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Technology Stocks : Ascend Communications (ASND)
ASND 217.34-1.5%1:07 PM EST
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To: The Phoenix who wrote (51881)8/11/1998 1:55:00 AM
From: bucky89  Read Replies (1) of 61433
 
>An emerging class of high-speed IP switches
>can read the beginning and end of packets at
>line speeds, a capability that will go a long
>way toward enabling QoS in IP environments.

your remarks Gary:

>What does speed of an IP
>switch have to do with it's ability to discern packet types? I mean, yes, certainly
>processor speed is fundamental but what does this have to do with trunk speed?

I think the author is talking about the ability of high-speed IP switches to quickly determine the length of each oncoming IP packet. This is indeed one of the major hurdles in providing IP QoS. The TOS byte is easy to read and use, as opposed to determining packet length is where much of the work is at. Once you do this, you can sort the packets out into different queues by packet length. That way you can prevent long packets from blocking shorter, time-sensitive packets.

This is a very processor-intensive task, and becomes even more difficult when packets rush at you at OC-48 or OC-192 speeds. You have to come up with special router h/w architectures to distribute the processing load among multiple processors. I'm sure there are lots of other technical issues that I'm not familiar with.

ATM circumvents this work by cutting all data up into nice 48-byte chunks for easier processing and prioritizing. In the process you add a lot of cell headers and with fragmentation end up with a cell tax of about 20-25%.

bucky89
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