SIP vs H323
Both communication protocols, SIP and H323, were introduced approximately the same time about 15 years ago, but there is some difference between SIP and H323 in their scope, thus leading to some other differences as well. SIP and H323 are both communication protocols used for multimedia calls and conferencing over internet protocol (IP) based networks. SIP supports other multimedia communications such as instant messaging, online gaming, and even file sharing, apart from multimedia conferencing, which it was originally designed for. However, H323 only focuses on multimedia conferencing. The fact that H323 has a constrained scope has made it less complex than SIP and make s is more interoperable. H323 has other advantages such as reliability, NAT traversal, flexible addressing, and load balancing over SIP.
What is SIP?
SIP, which stands for Session Initiation Protocol, is an application layer protocol used for VOIP (Voice over Internet Protocol). It is used for controlling multimedia communication sessions and, apart from VOIP, it can be used for other multimedia sessions like instant messaging, video conferencing, online games, fax over IP, and even for file transfer. SIP was introduced in 1996 and now it has been standardized by Internet Engineering Task Force (IETF).
SIP is a text-based protocol and it resembles features from other famous text based protocols like HTTP (Hyper Text Transfer Protocol) and SMTP (Simple Mail Transfer Protocol). SIP is independent on the lower layer protocols where it supports both UDP (User Datagram Protocol) and TCP (Transmission Control Protocol). It has the capability to be used together with TLS (Transport Layer Security) to provide encryption.
What is H323?
H323 is also an application layer protocol used for VOIP. This is widely used for audio and video conferences. This is not used for other purposes like application/file sharing, online games, but only focuses on multimedia conferencing, making it less complex than SIP. It was approved in 1996 by International Telecommunication Union (ITU) as a standard for multimedia conferencing over IP. This protocol is widely used by multimedia conferencing equipment manufacturers and also by multimedia conferencing service providers.
H323 is not a text based protocol, but a binary protocol where messages are compacted to binary, making ideal for narrowband connections. An advantage of H323 is the high level of interoperability it has. It has additional features and capabilities such as NAT traversal, support for multiple addressing schemes, load balancing and data conferencing. Also, it has mechanisms that provide reliability by detecting problems in network connectivity equipment. The protocol inherits certain features from PSTN, so it is much interoperable with PSTN.
What is the difference between SIP and H323?
• SIP can be used for file sharing, instant messaging, online gaming, and other multimedia communications as well, apart from multimedia conferencing. However, H323 is targeting only multimedia conferencing.
• Fact that H323 has a constrained scope than SIP makes it less complex than SIP.
• H323 has more interoperability than SIP.
• H323 is more reliable than SIP as it has features to handle failures of network connections and devices while SIP does not have such high level failure detection and recovery mechanisms.
• SIP is a text-based protocol where messages are encoded in ASCII. On the other hand, H323 messages are compacted binary. SIP is hence easily readable than H323, but that trades off with the bandwidth requirement for messages.
• H323 has the capability to do load balancing while SIP does not have that capability.
• The addressing used in H323 is more flexible than what is used in SIP. SIP only understand URI, but H323 supports many other addresses such as email, E.164 numbers, transport address, mobile UIM, and so on apart from URI.
• H323 resembles certain features of PSTN (Public Switched Telephone Networks) and hence can be easily integrated with PSTN. However, this is not the case in SIP.
• H323 has NAT (Network Address Translation) traversal capability while such is not defined in SIP protocol.
• H323 has full support for data conferencing while SIP has limited support for that.
H323 vs SIP
SIP protocols can be used for many multimedia communication purposes such as online gaming, instant messaging, and file sharing as well, apart from the intended application for multimedia conferencing. However,H323 is limited to multimedia conferencing. This fact makes H323 less complicated and interoperable than SIP. Using H323 gives additional advantages such as NAT traversal, Load balancing, reliability, and flexible addressing, as well. The messages in SIP is text based hence is human readable, but the messages in H323 are compacted binary. However, when bandwidth for messages is considered H323 uses less bandwidth for its compacted binary messages.