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GSM versus GPRS

This page GSM versus GPRS describes difference between GSM and GPRS technologies.

• Air interface is same TDMA/FDMA.

• In GPRS multiple timeslots are allocated to one UE while in GSM one timeslot is allocated to one UE.

• In GSM signaling and traffic follow different multi frame structure. 51 frame MF is used for signaling and 26 frame MF is used for traffic. In GPRS signaling and traffic both follow common one multi frame structure i.e. 52 frame MF structure. Here 52 Multiframe composed of total 12 radio blocks, two idle slots and two slots are for PTCCH used fo timing advance purpose. Each Radio Block spans over 4 consecutive TDMA frames of one time slot.

•  In GPRS Synchronization is done using BCCH and hence FCCH/SCH of GSM is not needed. There is optional channel PBCCH, which carry GPRS specific SIs, may or may not be used by GSM Base Stations.

• Common Control channels are similar in both GSM and GPRS,PRACH to RACH, PAGCH to AGCH and PPCH to PCH of GSM is available here.

• GSM is used for circuit switched traffic (mainly voice) and GPRS is used for packet switched traffic (mainly internet/MMS). Due to this in GPRS PDTCH(Packet Data Traffic Channel) is allocated on demand unlike static nature of TCH in GSM.

•  There is no direct relevance to SACCH and FACCH of GSM in GPRS. In GPRS, PTCCH(Packet Timing Advance Control Channel) is used for timing advance purposes. For other signalling stuff, PACCH(Packet Associated Control Channel) is used. • Unlike GSM, in GPRS same time slot can be used by multiple UEs at different times, each will have unique identifiers both in downlink (called TFI) and uplink (called USF). In GSM time slots are dedicatedly reserved for particular UEs till they are released.

• In GSM time slot is allocated both in uplink and downlink hence in GSM radio resource allocation is called symmetric allocation. While in GPRS it is asymmetric, for example it is possible to allocate time slot only in downlink and not in uplink when user is only downloading some file.

• In GSM location area concept is used while in GPRS routing area concept is used.

• In GSM Mobile or UE will be in two states i.e. IDLE and READY while in GPRS UE will be in three states i.e. IDLE, STANDBY and READY.

•  Paging channel is required to be transmitted frequently in GPRS as traffic is bursty compare to GSM.

•  In network architecture PCU, SGSN and GGSN is added to normal GSM architecture components to support packet traffic. In addition, channel coding units are upgraded at BTS to support various GPRS rates.

There is difference between GSM architecture and GPRS architecture. Refer GSM tutorial and GPRS tutorial which depicts GSM and GPRS architectures respectively.

GPRS useful Links

GPRS protocol stack
GPRS Modem vendors
GSM versus GPRS
What is GPRS
GPRS/EGPRS Modulation-Coding Schemes

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