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127 notes > lecture 5 > Flashcards

lecture 5 Flashcards

1
Q

why do we need software abstraction

A

to make hardware convenient

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2
Q

how do we deal with complex problems

A
  • by layering, each layer deals with a certain part of the problem (divide and conquer)
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3
Q

what is a protocol

A
  • a set of rules/procedures that define how data is transmitted between different devices/routers
  • helps sender to communicate with the receiver and vice versa
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4
Q

difference between interface and protocol

A
  • interface is the protocol between corresponding layers (e.g layer 5 and layer 4) on the same stack
  • protocol is between layers of different stacks
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5
Q

what happens in the sender layers

A
  • checksums are added

- overheads are added

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6
Q

what happens in the receiver layers

A
  • decryption

- removal of the checksums and overheads added in the sender layers

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7
Q

protocol stack

A

layer n protocol

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8
Q

what is a checksum

A

is a small-sized block of data added for the purpose of detecting errors

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9
Q

what is an overhead

A

is any combination of excess computation time, memory, bandwidth, or other resources that are required to perform a specific task

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10
Q

as a network designer you need…

A
  • to decide on the amount of layers

- decide on the interfaces+protocol stack

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11
Q

the philosophy-translator-secretary architecture

A
  • message from philosopher 1 is in a different language
  • middle ground translators speak the same language
  • from philosopher to translator
  • translator to secretary
  • secretary to secretary 2
  • secretary 2 to translator 2
  • translator 2 to philosopher 2
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12
Q

two fundamental concepts of network architecture

A
  • message

- encapsulation

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13
Q

what is fragmentation

A

the process of splitting a big message into smaller parts

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14
Q

opposite of fragmentation is…

A

defragmentation

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15
Q

ethernet’s minimum and maximum frame size is

A

minimum: 64 bytes
maximum: 1518 bytes

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16
Q

what is a header

A

a header is supplemental data placed at the beginning of a block of data being transmitted/stored

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17
Q

what does header help with

A
  • when a header is clear and unambiguous, it allows for parsing to happen
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18
Q

why do messages have a control and header (4)

A
  • used to synchronise with the remote peer
  • contain instructions that tell the remote peer what to do with the message (protocol)
  • security purposes(protocol)
  • error detection
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19
Q

what is encapsulation

A

it is when layer N-1 encapsulates and treats the data portion received from layer N as an entire integral unit

e.g layer 4 encapsulates data from layer 5 (transport encapsulate session’s)

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20
Q

what happens when the remote peer receives the encapsulated message

A
  • it strips off the header, trailer, overheads, checksums off the data and passes it to the layer above
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21
Q

what is peer to peer process

A

when layer N of machine A communicates with layer N of machine B

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22
Q

design issues of layers

A
  1. identifying senders and receivers
  2. rules of data transfer (simplex, half duplex, full duplex)
  3. error control
  4. order and length of messages
  5. fast sender, slow receiver
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23
Q

what is addressing

A

number or address that is assigned to any device that seeks access to or is part of a network

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24
Q

2 types of layer services

A
  • connectionless

- connection oriented

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25
Q

features of a connectionless service

A
  • does not require protocols
  • message delivery not guaranteed
  • considers each packet of the same message independent of each other:
    1. can have different addressing
    2. different route taken
  • service interface is message based
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26
Q

features of a connection oriented service

A
  • first establishes a connection between the source and destination
  • authentication is needed
  • error received if message delivery fails
  • service interface is stream based
  • reliable
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27
Q

the 5 service primitives of a connection oriented service (system calls)

A
  • LISTEN
  • CONNECT
  • RECEIVE
  • SEND
  • DISCONNECT
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28
Q

meaning of: LISTEN

A

block waiting for an incoming connection

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29
Q

meaning of: CONNECT

A

establish a connection with a waiting peer

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30
Q

meaning of: RECEIVE

A

block waiting for an incoming message

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31
Q

meaning of: SEND

A

send a message to the peer

32
Q

meaning of: DISCONNECT

A

terminate a connection

33
Q

sequence of system calls

A
  1. request connection
  2. acknowledge connection
  3. request for data
  4. reply
  5. disconnect
  6. disconnect back
34
Q

two kinds of protocol stacks

A
  1. OSI model

2. TCP/IP

35
Q

7 layers of the OSI

A
  1. application
  2. presentation
  3. session
  4. transport
  5. network
  6. data link
  7. physical
36
Q

what 3 layers of the OSI are in the subnet

A
  • physical
  • data link
  • network
37
Q

what communication technique does the OSI subnet use

A
  • store and forward

- hop by hop

38
Q

what is store and forward

A

a data communication technique in which a message transmitted from a source node is stored at an intermediary device before being forwarded to the destination node

