Kbase P62592: What is a WAN?
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
9/9/2010 |
|
Status: Verified
GOAL:
What is a WAN?
FIX:
WAN (Wide Area Network).
A WAN is generally an extension of an internal network into the wide area using private circuits such as T1 lines or virtual circuits in cell and packet switched networks such as ATM and frame relay. WANs links geographically dispersed offices in other cities or around the globe. Because WANs have been built with private leased lines, bandwidth has traditionally been low and costs have been high, which required careful monitoring and filtering of traffic between sites. WANs can also be constructed across the Internet by implementing VPN (virtual private network) technology.
With VPNs private circuits are emulated in the form of encrypted tunnels from one site to another.
Dedicated leased lines (circuit-oriented) such as T1 lines are still common, although expensive. The advantage of leased lines is that they are private, no one else shares the line. An alternative is available with packet-switched networks such as frame relay, ATM, and the Internet. Many users share the networks, which helps lower costs.
Dial-up lines can provide an economical WAN connection in a number of scenarios. For example, a dial-on-demand line can be used to provide additional bandwidth when an existing dedicated leased-line WAN link becomes overburdened. These lines can be multilinked as discussed under "Inverse Multiplexing" and "MLPPP (Multilink PPP)."
Broadband communications is usually considered to be any link with transmission rates above dial-up lines. Broadband transmission systems typically provide channels for data transmissions in different directions and by many different users. Typical broadband communication systems are outlined here and discussed elsewhere.
ISDN (Integrated Services Digital Network)
A circuit oriented service operating at 64-Kbit/sec or 128-Kbit/sec data channel. Primary rate ISDN provides additional bandwidth in increments of 64Kbits/sec.
X.25
An early packet-switching protocol still used for many low-bandwidth requirements (credit card authorization).
ATM (Asynchronous Transfer Mode)
A cell-switched any-to-any virtual circuit service.
Frame relay
A frame-based any-to-any virtual circuit service.
Leased lines T1, T3:
A dedicated leased line TDM (time division multiplexing) service. See "TDM."
DSL (Digital Subscriber Line)
A high-speed circuit-oriented service that runs over the local loop.
Broadband wireless
A variety of wireless broadband services are now available or under development. See "Wireless Broadband Access Technologies."
Inverse multiplexing:
Is the process of splitting a data stream for transmission over multiple channels. At the receiving end, the data is recombined into a single stream. The links may be dial-up or permanent leased lines. Inverse multiplexing provides more bandwidth and can provide bandwidth on demand by establishing additional links when loads increase beyond the capacity of existing links. Inverse multiplexing isthe opposite of multiplexing, which combines data streams from multiple sources into a single line.
PPP Multilink:
Is a bandwidth-on-demand protocol that can connect multiple links between two systems as needed to provide bandwidth on demand. The technique is often called bonding or link aggregation. For example, the two 64-Kbit/sec B channels of ISDN can be combined to form a single128-Kbit/sec data channel. Another example would be to bind one or more dial-up asynchronous channels with a leased synchronous line to provide more bandwidth at peak hours of the day.
MLPPP:
Is defined in RFC 1990 (PPP Multilink Protocol, August 1996). It is an extension to the PPP (Point-to-Point Protocol). See "PPP (Point-to-Point Protocol)" for information about the basic protocol. Microsoft Windows, Linux, and other operating .systems support multilink. Many routers also support Multilink PPP and the ability to connect remote LANs with multiple dial-up or ISDN lines.
TDM:
Is a multiplexing technique that divides a circuit into multiple channels based on time. The technique is associated with telephone company voice services. T1 and T3 circuits are divided into multiple channels using time division multiplexing. The most common TDM circuit for business users is the T1 line (1.544 Mbits/sec). It consists of 24 multiplexed 64-Kbit/sec voice channels. Each channel may carry a single phone call, or the entire circuit may be dedicated to data.
Wireless broadband access technologies:
Refers to high-speed wireless access services that businesses can use to build metropolitan area networks or gain Internet access. These wireless services take the place of traditional TDM circuits.
Wireless access systems are usually owned by a service provider that operates within a metropolitan areas. Services include Internet access for businesses, MTUs (multitenant units), and homes, as well as private LAN bridging in metro areas. The topic "Wireless LANs" covers enterprise wireless networking in which an enterprise owns and manages wireless systems used to interconnect its users and systems. Even shorter in range than wireless LANs are wireless PANs (personal area networks) that let nearby users create spontaneous networks.
WPAN (Wireless PAN)
Is a short-distance wireless network specifically designed to support portable and mobile computing devices such as PCs, PDAs, wireless printers and storage devices, cell phones, pagers, set-top boxes, and a variety of consumer electronics equipment.
WPANs provide the bandwidth and convenience to make data exchange practical for mobile devices such as palm computers..