Ref: 13680011
Title: Measuring Round-Trip Delay Between IBs
Date: 4/9/90

Copyright 3Com Corporation, 1991.  All rights reserved.

The round-trip delay of a packet includes the local bridge delay,
network delay, and remote bridge delay.  To estimate the delay time
when an IB forwards a packet from one end station to another, divide the
value of the round-trip delay by two.

To measure round-trip delay, use the IB command "Data Link Test" (DLTest).
The DLTest command allows you to initiate the datalink test, to specify
how the test is run, and to display the test results.  The test also helps
you determine whether a pair of IBs can properly exchange packets and
calculates the round-trip delay of packets.

Only one data link test can be run at a time on an IB.  The IB on which
you initiated the test accepts only the echoed packets from the
destination IB.  The test detects line errors if packets cannot be
transmitted or received, and records the number of packets misordered,
lost, duplicated, or corrupted.

To run DLTest, you need the destination address.  The destination
address must be an Ethernet address (for example, %080002XXXXXX).  It
cannot be an IP address (for example, 129.213.xxx.xxx).  On IB software
version 2.x, use "SHow SystemStatus" or "SHow NetMap <port number> L" to
get the destination address.  On IB software version 3.x or Brouter software
version 1.0 or higher, use "SHow -Bridge CONFiguration" or "SHow NetMap L."

DLT DestAddr = %080002XXXXXX   (IB software 2.x)
DLT DestAddr   %080002XXXXXX   (IB software 3.x or Brouter 1.0 or later)


To check received packets from the destination IB, set the RemoteEcho
parameter to ON.  When it is set to OFF (default value), DLTest acts as a
one-way traffic generator, and you will not see the number increasing for
the Receive Statistics with "DLTest STAT" command.

DLT RemoteEcho = ON   (IB software 2.x)
DLT RemoteEcho   ON   (IB software 3.x or Brouter 1.0 or later)


To display the DLTest parameters, type "DLT Parameters."


To start DLTest, type "DLTest START" and a message like the following will
appear:

   Wed Mar 28 12:00:00 1990 DLTest Sending Packets to %080002XXXXXX


To stop DLTest, type "DLTest Abort" and a message like the following will
appear:

   Wed Mar 28 12:30:00 1990 DLTest Done


To display the DLTest statistics, type "DLT STATistics."  A display like
the following will appear:

                          DLTEST PARAMETERS
src address = %080002XXXXXX            dest address = %080002XXXXXX
remote echo . . . . . . . . ON         transmit packt count. . . . Infinite
min xmit pkt size (bytes) . 60         max xmit pkt size (bytes) . 1514
packet size increment . . . 1          rcv checking ode. . . . . . None
transmit rate (pkt/sec) . . 10

                          TRANSMIT STATISTICS
number of packets . . . . . 210        number of bytes . . . . . . 34545
ave xmit rate (pkt/ec)  . . 10

                          RECEIVE STATISTICS
number of packets . . . . . 210        number of bytes . . . . . . 34545
max rcv pkt rate pkt/sec) . 10         ave rcv pkt rate (pkt/sec). 10
min rcv pkt rate (pkt/sec). 10         cur rcv pkt rate (pkt/sec). 10
max round trip delay (ms) . 299        good packets  . . . . . . . 210
min round trip delay (ms) . 27         ave round trip delay (ms) . 101


                       RECEIVE ERROR STATISTICS
lost packets. . . . . . . . 0          misordered packets. . . . . 0
length error packets. . . . 0          data corruted packets . . . 0
duplicated packets. . . . . 0


This example shows that the average round-trip dealy is 101ms.

Note:  The round-trip delay value is valid only if the remote echo
parameter is set to ON.


To find out more about DLTest, see the following manuals:

   IB Installation and Operation Guide (March 1989)  p. 6-14

   NetBuilder Operation Guide (March 1989)  p. 92

   Brouter Commands and Parameters Guide (March 1990)  p. 3-39

