Help needed to troubleshoot UDP transfer issue

[thiyagarajankalaiselvan]

Hi All,

I'm facing a strange issue, Data transfer through UDP is very slow wheras data transfer through TCP is very fast for the same source and destination.

I have the wireshark output captured from the client and server. Can anybody help me to know how much bytes of data is getting transfered with the help of wireshark output

I could see the UDP, length as 1464, Does it mean 1464 bytes if data getting transfered betweeen client and server?

Regards,

Thiyagu

[lgijssel]

The theoretical maximum payload for UDP is as follows:

ip mtu 1500 minus 20 bytes ip header (without options) minus 8 bytes UDP header equals 1472 bytes of data.

Your transfer is slightly less but that is probably not the problem.

Depending on the application, it can be that every UDP packet must be acknowledged before sending the next one.

If your round trip time is long (>20ms) this has a big impact on the effective througput.

Taking the above example value, no more than 1000ms / 20=50 packets (50 x 1472 bytes=73,6k) can be transferred per second.

TCP handles this superior because it can send multiple packets before requiring an ACK.

This likely explains the difference in througput.

UDP is only faster when the round-trip delay is small, i.e. the hosts are on the same local LAN.

regards,

Leo

[gfcisco31]

Friend...

I would configure IP sla in the endpoints with UDP echo and monitor it, use the same port used by application of course.

Also you could run a ip sla for TCP and then compare.... this is probably something with the application, but just to make sure IP sla can show you if it might be something with the network devices or not.

Hope this helps..

Please, rate helpful posts.

[Joseph W. Doherty]

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Posting

Leo's post accurately describes a common WAN performance difference between UDP and TCP applications.

On a LAN, it's possible a UDP application might run much slower since it might be more involved with the network processing.  If the application has to ACK individual packets, but if the application has poor resource priority, it could run slower than TCP, where the TCP stack would ACK packets, perhaps with better resouce priority.

On both LAN and WAN, TCP applications are more likely to deal with in-path lower MTU than a UDP application.  If this happens, i.e. IP packet fragmentation, UDP might be slowed vs. TCP.

[ftomek]

I have the same problem with UDP low transfer. Btest by MikroTIK shows about 10% of access link on UDP and 80% of access link on TCP. I have 3560G - 1GE SX - 2960 (100Mb). Tests were made from 3560 to 2960. When test stations are in he same switch UDP tranfer is high.