coursera:network_model
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| + | ====== Information ====== | ||
| + | * 5-layer network model description | ||
| + | * For Coursera The Bits and Bytes of Computer Networking week 3 | ||
| + | |||
| + | ====== Physical Layer ====== | ||
| + | |||
| + | * Lowest level | ||
| + | * Where data transfers via electrical currents, voltage, radio frequency, and modulation takes place | ||
| + | * A simple problem at this layer could be an Ethernet cable being severed or unplugged from a network switch | ||
| + | |||
| + | ====== Data link layer ====== | ||
| + | |||
| + | * Handles error-correction with data packets received from the physical layer | ||
| + | * Handles transferring data packets received from the physical layer, to network interfaces via MAC addresses | ||
| + | |||
| + | ====== Network layer ====== | ||
| + | |||
| + | * Routing occurs in this layer, where packets need to be transferred to their destination | ||
| + | * Packets may have to travel between many different network switches in large-scale networks (like the internet) depending on the destination' | ||
| + | * Packets hopping to each router has the TTL header subtracted from | ||
| + | |||
| + | ====== Transport layer ====== | ||
| + | |||
| + | * Various protocols (commonly TCP and UDP) are specified and used here | ||
| + | * TCP is used here and operates on a response-based system where packets received need to be acknowledged | ||
| + | * UDP is used here and does not need packets to be acknowledged | ||
| + | * TCP is good for reliability, | ||
| + | * TCP is typically used for web server and file transfer connections | ||
| + | * UDP is typically used for game server and VPN connections | ||
| + | |||
| + | ====== MAC address ====== | ||
| + | |||
| + | * Identifier assigned to the network interface of a device | ||
| + | * All network interfaces have an unique MAC address | ||
| + | * A MAC address does **not** change depending on where the network interface is connected | ||
| + | * Composed of hexadecimal digits (0-9, A-F, and a-f), normally in groups of two separated by '' | ||
| + | * Exists at data link layer | ||
| + | |||
| + | ====== IP address ====== | ||
| + | |||
| + | * Address assigned to a device on a network | ||
| + | * Addresses can be assigned dynamically (DHCP) or statically based on the network the interface is connected to | ||
| + | * IP address can change depending on the network the network interface is connected to | ||
| + | * IPv4 is the most common version at 32-bits of data, and represented in dot-decimal notation | ||
| + | * The total number of possible IPv4 addresses are exhausted at large-scale | ||
| + | * IPv6 is gaining popularity, is 128-bits of data, and contains a significantly larger pool of available addresses than IPv4 | ||
| + | |||
| + | ====== TCP port ====== | ||
| + | |||
| + | * Defined in the Transport layer | ||
| + | * Is an endpoint that defines what a service is that is sending or receiving packets | ||
| + | * Popular services have well-known port assignments, | ||
| + | * Typically referred to in firewall applications, | ||
| + | |||
| + | ====== Checksum check ====== | ||
| + | |||
| + | * When the data in a payload section is checked to verify its contents | ||
| + | |||
| + | ====== Routing table ====== | ||
| + | |||
| + | * Defines where network interfaces are | ||
| + | * Exists on most network switches, including consumer routers | ||
| + | * Normally automatically maintained and updated by the network switch | ||
| + | |||
| + | ====== TTL ====== | ||
| + | |||
| + | * A header in an IP packet that exists at the Network layer | ||
| + | * Defines how many hops a packet is allowed to perform | ||
| + | * When a packet transfers from a network switch to another network, the TTL header is subtracted from by one | ||
| + | * Used to prevent mis-configured packets from endlessly looping between devices | ||
| + | |||
| + | ====== Encapsulation ====== | ||
| + | |||
| + | * Data is encapsulated at various points in the network layer | ||
| + | * The data that exists in a TCP or UDP (or any protocol at the network layer) packet is encapsulated as the data payload in the IP datagram | ||
| + | * The headers specific to an IP datagram, and the data payload that exists in it are then encapsulated as the payload for an Ethernet frame | ||