In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss WAN Concepts and Terminology.
WAN Concepts and Terminology
 
Wide-area networks (WANs) connect networks, users, and services across broad geographic areas. Companies use WANs to connect company sites for information exchange.
 
 
Three WAN Connection Types
 
WAN services are generally leased from service providers on a subscription basis. There are three main types of WAN connections (services):
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    		•  Leased-line—Provides a preestablished connection through the service provider’s network (WAN) to a remote network. Leased lines provide a reserved connection for the client but are costly. Leased-line connections are typically synchronous serial connections with speeds up to 45 Mbps (E3).
     
     
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    		•  Circuit-switched—Provides a dedicated circuit path between sender and receiver for the duration of the “call.” Circuit switching is used for basic telephone service or Integrated Services Digital Network(ISDN). Circuit-switched connections are best for clients that require only sporadic WAN usage.
     
     
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    		•  Packet-switched— Devices transportpackets using virtual circuits (VCs) that provide end-to-end connectivity. Programmed switching devices provide physical connections. Packet headers are used to identify the destination. Packet switching offers leased-line-type services over shared lines, but at a much lower cost. Packet-switched networks typically use serial connections with speeds ranging from 56 Kbps to E3.
     
     
    Other WAN Connections
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    		•  Digital Subscriber Line (DSL)—Delivers high-bandwidth connections over existing copper telephone lines. There are four varieties of DSL:
    – Asymmetric digital subscriber line (ADSL)
    – High-data-rate digital subscriber line (HDSL)
    – Single-line digital subscriber line (SDSL)
    – Very-high-data-rate digital subscriber line (VDSL)
    DSL does not use the entire bandwidth available on the twisted pair, leaving room for a voice channel.
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    		•  Cable—Uses a coaxial cable to transport the data.
     
    WAN Cabling
     
    The router end of the cable connects to the DB-60 port on a serial WAN interface card (using a DB-60 connector). The connector on the other end of the serial cable is specified according to the standard used. The ports on either end of a WAN connection are specified as DTE (data terminal equipment) or data communications equipment (DCE). DCE converts user data into the service provider’s preferred format. The port configured as DTE requires external clocking from the CSU/DSU or another DCE device.
     
    Physical Parameters for WAN Connections
     
    A WAN service provider assigns your organization the parameters required for making the WAN link connection.
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    		•  Customer premises equipment (CPE) is located on the subscriber’s premises. It includes both equipment owned by the subscriber and devices leased by the service provider.
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    		•  Demarcation, or demarc, marks the point where CPE ends and the local loop begins. Usually, it is located in the telecommunications closet.
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    		•  Local loop, or “last-mile,” is the cabling from the demarc into the WAN service provider’s central office (CO).
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    		•  The central office is a switching facility that provides a point of presence for WAN service. The central office is the entry point to the WAN cloud and the exit point from the WAN for called devices.
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    		•  A switching point for calls.
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    		•  The toll network is a collection of trunks inside the WAN cloud.
     
     
    Layer 2 Encapsulation Protocols
     
    High-level data link control (HDLC) is the default encapsulation type on point-to-point dedicated links and circuit switched connections. HDLC should be used for communication between Cisco devices.
    Point-to-Point Protocol (PPP) provides connections between devices over several types of physical interfaces, such as asynchronous serial, HSSI, ISDN, and synchronous. PPP works with several network layer protocols, including IP and IPX. PPP uses PAP and CHAP for basic security.
    X.25/Link Access Procedure, Balanced (LAPB) defines connections between DTE and DCE for remote terminal access. LAPB is a data link layer protocol specified by X.25. Frame Relay is the industry-standard switched data link layer protocol. Frame Relay (based on X.25) can handle multiple virtual circuits.
    Asynchronous Transfer Mode (ATM) is the international standard for cell relay using fixed-length (53-byte) cells for multiple service types. Fixed-length cells allow hardware processing, which greatly reduces transit delays. ATM takes advantage of high-speed transmission media, such as E3, T3, and SONET.
     
     
    WAN Concepts and Terminology Summary
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    		•  WANs connect devices across broad geographic regions. Companies use WANs to connect various sites.
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    		•  Leased-line or point-to-point connections provide a dedicated connection.
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    		•  Circuit-switched connections provide a dedicated circuit path for the duration of the call. Circuit switching is best for sporadic WAN usage.
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    		•  Packet-switched connections use virtual circuits to provide end-to-end connectivity.
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    		•  The five serial standards supported by Cisco devices are EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530.
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    		•  Typical WAN protocols include HDLC, PPP, SLIP, and ATM.
     

    I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. I am sure you will quickly find out that hands-on real world experience is the best way to cement the CCNA concepts in your head to help you pass your CCNA exam!