14 - communincation Flashcards
protocol
- set of rules governing communication across a network - agreed by
both sender and recipient
need for protocols
- both parties need to agree on the protocol to ensure communication is successful
- without agreeing cant use parity checking
TCIP/IP
DARPA Layers
Application
Transport
Internet
Link network
↓sending ↑receiving
TCIP/IP +
+ layers breaks down the process into manageable self contained modules (DECOMPOSITION)
+ its easier to develop and make hardware/ software compatible
application layer
- what the user sees
- contains programs that exchange data eg web browsers of server software
- sends files to transport
- includes: HTTP, SMTP, POP, IMAP, DNS, FTP, RIP, SNMP
HTTP
hypertext transfer protocol
- for transferring files that make up web pages on the WWW
- uses hyperlinks
- client server
HTTP process - how its used to request resources
- User types URL
- HTTP transmits request from application to transport (TCP)
- TCP creates packet and sends to destination ports
- DNS server uses domain name to look up IP address
- Server TCP sends back acknowledgement
- Now communication has been established the web server sends the web page back in HTML to the browser
- Browser displays page
SMTP
simple mail transfer protocol
- sending emails
- text based
- push protocol
- no binary files eg media/ images/ video/ music - need to use MIME (multi purpose internet mail extension)
push protocol
eg SMTP
a client opens connection with server and keeps the connection active, then the client uploads a new email
pull protocol
eg POP and IMAP
client connects to server, checks for and downloads new emails, connection is then closed - this is the repeated
POP
Post office protocol
- recieving emails
- pull protocol
IMAP
Internet message access protocol
- recieving emails
- pull protocol
POP vs IMAP
- POP doesn’t keep server and client synchronised - when emails are downloaded they are deleted from the server
- IMAP - is synchronisation - a copy remains on the server
FTP
file transfer protocol
- Used to transfer files from one device to another via internet/ networks
FTP features
- Anonymous ftp - allows the user to access without identifying themself
- Ftp commands - a user can carry out actions that change files on an ftp server eg delete, close, rename
- Ftp server - where files are stored
packet
a message/data is split up into smaller groups of bits for transmission over a network.
MIME
multi-purpose internet mail extension. A protocol that allows email attachments containing media files as well as text to be sent
binary file
a file that does not contain text only. The file is machine-readable but not human- readable.
transport
- Regulates network connections
- data is broken into packets
- Adds segment number and port number
- Ensures packets arrive in sequence without errors - swap acknowledgments and retransmit corrupted/lost packets
Includes: TCP, UDP, SCTP
TCP
- responsible for safe delivery of messages by creating sufficient packets
- positive acknowledgement - PAR - automatically resends packets if it doesn’t receive acknowledgment
- Connection oriented - establishes end-to-end connection between hosts
- Host to host - connects hosts using handshakes
steps in connection TCP
- Host1 sends host2 a segment (including synchronisation sequence bits to ensure correct order)
- Host2 responds by sending back a segment (containing acknowledgement and its own synchronisation sequence bits)
- Host1 sends out its acknowledgement that the segment was received
- Transmission between 1 and 2 now takes place
internet
- Identifies the intended network and host
- Uses IP
IP functions
- Ensures correct routing of packets
- Takes packet from transport - adds its own header (inc IP address of sender/ recipient)
- IP packets (datagram) is sent to data-link layer where it assembles datagrams into frames
network / link layer
- Identifies and moves traffic across local segments
- encapsulates IP packets into frames for transmission
- Maps IP to MAC and ensures correct protocols
- Physical network layer - specifies requirements of hardware to be used
- Data link layer - identifies protocols in the packet header (TCP/IP in this case) and delivers packets to network