Network Layers - the OSI model
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14 Terms
OSI
Open Systems Interconnection - internationally agreed standard describing how data is transmitted from one device to another
How many OSI layers are there?
5, which organise and synchronise data exchange (2 - 5 are conceptual)
Layer 1 of the OSI model
Physical - The cabling and the ports the cables are connected to. A carrying path.
What is most internal cabling these days?
CAT-6 (ethernet)
Layer 2 of the OSI model
Data link layer - where the correct receiving addresses are matched with the correct sending addresses.
What is layer 2 used for?
To find the MAC address of the correct devices.
What is Ethernet?
A network protocol used on the data link layer that defines when to transmit, transmission speeds and media. It has transfer speeds of more than a gigabit per second.
What does the second protocol on the data link layer do?
Ensures an address can only have one set of packets arriving at it at a time, avoiding cross-talk / data mix-up.
Layer 3 - OSI model
Network Layer - IP is used on this layer to find the correct network.
What do routers do?
They hold tables of IP addresses and use them to send data packets to the right address. If their table does not hold the required address, they pass the data packet to another router.
How many attempts are there before a data packet is discarded?
64, but can be 0 - 255. Time to Live variable used.
Layer 4 - OSI model
Transport Layer - where data is broken down into packets. Transmission Control Protocol (TCP) used.
What are acknowledgements used for?
To make sure the connection is in a proper state (packets in order, data error-free), every time a communication is made between devices. Necessary for connections that need accurate data transfer (phone calls).
Layer 5 - OSI model
Application Layer - Various protocols are used on this layer, to do with the applications the data packets will be used with. (e.g. Hypertext Transfer protocol (HTTP) is used when transferring HTML files, Simple Mail Transfer protocol (SMTP) is used for sending emails)