传真SIP会话发起协议（SIP）

传真SIP会话发起协议（SIP）

SIP是一种用于在IP网络中创建会话的VoIP信令协议。一个SIP的传真会话可以是一个普通的电话或T.38传真呼叫，或者它可能是一个多媒体电话会议。SIP的传真，已发展为一种机制来建立会话，一个会话的细节，不知道它刚刚启动，终止和修改会话。这种简单的手段，SIP传真尺度，是可扩展的，相当不错，适合在各种架构和部署方案。SIP对话，为保证可靠性，排序或数据的完整性。因此，UDP提供anacts一个请求 - 响应协议，类似的互联网协议，超文本传输​​协议（HTTP），简单邮件传输协议（SMTP），驱动万维网和电子邮件的协议。传真SIP消息被编码为ASCII文本格式，适合人阅读。

尽管存在其他VoIP信令协议，SIP传真方式进行了标准化和管理主要由IETF（互联网工程任务组），而其他协议，如H.323，已经确定由国际电讯联盟（ITU），电话产业群。因此，SIP的特点是它的支持者有根的IP社会，而不是电信行业的。与H.323相比，SIP传真方法，在市场上具有强劲的发展势头，。然而，SIP传真通话和提供了一个松散的概念，有时不同的标准主要是整合到每个供应商。SIP传真方式作为一项成果，已成为一个载有不少的互操作性问题的协议 - 以及它与传真等问题。

T.38，ITU-IP传真（FoIP的标准），获得强大的采用在企业领域，因为它可以帮助企业降低通信成本，提高客户服务水平，并坚持合规性规则。然而，在过去的一年中，市场形势的FoIP的发展。在此之前，企业将创造一个IP局域网传真标准SIP或H.323的基础上，并把它连接到PSTN的网关通过。这使得很容易地实现IP传真，因为所有的企业需要做的就是安装一个网关的IP网络的边缘，IP传真服务器的IP传真电话网关的呼叫将被转换为传统的TDM流传真到目的地。因此，重要的是在本地网络上的网关转换的性能。然而，今天，企业和运营商的资本开支为电信主要方面的SIP传真基础设施，建立SIP中继的需求，并减少需要网关。SIP中继网关和替代的情况下导致的问题传真接入提供者和骨干IP网络的有效支持。

这并不是说，SIP传真方式有过错的。事实上，SIP的传真问题所产生的，因为成功的SIP。SIP，遵守不保证FoIP的将工作做好，通过SIP中继。这是，因为SIP传真供应商有时会执行不同的标准，可以创造真正的问题。

一些SIP提供商处理传真的交通，通过G.711，这是一个语音传输技术，已被改编进行传真通信。但是，这个计划是不是最佳的传真功能。T.38协议在IP网络上进行传真，保障措施，其中包括欺骗其他节点，所以他们没有意识到，一些数据包到达的顺序（传统的传真，语音通信一样，是一个真正的时间，一个简单的同步过程，这使得时间的到来传真信号情况。的IP过程是异步的。但是，数据通信流被分成数据包，不同的网络线路上传送的数据包，然后通过异步网络传真 - 在延迟，抖动和数据包丢失通常发生 - 可以增加传输失败。T.38使，它似乎传真节点通信的实时同步​​的方式。）

另外，许多IP网络还没有被优化的传真，而是为语音流量。用户数据报协议（UDP）是一种IP协议，通常用于SIP传真网络内。UDP使用一个简单的传输模式，没有隐含的握手对话，排序，数据的完整性，或保证可靠性。因此，UDP提供不可靠的服务，可能会出现重复的数据包，不按顺序到达，或完全失踪。但是，这种网络的特点，因为他们必须考虑影响的FoIP系统的呼叫成功在SIP传真功能的网络。对于优秀的传真优质的服务，建议网络的性能特点包括：

• 抖动应小于300毫秒
• 数据包丢失应等于零
• 单向延迟应该是小于150毫秒

网络测试应该被用来作为衡量的高低来决定在苏州工业园区传真网络FoIP的作战准备。

SIP Fax & The Session Initiation Protocol (SIP)

