The GPRS can be described using the simplified reference model in Figure 1.
GPRS provides data transfer capabilities between a sending entity and one or more receiving entities. These entities may be an UE or a Terminal Equipment, the latter being attached either to a GPRS network or to an external data network. The base station provides radio channel access for UEs to the GPRS network. User data may be transferred between four types of UEs as described in TS 22.001 and TS 24.002.
Each PLMN has two access points, the radio interface (labelled Um for GERAN and Uu for UTRAN) used for mobile access and the R reference point used for origination or reception of messages. The R reference point for the UEs is defined in TS 27.060.
Network interworking is required whenever a PLMN and a non-PLMN are involved in the execution of a GPRS Service request.
In general the mobile user of a GPRS network will receive and experience all the services provided by an external data network. In this case the external data network refers to the network that the GPRS PLMN interworks with as determined by the network operator. With this in mind it can be said that a user:
will require a universal identity(ies) of the form compatible with the interworked with network(s);
and experience access to and provision of all services as offered by the interworked with networks (some reduction of capability may result from unavoidable restrictions due to the complexity of implementation).
GPRS shall provide means to interwork with external data networks. The GPRS operator may provide an appropriate address to the external data network for the subscriber as part of the GPRS subscription. That address can be either dynamic (e.g. the user's IP address is allocated from a pool of unused IP addresses every time the subscriber activates the access to an IP network) or static (e.g. a certain IP address is permanently allocated to a particular subscriber). In addition, the GPRS network shall be able to notify the server IP address (e.g. the gateway IP address) to the subscriber, when the subscriber activates. When connected with some external data networks, the routeing protocols of these networks may limit the data network addresses that can be allocated. For example, when interworking with IP networks, the IP address for the GPRS subscriber shall belong to that GPRS operator's IP subnetwork that allocates the address. In the case of a simple point to point connection, a GPRS subscriber need not have an associated network address.
The type of interworking between a PLMN and data networks is determined by the network operator.
Interworking with the following types of data networks shall be defined:
A GPRS subscriber identified by an IMSI, may have a network layer address(es) temporarily and/or permanently associated with it that conforms to the standard addressing scheme of the respective network layer service used, e.g.:
IP Version 4 and 6 addresses for Internet CLNS.
In the case of a simple point to point connection, a GPRS subscriber need not have an associated network layer address.
Interworking between different GPRS PLMNs is required in order to support subscriber roaming.
It shall be possible for the VPLMN to provide access to the external data network when the external non-3GPP data network address is dynamically assigned by the VPLMN.
The PTP service provides a transmission of one or more packets between two users, initiated by a service requester and received by a receiver.
There is one PTP service: - PTP Connectionless Network Service (PTP-CLNS). The PTM service provides a transmission of packets between a service requester and a receiver group.
There is one PTM service:
IP Multicast (IP-M).
An invocation of the service request by a service requester is possible from the fixed and mobile access points.
Table 1 presents the relationship between service requests and the Service Requester/Receiver.
Point-To-Point Connectionless Network Service (PTP-CLNS) is a service in which one (or more) single packet(s) is (are) sent from a single service subscriber "A" to a single destination user "B". Each packet is independent of the preceding and succeeding packet. This service is of the datagram type and is intended to support bursty applications. On the radio interface PTP-CLNS supports the acknowledged transfer mode for reliable delivery.
GPRS provides data communications services consistent with the connectionless network layer service definition ISO 8348 . Specifically, GPRS shall be able to support applications based on the following network layer protocol:
Internet Protocol (IP);
IP is the network layer protocol of the Internet TCP/IP protocol suite defined by Internet STD 5 .
A PTM service is the transmission of a single message to multiple subscribers. The GPRS PTM services provide the capability for a subscriber to send data to multiple destinations.
There is one PTM service:
IP Multicast (IP-M), which is a service defined as a part of the IP protocol suite. In IP-M messages are sent between participants of an IP-M group. An IP-M group can be internal to the PLMN or distributed across the Internet. Participation and data transfer in the IP-M service shall be compliant with the Internet protocols. See RFC 1920, RFC 1458, RFC 1301 and RFC 1112. The Service Receiver of a point-to-multipoint service request shall be able to filter out packets at a network level, through use of the Packet Identities, which are of no interest either because they are for a service for which no subscription is held, or the packet belongs to a sub-group within the offered application service which is of no interest. It is required that the UE-Application resources shall not be utilized for this function.
