chapter 14

what are protocols

set rules for data transmission which are agreed by the sender and receiver 

what are some features of a protocol stack

Each layer can only accept input from the layer higher or lower than it. A layer may have sub-layers; only the bottom layer is hardware/ has direct access to the hardware, and user interactions occur with the first layer’s protocols in place

what is the files transfer protocol (FTP)

it’s used to transfer files between a client/server over the internet, and its only job is the application protocol for the transfer of files

what is the hypertext transfer protocol (HTTP)

it transfers web pages from the WWW to web servers to clients, it’s in charge of transferring the correct data and it uses client/server protocol

what is a pro of HTTP 

it uses secure addresses that have been encrypted 

what is a client/server protocol 

when request messages are sent to the web server which then responds 

what is the simple mail transfer protocol (SMTP)

It’s used when sending emails, and it doesn’t handle binary files; it’s computer-readable only

what extension is needed for binary files

A multi-purpose internet email extension (MIME) for media/images / music 

what is SMTP sometimes known as

a push protocol, a client opens a connection to a server - which is kept active - then the client uploads a new email to the server 

the layers of TCP/IP protocols

the application layer, transport layer, internet/network layer and the data-link layer 

what is post office and internet message access protocol (P0P3 & IMAP)

it’s used when receiving emails from the email server, where mail is held by a remote server until you download it and uses pull protocol 

what is a pull protocol 

when a client connects to a server, checks for downloads and new emails, and then the connection is closed. this is repeated to ensure the client is updated 

how does POP3 work compared to IMAP 

it doesn’t keep the server and client synchronised so when emails are downloaded they are deleted by the server / no longer updates 

how does IMAP work compared to POP3

it’s more recent, keeping the client/ server synchronised as clients download a copy while the server holds the original until the client deletes it 

what is the application layer 

it contains all the programs that exchange data and it sends files to the transport layer. It allows applications to access services used in other layers and defines the protocols that any app uses 

what is the transport layer

It monitors network connections where data is broken up into packets and sent to the internet/ network layer. It ensures packets arrive in sequence and without errors via acknowledgements and retransmission 

what is the internet/ network layer and network / data-link layer 

they identify the intended network and host and it’s main protocol is internet protocol (IP)

what is the transmission control protocol (TCP)

it creates packets that hold headers to ensure data is delivered safely, and it uses PAR to automatically re-send a data packet if a positive acknowledgement hasn’t been received 

what’s a function of the internet protocol (IP)

it takes packets from the transport layer and adds a header (including the IP addresses of the sender and receiver) to ensure correct routing. The data link layer then turns the datagrams (packets) into frames for transmission.

what is the BitTorrent protocol

a protocol based on the P2P networking concept, it’s the most used protocol because it allows files to be shared quickly/ directly to other user computers rather than a web server 

what’s the difference between P2P file sharing and BitTorrent protocol 

P2P is better for a small number of computers while BitTorrent can be used by thousands of users who connect together over the internet 

how does the BitTorrent protocol work 

a bitTorrent client saves a .torrent file and contacts a tracker specified in the file. Once connected the client downloads bits of the file in small pieces and uploads the data to other bitTorrent clients in the swarm. Each downloader contributes upload bandwidth to other downloads, letting the torrent stay fast

what is a swarm

a group of peers

what is a seed

a peer that downloads a file and makes it available to other peers in the swarm

what’s a tracker

a central server that stores details about other computers that make up the swarm , allowing peers to locate each other

what is a leech

a peer that has a neg impact on the swarm by downloading more than they are uploading 

what is a lurker

a peer that downloads files but doesn’t make any new content

when is circuit switching used

PTSN

how does circuit switching work 

a dedicated channel is established, data transfer takes place, and once complete, the connection is terminated. 

what are some pros of circuit switching

Data transfer is quicker than it is with packet switching, frames arrive in the same order they were sent, a packet of data can’t get lost because all follow the same sequence along a singular route, and it works better for real-time applications

what are some cons of circuit switching

It has to use a single/dedicated line and will send empty frames (not flexible). No one else can connect to the channel, even when it’s idle. If there’s a failure on the dedicated line, there’s no alternative routing. Establishing the link can take a while, and it charges users based on distance and duration of connection 

when is circuit switching best used

for voice communication that requires real-time services without much delay 

where is packet switching used 

VoIP

what is packet switching 

when a message is broken up into several packets that can be sent independently before being reassembled at the destination. It doesn’t need to establish a connection and it's available to many but may lead to congestion in the network

what are the pros of packet switiching

doesn’t tie up the communication line, can re-route if the line fails or is faulty, easy to expand traffic usage, only charges users for duration of connection, and uses digital  networks so digital data is transmitted directly to destination 

what are the cons of packet switching 

Protocols can be more complicated than circuit switching, if a packet is lost the user must re-send which wastes time, it doesn’t work well with real-time data streams, it needs a large amount of RAM when handling large data and there are delays when packets need to reassemble 

when is packet switching best used

for data and voice applications that require non-real-time scenarios

what may occur when transmitting packets to routers

They may get lost and stuck in a loop from bouncing from one router to the next, overtime this would clog the system. To overcome this, hopping is used

what is hopping

when a hop number is added to the header of each data packet. Everytime a router is passed this number is decreased, and when it’s 0, it will be deleted at the next router.

what is the function of a router

it examines the packet header, reads the IP address of destination and decides the best route/ sends the packets on its next hop