The general packet Radio Service (GPRS) presents packet mode transfer for applications that show traffic patterns such as the frequent transmission of small volumes or infrequent transmissions of small or medium volumes according to essential specifications. Comparative existing data transfer services, GPRS should use the existing network resources more efficiently for packet mode applications and should give a selection of Qos parameters for the service requesters.
Furthermore, GPRS should allow for broadcast, multicast, and unicast service. The overall goal in this context is the provision of a more efficient and, thus, cheaper packet transfer service for typical internet applications that usually rely solely on packet transfer. The network provides could support this model by changing on volume and not connection time as is done today.
Clearly, GPRS was given by the tremendous success of the packet-oriented internet, and by the new traffic models and applications. The main concepts of GPRS are the following:
For the new GPRS radio channels, the GSM system can allot between one and eight-time slots within a TDMA frame. Time slots are not allotted in a fixed, decided manner but on need. Best slots can be shared by the active users, up and downlinks are designated separately. Allocation of the slots is based on current load and operator choices. Depending and decoding, a transfer rate of up to 150 kilobytes is possible. However, the GPRS concept is independent of channel features and of the type of channel, and it does not limit the maximum data rate. All GPRS services can be used parallel to convention services.
In Phase 1, GPRS offers a point to point packet transfer service. One of the PTP versions offered is the PTP connection-oriented network service, which includes the ability of GPRS to maintain virtual corresponds to X25, the typical circuit-switched packet-oriented transfer protocol available wild world. The other PTP version offered is the PTP connectionless network service, which supports applications that are based on the internet protocol IP. Multicasting, called point-to-multipoint service, is left for GPRS phase 2.
Users of GPRS can specify a QoS-profile. This profile determines the service presidency, reliability class and delay class of the transmission, and user data throughput. GPRS should adaptively allocate radio resources to fulfill these user specifications.
Delay within a GPRS network is detected by channel access delay and transfer delays in the fixed and wireless portion of the GPRS system. The delay presented by external fixed networks is out of scope. However, GPRS does not provide additional delay by buffering packets as store and forward networks do. If possible, GPRS attempts to forward packets as fast as possible. This is a very important thing that has to be taken into account when achieving higher layer protocols such as TCP on top of GPRS networks.
Finally, GPRS includes several Security Services such as authentication, access control, user identity confidentiality, and user information confidentiality. Even a completely anonymous service is possible, as, e.g., applied for road toll systems that only change a user via the MS independent of the user's identity.
The GPRS architecture introduces two new network elements, which are called GPRS support nodes (GSN). All GSNs are integrated into standard GSM architecture. The Gateway GPRS support node is the interworking unit between the GPRS network and external packet data networks. This node contains routing information for GPRS users, performs address conversion, and tunnels data to the user via encapsulation. The GGSN is connected to external networks via the Gi interface and transfers packets to the SGSN via a GPRS backbone network.
The other new e element is the serving GPRS support node which supports the MS via the e Gb interface, the SGNS, for example, requests user addresses from the GPRS register, keeps track of the individual MSs' location, is responsible for collecting billing information, and performs several security functions such as access control.
Before sending any data over the GPRS network, an MS must attach to it, following the procedures of mobility management. The attachment procedure includes assigning a temporal identifier, called a temporary logical link identity, and a ciphering key sequence number for data encryption. For each MS, a GPRS context is shut up understood in the MS and in the corresponding SGSN. This contact comprises the status of the MS.
A very important factor for any application working end to end is is that it does not notice any details from them GPRS related infrastructure. The application uses, for example, TCP on top of IP, IP packets are tunneled to the GGSN, which forwards them into the PDN. All PDNs forward their packets for a GPRS user to the GGSN asks the current SGSN for tunnel parameters, and forwards the packets via SGSN to the MS.
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