 market. It offered cost-saving features, such as over-the-air technical support, which reduces operations, administration, and maintenance (OA&M) costs. Its reliability and consistency made it interoperable, and at the same time, the user in- terface and interactions with other systems were left open, allowing for innovation. Competition was fostered because interfaces were standardized, but devices were not specified. EMS and MMS expand on SMS but only add features that may enhance the con- sumer's experience of the cellular telephone. They in no way enhance the experience of placing a telephone call. It is unclear if these services will increase revenue in the short term as a fad and then either fade away or be offered as standard features at low cost or no cost or if they will have lasting benefit as a source of revenue. Even if they do con- tinue to bring in revenue, will that increase revenue for the entire cellular industry or just help each vendor in the battle for market share? And will that revenue justify the cost of designing new user terminals and installing MMS-capable networks, not to mention the cost of other 3G components? One other set of questions needs to be answered: Is there a limit to the capacity available for SMS, EMS, and MMS? The original design assumed that these would low-volume services, short messages squeezed in between essential control signals. As messages grow larger and more common and they are concatenated, what happens? Our research has not turned up any discussion of these issues. At what point would SMS, EMS, or MMS messages exceed either the capacity of the ANSI-41 signaling channel or of the paging and access channel on the air interface? If this capacity is ex- ceeded, what happens? If a priority system is in place, then short messages simply will wait behind control signals. However, if it is not, then short messages might interfere with the signaling channel. It is unclear what effect this would have on a user termi- Downloaded from Digital Engineering Library @ McGraw