Explanation/Reference:
Section: Enterprise Network Design Explanation
Explanation:
Integrated Services Digital Network (ISDN) is a circuit-switched WAN technology that offers less than 2 Mbps of bandwidth. Circuit-switched WAN technologies rely on dedicated physical paths between nodes in a network. For example, when RouterA needs to contact RouterB, a dedicated path is established between the routers and then data is transmitted. While the circuit is established, RouterA cannot use the WAN link to transmit any data that is not destined for networks accessible through RouterB. When RouterA no longer has data for RouterB, the circuit is torn down until it is needed again.
Because circuit-switched links rely on dedicated physical paths, they are considered leased WAN technologies. Other examples of leased WAN technologies are time division multiplexing (TDM) and Synchronous Optical Network (SONET).
Metro Ethernet is a WAN technology that is commonly used to connect networks in the same metropolitan area. However, Metro Ethernet providers typically provide up to 1,000 Mbps of bandwidth. A company that has multiple branch offices within the same city can use Metro Ethernet to connect the branch offices to the corporate headquarters.
Packet-switched networks do not rely on dedicated physical paths between nodes in a network. In a packet-switched network, a node establishes a single physical circuit to a service provider. Multiple virtual circuits can share this physical circuit, allowing a single device to send data to several destinations.
Because packet-switched links do not rely on dedicated physical paths, they are considered shared WAN links. Frame Relay, X.25, Multiprotocol Label Switching (MPLS), and Switched Multimegabit Data Service (SMDS) are examples of packet-switched, shared WAN technologies.
Asynchronous Transfer Mode (ATM) is a shared WAN technology that transports its payload in a series of fixed-sized 53byte cells. ATM has the unique ability to transport different types of traffic, including IP packets, traditional circuit-switched voice, and video, while still maintaining a high quality of service for delay-sensitive traffic such as voice and video services. Although ATM could be categorized as a packet- switched WAN technology, it is often listed in its own category as a cell-switched WAN technology instead.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 6, ISDN, pp. 221-222
Cisco: Introduction to WAN Technologies: Circuit Switching
Cisco: Asynchronous Transfer Mode Switching: ATM Devices and the Network Environment