Talk:Global System for Mobile Communications

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This article needs more context around or a better explanation of technical details to make it more accessible to general readers and technical readers outside the specialty, without removing technical details. See below for more information.


(Cleanup-clarity tag has been moved to the article. -- Kjkolb 19:50, 13 April 2006 (UTC))

(see below for explanations)

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I think that AMR is only available for UMTS. GSM only provides fixed rate channels right now, and EDGE only transports data normally... Is that not right Mozzerati 06:56, 2004 May 21 (UTC) (no..it's not right it seems.. AMR is available in recent _GSM_ standards.. too much time on packet stuff..)Mozzerati 19:39, 2004 May 27 (UTC)

AMR is available on all GSM and only corresponds to only voice, not data. Cacophony 18:53, 4 April 2006 (UTC)

I wonder about the disposable cell phone link at the bottom of the page. These have always seemed to be vapourware designed to build hype for an investment con job. Does anyone have any concrete example of something useful coming out of this or should we just remove the link / move it to a page of fake products?? Mozzerati 05:30, 2004 Jun 9 (UTC)

Any idea about health risks?

There are many theories, and not a whole lot of data at this point. Cacophony 18:53, 4 April 2006 (UTC)

GPRS shares the BSS with GSM, can only be integrated with a GSM network, is a standard retrofit available for almost all GSM networkss, is now almost universally available to GSM customers, is included as standard in almost all GSM mobile phones, isn't used by any other standard and is standardised as an integral part of the GSM standard. I don't think that an argument can be sustained which sees it as in any way a separate network. I plan to delete the disputed tag. Mozzerati 20:33, 2004 Aug 1 (UTC)

Contents

[edit] procedures?

I'd like to do a page on the key GSM system procedures:

  • paging
  • HLR enquiry
  • random access
  • location update

but I'm not sure what to title it; especially, I think much of the material should be common with WCDMA/3-GSM. Any suggestions? What else should be there? Is this a good split of topics?

Network Switching Subsystem, Base Station Subsystem, Mobility management would be good places to start looking. Cacophony 18:53, 4 April 2006 (UTC)

[edit] thoughts on procedures.....

I changed the format of the GSM page to move some of the detailed technical descriptions to a new page called GSM services. I didnt change material, but just stuck it all together, so it probably needs a rewrite anyway which I was planning to do sometime. I think that this page should be a relatively non technical introduction that the casual reader could follow.

But I also had the same kind of idea as you that there should be a procedures page which went into a bit more detail.

Perhaps you could start a page called GSM Protocols and do sub pages for calls, SMS. GPRS and supp services. The main page could explain about MAP, A interface etc etc at the high level, and the sub pages could describe message flows and contents.

I noticed that there is a wiki link created on one of the pages for suupplementary services with no actual content - I had planned to add that in at some stage.

I do think that the main GSM page should be kept as clean as possible - evetually perhaps including an alphabetic index of related categories.

ChrisUK

[edit] Cleanup for clarity and technicalness

See also Talk:GSM services. -- Beland 12:00, 29 Dec 2004 (UTC)

Visitor Location Register and Home Location Register don't seem to deserve their own articles. The terms are really only meaningful in the context of the GSM system, and they are already or should be fully explained either in this article or in GSM services.

I would recommend moving all the material on SIMs (which is interesting and useful, BTW) to Subscriber Identity Module, and putting a link with a sentence or two of context. Then all the people that get to Subscriber Identity Module from other places will get the benefit of the excellent content currently on this page.

When the term TDMA is used on this page, it's very confusing, because as an American cell phone user, I immediately parse it as "older technology that is not compatible with GSM". It would be good to include a parenthetical clarification or say "the technique of time division multiple access" - not that non-technical users will know what that means unless they click on the link.

mjlodge : Actually, it should be TDM (as in Time Division Multiplexing), not TDMA. This is an accurate statement of what is actually going on (i.e. multiple handset streams are multiplexed into different time slots)


Many of the acronyms used on this page should be written out (for display purposes), otherwise readers not already familiar with the technology will have no idea what article they will get after they click on it (or why they should want to in the first place), or have trouble understanding the meaning of the term in the context of a sentence.

The first paragraph of the "Radio interface" is especially opaque to non-technical readers. I'm sure it could be improved at the price of being slightly longer. Also, when it says, "between stations", does it mean between phones and towers, or between towers, or both? Are all the *DMA techniques used simultaneously, or do they represent mutually incompatible subformats?

