G-standard GSM. Network for mobile communications second generation 2G standard GSM.

2G started in 1991 with a speed of data transmission of 9.6 kbit / s. In 1999, the GSM standard to be embedded and standard GPRS (considered intermediate pokolenie- 2.5G), which provides mobile Internet with higher speeds.

The GSM (an acronym from the name of the group Groupe Spécial Mobile, later renamed the Global the System for Mobile: Communications ) is a global digital standard for mobile cellular communication, a division of channel principle TDMA and with a high degree of safety thanks to encryption open key . Developed under the auspices of the European Institute for Standardization messages (ETSI) in the 80 years of the 20th century.

GSM refers to networks of second generation (2nd Generation), although in 2006 it provisionally entered phase 2, 5G and is the most common standard for mobile cellular communication in the world. Mobile phones are manufactured for use in a range of 4 frequencies: 850 MHz, 900 MHz, 1800 MHz, 1900 MHz. In the GSM standard used GMSK modulation .

Architecture of the GSM network

The base station (BS) is priemopredvatel connecting your cell phone to the cellular network. Each base station is called a cell, because it covers a specific area. All base stations are connected to be able to receive reliable connection when you move from one cell to another. This process is called “transfer” ( hand- the over ). Group base stations are included in certain base station controller (the BSC).

The set (the mobile station or terminal) from your cell phone and SIM- module represents a kind of digital signature (including your subscriber number) that is sent to the nearest cell as a request that you as a subscriber you want access to the system. BSC transmits the request to the heart of the cell wall outlet MSC (IMO MSC). MSC takes care of providing a connection route for incoming and outgoing calls to and from fixed or mobile networks. MSC contains a critical component called the HLR (Home The the Register the Location) – internal register (register of internal locations) providing administrative information identifying you as a specific subscriber. Once receiving a request from the cell phone, HLR immediately compares the special signature in the application with that data subscriber. If your subscription is correct, MSC sent way back through the cell phone to your message that you are admitted to the network. Usually at this time on the screen of the camera displays the name of the cellular network. From here you can take and make calls. At the moment HLR register connection to your network, notes the scope of which one cell are to be able subsequently to provide MSC route for calls to your number. When receiving a call, MSC will first check the HLR, to see your location. At any moment, the cell phone sends a message to the nearest cell to inform the network where you are. This process is known as Polling.

Each base station uses pure digital technology can support an impressive number of subscribers simultaneously connected to the cellular network, and also allow them to make and receive calls. This technique is called fragmentation multiplexing.

Sledejki Your location abonatna electronic signatures, network anesthetize obaždaniâta to redirect you to bazovata station in whose range is telefont You, come and other Subscribers in the same moment that relate to the NEA. When the prehvʺrlite cage to another (for example, while SOFIR), the information in the HLR is updated automatically, for that is exactly osʺŝestvi rotated with a signal for Your calls.

When you make an outgoing call, activate another module MSC called the VLR (the Visitor the Location the Register)-register, verify that you actually allowed to make calls. (For example, your subscriber number can be banned international calls). The answer to the VLR is forwarded back to your phone. Voicemail (Voicemail) and the Centre for short messages (SMS) are other services that MSC provides. SMS messages are transmitted on a separate channel of conversation, and you can receive short messages even when you’re talking about.

Radio interface digital cellular network GSM.

Interfaces are two types:

  1. Interface for connection to external networks (signaling system released No7- SS7):
  • Abis- interface m / s from the BS and the BSC;
  • A- Interface m / y BSC and MSC;
  • B- интерфейс м / у и MSC VLR;
  • C- Interface m / from MSC and HLR;
  • D- интерфейс м / у и VLR HLR;
  • E- interface m / s from the MSC and the EIR;
  • F- interface m / u two plants;
  • Um- Radiointerfejs m / to the MS and the BS.
  1. Contact the elements in the network itself:
  • normal (normal burst);
  • for frequency adjustment;
  • for synchronization;
  • series for Random Access (shortened series);
  • empty (deaf series).

Logical channel networking for mobile communications second pokolenie- GSM standard

logical channel Direction of transmission Type of information transmitted
AGCH MS→BS Application of outgoing call
RACH BS←MS Information standalone dedicated channel (channel number, time interval)
SDCCH MS→BS Send number of the called subscriber
SDCCH BS→MS Request authentication
SDCCH MS→BS Response authentication
SDCCH BS→MS Permission to access the services of the mobile network, appointing a number of PC and slot for transmitting speech information
SDCCH MS→BS acknowledgment
SDCCH MS→BS Release Channel
TCH MS↔BS Transmission of voice information
At end of the link
BSCH BS→MS Correction of frequency and synchronization
LMHR MS←BS Exchange of official control information