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Module 2

Module 2. WAN Technologies. A Wide Area Network (WAN) is used to interconnect Local Area Networks (LANs) that are separated by a large geographical distance. A Wide Area Network predominately operates at the OSI physical and data link layers .

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Module 2

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  1. Module 2 WAN Technologies

  2. A Wide Area Network (WAN) is used to interconnect Local Area Networks (LANs) that are separated by a large geographical distance. A Wide Area Network predominately operates at the OSI physical and data link layers. The WAN provides a data path between routersand the LANs that each router supports. WAN Technology

  3. MAJOR CHARACTERISTICS OF WANS • The network operates beyond the local LAN’s geographic scope. It uses the services of carriers such as Regional Bell Operating Companies (RBOCs). • WANs use serial connections of various types to access bandwidth over wide-area geographies. • By definition, the WAN connects devices separated by wide areas.

  4. WAN DEVICES INCLUDE: • Routers that offer many services including internetworking and WAN interface ports. • Switches that connect to WAN bandwidth for voice, data, and video communication. • Modems that interface voice-grade services; Include channel service units/digital service units (CSU/DSU) that interface T1/E1 services; Terminal Adapters/Network Termination 1 (TA/NT1) that interface Integrated Services Digital Network (ISDN) services. • Communication servers that concentrate dial-in and dial-out user communication. • WANS use the OSI layered approach for encapsulation just like LAN's but are mainly focused on the physical and data link layers.

  5. WAN Physical Layer • WAN physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections for wide-area networking services. • These services are most often obtained from WAN service providers such as Regional Bell Operating Companies (RBOCs), alternate carriers, and Post, Telephone, and Telegraph (PTT) agencies.

  6. WAN Data Link Protocols • WAN data link protocols describe how frames are carried between systems on a single data path. • They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services such as Frame Relay.

  7. WAN Standards • WAN standards typically describe both physical layer delivery methods and data link layer requirements including addressing and flow control encapsulation

  8. describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).

  9. DTE & DCE • DTE - data terminal equipment. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. • DTE includes such devices as computers, routers, and multiplexers. • DCE - Data communications equipment (EIA) or data circuit-terminating equipment (ITU-T). The devices and connections of a communications network that comprise the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Ex: Modems and interface cards

  10. The WAN data-link protocols describe how frames are carried between systems on a single path

  11. The Data Link Layer: WAN Protocols High-Level Data Link Control (HDLC)—HDLC is an IEEE standard. It might not be compatible between different vendors because of the way each vendor has chosen to implement it. • HDLC supports both point-to-point and multipoint configurations with minimal overhead Frame Relay - Frame Relay uses high-quality digital facilities. By using a simplified framing with no error correction mechanisms, Frame Relay can send Layer 2 information much more rapidly than these other WAN protocols. Point-to-Point Protocol - Described by RFC 1661. PPP contains a protocol field to identify the network-layer protocol. Integrated Services Digital Network (ISDN) - ISDN is a set of digital services that transmits voice and data over existing phone lines.

  12. Wide Area Networking

  13. The WAN Cloud • An overview of the WAN cloud organizes WAN provider services into: • Call setup service—Sets up and clears calls between telephone users. • Also called signaling, call setup uses a separate telephone channel not used for other traffic. • The most commonly used call setup is Signaling System number 7 (SS7). SS7 is an out-of-band signaling system for the exchange of call control information between network switching offices, in support of voice and nonvoice services

  14. Time-division multiplexing (TDM) • Information from many sources has bandwidth allocation on a single media. • Circuit switching uses signaling to determine the call route, which is a dedicated path between the sender and the receiver. • By multiplexing traffic into fixed time slots, TDM avoids congested facilities and variable delays. • Basic telephone service and ISDN services use TDM circuits.

  15. Time-division multiplexing (TDM) • Transmits multiple signals simultaneously over a single transmission path. Each lower-speed signal is time sliced into one high-speed transmission. • Example: Three incoming 1,000 bps signals (A, B and C) can be interleaved into one 3,000 bps signal (AABBCCAABBCCAABBCC). • The receiving end divides the single stream back into its original signals.

  16. When your organization subscribes to an outside WAN provider for network connections, the provider assigns your organization the rules for connecting WAN calls. • Your organization makes connections to destinations as point-to-point calls.

