Partial Request are coming... please help

Hi All,
We are having the system, where we are using the socket programming (TCP/IP), a system called plugin playing a role in between two system, where its getting the request from system1 and its processing it and re-directing the request after its validation, to system2.

Normally, message sending and receiving are fine. but I between some times, the mediation(plugin) is receiving some partial data, even thought the system1 has delivered the message single time.

The partial data coming in the following fasion
like full data is abc...xyz

here first its receving abcdefgh
second : abcdefghigklmno
third : abcde....s
:
:
finally : abcde..xyz

so i am in confusion until unless the first system, send again, there is no possibility to receive the data again..

so can anyone help me to solve this problem. why the partial data is coming... how to resolve it.