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To: JGoren who wrote (19734)	12/14/1998 11:55:00 PM
From: Clarksterh	Respond to of 152472

JG - Could you elaborate on the distinction between air interface and infrastructure, ground interface for GSM? WARNING! Super long post - probably more than you ever wanted to know. Yes and no. The specs are a morass, and since I use them, at best, infrequently, I can only give some generalities off hand. To state some of the obvious, there has to be a spec between every two pieces of equipment in a mobile system which communicate with each other unless you expect that those two pieces will always be bought and operated as one. Thus there are specs to cover the air interface (since the phones and basestations are not a 'unit'), another between the basestations and the mobile switching centers (the MSC coordinates basestations, handoffs, ...) and yet another to PSTN (the standard telephone system). At first glance it may appear that the information being transmitted through each interface is largely the same, so why not just have one standard? But there are two problems with this - the first is that the media of transmission are substantially different (air interface is noisy, cannot support low frequency transmission and has multipath problems - none of which are a problem for communication over a copper wire or fiber optics), and the second is that there are substantial differences in the types of information that need to be transmitted (e.g. power control is something that is only important in an air interface largely due to multipath). Thus, in a digital system the solution is: 1) Reconstruct the data after each transmission and correct the mistakes made in transmission. (This is a very important piece because it almost completely isolates one media/standard from another. It makes the standards largely modular although there are undoubtedly some changes that will have ripple effects.) 2) 'Reformat' the data for the new transmission media and send it off. Bottom line - the air interface can be largely separated from the ground interfaces due to the modularity. Note, however, that what Qualcomm wants is that two very separate ground interfaces be available. Is this a big deal? No, largely because Gilders vision has already come to pass for this media of transmission (in contrast to the air interface which is much noisier and higher frequency). With today's technology it is probably possible to do almost all of the switching between standards in software or with the swap-out of one or two units (e.g. I don't remember if the RF link between basestation and MSC is spec'd, but even if it is, it is only one relatively cheap unit on each end.) This wasn't exactly what you asked for, but, off-the-cuff, it is the best I can do. Hope it helps. Clark