First, though, it might be good to clarify what I mean by "GSM" and "CDMA" as underlying technologies are confusing the issue since just about every new low-level wireless cellular protocol is based on a form of Code Division Multiple Access rather than Time Division Multiple Access.  That's another topic completely, though.  For the purposes of this article, a "GSM" carrier is simply someone like AT&T or T-Mobile in the US and a "CDMA" carrier is simple someone like Verizon, Sprint, or Alltel.

If you see GSM carrier phones you'll often see them as having "GPRS" or "EDGE" or "HSDPA" and, likewise, on a CDMA carrier you may see such things as "1x" or "EVDO" or "EVDO Rev A" or the likes.  More likely, though, you'll have to look for the underlying technologies because they'll be listed as "High Speed Broadband Access" or "3G data capable" or something more mundane.

However, before even any of those technologies, all GSM and CDMA phones could do data calls, back when it was simply just GSM data and CDMA data.  On the CDMA side, this was listed often as IS-95A or IS-95B access.  IS-95A would give a single 14.4 Kbps link while IS-95B could give multiple 14.4 Kbps links for up to 64 Kbps.  Back when ISDN was still the fastest way to the net for consumers, this wasn't too bad -- especially since it was wireless.  This was similar on the GSM side, but worked on  9600 bps slices of bandwidth and was called a "CSD" connection, simple standing for circuit switched data (using the same paths that your voice would follow).  You could get this in 28.8 Kbps and 43.2 Kbps forms, too.

I would like to clarify the numbers before I go on.  In all of these cases (old and new) the bandwidth numbers were always the maximum potential of the protocol.  This like like saying your Ethernet connection is 100 Mbps or 1 Gbps or your WiFi connection is 54 Mbps.  It is unlikely over those transports you'd ever get the full rates.  This is no different over a cellular wireless connection and, in fact, is magnified as you get farther away from a particular tower and can often vary by the number of people connected (much like a shared DSL connection) as voice tends to always take priority over data traffic.

1xRTT came out on the CDMA side, often called simply "1x" and it offered rates of up to 144 Kbps.  This was a full ten times improvement but was never really considered 3G for some reason.  On the GSM side, various flavors of GPRS started becoming available with speeds of 60 Kbps and 80 Kbps.  This was not quite as big of a leap over CSD and was definitely not referred to as 3G but was a welcome improvement in speed.  It was enhanced to speeds of 177 Kbps to 236 Kbps in a form called EGPRS which is commonly called EDGE.  This ranged from slightly faster than 1xRTT to not quite twice the speed of 1xRTT, depending on your carrier and equipment.

Surprisingly not long after either of these, we started seeing speeds that were often called true 3G speeds.  The first of this was with 1xEV-DO, normally referred to as just EVDO or in some circles as DO (standing for 1x Evolution, Data Only or sometimes Data Optimized, as opposed to the now defunct 1xEV-DV standard for "Data and Voice").  In it's first form, it offered rates of up to 2.4 Mbps on the downlink, but had only a mere 153 Kbps available for uploading data.  In the second form, currently being rolled out, the download was increased to 3.1 Mbps and the upload boosted all the way to 1.8 Mbps.  The first form is now commonly called EVDO Rev 0 while the second form is EVDO Rev A.

Not to be left behind, the powers that be for the GSM carriers introduced HSDPA.  HSDPA, for High Speed Downlink Packet Access, offers a range of speeds from 1.8 Mbps through 14.4 Mbps.  The speed one can get varies depending on ones equipment and carrier.  European carriers tend to have 1.8 Mbps or 3.6 Mbps deployed while Australia has a full 14.4 Mbps deployed.  Since these speeds range from decent to pretty fast compared networks that were around when deployed, some of these are being called 3.5G networks much like the slower ones were initially called 2.5G networks.  How you can have half a generation escapes me, but it doesn't matter.  Current uplink speeds are 384 Kbps but will be increased to 1.8 Mbps as higher speed "HSUPA" (U for uplink) equipment is rolled out.

Most of the networks that do HSDPA started with GSM and became known as "UMTS" or "WCDMA" networks, which is why the terminology is getting confused.  HSDPA is based on the older WCDMA standards (for Wide CDMA).

So, what does all of this mean?  Quite simply:

• IS-95A is the loose equivalent of CSD
• 1xRTT is loosely equivalent to EDGE
• 1xEVDO (in it's Rev 0, Rev A, Rev B forms) is loosely equivalent to HSDPA (in it's Category 1 through 10 forms)

What's coming up?  It depends on who you ask and how the names will change over time. I won't name anything since it's far too early to tell.  Various companies have been testing true mobile speeds in the 300-5 Gbps range, though.

Disclaimer: My main reference for this, other than my memory, was Wikipedia.  I didn't see anything on Wikipedia that would lead me to believe the information was incorrect.  I don't know the "GSM" side as well as the "CDMA" side.  Each technology will have a different performance characteristic based on environmental conditions (usage, weather, distance from tower, etc.) that can make one or the other perform better in the typical usage scenario.  I am not comparing technologies to see which is better, just to see which are loosely equivalent to the consumer in a typical US market.

I wrote this because I was getting confused over a few, such as EDGE and where it ranked in the big picture.  Perhaps I was the only one, though, so if this wasn't useful to you, sorry! ;)

Posted by Shane on April 5, 2007 8:44 AM | Permalink