  17. Demarcation (or demarc)— • The point at which the CPE ends and the local loop portion of the service begins. • Often occurs at the Point of Presence (POP) of a building. Local loop (or “last-mile”) • Cabling (usually copper wiring) that extends from the demarcinto the WAN service provider’s central office.

  18. Central office (CO) switch • A switching facility that provides the nearest point of presence for the provider’s WAN service.

  19. Toll network • The collective switches and facilities (called trunks) inside the WAN provider’s cloud. • The caller’s traffic may cross a trunk to a primary center, then go to a sectional center, and then to a regional- or international-carrier center as the call goes the long distance to its destination. • Switches operate in provider offices with toll charges based on tariffs or authorized rates.

  20. A key interface in the customer site occurs between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE). • Typically, DTE is the router.

  21. DCE is the device used to convert the user data from the DTE into a formacceptable to the WAN service’s facility. • In the graphic, the DCE is the attached modem, channel service unit/data service unit (CSU/DSU) or Terminal Adapter/Network Termination 1 (TA/NT1).

  22. Data communication over WANs interconnects DTEs so they can share resources over a wide area. • The WAN path between the DTEs is called the link, circuit, channel, or line. • The DCE primarily provides an interface for the DTE into the communication link in the WAN cloud. • The DTE/DCE interface acts as a boundary where responsibility for the traffic passes between the WAN subscriber and the WAN provider.

  23. DSU/CSU • A pair of communicating devices that connect an in-house line to an external digital circuit (T1). It is similar to a modem, but connects a digital circuit rather than an analog one.

  24. CSU • Terminates the external line at the customer premises. • Provides diagnostics and allows for remote testing. • If the customer's communications devices are T1 ready and have the proper interface, then the CSU is not required, only the DSU.

  25. DSU • Does the actual transmission and receiving of the signal and provides buffering and flow control. • DSU and CSU can be in the same unit. • DSU may also be built into the multiplexor, (combines digital signals for high-speed lines).

  26. Forms of WAN services with routers. The most common are: • Switched or relayed services. • Frame Relay • ISDN (Integrated Services Digital Network) • ATM (Asynchronous Transfer Mode) • X.25 • Peer Devices • HDLC (High-level Data Link Control) • PPP (Point-to-Point Protocol) • DDR (Dial on Demand Routing) • LAPB - point to point and X.25

  27. Both Frame Rely and X.25 use the concept of virtual circuits

  28. X.25 • The first packet switched networks • X.25 provides a connection-oriented technology for transmission over highly-error prone facilities. • Error checking is performed at each node, which can slow overall throughput and and therefore would not make X.25 a choice for voice and video • X.25 can be very cost effective because tariffs are based on the amount of data delivered rather than connection time or distance

  29. Asynchronous Transfer Mode (ATM) • Lower latency at higher bandwidths • Data rates beyond 155 Mbps • Cell-based rather than frame-based • Cell are a fixed length of 53 bytes • Also uses PVCs • Less efficient because of the small size

  30. Digital Subscriber Line (DSL) • Uses existing telephone lines • Uses multiple frequencies within the same physical medium to transmit data • Bandwidth can vary • Distance of the local loop is a factor – must be less than 3.5 miles

  31. Cable Modem • Two-way, high-speed data transmissions using the same coaxial lines that transmit cable television. • Always on

  32. WAN Frame Encapsulation Formats

  33. Layer 2 Encapsulation • Each WAN connection type uses a Layer 2 protocol to encapsulate traffic while it is crossing the WAN link. • To ensure that the correct encapsulation protocol is used, you will need to configure the Layer 2 encapsulation type to use. • The choice of encapsulation protocol depends on the WAN technology and the communicating equipment.

  34. PPP • Common for dialup single-user-to-LAN (dialup and ISDN) or LAN-to-LAN (router-to-router) access. • PPP is standardized, so it supports vendor interoperability. • It also supports the encapsulation of multiple upper-layer protocols including IP and IPX.

  35. HDLC • The Cisco default encapsulation type on point-to-point links. • It is used typically when communicating with another Cisco device. • If communicating with a non-Cisco device, synchronous PPP is a viable option. • HDLC is normally proprietary between vendors.

  36. LAPB (layer 2 of the X.25 protocol stack) • For packet-switched networks, the LAPB protocol is used to encapsulate X.25 packets. • It can also be used over point-to-point links, if the link is unreliable or there is an inherent delay associated with the link, such as in a satellite link. • LAPB provides reliability and flow control on a point-to-point basis.

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