H.323 and SIP are the main IP signaling protocols for voice and video coding within corporate networks. The first was developed by IТU before SIP was released, while the second is recognized as the IЕTF standard. Despite the apparently similar principle of operation, these protocols have become competitive due to gradual packet network expansion. Thus, which one is better? Let’s find it out.
H.323 Definition
H.323 is one of the oldest standards used for VoIP telephony and video conferencing. This is a set of protocols that enables point-to-point or point-to-multipoint media streams transmission over computer networks with unguaranteed bandwidth.
The H.323 recommendation provides a variety of communication options: from voice telephony to full-fledged video conferencing, with the ability to send and transmit media streams.
Fundamental components of H.323:
- Terminal – a device or software product that transmits multimedia data directly to the endpoint.
- Gateway – the connecting path between networks or different standards endpoints that provides two-way communication.
- Gatekeepers – auxiliary devices that perform a number of additional functions, such as user authentication, endpoints registration, and communication.
SIP Definition
SIP (Session Initiation Protocol) is a technology that allows telephone network subscribers to communicate with each other, exchange multimedia, make video calls, and send messages. Information is transmitted over IP (Internet Protocol).
Key functional elements of SIP:
- User-Agent which consists of a User Agent Client (UAC) that sends SIP requests and a User Agent Server (UAS) that sends responses to such requests.
- Proxy Server – is a device that receives and processes requests from endpoints and performs corresponding actions within the network.
- Redirect Server – is a device that keeps a record of the current endpoints and proxy servers location in the network.
- Location Server – is a database of address information needed to provide personal mobility for users.
H.323 vs SIP Comparison Table
Let’s compare H.323 and SIP:
| Basis of Comparison | H.323 | SIP |
| Designer | ITU | IETF |
| Origins | Telephony | Internet |
| Architecture | Monolithic | Modular |
| Scalability | Less scalable | More scalable |
| Network intelligence | Provided by the gatekeeper | Provided by servers |
| Encoding | Binary | Text (similar to HTTP) |
| Signaling protocol | TCP | TCP or UDP |
| Media protocol | RTP | RTP |
| Conferencing | Via MCU | Via IP multicast |
| Complexity | Less scalable and flexible, difficult to implement and adapt | More scalable and flexible, easy to implement and adapt |
SIP is a human-readable protocol, so SIP is simpler than H.323 when developing and supporting software. Google Trends information also confirms the popularity of this protocol.
Can SIP Completely Replace H.323?
Yes! Every H.323 extension already handles an SIP extension. Session Initiation Protocol is more flexible in this respect (for example, when adding a new field: if someone does not understand it, it is simply ignored). Major hardware solutions support both protocols.
Basically, H.323 and SIP are functionally equivalent when it comes to video conferencing solutions development.
Nevertheless, the transition to SIP is not a panacea for the problems of incompatibility between the solutions made by different producers (during functional fixes). This problem is inherent in any protocol on the video conferencing market, including H.323.
Manufacturers are not particularly interested in the compatibility of proprietary extensions. They cannot afford to be completely incompatible, but try to limit the maximum compatibility. A good example is Microsoft Lync: SIP connections are limited to CIF at much higher theoretical possibilities.
One of the most important points is to provide security of transmitted data. One of the sections of RFC 3261 is dedicated to the security concerns of SIP. Traffic signal encryption via TLS is possible at the transport layer. In addition, a standard SIPS, imposing additional agreements on the safe transfer of data through SIP. For multimedia content, SRTP encryption protocol is used.
What Protocol is the Best for Video Conferencing?
Both H.323 and SIP are respectively used for holding video conferencing sessions. That’s why the majority of online meeting solutions support both of these protocols, enabling users to choose the best for fitting their actual communication needs.
TrueConf Server also allows you to communicate via SIP and H.323 endpoints, as well as connect to conferences hosted on third-party services. Plus, this platform uses a proprietary protocol based on SVC technology that generates multiple video stream layers, from the main layer (with the lowest bitrate) to many additional ones that drastically improve final picture quality. As a result, every meeting participant gets the best possible video and audio quality.
The SVC architecture has taken video communications beyond expensive conference rooms. Now we can enjoy high-quality video collaboration and stable operation on any device wherever you are.
