在我們學(xué)習(xí)SIP協(xié)議的過(guò)程中，對(duì)于一個(gè)概念要清楚，那就是SIP中繼的概念。為了讓大家更好地理解這方面內(nèi)容，我們采用中英文互譯的對(duì)照形式，幫助大家了解這方面的知識(shí)，具體資料如下：

A SIP Trunk is a logical connection between an IP PBX and a Service Provider’s application servers that allows voice over IP traffic to be exchanged between the two. When a call is placed from an internal phone to an external number, the PBX sends the necessary information to the SIP Trunk provider who establishes the call to the dialed number and acts as an intermediary for the call. All signaling and voice traffic between the PBX and the provider is exchanged using SIP and RTP protocol packets over the IP network.

一個(gè)SIP中繼是一個(gè)IP PBX和服務(wù)提供商的應(yīng)用服務(wù)器，使語(yǔ)音的邏輯聯(lián)系 IP流量 將兩者之間的交換。當(dāng)一個(gè)呼叫從內(nèi)部到外部電話(huà)放在號(hào)碼，交換機(jī)發(fā)送必要的信息提供者的SIP中繼誰(shuí)建立了調(diào)用撥打的號(hào)碼，并作為為調(diào)用中介行為。所有的信號(hào)和 語(yǔ)音通信 交換機(jī)之間的交換和提供者是通過(guò)IP使用SIP和RTP協(xié)議包 網(wǎng)絡(luò)。

If the number being called is a traditional PSTN telephone, the trunk provider routes the IP packets to a PSTN Gateway that is closest to the number being called, to minimize possible long distance charges. The provider can also terminate PSTN numbers, and route incoming calls for those numbers back to the IP PBX over the SIP can also Trunk. This allows businesses to offer local phone numbers in several geographical areas, but service them all from a single location.

如果數(shù)字被稱(chēng)為是一種傳統(tǒng)的PSTN電話(huà)，樹(shù)干提供IP數(shù)據(jù)包路由到PSTN網(wǎng)關(guān)是最接近的號(hào)碼被稱(chēng)為，以盡量減少可能的長(zhǎng)途電話(huà)費(fèi)。提供者也可以終止的PSTN號(hào)碼，并在園區(qū)路線(xiàn)為這些號(hào)碼來(lái)電返回的IP PBX還可以干。這使得企業(yè)能夠在幾個(gè)地理區(qū)域提供本地電話(huà)號(hào)碼，但服務(wù)從一個(gè)位置全部。

If the number being called can be reached over a SIP Trunk, the call does not need to be routed over the PSTN, but can be carried on the IP network end to end. Providers can deliver these calls to their customers for very little cost, and many offer them at no charge. Some service providers have agreements and exchange calls for each others customers directly over their IP networks. Where no such agreements are in place, calls are routed over the PSTN, even though both endpoints may ultimately be reachable over a SIP Trunk.

如果這個(gè)數(shù)字被稱(chēng)為可以通過(guò)一個(gè)SIP中繼達(dá)成共識(shí)，呼吁不須在PSTN路由，但可以對(duì)IP進(jìn)行 網(wǎng)絡(luò) 年底結(jié)束。供應(yīng)商可以提供這些客戶(hù)的要求非常低的成本，很多免費(fèi)提供他們。有些服務(wù)提供者直接通過(guò)IP網(wǎng)絡(luò)協(xié)議，為彼此交換客戶(hù)要求。如果沒(méi)有這樣的協(xié)議落實(shí)到位，呼叫路由在PSTN，即使這兩個(gè)端點(diǎn)最終可能超過(guò)一個(gè)SIP中繼到達(dá)。

The SIP Trunk can be provided by the Internet Service Provider, or by an independent Internet Telephony Service Provider. In fact, there can be several parties involved, each one providing a different part of the service needed to deliver the end-to-end communication: Internet access, SIP termination, PSTN gateway, etc.

該 SIP中繼 可提供的互聯(lián)網(wǎng)服務(wù)供應(yīng)商，或由一個(gè)獨(dú)立的 互聯(lián)網(wǎng)電話(huà)服務(wù)提供商。事實(shí)上，可以有幾個(gè)當(dāng)事人，每一個(gè)提供了所需提供的終端到終端的通訊：互聯(lián)網(wǎng)接入，SIP協(xié)議終止，PSTN網(wǎng)關(guān)等服務(wù)的不同部分

Because a SIP Trunk is not a physical connection, there is no explicit limit on the number of calls that can be carried over a single trunk. Each call consumes a certain amount of network bandwidth, so the number of calls is limited by the amount of bandwidth that can flow between the IP PBX and the provider’s equipment.

因?yàn)橐粋€(gè)SIP中繼不是物理連接，也沒(méi)有就可以在一個(gè)單一的電話(huà)號(hào)碼進(jìn)行明確的主干限制。每個(gè)調(diào)用都會(huì)消耗一定量的 網(wǎng)絡(luò) 帶寬，所以電話(huà)的數(shù)量是有限的帶寬，可以流動(dòng)之間的IP PBX和供應(yīng)商的設(shè)備的數(shù)量。

For marketing reasons, many providers associate a SIP Trunk with a single phone call. When you purchase such a SIP Trunk, it provides the ability to place one call at a time through the service provider’s network. Organizations purchase as many trunks as they need to support their specific needs,typically one trunk per 3-5 employees. Some providers allow several calls to be carried over a single trunk.

對(duì)于市場(chǎng)的原因，許多供應(yīng)商帶來(lái)一個(gè)單一的電話(huà)呼叫的SIP中繼。當(dāng)你購(gòu)買(mǎi)這樣一個(gè)SIP中繼，它提供了能夠在一個(gè)地方通過(guò)一次電話(huà)服務(wù)供應(yīng)商的 網(wǎng)絡(luò)。組織購(gòu)買(mǎi)盡可能多的樹(shù)干，因?yàn)樗麄冃枰С炙麄兊木唧w需要，一般每3-5員工主干。有些供應(yīng)商允許多次打電話(huà)給超過(guò)一個(gè)主干進(jìn)行。