IS 450 Exam 1

streaming applications vs. traditional web page delivery

humans consume audio and video streams in a continuous manner, and discontinuity. By contrast, a regular (nonstreaming) page can be delivered and read in bits and pieces.

what characterizes real-time audio and video applications

tighter timing constraints than streaming applications

during the initial years of internet access, how did most people obtain internet connectivity

work, school, dial-up modem at home

network

term used to describe physical links connecting two or more computers directly

what distinguishes multiple-access links from point-to-point links

the physical links of point-to-point are limited by a pair of nodes while multiple-access links can have more than a pair of nodes sharing a single link

characteristic of packet-switched networks

the nodes send discrete blocks of data to each other.

what is one of the most crucial functions that a network must provide

connectivity among a set of computers

what is multiplexing in network communication

a system resource is shared among multiple users

synchronous time-division multiplexing (STDM)

divides time into equal-sized quanta to share the physical link among multiple flows

what distinguishes statistical multiplexing from STDM

data are transmitted from each flow on demand rather than during a predetermined time slot

how does the concept of layering relate to logical process-to-process channels

implemented on top of a collection of physical host-to-host channels.

what happens when a switch receives packets faster than the shared link can accommodate

the switch is forced to buffer these packets in its memory. After an extended period of time, the switch will eventually run out of buffer space, and some packets will have to be dropped.

what functionality characterizes the request/reply channel used by file transfer and digital library applications

guarantees that every message sent by one side is received by the other side and that only one copy of each message is delivered.

purpose of abstraction in system design

to manage complexity

what are the 2 interfaces defined by a protocol

1. service

2. peer

body (payload)

the part of the message that contains the application’s data

what is the fundamental idea of packet switching

to multiplex multiple flows of data over a single physical link

what is the purpose of a demultiplexing key in a protocol’s header

determine which messages to pass up to RRP and which to pass up to MSP

7 layer OSI model

1. physical

2. data link

3. network

4. transport

5. session

6. presentation

7. application

which layer of the OSI model implements process-to-process channels

transport

what is the primary function of the physical layer in the OSI model

handles the transmission of raw bits over a communications link

message

the unit of data exchanged at the transport layer

which layer of the OSI model manages the format of data exchanged between peers

presentation

which layer of the OSI model is responsible for tying together different transport streams in a single application

session

what is the purpose of the application layer in the OSI model?

enables web browsers to request pages from web servers

what is the fundamental unit of data exchanged at the data link layer

frame

what is the role of protocols in network communication

provides a communication service that higher-level objects (such as application processes, or perhaps higher-level protocols) use to exchange messages

what is the purpose of a protocol graph

the suite of protocols that make up a network system

how does the process of encapsulation work in a protocol graph

the process repeats on each level of the protocol graph;

HHP encapsulates RRP’s message by attaching a header of its own, then arrives to destination host

what happens when a message arrives at the destination host in terms of encapsulation

it is processed in the opposite order

latency in terms of propagation

propagation = distance/speed of light

latency in terms of transmit

transmit = size/bandwidth

latency in terms of queue delay

time packets are stored before forwarding them on an outbound link;

time taken for a signal to propagate from one end of a link to another

latency

propagation + transmit + queue

what does it mean when bits in the pipe are said to be “in flight”

if the receiver tells the sender to stop transmitting, it might receive up to one RTT × bandwidth's worth of data before the sender manages to respond.

what remains constant as bandwidth increases in high-speed networks

the speed of light

how does the RTT compare between 1-Gbps and a 1-Mbps network

Gbps link is the same 100 ms as Mbps

latency

starts to dominate network design thinking as bandwidth increases

jitter

variation in latency experienced by packets in a network

what is the purpose of storing frames in a buffer in the presence of jitter

receiver delays the frame, effectively smoothing out the jitter

how are links characterized

by the medium they use:

copper wire, twisted pair, coaxial cable, optical fiber

what is the main purpose of a network architecture

to provide a common abstraction of something as complex and diverse as a link.

what technology is likely to become an important part of the 5G mobile network

mmWave band

what is the role of modulation in the context of encoding binary data onto electromagnetic signals

vary the amplitude of a single wavelength

which technology is commonly used to connect homes and businesses over recently deployed fiber

PON (passive optical network)

what is the main task when turning nodes and links into usable building blocks

understand how to connect them in such a way that bits can be transmitted from one node to the other

which encoding scheme maps the data value 1 onto the high signal and 0 onto the low signal

nonreturn to zero (NRZ)

what problem is associated with long strings of consecutive 1s or 0s in NRZ encoding

several consecutive 1s means that the signal stays high on the link for an extended period of time; similarly, several consecutive 0s mean that the signal stays low for a long time;

1. baseline wander: too many consecutive 1s or 0s cause this average to change, making it more difficult to detect a significant change in the signal.

