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Networks II > The Transport Layer > Flashcards

The Transport Layer Flashcards

1
Q

What does the transport layer do?

A

It is an end to end layer that provides services to the application layer. It isolates the application layer from technology, design and imperfections of lower layers

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2
Q

What does the data link layer do?

A

This moves frames from one end of the wire to the other

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3
Q

What does the network layer do?

A

It gets packets from the source all the way to the destination. Overall it provides routing

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4
Q

What are the differences between the transport layer and the network layer?

A

The transport layer code runs entirely on users’ machines but the network layer mostly runs on the routers which are operated by the carrier.

Users have no real control over the network layer so they cannot solve the problem of unreliable network layer service by using better routers or putting more error handling in the data link layer but in the transport layer lost packets and mangled data can be detected and compensated for.

The transport layer has abstraction because transport service primitives can be implemented as library procedures in order to make them independent of the network service primitives.

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5
Q

What services and protocols does the transport provide?

A

Logical communication between app processes running on different hosts.

Transport protocols run in end systems. Which means it is typically handled by processes in the host compute OS and not routers

Allows more than one transport protocol to be available to apps TCP, UDP

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6
Q

What is a socket?

A

The combination of an IP address and a port number

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7
Q

What is multiplexing?

A

This is where multiple distinct transport sessions all using the same IP address connect to different servers/clients. Each transport session uses a different port.

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8
Q

What is the breakdown of multiplexing/demultiplexing?

A

Each IP packet has a source IP address, destination IP address.

Each IP packet carries 1 transport layer segment/datagram

Each transport layer segment/datagram has source, destination port number

Host uses network layer IP address & transport layer port number to direct segment/datagram to appropriate socket

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9
Q

What does the UAPRSF stand for in TCP segment structure?

A

U- URG: urgent data
A- ACK #
P - PSH push data now
RSF - RST, SYN, FIN which are connection establishment (setup, teardown commands)

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10
Q

What does checksum mean in TCP segment structure?

A

Internet checksum such as UDP (User datagram protocol)

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11
Q

What is the receive window in TCP segment structure?

A

This is the # of bytes the rcvr is willing to accept

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12
Q

What is the sequence number and acknowledgement number counting by in TCP segment structure?

A

It is counting by bytes of data and not segments

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13
Q

What does ver, head len, type of service, time to live, upper layer and length mean in IP packet format?

A

ver - the ip protocol version number
head len - the header length
type of service - type of data
time to live - max number remaining hops this is decremented at each router
upper layer - the upper layer protocol to deliver payload to
length - total packet length

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14
Q

How much overhead with TCP?

A

20 bytes of TCP + 20 bytes of IP = 40 bytes + app layer overhead

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15
Q

What are ports 21, 23, 25, 69, 79, 80, 110 and 119 used for?

A

21 - FTP and is used for file transfer
23 - Telnet and is used remote login
25 - SMTP and is used for E-mail
69 - TFTP and is used for Trivial File Transfer Protocol
79 - Finger and is used for lookup info about a user
80 - HTTP and is used for World Wide Web
110 - POP-3 and is used for remote e-mail access
119 - NNTP and is used for USENET news

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16
Q

Is UDP is connectionless or connection-oriented?

A

It is connectionless

17
Q

What are UDP segments called?

A

They are called datagrams rather than segments

18
Q

Does the UDP provide virtual circuits and reliable communication?

A

No it doesn’t it leaves these to the application

19
Q

What can UDP be used for and why?

A

It can be used for multicasting and broadcasting since retransmissions are not possible to a large amount of hosts

20
Q

Why is UDP often used for real time multimedia communication?

A

Because it typically gives higher throughput and shorter latency.

21
Q

Which provides end to end reliable communication? UDP or TCP?

A

TCP through ARQ automatic repeat request protocol. This also provides flow control which can be combined with congestion control

22
Q

What is TCP used for?

A

HTTP web browsing and email transfer

23
Q

What are the different Internet transport layer protocols?

A

TCP (reliable in order delivery)
UDP (Unreliable, unordered delivery)

24
Q

What services aren’t available in Internet transport layer protocols?

A

Delay guarantees
Bandwidth guarantees

25
Q

What is the main value of having UDP over IP?

A

The addition of source and destination ports

26
Q

What does UDP provide to the IP protocol?

A

An interface with multiplexing/demultiplexing multiple processes using the ports, allowing multiple processes on a host to use the same IP address

27
Q

What is the no frills, bare bones Internet transport protocol?

A

UDP - User Datagram Protocol

28
Q

If the data link layer is reliable and has flow and error control, do we need this at the transport layer too?

A

Yes reliability at the data link layer is between two nodes, we need reliability between two ends. The network layer in the Internet is unreliable we need to implement reliability at the transport layer

29
Q

What is the goal of ARQ protocols?

A

To build a reliable protocol using an unreliable channel

30
Q

What is the stop and wait protocol?

A

A protocol in which the sender sends one frame and then waits for an acknowledgement before sending the next frame

31
Q

What is the Automatic Repeat reQuest protocol?

A

An error control method for data transmission which uses positive acknowledgments, timeouts, retransmissions and sequence numbers to achieve reliable data transmission

32
Q

What is the stop and wait ARQ protocol?

A

A protocol which uses the ARQ method and in which the communication is done one frame at time

33
Q

What does pipelining protocols do?

A

Increases efficiency (throughput) since the sender allows multiple in-flight, yet to be acknowledged frames

34
Q

What are two forms of pipelined protocols?

A

Go Back N, Selective Repeat

35
Q

What is the sliding window protocol?

A

A protocol in which the sender can have multiple unacknowledged frames. The sender and receiver each use a sliding window that defines the range of frame sequence numbers that is of concern to the sender/receiver

36
Q

What are examples of protocols in the transport layer?

A

Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)
Stream Control Transmission Protocol (SCTP)

Networks II (7 decks)

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