[e2e] Packet Corruption in a Wireless Medium!

Spencer Dawkins spencer_dawkins at yahoo.com
Tue Jul 29 08:59:03 PDT 2003

Dear Arjuna,

Dave did a nice job of replying in a separate e-mail, so I'll
just send the "other" reply, asking "so, why do you want to

My own interest in ELN was for transport feedback - "since you
know it's not congestion loss, retransmit but don't slow down".
This worked nicely in isolation, and ran into a wall when you
were experiencing both congestion and transmission error loss
simultaneously - we couldn't come up with a decent mechanism
that says "take this loss seriously, not this next loss, but the
following loss is also serious", with RTT-scale feedback loops.

Phil Karn (among others) keeps reminding me that "transmission
errors" in a CDMA environment can ALSO reflect "congestion" - at
a cell level, when two senders are colliding with each other -
so not slowing either one down is not a good plan.

We wrote this up in http://www.ietf.org/rfc/rfc3155.txt,
following up on our wishful thinking in

Dave also referred to the possibility of protecting header
fields (so you can send ELNs to the right place based on source
addresses in the damaged packets) - UDPlite is trying to provide
some help here, but it's not clear to me how much help it can

Hope this helps,


--- arjuna at dcs.kcl.ac.uk wrote:
> Dear All,
>  I would like to know :
> 1)Can the headers of ALL packets that are corrupted while
> traversing a
> wireless link be retrieved by the MAC layer at the receiver
> (as proposed
> by the Header Checksum Option), so that the ELN mechanism can
> detect
> packet corruption?
> 2)If no, what percentage of them can be retrieved
> successfully? Are there
> any papers that address this issue?
> Regards,
> Arjuna

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