question on draft charter

[Rae McLellan <rae@research.bell-labs.com>]

>> In the current draft charter for the PSAMP working group,
>> Nick Duffield wrote:
>> 
>>     Network elements shall support several parallel packet samplers,
>>     each with independently configurable packet selectors, reports,
>>     report streams, and export.
>> 
>> Are you using "network element" to refer to a an entire IP router,
>> or individual linecards within an IP router?  Is each linecard
>> generating a single report stream and the sum of all linecards
>> within a network element creating the "independently configurable
>> packet selectors, reports, report streams, and export"?  Or are
>> you suggesting each linecard support multiple "parallel packet
>> samplers, each with independently configurable packet selectors,
>> reports, report streams, and export"?
>> 
>> The use of "shall" in your text makes me worry if its the latter.
>>
>>				Rae McLellan
>
> can you be more specific about why you are worried?

well... my biggest concern is for the amount and type of buffering
for accumulating the samples prior to their being sent via a
report stream.  Multiple report streams imply multiple buffers.
These buffers behave differently than other packet buffers in 
a linecard because their contents grows not in full packet
increments, but sporadically as packets are sampled.  They have
to be kept separate to maintain their integrity (to prevent
interdigitation of other data).  Each report stream also requires
a separate destination IP address and sequence number generator.
For high speed routers, this will have to be maintained in
hardware registers.  Since there is a limit, (i.e. it can't be
infinite) I'd suggest it be just one.  Let the downstream collector
create the multiple logical report streams for their potentially
multiple network analysis stations based on a single physical
report stream coming from each linecard.  What is to be done for
example if a single packet is sampled by multiple rulesets in
a linecard and must go out on several different report streams?
Copying the packet sample to each report stream creates an ugly
bandwidth multiplication.  This is much easier and cleanly
performed at a collection agent handling a geographical part
of the network on behalf of multiple network management agents.
Putting it all in the linecard is excessive, IMHO.

				Rae McLellan




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