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Oral Exams - Concentration > Advanced Networking > Flashcards

Advanced Networking Flashcards

1
Q

What is the Internet?

A

Internet “network of networks” - Interconnected ISPs

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2
Q

Name 2 Internet standards

A

RFC: request for comments

IETF: Internet Engineering Task Force

Additional info: Request for Comments (RFC), in information and communications technology, is a type of text document from the technology community. … The IETF adopts some of the proposals published as RFCs as Internet Standards. However, many RFCs are informational or experimental in nature and are not standards.

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3
Q

Examples of Protocols?

A

TCP, IP (network layer)

HTTP (Application layer)

Skype (Application layer)

802.11 (link layer)

Ethernet (data layer)

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4
Q

What are some characteristics of a MAC (or LAN or physical or Ethernet) address?

A
  • Used ‘locally’ to get frame from one interface to another physically-connected interface
  • 48 bit MAC address (for most LANs)
  • Administered by IEEE
  • MAC address like SSN - flat address portable
  • IP address like postal address - not portable (depends on IP subnet to which it’s attached)
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5
Q

Address Resolution Protocol (ARP)

A

A communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address.

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6
Q

TRUE/FALSE

Each adapter on LAN has unique LAN address

A

TRUE

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7
Q

Time to Live (TTL)

A

Time after which address mapping will be forgotten (typically 20 min) - limits the lifespan or lifetime of data in a computer or network

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8
Q

Ethernet frame structure

A

7 byte Preamble - used to synchronize receivers, senders clock rates

6 byte Addresses: dest and source

Type: indicates higher layer protocol (mostly IP but others possible, e.g., Novell IPX, AppleTalk)

data (payload)

CRC: cyclic redundancy check at receiver
- error detected: frame is dropped

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9
Q

Explain the following characteristics of Ethernet?

  • connectionless
  • unreliable
  • protocol
A

connectionless: no handshaking between sending and receiving NICs

unreliable: receiving NIC doesn’t send acks or nacks to sending NIC
- data in dropped frames recovered only if initial sender uses higher layer rdt (e.g., TCP), otherwise dropped data lost

Ethernet’s MAC protocol: unslotted CSMA/CD with binary backoff

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10
Q

What is an Ethernet switch?

A

link-layer device: takes an active role

  • store, forward Ethernet frames
  • examine incoming frame’s MAC address, selectively forward frame to one-or-more outgoing links when frame is to be forwarded on segment, uses CSMA/CD to access segment
  • Ethernet protocol used on each incoming link, but no collisions; full duplex - each link is its own collision domain - A-to-A’ and B-to-B’
  • switches buffer packets

transparent

  • hosts are unaware of presence of switches
  • hosts have dedicated, direct connection to switch

plug-and-play, self-learning
- switches do not need to be configured

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11
Q

8 facts about TCP

A

Reliable, in-order delivery
o Congestion control

Point-to-point
o One sender, one receiver

Reliable, in-order byte
o Stream: no message boundaries

Pipelined
o TCP congestion and flow control set window size

Full duplex data
o Bi-directional data flow in same connection
o MSS: max segment size

Connection-oriented
o Handshaking inits sender, receive state before data exchange

Flow controlled
o Sender will not overwhelm receiver

Parity checking
o Single bit parity
 Detect single bit errors
 Network signal can be unreliable, hence needs error checking
 Simplest error checking mechanism with very limited reliability
 Can be used tougher with error detection/correction codes
 Can only delete, NOT correct, NOR identify if the error was in parity bit or one of the data bits
o 2-dimensional bit parity
 Detect and correct single bit errors

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12
Q

A challenge of wireless networks

A challenge of mobile networks

A

wireless: communication over wireless link
mobility: handling the mobile user who changes point of attachment to network

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13
Q

Examples of wireless hosts

A

o laptop, smartphone
o run applications
o may be stationary (non-mobile) or mobile
o wireless does not always mean mobility

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14
Q

How does wireless differ from wired link?

A

decreased signal strength: radio signal attenuates as it propagates through matter (path loss)

interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well

multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times

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15
Q

What are some problems from multiple wireless senders and receivers? (2)

A

Hidden terminal problem

Signal attenuation (weakening) and interference

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16
Q

What are the differences between 802.11: passive and active scanning?