SIP is a VoIP signaling protocol used for creating sessions in an IP network. A SIP Fax session can be an ordinary telephone call or T.38 fax call or it could be a multi-media conference call. A SIP fax, having been developed as a mechanism to establish sessions, does not know about the details of a session, it just initiates, terminates and modifies sessions. This simplicity means that a SIP fax scales, is extensible, and fits reasonably well in various architectures and deployment scenarios. SIP dialogues for guaranteeing reliability, ordering, or data integrity. thus, udp provides anacts a request-response protocol and resembles two other Internet protocols, Hypertext Transfer Protocol (HTTP) and the Simple Mail Transfer Protocol (SMTP), protocols that drive the world wide web and email. SIP fax messages are encoded in ASCII text format, suitable for humans to read.

Although other VoIP signaling protocols exist, SIP fax methods have been standardized and governed primarily by the IETF (Internet Engineering Task Force), while other protocols, such as H.323, have been set by the International Telecommunication Union (ITU), a telephone industry group. So SIP is distinguished by its proponents having roots in the IP community rather than the telecommunications industry. SIP fax methodologies have strong momentum in the marketplace, compared with H.323. Nevertheless, a SIP fax offers a loose concept of a call and the integration of sometimes disparate standards is largely left up to each provider. As an outcome, the SIP fax method has become a protocol carrying quite a few interoperability problems – and it such problems with fax.

T.38, the ITU standard for Fax-over-IP (FoIP), is gaining strong adoption in the enterprise space, as it helps companies lower their communications costs, improve customer service, and adhere to regulatory compliance rules. However, in the last year, the market situation for FoIP has evolved. Previously, enterprises would create an IP LAN based on SIP fax standards or H.323 and connect it to the PSTN via a gateway. This made it easy to implement IP fax because all corporations had to do was install a gateway at the edge of the IP network and have the IP fax server make IP fax calls to the gateway, where the call would be converted to TDM streams for conventional faxing to the destination. So all that mattered was the performance on the local network and the gateway conversion. Today, however, enterprises and carriers are making capital expenditures for telecom largely in terms of SIP fax infrastructure, creating demand for SIP trunking and reducing the need for gateways. The absence of gateways and substitution of SIP trunking is causing problems with effective support of fax in access-provider and backbone IP networks.

This is not to say that SIP fax methods are at fault. In fact, SIP fax problems are arising because of the success of SIP. SIP compliance does not guarantee FoIP will work well over SIP trunks. This is because SIP fax providers sometimes implement disparate standards which can creates real problems.

Some SIP providers handle fax traffic via G.711 which is a voice transport technology that has been adapted to carry fax traffic.  But this scheme is not optimal for faxing.  T.38 is the protocol for carrying fax over IP networks and it has safeguards in it that include spoofing other nodes so they don’t realize that some packets arrive out of order (Conventional faxing, like voice communications, is a real-time, synchronous process, which makes timing the arrival of fax signals a straightforward situation. The IP process is asynchronous. However, data in the communication stream is broken into packets and the packets then sent over different network routes. Faxing over an asynchronous network – where delay, jitter and packet loss commonly occur – can increase transmission failures. T.38 makes it seem to fax nodes that a communication is coming in a real-time synchronous manner.)

Also, many IP networks have not have been optimized for fax, but rather for voice traffic. The User Datagram Protocol (UDP) is an IP protocol that is typically used within SIP fax networks. UDP uses a simple transmission model without implicit hand-shaking dialogues for, ordering, data integrity, or guaranteeing reliability. Thus, UDP provides an unreliable service and packets may appear duplicated, arrive out of order, or go missing entirely. But such network characteristics must be considered because they impact the FoIP system’s call success within a SIP fax enabled network. For excellent fax quality service, recommended network performance characteristics include:

• Jitter should be less than 300 ms
• Packet loss should equal zero
• One-way delays should be less than 150 ms

Network testing should be used as a gauge to determine the level of FoIP operational readiness in SIP fax networks.

http://www.allaboutfoip.com/sip.html