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CSCI 4171 > Final > Flashcards

Final Flashcards

1
Q

What is an important function of a router?

A

Path Determination

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2
Q

How does a router accomplish path of determination?

A

Routing table

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3
Q

How are routing tables built?

A

Routing protocols

Routing algorithms

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4
Q

Why do we need dynamic routing (auto) algorithms?

A
  • Topologies can change
  • Link costs can change
  • Nodes and links can fail
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5
Q

What are the two broad types of dynamic routing algorithms?

A
  • Distance vector (DV)

- Link state (LS)

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6
Q

What is the basic strategy for DV?

A
  • If a router receives an update about an unknown network, it accepts the update.
  • If a router gets a better update about a known network, it accepts the update. (modifies the the table)
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7
Q

What is the updated DV algo to detect faults?

A
  • If a router receives an update about an unknown network, it accepts the update.
  • If a router gets a better update about a known network, it accepts the update.
  • If the update isn’t better than existing entry - don’t accept the new update.
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8
Q

What is the classic problem in DV?

A

Count to infinity

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9
Q

Summarize the count to infinity problem?

A
  • Detects a fault
  • Set the distance to infinity
  • Then propagates this reading to other routers
  • Then all the other routers ‘spinning’ in infinity
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10
Q

What are the three solutions to the count to infinity problem?

A
  • Sol 1: Set a max number to infinity (e.g. 16)
  • Sol 2: Split horizon (prevent neighbours from sending info of a router that they are not directly connected to)
  • Sol 3: Hold-down timer: temporary timer until the network stabilizes OR until you start updating the DV tables again.
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11
Q

What are the two important concepts of the link state dynamic routing algorithm?

A
  • Send (original) information to all nodes, not just neighbours.
  • Send information about directly connected links only, not the entire table.
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12
Q

What are the main characteristics of the link state algorithm?

A
  • Link state packet (LSP) sent to directly connected nodes
  • LSPs are forwarded to every node on the network
  • Each router builds a link state DB with the LSPs which is a topology or graph of the entire network
  • From this DB routers can calculate the shortest path
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13
Q

What are the components of the LSP?

A
  • RouterID
  • Link state (x’s neighbours & costs)
  • Sequence number (first LSP has seq=0 and goes seq++)
  • Age (Set to max when LSP is created and decrements at every hop until discarded when age=0)
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14
Q

Why LSP uses a sequence number?

A

Tells router which LSP is more recent.

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15
Q

Why LSP uses age?

A

Prevent unnecessary floodings, LSPs are not forwarded unless they contain new information. However, flooding is needing sometimes to flush the shit out.

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16
Q

What is the flow chart for an LSP?

A
  • Receive LSP of X
  • Is there an LSP of X in the DB (yes –> is it new? no –> discard it)
  • Accept LSP decrement age
  • Send on outlines
  • Re-run shortest path algorithm
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17
Q

What are the border gateway protocol principles?

A
  • Path Vector Routing
  • Path Vector Messayges
  • Policy Routing
  • Path Attributes
  • TCP Connection
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18
Q

What is ICANN?

A

Internet Corporation for Assigned Numbers and Names

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19
Q

When was the last IP address assigned?

A

Feb. 2011

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20
Q

What is subnetting?

A

The process of dividing a network into multiple smaller networks so that each smaller network has its own network address.

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21
Q

What is supernetting?

A

Supernetting is the opposite of subnetting, and involves combining smaller networks into one larger network.

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22
Q

What is VSLM? Why is it used?

A

Variable length subnet masking. It is used to prevent the waste of IP addresses in basic subnetting.

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23
Q

What are some issues with basic subnetting?

A

You waste a lot of addresses, because they get equal chunks of IP address.

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24
Q

What are the rules to create a supernet?

A
  1. The number of blocks must be a power of 2
  2. The block addresses must be contiguous
  3. The third byte of the first address block must be evenly divisible by the number of blocks.
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25
Q

What is supernetting?

A

Supernetting is the opposite of subnetting, and involves combining smaller networks into one larger network.

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26
Q

How is IPv6 better than IPv4?

A
  • Better utilization of addresses (no classes)
  • Support for resource utilization
  • Support for security
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27
Q

What are some issues with basic subnetting?

A

You waste a lot of addresses, because they get equal chunks of IP address.

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28
Q

What are the rules to create a supernet?

A
  1. The number of blocks must be a power of 2
  2. The block addresses must be contiguous
  3. The third byte of the first address block must be evenly divisible by the number of blocks.
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29
Q

What is the size of an IPv6 address?

A

128 bits

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30
Q

How is IPv6 better than IPv4?

