sip

– the confluence of IP speech and data (IPT)
　　
　　
　　
Compose establishs a complete, IP phone framework that can expand is the job that we should finish in this article.
　　
　　
　　
Consultative foundation:
　　
Current, a lot of agreements reach consultative a group of things with common features to support in group speech technology, their some needs mutual cooperation, some but complete support Voip, some is no good. They include H323, SIP, Skinny, MGCP to wait, we understand the in-house framework of all agreements impossibly, so these agreements are in try in us approach is quiet cooperation concerns between them, act a part (in in group in speech technology) , optional / when selecting the issue such as the gender surely, feel puzzle, next we try systematic introduction and comb the relation between them:
　　
　　
　　
H.323:
　　
It is a whole agreement a group of things with common features, h. 3 2 3 is an international Telecommunication Union (I T U) standard, to be based on in group the frequency on network infrastructure, video and data communication provide a basis. It is the IP network that is supported extensively most and imitate network between coal body bridge. It can finish minute of group speech independently in almost all things, so its system also is giant. . H.3 2 3 offers speech the standard such as control of changeover of control of encode, simple bandwidth management, license, address, call and management and exterior network link. Bound of Vo I P adopts H. Standard of 3 2 3, realize the each other operation of much manufacturer equipment hard. Chinese net is in charge of forum Bbs.bitsCN.com
　　
Its consultative component includes:
　　
1, coal aspect is relevant
　　
H.261 and video of H.263 – code;
　　
G.711, g.723, frequency of G.729 – codes. ;
　　
Body of coal of RTP/RTCP – circulates be defeated.
　　
2, data / fax
　　
T.120 – is counted child the conference
　　
T.38 – is faxed
　　
3, call control and letter make
　　
Capacity of H.245 – / ability announce, coal body passageway is built, conference control.
　　
H.225
　　
Letter of call of Q.931 – makes be built with call.
　　
RAS – is registered, license and condition, nod with Yu Duan (terminal and gateway) with the agreement between G ATEKEEPER. It is used to carry out from inside G ATEKEEPER register, permissive control, the function such as bandwidth change, status change and detached end points.
　　
　　
　　
Be worth what carry is the development with mature already H.323 to the 4th edition, introduce truly in this edition 』 dumb 』 media gateway concept, parted the control function of gateway and gateway namely (cent becomes MG and MGC) , it is become by MGCP and MDCP confluence, the standard is H.248. By this token is very so difficult these 2 agreement a group of things with common features (H.323 and MGCP) part thoroughly and work independently, they go up to often also coexist chime is made in actual network.
　　
　　
　　
Everybody may know H.323 part component includes: Gateway of H.323 terminal, H.323 (Gateway, GW) , the net is defended (Gatekeeper, GK) , MCU (many bits of control is unit) , about H.323 terminal and H.323 gateway I think need not give uncecessary details, MCU often is the one part of GK in actual VOIP implementation, its role is very specific also: Control many bits of conference and group to sow. We often deceptive is GK, it is considered as the most useful component in H.323, where be but don’t we know it should be decorated, ? Perhaps deny this to be decorated? Such really, in it and consist in M G C P, call Call Agent call to act as agent (the concept that call acts as agent now is mixed to replace by confluence of concept of controller of MGC media gateway gradually) special likeness. Distinction is MGC it is pair of MG and SG (here involves SG to believe your gateway again: It offers H. What 3 2 3 and SS7 ISUP letter make operate is mutual cooperate. As call representative it also was mixed to replace by MG confluence) undertake controlling, and the GK of H.323 is pair of H.323 in IP network the operation undertakes controlling, include MG and H.323 terminal. In character of the GK in CISCO implementation the one part that is CCM3.3, as a result of the reason of technical type selecting, the RAS character that Cisco did not use GK truly will finish terminal and MG (media gateway) register, license, management. The GK option in CCM basically uses the control that finish other CCM group, implementation bandwidth is controlled and call allocation, use control CCM namely (Cisco Callmanager) . It is actually in a simple VOIP implementation, GK is optional really, if do not choose it so what you use is media end points (the Cisco2600 road that serves as MG for instance by implement) the direct call that picks a way by oneself believes your way by. Best example dials with respect to the VOIP that is Cisco quits body configures a concept.