39
Q

the unit in the physical layer

A

bit

40
Q

voltage and binary bits

A
  • 1 is represented using high v
41
Q

five problems with the physical layer

A
  1. how many volts represents a “1” or “0”?
  2. how initial connection is established?
  3. how long does a bit time last?
  4. how many wires does the transmission media have+require?
  5. are pulses electrical or optical or waves?
42
Q

the unit in the data link layer

A

frames

43
Q

what does the data link layer handle

A
  1. transferring the frames to the network layer free of errors
  2. handles damaged, lost and duplicate frames
  3. slows down a fast transmitter (flow control)
  4. creates and recognizes frames (physical layer just transmits bit stream but with no regard of meaning and structure)
44
Q

two sublayers of the data link layer

A
  1. MAC (MEDIA ACCESS CONTROL)

2. LLC (LOGIC LINK CONTROL)

45
Q

the unit in the network layer

A

packets

46
Q

difference between frame and packet

A
  • frame includes the source and destination MAC addresses (i.e., the physical address of the machine)
  • packet includes the source and destination IP addresses
47
Q

what does the network layer do (THE BOSS)

A
  • controls operations in the subnet (communication between hosts)
  • deals with routing
  • handles congestion
  • handles addressing
48
Q

what is routing (network layer)

A

the process of transferring packets received from the Data Link Layer of the source network to the Data Link Layer of the correct destination network.

49
Q

what does routing involve

A

involves decision making at each intermediate node on where to send the packet next so that it eventually reaches its destination

50
Q

what is congestion

A

If the incoming rate of the packets arriving at any router is more than the outgoing rate

51
Q

what causes congestion

A
  • when packets arriving on an input line all need the same output line (queue)
  • insufficient memory to hold all of them (packet loss)
  • increased time which causes the packets that reached to the front of the queue to time out (duplicates will be sent, more congestion)
  • slow processors
  • low bandwidth
52
Q

where is routing simple (network layer)

A

during broadcasting

53
Q

unit of the transport layer

A

PDU (protocol data unit)

54
Q

most important job of the transport layer

A
  • process to process delivery

- makes sure data gets delivered to a specific process on a specific machine

55
Q

the network layer does not guarantee

A

the packet will reach its intended destination

56
Q

what does the transport layer handle

A
  • retransmissions
  • duplicates
  • end to end protocol
  • flow control
57
Q

what does the session layer do

A
  • dialogue control
  • provide synchronization
  • recovers failure from transport layer (e.g. you download a file but internet cuts off halfway, file down pauses and continues when internet is back)
58
Q

what does the presentation layer do

A
  • compress data
  • encryption
  • apply/encode syntax and semantics to the data
  • format data (names, IDs etc)
59
Q

what does the application layer do

A
  • responsible for providing services to the user
  • links a specific protocol to the service
    e.g.
    HTTP
    SMTP
    FTP
    telnet
60
Q

4 layers of the TCP/IP

A
  1. application layer
  2. host to host transport layer
  3. internet layer
  4. network interface layer
61
Q

TCP/IP in relations to OSI

A
  • physical and data link layer = network interface layer
  • network layer = internet layer
  • transport layer = host to host transport layer
  • session, presentation and application = application layer
62
Q

4 protocols used in the network interface layer

A
  • ethernet
  • token ring
  • frame relay
  • ATM (asynchronous transfer mode)
63
Q

protocol used in the internet layer

A
  • IP
64
Q

protocols used in the host to host transport layer

A
  • UDP (user datagram protocol)

- TCP (transmission control protocol)

65
Q

protocols used in the application layer under TCP

A
  • telnet
  • FTP (file transfer protocol)
  • SMTP (simple mail transfer protocol)
66
Q

protocols used in the application layer under UDP

A
  • DNS (domain name system)
  • RIP (routing information protocol)
  • SNMP (simple network management protocol)
67
Q

TCP features

A
  • connection oriented
  • reliable
  • used for flow control
  • byte stream
  • high quality
68
Q

UDP

A
  • connectionless
  • unreliable
  • does not do flow control
  • datagram
  • used for transmitting voice/speech/video
  • faster delivery
69
Q

TCP/IP layers and addresses

A
  • network interface layer: physical address
  • internet layer: logical address
  • transport layer: port address
  • application: specific address
70
Q

sender physical address is on the

A

RIGHT (next to it is the logical address)

71
Q

receiver physical address is on the

A

LEFT

72
Q

size of physical address

A

6 bytes (12 hexadecimal digits)

73
Q

why does the physical address change but the port and logic address don’t

A

because the physical address goes hop by hop

74
Q

5 main differences between OSI and TCP/IP

A
  1. OSI focused on model before the protocol, TCP/IP focused on the protocols before the model
  2. OSI’s network layer is connection oriented and connectionless
  3. TCP/IP’s network layer is connectionless
  4. OSI’s transport layer is connection oriented ONLY
  5. TCP/IP’s transport layer is connection oriented and connectionless
75
Q

which protocol stack is best for designing new networks

A

OSI model

127 notes (11 decks)

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