This post is about the differences between H.323 and SIP. Please see below for details.
H.323 and SIP are protocols used in the communications field and the Internet domain respectively. Both protocols have requirements for voice coding and decompression. They provide a complete solution to the (VoIP) signaling of the IP network telephone system. They have the capability of establishing, managing, and releasing call connections, and have the functions of network management and capability exchange, the call setup and interaction of end users have the QoS capability, and the new functions are easy to be expanded to support different types of interoperation.
H.323 and SIP have a lot in common and have certain overlap in positioning. In addition, H.323 and SIP have become the two competing protocols in the packet network because of the development of the protocol and the rapid expansion of the network. What are the differences between H.323 and SIP?
What is H.323
H.323 is an agreement proposed by ITU-T Working Group 16, which is a set of agreements. There are signaling for encoding, decoding, and encapsulation of voice and video signals, signaling for sending and receiving call signaling, and signaling for capability exchange. The H.323 protocol family defines the components, protocols, and procedures for providing multimedia communication on a packet switched network PBN (such as an IP network).
H.323 supports point-to-point or point-to-multipoint communication of audio, video, and data. The H.323 protocol family includes an H.225.0 for establishing a call, an H.245 for control, an H.332 for a large conference, an H.450.X for supplementary services, a secure H.235, and an H.246 for interworking with a circuit switched service.
What is SIP
SIP (Session Initiation Protocol) is an applicatication control (signaling) protocol implemented by the IETF MUSIC team in 1999 to implement real-time communication. It can be used to create, modify, and terminate multimedia session processes involving multiple participants. The (Session) refers to the data exchange between users.
The members participating in the session can communicate in multicast mode, unicast network mode, or combination mode. It is a part of the Internet multimedia communication and control protocol system, including the Session Description Protocol (SDP), Session Release Protocol (SAP), and Session Initiation Protocol (SIP). Such sessions can be voice, video, text chat, interactive games, or even virtual reality.
The basic structure of the SIP network consists of the user agent and IP network. The IP network includes various network servers required by the SIP system. The user agent has the user agent client (UAC) and the user proxy server (UAS). There are also two types of network servers, which are proxy servers and redirect servers.
What are the differences?
From the perspective of origin:
The fundamental power of the H.323 protocol is the integration of three networks. At that time, the IP technology and Ethernet technology developed rapidly. Many enterprises and enterprises had their own LANs. Therefore, a network with voice, video, and data services based on the Ethernet or IP network was urgently required. Therefore, the H.323 protocol came into being, it is an agreement in the communications field. The SIP protocol is a multimedia communication protocol based on computer and network proposed by computer workers in the case of rapid Internet development.
It is a protocol in the field of computer network. Because of different starting points, their control structure is also different. In terms of call control and signaling, H.323 mainly refers to the call control and signaling architecture of the traditional PSTN (public switched telephone network). The PSTN is a
hierarchical, master-slave, and centralized control mode for call control and signaling. The H.323 also uses this control mode. The Internet is a distributed, client/server, and horizontal control network. Therefore, the communication mode implemented by the SIP protocol is based on a distributed, client/server, and horizontal control structure.
Different design ideas, reference different standards and different development purposes, make the two major agreements distinctive. The H.323 protocol uses the ISDN design idea. It uses the Q.931 protocol to establish and release calls. It has the working mode of centralized processing and management of the telecommunication network, and has the capability of making an IP phone system of any scale. The H.323 development aims to provide users with VoIP and video communication services that replace common phones on the packet switched network.
As an IETF standard, SIP greatly draws on other widely used Internet protocols, such as Hypertext Transfer Protocol (HTTP) and Simple Mail Transfer Protocol (SMTP). It is also a text protocol.
Based on the experience of successful web services, the SIP protocol is used to construct the IP phone service network based on the existing Internet.
In terms of time:
H.323 is earlier than SIP. It is more strict than SIP in terms of management control and QoS mechanism, and is more complex.
