Cisco Systems Interview Question Bank – Part 2

Cisco Systems Interview Question Bank continued from Part 1

Q : What is PAT? Give one real-life application of it.

A : PAT (Port Address Translation) is an extension to NAT that allows multiple devices connected on a LAN to be mapped onto a single public IP address. PAT aims to conserve IP addresses. For example, when we want to provide multiple web services from a private network using a single public IP address, the requests from clients are forwarded based on destination port numbers.

Q : What is Routing?

A : Packet-switched networks (for example, the Internet), use a device (in some cases, it’s a software in a computer), that determines the next node on the network to which a packet should be forwarded in order to reach its destination. This device is called a router and the above process is known as routing. Routing is associated with Network Layer of the OSI model.

Q : What is half-duplex channel? Give a real-life application of it.

A : Half-duplex channel is a medium of communication in which the sender and receiver are capable of transmitting or receiving but not both at the same time for example, a walkie-talkie.

Q : What is full-duplex channel? Give an example.

A : Full-duplex channel is a medium of communication in which the sender and receiver are capable of transmitting or receiving and both can transmit/receive at the same time for example, a telephone.

Q : What are the OSI layers. Briefly explain their functions.

A : All the OSI layers and their functions can be briefly described as follows –

Source - Data Communications and Networking, Behrouz A Forouzan

Source – Data Communications and Networking, Behrouz A Forouzan

Q : What is the sender and receiver window size in Selective Repeat protocol?

A : In selective repeat ARQ (Automatic Repeat Request) protocol, the sender and receiver both have a window size of 2n-1 where n is the number of data bits.

Q : What does a PLL consist of?

A : A PLL (Phase Locked Loop) mainly consists of a Phase Detector (PD), Voltage Controlled Oscillator (VCO) and Loop Filter. Sometimes, PLL may also have a reference signal but it is usually not a part of the whole loop (circuit).

(Continued to Part 3…)

Gautam Vashisht