　　
　　
　　
MGCP:
　　
Be by group of Internet project assignment (I E T F, internet Engineering Task Force) the media gateway that announces dominates a deliberation. MG C P uses at centralizing control: Gateway of Vo I P, the network accepts server and circuit trade. Character of place of name of no less than, its special skill is to pass MG and gateway of MGC control media, apply to the use of large-scale IP phone. It often with H.323 network of consist in VOIP is medium at the same time, it can come true with H.323 alternant, right now, its MGC (or call acts as agent) with a H. Net of 3 2 3 is defended (GK) the identity has the job. Such processing are mixed H. The function that net of 3 2 3 defends keeps consistent, need pair of H namely. Terminal of 3 2 3 undertakes address changeover and call dominate a service. CISCO recommends use MGCP to regard the control of VOIP gateway as the agreement, actually the product of major speech gateway of CISCO (include Cisco 26/36/3700, VGA200, Catalyst4200 to wait) acquiescent support it.
　　
　　
　　
SIP:
　　
Be turn for now in group the 3 big competitors of speech technology (H.323, MGCP, SIP) also be last in most 』 young 』 』 hale 』 』 have an outlook 』 a: SIP (agreement of conversational and initiative word) came on the stage. S I P is to be used at what Internet conference and phone serve to believe your agreement simply. It is based on S M T P and HTTP, it is to be in IETF is various multimedia conversation is controlled (M M U S I C) the development in the working group rises. It defined the course of Internet electrify word and multimedia conference. S I P is applied layer agreement. S I P is afterwards the client is based on after the S M T P that is based on text and HTTP agreement / the model of server structure. In the client / in server structure, client computer initiates call, the server answers call. Through abiding by these already some Internet standards that are based on text, breakdown is diagnosed and the network is debugged become very simple. System of S I P includes two shares: User representative and network server.

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The user acts as agent (U A) it is the S I P that form and receives call of S I P, it includes:
　　
　　 ．Client computer is called user representative client computer (U A C) , it is used to initiate request of S I P.
　　
　　 ．The server is called user representative server (U A S) , it receives the request that comes from U A C to be returned to the user send answer.
　　
S I P has the network server of two kinds of types:
　　
　　 ．Acting server
　　
　　．Weigh directional server
　　
Advantage:
　　
　　 ．Simple and easy sex
　　
　　．But expansibility
　　
　　．Modular S I P is had very tall modular degree.
　　
　　 ．Can upgrade quality
　　
　　．Compositive sex because S I P can sort We B, email, media application and other agreement compositive arrive one case.
　　
　　
　　
Simple point says it is direct IP terminal (like IP Phone, Netmeeting, MSN) between the simplest and feasible speech treats an agreement. It often coexists with MGCP cooperation in order to support the communication between more intricate VOIP network. CISCO also sees its advantage, the Cisco in the IPT network that so CCM and IP Phone form also uses SIP to complete call, right now IP Phone is an UA, and CCM acts UAS. It is OK to should expand the round area load that supports 10000 IP telephone call also is true so of implementation. (simple also be to should pay price, it is poorer to imitate network support on one hand, because be,send through proclaimed in writing on the other hand, the VOIP conversation that I think SIP comes true is put in serious safe hidden danger, withstand the assault such as electronic deceit and bag replay very hard. )

　　
　　
　　
Skinny:
　　
『Thin 』 the client carries an agreement. Basically use as in the IPT network of Cisco Cisco Ip Phone to the enrollment between CCM / administrative agreement. Actually Skinny also can pass SCCP (Skinny Client Conrtroll Protocol) will manage and control MG, but if the ability on DT12+ supports,this already was old speech gateway equipment. Cisco does not prepare to support it again.
　　
　　
　　
SS7:
　　
S S 7 is at present the in order to in PSTN public network is built cover with the agreement that terminates phone call. Application of S S 7 exchanges a network at the bag, this kind of network uses appropriative link, node and device below most circumstance. Normally, of correlation of dispute of S S 7, your network is believed outside common signal channel, belt. But, s S 7 can be on the link that carries speech discharge, the course is true or fictitious circuit is transmitted. To SS7, network engineer knows it but need not have a good command of however it, be in only with PSTN network take on lease it is involved when circuit, the article explains in detail no longer, if have fun at,can consult ULTRA forum another article about SS7: Http://www.ultratechnology.net/forums/showthread.php? S=&threadid=15889&highlight=ss7
　　
　　
　　
Come here, we can have seen the agreement of the IPT framework of Cisco comes true: IP Phone is registered to CCM through Skinny, win license and limits of authority, use SIP agreement establishs conversation and communication, pass MGCP or H.323 management gateway, use GK manages the bandwidth of CCM and group to allocate.
　　
　　

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We spent above principle of very big length introduction VOIP and agreement, the intercrop that waits in H.323, MGCP, SIP of a clarity elaborate, this itself is a complex and troublesome theme, have inadequacy and wrong place for certain so, hope everybody offers make a comment or criticism. But this one pace is significant however: Promiscuous at the beginning to agreement and implementation not clear, and should design feasible, can expand and hale IPT network (or call VOIP the network) , it is very not easy impossible even. Next we will introduce product and character to come compose builds a specific IPT network.
　　
(unfinished. . . To be continued)
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