RE: [AVT] I-D ACTION:draft-ietf-avt-tcrtp-08.txt

["Dan Wing" <dwing at cisco.com>]

> While I completely agree with the motivation behind this draft,
> I have problems with the proposed technique.
>
> In section 1.1 we find:
>
>    While some voice-over-packet technologies such as Voice over
>    ATM (VoAAL2, [I.363.2]) and Voice over MPLS provide bandwidth
>    efficiencies because both technologies lack IP, UDP, and RTP
>    headers, neither VoATM nor VoMPLS provide direct access to voice-
>    over-packet services available to Voice over IP.
>
> The savings of VoATM and VoMPLS (and now ITU Y.1414) are mainly
> due to multiplexing multiple channels into a packet with a single
> header, and not merely to not having the RTP/UDP/IP headers.

ATM's multiplexing only helps significantly if you can take
advantage of it, which requires chosing a codec and packetization
interval the fit into the user payload, and requires multiple streams
terminating on the same VPI/VCI.

> Indeed, the significance of the overhead diminishes with the number
> of multiplexed channels.
>
> So to solve the efficiency problem we need a simple method to multiplex
> multiple
> channels into a single packet, such as the mechanisms specified in
> Y.1414.
>
> The TCRTP draft indeed uses standard mechanisms to multiplexing
> channels,
> but, its mechanisms are needlessly complex
> (compression techniques to reduce the overhead, then PPP muxing to
> combine them,
> then placing the resulting stream into an L2TP tunnel, and then
> performing a further
> header compression on the L2TP/IP headers).
>
> Why should we go to such lengths when much simpler mechanisms can be
> used?

We needed a compression technique that saved bandwidth even in the absence
of multiplexing -- such as a branch office doing VoIP with a single user.

-d

> Y(J)S
>
> _______________________________________________
> Audio/Video Transport Working Group
> avt at ietf.org
> https://www1.ietf.org/mailman/listinfo/avt


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