Chapter 14 Study Guide

Well-known Ports

0 to 1,023

Control bits

A 6-bit field used that includes bit codes, or flags, which indicate the purpose and function of the TCP segment.

Registered Ports

1,024 to 49,151

Which number or set of numbers represents a socket?

192.168.1.1:80

Do the below characteristics describe TCP, UDP or both?

3-way handshake - TCP Window size - TCP Connectionless - UDP Best for VoIP - UDP Port numbers - TCP / UDP Checksum - TCP / UDP Four exchanges to end session - UDP Sequence numbers - TCP / UDP Acknowledgments - TCP

Private and/or Dynamic Ports

49,152 to 65,535

Length

A 16-bit field that indicates the length of the UDP datagram header.

Checksum

A 16-bit field used for error checking of the datagram header and data.

Checksum

A 16-bit field used for error checking of the segment header and data.

Destination Port

A 16-bit field used to identify the destination application by port number.

Source Port

A 16-bit field used to identify the source application by port number.

Urgent

A 16-bit field used to indicate if the contained data is urgent.

Window size

A 16-bit field used to indicate the number of bytes that can be accepted at one time.

Sequence Number

A 32-bit field used for data reassembly purposes.

Acknowledgment Number

A 32-bit field used to indicate that data has been received and the next byte expected from the source.

Header Length

A 4-bit field known as ʺdata offsetʺ that indicates the length of the TCP segment header.

Reserved

A 6-bit field that is reserved for future use.

ACK

Acknowledgment flag used in connection establishment and session termination

What is SACKs used for?

Alleviates congestion from retransmission of lost packets, by identifying and only resending missed information rather than all of the information

What is window size and how is it determined?

An advertisement of how much data the receive devices is willing to receive. It is determined via checksum

Which entities are involved in a temporary communication that is established by the transport layer?

Applications

Provides Same-Order Delivery

Because networks may provide multiple routes that can have different transmission rates, data can arrive in the wrong order.

Which two applications use UDP as the transport layer protocol? (Choose two.)

DHCP DNS queries

What applications use UDP?

DNS, Streaming, Gaming, VOIP

What are ephemeral ports?

Dynamic / private ports

Do the below applications use TPC or UDP?

FTP - TCP TFTP - UDP SSH - TCP VoIP - UDP SNMP - UDP HTTP - TCP SMTP - TCP DNS - UDP DHCP - UDP Telnet - TCP

Ensures Reliable Delivery

For many reasons, it is possible for a segment to become corrupted or lost completely, as it is transmitted over the network. TCP ensures that each segment that is sent by the source arrives at the destination.

What does the transport layer add to a PDU?

Header / Trailer

How does UDP reassemble packets that is more than one datagram in length?

In the order that it was recieved

How does TCP reassemble packets that is more than one datagram in length?

In the original order

Why do we use multiplexing?

Increases efficiency of data transmission, therefore lowering costs

When using TCP what happens if part of the message is lost?

It is detected and then retransmitted

Which three fields are used in a UDP segment header?

Length Checksum Source Port

Supports Flow Control

Network hosts have limited resources (i.e., memory and processing power). When TCP is aware that these resources are overtaxed, it can request that the sending application reduce the rate of data flow.

FIN

No more data from sender and used in session termination

When using UDP what happens if part of the message is lost?

Nothing, the data is lost

What is the primary purpose of the transport layer?

Providing an end to end connection with as little errors as possible

PSH

Push function

RST

Reset the connection when an error or timeout occurs

What is it called when we combine the source IP address and source port number, or destination IP address and destination port number?

Sockets

Match the TCP flag to the correct step in the session establishment sequence.

Step 1 - SYN Step 2 - SYN + ACK Step 3 - ACK

SYN

Synchronize sequence numbers used in connection establishment

establishes a Session

TCP is a connection-oriented protocol that negotiates and establishes a permanent connection (or session) between source and destination devices prior to forwarding any traffic.

Which action is performed by a client when establishing communication with a server via the use of UDP at the transport layer?

The client randomly selects a source port number.

What happens if part of an FTP message is not delivered to the destination?

The part of the FTP message that was lost is re-sent.

What are the ACK, SYN and FIN flags used in and for?

They are used in packet transmission and are used for tracing the route that IPs take

What are the advantages UDP has over TPC and vice versa?

UDP -has smaller packets, -is connectionless -and has more control TCP - has less corruption, - retransmission - and in order delivery

What are the characteristics of UDP and TCP?

UDP - Datagram oriented protocol Not 100% reliable basic error checking No sequencing of data Faster No retransmission 8 bytes fixed header length Lightweight Supports broadcasting DNS, DHCP, TFTP, SNMP, RIP, and VoIP.

What is an advantage of UDP over TCP?

UDP communication requires less overhead.

URG

Urgent pointer field significant

What are the three port groups, number range and description of the ports the transport layer uses?

Well known - 0 through 1023, controlled and assigned by IANA Registered - 1024 through 49151 - Not controlled by, but LOGGED by IANA Dynamic / private - 49152 through 65535 - IANA gives no information on these

Why would an application use UDP?

When an application requires lossless data transmission, or when transferring a large file

What are sequence numbers and acknowledgment numbers used for?

enable ordered reliable data transfer for TCP streams.

TCP connection-oriented protocol

is reliable provides extensive error checking sequencing of data slower retransmission 20-80 bytes header length Heavy weight Doesn't support broadcasting HTTP, HTTPs, FTP, SMTP and Telnet.

When a client connects to an HTTP server by the use of a randomly generated source port number, what destination port number will the HTTP server use when building a response?

the original source port number that was randomly generated by the client

What is the purpose of using a source port number in a TCP communication?

to keep track of multiple conversations between devices