Wide Area Networks - Types of Connection
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- Přidal/a: anonymous
- Datum přidání: 01. července 2007
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Wide Area Networks - Types of Connection
WIDE AREA NETWORKS–TYPES OF CONNECTIONS
WIDE AREA NERWORK (WAN)
The term WIDE AREA NETWORK (WAN) usually refers to a network which covers a large geographical area, and use communications circuits to connect the intermediate nodes. A major factor impacting WAN design and performance is a requirement that they lease communications circuits from telephone companies or other communications carriers.
Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks. Some WANs are very extensive, spanning the globe, but most do not provide true global coverage. Organizations supporting WANs using the Internet Protocol are known as Network Service Providers (NSPs). These form the core of the Internet. By connecting the NETWORK SERVICE PROVIDER WANs together using links at Internet Packet Interchanges (sometimes called "peering points") a global communication infrastructure is formed. NSPs do not generally handle individual customer accounts (except for the major corporate customers), but instead deal with intermediate organizations whom they can charge for high capacity communications. They generally have an agreement to exchange certain volumes of data at a certain "quality of service" with other NSPs. So practically any NSP can reach any other NSP, but may require the use of one or more other NSP networks to reach the required destination. NSPs vary in terms of the transit delay, transmission rate, and connectivity offered.
The characteristics of the transmission facilities lead to an emphasis on efficiency of communications techniques in the design of WANs. Controlling the volume of traffic and avoiding excessive delays is important. Since the topologies of WANs are likely to be more complex than those of LAN (Local Area Network), routing algorithms also receive more emphasis.
TYPES OF CONNECTIONS
WAN is used across a state and country or even around the global. Many LANs are connected to each others using WAN communications under a high speed communication. Bridges, routers and multiplexers and other devices are used for correct data transmission.
DIAL-UP TELEPHONE CONNECTIONS
DEDICATED DIGITAL TELEPHONE LINES
CONNECTIONS OVER PACKET-SWITCHED NETWORKS
Are all WAN links
CONNECTION THROUGH THE TELEPHONE SYSTEM
Dial-up connection that uses the telephone line and it’s very popular in our daily life. It is analog and the computer uses modems to change the signals from analog to digital signals. DEDICATED LEASED LINES
It provides a full-time connection between two points. Lease lines are expensive but offer high speed data transmission. They are available as analog and digital lines. ISDN (INTEGRATED SERVICE DIGITAL NETWORK)
Offers voice, video, and data transmission where T1 = 23B + D (B: used for voice or data, D: used to handle control information, T1: 1.544 Mbps). Its speed can be up to 128 kbps. USING X.25
X.25 is the first wide speed implementation of packet switching. It is based on technology concepts that date back to the 1960’s. It was developed at 1992 and the speed of transmission increased up to 2Mbps and today it is used to allow communication between many different computer systems on a world wide basis. ADVANTAGES
It maybe the only way to set up international networks links to countries with unreliable telephone systems. It is reliable. It provides for any-device-to-any-device type connection for simultaneous users. DISADVANTAGES
Packets must travel through shared ports on routers. Not acceptable technology for most real time LAN to LAN applications. FRAME RELAY
It is a connection oriented service similar to X.25 which provides error-checking at each intermediate node in the network. Frame relay provides for error-checking only at the source and destination devices. ASYNCHRONOUS TRANSFER MODE (ATM)
It is a cell switching technique using time division Multiplexing. Information is transferred in packets of fixed size called cells. ATM cells posses fixed size 53bytes. IMPORTANT TERMS
The basic data communication configuration consists of a sending and receiving remote TERMINAL, a MODEM (modulator/demodulator) and a COMPUTER SYSTEM to receive the data and to process and prepare information for retransmission through the communication system. The telephone is still the main method of transferring data over a communication system. The telephone system is an analog system, but the terminals and computers produce digital pulses. The modem is a device that provides an interface for digital pulses to and from the terminals and computer, through the telephone circuits. The modem converts electrical signals to modulated signals that can be transmitted.
The HOST COMPUTER, also called the SERVER, is the main processing device in a network.
Originally, the host computer would handle all of the functions now divided among other devices in the system. Essentially, the host computer is being moved further away from the communications control functions. Hardware and software have been developed and are being developed for peripheral devices to handle communication duties. The COMMUNICATIONS CONTROL UNIT is an interface between the communications line and the computer. The communication control unit is basically a peripheral device that purifies data transmission signals and relieves the computer of unnecessary monitoring duties. It is also called the ROUTER.
The CONCETRATOR is normally located on the terminal side of the data communication system. The concentrator takes data from a large number of low- and medium-speed lines and combines them for retransmission over one or more high-speed lines. Factors that can affect TRANSMISSION RATE include: type of modem, line discipline, type of communication channel and transmission medium. Analog transmission is the most readily available and can be used on switched or leased telephone lines.
PROTOCOLS are groups of rules and procedures that initiate and maintain communication. They give the messages the right priority. Well known protocols are TCP/IP- Transfer and Communication Protocol/Internet Protocol used by the Internet, and PPP- Point to Point Protocol.