Home > WAN Questions

WAN Questions

May 31st, 2017 Go to comments

If you are not sure about WAN, please read our WAN tutorial.

Question 1


An example of the output of the “show interface serial …” command is shown below. We can see the line “Encapsulation HDLC”.


Question 2


PPP supports both synchronous (like analog phone lines) and asynchronous circuits (such as ISDN or digital links). With synchronous circuits we need to use clock rate.

Note: Serial links can be synchronous or asynchronous. Asynchronous connections used to be only available on low-speed (<2MB) serial interfaces, but now, there are the new HWICs (High-Speed WAN Interface Cards) which also support asynchronous mode. To learn more about them please visit http://www.cisco.com/en/US/prod/collateral/modules/ps5949/ps6182/prod_qas0900aecd80274424.html.

Question 3


The advantages of leased lines include:
+ Simplicity: Point-to-point communication links require minimal expertise to install and maintain.
+ Quality: Point-to-point communication links usually offer high service quality, if they have adequate bandwidth. The dedicated capacity removes latency or jitter between the endpoints.
+ Availability: Constant availability is essential for some applications, such as e-commerce. Point-to-point communication links provide permanent, dedicated capacity, which is required for VoIP or Video over IP.

The disadvantages of leased lines include:
+ Cost: Point-to-point links are generally the most expensive type of WAN access. The cost of leased line solutions can become significant when they are used to connect many sites over increasing distances. In addition, each endpoint requires an interface on the router, which increases equipment costs.
+ Limited flexibility: WAN traffic is often variable, and leased lines have a fixed capacity, so that the bandwidth of the line seldom matches the need exactly (therefore answer D is not correct). Any change to the leased line generally requires a site visit by ISP personnel to adjust capacity.

(Reference: Connecting Networks Companion Guide Book published by Cisco Networking Academy – Page 54)

Question 4

Question 5


The idea behind a WAN is to be able to connect two DTE networks together through a DCE network. The network’s DCE device (includes CSU/DSU) provides clocking to the DTE-connected interface (the router’s serial interface).


A modem modulates outgoing digital signals from a computer or other digital device to analog signals for a conventional copper twisted pair telephone line and demodulates the incoming analog signal and converts it to a digital signal for the digital device. A CSU/DSU is used between two digital lines -> A & D are correct but B & C are not correct.

For more explanation of answer D, in telephony the local loop (also referred to as a subscriber line) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the carrier or telecommunications service provider’s network. Therefore a modem terminates an analog local loop is correct.


Question 6


Below is an example of the output of this command:


The “show controllers serial …” command tells us about the type of the cable (in the case V.35 DTE cable) and the status of the physical layer of the interface. In above output we learn that there is an cable attached on S0/0 interface. If no cable is found we will see the line “No DTE cable” instead.

Question 7


Nowadays all serial links are full-duplex (as serial interfaces have separate Rx & Tx pins) so maybe this question wants to ask about how to check the speed of the serial link. The “show interface” command gives us information about this. An example of this command is shown below:


In this output the speed of S0/0 interface is 1544 Kbits.

Question 8


Full-mesh is a network topology in which there is a direct link between all pairs of nodes. Below is an example of full-mesh topology.


Question 9

Question 10

Question 11

Comments (6) Comments
Comment pages
1 2 2984
  1. ali
    September 29th, 2017

    Which statements about using leased lines for your WAN infrastructure are true?
    A. Leased lines provide inexpensive WAN access.
    B. Leased lines with sufficient bandwidth can avoid latency between endpoints.
    C. Leased lines require little installation and maintenance expertise.
    D. Leased lines provide highly flexible bandwidth scaling.
    E. Multiple leased lines can share a router interface.
    F. Leased lines support up to T1 link speeds.

    what is the correct answerrrrrrrrrrrr pleaaaaaaaaaaaase confiuse

  2. Anonymous
    October 13th, 2017

    B & C

  3. Bhagya
    October 15th, 2017

    @Buddy, there should be in same subnet. or Those two routers in different networks. /24 says 192.168.x is locked. You can change the last 3 digits only. So that connectivity will be up if those two routers become one of 192.168.10.x or 192.168.11.x.

  4. Bhagya
    October 15th, 2017

    ali, B can be happened because lease line are dedicated, not shared.. So if the ISP sends the sufficient bandwidth/throughput, no more latency or traffic issues.
    look C, it is easy of installation because point to point dedicated link with static IP. Once the connections is up, no needs to look at it again till the error are popping up. Expert knowledge is good for repairs again.

  5. mashith
    October 18th, 2017

    Thanks Anonymous will definitely do

  6. mashith
    October 18th, 2017

    is still valid from

Comment pages
1 2 2984
Add a Comment