Départ. Technical support- CM640
PROCEDURE
COMPANY RESTRICTED
PHILIPS Consumer
Communications
Centre du Mans
Service Repair Support
VY-V-640-620-3
Page : 22
of
63
Language : EN
Date : 11/02/03
PHILIPS ELECTRONICS N.V. 1999
VY-V-640-620-3
All rights reserved. Reproduction in whole
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consent of the copyright owner.
In the mobile terminal, appears from the bottom to the top the following layers :
n
The physical layer, constituted of two functional sub-layers;
•
The RF sub-layer, which manage the radio operations of the terminal. It emits the data received from
the physical layer. It decodes the data coming from the base station (BTS) and transmits it to the
physical layer .for interpretation
•
The physical layer produces the frames, those ones will be emitted by the RF layer; about the frames
received from the network, it detects and corrects transmission errors.
n
The MAC layer (or RLC for Radio Link Control) manages the radio link between the terminal and the Base
Station (BTS), that means re-emission mechanisms in case of error, The function of access controller for
the radio resources when several air terminals are in competition. The RLC can request the re-emission of
a data packet ;
n
The higher layer SNDC (Sub-Network Dependant Convergence) manages the mobility, the ciphering and
data compression.
GGSN : Gateway GPRS Support Node ,
The GGSN provides the interface towards the external IP packet networks. Actually, from the external IP network’s
point of view, the GGSN acts as a router for the IP-addresses of all subscribers served by the GPRS-networks. To
make this possible the GGSN exchanges routing information with the external networks and sets up connections
towards external networks. Similar to the SGSN, the GGSN deals with session management, specifically the
connection towards the external networks. Also, as many SGSN can connect to one GGSN, it has to associate
subscribers to the right SGSN.
SGSN : Serving GPRS Support Node
The SGSN forwards incoming and outgoing IP packets addressed to and from a mobile station. It serves all GPRS-
subscribers that are located and attached within the geographic SGSN service area.. A subscriber may be served
by any SGSN in the GPRS network depending on location. The traffic is rooted from the SGSN to the BSC, via the
BTS to the mobile station. O make this packet traffic possible, signalling with several other nodes is necessary, for
instance the Home Location Register (HLR) , the Mobile Switching Centre (MSC), the BSC and the GGSN, as well
Short Message Service-nodes (SMS). From these signalling connections the SGSN handles important GPRS
functions such as ciphering and authentication, session management, mobility management and the logical link
management towards the mobile station.
Packets routing
The routing of every packet is independent from the one who precedes it or by the one who follows it. During the
connection phase of a GSM terminal in a network, the signalling exchanges are multiple, and to face the
constraints of the packet mode, the information of routing obtained to forward the first packet to a GSM terminal is
stored in the GGSN. So, the routing of following packets is selected according the context stored in the GGSN ( the
Temporary Logical Link Identity or TLLI).