A

Active scan
- The client radio transmits a probe request and listens for a probe response from an AP.

Passive scan

  • The client radio listens on each channel for beacons sent periodically by an AP.
  • Generally takes more time, since the client must listen and wait for a beacon.
  • Another limitation with a passive scan is that if the client does not wait long enough on a channel, then the client may miss an AP beacon.
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17
Q

How to avoid collisions?

A

RTS/CTS

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18
Q

11 facts about UDP

A

Unreliable, unordered delivery
o No-frills extension of “best-effort” IP

Segments may be lost

Segments may be delivered out of order

Connectionless
o No handshaking between UDP sender, receiver
o Each UDP segment handled independently of others

Uses:
o Streaming multimedia apps (loss tolerant, rate sensitive)
o DNS
o SNMP

Add reliability at application layer - Application-specific error recovery

Use checksum to check if error-free
o Detect “errors” (e.g., flipped bits) in transmitted segment
o Simple method of error detection
o Calculates the aggregate sum of all data bits – Data sum

Small header size

No congestion control
o UDP can blast away as fast as desired

No connection establishment (which can add delay)

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19
Q

What services are not available with UDP?

A
  • Delay guarantees

* Bandwidth guarantees

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20
Q

3 facts about Reliable Data Transfer (RDT)

A
  • stop-and-wait operation
  • High overhead
  • Network protocol limits use of physical resources
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21
Q

Pipelining

A

Sender allows multiple “in-flight” yet to be acknowledged packets

o Range of sequence numbers must be increased
o Buffering at sender and/or receiver

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22
Q

2 generic forms of pipelined protocols

A

Go-Back-N
 Sender can have up to N unacknowledged packets in pipeline
 Receiver only sends cumulative acknowledgement - Doesn’t ack packet if there’s a gap
 Sender has timer for older unacked packet - When timer expires, retransmit all uancked packets

Selective Repeat
 Sender can have up to N unack’d packets in pipeline
 Receiver sends individual ack for each packet
 Sender maintains timer for each unacked packet - When timer expires, retransmit only that unacked packet

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23
Q

What do Network protocols govern?

A 
All Internet communication activity
o	Defines format
o	Order of messages sent and received among network entities
o	Actions taken on message transmission
o	Receipt

Example
 TCP connection request
 TCP connection response
 Get

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24
Q

What are 2 components of a Network Structure?

A

Network edge

Network core

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25
Q

Network edge

A

Also known as the WAN edge, is where an enterprise network connects to third-party network services
(E.g., for remote offices)

Hosts: clients and servers
Servers often in data centers
Access networks, physical media
- Wired, wireless communication links

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26
Q

Network core

A

o Interconnected routers

o Network of networks

o packet-switching: hosts break application-layer messages into packets

  • forward packets from one router to the next, across links on path from source to destination
  • each packet transmitted at full link capacity
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27
Q

Packet switching vs circuit switching

A

Circuit Switching is connection oriented that means a path is established between source and destination before the transmission occurs. On the other hand, Packet Switching is Connectionless that means a dynamic route is decided for each packet while transmission.
Circuit Switching was originally designed for voice communication whereas, Packet Switching was originally designed for data communication.
Circuit Switching is inflexible as once a path is established for transmission, it doesn’t change while the duration of the session. On the other hand, Packet Switching is flexible as each packet may travel through a different route to reach its destination.
In packet switching, as each packet travels a different path hence, the packet are received out of order at the receiver side and later arranged in order. On the other hand, in circuit switching the entire message is received as it is as sent from a sender to receiver.
Space Division Switching or Time-Division Switching can be used to implement Circuit Switching whereas, Packet Switching can be implemented using two approaches Datagram Approach and Virtual Circuit Approach.
Circuit Switching is always implemented at physical layer whereas, Packet Switching is implemented on the network layer.

Is packet switching a “slam dunk winner?”
o Great for bursty data - Resource sharing
- Simpler, no call setup
o Excessive congestion possible: packet delay and loss
- Protocols needed for reliable data transfer, congestion control
- BUT bandwidth guarantees needed for audio/video apps

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28
Q

When does queueing delay loss occur with Packet switching?

