[j-nsp] Latency FastEthernet & Testing with Anritsu, Agilent, SmartBits

[Anil Chaudhary]

Hi Alex,

Regardless of what test device (Agilent N2X, Spirent SmartBits etc) you use
to measure the latency of SUT, they will introduce their own internal
latency. So, the latency measurements you will get from these devices will
include their own internal delays as well and therefore for absolute results
(i.e. the true latency of M20) you need to find out the internal latency of
the test device used and then subtract it from the latency measurement
obtained above.
And as mentioned by Chris, it also depends upon the type of measurement used
i.e. FIFO or LILO. For your information Agilent's N2X uses FIFO style of
measurements. 

Hope this helps.

Cheers,
-anil


> -----Original Message-----
> From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-
> bounces at puck.nether.net] On Behalf Of McCoy, Chris
> Sent: Friday, 29 April 2005 12:01 AM
> To: 'Alex Kitschkiruk'; 'juniper-nsp at puck.nether.net'
> Subject: RE: [j-nsp] Latency FastEthernet & Testing with Anritsu,
> Agilent,SmartBits
> 
> Hi Alex,
> 
>   I happen to work for Spirent, so I can't speak for the other companies.
> SmartBits uses "LILO" (last in-last out) measurement for latency.  The
> timestamp that is inserted at the end of the frame is based on the last
> bit
> of the frame that egresses the test port and by the same token, the
> timestamp is noted when the last bit of the frame enters another test
> port.
> It then computes the difference.  Some companies use FIFO or LIFO (see
> RFC-1242 section 3.8).  This could be the source of your inconsistent
> results.
> 
> Chris M.
> 
> -----Original Message-----
> From: Alex Kitschkiruk [mailto:juniper.m20 at gmail.com]
> Sent: Thursday, April 28, 2005 4:32 AM
> To: juniper-nsp at puck.nether.net
> Subject: [j-nsp] Latency FastEthernet & Testing with Anritsu, Agilent,
> SmartBits
> 
> 
> Hello everybody! I tested M20 (RFC 2544).
> The results:
> (Juniper M20, 4 Port FastEthernet, Average Latency, in microseconds)
> 
> 128 Byte
> ------------------------------------------------------
> NetStat   26 mcs
> Anritsu MD1230B  20 mcs
> Agilent N2X   48 (!!!) mcs (Min=32, Max=71)
> Spirent SmartBits 600B  N/A (Min=26, Max=51)
> ------------------------------------------------------
> 
> 1024 Byte
> ------------------------------------------------------
> NetStat   100 mcs
> Anritsu MD1230B  28 mcs
> Agilent N2X   177 (!!!!) mcs (Min=106, Max=293)
> Spirent SmartBits 600B N/A (Min=99, Max=289)
> ------------------------------------------------------
> 
> Which are correct? What is in specifications?
> 
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