ITN 101 TCC CH2
The destination port field of the TCP message
When the HTTP program sends an HTTP response message to a client PC, in what field of what message will it place the value 80?
Segment
What is the TCP PDU called?
Datagram
What is the UDP PDU called?
IETF
What is the standards agency for TCP/IP?
None
What kind of message does the destination host send if it does it receive a segment that has an error during a TCP connection?
None
What kind of message does the destination host send if it does not receive a segment during a TCP connection?
Timing (what happens when; ex. Flow control) Semantics (what means what; ex. flags) Syntax (what goes where; ex. Ethernet frame bits 0-16 are part of the preamble)
What three main things must communications protocols govern? Describe what each means, and give an example.
Reliable and connection oriented
What type of communication does TCP have (connection/reliability)?
Unreliable and connectionless
What type of communication does UDP have (connection/reliability)?
Sequence number, acknowledgement number, source and destination port numbers
What are the major header fields for a TCP segment?
Source and destination port numbers
What are the major header fields for a UDP datagram?
Source and destination MAC address
What are the major header fields for an Ethernet frame?
Source and destination IP address
What are the major header fields for an IP packet?
a header, a data field, and a trailer
What are the three general parts of messages?
Router
What device in an internet besides the destination host reads the destination IP address?
switches
What devices read Ethernet destination MAC addresses?
Protocol data units
What does PDU stand for?
Three way handshake; syn, syn/ack, ack
What does TCP use to open a connection?
the content being delivered by a message
What does the data field contain?
255
What is 11111111 in base 10?
Placing a message in the data field of another message
What is encapsulation
Converting messages into bits at the application layer
What is encoding?
Semantics
What a message means
Application programs
What are a server's port numbers associated with?
2N
...
Data field
As a message is encapsulated from the application layer to the transport layer, in which field in the transport layer is the message from the application layer placed?
Bigger
As a packet gets encapsulated does it get bigger or smaller.
None
At layer 1, what is the PDU called?
Frame
At layer 2, what is the PDU called?
Packet
At layer 3, what is the PDU called?
Data link
At which layer would Ethernet standard be used?
Application
At which layer would the HTTP standard be used?
Network
At which layer would the IP standard be used?
Transport
At which layer would the User Datagram Protocol (UDP) standard be used?
Transport
At which layer would the transmission control protocol (TCP) standard be used?
Connection-oriented
Connections with distinct openings and closings
The simple message ordering: client sends request, and then server sends response.
Describe the simple message ordering in HTTP.
Host A sends SYN; Host B sends SYN/ACK; Host A sends ACK
Describe the three-way handshake in TCP connection openings.
Semantics is what a message means; syntax is how a message is organized.
Distinguish between syntax and semantics.
Syntax
How a message is organized
It would discard one of the duplicated segments
How do you think TCP would handle the problem if an acknowledgement were lost, so that the sender retransmitted the unacknowledged TCP segment, therefore causing the receiving transport process to receive the same segment twice?
48 bits
How long are Ethernet MAC addresses?
128 bits
How long is an IPv6 address?
64
How many characters can be represented by 6 bits?
2n
If a field is N bits long, how many alternatives can it represent?
The receiver would discard the frame.
If the receiver detects an error on the basis of the value in the Frame Check Sequence field, what does it do?
7 bits
If you need to represent 128 alternatives in a field, how many bits long must the field be?
No
In HTTP, can the server transmit if it has not received a request message from the client?
No
Is there always a data field in a message?
Repeater or hubs (uncommon)
Layer 1 typical device
Switches or bridges
Layer 2 typical device
Routers; layer 3 switches
Layer 3 typical device
Layer 4 switches
Layer 4 typical devices
Client and server hosts
Layer 7 typical devices
FTP-file transfer protocol SMTP-simple message transfer protocol http-hypertext transfer protocol
List 5 application layer protocols by acronym, expanded name, and function.
Detects and corrects errors
Network reliability
Network standards
Rules of operation that govern the exchange of messages between two hardware or software processes.
False
The SPOT satellite tracking device shown in class assumes an underlying reliable data communications system.
If it does not receive and ACK message from the destination host
Under what conditions will a source host TCP process retransmit a segment?
Layer 2; datalink
Which layer has a header and a trailer?
Application
Which layer has the most standards?
20 or 21
Which port is used for FTP?
80
Which port is used for HTTP (web server)?
25
Which port is used for SMTP (e-mail)?
It does this so that it can apply sequence numbers to segements which are later used for error correction.
Why does TCP use a three-step handshaking protocol (also called a three-way opening) to establish connections?
The trailer is used for error detection. If there is an error, the packet is discarded.
Why does only the data link layer typically have a trailer in its protocol data unit?
This allows layer 4 to pass clean data to the application layer regardless of errors at lower levels and error correction is only done once on the two hosts which reduces how much resources are used for error correction.
Why make only layer 4 reliable?
11 bits
You need to represent 1,026 different city names. How many bits will this take if you give each city a different binary number?
