coursera:network_model
Table of Contents
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's physical location
- 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, whereas UDP is good for speed and lower latency
- 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
-
or:
- 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, such as 80 for HTTP, 443 for HTTPS, 21 for FTP, and 6112 for various game servers
- Typically referred to in firewall applications, and can be used to block services on a specific device, or network-wide
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
C:/www/wiki/data/pages/coursera/network_model.txt · Last modified: by 127.0.0.1