[xcp] Notes from XCP meeting at ISI
braden at ISI.EDU
Fri Feb 20 13:57:01 PST 2004
19 Feb 2004 XCP Meeting at ISI
Aaron was out of town.
* Two major research areas still open:
-- Varying link error rates
-- Effect of mice on XCP (Need ideas here... Ted tried to dangle it
as a thesis topic.)
-- Clarified how TCP checksums currently work with XCP.
-- Ted's FreeBSD code does not support hardware checksumming.
-- NOTE: The XCP header is currently not covered by ANY checksum!!
We should probably fix this!
-- Ted asked: if XCP header checksum fails, what do you do?
Bob argued: better drop the packet, to prevent a simple
attack on XCP.
* XCP header format
-- Bob asked if it wasn't time to deep-six the cwnd version of the
XCP header. Agreed; Eric/Aman will test the throughput
version, and hopefully be able to easily fix any bugs
that show up.
-- The first nibble is now "XCP version #". Bob suggested that
we should that imagine the header we are designing may
be more generally useful, for a variety of congestion
control schemes. Then the first nibble could be
registered with IANA as the "Congestion Control Scheme".
* Detecting Non-XCP routers
-- It will be important to detect non-XCP routers
in the path. For this purpose, we need a TTL field in the
XCP header. It will be initialized to the IP TTL, and
each router's XCP will decrement it. If there are only
XCP routers, its value at the receiver will match the TTL
in the IP header.
-- This does not quite work with MPLS; something special has to
be done. MPLS does not decrement the IP TTL, but
XCP-capable MPLS hops might decrement the XCP TTL.
Have to teach an XCP-capable MPLS router to not do
* Kudos and thanks to Eric and Aman!!!
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