TETRA Broadcast PDUs

[ecarl65]

I'm an EE and was looking for some potential open source or similar projects to contribute to. Because the spec is available online and it's got some cool digital aspects, as well as a few systems in my region, I thought I'd take a look at TETRA (maybe osmocom-tetra or something). I do have one question though. Looking at the spec (EN ETSI 300 392-2 section 21.4.4.0) it says that there are multiple types of Broadcast PDU. If the "broadcast type" field is 00 then it's a SYSINFO PDU, which is one of the first things I wanted to decode. 01 is an ACCESS-DEFINE PDU. 10 is a SYSINFO-DA PDU, which is a SYSINFO message for QAM. But then 11 says "Reserved." What does that mean? What if data comes with that type, what to do with it? Is there any place that's used? Does it just mean they will introduce the spec later or that manufacturers can do what they want with it?

 

[slicerwizard]

But then 11 says "Reserved." What does that mean? What if data comes with that type, what to do with it?

Not much other than display the raw data and try to reverse engineer it.

Does it just mean they will introduce the spec later

They might.

or that manufacturers can do what they want with it?

No, it's a reserved value.

 

[thewraith2008]

looking for some potential open source or similar projects to contribute to.

Telive is open source. Not sure if it's open to contributions.

That I'm aware, all current TETRA networks are Pi/4-DQPSK modulation, so only SYSINFO and the rarely seen (if ever) ACCESS-DEFINE PDUs are used. The SYSINFO-Q, SYSINFO-DA are for different modulations.

I see 2 'Reserved' elements used in the MLE (000,011) 'Protocol discriminator' and the PDU 'AL-SETUP' from LLC protocol even though the option for 'Advance link supported' is not enabled in BS Service information element (18.5.2.1 BS service details).

Barring some error in the decoding, why these elements are active is unknown and likely to stay that way without documentation to explain them.
This is the lastest version of ETSI EN 300 392-2 v3.8.1 (2016-08)

It could be possible that the equipment manufactures have implemented these reserved elements for there own purposes, but it does go against the whole point of having a standards.