Bearer services provide the capability for information transfer between access points and involve only low layer functions. These functions are sometimes referred as low layer capabilities (in reference to OSI layers). The user may choose any set of high layer protocols for his communication and the PLMN does not ascertain compatibility at these layers between users.
In the general case a communication link between access points provides a general service for information transport. The communication link may span over different networks such as Internet, Intranets, LANs and ATM based transit networks, having network specific means for bearer control. Each network contributes to the end-to-end QoS perceived by the end-user.
PS and CS domains provide a specific set of bearer capabilities. The Circuit bearer services are described in 22.002 . The packet services (GPRS) is described in TS 22.060
. Following chapters describe the overall requirements for both the CS and PS domain bearers and also for the bearers used by teleservices.
Bearer services are characterised by a set of end-to-end characteristics with requirements on QoS. The characteristics and requirements shall cover major network scenarios, i.e. the cases when the terminating network is PSTN, ISDN, IP networks/LANs, X.25 and a PLMN.
Quality of Service is the quality of a requested service (Teleservice or Bearer Service or any other service, e.g. customer care) as perceived by the customer (ITU-T Recommendation E.800 ). QoS is always meant end-to-end. Network Performance of several network elements of the originating and terminating network(s) contribute to the QoS as perceived by the customer including terminals and terminal attachments. In order to offer the customer a certain QoS the serving network need to take into account network performance components of their network, reflect the performance of the terminal and ad sufficient margin for the terminating networks in case network performance requirements cannot be negotiated.
As far as the QoS to the subscriber is concerned network elements have to provide sufficient performance (reflecting possible performance constraints in terminating networks) so that the PLMN cannot be considered as a bottleneck.
This section outlines the requirements on bearer services in two main groups;
Requirements on information transfer, which characterise the networks transfer capabilities for transferring user data between two or more access points.
Information quality characteristics, which describe the quality of the user information transferred between two or more access points.
It shall be possible to negotiate / re negotiate the characteristics of a bearer service at session / connection establishment and during an on going session / connection.
It shall be possible to allocate a particular QoS to any specific service of the user. The association between services and QoS can be handled either network based or UE based. In the case of a UE based association it shall be possible to be programmed by the Home Environment operator into the ME or the USIM. If the association exists in the UE the specific QoS for the invoked service shall be requested at session / connection establishment.
Connection oriented / connectionless services
Both Connection oriented and connectionless services shall be supported.
Traffic type: It is required that the bearer service provides one of the following:
guaranteed/constant bit rate,
non-guaranteed/dynamically variable bit rate, and
real time dynamically variable bit rate with a minimum guaranteed bit rate..
Real time and non real time applications shall be supported.
Real time video, audio and speech shall be supported. This implies the:
ability to provide a real time stream of guaranteed bit rate, end to end delay and delay variation.
ability to provide a real time conversational service of guaranteed bit rate, end to end delay and delay variation.
Non real time interactive and file transfer service shall be supported. This implies the:
ability to support message transport with differentiation as regards QoS between different users.
Multimedia applications shall be supported. This implies the:
ability to support several user flows to/from one user having different traffic types (e.g. real time, non real time)
It shall be possible for an application to specify its traffic requirements to the network by requesting a bearer service with one of the following configurations
A multicast topology is one in which sink parties are specified before the connection is established, or by subsequent operations to add or remove parties from the connection. The source of the connection shall always be aware of all parties to which the connection travels.
A broadcast topology is one in which the sink parties are not always known to the source. The connection to individual sink parties is not under the control of the source, but is by request of each sink party.
In the case of a mobile termination with several active bearer services simultaneously, it shall be possible for each bearer service to have independent configurations and source/sink parties.
5.2.2 Information Quality Word‑p. 12
Information quality a characterises the bit integrity and delay requirements of the applications.
Other parameters may be needed.
Maximum transfer delay
Transfer delay is the time between the request to transfer the information at one access point to its delivery at the other access point. In clause 5.5
requirements on maximum transfer delay is defined.
The delay variation of the information received information over the bearer has to be controlled to support real-time services. The possible values for delay variation are not a limited set, but a continuous range of values.
Bit error ratio
The ratio between incorrect and total transferred information bits. The possible values for Bit error ratio are not a limited set, but a continuous range of values.
The data rate is the amount of data transferred between the two access points in a given period of time.