What is the difference between H.248 and H.323?
These two International Telecommunication Union (ITU)-based protocols are widely associated with VoIP, although both can handle other modes of real-time IP-based communications, such as video. H.248 is the predecessor to H.323, and has its roots in the legacy world. H.248, also known as Megaco, was designed to facilitate the control of media gateways by media gateway controllers. This function was critical in the early days of VoIP, when most of this traffic needed to interface with public switched telephone networks (PSTN) via media gateways.
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While H.248 was initially the dominant signaling protocol for VoIP, it has largely been supplanted by H.323, which was developed from the ground up to support multimedia traffic on IP networks. Since PSTN is still with us, H.248 persists because it supports Signaling System 7 (SS7), the signaling standard for legacy telephony. The future, however, belongs to IP networks, and H.323 is simply better suited to support all forms of IP-based applications, such as voice, fax, conferencing and video.
Not only is H.323 more compatible with SIP, but it supports quality of service (QoS). This is a critical capability that prioritizes real-time traffic, such as voice or video, over other modes in an IP network. When bandwidth resources are constrained, QoS ensures that applications such as VoIP perform properly. Otherwise, quality is degraded and callers experience annoying things like packet loss, echo and jitter.
For more information on H.248 and H.323:
- What are media gateways and how do H.248, H.323 and other support protocols work?
- VoIP protocol listing: A glossary of VoIP protocols and standards