GPRS Network Architecture [Under GPRS] §
Below diagram depicts GPRS network element and their interfaces.
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GSM/GPRS Network architecture - 23.002 «
» GPRS
description - 23.060 «
MS
ME is same as GSM ME with additional protocol capabilities for GPRS (for packet data transmission and reception). SIM still remain same.
Traditional term for GSM operations of having dedicated traffic channels is circuit switched (CS) operations or traffic. On the same lines, packet traffic introduced by GPRS can be called packet switched (PS) traffic.
Based on capabilities, GPRS introduced MS classes. Well known classes are, A, B, and C.
| A | Class A support CS and PS simultaneously. |
| B | Class B support both PS and CS but not simultaneously. Say GPRS packet traffic is in progress and GSM call is to be made, then packet traffic will be suspended for GSM call to begin. Also, when GSM call is in progress, packet traffic can not begin or continue. |
| C | MS which support either GPRS (PS) or GSM (CS), but not both. |
BSS
BSS also need to be enhanced for packet channels.
Instead of location areas, GPRS uses concept of routing areas (not shown in diagram) for mobility management. Usually routing areas are smaller compared to location area (in fact, location area is divided in number of routing areas) considering more signaling load required for GPRS paging than that for GSM.
Packet Control Unit (PCU), though logically part of BSS, is usually placed near to SGSN. PCU carries out RLC/MAC functions on one side and BSSGP/NS functions on the other side. It is also in charge of scheduling (allocation) decisions. Input to BSS from PCU side is PCU frames (similar to TRAU frames) and vice versa. Please refer 23.060:12.8 for more information.
Network
SGSN (Serving GPRS Serving node) sitting along with MSC, interact with BSS. SGSN tunnels user data to GGSN (Gateway GSN). GGSN is an entry point to PDN.
Note that SGSN do not have interface with VLR; mobility related to packet connections are taken care by SGSN (along with other SGSNs). MSC interface allows doing combined location updates.
Authentication, Security related functions require SGSN-HLR interface. In addition, HLR is queried for information related to subscribed (packet) services for the users.
SGSN can also directly to talk GGSN belonging to other PLMN through Gp interface (which pass through firewall).
References: GPRS in Practice by McGuiggan, GPRS whitepaper from Christian Bettstetter et al.
© Copyright Samir Amberkar 2010
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