[e2e] Delays / service times / delivery times in wireless networks.

[David P. Reed]

An IP packet should be dropped quickly if it cannot be delivered 
quickly.   What ETSI standard are you referring to?   IETF has nothing 
to do with ETSI...

Detlef Bosau wrote:
> Hi to all,
>
> I go in circles here and perhaps, someone can help me out.
>
> In networks like GPRS, IP packets can experience extremely large 
> delivery times. The ETSI standard accepts up to 10 minutes.
>
> The effects of large and varying latencies on TCP are widely 
> discussed. However, I still do not really understand where these 
> delays come from.
> When delivery times vary from 1 ms to 10 minutes, we talk about 6 
> orders of magnitude. My question is: What is the reason for this?
>
> Possible delay sources (except processing, serialization, queieng, 
> propagation) are:
>
> - recovery / retransmission,
> - roaming
> - scheduling.
>
> I hardly belive that recovery latencies are that large because I can 
> hardly imagine that a packet in the whole or in pieces is repeated up 
> to 1 million times. And even if this would be the case, it is 
> interesting to see the variation of such latencies.
>
> In addition, I hardly believe in roaming latencies. Years ago, I was 
> told extremely large latencies would result from roaming. However, if 
> e.g. a mobile roams from one cell to another, to my understanding it 
> keeps its SGSN in many cases and only the antenna station changes. So, 
> this situation is basically not different from roaming with a normal 
> voice stream. And that works transparent to the user.
>
> The only source where I ever read latencies and delay spikes of 
> several seconds is the Globecom 2004 paper by Thierry Klein, which 
> reported delay spikes of up to 2 seconds. And when I think about 
> proportional fair scheduling, I think this _can_ be a source of large 
> delay spikes.
> However, I do not have access to any reliable material here.
>
> The problem appears to be quite technical and not very much TCP 
> related. However, I´m admittedly somewhat tired to think about dely 
> variations and delay spikes and possible adverse consequences upon TCP 
> without having really understood the reasons for large delays and
> delay spikes.
>
> I don´t know whether this topic is of intereset here, but I would 
> greatly appreciate any discussion of this matter. If someone can help 
> me on this one, he is welcome to contact me off list, if this topic is 
> not of general interest here.
>
> However, I´m somewhat helpless here.
>
> Thanks.
>
> Detlef
>
>
>