[e2e] TCP over mobile networks: Are there any problems left?

[Detlef Bosau]

> weigengyu wrote:
> 
> 
> The mobility in a pico-cell based mobile networks affect the
> transmission rates
> and quality. This had proved in a PHS mobile networks.
> In PHS network, the terminal would not permit to move faster than
> 20kilometer,
> and one voice channel can support 64kbps digital transmission.
> 

Is this a scientific problem? Or is this a technological problem?

Varying throughput rates per se are neither a scientific problem nor a
problem at all: They are a property of the channel.
Particularly TCP will send with the correct rate due to the ACK pacing
mechanism.

> It can be estimate that there is the limitation due to terminal
> handoff in wlan--IEEE802.11
> based network, especially with more than 10M or 100M transmission
> rate.


Perhaps I should say that I´m primarily interested in cellular networks.

And I don´t see any handoff problem for TCP there. I´m using my mobile
phone for more than 10 years now - and for voice calls
roaming is hidden that fine that I don´t even notice it. O.k., there is
some interpolation stuff and error correction stuff, but I think
the disconnect time is less then 0.1 s. I expect horizontal cell
handovers to stay within this limits. O.k., then we have 0.1 s
disconnect time.
This might be inappropriate for some applications, but it is no real
problem for TCP. In addition, there are lots of approaches 
like Freeze TCP or M-TCP (hopefully I don´t mix it up with MTCP ;-))
which address exactly this problem by slowing down the sender 
e.g. with a zero window.


What I do not understand yet is: 
-Are there scheduling mechanisms like Proportional Fair etc. generally
used in cellular networks? I read about this in UMTS 2000,
but what about GPRs?
-If so: What´s the reason for that?
-If so: Are there consequences for TCP resulting from the scheduling
mechanisms? (Thierry Klein addressed this topic for Proportional Fair
in his Globecom 04 paper).


Detlef


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Detlef Bosau
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