Unit 5

Question 1

Protocol to get own IP addr, first-hop router addr, and DNS server addr

Answer 1

DHCP

Question 2

Binary Exponential Backoff

Answer 2

Time a host waits for before transmitting a packet to avoid collision
After mth collision, k is chosen from { 0,1,2, …. ,2^m-1 }
Waits for [k*512 bit] length before transmission

Question 3

Self Learning Switch

Answer 3

Switch floods the network with frames / sends a frame with a specific destination
The host(s) respond to the frame with IP address and MAC address. The switch then enters the necessary details i.e { MAC address, Interface to reach host, TTL } into the switch table.

Question 4

Ethernet Broadcast

Answer 4

FF-FF-FF-FF-FF-FF

Question 5

Day in the life of a web request

Answer 5

DHCP > ARP > DNS > TCP + HTTP > HTTP req/reply

Question 6

OSI stack layers

Answer 6

Application - [Presentation - Session] - Transport -Network - Link Layer - Physical

Question 7

Bit Time

Answer 7

Time taken by a bit to occupy the media

Question 8

Bandwidth

Answer 8

Physical Layer: Total capacity of a medium to carry data at any given amount of time.
Depends on the properties of the medium and signaling methods

Question 9

Throughput

Answer 9

PHYSICAL LAYER: Transfer rate of data over the medium

Factors that affect: Amount and type of traffic, number of devices

Question 10

Goodput

Answer 10

PHYSICAL LAYER: Transfer rate of actual usable data bits

Throughput less the data protocol overhead, error corrections, and retransmissions

Question 11

Optical Fibre (Indexing)

Answer 11

1) Multimode Step Index: Total Internal Reflection of light within cable, zig-zag path, path function of angle of incidence
2) Multimode Graded Index: Sinusoidal oscillations, better performance, 10-12kms
3) Single-mode Step Index: Propagation of one transverse EM mode (solution to Helmholtz equation (del^2)f = -(k^2)*f), high capacity

Question 12

Access Point (AP)

Answer 12

An entity that has station functionality and provides access to the distribution system via the wireless medium for associated stations.

Question 13

Basic Service Set (BSS)

Answer 13

A set of stations controlled by a single coordination function.

Question 14

Coordination Function

Answer 14

The logical function that determines when a station operating within a BSS is permitted to transmit and receive PDUs

Question 15

Distribution System

Answer 15

A system used to interconnect a set of BSSs and integrated LANs to create ESS (Extended Service Set)

Question 16

Extended Service Set (ESS)

Answer 16

A set of interconnected BSSs and integrated LANs that appear as a single BSS at the LLC(Logical Link Control) layer at any given station associated with these BSSs

Question 17

Station

Answer 17

Any system that contains an 802.11 conformant MAC and Physical Layer

Question 18

MPDU & MSDU

Answer 18

MAC Protocol Data Unit

MAC Service Data Unit

Question 19

CSMA in Ethernet and WiFi

Answer 19

Ethernet -> CSMA/CD

WiFi -> CSMA/CA

Question 20

Sublayers of Data Link Layer

Answer 20

LLC (Logic Link Control) -> IEEE 802.1 (LAN, MAN, WAN, internetworking and security)
MAC (Media Access Control) -> PCF(Point coordination func), DCF (Distributed coordination functions)

Question 21

SIFS, DIFS & PISF

Answer 21

SIFS (Shorter Inter-frame Space): time interval required by a wireless device in between receiving a frame and responding to the frame.
DISF (DCF inter-frame Space): Using the DCF technique, a station needs to sense the status of the wireless channel before it can place its request to transmit a frame. The time interval that a station should wait before it sends its request frame is known as DIFS. = SISF + 2*slot time
PISF (PCF Inter-frame Space): Access Point (AP) coordinating with the communications centrally, waits for PIFS duration to grasp the channel. Since PIFS is less than DIFS duration, the AP always has the priority to access the channel over the other stations. PISF = SISF + slot time.

Question 22

RTS, CTS

Answer 22

Request To Send

Clear To Send -> handshake in CSMA/CA can avoid a collision from a hidden station.