Here we are going to explain that H.323 and SIP protocols. For this we need to learn to compare, then look at the specific content of it.
In the communication network, we should know that H.323 and SIP. So for these two aspects of the agreement we have here is simply to find out. At present, the main international standard IP network communications are H.323 and SIP, both for IP telephony signaling system presents a complete solution. But both the design style is different, H.323 uses a traditional telephone letter order patterns, including a series of agreements; and learn from internet SIP protocol, the use of text-based protocol.
When using H.323 protocol, various manufacturers of multimedia products and applications may operate with each other, the user does not have to consider compatibility issues; and the SIP application more flexible, scalable two different emphases.
Structural differences system
Firstly, the structure of the system. In the H.323 system, provides data to the terminal main communication medium, relatively simple, and realize the control of the call, the media transmission control functions are mainly done by the gatekeeper .H. 323 system embodies a centralized, hierarchical control mode.
SIP uses the Client / Server architecture message mechanism, control of the call control information is encapsulated into a message header field, is achieved by passing messages. SIP terminal system thus is more intelligent, it provides not only data, but also providing call control information, various other servers are used for positioning, forward or receive messages. Thus, the complexity of the SIP network devices into a network terminal device, and therefore more suitable for building intelligent system reflects the user terminal .SIP It is a distributed control mode.
In contrast, H.323 manageable centralized control mode, like billing management, bandwidth management, call management to implement in a centralized control is more convenient, it is easy to cause a bottleneck limitations while SIP distribution pattern is not easy to bottlenecks, but the management is more complex to implement.
Sub-areas of application
H.323 and SIP protocols are implement a communication protocol .H.323 VoIP and multimedia applications developed to provide the VoIP service substituted ordinary telephone and video communication systems for the user over the packet switched network. SIP was developed to be used provide advanced telephony services across the Internet. locate these two protocols have some overlap, and with the agreement to develop in depth, which coincides with intensifying competition in the relationship, but both aim to be achieved is the same, it is to build IP multimedia communication network. Depending on the method they use, so they are compatible with each other is not possible, there is only interoperability problems between the two.
H.323 is a standard part of the ITU (ITU), in order to build H.323 standard for multimedia communications network is easily compatible with traditional PSTN telephone network, this point of view, H.323 is more suitable for large carrier-class building net. almost all of the commercial telephone network or IP video conferencing networks are based on the H.323 international basis. Moreover, different versions of the H.323 protocol through continuous upgrading and expansion, has been maturing, based H.323 IP multimedia services provide a good protection.
SIP is submitted by a number of Internet enthusiasts, the agreement is relatively simple, but the function is relatively simple. Also, update the SIP with respect to the H.323 protocol is also lagging behind. At present, there are many operators are taking advantage of SIP trial network building, but if you want to use to build carrier-class SIP big network, it must be added that to improve, so that SIP will inevitably become complicated. in fact, the development trend is the case of SIP. SIP can also be widely used to promote the evolution of next generation networks.
Life experience of the other
H.323 protocol was developed by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), and based telecommunications network signaling protocol developed IP multimedia standards, rather than IP phones specifically raised. But IP telephony, in particular via the telephone gateway to this way of working the phone, it can be recommended to implement H.323, H.323 protocol and therefore are often "borrowed" as a standard IP phones.
IP for multimedia applications (such as IP telephony or video conferencing), it not only with the H.323 protocol, but also with a series of agreements, including H.225, H.245, H.235, H.450, H. 341, etc. H.323 protocol is just "general technical requirements", which is usually the IP telephony or video conferencing in this way is called H.323IP telephone or video conference .H.323 H.323 protocol is a more comprehensive agreement it provides a centralized mode of treatment and management. this mode of operation and management of telecommunications network is adapted, especially for building end-to-end IP telephone network or video conference network theory and practice show, H.323 has the ability to make an arbitrary scale IP telephony systems and video conferencing systems.
SIP is a protocol proposed by the Internet Engineering Task Force (IETF), which uses the existing IP network protocol to provide multimedia services, is a parallel with the H.323 protocol. Compared with H.323 system, its role is similar to H. 225.0.SIP simple, good scalability and existing Internet applications and features closely.
SIP is the starting point want to existing Internet-based telephone service to IP network architecture. Therefore, SIP and H.323 has a completely different design concept, it is a decentralized protocol, aptitude complex network edge push network equipment compared to the H.323 protocol-based IP telephony, SIP requires a relatively intelligent terminal. for applications user terminal non-intelligent terminal can also be used as a SIP call signaling, this would greatly weaken the unique advantage of SIP, therefore more suitable for intelligent SIP user terminals. in addition, consider adding front-end way before the user to replace the telephone gateway device, the cost of doing so is to increase the cost of front-end users to buy.
