sending a packet from transport layer

I am facing this problem since long and really hampering my progress in
implementing

cisco's pgm protocol in linux kernel 2.6.15 . Basically its a reliable
multicast protocol

works at a transport layer. So for as of now, i am trying to change my
udp functionality

from net/ipv4/udp.c changed to refect pgm. I have implmented my own
header instead on udp

header and i am receving it fine at the other end. But now as for
implemenation of NACK (

negative ack) i have to check header of received packet sequence
number ( my own header

has it as per pgm sepecifications) and generate reply for nack from
udp_rcv() function

only. Thats where I am facing the problem. I dont know how to send any
packet from the

transport layer itslef. I tried using calling ip_push_pending_frames()
directly but not

working as I would not be having any sock for the packet I received.
Can I just call

sys_socket and sys_sendto to send a packet . ( I tried that too but now
working , both my

tries gives me some sleeping from invalid context error) . Is there any
body who can help

me out? echo echo .....