II. OSI Transport Layer Flashcards
- Tracking the individual communications between applications on the source and destination hosts.
- Segmenting data and managing each piece.
- Reassembling the segments into streams of application data at the receiving host.
- Identifying the different applications using port numbers.
- Performing flow control between end users.
- Enabling error recovery
- Initiating a session
the primary responsibilities of the transport layer:
Numbering and sequencing the segments ensure that segments are reassembled into the proper order.
Reassembling Segments
an identifier to an application, used in the transport layer header to indicate to which application that piece of data is associated.
Port Number
each particular set of pieces flowing between a source application and a destination application
Conversation
____ can prevent the loss of segments on the network and avoid the need for retransmission.
Flow Control
ensure that all pieces reach their destination by having the source device retransmit any data that is lost.
Error Recovery
can provide connection orientation by creating a session between the applications.
Initiating a Session
is connectionless, and provide just the basic functions for efficiently delivering the data pieces between the appropriate applications.
useful for applications whose data is sensitive to delays.
UDP (User Datagram Protocol)
- connection-oriented
- describe processes that provide additional features, such as ensuring reliable delivery between the applications.
TCP (Transmission Control Protocol)
At the transport layer, the three basic operations of reliability are
- Tracking transmitted data
- Acknowledging received data
- Retransmitting any unacknowledged data
Additional functions of TCP
same-order delivery, reliable delivery, and flow control
Each segment has ___ bytes of overhead
20
To support these reliability operations, more ____ is exchanged between the sending and receiving hosts.
control data
simple, connectionless protocol
UDP
- has the advantage of providing low-overhead data delivery
- sends datagrams (segments of communication) as “best effort”
- each segment has only 8 bytes of overhead.
UDP
In UDP, it sends datagrams (segments of communication) as “____”
best effort
- the number for a communication associated with the originating application on the local host
- must not conflict with other ports in use at the time
- acts as a ‘return address’ of sorts for the requesting application
source port number
- the number for a communication associated with the destination application on the remote host
- assigned to the service daemon running on the remote host
destination port number
- combination of the transport layer port number and the network layer IP address assigned to the host
- uniquely identifies a particular process running on a specific host device
Socket
- assigns port numbers
- standards body that is responsible for assigning various addressing standards.
Internet Assigned Numbers Authority (IANA)
● An important network utility that can be used to verify which active TCP connections are open and running on a networked host
● Lists the protocol in use, the local address and port number, the destination address and port number, and the state of the connection
netstat Command
Use ____ to examine the open connections on a host when performance appears to be compromised.
netstat
Dividing data into manageable pieces ensures data is transmitted within the limits of the media
and can be multiplexed onto the media.
Segmentation and Reassembly
○ sequence numbers are used for reassembly at the destination in the correct order.
○ data is ensured to be in the exact form the sender intended.
TCP Segmentation and Reassembly
○ not concerned with order or maintaining a connection.
○ generates less overhead which means faster data transfer.
○ applications that use UDP must tolerate the fact that data may not arrive in the order that
it was sent.
○ does NOT require reliable delivery of packets.
UDP Segmentation and Reassembly
The key distinction between TCP and UDP is _____.
reliability
Before a host using TCP sends data to another host, the transport layer initiates a ______ with the destination.
process to create a connection
This connection enables ____, between the hosts.
the tracking of a session, or communication stream
This process ensures that each host is____ for the communication.
aware of and prepared
When two hosts communicate using TCP, a ____ is established before data can be exchanged.
connection
After the communication is completed, the ___ and the connection is terminated.
sessions are closed
● Establishes that the destination device is present on the network.
● Verifies that the destination device has an active service and is accepting requests on the
destination port number that the initiating client intends to use for the session.
● Informs the destination device that the source client intends to establish a communication session
on that port number.
TCP Three-Way Handshake
If an acknowledgement isn’t sent that data was received, the host will ____ the data because it has reached a timeout.
Resend
the amount of data a source can transmit before an ACK must be received. It enables the mgt. of lost data and flow control.
Window size
also known as ephemeral ports, are
usually assigned dynamically to client applications when initiating a connection.
Dynamic or Private Ports
is a standards body that is responsible for assigning various addressing standards.
Internet Assigned Numbers Authority (IANA)