A
  • Better utilization of addresses (no classes)
  • Support for resource utilization
  • Support for security
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31
Q

What are the rules of simplification of IPv6 addresses?

A
  • Remove leading zeros

- Consecutive groups of zeros to double colon notation (only once per address)

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32
Q

What is a loopback address IPv6?

A

All 128 bits are 0 except the last bit.

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33
Q

What is the unspecified IPv6 address used for?

A

Finding the devices IP address (RARP).

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34
Q

What is an IPv6 multicast address?

A

Defined a group of hosts.

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35
Q

What is an IPv6 mapped address?

A

8 zero bits - 72 zero bits - 16 one bits - 32 bits (IPv4 address)

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36
Q

What are the security goals of ESP (IPv6 Datagrams)?

A
  • Confidentiality
  • Integrity
  • Authentication
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37
Q

What is the unspecified IPv6 address used for?

A

Finding the devices IP address (RARP).

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38
Q

What is an IPv6 multicast address?

A

Defined a group of hosts.

39
Q

What is ESP?

A

Encrypted Security Payload

40
Q

What are the security goals of ESP (IPv6 Datagrams)?

A
  • Confidentiality
  • Integrity
  • Authentication=
41
Q

What are the two modes for ESP deployment?

A
  • Transport mode

- Tunnel mode

42
Q

What is ESP transport mode?

A

Encrypting only the payload

43
Q

What is ESP tunnel mode?

A

Encrypting the payload and the base header

44
Q

What are the three strategies to transition from IPv4 to IPv6?

A
  • Dual stack
  • Tunneling (auto or config)
  • Header translation
45
Q

What is the frequency of wireless networks?

A

800KHz to 5GHz

46
Q

What is the WLAN protocol?

A

IEEE 802.11

47
Q

What are frequencies measured with?

A

Hertz

48
Q

What is a Hertz?

A

1 Hertz = 1 cycle per second

49
Q

What is the frequency of wireless networks?

A

800KHz to 5GHz

50
Q

What is the WLAN protocol?

A

IEEE 802.11

51
Q

What is WiMAX?

A

802.20 can operate on the 2, 2.5, 3G

52
Q

What wireless metropolitan?

A

802.16 Fixed WiMAX

53
Q

What is a passive association (or beaconing) for wireless access points?

A
  • APs can be set to beacon mode, where they periodically send beacon frames with an SSID
  • Wireless client in the range can detect the beacon frame
  • Clients select one access point with the strongest signal and sends association request
  • Selected AP sends association response
54
Q

What is an ESS?

A

Extended service set, a set of infrastructure BSS

55
Q

What are two significant addresses of an infrastructure BSS?

A
  • BSS ID –> MAC address of the AP serving the BSS

- ESS ID –> Character string (max 32 bytes) assigned by admin (e.g. the fucking name of the network asshole)

56
Q

What is an active association for wireless access points?

A
  • Client sends a Probe request frame
  • All APs within reach respond with a probe response
  • Clients select one access point with the strongest signal and sends association request
  • Selected AP sends association response
57
Q

What is a passive association (or beaconing) for wireless access points?

A
  • APs can be set to beacon mode, where they periodically send beacon frames with an SSID
  • Wireless client in the range can detect the beacon frame
  • Clients select one access point with the strongest signal and sends association request
  • Selected AP sends association response
58
Q

Which wireless connection methods use SSID?

A

Active association NOT beaconing

59
Q

What is a problem with CSMA/CA?

A

Hidden nodes causing frames to collide.

60
Q

What is wireless disassociation?

A
  • If a client or an AP wants to terminate an association, it sends a Dissassociation frame.
61
Q

What is wireless authentication?

A
  • For secure connections in wireless networks using protocols such as WEP and WPA1
  • The legit wireless client and AP share a secret key
  • Client send auth request
  • AP sends a challenge text
  • Client encrypts the challenge text with the secret key
  • Sends it back to the AP
  • AP decrypts it, if it passes then ACK success
  • Client sends an association request
  • AP responds
62
Q

Can an RTS collide with a CTS in CSMA/CA?

A

Small probability which is reduced with used two wait times:

  • DIFS (distributed interframe space) wait time for RTS (50 microsecs)
  • SIFS (Short interframe space): wait time for CTS (10 microseconds)
63
Q

What is a problem with CSMA/CA?

A

Hidden nodes

64
Q

What is the solution for the hidden nodes problem in CSMA/CA?

A

Modification to the CSMA/CA protocol:

  • Use two control frames
  • RTS (request to send)
  • CTS (clear to send)
65
Q

What if two RTSs collide in CSMA/CA?

A

This can happen, but the AP will not send CTS to either station.

66
Q

Can an RTS collide with a CTS in CSMA/CA?

