Howdy!When you run UDP tests, you should never rely on the results reported by sending peer[*]. Any network node between peers is free to drop any packet in case of congestion. TCP resolves this by retransmissions and application will normally detect this by seeing lower throughput. Even sending peer will detect lower end-to-end throughput with some delay (depending on Tx buffer size and TCP Window size) and in long-term the results (as reported by sending and receiving peer) should be roughly the same. UDP however does not implement retransmissions by itself. Which means that application at the receiving peer will see missing (dropped) packets while application at the sending peer will have no idea about that[**].
If you're doing tests using UDP I'd suggest to run tests single direction only and alternating peer configuration (first run Helsinki peer as client and London peer as server - results reported from London peer will tell you bandwidth from FI to UK - then run Helsinki peer as sevfer and London peer as client and results from Helsinki peer will tell you bandwidth from UK to FI).
[*] The only time that sendin peer will tell you correct throughput is when the first leg is the bottleneck as IP stack on sending peer will not drop packets but rather throttle down application (Tx buffer full) - this can happen with dial-up setups.
[**] When using UDP as transport protocol, it's up to application to detect any inconsistencies - such as dropped packets, out-of-order delivery etc. and to react to those as desired. One app that does all of it is NFS - it traditionally ran over UDP. Recent implementations avoid burden of data integrity checking by using TCP as transport protocol.
Peace! Mkx -- perl -e 'print $i=pack(c5,(41*2),sqrt(7056),(unpack(c,H)-2),oct(115),10);' -- echo 16i[q]sa[ln0=aln100%Pln100/snlbx]sbA0D4D465452snlb xq | dc ------------------------------------------------------------------------ BOFH excuse #127: Sticky bits on disk. martin je dne 12/02/10 01:18 napisal-a:
I did iperf test from one Linux server to another. One server is in Helsinki, other is in London and they are connected with a VPN tunnel(should be 100Mbps/100Mbps connection). I started iperf server in London(192.168.1.2) and iperf client in Helsinki(192.168.1.1). I started server with this "iperf -s -u -fm" command and client with "iperf -c 192.168.1.2 -fm -d -t600 -u -b 100m" command. Output was fallowing: #iperf -c 192.168.1.2 -fm -d -t600 -u -b 100m Server listening on UDP port 5001 Receiving 1470 byte datagrams UDP buffer size: 0.10 MByte (default) ------------------------------------------------------------ ------------------------------------------------------------ Client connecting to 192.168.1.2, UDP port 5001 Sending 1470 byte datagrams UDP buffer size: 0.10 MByte (default) ------------------------------------------------------------ [ 4] local 192.168.1.1 port 44456 connected with 192.168.1.2 port 5001 [ 3] local 192.168.1.1 port 5001 connected with 192.168.1.2 port 31435 [ ID] Interval Transfer Bandwidth [ 4] 0.0-600.0 sec 7189 MBytes 101 Mbits/sec [ 4] Sent 5128207 datagrams [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams [ 3] 0.0-600.2 sec 2396 MBytes 33.5 Mbits/sec 0.244 ms 3419123/5128199 (67%) [ 4] Server Report: [ ID] Interval Transfer Bandwidth Jitter Lost/Total Datagrams [ 4] 0.0-600.1 sec 2411 MBytes 33.7 Mbits/sec 0.199 ms 3408321/5128207 (66%) [ 4] 0.0-600.1 sec 299 datagrams received out-of-order How can there be bandwidth from Helsinki to London 101 Mbits/sec when Iperf server from London raports 33.7 Mbits/sec? How can there be such a huge packet loss(67% from London to Helsinki and 66% from Helsinki to London)? I would appriciate any comments about inner workings of Iperf or explanations about Iperf output :) Thank you in advance!! ------------------------------------------------------------------------------ SOLARIS 10 is the OS for Data Centers - provides features such as DTrace, Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW http://p.sf.net/sfu/solaris-dev2dev _______________________________________________ Iperf-users mailing list Iperf-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/iperf-users
------------------------------------------------------------------------------ SOLARIS 10 is the OS for Data Centers - provides features such as DTrace, Predictive Self Healing and Award Winning ZFS. Get Solaris 10 NOW http://p.sf.net/sfu/solaris-dev2dev
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