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Point-to-Point (PTP) packet transfer service 
This service transmits packets between users, a service requester and a 
receiver. In this type of service one or more single packets are sent from a 
single sender to one single receiver. 
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Point-to-Multipoint (PTM) packet transfer service 
This service provides transmission of packets between a service requester 
and a receiver group. This means transmission of a single message to 
multiple subscribers. 
The figure below shows a simplified version of the GPRS architecture. The complete 
logical architecture of GPRS may be seen in [27]. 
Figure 3-1: Overview of the GPRS architecture
 

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3.1 TMMS Service based on GPRS: : Overview 
Page 30 of 93 
The GPRS architecture introduces a new network node type: GPRS Support Node 
(GSN), which is a router and is integrated into the network architecture by some well-
known reference points. It is also responsible for collecting billing information. There are 
two kinds of GSNs: 
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Gateway GPRS Support Node (GGSN) 
This is a unit which provides the interface towards external data 
networks. GGSN contains routing information and tunnels data to a user 
using encapsulation. It also translates data formats, signaling protocols 
and address information in order to permit communication between the 
different networks.
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Serving GPRS Support Node (SGSN)
Requests user addresses from the GPRS register (GR), keeps track of 
individual User Equipment (UE) locations, and handles security 
functions, such as access control. SGSN is connected to GERAN Base 
Station (BS) system through the Gb or Iu interface, and/or to the 
UTRAN system through the Iu interface. SGSN is the node that is 
serving the UEs. 
The SGSN and GGSN can be combined in the same physical node or they may reside in 
two different nodes. When they reside in different nodes they communicate with the Gn 
interface. They contain IP or other routing functionality, and may be interconnected with 
IP routers. When the SGSN and the GGSN are in different PLMNs they are 
interconnected via the Gp interface.
 
Before the UE can send or receive data it has to be connected to the GPRS network. To 
connect to this network the UE assigns a temporal identifier, called TLLIdentity (TLLI), 
and a CKSNumber (CKSN), for data encryption. Then a GPRS context is created for 
each UE, which is stored in the UE it self as well as the corresponding SGSN. This is 
called a GPRS Attach. A GPRS attach is performed when the UE indicates its presence 
to the network. This can be done immediately after the UE has been switched on or later 
when the UE decides to use a GPRS service. When the UE is finished using the GPRS 
services it performs a GPRS detach. The network can also perform a GPRS detach. This 
can happen for several reasons, i.e. ill behaving UE, congested network and immediate 
service termination among others.