How [Under GPRS]
Let us give a little thought as to how we can modify or enhance GSM for packet based (internet) traffic.
Radio interface (or Access side)
We can keep GSM radio channel configuration in terms of frames, multi-frames same, but keep aside few channels for packet traffic and related signaling. The information can be broadcast same way as for GSM channels (i.e. over BCCH).
Access to packet channel can be requested in similar way to GSM i.e. through RACH, but may be with separate RACH channels.
Will we need dedicated signaling channels for getting allocation on packet channels ? Packet traffic is bursty in nature, so allocation needed change over time. Thus we should not use dedicated signaling channels. Rather we can use the packet channel itself to make allocation request. Even initial signaling required before start of transmission of user data (first after MS power on) can also happen through same packet channels meant for traffic.
As packet channels are shared, there should be a way by which MS should know about time slots it need to use (UL), whether the data sent in traffic channel is meant for it (DL). We need these "Access Resolution" procedures.
Allocation of resources should be such that variable and higher date rate can be supported without sacrificing on efficiency of traffic channels.
Network side
On network side, we will need a node which would manage a session (and corresponding user data) with MS. This node can then tunnel the user data to another node (gateway node). The gateway node need to then inject the tunneled user data to Internet or other PDN.
We will need handover procedures to maintain packet traffic as MS moves from cell to cell.
As for authentication, we can continue to use HLR.
With this as background, let us see how GPRS works.
© Copyright Samir Amberkar 2010
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