The packet multiplexing mechanisms developed for GPRS shall be independent of a given channel type. It shall be possible to operate GPRS over low and high capacity channels. Table 3 is only applicable to the GPRS part of the connection.
Service data unit integrity Data sequence integrity
Point to point Point to multipoint
Establishment of Communication (d)
Demand mobile originated or mobile terminated
Out of band In band
Radio Channel assignment
Traffic type: describing data streams with constant bit rate or variable bit rate characteristics.
Timing end-to-end: describing the timing relation between the source and destination of signals.
Flexible channels with a maximum bit rate that depends on the type of channel and the number of time slots in GERAN that are used. This capability defines the maximum capability associated with the channel(s). The actual bit rate for a particular user may be any value up to this maximum value.
Establishment of communication: may be on demand, reserved or permanent.
An invocation of a service by any user with the appropriate subscription profile shall be possible.
It shall be possible to validate a service request against a service subscriber's subscription profile.
The mapping of user application QoS parameters to GPRS QoS parameters is an implementation issue and is not part of GPRS specifications.
It shall be possible to respond to local data traffic conditions adaptively. GPRS shall include the functionality to increase or decrease the amount of radio resources allocated to GPRS on a dynamic basis. The criteria used to decide on dynamic changes of the GPRS part of the radio resource should not be specified. Thus, only the necessary procedure, including radio protocol and timers, needed to perform the change of radio resources shall be specified within the ETSI specifications.
Within GPRS the dynamic allocation of the radio resource for bursty or lengthy file transfer applications shall be such that it can be controlled by the network operator.
The defined QoS parameter values, assume the user is at a location with acceptable -coverage and refer to and are valid for normal network operating conditions or, as in the case of the service precedence parameter, regulate how the network shall handle abnormal conditions.
The service precedence indicates the relative priority of maintaining the service. For example under abnormal conditions (e.g. network congestion) packets which may be discarded can be identified. The following precedence levels are defined:
High precedence: Service commitments will be maintained ahead of all other precedence levels.
Normal precedence: Service commitments will be maintained ahead of low priority users.
Low precedence: Service commitments will be maintained after the high and normal priority commitments have been fulfilled.
The reliability parameter indicates the transmission characteristics that are required by an application. The reliability class defines the probability of loss of, duplication of, mis-sequencing of or corruption of SDUs.
Table 4 lists the three classes of the data reliability.
Error sensitive, no error correction capability, limited error tolerance capability.
Error sensitive, limited error correction capability, good error tolerance capability.
Not error sensitive, error correction capability and/or very good error tolerance capability.
To protect against buffer overflow or a protocol malfunction, there is a maximum holding time for each SDU in the GPRS network after which the SDU is discarded. The maximum holding time depends on the protocols used (e.g., TCP/IP).
Corrupt SDU probability: the probability that a SDU will be delivered to the user with an undetected error.
GPRS is not a "store and forward" service - although data is temporarily stored at network nodes during transmission - thus, any delay incurred is due to technical transmission characteristics (or limitations) of the system and is to be minimised for a particular delay class. The delay parameter thus defines the maximum values for the mean delay and 95-percentile delay to be incurred by the transfer of data through the GPRS network(s). The delay parameter defines the end-to-end transfer delay incurred in the transmission of SDUs through the GPRS network(s).
This includes the radio channel access delay (on uplink) or radio channel scheduling delay (on downlink), the radio channel transit delay (uplink and/or downlink paths) and the GPRS-network transit delay (multiple hops). It does not include transfer delays in external networks.
Delay is measured between the R or S (for UE) and Gi (for FS) reference points when applied to "UE to fixed station (FS)" or "FS to UE" transmissions.
The throughput parameter indicates the user data throughput requested by the user.
Throughput is defined by two negotiable parameters:
Maximum bit rate
Mean bit rate (includes, for example for "bursty" transmissions, the periods in which no data is transmitted.)
The maximum and mean bit rates can be negotiated to a value up to the Information Transfer Rate value (see Table 3).
It shall be possible for the network to re-negotiate the throughput parameters at any time during a session.