Networking Basics Questions and Answers

Answer: D

Physical transmission of bits is handled by the Physical layer.

Layer 1 of the OSI model deals with the raw bit stream: the electrical, optical or radio signals, voltages, timing, connectors and cables, and the encoding of 0s and 1s onto the medium.

The data link layer above it groups the bits into frames and handles physical addressing and link-level error control. The network layer routes packets, and the transport layer provides end-to-end delivery.

Answer: D

The device working at both layer 2 and layer 3 is the multilayer switch.

A multilayer (layer 3) switch switches frames by MAC address within a VLAN, like an ordinary switch, and also routes packets between VLANs and subnets by IP address in hardware, combining the two functions in one device.

A hub works only at layer 1. A bridge works at layer 2, joining segments by MAC address. A router is a layer 3 device built for routing between networks rather than for layer 2 switching across many ports.

Answer: A

The method is store-and-forward switching.

A store-and-forward switch receives the whole frame into its buffer and checks it, using the frame check sequence, before sending it out of the right port. Damaged frames are discarded, at the cost of a little more delay.

Cut-through switching starts forwarding as soon as it has read the destination address, before the rest of the frame arrives. Circuit switching and packet switching are broad network switching techniques, not ways a LAN switch handles a frame.

Answer: B

The architecture is client-server.

In client-server architecture the roles are separate: servers provide services and resources (web pages, files, databases, email) and clients request and consume them. A web browser talking to a web server is the everyday example.

In peer-to-peer networks every node can be both provider and consumer, so there is no such separation. Bus and ring are physical topologies that describe how devices are wired, not how services are divided.

Answer: C

Block parity is a MULTI-bit error detection code.

Block (two-dimensional) parity arranges the data as a table of rows and adds a parity bit to every row and to every column. Forouzan's account presents it as a detection method that improves on a single parity bit: it catches all errors of up to three bits anywhere in the block and most burst errors, which a single parity bit misses whenever an even number of bits flip.

A single parity bit is the 1-bit error detection code. The crossing of a failing row and column can locate one flipped bit, but block parity is classed and examined as a detection scheme; multi-bit correction needs codes such as Hamming or Reed-Solomon.

Answer: A

Maximum throughput occurs at G = 0.5.

For pure ALOHA the throughput is \(S = G e^{-2G}\), because a frame is safe only if no other frame starts within a vulnerable period of two frame times.

\[ \begin{aligned} \frac{dS}{dG} &= e^{-2G}(1 - 2G) = 0 \\ G &= 0.5 \\ S_{max} &= 0.5\,e^{-1} \approx 0.184 \end{aligned} \]

G = 1.0 is the trap: it is where slotted ALOHA, with \(S = G e^{-G}\), reaches its maximum of about 0.368. 1.5 and 2.0 lie past both peaks.

Answer: C

Error control is done at the Data Link layer.

The data link layer provides node-to-node delivery of frames and is responsible for error control (detecting and retransmitting damaged or lost frames, using CRC and ARQ) and flow control between adjacent nodes.

The physical layer only transmits raw bits. The network layer handles logical addressing and routing, and the session layer manages dialogues between applications. Error control end to end is also done at the transport layer, but among these options the data link layer is the one defined by it.

Answer: C

Devices at the data link layer are identified by MAC addresses.

A MAC (Media Access Control) address is a 48-bit physical address burned into each network interface card. Switches and bridges use it to deliver frames to the right device on the local network.

IP addresses are logical addresses used at the network layer for routing between networks. Port numbers identify processes at the transport layer, and URLs identify resources at the application layer.

Answer: B

The endpoint is a Socket.

A socket is one endpoint of a two-way communication link between two processes on a network. It is identified by an IP address combined with a port number and a transport protocol, and applications read and write data through it.

A port is only part of a socket's address, the number that identifies the process on a host. A pipe connects processes on the same machine, not across a network, and a machine is a host, not an endpoint of a flow.

Answer: B

The difference is that Hubs broadcast data to all ports while Switches send only to the destination port.

A hub is a physical-layer repeater: a frame arriving on one port is copied to every other port, so all devices share one collision domain. A switch is a data-link-layer device that learns which MAC address is on which port and forwards each frame only to the port of its destination.

The layers in option A are reversed. Neither device provides firewall security, and both are used in wired LANs, so options C and D are wrong.