On Thu, May 05, 2005 at 11:52:23AM -0700, Eric Blossom wrote: > On Mon, May 02, 2005 at 04:07:04PM -0700, Richard Cagley wrote: > > To implement MAC layer elements, i.e. waiting for data to arrive, is the > > best strategy to program these elements in python? > > This is an area of active exploration. > > Some are working in python, some with blocks in C++, some using the > message and message queue abstractions. It's not sorted out. > > > Are there any example apps that implement packet modem like functionality? > > Rahul, care to chime in here about your work?
I'm working on CSMA/CA-over-GNU Radio. Here's a long-winded summary: The end goal is an 802.11-like protocol (probably with relaxed timing requirements), so CSMA/CA is a necessary first step. To keep things simple, I'm using wires (wireless will come...later) The flowgraph makes things very modular, and once you understand the programming model, things fall into place nicely (Eric, thanks for you all your help!) GNU Radio provides message queues, which are very useful for passing state information between blocks and also link subgraphs nicely. Incidentally, I'm told the OSSIE project at Virginia Tech is compatible with GNU Radio. I'm not sure if that means the full platform or just the USRP, though. The main problems that I've encountered are lack of a good way to handle timing and difficulty implementing physical carrier sensing. Timing has been mentioned a few times, and the consensus seems to be that it will require some changes in GNU Radio. Eric mentioned setting up something running alongside the ADCs/DACs to do this (off-list discussion). Until then, I'm planning on hacking in something to emulate timeouts and retransmissions. In general, it's a bad idea to sleep in a block, but if I set up the flowgraph right, I think I can get away with it. Maybe using SIGALRM will help also. As already noted, keeping up with DIFS and SIFS will be difficult because of the latency issues. Putting some of the MAC in the FPGA sounds promising, but what are the implications for on-the-fly reconfigurationg? How long would it take to reprogram the FPGA if you needed to switch between 802.11a and b/g? As for carrier sensing, I'm pretty sure I'm just not doing something right and need to take another look at it (I'm wrapping up my thesis right now, so I'm tied up with that). Is there a way to shut of the Tx port to make sure there's no carrier? How long does it take to go back to a ready-to-transmit state after it's been shut off? -Rahul -- Rahul Dhar [EMAIL PROTECTED] Actually, my goal is to have a sandwich named after me.
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