A

Small probability which is reduced with used two wait times:

  • DIFS (distributed interframe space) wait time for RTS (50 microsecs)
  • SIFS (Short interframe space): wait time for CTS (10 microseconds)
67
Q

What technology is used for the physical layer for the wireless transmission?

A

Spread spectrum - key idea is to spread the information signal over a wider bandwidth in order to make jamming or interception more difficult

68
Q

What are the two broad types of spectrum techniques

A
  • Frequency hopping spread spectrum (FHSS)

- Direct sequence spread spectrum (DSSS)

69
Q

What do FHSS and DSSS use in the physical layer of a wireless network?

A

Pseudorandom Sequence Number Generator PSNG

70
Q

What is a PSNG?

A

Uses a specific hardware circuit.

71
Q

What are the characteristics of 1G cellular networks?

A
  • Voice only analog
  • Circuit switched
  • FDMA
72
Q

What are the characteristics of 2G cellular networks?

A
  • Voice + SMS
  • Analog (Voice)
  • Digital (SMS)
  • Circuit switched
  • TDMA
73
Q

What are the characteristics of 2.5G cellular networks?

A
  • Voice + medium speed data
  • Digital
  • Circuit switching and Packet switching
    CDMA
74
Q

What are the characteristics of 3G and 3G+ cellular networks?

A
  • Voice + highspeed data
  • Digital
  • Packet switching
    CDMA
75
Q

What are the characteristics of 4G cellular networks?

A
  • All IP Network

- Fully packet switched

76
Q

How does the 3G cellular network work?

A 
Step 1: USIM (i.e. SIM card) device transmit
Step 2: BTS (Cell tower)
Step 3: RNC (radio network controller)
Wired from now on
Step 4: Mobile switching center 
Step 5: Global mobile mobile switching center
Step 6: Router
Step 7: The Internet
77
Q

What are the advantages of optical networks?

A
  • Highspeed over long distances without repeaters
  • Small size
  • Immunity to crosstalk (not interference)
  • Longer lifetimes (no corrosive materials)
  • More secure (absence of the power dissipation and electromagnetic radiation)
78
Q

What are the characteristics of a first generation optical network?

A
  • Fiber used purely as a transmission medium
  • Switching and processing by electronics
  • Examples: SONET, FDDI
79
Q

What are the characteristics of a second generation optical network?

A
  • As data rates get higher, more difficult to process data electronically
  • Drive to incorporate switching and routing into the optical domain –> Development of All-optical networks.
80
Q

All-optical networks use what type of multiplexing?

A

Wave division multiplexing (WDM).

Recently, more than 100 channels at 10 Gbps –> 1Tbps per fiber per second

81
Q

What is a step index optical fiber?

A

Density of core is constant

82
Q

How does an optical cable work?

A

Optical fibers use total internal reflection to guide the light beam through the core.

83
Q

What is a graded index optical fiber?

A

Density of core decreases gradually outward.

84
Q

What are modes in optical fiber cables?

A

Mode refers to the distribution of light energy within the fiber.

Larger the core, more the number of modes and more the attenuation.

85
Q

What is the single mode for optical cables?

A

Small core diameter: all the signal energy travels in a single mode

86
Q

What is the multiple mode for optical cables?

A

Large core diameter; light energy propagates in the form of multiple modes.

87
Q

What is wavelength filter in optical cables?

A
  • Device that selects one wavelength and rejects others.

- Building block for other optical devices

88
Q

What is wavelength multiplexer in optical cables?

A
  • A multiplexer combines signals at different wavelengths on its input ports onto a common output port (a demux performs the opposite function)
89
Q

Describe wavelength router/switch?

A
  • Consists of input and output ports
  • Each input port carries a WDM signal consisting of a set of wavelengths
  • The router exchanges some wavelengths between inputs and outputs
  • There are two types: static and dynamic
90
Q

What is a wavelength add/drop MUX?

A
  • Simple form of router: 1 input and 1 output

- Has a local port wherein wavelengths are added to or dropped from the incoming light stream

91
Q

What is an optical transmitter?

A
  • Consists of an LED or laser source enclosed within a reflective cavity causes it to oscillate with positive feedback to give amplifications.
92
Q

What is an optical receiver?

A
  • Restores electrical signals from optical data
  • Consists of a photodiode (detects optical signals and converts them to electrical signals), a signal conditioner and a signal-to-bit converter.
93
Q

What are broadcast and select on optical networks?

A
  • Each node transmits at a specific wavelength
  • A MUX/DEMUX (called coupler) receives signals from the nodes and broadcasts them to all nodes.
  • Each node has a tunable optical filter to select the desired wavelength for the reception

CSCI 4171 (2 decks)

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