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Cell Relay Retreat>List Archive>month:1995-Apr> msg00267



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Re: ATM vendors

  • From: jfinley@netcom.com (John Finley)
  • Date: Wed, 19 Apr 1995 17:31:36 -0500, Wed, 19 Apr 1995 22:15:22 GMT

Bill Schultz (guru@deltanet.com) wrote:
: In <D7AFpo.1xz@melpar.esys.com>, jwills@melpar.esys.com (Jeffrey M. Wills) writes:

: [my original post deleted]

: :> [followup deleted]
: :>Dr Jeff
: :>jwills@melpar.esys.com
: :>E-Systems, Inc. Ashburn, VA.

: [deleted]

: What is the acceptable end-to-end latency?  I think for voice use, most
: folks are disturbed by satellite hop delays (roughly 250ms), so I would
: look for end-to-end latency of under 100ms.  Since most switch vendors
: would seem to promise no worse than 20ms per switch for higher priority
: cells (given that the higher level control program does not over-burden
: a given link with too many higher priority cells), it would appear to me
: [edited]

At 51 Mbits/sec, one cell is about 8.3 usec, so 20 msec represents
over 2K cells, assuming the line's at capacity.  I'd have expected a
few cells (tens?) worth of buffering for "higher priority" cells; it
would seem that getting up to 2K means you're already in trouble.

Do current switches really buffer this much?

John Finley