steveg (06/02/82)
Don't have it yet, but the order is as good as signed. We have gone into detailed analysis of the differences between 3Com and Interlan. Basically the 3Com is cheaper and gives you less. This is no problem if you are a stand-alone system (Indeed, we will probably get 3Com for our SUNs) but on a Timeshare VAX it can be hell. Let me illustrate: o On a 3Com you have to carry the data from the SBI memory to the UNIBUS memory in has on its card. This is a big expensive loop of 16 bit word transfers, withi much unibus window turning. The Interlan board does cycle stealing to the SBI memory. No processor intervention needed. o If a collision occurs on the 3Com, you have to go in and dump the queued output datagrams, if you don't you will not know who the next collision belongs to. You also have to do the backoff and retry in the driver at interrupt level. (you have to wait a precise number of microseconds). The Interlan does backoffs by itself. o The 3Com driver does not allow you to cancel pending messages. If you hit ^C to stop a remote disk file transfer, you can't abort it. o Don't Believe 3Com about collisions being very rare. Those measure ments were taken under fairly controlled enviroments by Shoch. There are other articles that point in other directions. Use your head and what you think your net environment will eventually look like when deciding if collisions are so rare. If you are single user micro, none of this is any worry. So the Interlan is no big win (and is more expensive). Look at what you are going to use it for, and make your decision on this basis