TCP static flow problem

static-flow is configured to make SBC(ecze730) installed on vmware  as   TCP proxy  .

static-flow

        in-realm-id                             ACCESS

        description

        in-source                               0.0.0.0

        in-destination                          22.1.2.7

        out-realm-id                            CORE

        out-source                              10.50.0.60

        out-destination                         10.20.1.134:3

        protocol                                TCP

        alg-type                                NAPT

        start-port                              40000

        end-port                                41000

        flow-time-limit                         0

        initial-guard-timer                     6000

        subsq-guard-timer                       6000

        average-rate-limit                      0

The problem is everytime I had sent 4 bytes data through the tcp connection , the connection would be closed .

how to keep the connection open all the time ?