Week 3 Flashcards

1
Q

What sets the transport layer apart from the other layers?

A

That multiplexing and demultiplexing take place in it.

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2
Q

What is the medium through which multiplexing and demultiplexing take place?

A

Ports

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3
Q

Port

A

A 16 bit number that’s used to direct traffic to specific services running on a networked computer.

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4
Q

Destination port

A

The port of the service the traffic is intended for

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5
Q

Source port

A

A high-numbered port chosen from a special section of ports known as ephemeral ports

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6
Q

Sequence number

A

A 32 bit number that’s used to keep track of where in a sequence of TCP segments this one is expected to be

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7
Q

Acknowledgement number

A

The number of the next expected segment

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8
Q

Data offset field

A

A 4 bit number that communicates how long the TCP header for this segment is

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9
Q

TCP window

A

Specifies the range of sequence numbers that might be sent before an acknowledgement is required

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10
Q

TCP checksum

A

Operates just like the checksum fields at the IP and the Ethernet level

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11
Q

Urgent pointer field

A

Used in conjunction with one of the TCP control flags to point out particular segments that might be more important than others.

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12
Q

Options field

A

Sometimes used for more complicated flow control protocols

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13
Q

Padding

A

Same as network level padding in datagram header. Series of zeroes to ensure header is correct length so payload begins at right point of the TCP segment

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14
Q

URG (Urgent) flag

A

A value of one here indicates that the segment is considered urgent and that the urgent pointer field has more data about this

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15
Q

ACK (Acknowledged) flag

A

A value of one in this field means that the acknowledgement number field should be examined

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16
Q

PSH (Push) flag

A

The transmitting device wants the receiving device to push currently-buffered data to the application on the receiving end as soon as possible

17
Q

RST (Reset) flag

A

One of the sides in a TCP connection hasn’t been able to properly recover from a series of missing or malformed segments

18
Q

SYN (Synchronized) flag

A

It’s used when first establishing a TCP connection and makes sure the receiving end knows to examine the sequence number field

19
Q

FIN (Finish)

A

When this flag is set to one, it means the transmitting computer doesn’t have any more data to send and the connection can be closed

20
Q

Handshake

A

A way for two devices to ensure that they’re speaking the same protocol and will be able to understand each other

21
Q

Socket

A

The instantiation of an end point in a potential TCP connection

22
Q

Instantiation

A

The actual implementation of something defined elsewhere

23
Q

LISTEN

A

A TCP socket is ready and listening for incoming connections

24
Q

SYN_SENT

A

A synchronization request has been sent, but the connection hasn’t been established yet

25
Q

SYN_RECEIVED

A

A socket previously in a a LISTEN state has received a synchronization request and sent a SYN/ACK back

26
Q

ESTABLISHED

A

The TCP connection is in working order and both sides are free to send each other data

27
Q

FIN_WAIT

A

A FIN has been sent, but the corresponding ACK from the other end hasn’t been received yet

28
Q

CLOSE_WAIT

A

The connection has been closed at the TCP layer, but the application that opened the socket hasn’t released its hold on the socket yet

29
Q

CLOSED

A

The connection has been fully terminated and that no further communication is possible

30
Q

Connection oriented protocol

A

Establishes a connection, and uses this to ensure that all data has been properly transmitted

31
Q

Port 0

A

Not in use for network traffic, but is sometimes used in communications between programs on the same computer

32
Q

Ports 1 - 1023

A

System ports, or well-known ports : represent official ports for most well known network services such as HTTP

33
Q

Ports 1024 - 49151

A

Registered ppoets: could be used for less common network services that may or may not be registered and acknowledged by IANA : a lot of databases listen on port 3306

34
Q

Ports 49152 - 65535

A

Private or ephemeral ports : can’t be registered with IANA and are used for establishing outbound connections : no modern OS will ever use a system port for outbound communication

35
Q

Firewall

A

A device that blocks traffic that meets certain criteria : can be used at many of the layers but are primarily used at the transport layer

36
Q

Session layer in the OSI model

A

Facilitates the communication between actual applications and the transport layer

It takes application layer data and hands it off to the presentation layer

37
Q

Presentation layer

A

Responsible for making sure the unencapsulated application layer data is able to be understood by the application in question