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What is GSM

A lot of people seem confused about what GSM actually is. Most just assume it is an older single technology that a cellular provider either uses or does not. While this assumption works to a certain extent, it doesn’t really explain much as going forward, as just about every provider on the planet is going to be using GSM in one flavor or another, and yet not everyone uses the exact same technology (as phones are often not directly compatible), so let’s put the record straight on what GSM really is.

We’ll begin the story by looking back at the world in the days of analog cellular in the mid ’80s. In those days things were just fine in North America, because both Canada and the US used the same cellular technology (known as AMPS) on the same frequencies. Cell phones bought in either country could be used without issue on either side of the border. In Europe however, it was a completely different story.

Prior to the ‘80s we didn’t have the EU and there wasn’t much that was done in Europe that was coordinated and that went for radio telephone technologies too. There were countless standards running on countless different frequencies. It was therefore virtually impossible for a European cell phone user to roam outside of his or her home country. Fortunately many in Europe realized that this couldn’t go on, and so they formed the European Telecommunications Standards Institute.

There wasn’t much they could do to fix the mess in first-generation analog systems, but as no standards for digital wireless communication had yet been settled, they could most certainly have an influence there. Subsequently they set about creating a 2nd-generation standard that they dubbed Group Spécial Mobile, or GSM for short. From this was formed the GSM Association, which owns the copyright on the name “GSM” and the standards it represents.

Somewhere along the line someone decided that what GSM stood for wouldn’t make a lot of sense, and so they came up with a “new” definition of those initials and it now stands for Global System for Mobile Communication (the “C” in that definition is clearly not important).

The standards governed by GSM included many facets of the communication process, but the one that’s closest to the consumer, and therefore the one that consumers naturally associated these letters with, is the air interface. This is the technology that gets digital information from point A to point B. The first air interface defined for GSM, now known simply as 2G GSM, was the one that many people came to associated with it. This early digital air interface divided a channel into 8 “slots” (separated by time) and each user on this channel shared it by being assigned to one of those slots.

Of course, the early air interfaces were only concerned with voice communication, and so when the need for data communication first came along, a way of piggybacking that data onto a system designed primary for voice was required. The first approach went by the name of GPRS, which stood for General Packet Radio Service. One or more of the 8 available slots was used to send the data, and so how many of the slots were used determined the speed, though compared to today’s data rates, it was extremely slow.

This concept was “evolved” and they introduced a faster version called EDGE, stood for Enhanced Data Rates for GSM Evolution. This approach increased the speeds possible over an old 2G GSM phone, but again the speed was nothing compared to what we expect now.

As the need for data became greater and greater, a different method for transmitting data...



over the air was called for. Qualcomm had already proven the viability of CDMA on their 2nd-generation system in North America and the ETSI turned its attention to that technology. They didn’t use exactly the same specifications as the Qualcomm system and thus the GSM version, known as WCDMA (for WIDE CDMA, as it used a 5 MHz-wide channel) was completely incompatible with it.

Within this air interface standard a number of acronyms appeared that made things increasingly confusing for consumers. The first was UMTS, which stands for Universal Mobile Telecommunications System. This is actually umbrella name for the WCDMA technologies that encompass the GSM 3G standards. For most users however, the more specific HSPA (High-Speed Packet Access) would be more familiar. This technology defines the transmission of data over a UMTS network.

While the future of CDMA looked bright, it was discovered that the technology wasn’t particularly scaleable. For that reason the ETSI began work on a 4th-generation standard called LTE, which stands for Long Term Evolution. This air interface abandons the CDMA structure used in favor of an FDMA technology not unlike that used for WiFi.

Unlike all previous air interface technologies, LTE was not designed first and foremost for circuit-switched voice communication. In fact, LTE doesn’t support circuit-switched voice AT ALL. It is a pure packet data interface that when first released had no means of carrying voice telephone conversations (other than pre-existing VoIP services). Just recently Voice-Over-LTE standards have been established and you’ll begin to see them deployed in 2014. For the time being, all LTE phones had to fall back to a previous-generation technology for telephone calls.

The ETSI were smart enough to make the LTE definition flexible enough to be shoehorned into just about any type of communications system (not just cellular), and so there has been a worldwide move to making LTE the ONLY standard for data communications going forward. Just about every cellular provider in the world has shifted to GSM to take advantage of LTE (including behemoth Verizon).

In Canada Bell Mobility and Telus launched a UMTS/HSPA GSM network 3 years ago to replace their CDMA networks and to make the transition to LTE much easier for them than it has been for Verizon. To make the switch Verizon has required special LTE/CDMA handsets that are incompatible with every other service provider in the world. Bell and Telus were able to offer the same LTE/UMTS phones that virtually everyone else uses.

As I noted above, a fallback to a 3rd-generation standard was initially necessary to continue providing voice services. As Verizon was a CDMA network its natural fallback was CDMA. Those networks already using the GSM standards had a UMTS/HSPA network (or in the case of some providers, just an old 2G GSM network) to fall back on, and as such the vast majority of new GSM phones support LTE, UMTS/HSPA, and the older 2G GSM/GPRS/EDGE standards. Providers already playing in the GSM sandbox are able to offer just about any GSM phone on the market. Verizon can only offer the special LTE/CDMA phones, which limits what you can run on their network.

While this article may have left you just as confused as you were at the start, I hope that you can at least appreciate that GSM is NOT a single air interface standard. It encompasses a large number of specific air interfaces that come under the GSM umbrella. Since everyone seems to be moving toward LTE, there will be only GSM in future, and so this acronym may begin to have less and less relevancy to the average subscriber. Before that happens, at least you’ll know where the name comes from.

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