Mobile Device Designers: You Can Relax Now - Part 2
“Flexibility” sounds like a good thing when you’re talking about a new wireless technology, and for the most part it is. A flexible technology gives a mobile device developer a wide variety of options when implementing a design. Unfortunately for anyone designing for a flexible technology, whatever is being developed will someday have to interoperate with some entity whose designers were offered the same flexibility.
Such was the case when Wideband-CDMA was first rolled out. WCDMA system engineers laughed at the poor CDMA engineers who were constrained by pre-defined service options, for example. The WCDMA folks had a lot of flexibility to configure low-level parameters and optimize systems the way they wanted to.
The result was messy… with so many possible ways to set up a network, no one seemed to be 100% in agreement as to which was the “optimal” way. Device designers relied on whatever test equipment was available and found that while the configurations offered were valid, they bore little resemblance to any real-life network.
Weeks were reserved for inter-op testing but flew by as participants spent much of their time blaming each other for the inability to establish a working connection . Even when connections could be made, some systems were unable to support certain services. The result was that subscribers bought brand new high-end phones, paid for highly-touted new data services and often found that they couldn’t make simple voice calls.
Why bring up old history? Because history repeats itself, and sometimes to our detriment. Today, as we prepare for the wide-scale launch of IMS services, it’s worth noting that IMS is an extremely flexible subsystem. Operators and network equipment manufacturers have incredible flexibility in configuration leading to a staggering number of possible permutations, even when the operator and NEM configurations are known. While some may point to the GSMA’s IMS profile (Document IR.92) a close read makes it clear that it allows for a lot of flexibility… clearly stating in the Scope section, “The profile does not limit anybody, by any means, to deploy other standardized features or optional features, in addition to the defined profile.” As another datum point, IR.92 refers to 3GPP TS 24.229 to define SIP registration call control. That document uses the word “optional” 80 times when referring to features of UEs or network elements.