Jim Forster <forster@cisco.com> (03/27/91)
Archive-name: internet/route/cisco-igrp-doc/1991-03-26
Archive: ftp.cisco.com:/igrp.doc [131.108.1.111]
Original-posting-by: Jim Forster <forster@cisco.com>
Original-subject: Re: delay of an interface
Reposted-by: emv@msen.com (Edward Vielmetti, MSEN)
Francis,
For the purposes of measuring the delay to be used in IGRP, the simplest
thing to do is run a bunch of 1500 bit ping packets, and use the average delay.
That's 1500 bits, not bytes.
Quoting from ftp.cisco.com:~ftp/igrp.doc
"In principle the composite delay, Dc, could be determined as follows:
Dc = Ds + Dcir + Dt Eq. 2
Where:
Ds = switching delay;
Dcir = circuit delay (propagation delay of 1 bit); and
Dt = transmission delay (no-load delay for a 1500 bit message)."
Walt Prue's method of plotting the delay of various size packets is
interesting, as it yields Ds+Dcir. The slope of the line is the bandwidth.
If you do this over a long path, or a line with some background traffic, you
can deduce the effective bandwidth of the path.
>> 10000*Bandwidth+Delay/10 with Bandwidth in kb/s and Delay in us
The Bandwidth must be inverted and scaled by 10E10. Also quoting from
the same source:
"Bandwidth is inverse bandwidth in bits per sec scaled by a factor of
10e10. The range is from a 1200 bps line to 10 Gbps.... Reliability is
given as a fraction of 255. That is, 255 is 100%. Load is given as a
fraction of 255....
Because of the somewhat wierd units used for bandwidth and delay, some examples
seem in order. These are the default values used for several common media.
Delay Bandwidth
Satellite 200,000 (2 sec) 20 (500 Mbit)
Ethernet 100 (1 ms) 1,000
1.544 Mbit 2000 (20 ms) 6,476
64 Kbit 2000 156,250
56 Kbit 2000 178,571
10 Kbit 2000 1,000,000
1 Kbit 2000 10,000,000
6.3 Metric computations
Here is a description of the way the composite metric is actually computed...
metric = [K1*bandwidth + (K2*bandwidth)/(256 - load) + K3*delay] *
[(reliability + K4)/K5]
If K5 == 0, then there is no reliability term.
The default version of IGRP has K1 == K3 == 1, K2 == K3 == K5 == 0"
-- Jimaggarwal@jvnc.net (Vikas Aggarwal) (04/02/91)
Archive-name: internet/route/hedrick-igrp-doc/1991-04-01 Archive: nicol.jvnc.net:/pub/igrp.* [128.121.50.7] Original-posting-by: aggarwal@jvnc.net (Vikas Aggarwal) Original-subject: Re: delay of an interface Reposted-by: emv@msen.com (Edward Vielmetti, MSEN) > (Those truly interested in IGRP should read Chuck Hedrick's > description of IGRP from a couple of years ago. I packed all my RFCs > for a move next week or I would be able to offer a place to find this > document. Perhaps someone else could say? Might be at rutgers in > anon FTP... At any rate, a good description of the protocol and an > explanation of how the metric equations allegedly work.) > > --Kent The paper is available for anonymous ftp on nicol.jvnc.net (pub/igrp.ps and pub/igrp.doc in postscript and text versions). -vikas vikas@jvnc.net (609) 258-2403 --------------------------------------------------------------------------