[Cisco Networking Academy] Del Mar College
ITNW 1392-Beginning Router Configuration
 Instructor:Michael P. Harris
Sem2Les4

Semester 2, Lesson 4 Notes:

Introduction to WAN Technologies

WAN (Wide Area Network) operates at OSI Layer 1(Physical) and Layer 2 (Data link) layers. The WAN provides for the exchanging of data packets between Routers and the LAN's that the routers support.

1. Name and briefly describe four WAN devices.

  1. "Routers" (which offer internetworking and WAN interface ports) Network layer device that uses one or more metrics to determine the optimal path which network traffic should be forwarded. Routers forward traffic from one network to another based on network layer information. Occasionally called a gateway (Although this definition of gateway is becoming increasingly outdated).

  2. "Switches" (for sharing bandwidth) Network device that filters, forwards, and floods frames based on the destination address of each frame. The switch operates at the data link layer (layer 2) of the OSI model.

  3. "Modems", "CSU/DSU"s, and "Terminal Adapters" (which allow a variety of data connection services)

  • "Modem" - modulator-demodulator. Device that converts digital and analog signals. At the source, a modem converts digital signals to a form suitable for transmssion over analog communication facilities. At the destination, the analog signals are returned to their digital form. Modems allow data to be transmitted over voice-grade telephone lines.

  • "CSU/DSU" - "Channel Service Unit/Data (digital) Service Unit"

  1. "Channel Service Unit" - digital interface device that connects end-user equipment to the local digital telephone loop.

  2. "Data (digital) Service Unit" - device used in digital transmission that adapts the physical interface on a DTE device to a transmission facility such as signal T1 or E1. The DSU is also responsible for such funtions as signal timing.

  • "Terminal Adapter" - Device used to connect ISDN BRI connections to existing interfaces such as EIA/TIA-232. Essentially, an ISDN modem.

(4) "Communication servers" (which concentrate dial-in and dial-out user Communications). Communications processor that connects asynchronous devices to a LAN or WAN through network and terminal emulation software. Performs only asynchronous routing of IP and IPX.

2. Name two ways in which WANs differ from LANs.

  1. WANs operate over a large geographical area, and offer full- time and part-time connectivity (LANs do not);
  2. WANs emphasize access over 'serial interfaces' and operating at lower speeds to ensure reliability (LANs can operate reliably at very high speeds with mulitple access).

3. What do the acronyms "DTE" and "DCE" stand for?

The WAN physical layer describes the interface between the data terminal equipment (DTE) and data circuit-terminating equipment (DCE).
"DTE" - 'Data Terminal Equipment', which refers to the end of the user's devices on a WAN link. 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, protocol translators, and multiplexers.
"DCE" - 'Data Circuit-Terminating Terminating Equipment' (ITU-T expansion), or 'Data Communications Equipment' (EIA expansion). The devices and connections of a communications network that comprise the network end of the user-network-interface. The DCE provides a connection to the network, forwards traffic, and provides a clocking signal used to synchronize data tansmission between DCE and DTE devices. Modems and interface cards are examples of DCE, which refers to the end of the WAN provider's side of the communication facility.

4. List three WAN 'physical layer' (layer 1) standards in commno use:

  1. EIA/TIA-232, Common physical layer interface standard, developed by EIA and TIA, that supports unbalanced circuits at signal speeds of up to 64 kbps. Closely resembles the V.24 specification. Formerly known as RS-232.
  2. V.35, ITU-T standard decribing a synchronous, physical layer protocol used for communications between a network access device and a packet network. V.35 is most commonly used in the United States and in Europe, and is recommended for speeds up to 48kbps.
  3. X.21, ITU-T standard for serial communications over synchronous digital lines. The X.21 protocol is used primarily in Europe and Japan.

(5) List four WAN "data link layer" (layer 2) protocols:

  1. "HDLC" (High-Level Data Link Control). Bit oriented synchronous data link layer protocol delevoped by ISO. Derived from SDLC, HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
  2. "Frame Relay" (a simplified version of HDLC framing), uses high-quality digital facilities, simple framing with no error -correction mechanisms, and can send layer 2 (data link) information very rapidly compared to other WAN protocols. Industry-standard, switched data link layer protocol that handles mutiple virtual circuits using HDLC encapsulation between connected devices. Frame relay is more efficient than X.25, the protocol for which it is generally considered a replacemment.
  3. "PPP" (Point-to-Point protocol), contains a protocol field to indentify the network-layer protocol being and supports point -to-point configurations. A successor tp SLIP, PPP provides router-to-router and host-to-host connections over synchronous and asynchronous circuits.
  4. "ISDN" (Integrated Services Digital Network), a set of services transmit voice and data over existing phone lines.

Wan standards organizations:
"ITU" - International Telecommunication Union-Telecommunication Standardization Sector (ITU-T), formerly the Consultative Committee for International Telegraph and Telephone (CCITT)
"ISO" - International Organization for Standardization (ISO)
"IETF" - International Engineering Task Force (IETF)
"EIA" - Electronic Industries Association (EIA)
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