[rmcat] Review of rmcat-cc-codec-interactions

["Michael Ramalho (mramalho)" <[e-mail]>]

All,

I have reviewed draft-zanaty-rmcat-cc-codec-interactions. My only comments concern Section 5.2.2 (Startup Ramp).

In what follows I have added two sentences and modified a sentence in this section.

****EXISTING TEXT****
5.2.2.  Startup Ramp

Startup Ramp (from Codec to CC, and from CC to Codec): Startup is an important moment in a conversation.  Rapid rate adaptation during startup is therefore important.  The codec should minimize its startup media rate as much as possible without adversely impacting the user experience, and support a strategy for rapid rate ramp.  The CC should allow the highest startup media rate as possible without adversely impacting network conditions, and also support rapid rate ramp until stabilizing on the available bandwidth.  Startup can be viewed as a negotiation between the codec and the CC.  The codec requests a startup rate and ramp, and the CC responds with the allowable parameters which may be lower/slower.  The RMCAT requirements also include the possibility of bandwidth history to further accelerate or even eliminate startup ramp time.  While this is highly desirable from an application viewpoint, it may be less acceptable to network operators, since it is in essence a gamble on current congestion state matching historical state, with the potential for significant congestion contribution if the gamble was wrong.  Note that startup can often commence before user interaction or conversation to reduce the chance of clipped media.
****EXISTING TEXT****

****PROPOSED TEXT****
5.2.2.  Startup Ramp

Startup Ramp (from Codec to CC, and from CC to Codec): Startup is an important moment in a conversation.  Rapid rate adaptation during startup is therefore important.  The codec should minimize its startup media rate as much as possible without adversely impacting the user experience, and support a strategy for rapid rate ramp.  The CC should allow the highest startup media rate as possible without adversely impacting network conditions, and also support rapid rate ramp until stabilizing on the available bandwidth.  Startup can be viewed as a negotiation between the codec and the CC.  The specification of the ramp may take a number of forms depending on the interface to the codec; for example, a percentage bit rate increase per RTT (or other time interval), or an increased transmit window (in number of packets and/or octets allowed outstanding) are all potential forms.  The codec requests a startup rate and ramp, and the CC responds with the allowable parameters which may be lower/slower.  The RMCAT requirements also include the possibility of bandwidth history to further accelerate or even eliminate startup ramp time. While this acceleration or elimination in ramp time is beneficial to the session user experience when bandwidth is sufficient, it can be detrimental if significant congestion results (the user experience of this session and all other sessions traversing the point of congestion may unnecessarily degrade).  Therefore, it is recommended that use of potentially stale congestion state for acceleration or elimination in ramp up be limited to topologies or deployments believed to have sufficient bandwidth margin or those in which the potential transient congestion risk is acceptable.  Note that startup can often commence before user interaction or conversation to reduce the chance of clipped media.
****PROPOSED TEXT****

The modification deletes the reference to "network operators", as I think the point may be made that many network administrators (be they service providers or other "network operators") or network designers/sizers would also have the same concern.

I have reviewed this change with the present authors and they generally approve of it. Other edits are welcome.

Regards,

Michael A. Ramalho, Ph.D.