H.320

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What is H.320?

H.320 is the ITU recommendation for video conferencing using ISDN networks. ISDN means "Integrated Services Digital Networking" and it is a form of digital communications that can provide up to 64 kbits/second of bandwidth per ISDN channel.

In order for video conferencing systems to fully utilize the ability of ISDN to deliver dial-up digital bandwidth, some form of reverse multiplexing or bandwidth aggregation technique is required.

BONDING algorithms were developed to do just this. These algorithms enabled Inverse Multiplexing of channels to create higher bandwidth call sessions. BONDING stands for "Bandwidth On Demand" and several Bonding algorithms were developed to create aggregated high bandwidth ISDN calls. BONDING is essential to H.320 video conferencing.

Variants of BONDING

Three primary variants of BONDING were developed to enable inverse multiplexing of ISDN Bearer channels into higher bandwidth call sessions. They are:

BONDING Mode 1: Most commonly accepted and widely used variant. Delay equalization between Bearer channels is negotiated primarily at call startup. This BONDING algorithm does not generally revise sync in response to dynamic changes in Bearer channel delay and so call sessions based on this algorithm can fail if Bearer channels deliver data in varying timeframes.

AIM: This is a dynamically changing BONDING method that can accommodate some changes in transport delay among Bearer channels. Originally named "AIM" after the source of its creation at Ascend Communications, later acquired by Lucent, AIM stands for Ascend Inverse Multiplexing. This BONDING mode is resilient and will maintain call sessions even with some changes in the delay synchronization between Bearer channels.

STATIC: This BONDING algorithm negotiates delay sync just after call setup acknowledge and performs minimal revision to the delay equalization timing. It is prone to sync loss and therefore, call drop, if delay between channels varies. This algorithm most closely matches the BONDING Mode 1 algorithm that has been widely adopted as an inverse multiplexing standard.