Distribution Services

Distribution is the transfer of information throughout a geographic area or through a network. Distribution services include broadcast, multicast, and point-to-point communication.

Broadcast
Broadcast transmission is the distribution of an information signal to a specified geographic area or network system. Broadcasting allows the same information to be received by all customers in that geographic area that can successfully receive (demodulate) and decode the information.

Figure below shows broadcast communication service. This diagram shows two broadcast examples: radio broadcast and network broadcast. Part (a) shows a radio broadcast tower that is sending an audio broadcast to all radios that are within its radio signal coverage area. Part (b) shows a network broadcast system that sends a data message that is coded to indicate the message is a broadcast message. This message contains an address that indicates it is a broadcast message. When routers or other data distribution devices receive this message, each distribution device forwards the data broadcast message to the other network parts for which it is connected to. All communication devices that are connected to the network can receive the broadcast message.


broadcast communication

Multicast
Multicast transmission is a communications service where a single message or information transmission contains an address (code) that is designated for several devices (nodes) in a network. Devices must contain the matching code to successfully forward or decode the message.

Figure below shows examples of how multicast services can be implemented. The first method uses encoded video broadcast transmission and encoded messaging to allow only a select group to view the received information. While all the television broadcast receivers all receive the same radio signal, only the receivers with the correct code will be able to descramble the television signal. The second method uses multicast routing in the Internet to store and forward data to an authorized group of recipients that are connected to its router. When a router in the Internet that is capable of multicast service receives a multicast message, it will store the message for forwarding. It then uses the multicast address to lookup a list of authorized recipients in its routing table. The stored message is then forwarded to the authorized receiving device or next router that is part of the multicast service.



multicast communication

Point-to-Point
Point-to-point communication is the transmission of signals from one specific point to another. Point-to-point communication uses addressing to deliver information to a specific receiver of the information. It is possible to implement point-to-point communication through a broadcast network by using device addressing or through a network using network routing.

Figure below shows examples of how point-to-point services can be implemented. The first method is a paging system that uses device addressing to uniquely identify a specific receiver of the information. While all the pager devices receive the same radio signal, only the receiver that has the correct paging code will be able to descramble the paging message. The second method uses network routing in the Internet to store and forward data to a specific recipient in the network. When a router in the Internet receives a point-to-point message, it will use the address to lookup the best forwarding path to transfer the information towards its destination. Using point-to-point communications by network routing, only the designated recipient will receive the data.


point-to-point communication

Wireless Networks

Wireless networks are primarily designed to transfer voice and or data from one point to one or more other points, (multipoint). Many networks make use of some wireless technologies as a transport medium even though we do not consider them to be wireless networks. Examples of wireless networks include cellular, personal communication service, (PCS), paging, wireless data, satellite, and broadcast radio and television.

Cellular and PCS
Cellular and PCS systems are comprised of a set of radio towers that are strategically distributed over a geographical area in order to provide a continuous service coverage area. A mobile switching center (MSC) provides the switching and control functions necessary to connect calls from the public switched telephone network (PSTN) to the individual mobile telephones. The MSC also manages the radio resources within the entire network.

Several service providers (carriers) within a particular geographical area can provide wireless services simultaneously as long as they use a different set of radio frequencies that do not interfere with each other. Specific sets of radio frequencies are allocated for use in cellular communications systems. Typically a government agency is responsible for assigning these frequencies and licensing them to specific service providers.

Paging
Paging is a wireless system that is capable of delivering message to one or more people whose exact whereabouts are unknown by the sender of the message. Users typically carry a small paging receiver that displays a numeric or alphanumeric message displayed on an electronic readout. It also could be sent and received as voice message or other data. Pager systems may be classified based upon their capabilities as numeric, alphanumeric, tone, or voice.

Paging networks are comprised of terrestrial based antennas all interconnected by means of some other type of physical network. Satellite transmission systems are often used to distribute the messages to multiple towers for retransmission. The use of satellite interconnection systems permits regional, nationwide, or global paging service. Some paging systems are capable of providing two-way communications.

Each pager in the network has a unique identifier (address) that is stored to the pager’s memory. This address is also stored in the paging network. When an incoming telephone call accesses the pager customer’s account, the network transmits the address of the pager on its radio tower. In addition to sending a specific paging address, the system may send other digits, text, or even voice information that follows the addressing message.

Wireless Data
Wireless data networks transfer data between network access points (wireless data devices) through radio transmission and are primarily designed to transfer data from one point to one or more points (multipoint). These networks may be composed of a variety of communication systems including: mobile data terminals, radio access nodes, packet switching networks. Wireless data networks provide a variety of services including: equipment status monitoring, dispatch services, vehicle and goods tracking, credit card validation, and include wireless Internet access.

Broadcast
Broadcasting is a process that sends voice, data, or video signals simultaneously to group of people or companies in a specific geographic area or who are connected to the broadcast network system (e.g., satellite or cable television system). It is typically associated with radio or television radio transmission systems that send the same radio signal to many receivers in a geographic area. Broadcasting can also be applied to wired distribution or point-to-point networks where all users that are connected to the network can receive the same information signal.

Figure below shows the different types of wireless networks. This diagram shows a private land mobile radio system, television broadcast system, paging system, mobile telephone system, and satellite communication system. Although all wireless networks can transmit information from one point to another, different types of networks better suited to provide specific types of services (e.g., paging compared to television broadcasting).


Wireless Networks