3750 1Gig Uplink port - buffers

[j1mbo78]

Hi,

Has anybody here connected a Telepresence CTS 3010 unit to a catalyst 3750 switch (not V2/G/E/X). I have a customer that wants to use one of the 1Gig uplink ports (with a GLC-T SFP) to connect a TP unit but I'm having a hardtime finding out whether these ports have sufficient buffering capacity etc.to deal with the traffic.

Any thoughts greatly appreciated.

Cheers,

James Smith

[Shashank Singh]

Hi,

Please post the exact model of the 3750 switch you are interested in.

Regards,

Shashank

[paolo bevilacqua]

Your concerns are largely unwarranted for very simple reasons.

All the 3750 models are able to switch at line rate under all circumstances.

Buffers are there only to deal with temporary port oversubscribing. That is when trying to send more traffic than a port can handle. They are a small and for good reasons.

At the end of the day a telepresence unit is not different from anything else. Cisco does not have a recommended switch model to use, because all their model performs as described above - line rate.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained  within this posting without consideration and with the reader's  understanding that there's no implied or expressed suitability or  fitness for any purpose.  Information provided is for informational  purposes only and should not be construed as rendering professional  advice of any kind.  Usage of this posting's information is solely at  reader's own risk.

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Posting

I might be mistaken, but my reading and understanding of the performance specs for some 3750 models indicate some are not line rate capable under all circumstances.  Specifically, the G series which has a 32 Gbps fabric and up to 38.7 Mpps.  Compare to (Cisco described "wire-speed") 4948 specs which are 96 Gbps fabric and 72 Mpps.

The -E and -X series, though, also have fabric and PPS rates that imply wire-speed or line-rate performance.

The original (or V2) series with FastE ports, I believe, also have the 32 Gbps fabric, and a lower PPS rating but the latter usually being enough for line-rate.

Documented specs for original 3750 models:

• 32-Gbps switching fabric 

• Stack-forwarding rate of 38.7 mpps for 64-byte packets

•  Forwarding rate: 6.5 mpps (Cisco Catalyst 3750-24TS, 3750-24FS, and  3750-24PS), 13.1 mpps (Cisco Catalyst 3750-48TS and 3750-48PS), 17.8  mpps (Cisco Catalyst 3750G-12S), 35.7 mpps (Cisco Catalyst 3750G-24T),  38.7 mpps (Cisco Catalyst 3750G-24TS and 3750G-24WS), 35.7 mpps (Cisco  Catalyst 3750G-16TD), 38.7 mpps (Cisco Catalyst 3750G-24TS-1U),  38.7 mpps (Cisco Catalyst 3750G-24PS), 38.7 mpps (Cisco Catalyst  3750G-48TS), 38.7 mpps (Cisco Catalyst 3750G-48PS)

3750V2-48TS 13.1 (million packets per second (mpps)

3750V2-48PS 13.1 mpps

3750V2-24TS 6.5 mpps

3750V2-24PS 6.5 mpps

3750V2-24FS 6.5 mpps

PS:

Ethernet line rate requires:

fabric 2x port bandwidths

port bandwidth, in gig, times 1.488 Mpps

e.g.

48 gig ports requires 96 Gbps fabric, 71.4 Mpps (like the 4948)

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind.  Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

An original 3750, non-G, should be able to deal with telepresence video stream although with a couple of caveats.

Since, in theory, even 24 FastE ports can oversubscribe a gig uplink, you'll likely want to enable QoS.  However, when the 3750 reallocates its buffers for an interface's four egress queues, the queues seem to default to being smaller than the original non-QoS egress queue.  You may need to manually tune buffer resources.  (NB: believe default buffer allocations have changed across different IOS versions.)  Even if you don't enable QoS, the single interface default queue might require some manual tuning.

[paolo bevilacqua]

Actually a telepresence / videoconf device requires less planning (if any) than other devices like a server.

The reason is that you will know in advance how much bandwitdh it will receive at any time.

For example, 10 remote sessions sending 4 Mbps each. Total, 40 Mbps. Hardly worrying in Gigabit networking.

You do not want any special queing or anything, The port cannot be oversubscribed - ever.

No other device will send data, there is no reason why they should.

Unlike for example a backup server, where a multiple devices can require consurrent high bandwidth sessions at any time.

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind.  Usage of  this posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

"No other device will send data, there is no reason why they should."

Ah, we're comparing apples and oranges because I guess wasn't sufficiently clear, i.e. "oversubscribe a gig uplink".  I wasn't thinking of the port to the TP unit, where I agree with you there shouldn't be any issues, I was thinking about the uplink port (assuming the TP unit is not connected to the other gig uplink).  The latter is where buffering may be an issue because of other hosts, if any, attached to the same switch.