2.5G - General Packet Radio Service (GPRS)
GPRS
GPRS: General Packet Radio Service.
Packet-oriented transport service, for data network connections (Internet).
Better transmission bit rates (max 150kbps).
Allows burst communications (“immediate”: connections in <1s).
New network applications.
New billing mechanisms (user-oriented: by traffic, p.ex.).
Architecture
New entities are defined.
SGSN – serving GPRS support node.
GGSN – gateway GPRS support node.
Interfaces between entities GPRS, GSM, core and PSTN.
Transmission plane.
Data packets are transmitted by a tunnel mechanism.
Control plane.
GTP: a protocol for tunnel management (create, remove, etc..).
Radio interface.
Changed the logical channels and how they are managed.
Remains the concept of “master-slave”.
GGSN (Gateway GPRS Support Node) Functions
Gateway
Allows the connection to other IP or GPRS networks.
Routing
IP router which supports dynamic or static routing,
Mobility management
Use of routing areas.
Handover management between the BSCs and other SGSNs.
Allows the routing of the packets towards the users SGSNs, according to their mobility.
Sessions management
At each session, the SGSN activates a PDP (Packet Data Protocol) context, and allocates an IP address to the MT.
Security
Ciphers the communications towards or from the mobiles.
Includes firewalls for filtering the packets coming from external IP networks.
Authentication
At Attach and inter-SGSN RA updates.
Billing
Production of the CDRs according to the quantity of information and the session duration (attachment, duration of active PDP context).
SMS
Supports the Gd interface for the communications with the SMS-GMSC and the SMS-IWMSC.
The PDP Context
An Access Point Name (APN) is the name of a gateway between a GSM, GPRS, 3G and 4G mobile network and another computer network, frequently the public Internet. Later called DNN in 5G.
GTP and PDP Context
GTP
GPRS Tunneling Protocol is a simple tunneling protocol based on UDP/IP - used both in GSM/GPRS and UMTS.
Identified by a Tunnel Endpoint Identifier (TEID).
For every MS:
one GTP-C tunnel is established for signalling.
Multiple GTP-U tunnels, one per PDP context (i.e. session), are established for user traffic.
PDP Context
When an MS attaches to the Network:
SGSN creates a Mobility Management context with information about mobility and security for the MS.
At PDP Context Activation (PDP - Packet Data Protocol), both SGSN and GGSN create a PDP context, with information about the session (e.g. IP address, QoS, routing information , etc.).
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