In my previous posts I have been decoding LTE PDSCH (physical downlink shared channel) transmissions from an IQ recording of an eNB and looking at the MAC PDUs with Wireshark. The analysis I have done of the upper layer protocols is somewhat limited because I have decoded only 500 ms of traffic and because I don’t have the encryption keys, and also because I’m just beginning to learn how the LTE upper layers work. When doing this analysis I thought that it would be good to have a more complete example that I could use as a reference. A Google search for examples of PCAP files containing LTE MAC PDUs yields very little, so I thought I would make my own example with srsRAN. In this post I show how to set up an srsRAN LTE eNB and UE communicating over ZMQ on a single machine and then analyze the traffic in Wireshark.
Tag: networks
NPR: Hamnet over 70cm
Some days ago, Guillaume F4HDK emailed me to introduce me his latest project, NPR (New Packet Radio). This is an open-source modem designed to carry IP traffic over the 70cm Amateur radio band, with data rates of up to 500kbps. The goal of this modem is to be used for the Hamnet Amateur radio IP network, to give access to end users where coverage on the 2.3GHz and 5GHz bands is poor due to the terrain.
Guillaume knew that I had worked on IP over 70cm with my CC1101 and Beaglebone black project, so he wanted to know what I though about NPR. After reading all the available documentation, I found NPR very interesting. Indeed, Guillaume has come up with clever ways of solving some of the difficulties I foresaw when planning out my experiments with the CC1101.
The most important aspect about NPR is that it is already a finished product that people can build as a kit and start using. My experiments with the CC1101 were a mixture of proof of concept and play around, and never progressed from that stage due to lack of interest in my local Amateur community. However, Guillaume has put a lot of time, thought and effort in developing NPR. Of course the project can evolve further, but it is usable in its present stage. In what follows, I do a detailed analysis of the technical aspects of NPR.
IPv6 for Amateur radio
Back in September 26 2016, I posted an email in Spanish to the Hamnet.es mailing list detailing my proposal for an IPv6 Amateur radio network, and trying to engage people into some preliminary tests. In October 1 2016, I posted a summary (in English) of my message to the 44net mailing list. There was some discussion afterwards in the list, but no real actions were taken. Since then, no much interest in IPv6 for Amateur radio seems to have sprung. Still, I think that the time for IPv6 will come. I have collected my IPv6 for Amateur radio proposal in a page here for future reference. At least I hope that this pops up on Google searches for IPv6 and Amateur radio, since there is not much material about this on the Internet, and most of what one can find is quite dated.
Reverse engineering Outernet: time and file services
In my last two posts, I’ve being talking about my reverse engineering efforts with the Outernet signal and I’ve described the modulation, coding and framing and the L3 and L4 network protocols used in Outernet. This post is the last in this series. Here I talk about how the time and file services work. Recall that a Free Software implementation of an Outernet receiver based on these descriptions is now available at gr-outernet and free-outernet.
Reverse engineering Outernet: L3 and L4 protocols
This is a follow-up to my last post, where I talked about my efforts to reverse engineer the protocols used in the Outernet L-band signal. Here I will describe the L3 and L4 protocols that are used in Outernet.
This description is solely based upon my reverse engineering efforts. As there is no documentation available for this protocols, I get to name them as I like. Also, I’ll describe the protocols just from how they appear to work. Probably the developers at Outernet had something a bit different in mind. In any case, my understanding of how the protocols work seems quite good, as I have now a functional file receiver called free-outernet. In my next post I’ll talk about how the Outernet time service and file service work.