The Internet Engineering Task Force (IETF) has formulated the SIP protocol based on the H.323. Compared with the H.323, the SIP is simpler, better expandable, and more closely related to the existing Internet applications.
The H.323 uses the traditional mode of implementing the telephone signaling, which complies with the traditional design idea in the communication field and implements centralized and hierarchical control. The H.323 protocol is used to connect to the traditional telephone network. Therefore, the related products are more abundant. Due to the short launch time, the SIP protocol is not as mature as the H.323 protocol. It is inconvenient to connect to many existing traditional networks. However, due to the excellent connectivity with the Internet, more and more emerging network products support SIP, which presents a broad development prospect.
The key to implementing IP telephony is the signaling protocol. According to the signaling protocol, the IP phone supported by the H.323 is not much different from the traditional telephone on the surface. The difference is that the circuit switching mode of the traditional telephone is changed to the current packet switching mode. SIP is an application that expands IP phones into the Internet. Compared with other network applications such as FTP and E-mail, SIP adds signaling and QoS requirements. From this perspective, both of them support the IP phone service and use the RTP (real-time transport) as the media transmission protocol.
From the coding method of the message:
The H.323 protocol supports the ITU-T standard and uses the binary method based on the ASN.1 and compression coding rules to represent the message. ASN.1 usually requires a special code generator for analysis, which is complex.
SIP has the capability to support any codec protocol. Because SIP is based on text, its code generation and syntax parsing are simple. Sip coding means that the meaning of the header is clear, such as From, To, and Subject, moreover, it also facilitates the extension and debugging of the protocol, improves the degree of user localization, and has fully embodied its superiority in practice.
The scope of use of H.323 and SIP
Currently, many countries, including China, use H.323 as the protocol between IP phone gateways. The entire IP phone system uses only the IP network as the transmission medium. The IP phone gateway is used as the interface between the circuit switched network and the IP network.
The H.323 adopts strict centralized control. The reliability is high and the call processing capability is reduced. This shows that the reliability of the H.323 is more flexible than that of the SIP. Therefore, SIP is usually used in mass instant messaging, such as individuals and enterprises, that have low reliability requirements. In the industry network, for example, for videoconferencing, H.323 is used.
In addition, the H.323 protocol is widely used in professional videoconferencing. This is because the videoconferencing technology is mainly used for videoconferencing service operation or internal videoconferencing. The network structure is hierarchical and domain-based.
H.323 is especially suitable for this structure, and H.323 is centralized control and facilitates charging, broadband management is simple and effective.
However, the H.323 is not perfect in application. The H.323 does not support the multicast function of the signaling. The function of the H.323 does not support the scalability and reduces the reliability. Compared with SIP, SIP is a distributed call model and has a distributed multicast function. The multicast function facilitates conference control, simplifies user positioning and group invitation, and saves broadband. In addition, SIP has a strong development space for conference calls, if a vendor uses a computer to implement the videoconferencing system, the SIP protocol is often used to implement the system. The SIP has received many responses, including communications device manufacturers and Internet service providers. They increasingly claim that their devices support SIP.
Can H.323-registered endpoints communicate with SIP-registered endpoints?
No.
The two protocols cannot communicate with each other. However, you can use dual registration. The endpoint registers with both H.323 and SIP. In this way, a dual-registration terminal can communicate with both the H.323-registered terminal and the SIP-registered terminal.
Let’s Sum Up
Although the H.323 protocol and SIP protocol propose two sets of IP phone system structures, they pursue the same objectives. They are completely independent of each other and cannot be compatible with each other. That is, only one of them can be selected in one implementation. Although the SIP protocol is later than the H.323 protocol and is formulated after analyzing many H.323 problems, SIP is not an upgrade version of the H.323. They are developed and modified separately based on different development application systems.
However, H.323 and SIP can communicate with each other. Different protocols can be used in different phases to achieve the best solution. From the development history of H.323 and SIP, they play an important role in the application of VoIP. Looking into the future NGN, both will play an important role.
Related topic:
H.323 sip
