Session is not terminated while using kannel is ussd as gateway

I have tried to connect kannel to USSD gateway, its connected but session is not terminated, the message is appearing continuously.
can someone help on this.
group = smsc
smsc = smpp
smsc-id = ussd
host = xx.xx.xx.xx
port = 7376
transceiver-mode = yes
smsc-username = xxxx
smsc-password = yyyy
msg-id-type = 1
system-type = "SMPP"
service-type = "USSD"
log-file = "/var/log/kannel/ussd.log"
log-level = 0
max-pending-submits=10
source-addr-ton=4
source-addr-npi=1
dest-addr-ton=4
dest-addr-npi=1

group = smpp-tlv
name = ussd_service_op
tag = 0x0501
type = integer
length = 1
smsc-id = ussd