[Cerowrt-devel] Baby jumbo frames support?

[dpreed at reed.com]

Digging deeper, there is also a good reason for bigger frames when one is using 600 Mbit 802.11 signalling ( that's 75 bytes per microsecond).  A 1500 byte frame occupies only 50 microseconds of airtime. Not much return for the investment in contention time (5-10 microseconds) by the transmitting station.  9000 byte frames would be good, just as they are for GigE.
 
-----Original Message-----
From: "Alexander Hulse" <ah at amch.net>
Sent: Saturday, June 16, 2012 5:53am
To: cerowrt-devel at lists.bufferbloat.net
Subject: [Cerowrt-devel] Baby jumbo frames support?



I've done some basic research and some (unsuccessful) hacking the on the driver source for the ag71xx driver and was wondering about baby jumbo frame support?

I know that the WNDR37/800's built in switch supports passing jumbo frames, but the underlying router interfaces do not support large MTU frames.

However, this:

http://wiki.mikrotik.com/wiki/Manual:Maximum_Transmission_Unit_on_RouterBoards

seems to imply that the built-in interfaces ought to support baby jumbo frames, unless I'm misunderstanding what they are saying.

As to the "Why?", in the UK, the fibre offering by BT using FTTC uses a PPPoE modem that can understand PPPoE packets with an MTU 1508, as described in RFC 4638.

It was possible using a Netgear WNR834T with the application of some patches from the pppd git:

http://git.ozlabs.org/?p=ppp.git;a=commit;h=fd1dcdf758418f040da3ed801ab001b5e46854e7
http://wiki.aa.net.uk/index.php/FTTC_Modem

Would this be a useful feature to add (if possible) to CeroWrt so that full sized frames can be used if the ISP / connection supports it?

Alex
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