A GSM network is composed of three main systems, Switching Systems (SS), the Base Station System (BSS), and the Operation and Support System (OSS). The GSM Switching System components include, the Home Locator Register (HLR), the Visitor Locator Register (VLR), the Mobile services Switching Center (MSC), the Authentication Center (AuC), and the Equipment Identity Register (EIR). Th

Now that we have the GSM cells covered, I need to explain how a lot of callers can make calls from within one cell. GSM uses a form of air interface called TDMA, which stands for Time Division Multiple Access. The TDMA frame requires GSM to use physical channels, but each of those channels is divided into eight time slots. One user consumes one slot, thus allowing 8 users to be on a GSM channel simultaneously. There are several control channels that are implemented in time slot 0 on the TDMA frame. One of which is the Broadcast Channel (BCH), which is on all the time, in every cell. It allows Mobile Stations to synchronize and it carries information that identifies the network. While the BCH information is carried in time slot 0, other time slots can be used for TCH (Traffic Channel) or filled with dummy data. The BCCH also has many sub-channels such as the Common Control Channel (CCCH), the Paging Channel (PCH), the Access Grant Channel (AGCH), and the Random Access Channel (RACH).

All in all, I believe I have tried to show the technical aspects of the GSM service from what I learned in the GWEC article. I believe the GSM service has many advantages, the main advantage being the implementation of the SIM card. The SIM card lets the user change phones and bring their number and services wherever they go. The other advantages include GSM being highly scalable, it offers many standard protocols between components, and it reduces probability of total corruption of speech. The only disadvantages are that each user has a predefined time slot and macrocells are affected by multipath signal loss.

The TCH channel carries digitally encoded user speech or user data. In the event of a GSM handoff, the mobile constantly monitors received TCH quality (RxQual & RxLev). The RACH is used by the Mobile Station to “be heard”, acknowledge pages, request traffic channels, and get location updates. In addition to the channels mentioned above, GSM uses the Stand-Alone Dedicated Control Channel (SDCCH). This particular channel is a dedicated, bi-directional channel which is used for location updating, call set-up, and authentication. The SDCCH improves efficiency and is the holding channel for the Mobile Station during call set-up. Another channel, called the Slow Associated Control Channel (SACCH) is also always present when a dedicated link is active between the Mobile Station and the BTS. On the downlink, the SACCH is used to monitor mobile Tx power c

Some topics in this essay:
Class II, Base Station, MSC HLR, Mobile Station, System OSS, Station BTS, SIM SIM, Access TDMA, Mobile GSM, Station Subsystem, mobile station, base station, switching center, sim card, station subsystem, mobile services, base station subsystem, control channel, services switching center, cell phone, bits error, switching system, bits error correction, mobile services switching, sim card gsm,