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RE: frame relay to atm conversion tool?

  • From: Swaminathan, Sekar
  • Date: Thu Jan 09 18:49:04 2003

Instead of Frame Relay frames, you have to look at the
payload which is usually IP packets. Here is the formula
that I would use:
   BW = IP bandwidth in bits per second (bps)
   PS = average IP packet size; typically 256 bytes
   AO = AAL5 Overhead = 8 bytes
   OH = overhead factor
        Ceiling((PS+AO)/48) * 53
      = ------------------------
                 PS
        Ceiling((256+8)/48) * 53    6 * 53
      = ------------------------ =  ------ = 1.24 (for our 256B example)
                 256                 256
  EBW = effective ATM bandwidth in cells per second 
        BW * OH
      = -------
         53*8

Thus for 512 Kbps IP bandwidth, you need 1497 cps ATM bandwidth
assuming 256 byte average packet size. SCR should be at least this.
The PCR could be the line rate or equal to SCR. The MBS could
be 32 cells (1 MTU packet size at least) for low jitter applications
and as high as 256 cells for bursty applications.

-Sekar

-----Original Message-----
From: Brennan_Murphy@NAI.com [mailto:Brennan_Murphy@NAI.com]
Sent: Thursday, January 09, 2003 3:08 PM
To: nanog@merit.edu
Subject: frame relay to atm conversion tool? 



I'm trying to locate a tool (eg, spreadsheet) to convert throughput
on a frame circuit to an ATM circuit. So, for example if you have
a 512k CIR with burst to 1024k and 80% of the time you get your
burst bandwidth and you want to convert that link to ATM,
what corresponding SCR/PCR/MBS values would you need.
I'm less concerned with Frame vs ATM protocol overhead
than I am with calculating the difference in the way the burst
bandwidth is meted out. Any recommendations?

Supposing no one knows of such a tool. Would anyone be
interesting in helping me put one together?  

Best Regards,
-BM




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