What does the Transport Layer header provide?

It identifies the segment of data and provides for identification of the Transport Layer Protocol to use.

Describe the process of segmentation and reassembly?

The process divides application data into blocks of data that are an appropriate size, then reassembles the data before sending it to the destination application or service.

How does the Transport Layer accomplish conversation multiplexing?

Each of these applications or services is assigned an address known as a port so that the Transport layer can determine with which application or service the data is identified.

Connection-oriented conversations

•  Reliable delivery
•  Ordered data reconstruction
•  Flow control

What are the four processes that the Transport Layer uses to control conversations?

 Establishing a Session

•  Reliable Delivery
•  Same Order Delivery
•  Flow Control

What does reliability mean to a network?

Ensuring that each piece of data that the source sends arrives at the destination.

What are the three basic operations of reliability at the transport layer?

 tracking transmitted data

•  acknowledging received data
•  retransmitting any unacknowledged data

What trade-off is necessary to ensure reliability?

The value of reliability and the burden it places on the network.

How is a best-effort protocol different than a reliable protocol?

There is no acknowledgement that the data is received at the destination.

What is another term used to describe a best-effort protocol?

Unreliable

List some examples of applications that require reliable transmission.

Databases, web pages, and e-mail

Give an example of an application that can use unreliable transmission.

Streaming video

What are the two most common protocols at the Transport Layer?

Transmission Control Protocol (TCP) and 

User Datagram Protocol (UDP)

What is the advantage of using UDP?

Speed

What are the pieces of UDP information called?

Datagram

What are some applications that use UDP?

Applications that use UDP include:

Domain Name System (DNS)

Video Streaming

Voice over IP (VoIP)

What are the 3 additional functions that TCP offers?

Same order delivery, reliable delivery, and flow control.

How much overhead is required to offer the 3 functions of TCP?

20 bytes

What are the pieces of TCP information called?

Segments

What are some applications that use TCP?

Applications that use TCP are:

Web Browsers

E-mail 

File Transfers

What are the unique identifiers that define the conversations called?

Port numbers

In the originating message what is the source port?

The number for this communication associated with the originating application on the local host.

In the originating message what is the destination port?

The number for this communication associated with the destination application on the remote host.

How do server processes have port numbers assigned?

Statically

How do clients have port numbers assigned?

Dynamically

What is another term sometimes used instead of port number?

Socket number

For this course, what does a socket pair describe?

The source and destination IP addresses and port numbers, is also unique and identifies the conversation between the two hosts.

What organization is responsible for assigning port numbers?

IANA Internet Assigned Numbers Authority

What is the range of Well Known Ports?

0 to 1023

What is the range of Registered Ports?

What is the range for Dynamic or Private Ports?

What are dynamic or private ports?

49152 to 65535

Is it possible for a port number to be used by both TCP and UDP?

yes

What is the utility that can be used to view open connections?

Netstat

What are the two reasons data is divided into pieces before it is sent?

This ensures that data is transmitted within the limits of the media, and that data from different applications can be multiplexed on to the media.

What is provided in a UDP header?

Port Numbers

What is provided in a TCP header?

Port, sequence, acknowledgement, and flow control numbers

In which protocol do segments arrive in an unspecified order?

UDP

What makes TCP a reliable protocol?

Connection-oriented sessions

What do acknowledgements do?

Let the sender know you received the data

What happens if the acknowledgment does not arrive in the predetermined time?

It retransmits that data to the destination.

What is the additional overhead created in the hosts by using TCP?

The necessity to keep track of which segments are awaiting acknowledgement and by the retransmission process.

Which device initiates the communication process?

Client

What can never happen in two server conversations?

Two services assigned to the same port number within the same Transport layer services.

What are the three steps in TCP connection establishment?

1. Client sends server a SYN request to synchronize sequence numbers. (Currently 0)
2. Server confirms by returning an ACK flag (the sequence number plus one).
3. Client sends ACK flag, connectiom is established.

What are the six control bit fields possible and what do they mean?