2. clock recovery: both the encoding and decoding processes are driven by a clock—every clock cycle, the sender transmits a bit and the receiver recovers a bit. If the receiver's clock is even slightly faster or slower than the sender's clock, then it does not correctly decode the signal.

how does NRZI address the issue of consecutive 1s in encoding

has the sender make a transition from the current signal to encode a 1 and stay at the current signal to encode a 0

what is the primary disadvantage of Manchester encoding

it doubles the rate at which signal transitions are made on the link, which means that the receiver has half the time to detect each pulse of the signal

which modulation scheme allows the encoding of 16 or even 64 different patterns during each clock interval

Quadrature Amplitude Modulation (QAM)

what is the relationship between bit rate and baud rate in Manchester encoding

bit rate is half the baud rate

what is the efficiency of the 4B/5B encoding

80% efficiency

how does 4B/5B encoding address the inefficiency of Manchester encoding

inserts extra bits into the bit stream so as to break up long sequences of 0s or 1s.

which of the following protocols uses only sentinel characters for framing

byte-oriented protocol

what is the problem with using sentinel characters for framing

one of the special characters might appear in the data portion of the frame

which protocol uses sentinels and character stuffing for framing

point-to-point protocol (PPP)

what action does the receiver take when it encounters five consecutive 1s during bit stuffing (HDLC protocol)

the receiver makes its decision based on the next bit it sees

if 0: receiver removes

if 1: error, whole frame discarded

how does the receiver determine the start and end of a frame in SONET

The first 2 bytes of the frame contain a special bit pattern

what is the purpose of scrambling the payload bytes in SONET

to ensure that there are plenty of transitions to allow the receiver to recover the sender's clock

how are packets transmitted in the PPP frame format

starting at the leftmost field

what action does the receiver take if the result of applying the error-detecting algorithm to the received message does not match the sender’s result

discarding the message of correcting it if possible

why is the term “checksum” sometimes used imprecisely in networking

it is used imprecisely to mean any form of error-detecting code, including CRCs

what combination of mechanisms is commonly used to achieve reliable delivery in networking

acknowledgments (ACK) and timeouts

what is the term for the general strategy of using acknowledgments and timeouts to implement reliable delivery

automatic repeat request (ARQ)

which ARQ algorithm is the simplest

stop-and-wait

what are the 3 roles that the sliding window algorithm can serve

1. reliably deliver frames across an unreliable link

2. to preserve the order in which frames are transmitted

3. support flow control (keep the sender from overrunning the receiver)

what is the distinguishing feature of the ARPANET protocol compared to the sliding window protocol

it is able to keep the pipe full while still using the simple stop-and-wait algorithm.

what does the term “carrier sense” mean in the context of CSMA/CD

all the nodes can distinguish between an idle and a busy link

what does it mean for hosts in an Ethernet network to be in the same collision domain

they are all competing for access to the same link

what is the purpose of the preamble in an Ethernet frame

allows the receiver to synchronize with the signal

why must an Ethernet frame contain at least 46 bytes of data

it’s long enough to detect a collision

how are Ethernet addresses typically represented

48-bit address

why did the switch-based variant of the Ethernet succeed in replacing multi-access Ethernet

it could be deployed incrementally

why is media access control a central issue for wireless links

it is hard to control who receives your signal when you transmit over the air, issues of eavesdropping may also have to be addressed

frequency hopping

spread spectrum technique involving transmitting the signal over a random sequence of frequency

what does MIMO stand for in the context of wireless networks

multiple-input multiple-output

what is the purpose of spread spectrum techniques in wireless communication

deals with possible interference in the band. Provides a natural time slot for Bluetooth to use for synchronous time division multiplexing.

which spread spectrum technique adds redundancy to transmitted bits for greater tolerance of interference

direct sequence

what is the purpose of the RTS-CTS mechanism in the 802.11 networks

tells the nodes within range of the receiver that they should not send anything for a while

what is a commonly used mechanism for controlling access to wireless networks and transmitted data

wireless security

how many devices can be connected to a master device in a Bluetooth piconet

225

frequency hopping

spread spectrum technique Bluetooth uses to mitigate interference

role of the four addresses in the 802.11 frame format

1. node sends probe frame

2. APs reply with probe response frame

3. node sends AP an association request frame

4. AP replies with an association response frame

what is the purpose of the distribution system in an 802.11 network

connects access points (APs)

what happens if two nodes sent RTS frames at the same time in 802.11 networks

RTS frames collide. Nodes wait for a CTS frame, and if not received, they retry after a random delay

which standard is based on Bluetooth but excludes application protocols? It is designed for situations where low bandwidth and power consumption are crucial

IEEE 801.15.1

what is the primary technology used for fiber-based broadband delivery to homes and businesses

PON (passive optical network)

how is upstream traffic managed in a PON network

it is time-division multiplexed on the upstream wavelength, with each ONU periodically getting a turn to transmit

what is the primary difference between 4G and 5G regarding waveforms

5G defines a family of waveforms while 4G defines only one

what is the main innovation of LTE’s air interface

the allocation of available radio spectrum to UEs

what is the primary purpose of the Broadband Network Gateway (BNG) in a PON network

gateway between the access network and internet

what is the current bandwidth supported by G-PON (Gigabit-PON)

2.25 Gbps