Max full duplex streaming data rate between 12 concurrent sessions on the same 24 port switch?

[wallacehb1]

Will a 24 port Ethernet switch with 1 Gbps port access speeds, a throughput of 95.2 Mpps with 64 byte packets and a routing/switching capacity of 128 Gbps sustain 12  concurrent full duplex streaming sessions on the switch, each at 1 Gbps speed in both directions? If not, what data rate?

I have an application that currently requires 10 mbps full duplex data rates on each session and that may increase to 40 mbps.  Moreover, I've heard most of today's ethernet switches are non-block at so-called wire speed.  I'd like understand how throughput and switching capacity specs are used to calculate the answer to my question.  Again, I'm only considering a single switch and realize there are additional considerations if/when sessions are between ports on different ethernet switches

[Joseph W. Doherty]

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Posting

For wire rate, 64 byte packets require 1.488 Mpps per Gbps.  (NB: the PPS rate drops as packet size increases.)

For a duplex port, you need to allow PPS for both directions, but remember on a switch, one ports ingress is another egress.  I.e. a single gig duplex, going across a switch, would use two gig ports, but there's only two gig of traffic.

For Cisco switches, fabric bandwidth is counted for all ports.

e.g.

24 (full duplex) gig ports would need:

24 * 1.488 = 35.7 Mpps

24 * 2 = 48 Gbps fabric bandwidth

or for your 128 Gbps and 95.2 Mpps switch, it would support:

95.2 / 1.488 = 64 Gbps

128 / 2 = 64 Gbps

[wallacehb1]

Thank you Joseph! Can you suggest a Cisco document or book that will provide additional information? I'd like to better understand the difference between throughput and switching capacity, among other things.

In my work I will actually be taking a pair of audio visual demonstration systems that consume 10 mbps two-way streaming bandwidth between two ports on the same Ethernet switch in a customer business office facility.  I need to work with their information technology department to consider whether our demo is going to affect other applications of users on the same switch such as VoIP and email. I'm just trying to understand enough to be able to carry on a conversation. 

My sense is that almost any Ethernet switch with 1 gigabit access speed deployed within the past several years will have absolutely no difficulty handling an incremental intra-switch 10 mbps full duplex load.  Do you agree?    wallacehb at wallaceco dot net

[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 wha2tsoever (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

I don't recall a book or even extensive documentation on this subject.  You can, though, find some additional information if you search the Internet on wire-speed or line-rate Ethernet.  Such as obtaining details for PPS for different packet sizes (which boils down to space on the wire at a certain bandwidth rate).

Many modern Enterprise switches often have wire-speed capacity for all their ports, but two remaining gotchas remain whether they might have an head-of-line blocking architecture (also rare in modern Enterprise switches) and how much buffering they support (and supported QoS).  The latter will often trip you up.  (Search these forums for performance issues with 3750 series switches, as an example.)

So yes, I agree, 10 Mbps, alone shouldn't be a "capacity" issue, on modern switches, but when you work with something like VoIP, QoS features can be important.

[Leo Laohoo]

Joe, 

Don't forget our favorite bugbear:  Buffer.

[Joseph W. Doherty]

Laugh, I didn't "... and how much buffering they support ...", but it's good that you noted  it again, as it's so important.