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Re: Quality of User Experience (was RE: image stream routers)

  • From: Lincoln Dale
  • Date: Sat Sep 17 03:56:42 2005


[let me preface this by saying that if you don't know this already, i do happen to work for a router vendor]

from the perspective of ANY router, "quality of end-user experience" is not something which fits into layers 1-7 - its a layer 8-10 thing. however, having said that, certainly routers "doing the wrong thing" can definitely negatively impact end-user experience.

i think its best to answer this by what 'role' various routers have, and what their primary function should be. that ultimately determines what the right 'boxes' are for given 'roles' - and if you put the wrong box in the wrong category, that can negatively impact service in a way that customers think your service sucks.

no doubt there are more roles than this & we can get more & more specific - but its my AU$0.02 worth:

note that i'm deliberately not getting into whether it should be IPv4, IPv6, MPLS, all of the above, none of the above .. thats up to what service you have, how you provision it and how you traffic engineer it.

1. Core router
- generally consist of interface speeds of OC12 upwards.
- move packets from A to B with minimal additional latency
and minimal jitter
- should be capable of implementing ACLs with no
performance degredation but primary role is to push packets

- just about mandatory these days that can handle interfaces
pushing maximum packets/sec with minimum packet size so
as to be able to withstand DDoS attacks - either at it, or
through it

2. Transit or peering-facing router
- interface speeds of >OC3, probably decent GbE density
desirable
- mandatory implementation of ACLs
- mandatory full-feature BGP features & widgets
- mandatory implementation of uRPF or similar
- ideally be capable of traffic 'accounting' mechanisms
(e.g. packet-sampling, netflow etc)

3. customer-facing router (FR/ATM/..)
- decent system-density for customer connections
- GbE uplink interface(s)
- mandatory implementation of ACLs
- mandatory full-feature BGP features & widgets
- mandatory implementation of uRPF or similar
- ideally be capable of traffic 'accounting' mechanisms
(e.g. packet-sampling, netflow, anomoly detection etc)
- ideally be able to implement 'better' queueing mechanisms
than just standard FIFO. e.g. low-latency queueing for
voice traffic, fair-queueing for fairness, deep(er) buffers
to attempt to minimize packet drop due to speed-mismatch

4. broadband aggregation router (e.g. LNS)
- handle large numbers of logical sessions from central
configuration/policy (e.g. tie into RADIUS server(s))
- GbE uplink interface(s)
- mandatory implementation of ACLs
- mandatory implementation of uRPF or similar
- ideally be capable of traffic 'accounting' mechanisms
(e.g. packet-sampling, netflow, anomoly detection etc)
- ideally be able to implement 'better' queueing mechanisms
than just standard FIFO. e.g. low-latency queueing for
voice traffic, fair-queueing for fairness, deep(er) buffers
to attempt to minimize packet drop due to speed-mismatch
- sufficient control-plane CPU to handle large # of connection
establishments/sec (e.g. connection to LAC being lost)

5. customer-premises router (CPE)
- generally low-speed (<30Mbps)
- end-users love ones with built-in NAT, DHCP, firewall,
wireless, probably VoIP, ...
- low-cost
- minimal CPU - no need to handle DoS attack because WAN
bandwidth is exhausted before PPS limit of CPU is hit


going through these, i'd say "ASIC based" or multiple-distributed-CPU is what you want for (1). anything less than that means you're likely to have reduced customer satisfaction.

(2), (3) & (4) generally are a mix of s/w and h/w-based routers - architectures vary quite greatly but with silicon developments in the last few years, most semi-recent products are typically a combination of h/w and s/w with (ideally) the work split 90/10. or 99/1. or 100/0 in an ideal world.

(5) can stay software.


cheers,

lincoln.

Christopher J. Wolff wrote:
Thanks for the thoughtful response.

One of the network architecture issues I'm always trying to gauge and get my
arms around is what I'll call, "Quality of user experience."  In other
words, what mix of network hardware, software, customer support, and
management will create a perception that the network is performing at
maximum efficiency.

Although the perception of network performance is entirely subjective there
are some factors that I'm sure we can all agree contribute to overall
satisfaction...i.e.

-WAN link latency.
-Packet Loss.
-Consistency in packet generation/serialization (A packet always enters
interface A and leaves interface B in .5 ms)

So, if all other elements (software, customer support, and management) are
equal, what router hardware architecture will contribute to a positive or
negative user experience?  In other words, if the routing device between my
workstation and server is a Juniper M7 instead of Pentium IV running
unix-flavor-of-the-day, how will that affect the quality of user experience?

Thank you,
Christopher

-----Original Message-----
From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of
Lincoln Dale
Sent: Friday, September 16, 2005 11:18 PM
To: Christopher J. Wolff
Cc: nanog@merit.edu
Subject: Re: image stream routers


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.










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