Direction of development
Currently, many countries including China have adopted H.323 as the protocol between the IP telephony gateway. IP phone system just put the entire IP network as a transmission medium, on the user's access to or the use of circuit-switched system, and the IP telephony gateway as a circuit-switched network and IP network interface. At the same time, most telecom operators have established as the preferred next-generation H.323 video conferencing system, the traditional circuit-based H.320 video conferencing applications to transfer H.323 systems to IP-based applications from the scale says, in reality telecommunications operations, H.323 VoIP and multimedia communication has become the de facto dominant protocol.
At the same time, taking into account the next generation network, because IP and IP gateway products will be large-scale use and integrated in the network, so that the end can adopt IP, in order to achieve a pure IP business applications. And based on pure IP the SIP draws HTTP (hypertext transfer protocol) and SMTP (simple Mail transfer protocol), a simple structure and is scalable and scalability. in addition, SIP also provide good QoS (quality of service) support for the IP NGN implement VoIP and multimedia communications network is concerned, SIP has a unique advantage in the application characteristics to meet the full requirements of NGN, VoIP will become an important next-generation network solutions.
Currently, the market support SIP products (especially terminals) more and more, there has been based on a variety of enterprise-class application solutions SIP call centers, video conferencing and so on.
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Currently, VoIP communications protocol is divided into two camps: SIP and H.323. H.323 attempt to IP telephony is well known as a traditional phone, but transmission has changed into a packet switching by the circuit switching. Focused on the SIP protocol IP telephony as an application on the Internet, than other applications (e.g., FTP, E-mail, etc.) and increases the signaling of QoS requirements, substantially the same operations they support, are also transmitted using RTP as a media agreement. But H.323 is a relatively complex protocol.
Using H.323 message indicates which compression method based on binary and ASN.1 encoding rules. ASN.1 typically require special code generator performs lexical and syntax analysis. The SIP is a text-based protocol, similar to HTTP. Encoding means based on the meaning of the text header fields are straightforward, such as From, To, Subject and other domain name. Standard Specification for this style distributed, almost no complex documentation, and its advantages have been well documented (now widely popular SMTP mail protocol is one such example) in the last practice. SIP uses SDP message body portion will be described, each of the SDP format = a, it is relatively simple.
In support of the conference call, H.323 due controlled by a multi-point unit (MCU) centralized executive session control function, all terminals participating in the conference are to send control messages to the MCU, MCU may be the neck, especially for large meetings with additional features ; and 323 do not support multicast signaling function, the single function limits the scalability, reliability is reduced. And the SIP call design is distributed model with distributed multicast function, which is not only easy to multicast session control, but also simplifies the user location, group invitation, etc., and can save broadband. However, to facilitate the billing H.323 centralized control, bandwidth management is relatively simple, and effective.
H.323 protocol is defined for the specific supplementary services, such as H.450.1, H.450.2 H.450.3, and the like. SIP protocol did not specifically defined for this purpose, but it is very easy to support supplementary services or intelligent service. As long as the full use of SIP header fields defined (such as the Contact header field), and a simple SIP extensions (such as increasing the number of domain), you can implement these services. For example, call forwarding, as long as the BYE request message to add the Contact header field, intended to go to third-party address of this service can be achieved. For business expansion by some clever header fields more difficult to achieve, you can increase the business agent in architecture, provide some additional service interface or with intelligent network devices.
In H.323, call establishment procedure involving the third signaling channel: RAS signaling channel, the call signaling channel and the H.245 Control Channel. By coordinating the three H.323 channel that makes a call to be carried out, a very long call setup time. In SIP, and the session process together with the request for media negotiation process. Although H.323v2 has been improved call setup process, but compared to SIP requires only 1.5 loop delay to set up the call, still can not be compared. H.323 and H.245 call signaling channel transport protocols require reliable control channel. SIP is independent of the lower layer protocol, such as UDP protocol generally used can not be connected with its own reliability mechanism to ensure reliable signaling transport layer message.
In short, follow a traditional H.323 for telephony signaling mode, more mature, there have been a lot of H.323 products. H.323 line with the traditional design communications, centralized, level control, connected using H.323 protocol to facilitate the traditional telephone network. SIP protocol draws on the design of other Internet standards and protocols of the Internet to follow consistent and concise in style, open, compatible and scalable principles, is relatively simple.
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SIP stands for the Session Initiation Protocol and is described by the rfc3261 (wich deprecates rfc2543). This library aims to provide multimedia and telecom software developers an easy and powerful interface to initiate and control SIP based sessions in their applications. SIP is a open standard replacement from IETF for H323.