ITNv7 Lesson 14 Transport Layer

Window size

The number of bytes that the sender will send prior to expecting an acknowledgement from the destination device.

It is agreed upon during the session startup via the three-way handshake between source and destination. It is determined by how much data the destination device of a TCP session is able to accept and process at one time.

UDP header

Consists of only the Source Port, Destination Port, Length, and Checksum fields. Sequence Number, Acknowledgment Number, and Window Size are TCP header fields.

Transport layer responsibilities

Tracking the individual communication streams between applications on the source and destination hosts

Segmenting data at the source and reassembling the data at the destination

Identifying the proper application for each communication stream through the use of port numbers

sequence numbers

used by TCP to reassemble and reorder received segments

destination and source port numbers

added to the TCP/IP transport layer header to ensure communication and connectivity with a remote network device

TCP

Provides tracking of transmitted data segments· Destination devices will acknowledge received data.· Source devices will retransmit unacknowledged data.

UDP

Provides basic connectionless transport layer functions

Relies on application layer protocols for error detection

Low overhead causing minimal delay

Does not provide sequencing or flow control mechanisms.

Provides no means for acknowledgement of received data

Terminating a TCP communication session

Client sends FIN

Server sends ACK

Server sends FIN

Client sends ACK

3-Way Handshake (TCP)

Client sends SYN

Server sends ACK, SYN

Clients sends ACK

What happens when a device receives a segment with the FIN flag set?

The connected device that receives the segment will respond with an ACK to acknowledge that segment.

What common protocol uses both TCP and UDP?

DNS

Registered port

Port that must be requested from IANA in order to be used with a specific application

Well known ports

port numbers in the range of 1-1024 that identify network applications that are well known such as web, email, and remote login applications

Private and/or Dynamic Ports

Port numbers 49152-65535

Which three application layer protocols use TCP?

SMTP, FTP, and HTTP

Fields that are included in the TCP header but not in the UDP header

sequence number, window, acknowledgement number, control bits, reserved, urgent, options

control bits

Field in the TCP header indicates the status of the three-way handshake process

Why do some protocols use TCP?

Because transmission reliability and completeness must be guaranteed

How are port numbers used in encapsulation?

The source port number is used to track the separate conversations, if multiple conversations occur that are using the same service

What type of applications are best suited for using UDP?

Applications that handle reliability themselves

Applications that can tolerate some data loss, but require little or no delay

What type of applications are best suited for using TCP?

Applications that require reliable delivery

Applications that need data flow control

Applications that need the reordering of segments

multiplexing

A form of transmission that allows multiple signals to travel simultaneously over one medium.

Best-effort protocol

A connectionless protocol.

Stateless Protocol

Doesn't require a server to retain the information of a session or the status of every communicating partner in multiple requests.

connectionless protocol

A type of Transport layer protocol that services a request without requiring a verified session and without guaranteeing delivery of data.

flow control

A method of gauging the appropriate rate of data transmission based on how fast the recipient can accept data.

Socket

Combination of the Source IP address and source port number

Port 20

FTP Data

Port 21

FTP Control

Port 22

SSH

Port 23

Telnet

Port 25

SMTP

Port 53

DNS

Port 67

DHCP server

Port 68

DHCP Client

Port 69

TFTP

Port 80

HTTP

Port 110

POP3

Port 143

IMAP

Port 161

SNMP

Port 443

HTTPS

Sliding window

A type of data window in which block sizes are variable. Window size is continually reevaluated during transmission, with the sender always attempting to send the largest

window it can to speed throughput.

MSS

Specifies the largest amount of data the device can receive in a single TCP segment