WAN
The three WAN connection types available are leased lines, circuit-switched, and packet-switched. Define the differences between each connection type.
Leased lines are dedicated point-to-point lines that provide a single preestablished WAN communication path from the customer's network to the remote network. Leased lines are usually employed over synchronous connections. They are generally expensive and are always up.
Circuit-switched connections are dedicated for only the duration of the call. The telephone system and ISDN are examples of circuit-switched networks. Packet-switched connections use virtual circuits (VCs) to provide end-to-end connectivity.
Packet-switched connections are similar to leased lines, except that the line is shared by other customers. A packet knows how to reach its destination by programming of switches. Frame Relay is an example of a packet-switched connection.
Define customer premises equipment (CPE), and give an example.
CPE is equipment that is located on the customer's (or subscriber's) premises. It is equipment owned by the customer or equipment leased by the service provider to the customer. An example is your router.
What is the demarcation point (demarc)?
The demarc is the point where the CPE ends and the local loop begins. It is the last responsibility of the service provider and is usually an RJ-45 jack located close to the CPE. Think of the demarc as the boundary between the customer's wiring and the service provider's wiring.
What is the local loop?
The local loop is the physical cable that extends from the demarc to the central office.
Describe the central office (CO).
The CO is the telco switching facility that connects the customer to the provider's switching network. The CO is sometimes referred to as a point of presence. It is the point where the local loop gains access to the service provider's access lines.
What is the toll network?
All the telco switches, COs, and trunk lines inside the WAN provider's network are the toll network.
What are synchronous links?
Synchronous links have identical frequencies and contain individual characters encapsulated in control bits, called start/stop bits, that designate the beginning and end of each character. Synchronous links try to use the same speed as the other end of a serial link.
What are Asynchronous links?
Asynchronous links send digital signals without timing. Asynchronous links agree on the same speed, but there is no check or adjustment of the rates if they are slightly different. Only 1 byte per transfer is sent.
List some typical Layer 2 encapsulation methods for WAN links.
. High-Level Data Link Control (HDLC)
• Point-to-Point Protocol (PPP)
• Serial Line Internet Protocol (SLIP)
• X.25/Link Access Procedure, Balanced (LAPB)
• Frame Relay• Asynchronous Transfer Mode (ATM)