[e2e] How do we deal with mobile networks?

Detlef Bosau detlef.bosau at web.de
Mon Feb 25 02:40:34 PST 2013

Am 24.02.2013 18:36, schrieb John Day:
> Re: [e2e] How do we deal with mobile networks?
> I don't know if this helps, but the fundamental premise of this form 
> of architecture (and understood from the beginning in the early 70s) 
> is that the purpose of the data link layer is to provide sufficient 
> error control to ensure that end-to-end reliability at the Transport 
> Layer is cost-effective.

Let me quote VJ's Rant on Queues from 2006 here:

> Suggestions (cont.)
> additional delay
> . Never introducewith packets): (apps will
> just try to fill it
> /? Let apps do their own FEC;//
> //avoid link layer Reed-Solomon and ARQ./
> ? Use smooth, simple downlink schedulers
> ? Use predictive and anticipatory uplink
> schedulers
(Accentuation done by me)

and RFC 791.

> 1.2.  Scope
>    The internet protocol is specifically limited in scope to provide the
>    functions necessary to deliver a package of bits (an internet
>    datagram) from a source to a destination over an interconnected system
>    of networks./  There are no mechanisms to augment end-to-end data
>    reliability/, flow control, sequencing, or other services commonly
>    found in host-to-host protocols.  The internet protocol can capitalize
>    on the services of its supporting networks to provide various types
>    and qualities of service.
(Acc. d. b.me )

And please note that the assumption "no flow control" should be 
understood as "we must not do flow control on link layer", e.g. in Ethernet.
Please note that enabling flow control on link layer may lead to 
communication deadlocks which are, without appropriate means, neither 
detected nor handled by IP.

So, it is a valid position to request that any retransmission of lost 
packets should be done end to end, as required by VJ.

However, I think, this position does not really hold.

> IOW, since most loss above the Data Link Layer is due to congestion, 
> the Data Link Layer should provide enough error recovery to stay well 
> within acceptable losses due to congestion in the layers above.

That should be the correct position, however to my understanding it is 
not fully supported in literature and apparently, this is not common 
sense at the moment.

Detlef Bosau
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