Loss measure in Argus

Desem, Can Can.Desem at team.telstra.com
Mon Aug 10 01:19:01 EDT 2009


Hi Carter

The manual on ra says that the "loss" measure shows "pkts retransmitted or dropped". It should probably also include out of order packets.
Here are the results of a simple tcp transmission experiment between a source and destination pc. All the packets are captured at both ends by tcpdump and then used for analysis;

Argus/ra shows 255 lost packets (sloss)  at the transmitter end (tcptrace gives 255 retransmitted packets). 

Argus/ra shows 3016 lost packets (sloss) at the receiver end (tcptrace gives 3016 out of order packets and 1 retransmitted packet). 

Clearly, at the receive end one will typically see the retransmitted packets as out of order packets and this number will be much higher than the number of the actual retransmitted packets. Therefore it is important to indicate this in the manual since one may mistakenly assume that the "loss" value is a direct indication of the retransmitted or dropped packets. Alternatively would it be possible to have separate measures for retransmitted and out-of-order packets as is the case in "tcptrace" ?

I checked this since I could not believe that the throughput could be so high given the high packet drop rate (initially collecting at the receive end only)

Regards,

C.Desem



  






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