For the intro, how many distinct versions of GSM are there? Which one do the "original" phones adhere to? -- Beland 12:00, 29 Dec 2004 (UTC)

History of mobile phones helped a lot to clarify which technologies are 1G, 2G, and 3G. This article doesn't talk much about GSM's relationship with other technologies. It might not be appropriate to do so here, but it would be nice if there were an explanation somewhere about the relative area covered by each technology, where that coverage is, and what its prospects are. This could be done in each technology's home article, but there would need to be tighter links between them, so readers could easily bounce between them. Also, I'm curious whether there are any phones that not only do multiple GSM bands, but also do multiple 2G technologies or 2+3 or 2+2.5 or whatever. Oh, I guess that's answered on Mobile_phone. Hmm. -- Beland 12:14, 29 Dec 2004 (UTC)

The sections on Radio interface, and GSM security should be integrated into GSM protocols (yet to be written), and the sections on SIMs, and Network structure should be integrated into GSM services, the "How GSM works" page. -- Beland 16:29, 9 Jan 2005 (UTC)

erm, one of these 2 articles gives wrong information about data-transfer in gsm:

http://en.wikipedia.org/wiki/GSM says: "This fact has also meant that data communication was built into the system from very early on."

http://en.wikipedia.org/wiki/2G says: "It cannot normally transfer data, such as email or software, other than the digital voice call itself, and other basic ancillary data such as time and date."

these two statements are totally opposing.. so, which one is right?!?

greetz Those conflicting statements resolved. JohnTechnologist 08:32, 24 March 2006 (UTC)

[edit] Substantial new material

I have pasted some material below that was added in directly to the history section of this page. I have done this for the following reasons:

  • there is some good original stuff amongst this that needs extracting and adding in again at the appropriate point
  • There is some repetition with other pages particularly GSM services. The material should be merged in there as appropriate
  • it was in the wrong context and badly formatted where it was in the main article.


This will take a bit of time to re-work. I suggest it is done in chunks and progress reported here. ChrisUK 5 July 2005 20:59 (UTC)


  • I have removed two chunks from the text below and placed back into this GSM page and also onto the GSM services page ChrisUK 5 July 2005 21:38 (UTC)

[edit] Remaining Article text to be edited

If you cut some stuff out of here to place else where, cut it rather than copy it so that we can see what remains to be merged.



Picture 2. GSM Network Elements


The Switching System The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units.


home location register (HLR) - The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator.

mobile services switching center (MSC) - The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others.

visitor location register (VLR) - The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time.

authentication center (AUC) - A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world.

equipment identity register (EIR) - The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.


The Base Station System (BSS) All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs).


BSC - The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC.

BTS - The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC.


The Operation and Support System The operations and maintenance center (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations.

Additional Functional Elements Other functional elements shown in Picture 2 are as follows:


message center (MXE) - The MXE is a node that provides integrated voice, fax, and data messaging. Specifically, the MXE handles short message service, cell broadcast, voice mail, fax mail, e-mail, and notification.

mobile service node (MSN) - The MSN is the node that handles the mobile intelligent network (IN) services.

gateway mobile services switching center (GMSC) - A gateway is a node used to interconnect two networks. The gateway is often implemented in an MSC. The MSC is then referred to as the GMSC.

GSM interworking unit (GIWU) - The GIWU consists of both hardware and software that provides an interface to various networks for data communications. Through the GIWU, users can alternate between speech and data during the same call. The GIWU hardware equipment is physically located at the MSC/VL. The GSM network is made up of geographic areas. As shown in Picture 3, these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.


The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by a single MSC (see Picture 4). Each LA is assigned a location area identity (LAI) number.


An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC (see Picture 5).


The PLMN service area is an area served by one network operator (see Picture 6).


before looking at the GSM specifications, it is important to understand the following basic terms:


bandwidth - the range of a channel's limits; the broader the bandwidth, the faster data can be sent

fbits per second (bps) - a single on-off pulse of data; eight bits are equivalent to one byte

frequency - the number of cycles per unit of time; frequency is measured in hertz (Hz)

kilo (k) - kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits per second

megahertz (MHz) - 1,000,000 hertz (cycles per second)

milliseconds (ms) - one-thousandth of a second

watt (W) - a measure of power of a transmitter


Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM.


frequency band - The frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station).{Take care, this frequency range is for USA, not Europe, Asia, Australasia. JohnT.]

duplex distance - The duplex distance is 80 MHz.[not for for GSM900 (45MHz) or GSM1800 (95MHZ). JohnT.] Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart.

channel separation - The separation between adjacent carrier frequencies. I n GSM, this is 200 kHz.

modulation - Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK).

transmission rate - GSM is a digital system with an over-the-air bit rate of 270 kbps.

access method - GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.

speech coder - GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps. [more commonly now at 12.2 kbps. JT]



There are two basic types of services offered through GSM: telephony (also referred to as teleservices) and data (also referred to as bearer services). Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers. Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM:


dual-tone multifrequency (DTMF) - DTMF is a tone signaling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF.

