TCP/IP protocol
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What are the layers of the TCP/IP stack from top to bottom
• application layer • transport layer • internet layer • link layer
Purpose of the application layer
Uses protocols designed to work with specific types of applications E.g. web browser uses HTTP, email client uses SMTP, IMAP and POP3
What is the purpose of the transport layer
Breaks the application data down into segments(TCP) and datagrams(UDP) Sequence numbers allocated, source and destination port numbers are added to header. For TCP, delivery acknowledged and lost segments retransmitted
Purpose of the internet/network layer
Encapsulates segments from the transport layer to create IP Packets. Source and destination IP addresses are added at this stage
Purpose of link layer
• Responsible for transporting IP packets across each individual link that make up path between client and server • Further encapsulates IP packets in Ethernet frames • At this level, networking protocols are used
Names of data block produced by each layer
Application- application data (HTTP, SMTP) transport - segments or datagrams Internet - Packets Link - Frames
What protocols does the transport layer use
Transmission control protocol and user datagram protocol
What does the TCP do
• keeps track of each generated segment, assigning a sequence number • at receiving end, TCP keeps record of incoming sequence numbers & acknowledges each segment • if sender doesn’t receive an acknowledgement, segment is resent
What does the UDP do
Transfers data at a fast rate
Uses of TCP compared to uses UDP
TCP - when complete data is required (reliable) UDP - when speed of data transfer is the most important criteria (unreliable)
What is a socket
A combination of an IP address and a port number. Persists throughout duration of the connection
What is the max amount of connections a server can keep track of
65, 534 per host
What does the socket facilitate
Asynchronous communication, meaning only one device can communicate at a time
What are the well-known port numbers
Port - protocol - use 20 - FTP(Data) - file transfer 21 - FTP(Control) - file transfer 22 - SSH - Secure remote access 25 - SMTP - Mail transfer 80 - HTTP - Website access 110 - POP - Mailbox access 143 - IMAP - Mailbox access 443 - HTTPS - Secure website access
What is a MAC address
Unique to a specific NIC Physically tied to hardware of computer often referred to as physical address
What does HTTP do
Requests web pages and linked resources from the web server
How does HTTP operate
Through requests and responses: - server waits and listens for requests - client sends HTTP request for web page to server - server receives the request - server sends HTTP response which encapsulates requested page - client receives response and displays web page in web browser
What are the extra steps for the HTTP operation for dynamic pages
• database may be accessed for up-to-date images and prices for online shopping • profile may be accessed for more personalised content • processing may happen on client-side
What are the HTTP request methods
GET - request data from resource POST - submit data, create new resource PUT - update/replace an existing resource DELETE - removes a resource from server HEAD - requests just header of data from server
What does HTTPS do
Encrypts data exchanged between client and server
How does HTTPS work
• Provides digital certificate containing public encryption key. • authenticity is checked automatically in browser through number of root certificates • your browser uses key to encrypt data • only the authorised server has corresponding private key to decrypt it
What does the FTP do
Used to move files between 2 devices
How does the FTP work
Client-server application: - client device runs FTP client software, responsible for initiation of all connections - another device runs the FTP server & has access to disk space to store the files
What can a user do once logged into the FTP client software
• access directories on FTP server & request list of files in directory • user can choose to download or upload file