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Evolution from 2G to LTE (Part 2 – GPRS)

Author: gokhankosem, on 15 Jan 12 - 1 Comment
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Evolution from 2G to LTE (Part 2 – GPRS)

The evolution had started with additional of the packet switched network to the GSM network architecture. And this new technology called GPRS(General Packet Radio Service). It is also called 2,5G. GPRS is important as a migration step toward third-generation (3G) networks and allows network operators to implement an IP-based core architecture for data applications, which will continue to be used and expanded for 3G services for integrated voice and data applications.

The GSM and GPRS network architecture shown below.


GPRS require some modifications to some GSM network elements.
These are :

  • New MS for GPRS with backward compatible with GSM.
  • Software upgrade in BTSes.
  • Software upgrade in BSCes and a new hardware called Packet Control Unit (PCU) is added. The PCU directs the data traffic to the GPRS network.
  • Installation of new core network elements called the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN).
  • Software upgrades in databases like HLR,VLR etc…

SGSN


Analogous to the MSC in circuit switched network. The SGSN is responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information for charging for the use of the air interface.

GGSN


Analogous to the GMSC in circuit switched network. The GGSN acts as an interface and a router to external networks. It contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct SGSN. The GGSN also collects charging information connected to the use of the external data networks and can act as a packet filter for incoming traffic.

SGSN and GGSN are routers with additional functionality capable of switching IP packets using non-IETF protocols.

GGSN is the primary vehicle that you can use to support Mobile IP. As you know there is a “foreign agent” in Mobile IP.This function can be installed to GGSN in GPRS network.

Interfaces


With addition of the GPRS packet switched network to the network architecture, some additional interfaces appered. Most importants are :

  • Gb : interface between BSC and SGSN
  • Gn : interface between SGSN and GGSN
  • Gi : interface to External networks

And the other interfaces are Gd, Gf, Gs, Gr, Gc, Gp interfaces. After UMTS lesson all the interfaces will be shown in an integrated network architecture.

GPRS Protocol Stack




Some Important Points for GPRS

Data rate : Maximum of 171.2 kbps
Channel coding : Outer block coding
Inner Convolutional coding
Interleaving scheme for error bursts
Modulation : Gaussian Minimum Shift Keying GMSK
Multiple Access : Combination of TDMA & FDMA
Transmit Frequency bands : Mobile Station Uplink Reverse ch. 890 – 915 MHz
Base Station Downlink Forward ch. 935 – 960 MHz
Duplex seperation : 45 MHz
RF carrier spacing : 200 kHz
Total number of RF Duplex channels : 124
Number of TDMA slots on each carrier : 8
Channel allocation : 1 to 8 time slots per TDMA
One time slot (Physical channel) 0.577 ms
Frame Interval : 4.615 ms
Asymmetric data traffic :Different time slots for Uplink and downlink
Connectivity : Packet switched data networks such as IP and X.25
Extra nodes : Gateway GPRS Support Node (GGSN)
Serving GPRS Support Node (SGSN)
Frequency Hopping : 217 hops/s (slow)
Equalizer : 16 µs time dispersion

You can continue with the other Evolution from 2G to LTE articles…

Evolution from 2G to LTE (Part 1 – GSM)
Evolution from 2G to LTE (Part 2 – GPRS)
Evolution from 2G to LTE (Part 3 – EDGE)

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About the Author
Gokhan Kosem is a telecommunation and network engineer. His ambition to IP networks and end-to-end system installation made him to prepare this web-site. By sharing his experiences about various networking protocols beside different system installation experiences and Cisco, Juniper, Alcatel-Lucent devices configurations, he is aimed to be helpful for his collegues in all over the world. He is currently lives in Istanbul, Turkey.

One comment for “Evolution from 2G to LTE (Part 2 – GPRS)”

1
adnnan

thanx so much Gokhan but we need to know about 3 G and 4 G

March 2nd, 2014 at 21:58

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