A

If arrival rate (in bits) to link exceeds transmission rate of link for a period of time

o Packets will queue, wait to be transmitted on link
o Packets can be dropped (lost) if memory (buffer) fills up

29
Q

Wireless access networks (3)

A

Shared wireless access network connects end system to router
o Via based station aka “access point”

Wireless LANs
o Within building (100 ft)
o 802.11 b/g/n (WiFi_: 11, 54, 450 Mbps transmission rate
 Latest is dual band routers 802.11se, higher capacity

Wide-area wireless access (cellular)
o Provided by telco (cellular) operator, 10’s km
o Between 1 and 10 Mbps
o 3G, 4GL:LTE

30
Q

3 parts of a Bluetooth Packet signature

A

Access Code
o Composite key -> Piconet ID + channel ID

Header
o Composite key -> defines

Payload
o Defines data

31
Q

Throughput (end to end)

A

Rate (bits/time unit) at which bits transferred between sender/receiver
o Instantaneous: rate at given point in time
o Average: rate over longer period of time

Bottleneck link
o Link on end-end path that constrains end-end throughput

32
Q

4 Bluetooth throughput methods

A

SDR – standard data rate
o Original rate of v.1.0 and how fallback mode

EDR – enhanced data rate
o Short range, high quality streaming

HS – high speed
o Uses wi-fi 802.11 to transfer files fast

LE – low energy
o Retains sleep mode between connections
o Short connection bursts w/ high data rates
o Devices retain months of battery life

33
Q

Factors that affect sound velocity underwater

A

Temperature

Pressure

Salinity

34
Q

5 layers in TCP/IP protocol stack

A 
Application layer (RDP)
o	Supporting network applications: FTP, SMTP, HTTP
Transport layer (end to end)
o	Process-process data transfer: TCP, UDP

Network layer
o Routing of datagrams from source to destination: IP, routing protocols

Data link layer (Bluetooth, cell)
o Data transfer between neighboring network elements: Ethernet, 802.11(WiFi), PPP

Physical layer (media device)
o	Bits “on the wire”
35
Q

DSRC

A

Dedicated short range communication technology

36
Q

USDOT’s vision for DSRC

A

USDOT’s vision is to have Connected and Autonomous Vehicles (CAVs)

Not currently used by autonomous vehicles

37
Q

Describe DSRC Technology

A

Uses 5.9 GHz freq band specifically allocated for automotive use by FCC (Federal Communications Commission)

Provides an omnidirectional range of about 300 to 1200 m

Can communicate reliably up to at least 155 mph

Standards defined by IEEE 802.11p, IEEE 1609.x, SAE J2735

38
Q

What is DSRC’s Protocol Implementation?

A

3-way handshake protocol using DSRC
• Control messages
• Synchronization messages
• Acknowledgement messages

39
Q

Applications of Underwater Sensor Networks

A

Ocean Sampling Networks

Pollution Monitoring and other environmental monitoring (chemical, biological)

Disaster Prevention (tsunami warnings)

Assisted Navigation

Distributed Tactical Surveillance

Mine Reconnaissance

40
Q

What is QoS and why is it important?

A

QoS refers to any technology that manages data traffic to reduce PACKET LOSS, LATENCY and JITTER on the network

Some applications running on your network are sensitive to delay

These applications commonly use the UDP protocol as opposed to the TCP protocol.

Links become overly congested - routers and switches start dropping packets because they are coming in/out faster that what can be processed

41
Q

How does QoS work?

A

Classification and Queuing

Classification identifies and marks traffic to ensure network devices know how to identify and prioritize data as it traverses a network.
Queues are buffers in devices that hold data to be processed. Queues provide bandwidth reservation and prioritization of traffic as it enters or leaves a network device. If the queues are not emptied, they overflow and drop traffic.

identify the traffic
o Class of Service (CoS) - Will mark a data stream in the layer 2 frame header
o Differentiated Services Code Point (DSCP) - Will mark a data stream in the layer 3 packet header

42
Q

What is Edge computing?

A

When edge device is between data source and cloud service

Allows for computations to be performed on edge device
o Computations can be performed faster
o Frees up previously used bandwidth

43
Q

What created the need for Edge computing?

A

The success of cloud computing

The rapid growth of devices connecting to IoT - 50 billion devices expected on IoT by 2020

Advancement of data-processing speed does NOT equal advancement of bandwidth available

44
Q

What are early problem areas in Edge computing?

