[e2e] Wireless Networks. An Example: GPRS.
detlef.bosau at web.de
Mon Mar 11 12:39:58 PDT 2013
Am 11.03.2013 17:12, schrieb Martin Heusse:
> (Although I would tend to think you might need to read a bit about GPRS and cellular networks,
Be assured: I read quite some literature. However: Could you please be a
bit more concrete?
> I'll stick to a more general remark, replacing your reflections in an end to end perspective. And forgive me if I misunderstood you.)
> A sliding window (congestion window, anticipation window) allows a sender to use the links on a multi hop paths in parallel when the network device are store and forward.
Hang on. Sliding window is used to utilize a channel which is able to
keep more than one packet in transit. Particularly on the media.
> So to use a GPRS network properly you need a least 4 packets.
> UE -> BSC
> -> SGSN
> -> GGSN
> -> gateway to dest network
At a first glance, I tend to agree, however from what I read so far
about mobile networks, these do not necessarily deal with IP packets
Nevertheless, when the technology allows to keep more than one packet in
transit and is underutilized otherweise, sliding window makes sense. On
the air interface (in GPRS actually perhaps "behind" the GGSN) this (at
least to my understanding) not always make sense.
Generally spoken: I've chosen GPRS because of it's huge latencies. And
any example I would take, may turn out to be "bad" because the huge
complexity of different technologies and implementation used in wireless
> And that's one way, the return path also count for what's “inflight".
> (ok, high speed links don't hurt as much a low speed links beyond the bottleneck, but I hope you get the idea…)
> Also: RLC-ack (Is that what you call RLP?) does use ARQ… (Are you happy now? ...)
This is no matter of happiness. It is a matter of fact and it is part of
the time necessary to convey a packet.
I mentioned the COMCAR project and I should provide a "QoS architecture"
there - which included to describe the "rate" available for a stream.
Later on, in a conference, the first question was: "Mr. Bosau, how do
you no the available rate?"
Latest in that moment, it became clear to me that TelCo guys and CS guys
(packet switching guys) simply don't understand each other. They talk at
cross purposes. Later on, it became clear to me that packet switching
and line switching (used for voice) use different APIs. We talk about
the years from 2000 to 2005 here.
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