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Networking > Midterm 2 > Flashcards

Midterm 2 Flashcards

Internet Protocols, Circuit and Packet Switching, Local Area Networks

1
Q

What is a Switching Node?

A

They form the topology of the network. receiving information and forwarding it to another node

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2
Q

Explain Circuit Switching

A

A communication method where a dedicated communication path, or circuit is established between two devices before data transmission begins. The circuit remains dedicated to the communication for the duration of the session, and no other devices can use it while the session is in progress

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3
Q

Advantages of Circuit Switching

A

Guaranteed bandwidth: due to dedicated path
Low Latency: no need to establish a connection
Predictable performance: no competition for resources
Suitable for real-time communication: voice calls…

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4
Q

Disadvantages of Circuit Switching

A

Inefficient use of bandwidth
High cost
Limited Scalability

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5
Q

Explain Packet Switching

A

Packet switching is a communication method where data is divided into smaller units called packets and transmitted over the network. Each packet contains routing information and can take different paths to get to their destination

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6
Q

Advantages of Packet Switching

A

Efficient use of bandwidth because bandwidth is shared among multiple users
Flexible: wide range of data rates and packet sizes
Scalable
Lower Cost

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7
Q

Disadvantages of Packet Switching

A

Higher latency: packets go through multiple nodes
Limited QoS
Packet loss: can result in loss due to congestion of the network
unsuitable for real-time communication

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8
Q

What is a datagram?

A

A type of packet that is designed as part of internet protocols

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9
Q

Explain what a Virtual Circuit is?

A

Essentially virtual circuit switching: the first packet reserves the resources and routing for the successive packets

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10
Q

Explain the functionality of Synchronization

A

Receiver must be able to identify when a signal begins and when it ends

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11
Q

What is the function of exchange management?

A

Manages the establishment of a connection, defines the communication types and amount of data to be sent at one time

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12
Q

What is the function of routing?

A

Determines the route to be used when transferring data from one node to another through packet switching

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13
Q

What is the function of cyber security?

A

It protects the confidentiality of transferred information and protects the users identity

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14
Q

Is Ethernet a switching or broadcast network?

A

Broadcast - the router is broadcasting a signal along the cables

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15
Q

Is a Geo Satellite based network a switching or broadcast network?

A

Switching, the satellite acts as an intermediary node between two other nodes

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16
Q

What is internetworking?

A

Interconnected-networking. you connect two different layers and technology

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17
Q

What is an Autonomous System?

A

A network or group of networks managed by a single entity with a consistent set of routing rules and policies. e.g. EDU Roam AS is a set of routers and a network managed by single organization all over the world with legal and performance responsibilities

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18
Q

What is a connected AS

A

It is an Autonomous system where there is always a path between nodes

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19
Q

What is an Interior Routing Protocol and What is its focus?

A

Within an AS the protocol interconnects different AS. It is concerned with cyber security and routing

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20
Q

Why use Layered Architecture?

A

Provide a flexible, modular structure, developed so that a change in one of the elements in a system requires minimal changes in the other
It allows upper layer to perform tasks on its own, exchanging info and requesting services from lower level
Allows us to divide complex tasks into smaller ones and give different tasks to each layer

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21
Q

What Is TCP/IP Protocol Architecture

A

A working model used all over the internet. It has 5 layers -> application layer, transport layer, internet layer, network access layer and the Physical Layer

22
Q

What Is OSI architecture

A

Open System interconnection model that isn’t used too much. It has 7 layers -> Application, presentation, session, transport, network, data link and physical

23
Q

Explain the differences between OSI and TCP

A

TCP OSI
Application - HTTP - Application
Presentation
Session
Transport - TCP, UDP - Transport
Internet - IP, ARP - Network
Network Interface - LAN - Data link

24
Q

Explain why the internet mostly uses TCP/IP

A
  1. Bad timing: OSI was designed after TCP was implemented
  2. OSI is designed for the perfect world which makes it impractical
  3. OSI is good for modeling processes and more modular
25
Q

Explain each of the Layers of OSI and their purpose

A
  1. Application - Access to the users (file transfer, e-mail…)
  2. Presentation - Data representation (syntax and ASCII)
  3. Session - Control Structure between applications (establish and manage connections)
  4. Transport - transport of data between end-points
  5. Network - establishes, maintains and terminates connections
  6. Data link - info transfer across physical link (manages frame sending)
  7. Physical - How signal is transmitted
26
Q

What are the functions of the Data Link Layer

A

The data link layer is responsible for node-to-node delivery of data. It can be subdivided into two layers:
1. Logical Link Control which is an interface to higher layers and manages errors
2. Media Access Control (MAC) which - assembles frames from packets sent by the network layer and turns frames into a packet and give back to Network layer

27
Q

What is the Topology of the unlink of a Geo Satellite Network

A

Star Topology - Each device in the network is connected to the satellite forming a physical star but logical bus

28
Q

What is a token Ring Topology

A

A logically or physically circular topology where frames are transmitted unidirectionally in a loop. A token is constantly circulating and in order to transmit a frame the node must receive the token. The token is then added to the front of the frame and the frame is sent. When the receiver receives a frame it sends out a new token

29
Q

What is a bus

A

A network topology where every node is a branch off-shooting one trunk

30
Q

What is FDDI

A

A topology based on token ring but allowing for multiple frames to be transmitting at once. Token is seized by a node, that node then sends its frame and sends a new token immediately after. Any new node can seize the token and transmit right after because the other frame would have already been copied and retransmitted by said node

31
Q

What is MAC?