facsimile group III - GSM supports CCITT Group 3 facsimile. As standard fax machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM-connected fax to communicate with any analog fax in the network.

short message services - A convenient facility of the GSM network is the short message service. A message consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. If the subscriber's mobile unit is powered off or has left the coverage area, the message is stored and offered back to the subscriber when the mobile is powered on or has reentered the coverage area of the network. This function ensures that the message will be received.

cell broadcast - A variation of the short message service is the cell broadcast facility. A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents.

voice mail - This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box and the subscriber checks for messages via a personal security code.

fax mail - With this service, the subscriber can receive fax messages at any fax machine. The messages are stored in a service center from which they can be retrieved by the subscriber via a personal security code to the desired fax number.

[edit] GMSK vs QPSK

I thought that GSM used GMSK instead of QPSK which is currently indicated in the article. Does anyone know for sure? -- Jeff3000 17:01, July 17, 2005 (UTC)

Fixed. R6144 16:59, 21 August 2005 (UTC)

[edit] Not in Japan?

http://www.engadget.com/entry/1234000260061488/

I cite: "They were quick to point out that since the phone is GSM, you can’t actually use it in Japan."

So what do they use in Japan? Shinobu 12:19, 3 October 2005 (UTC)

NTT DoCoMo uses MOVA (old/proprietary) and FOMA (WCDMA with proprietary core network). Their competitor JPhone (no article it seems..) uses UMTS if I remember correctly. No idea about others. Mozzerati 22:18, 3 October 2005 (UTC)

Interesting... thanks! On http://www.japan-zone.com/new/mobile_sim1.shtml they say something similar, although on GSM coverage maps some green blotches are shown around densely populated areas. Yet, if actual GSM is meant... Shinobu 23:01, 3 October 2005 (UTC)

That being said, an international WCDMA (UMTS 2100) phone should work in Japan. Or, at least that is what the cingular web site says. nipponese 16:22, 18 October 2006

[edit] roaming

Couldn't you also use roaming in NMT?

[edit] GSM

This article is about GSM. Not 3G. So I've removed comparisons between GSM and CDMA2000 since they're pointless. GSM should be compared to cdmaOne not CDMA2000. There might be some room for some comparisons, for example you could mention that CDMA2000 is a more direct upgrade route from cdmaOne then GSM to UMTS/w-CDMA. But talking about w-CDMA coverage or failings in itself is largely irrelevant. [CDMA2000 could be more correctly rendered as cdma2000. JohnT.]

[edit] Active editors: Have you thought of writing...

...an article about GPS/SMS bugs? These tiny devices, hidden somewhere at your car, determine its position via GPS and transmit the coordinates via GSM's (or other standards') SMS service to your surveillant(s). They are apparently widely abused by the LEC, secret services or private snoops, thereby infringing on basic civil liberties. Also the aspect of possible counter-weapons could be discussed.

Go to http://en.wikipedia.org/wiki/Talk:Global_Positioning_System and check out '14: GPS tracking'. Feel free to contact me directly, if you prefer.


Michael

http://worldimprover.net/EN/en8.html

[edit] A5/1 and A5/2

I removed the part in the article about why soem countries have A5/2 instead of the stronger A5/1 because that reason didn't make sense. A5/1 and A5/2 seems both equally simple to implement in hardware. They constis of three or four shift registres which are irregulary clocked and some XOR-gates. Very similar implementations and both cheap. My personal guess is that the true reason was politics but that is just my guess. Feel free to correct me if I'm wrong.

"A5/1 was developed first and is a stronger algorithm used within Europe and the United States; A5/2 is weaker and used in countries that may not be able to support the infrastructure necessary for A5/1."

Jeltz talk 19:09, 7 April 2006 (UTC)

[edit] Addendum to item 8

Calling all GSM experts:


There is now ample evidence that the newer GSM cellphones can be switched on remotely by 'the powers-that-be', and without you noticing it. From that moment on, they can not only be abused as a triangulation bug independent of GPS - cf

http://en.wikipedia.org/wiki/Gps_tracking -,

but also as an eaves-dropping device - their microphone remains 'always on', thus independent of phone calls.

They may be practical for you on the one side, but they can apparently also be a tool from hell.


Michael Laudahn

http://worldimprover.net/EN/en8.html

[edit] The state of GSM 850/900 in the US

I noticed a lot of newer 3G world phones are dropping GSM 850. Does this mean anything to us US Cingular customers? I called Cingular sales yesterday and they said using a tri-band phone without 850 in my area (SF bay area) should be no problem what-so-ever, but I think that probably remains to be seen. Can anyone comment on this topic?

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