GSM Protocol Architecture - Part 2 : User Plane:

As it mentioned in the previous blog post, User Plane handles the transportation of user data across the physical layer from a subscriber or a data channel. Thus it can be categorized under Layer 1 protocols. The communication services offered by this layer are defined under a set of connection types. In GSM connection is defined between reference points.

Three connection types that define GSM connection are;

1. Speech Transition

2. Transparent Data Transmission

3. Non-transparent Data Transmission

1. Speech transmission

In here, digital, source-coded speech signal of MS is transmitted across the physical layer in an error-protected and encrypted form. At the BTS (Base Transceiver Station), signal is de-ciphered and removes the error-protection prior to passing on.

2. Transparent Data Transmission (TDT)

When it comes to digital radio channels there would be severe quality variations and may generate burst errors. If the signal quality is too low, the resulting errors cannot be corrected.

Therefore in the TDT user data protected against transmission errors by Forward Error Correction (FEC – a mechanism for error controlling while data transmission, by the sender adding redundant data bit to its message. This enables receiver to correct errors if an erroneous message is received). But, in TDT further data transmission between the network and next MSC occurs unprotected.

3. Non-transparent Data Transmission

For the worst conditions even TDT quality is not enough and hence more redundancy bits will be added here to the data stream. Further an error-detection with automatic re-transmission of faulty data-blocks will be used. The protocol used in GSM for this purpose is RLP (Radio Link Protocol).

GSM Protocols - Part 1

GSM protocol stack

In any telecommunication system, signaling is required to coordinate the necessarily distributed functional entities of the network. In GSM networks signaling information transforms according to the OSI model.

• Layer 1:Physical Layer

– Radio Transmission

• Layer 2:Data Link Layer(DLL)

– Provides error-free transmission between adjacent entities, based on the ISDN’s LAPD protocol for the Um and Abis interfaces, and on SS7’s Message Transfer Protocol (MTP) for the other Layer interfaces

• Layer 3: Networking or Messaging Layer

– Responsible for the communication of network resources, mobility, code format and call-related management messages between various network entities

Figure: Simplified ISDN reference model

Logical channels are at the Service Access Point of Layer 1 (physical layer), where they are visible to the upper layers as transmission channels of the physical layer

User Plane - User data are transmitted in GSM across the air interface over traffic channels (TCH) from a subscriber or a data channel.

Controlling/ Signaling Plane - Handles subscriber access to the network and the control of the user plane

…To be continued

Reference :

1. J .Eberspächer et. al., GSM-Architecture, Protocols and Services (3rd Ed.)

GSM: Intro

GSM (Global System for Mobile) is a second generation cellular standard developed to cater voice services and data delivery using digital modulation. The prime influence of GSM is to achieve unbounded communication through the means of wireless technology. If there is a gap in terms of capabilities of wired vs. wireless, it would be the difference between data rates. There are two ways of achieving unbounded communication via GSM technology, viz. terminal mobility and personal mobility.

Terminal mobility is the mobility achieved through mobile handsets in laymen terms.Personal mobility is where the user is enabled to move across the network boundaries wearing a chip (or some embedded equipment) to identify them selves, thus enjoying all the local services independent of current location.

At present GSM family includes GSM, GPRS (General Packet radio Service) and EDGE (Enhanced Data Rates for Global Evolution). When it comes to the evolution of usage of GSM, the starting point is the speech/voice communication. SMS is the 2nd means of usage that GSM went in to users hands followed by HSCSD (High Speed Circuit Switched Data) & GPRS (Geberal Packet radio Service). The latest version is 3G (though we see a newer version which is 3.5G) but it still covers only hot spot areas. So GPRS is still prety much popular in mobile community.

Classification of wireless communication:

1. DECT (Digital Enhanced Codeless Telecommunication) & PBX (Private Branch Exchange)
2. LAN - Wireless LAN (IP based, adheres IEEE 802.11 standards)
3. Blue-tooth (calls Body Area Network, Personal Area Network) - Direct wireless information exchange between electronic devices
4. Public Mass Communication
5. Satellite-based - LEO (Low Earth Orbiting) & MEO (Medium Earth Orbiting)
6. Unidirectional - E.g. Paging

SUPL - Secure User Plane Location : Introdution

Mortive - It is claimed as one of the most effective technology which enable network operators to offer Location Based Services for their subscribers speedily and economically. As the empiric revealed the reluctant of network operators to implement LBS is basically because of the cost and complexity of modifying Control Plane (C-Plane, some refers as positioning) network elements and protocols. Thus SUPL facilitates network providers to achieve this with least impact on C-Plane.

Overview - SUPL was developed by OMA (Open Mobile Alliance - http://www.openmobilealliance.org/), which is organized to bring in open standards that ensures interoperability across devices in LBS industry.Therefore it supports location identification regardless of the location server used by the mobile carrier. Further, it has designed to facilitate A-GPS (Assisted GPS), which is regarded as one of the most efficient positioning mechanism.

Architecture of SUPL consists of two elements, viz. SET (SUPL Enabled Terminal) and SLP (SUPL location Platform). Set is a mobile phone or PDA configured to support SUPL transactions.SLP is a server that handles user authentications, LB requests, roaming and charging etc.

HLR - Intro

Home Location Register is the main database of permanent subscriber information.
There can be one or more HLRs in a single Publinc Mobile Network. It depends upon number of mobile subscribers, capacity of the equipements, organisation of network infrastructure etc. One core information stored in a HLR, specially related to LBS, is the location of a Mobile Subscriber (MS). Thus it enable HLR to route calls to those subscribers managed by that particular HLR. IMSI (International Mobile Subscriber Identity) and MSISDN (Mobile Subscriber Integrated Services Digital Network Number) are two numbers stored in a HLR attached to each subscriber.

Other than that HLR stores following information.
1. Current Location information (VLR number)
2. GSM services subscribed or given
3. Call divert settings
4. Service limitations

LBS - Industry environment

As LBS is still in a rapidly growing stage, it opens up a big market as well as number of technology integrations. Service platforms, mobile terminals, web services are leading aliases that energize LBS and Vice-versa. Since most of the mobile networks operates as service providers, it enabled them to become the providers of LBS as well.

But, to become this market more expandable, popular or profitable, few more players also need to play their roles. Contecnt providers, application developers, framework and middle-ware providers are those other players behind the curtain. Thus to come-up with a balanced or uninterrupted LBS service there should be a great deal of techno compromisation amongst them.

LBS - A Value Addttion

Next few posts on this topic will be dedicated to, but not restricted to, discuss about usage of LBS at present, market players,Infrasture Needs and trends in this technology. Lets start up with the ways that LBS been used today.The main service areas powered by LBS are tracking and
navigating, emergency services,advertising, localized service provisioning from operators, geo-base information provisioning such as hospitals, resturants, air ports etc. and in M-commerce.

Now lets see how LBS become a value addition to those above mentioned services. when an operator/ service provider got a news to circulate about offers in supermarket chain but in few suburbs only what normally happens is sending messages to all subscribers at large. But LBS will enable operators to select the subscribers in that particular area and forward the message. Thus it will become more focused, useful and highly cost-effective.