A

Media Access Control - a MAC address is the physical location of a node - One of its major duties is dealing with Channel Allocation (how to divide a single channel efficiently)

32
Q

What is static Channel Allocation?

A

Dividing a single channel of bandwidth into static sections. Frequency Division Multiplexing (FDM) - divides a channel into N = sized portions of bandwidth with N being each user of the network
Time division Multiplexing: each station is given a time slot

33
Q

Explain the Pros and Cons of Static Channel Allocation?

A

Static Is extremely useful for predictable systems but becomes unsuitable when there is a large number of users with variable bandwidth requirements

34
Q

What is Dynamic Channel Allocation?

A

frequency bands are not permanently assigned to the users. Instead channels are allotted to users dynamically as needed, from a central pool. The allocation is done considering a number of parameters so that transmission interference is minimized; optimizing bandwidth usage and making faster transmissions.

35
Q

Explain ALOHA channel Allocation

A

Its a random access protocol - designed for wireless LAN. It allows stations to transmit data at the same time. Data can collide and become garbled. A frame has a vulnerable period where a collision will be caused if another frame is transmitted

36
Q

Explain Pure Aloha

A

When a station sends data it waits for ack. if ack doesn’t come within allotted time then the station waits for a random amount of time and retransmits the data
Vulnderable time = 2frame transmission time
Througput = G exp{-2G}
18% utilization

37
Q

Slotted ALOHA

A

Similar to pure aloha except time is divided into slots and sending is only allowed at the beginning of these slots

38
Q

What is Carrier Sense Multiple Access

A

Way of causing fewer collisions, node is required to sense the medium to determine if it is busy before transmitting. A collision can still occur due to propagation delay

39
Q

Explain the Access modes of CSMA

A

Non-persistent: node senses channel, if idle sends otherwise it checks again after a random amount of time
p-persistent: node senses medium, if idle sends data with p probability. If data is not transmitted (1-p prob) then it waits for some time and checks again…..repeats until data is sent

40
Q

Explain Code Division Multiple Access (CDMA)

A

one channel carries all transmissions simultaneously. but each channel sends the transmission in a different code.

41
Q

CMSA/CD

A

A collision detection in CSMA, if a collision is detected the transmission is terminated and the transmitter retransmits after a random interval

42
Q

CMSA/CA

A

Collision Avoidance: 3 ways
1. Interframe space - avoids propagation delay by checking during a period called interframe space and checking again before sending
2. Contention window - amount of time divided into slots, if sender ready it chooses a random number of slots as wait time which doubles every time medium is busy
3. Acknowledgement - sender retransmits data if acknowledgement is not received before time-out

43
Q

List the pros and cons of CSMA

A

Pros:
increased efficiency - less collision
simplicity - easy to implement
flexibility - wide range of environments
low cost
Cons:
limited scalability
Delay: busy networks means lots of waiting
Limited reliability

44
Q

CD vs CA

A

CD is more efficient because it doesn’t require exchange of control packets before data transmissions but overall CA is much more reliable because a collision uses a ton of bandwidth

45
Q

What is DIFS, SIFS and PIFS

A

types of interframe spaces utilized within CSMA/CA to coordinate transmissions and avoid collisions in the network.
SIFS -> short interframe space
PIFS -> PCF interframe space
DIFS -> DCF interframe space

46
Q

Explain DIFS

A
  • DIFS is the longer interframe space used by CSMA/CA. It serves as the waiting period before a device can initiate a new transmission.
  • When a device has data to transmit, it first listens to the wireless medium. If it detects that the medium is idle for a duration longer than DIFS, it assumes it can initiate a transmission without causing a collision.
  • DIFS is designed to provide a longer waiting period to ensure that ongoing transmissions have a chance to finish and to reduce the probability of collisions.
47
Q

Explain SIFS

A

SIFS is a shorter interframe space compared to DIFS, used for certain types of transmissions that require higher priority or immediate attention.
When a device successfully transmits a frame and needs to send another frame immediately, it uses SIFS as the waiting period before initiating the next transmission.

48
Q

Explain how transmission of fragmented IP packets is safer In CSMA/CA

A

If a piece of the packet is lost the entire message must be thrown out. Thats why collision avoidance is used because a collision can cause losses in the packet.

49
Q

Explain RTS/CTS

A
  1. transmitting station sends an RTS message, specifying length of data and destination station
  2. receiving station issues a CTS frame which echoes the sender address and the NAV
  3. if the CTS frame is not received, it is assumed that a collision occurred and the RTS process starts over
  4. After data frame is received an ACK frame is sent back verifying transmission was successful
50
Q

Explain PCF - Point coordination function

A

Central access point controls medium access. Beacon frames sent by AP periodically to synchronize devices. Poll frames are sent from AP which invite data transmission. Devices transmit following poll frame and wait for ack.

51
Q

What is the NAV

A

Network Allocation Vector - - NAV is a countdown timer maintained by each station
station is not permitted to attempt accessing the medium until its NAV has reached zero

52
Q

Explain CFP

A

Contention free period - time interval where AP controls medium access in PCF
There is a contention period where devices contend for access using DCF

Networking (2 decks)

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