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Mobile Data Networks. Topics. General Packet Radio Service (GPRS) Short Messaging Service (SMS) Mobility Management and Mobile IP Application Protocols Security. GPRS - Overview. GPRS is an overlay on top of the GSM physical layer and network entities Extends data capabilities of GSM

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  • General Packet Radio Service (GPRS)

  • Short Messaging Service (SMS)

  • Mobility Management and Mobile IP

  • Application Protocols

  • Security

Gprs overview
GPRS - Overview

  • GPRS is an overlay on top of the GSM physical layer and network entities

  • Extends data capabilities of GSM

  • Provides connections to external packet data networks through the GSM infrastructure with short access time to the network for independent short packets (500-1000 bytes)

  • No hardware changes required for Base Station

  • Scalable, high throughput (21.4 kbps), support for voice and data


  • GPRS uses same physical radio channels, only new logical GPRS radio channels are defined

  • Active users share timeslots using TDMA; uplink and downlink are allocated separately

  • Capacity allocation in GPRS is based on the “on-demand” principle

  • GPRS terminals:

    • Class A: Operates GPRS and GSM services simultaneously

    • Class B: Operate either GPRS or GSM service at one time

    • Class C: Only GPRS service

  • Limitations:

    • Limited cell capacity

    • No store-and-forward service (SMS provides this service)

Gprs network services
GPRS Network Services

  • Point-to-point (PTP): packet data transfer

    • Connectionless based on IP

    • Connection oriented based on X.25

  • Point-to-multipoint (PTM-M): multicast service to all subscriber in one area

  • Point-to-multipoint (PTM-G): multicast source to a predetermined group

  • Short messaging service (SMS)

  • GPRS has parameters that specify a QoS based on service precedence, priority, reliability and required transmission characteristics

Reference architecture
Reference Architecture

  • Refer to handout

  • Uses GSM architecture

  • GPRS support nodes (GSN): responsible for delivery and routing of data packets between the MS and the external network

  • Serving GPRS support node (SGSN)

    • Controls access to MSs that are attached to a group of BSCs (routing area (RA) of SGSN)

  • Gateway GPRS support node (GGSN)

    • Logical interface to the Internet

  • GPRS Register (GR)

    • Colocated with HLR and stores routing information

Mobility support attachment
Mobility Support: Attachment

  • Before accessing GPRS services, the MS must register with the GPRS network

  • MS performs an attachment procedure with an SGSN that authenticates it by checking the GR

  • The MS is allocated a temporary logical link identity (TLLI)

  • A packet data protocol (PDP) context is created for the MS for each session and is stored at the MS, SGSN, and GGSN

  • PDP context: PDP type, address, QoS, GGSN address

  • A user may have several PDP context enabled. The PDP address may be statically or dynamically assigned

  • PDP context is used to route packets

Location management
Location Management

  • Location management depends on three states as shown in the figure

  • In the IDLE state, the MS is not reachable

  • In the STANDBY state, movement across routing areas is updated to the SGSN but not across cells

  • In the READY state, every movement of the MS is indicated to the SGSN


Packet Tx

Timer Expiry

GPRS Attach

GPRS Dettach



Timer Expiry

Routing area updates
Routing Area Updates

  • Intra-SGSN Update

    • The SGSN already has the user profile and PDP context

    • The home location register (HLR) need not be updated

    • A new temporary mobile subscriber identity is issued as a part of the RA update

  • Inter-SGSN Update

    • The new RA is serviced by a new SGSN

    • The new SGSN requests the old SGSN to send the PDP context

    • The SGSN informs the home GGSN, the GR, and other GGSNs about the user’s new routing context

Handoff management
Handoff Management

  • The MS listens to the broadcast control channel (BCCH) and decides which cell to connect using the RSS, cell ranking, path loss, etc.

  • The location is updated using the routing update procedure (see handout)

  • The SGSN updates the GGSN of the home network with the new SGSN and the tunneling information

Uplink downlink transmissions
Uplink/Downlink Transmissions

  • The uplink and downlink transmissions are independent

  • The Mac protocol is called “Master-Slave Dynamic Rate Access” or MSDRA

  • The organization of the time-slot assignment is done centrally by the BSS

  • Refer to the handout

Short message services sms
Short Message Services (SMS)

  • Extremely popular service, similar to the peer-to-peer instant messaging services in the Internet

  • Allows exchange of alphanumeric messages up to 160 characters

  • Two types of services:

    • Broadcast

    • Peer to peer

  • Uses the same infrastructure as GSM

  • SMS has instant delivery service as well as store-and-forward service


  • SMS makes use of the GSM infrastructure, protocols, and the physical layer to manage the delivery of messages

  • Each message is treated individually, and is maintained and transmitted by the SMS center (SMSC)

  • Short messages (160 char mapped into 140 bytes) are transmitted through the GSM infrastructure using SS-7

  • Short messages are transmitted in time slots that are freed up in the control channels

Reference architecture1
Reference Architecture








Cases of short messages
Cases of Short Messages

  • SM originating from an MS

    • Goes to MSC for processing

    • SMS-interworking MSC (SMS-IWMSC forwards the SM to the SMSC

  • Mobile terminated short message

    • SM is forwarded by the SMSC to the SMS-gateway MSC (SMS-GMSC)

    • Either the HLR or VLR is queried

    • SM is either delivered to the BSC or forwarded to another MSC