2015-05-20

GSM

(Up-to-date source of this post.)

Cellular network

  • a radio network distributed over land areas called cells
  • each cell is served by at least one transceiver - BTS (Base Transceiver Station) = cell site
  • this enables a large number of portable transceivers (e.g. mobile phones) to communicate with each other
  • example of a cellular network: the mobile phone network or PLMN

GSM

  • World's most popular standard for mobile telephony systems (80% of mobile market uses the standard)
  • both signaling and speech channels are digital (1G was analog, ex. NMT)
  • second generation (2G) of mobile phone system
  • GSM release '97 - added packet data capabilities via GPRS
  • GSM release '99 - higher data transmission via EDGE
  • UMTS (Universal Mobile Telecommunications System) - 3G mobile cellular technology for networks based on GSM standards
  • LTE - 4G, standard for wireless communication of high-speed data for mobile phones and data terminals, based on the GSM/EDGE and UMTS/HSPA

Mobile Technology Roadmap

Network Structure

GSM PLMN has two main logical domains:

  1. access network - most used access networks in western Europe as of 2009 (can be deployed in parallel):
    • GERAN (GSM EDGE radio access network)
    • UTRAN (UMTS terrestrial radio access network) - HSPA can be implemented into UMTS to increase data transfer speed
  2. core network
    • circuit switched domain
    • packet switched domain
    • IP multimedia subsystem (IMS)

GPRS/UMTS architecture with the main interfaces:

PLMN

The network is structured into a number of discrete sections:

  • the base station subsystem (BSS) - handles traffic and signaling between a mobile phone and the NSS (access network)
  • the network and switching subsystem (NSS) - part of the network most similar to a fixed network (VOICE, circuit switched)
  • the GPRS core network - optional part for packet based Internet connections (NON-VOICE, packet switched)
  • operations support system (OSS) for maintenance

See this picture for GSM communication.

BSC = Base Station Controller

  • intelligence behind the BTSs (allocation of radio channels, measurements from the mobile phones, handover control from BTS to BTS)
  • concentrator towards the mobile switching center (MSC)
  • the most robust element in the BSS
  • often based on a distributed computer architecture

PCU = Packet Control Unit

  • late addition to the GSM standard
  • processing tasks for packet data

MSC = Mobile Switching Centre

HLR = Home Location Register

  • database of subscribers
  • a central database that contains details of each mobile phone subscriber that is authorized to use the GSM and/or WCDMA core network of this PLMN

VLR = Visitor Location Register

  • register of roaming subscribers

AUC

  • database of authentication keys

EIR

  • stolen devices (phones) register

SS7 = Signaling System #7

  • a set of telephone signaling protocols
  • main purpose: setup/tear down telephone calls
  • other uses: number portability, SMS, etc.

SGSN = Serving GPRS Support Node

  • delivery of data packets from and to mobile stations withing its geographical service area
  • packet routing and transfer, mobility management, logical link management, authentication and charging functions

GGSN = Gateway GPRS Support Node

  • main component of the GPRS network
  • inter-networking between the GPRS network and external packet switched networks
  • router to a sub-network

AT commands

Huawei, Android

  • at+cgmi - manufacturer
  • at+cgmm - model
  • at+cimi - IMSI
  • at+cmgw="0914123456",145,"STO UNSENT" - store message to memory
  • at+cmgl="all" - show stored messages
  • at+cmss=3 - send message n. 3 from memory
  • at+cmgd=2 - delete message n. 2 from memory

Links

General

AT commands

Hacking

PDUSpy

Books

  • M. Grayson et al.: IP Design for Mobile Networks (Cisco Press, 2009)
  • A. Henry-Labordere, V. Jonack: SMS and MMS Interworking in Mobile Networks (Artech House, 2004)
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