URG - Urgent pointer field significant

ACK - Acknowledgement field significant

PSH - Push function

RST - Reset the connection

SYN - Synchronize sequence numbers

FIN- No more data from sender

What is the Initial Sequence Number (ISN)?

The initial value for the sequence number is randomly chosen and is used to begin tracking the flow of data from the client to the server for this session

What is sent back to the client in step 2?

the server sends a segment back to the client with the ACK flag set indicating that the Acknowledgment number is significant

What is the value of the acknowledgment number field?

Equal to the client initial sequence number plus 1

Explain what is meant by 2 one-way sessions exist in TCP?

One from the client to the server, and the other from the server to the client

What is the final step in the three-way hand shake?

The client responds with both the sequence and acknowledgement bit set and no data.

What are 3 ways in which security can be added?

•  Denying the establishment of TCP sessions
•  Only allowing sessions to be established for specific services
•  Only allowing traffic as a part of already established session

What must be sent to close a TCP session?

FIN finish control flag

What are the 4 exchanges needed to close a TCP conversation?

1. When the client has no more data to send in the stream, it sends a segment with the FIN flag set.

. The server sends an ACK to acknowledge the receipt of the FIN to terminate the session from client to server.

. The server sends a FIN to the client, to terminate the server to client session.

. The client responds with an ACK to acknowledge the FIN from the server.

How does TCP reassemble packets into the original data file?

Sequence numbers are assigned in the header of each packet to achieve this goal

How are sequence numbers incremented?

The sequence number is incremented by the number of bytes that have been transmitted.

What does the receiving process do with the TCP segment?

The receiving TCP process places the data from a segment into a receiving buffer.

Where do the reassemble segments go?

To the Application Layer

What happens when all the segments do not arrive?

Any segments that arrive with noncontiguous sequence numbers are held for later processing.

What is the relationship between sequence and acknowledgement numbers work?

The sequence number indicates the relative number of bytes that have been transmitted in this session including the bytes in the current segment. TCP uses the acknowledgement number in segments sent back to the source to indicate the next byte in this session that the receiver expects to receive

What is the process TCP uses with sequence and acknowledgement numbers called?

Expectational acknowledgement

What does TCP do to overcome the overhead of waiting for acknowledgements?

Multiple segments of data can be sent before and acknowledged with a single TCP message in the opposite direction.

What is the name for the amount of data that can be sent before an acknowledgement is received called?

Window size

How does TCP handle missing segments?

When TCP at the source host has not received an acknowledgement after a predetermined amount of time, it will go back to the last acknowledgement number that it received and retransmit data from that point forward.

What do hosts implement today to improve the TCP process?

If both hosts support Selective Acknowledgements, it is possible for the destination to acknowledge bytes in discontinuous segments and the host would only need to retransmit the missing data.

How does flow control assist the reliability of TCP transmissions?

By adjusting the effective rate of data flow between the two services in the session. When the source is informed that the specified amount of data in the segments is received, it can continue sending more data for this session.

What does window size specify?

The amount of data that can be transmitted before an acknowledgement must be received.

How does TCP use window size to improve communication?

TCP feedback mechanism adjusts the effective rate of data transmission to the maximum flow that the network and destination device can support without loss. TCP attempts to manage the rate of transmission so that all data will be received and retransmissions will be minimized.

What happens to window size when network resources are constrained?

TCP can reduce the window size to require that received segments be acknowledged more frequently

What happens after periods of transmission with no data losses or constrained resources?

The receiver will begin to increase the window field.

What do you think occurs with window size on the school network when a major update occurs district wide? (smaller, larger)

The window size would get smaller

According to the first 2 paragraphs, what is the major advantage of using UDP?

Lower overhead

What are the key Application layer protocols that use UDP includes?

Domain Name System (DNS)

Simple Network Management Protocol (SNMP)

Dynamic Host Configuration Protocol (DHCP)

Routing Information Protocol (RIP)

Trivial File Transfer Protocol (TFTP)

Online games

Transaction based

How are TCP and UDP similar?

They both use port numbers

What happens to port numbers in a response from the server?

The source and destination port numbers in the datagram header are reversed.