Interoperability in the Real World

By Oren Libis

Managing interoperability for 3G-324M is not easy if you are a handset developer. There’s a lot to be done and some of it doesn’t always make sense.

What happens when a handset manufacturer finish developing and testing his 3G handset and wants to go sell it through an operator?

This seems like a straightforward enough process: you take the handset, you make sure you test it properly in your labs with a professional QA team and you’re done. That may be the case for things long supported by 3G handsets, such as audio calls over GSM or sending SMS messages, but for 3G-324M this is usually a bit more complex.

3G-324M testing has several different test phases: there are the IMTC, which does interoperability events – and publishes test cases, you have the GCF test labs, which validate handsets using a subset of the IMTC test cases, and then you have handsets and servers that are already deployed.

I have been working for a long time now with handset manufacturers and I have come to the conclusion that sometimes the focus is on the wrong kind of tests.

It might take a bit of time, so let me start by focusing on the GCF.

Take the GCF selected test cases for example. Since most of them are important when you validate your handset – they are all mandatory. But from analyzing them closely you can easily split them up into 3 distinct groups:

1. Important test cases
2. “Nice to have” test cases
3. Unnecessary test cases

I’ll give an example of each. By the way, as the GCF test cases are simply references to the IMTC, you can find all of these test cases here, separated into two distinct documents: interoperability and compliance.

Important test case
An example of an important test case is test case 54. It deals with master slave conflicts – a situation that is common when you have a call between two handsets from different vendors. A few years ago, a lot of handsets on the market and those developed by IMTC companies were unable to pass this test case. As this one deals with a plausible and common scenario, it is important to test it.

“Nice to have” test case
A “Nice to have” test case is test case 47. It checks to see if a handset is capable of accepting a change in media transmission rate because the other terminal/server requested him to do so. I have never quite seen this kind of a scenario happen in real life (it might, I just never saw it). You can take my word for it that this procedure is not that necessary and effective when video is presented on a small screen like the one used in 3G handsets. So this is a “nice to have” test case in my view – it’s a good enough feature, but the problem it comes to fix is just not there most of the time.

Unnecessary test case
An unnecessary test case is test case 45 (and 45u). In this test case, you need to respond to a RequestMultiplexEntry message – either by acknowledging it and sending the entry’s information or rejecting it. If someone is sending it to you, it means that he is already in a lot of trouble, as he didn’t remember what you told him (there are only 16 entries, so this must make him a senile). Let’s assume you reject it – this makes him unable to do a thing about it but drop the call. So we have a test case where the one you are working against is faulty/senile – you choose, and you can decide you don’t support this feature, hence causing a disconnection (and you are still validated by the GCF!). I have never seen a real handset acting in this kind of a way when the terminal he was working against was doing his part of the job. This means that developers need to handle this test case (and a few others similar to it) although their handsets will never actually be in this scenario.

Distinguishing between the different test cases is not easy and requires some knowledge in 3G-324M and in what different products, both handsets and server, are doing. At the IMTC’s 3G-324M Activity Group each company gets to work against a large variety of companies and products with the actual QA and development teams of these companies. This provides important information that can assist any handset vendor to pass his interoperability tests once he gets to that point.

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