Re: [lwip-users] question about TCP retransmission

[yueyue papa]

I known the usage the TCP is nor properly. But I have no "right" to change the customer protocol.

 

The requriement is: one tcp connect is just for send, and response, the connection is disconnected.

 

I could see the connect may take 2~3s in certain condition, the send and response will be about 2s. but the requirement is for finished the transaction with 5s.   I do not knwon how to increase the lwIP performance in this condition.

 

I use lwIP replace the platfrom TCP/IP, due to the original TCP/IP is design for lan, it has quick response but not stable in GRPS environment (lot of strange problems happened.)  LwIP gives a stable performance.

 

With the time out, the transaction speed requireemnt comes in. I could hardly trace in GPRS environement. I just trace in the server side, some time I could the data retransmit is very later. (50s).  My test is simple echo server test.

 

Is there any suggest so that i me do the fast transaction?

 

Lee

On Tue, Mar 31, 2009 at 11:41 PM, Kieran Mansley <address@hidden> wrote:

On Tue, 2009-03-31 at 23:28 +0800, yueyue papa wrote:
> How could I increase the TCP retransmit as quick as possible.  The
> normal interact between server will be 1.4s ~ 2.5s. Some time the
> receive will be long than 20s, event to 50s. The interact is success,
> but it is extremely slow.

Do you have a packet capture of this?  100 bytes taking 50s is rather
unusual: I would expect multiple cycles of loss and retransmission if
this is the case, and TCP backs off its sending rate (for good reason)
in these circumstances.

Your suggestions are unlikely to help, and may make things worse or at
least have unintended side effects.  TCP is quite cautious when it sees
loss as it interprets this as meaning the network is congested.  There
have been some research projects over the years to modify TCP to make it
better at coping with environments like yours where loss is not due to
congestion, but lwIP doesn't have this sort of thing included.

Probably the best solution if you require something that TCP isn't good
at is to use UDP, and layer your own protocol on top to deal with loss.

Kieran



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