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How many T1's can a 2621 handle?

 
 
WAState
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      02-21-2005
What is the practical limit on the number of T1's that a 2621 (the
original, NOT the XM version) can handle before you run out of CPU?

By associating multiple T1's via MultiLink, I'm wondering how large a
WAN pipe the 2621 can handle. The device can *physically* accommodate
up to four WIC-1DSU-T1's: Two in its native WAN slots, and two more in
an optional NM-2W. So theoretically you could have four T1's, or ~6Mbps
in each direction (12Mbps total), in a MultiLink setup.

One reference on Cisco's website says the 2621 can handle ~8Mbps, but
1) I've always understood that the 2621 can sustain full FE wire
speeds, which is quite a bit more than 8Mbps; and 2) I don't know if
that 8Mbps figure means one side of a link or both sides. T1's are
commonly referred to as 1.544Mbps, but they are full duplex so the
total traffic is really ~3Mbps... I don't know if Cisco's "8Mbps"
figure means unidirectional or bidirectional traffic.

Anyone ever put three or four WIC's in a single 2621? Did it work OK?

 
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Andrey Tarasov
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      02-21-2005
Hello, WAState!
You wrote on 21 Feb 2005 10:39:11 -0800:

W> What is the practical limit on the number of T1's that a 2621 (the
W> original, NOT the XM version) can handle before you run out of
W> CPU?

W> By associating multiple T1's via MultiLink, I'm wondering how
W> large a WAN pipe the 2621 can handle. The device can *physically*
W> accommodate up to four WIC-1DSU-T1's: Two in its native WAN slots,
W> and two more in an optional NM-2W. So theoretically you could have
W> four T1's, or ~6Mbps in each direction (12Mbps total), in a
W> MultiLink setup.

Well, physically you can have 8 T1. You can use WICs with 2 serial port each and
external CSU/DSU. I didn't bother to check what the actual limitation on number
of serial ports/WICs you can have in 2621.

W> One reference on Cisco's website says the 2621 can handle ~8Mbps,
W> but 1) I've always understood that the 2621 can sustain full FE
W> wire speeds, which is quite a bit more than 8Mbps;

Never ever. According to

http://www.cisco.com/warp/public/765...erformance.pdf

2621 can handle up to 12.80 Mbps. I don't know which packet size they were using
to get this number. One friend of my claimed that he couldn't get more than 20
Mbps from one FE to another FE with 1500 packets. I didn't verify either number.

W> and 2) I don't know if that 8Mbps figure means one side of a link or both
W> sides. T1's are commonly referred to as 1.544Mbps, but they are full
W> duplex so the total traffic is really ~3Mbps... I don't know if
W> Cisco's "8Mbps" figure means unidirectional or bidirectional
W> traffic.

In this case I think it would be 4 T1. 6 Mbps one way and 6 another. Chances are
that 12.80 Mbps was squeezed from router without any additional processing like
NAT, ACL, PBR, etc. To be on a safe side I would say two T1 per 2621 looks like
a maximum. But if you T1 is not heavily utilized you might get away with more
than 2.

With best regards,
Andrey.

 
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WAState
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      02-22-2005
Thanks for the comments.

As an aside, I've been playing with throughput on 2600's lately. I seem
to get the same throughput no matter whether the packets are all
process-switched or if I enable CEF+NetFlow with flow acceleration. CPU
loading is about the same during the tests, too. I must say I was
rather surprised by those results, and my testing continues.

 
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anybody43@hotmail.com
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      02-23-2005
At a guess there is something wrong with your tests.

I have done tests on cisco routers and saw the 'expected' performance
variations and CPU loading changes. I reckon on a factor of 10 (or
more) difference between and fast switching and process switching.

MPPP is CPU intensive and the performance numbers with MPPP are not in
any way related to any general published performance figured. For n
links each packet is divided into n pieces and each piece sent down a
different link.

MPPP over 30 channels of 64k each on a European PRI sucked up a100% CPU
on a 4700M. (100MHz or was it 150MHz? R4700).

 
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Andrey Tarasov
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      02-23-2005
Hello, http://www.velocityreviews.com/forums/(E-Mail Removed)!
You wrote on 23 Feb 2005 03:24:45 -0800:

a> MPPP is CPU intensive and the performance numbers with MPPP are
a> not in any way related to any general published performance
a> figured. For n links each packet is divided into n pieces and each
a> piece sent down a different link.

It depends. What I seen on 2600 series, if you are not using interleaving or if
links in MPPP bundle are fast enough, there would be no fragmentation
whatsoever.

With best regards,
Andrey.

 
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AnyBody43
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      03-19-2005
"Andrey Tarasov" <(E-Mail Removed)> wrote in message news:<cviebj$1th9$(E-Mail Removed)>...
> Hello, (E-Mail Removed)!
> You wrote on 23 Feb 2005 03:24:45 -0800:
>
> a> MPPP is CPU intensive and the performance numbers with MPPP are
> a> not in any way related to any general published performance
> a> figured. For n links each packet is divided into n pieces and each
> a> piece sent down a different link.
>
> It depends. What I seen on 2600 series, if you are not using interleaving or if
> links in MPPP bundle are fast enough, there would be no fragmentation
> whatsoever.
>
> With best regards,
> Andrey.


Andrey,
I have only just noticed your response.

I believe that _by-definition_ MPPP divides the packets
such that in the case of N links there are N fragments.

However in general with respect to MPPP performance
I have no recent experience of mppp and may be out
of date. Clearly it would be perfectly possible to
fragment the packets in hardware and incur
no performance penalty whatsoever. It seems
unlikely to me that a 2621 does this.

A key benefit of fragmenting the packets in this way
is that the Transmission Delay is reduced. Additionally
packet order is conserved which is not the case with
some other load sharing techniques.
 
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Andrey Tarasov
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      03-19-2005
Hello, AnyBody43!
You wrote on 19 Mar 2005 05:32:20 -0800:

??>> It depends. What I seen on 2600 series, if you are not using
??>> interleaving or if links in MPPP bundle are fast enough, there
??>> would be no fragmentation whatsoever.

A> I believe that _by-definition_ MPPP divides the packets
A> such that in the case of N links there are N fragments.

From RFC 1990 -
....
Systems implementing the multilink procedure are not required to fragment small
packets. There is also no requirement that the segments be of equal sizes, or
that packets must be broken up at all.
....

A> However in general with respect to MPPP performance
A> I have no recent experience of mppp and may be out
A> of date. Clearly it would be perfectly possible to
A> fragment the packets in hardware and incur
A> no performance penalty whatsoever.

And that is normally found on IMA devices.

A> A key benefit of fragmenting the packets in this way
A> is that the Transmission Delay is reduced. Additionally
A> packet order is conserved which is not the case with
A> some other load sharing techniques.

Serialization delay on T1 for 1500 bytes is less than 8ms. Packet order is
preserved even though packets are not fragmented. There is a special MLPPP
buffer dealing with packets re-assembly and re-ordering.

With best regards,
Andrey.

 
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anybody43@hotmail.com
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      03-19-2005
Thanks.

I did consider heading for the RFCs but was pretty convinced.
Wrong, again!

Thanks a lot.

 
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