Is there a guideline published that considers the total number of 100 MB ethernet ports on a switch and then recommends an appropriate size for the gigabit ethernet channel (trunk) connecting the switch to the rest of the network ?
Not sure that a chart actually exists, but the answer is probably determined by several factors. What is the function of the trunk? Is it an uplink from an access layer switch or a connection between two core devices? Does the access layer switch have Servers connected to it, or general use desktop computers? How is your network used (lots of voice/video, large file transfer traffic)?
Oh and btw, in a wiring closet with desktop computers, you shouldn't be concerned with 15:1 or even 20:1, and that number seems to grow as more and more gigabit desktops are being sold. Just because that machine has a gigabit nic, doesn't mean it could actually perform at a level that would actually utilize 1 Gbps.
I think it would be interesting to consider all the scenerios, but let's just say generically it's a fully loaded 4500 series switch in a wiring closet and you're trunking it back to a core switch in the data center. The traffic is office printing, shared drive access on several W2K servers, and outlook e-mail primarily. I have yet to see a Cisco press book that explains how to do the actual engineering on different scenarios -- they are great for telling you the concepts and the configuration commands to make it happen -- but what about the math ? What should the assumptions be ? At least 1 megabit per second guaranteed under peak conditions ? More ?
Kev> Not sure that a chart actually exists, but the answer is probably
Here is a Cisco link pitching 10gig uplinks and it has some discussion of oversubscription from the closets. Of course they want you to buy the 10gig solution.
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I think it comes down to how demanding is the user base (ie. what applications are used and what kind of traffic load do they generate), and how much can you afford.
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