When network services must be distributed over large geographic areas, it is essential to have an understanding of the telecommunication systems on which such distribution depends. One of the most significant differences between wide area networks (WANs) and local area networks (LANs) is the general dependency on third-party carriers to provide these transmission services. Whenever data is being sent across a WAN it must be routed between locations.
Key Terms in this Chapter
Frame Relay (also found written as “frame-relay”): Consists of an efficient data transmission technique used to send digital information quickly and cheaply in a relay of frames to one or many destinations from one or many end-points. Network providers commonly implement frame relay for voice and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN).
Synchronous Optical Networking: A method for communicating digital information using lasers or light-emitting diodes (LEDs) over optical fiber. The method was developed for transporting large amounts of telephone and data traffic and to allow for interoperability between equipment from different vendors.
T1: Refers to Digital Signal 1, originally over a “T1” interoffice “trunk” or “Transmission Level 1” telecommunications line in North America and Japan.
Asynchronous Transfer Mode (ATM): A cell relay, circuit switching network and data link layer protocol which encodes data traffic into small fixed-sized cells. ATM provides data link layer services that run over SONET (Synchronous Optical Networking) Layer 1 links and differs from other technologies based on packet-switched networks (such as the Internet protocol or Ethernet), in which variable sized packets (sometimes known as frames ) are used. ATM is a connection-oriented technology, in which a logical connection is established between the two endpoints before the actual data exchange begins.
Border Gateway Protocol: ( BGP): The core routing protocol of the Internet. It works by maintaining a table of IP networks or ‘prefixes’ which designate network reachability among autonomous systems (AS). BGP does not use traditional metrics, but makes routing decisions based on path, network policies and/or rule sets. BGP was created to replace the previous routing protocol to allow fully decentralized routing in order to allow the removal of the Internet backbone network and allowed the Internet to become a truly decentralized system.
Open Shortest Path First: ( OSPF): Protocol is a link-state, hierarchical interior gateway protocol (IGP) for network routing. An algorithm is used to calculate the shortest path tree. It uses path cost as its routing metric. Path cost is determined generally by the speed (aka bandwidth) of the interface addressing the given route.
Routing Information Protocol (RIP): One of the most commonly used interior gateway protocol (IGP) routing protocols on internal networks (and to a lesser extent, networks connected to the Internet), which helps routers dynamically adapt to changes of network connections by communicating information about which networks each router can reach and how far away those networks are.
MultiProtocol Label Switching: ( MPLS ) : A data-carrying mechanism which emulates some properties of a circuit-switched network over a packet-switched network. MPLS operates at an OSI Model layer that is generally considered to lie between traditional definitions of Layer 2 (data link layer) and Layer 3 (network layer), and thus is often referred to as a “Layer 2.5” protocol. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic.