North American Network Operators Group
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Re: image stream routers

  • From: Lincoln Dale
  • Date: Sat Sep 17 02:21:24 2005 
Christopher J. Wolff wrote:

I'd be interested to know the relative pros and cons of switching packets in
software (Imagestream) versus handing them off to a dedicated ASIC (Cisco,
Juniper)
[without having looked at Imagestream in any way, shape or form..]

it would be _unlikely_ that any router vendor that wants to support >OC3 could do so with the 'standard' (non-modified) linux IP stack. if they are modifying the 'standard' linux IP stack then its very unlikely that one could do so without having to publish the source-code to it. (i.e. as per GPL).

'standard' linux on standard hardware isn't capable of much more than 100K PPS. sure - some folks have a few hundred packets/sec - but these are minimalist versus the demonstrated performance of ASIC-based forwarding, typically 30M-50M PPS.

one advantage of software is programmability. if there is a bug you can fix it.
if there is a bug in an ASIC, it may or may not be possible to fix it - it depends on awful lot on how the ASIC is built (whether its 100% fixed functionality or supports limited programmability in various stages of the forwarding pipeline).
it may be that its not fixable but that the ASIC allows software-workarounds - in essence, 'fixing' something by diverting it to a (slower) software-path.

note that there is a correction to make here: not all routers _ARE_ ASIC-based for forwarding. in fact, most of the Cisco /router/ product portfolio isn't hardware-forwarding based. generally speaking it isn't necessary - UNTIL you get to the point of having interface speeds & number-of-interfaces which exceed the capabilities of general-purpose processors. that is, typically somewhere between 100K PPS and 1M PPS.


cheers,

lincoln.