[e2e] Internet packet dynamics

[=?gb2312?q?Jing=20Shen?=]

>From viewpoint of e2e QoS, IMHO, other than its
current co-existing method voice will not be modulated
in the same DSL channel which is only used for data
transfering.  The reason is,  current method
guarantees a higher QoS level than packtizing
everything at subscriber's PC and transfering with
packets of a movie.

Considering packetizer at IP network edge, as VoIP
does not require a delay jitter of zero and Erlan
equation reflects the statistical characteristics in
PSTN,  the amount of processing ability & uplink
bandwidth for a Gatekeeper could be calculated easily
if a special amount of subscriber is considered. 

On othe contrary, it seems backbone network needs more
intellegence if overprovisioning level is not high
enough. To my understanding DiffServ devides a
best-effort IP backbone to several colocating logical
IP networks who uses the same QoS & routing mechanism
as BE networks. 

Jing Shen




--- "David P. Reed" <dpreed at reed.com> µÄÕýÎÄ£º> At
01:14 AM 3/15/2004, Jon Crowcroft wrote:
> >Iof course the right way to do voice of DSL is to
> use the ATM multiplex, 
> >and then pop the voice out at the POP and
> >THEN packetize it in IP where the linespeeds are
> enough that the 
> >serialisation delay, and queueing
> >delay jitter  are much less:)
> 
> You are being ironic here.   But for others on the
> list you are too 
> subtle.  Here's how to understand it:   If you track
> the timing of the 
> "last byte" of voice in each VoIP packet (not the
> first byte) or "packet 
> yet to be made" you find that the main difference is
> due to the delay in 
> serialization [we spell that with a "zed" :-)].  
> And if you look at the 
> system, the main effect here will be that your
> "packetizer" is a shared 
> resource among many users, if you put the function
> in the network.   This 
> introduces major delay variation that wouldn't be
> present if the packet 
> were built at the source by a dedicated packetizer.
> 
> I write this to emphasize that the "end to end
> argument" is a technical 
> argument, and "moving function to the edge" rather
> than doing it in the 
> middle of the network, is NOT a religious doctrine -
> though the routerheads 
> (who used to be the bellheads) still are looking to
> move functions to the 
> point they control, so their marketers can lock us
> in. (the latter is a 
> "political" statement, I know - it is worth,
> however, noting that there are 
> vested interests in the major router companies that
> constantly push to lock 
> function into the core of the network and into
> middleboxes).
>  

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