Bearer services are telecommunication services that are used to transfer user data and control signals between two pieces of equipment. Bearer services can range from the transfer of low speed messages (300 bps) to very high-speed data signals (10+ Gigabits).
Bearer services are typically categorized by their information transfer characteristics, methods of accessing the service, interworking requirements (to other networks), and other general attributes. Information characteristics include data transfer rate, direction(s) of data flow, type of data transfer (circuit or packet) and other physical characteristics. The access methods determine what parts of the system control could be affected by the bearer service. Some bearer services must cross different types of networks (e.g., wireless and wired) and the data and control information may need to be adjusted depending on the type of network. Other general attributes might specify a minimum quality level for the service or special conditional procedures such as automatic re-establishment of a bearer service after the service has been disconnected due to interference. Some categories of bearer services available via the telephone system include synchronous and asynchronous data, packet data, and alternate speech and data.
Figure below shows a typical bearer service. In this diagram, a customer decides to send a data file to a computer that is connected to a public telephone network (at the office). In this example, the bearer service is circuit-switched data. The customer uses a modem to adapt their portable computer to the telephone network. The portable dials the office computer telephone number via the modem. The telephone system routes this call to a modem that connects the office computer to the telephone network. When the office computer modem accepts the call, the customer’s modem begins to send data directly on the telephone line at channel at 28 kbps. All the telephone system provides is a standard voice communications path between the portable computer modem and the office computer modem. The key bearer service attribute is the transfer of real-time information in the audio frequency range of 300 Hz to 3300 Hz. This is the bearer service.
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