Identify different WAN Technologies

Exam: Cisco 200-120 - Interconnecting Cisco Networking Devices: Accelerated (CCNAX)

Both LAN (Local Area Network) and WAN (Wide Area Network) allow computers to communicate with each other and allow sharing of information. However, both of them operate differently and have different features. LAN is used to connect computers together and share resources in a comparatively smaller area such as an office complex with many buildings, university campus or a small house with a few computers.

WAN on the contrary covers a large network that spreads in entire state or a small country. WAN is typically used to connect LANs together. Both LAN and WAN use different technologies to provide connectivity.

LAN

In a LAN, the computers are connected to switches and bridges using Ethernet cables. The different types of cables used are coaxial, copper or fibre. Layer 2 switching used in LAN uses specialized hardware called ASIC (application-specific integrated circuit) to ensure very low latency rate.

Ethernet Networking

LAN uses Ethernet networking that allows all hosts on a network to use the same bandwidth. Ethernet infrastructure can be easily upgraded to a fast Ethernet infrastructure by using new technologies. It is easy to implement and troubleshoot. It uses both Data Link and Physical layer specifications.

Working of LAN on Ethernet Network

The switches and bridges are commonly used on a LAN. They build a filter table to send and receive data to the desired location and read each frame on the network that they come across. The switches and bridges save the hardware address of the sender and the port on which the frame is received in the filter table.

The bridges and switches then locate specific devices and forward the frames on to the segment where the destination hardware is located. The process of blocking the frame to be sent to any other segment if the source and the destination for the frame are on the same segment and sending the frame to the segment where the destination hardware is located is called transparent bridging.

When the switches receive frames whose destination address is not available in filter table, they forward the frame to all the connected segments except the source segment. When an unknown device replies to the mystery frame, the switches update their filter table. All devices to which the mystery frame was sent are considered to be in the same broadcast domain.

Broadcast domain

A broadcast domain can be defined as a group of devices on a network segment that hears all the broadcasts that are sent on that network segment. The network segment for a broadcast domain can be created by diving a large network using a physical media or through logical division.

Collision domain

A collision domain can be defined as a network scenario where one device sends a packet on a network segment and forcing other devices on the network segment to pay attention to the packet sent, thuscausing collisionby causing other devices on the network to transmit the data at the same time.

The Ethernet uses CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol to take care of the collisions on the network while sharing the bandwidth evenly among the network devices. The host with CSMA/CD protocol implemented checks the cable for any existing signal. If there is no signal, it proceeds with transmission of data. During transmission, if the host detects another signal, it sends an extended jam signal, which causes all the nodes on the network to stop sending signals for some time and then try again after a short duration.

Half-Duplex and Full-Duplex Ethernet

Half-duplex Ethernet is defined as 802.3 Ethernet. It uses CSMA/CD protocol and one pair of wire with digital signals running in both the directions. The Full duplex Ethernet on the contrary is a point-to-point connection between the sender and the receiver and uses two pair of wires. The Full duplex Ethernet allows fast data transfers because it uses one set of wires to send data and the other set of wires to receive data. Also a Full duplex Ethernet requires a dedicated switch port for each full-duplex node.

Full duplex Ethernet can be used between:

• switch to a host
• switch to a switch
• host to a host
• switch to a router
• a router to a router

WAN

As mentioned above, a WAN connects LANs together. The hardware required to create WAN include routers and a communication link. The routers are used to route packets received by the router through the connected LAN and a communication link is required to carry the packets to the destination LAN. A communication link is provided by a communication service provider to connect two WAN points together either as a single Point-to-Point leased line or as a packet-switching or circuit switching.

A leased line is a dedicated connection between two points of a pre-established WAN path. The HDLC and PPP encapsulations are used most commonly on leased lines. The circuit switching is similar to a phone call, where no data can transfer before a connection is established. The circuit switching uses dial-up modems.

The packet switching is efficient like a leased line and cost effective as circuit switching. However, it does not allow a constant data transfer. The examples of packet switching technologies include Frame Relay and X.25. These packet-switching technologies can have speeds that can range from 56Kbps up to T3 (45Mbps).

Just as LAN uses WiFi, WAN uses Wimax as a wireless technology. A WAN is never as fast as LAN because its main aim is to connect LANs together and not to transmit data between two devices.

The protocols used on WAN are Frame Relay, LAPB, ISDN, LAPD, PPP, HDLC, PPPoE, MPLS, DSL, Cable, and ATM. The protocols such as HDLC, PPP, and Frame Relay are configured only on a serial interface for WAN connections.

Example Question

Which of the following statement is correct about CSMA/CD protocol?

• CSMA/CD protocol help devices to share bandwidth evenly
• CSMA/CD protocol eliminate collisions
• CSMA/CD protocol increases retransmissions
• CSMA/CD protocol allows two devices to transmit data at the same time.

Answer: A

The CSMA/CD protocol CD protocol helps devices to share bandwidth evenly by reducing collisions among devices. It does not eliminate collisions but reduces them to a great extent. It stops two devices to transmit data at the same time.