How the data is transferred?
The most common methods used for data transfer are circuit-switching and packet-switching. With circuit-switched transmission the dedicated circuit is first established across a sequence of links and then the whole channel is allocated to a single user for the whole duration of the call. With packet switched transmission, the data is first cut in to small parts called packages which are then sent in sequence to the receiver, which again builds the packages back together. This ensures that the same link resources can be shared at the same time buy many different users. The link is used only when the user has something to send. When there is no data to be sent the link is free to be used by another call. Packet switching is ideal for bursty traffic, e.g. voice.
Technology used by GPRS
In order to meet these objectives the following technologies are applied. GPRS uses a packet-mode technique to transfer data and signaling in a cost-efficient manner over GSM radio networks and also optimizes the use of radio and network resources. Still a strict separation between the radio and network subsystems is maintained in order to allow the network subsystem to be reused with other radio access technologies.
New GPRS radio channels are also defined. The allocation of these timeslots is flexible, ranging from one to eight timeslots per TDMA frame, and they can be shared by active users. This allows GPRS to handle bitrates from 9 to even up to 150 kbit/s per user. With these bit rates all types of transmissions can be handled: from slow-speed short messages to the higher speeds needed e.g. when browsing Web pages. GPRS will also permit the user to receive voice calls simultaneously when sending or receiving data calls.
GPRS will provide a seamless connection to the existing standard data
services by using interfaces to TCP/IP and X.25. GPRS will also provide
fast reservation to begin transmission of packets, typically from 0,5 to
1 second. This means that the data users will not have to wait for the
phone to dial, but instead they will get through immediately. For example
the messages will be delivered direct to the user's phone, without the
need for a full end-to-end connection. When the user switches on their
phone, the message will be downloaded automatically.
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