# (no subject) **URL:** \ **Category:** GNU Radio\ **Created:** [July 3, 2014, 12:02am UTC](https://www.ruby-forum.com/t/no-subject/230761 "2014-07-03T00:02:47Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [July 3, 2014, 12:02am UTC](https://www.ruby-forum.com/t/no-subject/230761/1 "2014-07-03T00:02:47Z")
When I ran the example ofdm\_loopback.grc, i used a file source to send data through the transmitter and checked the output after the receiver in a file sink ; i found that if the packet required to be sent is less than the defined packet\_length ; then the packet is not sent ? how to send the last packet in this case ? ---
**Author:** ![GP\_2014](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/f08c70/32.png) [@GP\_2014](https://www.ruby-forum.com/u/GP_2014)\ **Post date:** [July 3, 2014, 8:43am UTC](https://www.ruby-forum.com/t/no-subject/230761/2 "2014-07-03T08:43:05Z")
Hi GP, ofdm\_loopback.grc covers only the physical aspects of the transmission. What you are describing is a flow control problem; you’d need to figure out yourself how to make your data stream fit into the packets. A typical way would be to send the length of your file, and then just fill up the last packet with random data/redundancy/zeros; however, what will happen if you lose one packet? In a real-world application, you’ll have some content header, you’d have channel coding/FEC, possibly some ARQ scheme, in case of multiple users a MAC etc; whereas you “only” stream bits out of a file. Complete, versatile transmission systems is what people build atop of transmission systems such as the GNU Radio-supplied OFDM packet transmitters (which primarily serve as good examples and showcases for the mechanisms involved). Hope that was a little helpful, Greetings, Marcus