Networking: Transport and Application Layers Flashcards
ACK flag
One of the TCP control flags. ACK is short for acknowledge. A value of one in this field means that the acknowledgment number field should be examined
Acknowledgement number
The number of the next expected segment in a TCP sequence
Application layer
The layer that allows network applications to communicate in a way they understand each other
Application layer payload
The entire contents of whatever data applications want to send to each other
CLOSE
A connection state that indicates that the connection has been fully terminated, and that no further communication is possible
CLOSE_WAIT
A connection state that indicates that the connection has been closed at the TCP layer, but that the application that opened the socket hasn’t released its hold on the socket yet
Connection-oriented protocol
A data-transmission protocol that establishes a connection at the transport layer, and uses this to ensure that all data has been properly transmitted
Connectionless protocol
A data-transmission protocol that allows data to be exchanged without an established connection at the transport layer. The most common of these is known as UDP, or User Datagram Protocol
Data offset field
The number of the next expected segment in a TCP packet/datagram
Demultiplexing
Taking traffic that’s all aimed at the same node and delivering it to the proper receiving service
Destination port
The port of the service the TCP packet is intended for
ESTABLISHED
Status indicating that the TCP connection is in working order, and both sides are free to send each other data
FIN
One of the TCP control flags. FIN is short for finish. When this flag is set to one, it means the transmitting computer doesn’t have any more data to send and the connection can be closed
FIN_WAIT
A TCP socket state indicating that a FIN has been sent, but the corresponding ACK from the other end hasn’t been received yet
Firewall
It is a device that blocks or allows traffic based on established rules
FTP
An older method used for transferring files from one computer to another, but you still see it in use today
Handshake
A way for two devices to ensure that they’re speaking the same protocol and will be able to understand each other
Instantiation
The actual implementation of something defined elsewhere
Listen
It means that a TCP socket is ready and listening for incoming connections
Multiplexing
It means that nodes on the network have the ability to direct traffic toward many different receiving services
Options field
It is sometimes used for more complicated flow control protocols
Port
It is a 16-bit number that’s used to direct traffic to specific services running on a networked computer
Presentation layer
It is responsible for making sure that the unencapsulated application layer data is actually able to be understood by the application in question
PSH flag
One of the TCP control flags. PSH is short for push. This flag means that the transmitting device wants the receiving device to push currently- buffered data to the application on the receiving end as soon as possible
RST flag
One of the TCP control flags. RST is short for reset. This flag means that one of the sides in a TCP connection hasn’t been able to properly recover from a series of missing or malformed segments
Sequence number
A 32-bit number that’s used to keep track of where in a sequence of TCP segments this one is expected to be
Server or Service
A program running on a computer waiting to be asked for data
Session layer
The network layer responsible for facilitating the communication between actual applications and the transport layer
Socket
The instantiation of an endpoint in a potential TCP connection
Source port
A high numbered port chosen from a special section of ports known as ephemeral ports
SYN flag
One of the TCP flags. SYN stands for synchronize. This flag is used when first establishing a TCP connection and make sure the receiving end knows to examine the sequence number field
SYN_RECEIVED
A TCP socket state that means that a socket previously in a listener state, has received a synchronization request and sent a SYN_ACK back
SYN_SENT
A TCP socket state that means that a synchronization request has been sent, but the connection hasn’t been established yet
TCP checksum
A mechanism that makes sure that no data is lost or corrupted during a transfer
TCP segment
A payload section of an IP datagram made up of a TCP header and a data section
TCP window
The range of sequence numbers that might be sent before an acknowledgement is required
URG flag
One of the TCP control flags. URG is short for urgent. A value of one here indicates that the segment is considered urgent and that the urgent pointer field has more data about this
Urgent pointer field
A field used in conjunction with one of the TCP control flags to point out particular segments that might be more important than others
