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Point taken, when switches are connected into the stacks if all 48 ports communicated with the other members cross ports the stack would not be enough. The speed of 32Gpbs would this be on one stackwise cable or would 2 cables allow 64Gpbs? Also is the internal switching fabric touch when data is passed by different members?
Also how did you calculate the maths behind your latter comment on the Mbps?
I know this thread is based on a switch, but I also have a router question.
Based on this guide http://www.cisco.com/web/partners/downloads/765/tools/quickreference/routerperformance.pdf
It is said that a 881 Model router roughly has a throughput of no more than 25 Mbps. But when conducting a speed test with a high speed Internet link, I'm able to archive 90 Mbps bidirectional?
An original series 3750 (or 3560) fabric is 32 Gbps. This is different from the stack ring's "32 Gbps" (which is really dual 8 Gbps, duplex).
An original series 3750 (or 3560) internal fabric, in theory, is oversubscribed by more than 16 gig ports (i.e. the "G" suffixed original models).
The terms non-blocking and blocking, when examining switch fabric isn't just sufficient bandwidth capacity to forward all port bandwidths, it's whether the fabric's architecture will block, or not, forwarding of frames even if there's "sufficient" bandwidth.
For example, you have three ingress ports. Two are sending to one egress port (2:1) and the other is sending to other egress port (1:1). If 2:1 congestion on the one egress port delays (or blocks) transmission on the 1:1 egress port, you have HOL (head-of-line) blocking even though the internal fabric's bandwidth could support each ingress port sending to a separate egress port (all 1:1).
StackWise (and StackWise+), when available, use both ring ports.
Original StackWise copies ALL member switch traffic to the stack ring. Original StackWise source stack member also removes the traffic it placed on the stack ring.
StackWise Plus only places unicast traffic on the stack ring when destination is not a local switch port. Additionally, destination switch member removes unicast packets. (I.e. StackWise+ uses it's ring much more intelligently. It also has dual 16 Gbps stack ring ports. NB:StackWise+, for the most part, reverts to StackWise operation if there's a StackWise only member switch in the stack [good reason not to use such mixed stacks].)
Bits per second, is the transmission rate supported by the media. So, for example, 100 Mbps allows transmission of 100,000,000 bits per seconds. However, transferring actual data, in something like physical segments (e.g. frames) uses some of this capacity for both framing overhead and framing delineation, so useful capacity is less than the often quoted bps rate. Useful capacity percentage (of overall rate) also generally decreases as frame size decreases. (BTW, similar issue with disk media. At least disk capacity isn't, generally, quoted for its unformatted capacity any longer.)
The 25 Mbps throughput is rated for minimum sized packets. Larger packets often allow much higher throughput as the packets per second requirement (for same bandwidth) decreases. (Sometimes the vendor will document PPS rates for multiple packet sizes. Without such documentation, or your own testing, just knowing documented performance for one packet size you cannot accurately predict a device's performance for other packet sizes.)
