塊(可選項)
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oSIP模塊
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圖4-1 oSIP應用
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Receive/Send
RTP/RTCP
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oSIP
Instance
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Transaction
Context
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①
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②
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③
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⑥
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④
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⑤
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⑦
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B
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A
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Application
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其中：
①：初始化oSIP和註冊CALL BACK函數；
②：添加事件A;
③：執行事務
④：取消事件A
⑤：解析消息
⑥：觸發CALL BACK函數
⑦：接收/發送消息
A：保存狀態
B：接收/發送語音包
5. oSIP使用概述
5.1 初始化oSIP
在使用oSIP前必須先初始化oSIP，主要調用函數
osip_global_init()和osip_init()，具體操作代碼如下：
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; |
需要註冊的call back函數主要包含發送消息、結束事務、發送失敗、4個狀態機(ICT、NICT、IST、NIST)相關函數。
註冊發送消息的CALL BACK函數：
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osip_setcb_send_message(osip, &application_cb_snd_message);
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註冊結束事務的CALL BACK函數：
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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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註冊發送失敗的CALL BACK函數：
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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);
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註冊ICT、NICT、IST、NIST CALL BACK函數
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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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在註冊完CALL BACK函數後，應用程序可以建立Transaction來調用oSIP的解析器和狀態機模塊的操作，來實現不同應用程序的需求。
6. 參考
[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/