Answer the followingquestions: i. If we can extendthe LAN then why we need aWAN?

Question

Answer the followingquestions:

i.         If we can extendthe LAN then why we need aWAN?                              [3]

ii.       How can a bridge knowwhether to forwardframes?                                  [2]

iii.      Can the length of an Ethernet beincreased to many segments of 500 meter each merely by adding arepeater to connect each additional segment?   [2]

iv.     How can a computer attach to a networkthat sends and receives bits faster than the computer’s CPUcan handle them?                                            [3]

Explanation / Answer

i.        If we can extendthe LAN then why we need a WAN?

Solution:

                   A bridge LAN is not considered a wide area technology becausebandwidth limitations prevent a bridge LAN from serving arbitrarilymany computers at arbitrarily many sites. Performance issue, an inLAN shared medium is used and only two computers are communicate atone time and where as in WAN more than two computers cancommunicate at one time. Scalability is another issue; a WAN mustbe able to grow as needed to connect many sites spread across largegeographic distance, with many computers at each site. Scalabilityis very expensive in the extended LAN.

ii.      How can a bridge know whetherto forwardframes?                             [2]

Solution:

              When a bridge first boots, it communication with other bridges onthe segment to which it connect. The bridges perform a computationknow as the distribution spanning tree (DST) algorithm to decidewhich bridge will not forward frames. DST allows a bridge todetermine whether forwarding will introduce a cycle. in essence, abridge does not forward frames if the bridge finds that eachsegment to which it attaches already contains a bridge that hasagreed to forward frames. after the DST algorithm completes, thebridges that agree to forward frames form a graph that does containany cycle.

iii.    Can the length of an Ethernet beincreased to many segments of 500 meter each merely by adding arepeater to connect each additionalsegment?      [2]

Solution:

              The answer is no. Although such an arrangement does guaranteesufficient signal strength, each repeater and segment along thepath increases delay. The Ethernet CSMA/CD scheme is designed forlow delay. If the delay becomes too large, the scheme fails. Infact, repeaters are a part of current Ethernet standard, whichspecifies that the network will not operate correctly if more thanfour repeaters separate any pair of station.

iv.    How can a computer attach to a networkthat sends and receives bits faster than the computer’s CPUcan handle them?                                           [3]

Solution:

The CPU does not handle the transmission or reception ofindividual bits. Instead, a special purpose hardware componentconnects a computer to a network, and handles all the details ofpacket transmission and reception. Physically, the special purposehardware usually consists of a printed circuit board that containselectronic components. Known as a network adapter card or networkinterface card (NIC), the printed circuit board plugs into thecomputer’s bus, and a cable connects it to the networkmedium.

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