A

Programmability
o Current solutions custom made
o Need frameworks

Naming
o No current standard for name edge devices
o Hard for edge devices to be found

Privacy and Security
o Hackers can gather info from IoT devices with poor security
o Need to ensure encryption of data on network and edge devices

45
Q

What are 4 sources of packet delay?

A

Nodal processing
o Check bit errors
o Determine output link
o Typical < msec

Queueing delay
o Time waiting at output link for transmission
o Depends on congestion level of router

Transmission delay
o L: packet length (bits)
o R: link bandwidth (bps)
o = L/R

Propagation delay
o D: length of physical link
o S: propagation speed (~2x10^8 m/sec)
o = D/S

46
Q

What is CRC?

A

Cyclic Redundancy Check

  • More powerful error-detection coding
  • Widely used in practice (Ethernet, 802.11 WiFi, ATM) – looks like long division
  • View data bits, D, as a binary number - based on the remainder of a polynomial division of their contents.
47
Q

Hamming code

A

Error correction code (single bit)

Can detect 2-bit error and correct 1-bit error
Cannot fix 2-bit

48
Q

Condition for 2 bit errors

A

If 2 bits have been altered, then
o At least one of the circles will have odd number of ones
o The total number of ones including the overall parity bit will be even

If 1 bits has been altered, then
o At least one of the circles will have odd number of ones
o The total number of ones including the overall parity bit will be odd

49
Q

Base station

A

o typically connected to wired network
o relay - responsible for sending packets between wired network and wireless host(s) in its “area”
o e.g., cell towers, 802.11 access points

50
Q

Wireless link

A

o typically used to connect mobile(s) to base station
o also used as backbone link
o multiple access protocol coordinates link access
o various data rates, transmission distance

51
Q

Infrastructure mode

A

wireless devices can communicate with each other or can communicate with a wired network

52
Q

Ad hoc mode

A

o no base stations
o nodes can only transmit to other nodes within link coverage
o nodes organize themselves into a network: route among themselves

53
Q

What OSI layer is bluetooth?

A

Physical/MAC

54
Q

What’s band frequency does Bluetooth operate?

A

2.4 GHz

55
Q

What is Bluetooth’s 3-step pairing process?

A

Inquiry
Paging
Bonding

56
Q

Functions of a Host?

A

Send packets of data

  • takes application message
  • breaks into smaller chunks, known as packets, of length L bits
  • transmits packet into access network at transmission rate
57
Q

Packet-switching: store-and-forward

A

Entire packet must arrive at router before it can be transmitted on next link

end-end delay = 2 L/R (assuming zero propagation delay)

58
Q

2 key network-core functions

A

Routing - determines source-destination route taken by packets

Forwarding - move packets from router’s input to appropriate router output

59
Q

What is Multiplexing?

A

The process of sending two or more individual signals over a single communication channel

This is usually achieved by an electronic circuit known as a multiplexer

60
Q

FDM vs TDM

A

TDM

  • share the timescale for the different signals
  • more efficient
  • can be used for both Analog and Digital signals.

FDM

  • shares the frequency scale for the different signals.
  • can be used for Analog signals only.
61
Q

point-to-point

A

one sender, one receiver

62
Q

full duplex data

A

bi-directional data flow in same connection

63
Q

connection-oriented

A

handshaking (exchange of control msgs) before data exchange

64
Q

flow controlled

A

sender will not overwhelm receiver

65
Q

IP address

A

32-bit

network-layer address for interface

used for layer 3 (network layer) forwarding

66
Q

MAC address

A

48 bit (For most LANs) burned into NIC ROM

used ‘locally’ to get frame from one interface to another physically-connected interface

67
Q

4 elements of a wireless network

A

wireless hosts - laptops, smartphones

base station - typically connected to wired network

wireless link - typically used to connect mobile(s) to base station

infrastructure mode - base station connects mobiles into wired network

68
Q

5G Security Concerns (4)

A

Authentication - needs to be fast, low latency, high data rates - can’t be based on only symmetric key

Integrity - prevent manipulation when modifying data

Availability - call reception, signal scrambling, DoS

Confidentiality - vehicle routing data, health monitoring data

69
Q

5G over DSRC

A

5G has:

higher throughput
higher reliability
cheaper (existing cellular infrastructure)
lower latency
wider range
symmetric
better with NLOS

Oral Exams - Concentration (4 decks)

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