Understanding GPRS

Guided By:Manan Thakkar

Prepared BySukant Debnath

What is GPRS??? GPRS (General Packet Radio Service ) = Mobile +

Internet Technology that permits mobile data

communication using packet switching technique. Circuit Switching and Packet Switching

Circuit Switched Packet Switched Telephone Network. End to end connection

establishment is needed. Dedicated Resource for 1

user are reserved during call establishment.

Only 30-40% of the resources are effectively used.

Speech is transferred in real time.

Speech does not accepts delays.

Error in transmission are not so critical for speech.

Charging is usually based on time.

Data Network No connection needed.

Resources are shared between different user sessions, not dedicated.

Resources are requested on demand, more efficient use.

Packet are not sent in real-time (Buffering and delay)

Error connection and detection possible.

Charging is usually based on volume (Number of packets)

GPRS Network Architecture

GPRS Network Architecture( Contd.)

GPRS: New Network Elements and New Interfaces

Service GPRS Support Node (SGSN) Control connection between network and mobile

station. Session management and GPRS mobility management

function (Handover, paging etc.) Counts the number of packet routed. Attached with HLR via Gr and MSC/VLR via Gs

interface. Responsible for routing data packet to correct GGSN. Connected with BSC through Gb interface.

Gateway GPRS Support Node (GGSN) Provides gateway between the GPRS network and the

public packet data network (PDN) or other GPRS network.

Contains routing information for attached GPRS users May provide a dynamic IP address for a requesting mobile

station Performs GPRS Mobility Management (GMM) Provide Quality of Service (QoS) support Counts the number of packet routed for accurate

billing. Connected with SGSN through Gn interface and HLR with Gc

interface.

Packet Control Unit (PCU)

GPRS/GSM Mobile Classes

Class A: MS can attach to both GPRS and other GSM services; MS supports simultaneous operation of GPRS and other GSM services.

Class B: MS can attach to both GPRS and other GSM services, but MS can operate only one set of service at a time and is capable of monitoring one paging channel at a time.

Class C: MS can exclusively attach to GPRS services.

GPRS Mobile Phone Operation States: Idle State: State in which the mobile

phone camps onto the GSM network. Phone recieves circuit switched paging and behaves as a GSM phone.

Ready State: The mobile can activate a packet data protocol (PDP) context which allows the phone to establish a packet transfer session with external network to send and receive data packets.

Standby State: State in which the mobile is connected to the GPRS network, but no data transmission occurs.

Coding Schemes In GPRS GPRS uses 4 coding

schemes according to the C/I ratio between the MS and BTS.

Coding scheme CS1 has the highest error correction and low data throughput.

CS4 has no error correction but the highest data throughput.

Coding Schemes (Contd..)

Link Adaptation (Code Switching)

The selection of the most appropriate coding scheme for coming transmissions, according to the estimated link quality, is called Link Adaptation or Code Switching.

How it works:1. Collect measurements and make an estimate of

the channel quality2. Compare the results with thresholds3. Make decision to change or maintain the current

CS

The decision is done by statistical testing methods based on the BLER measurements.

Link Adaptation (Contd..)

Retransmissions always with same coding scheme

GPRS Time Slots Dedicated Timeslot (CDED): Exclusively reserved for

GPRS traffic and no CS traffic can be transmitted on them.

Default Timeslot (CDEF): GPRS traffic that can be dynamically configured to handle CS load if needed.

Additional Timeslot: CS traffic timeslot can be dynamically configured into a GPRS time slot, during peak traffic period.

CS Traffic Leaves Some Capacity For PS Traffic:

GPRS Attach Procedure GPRS attach request is

made to SGSN, by notifying its identity as IMSI/P-TMSI.

MS sends old RAI, classmark and attach type.

SGSN attach mobile and inform HLR about RAI change and also update the location with VLR.

GPRS attach does not enable the MS to transmit and receive data

PDP Context Activation It activate packet

communication with SGSN. During the activation

procedure, the mobile phone either provides a static IP address or requests a temporary one from the network and also APN.

Upon receiving information from the mobile, the SGSN determines which GGSN is connected to the APN and forwards the request.

Practical Consideration ZEQO Command Used to Check CDED, CDEF, Cmax,

Coding Scheme, RAC, NSEI, UL/DL BLER for CS selection parameter etc.

ZFXL is used to check every PCU with is corresponding BCSU. And how many cells are attached to 1 PCU and NSEI.

Each PCU supports 2 NSEI. And each NSEI support 256 time-slots.

To reduce overload and less handovers between NSEI’s during GPRS access on the move, NSEI Load balancing process is done.

229 Report is used to check multi-slot assignment in downlink (%), GPRS territory upgrade reject (%), GPRS traffic, total RLC payload data (kbyte), Number of TBFs established in UL/DL.

Advantages of GPRS: User point of view:

Instant access to data on the move. Charging based on amount of data transferred

(Not the time connected). Higher transmission speed.

Operator point of view: More revenue. Huge potential market for data services. Fast roll out and continues network expansion. Efficient utilization of network.

Thank You…..