- Open Systems Interconnection Model
|Sr No||Layer||Data unit||Examples|
|1||Physical||bit||Ethernet, USB, Wi-Fi, Bluetooth, DSL|
|2||Data link||Frame||L2TP, PPP|
|4||Transport||Segment (Datagram)||TCP, UDP|
|5||Session||Data||HTTP, FTP, SMTP, DNS, IMAP, SSH, TLS|
- Structure: Frame header (e.g. Ethernet) + (Network header + Transport header + data) + Frame footer
- Source and destination MAC addresses, length, checksum
- Structure: Network header (e.g. IP) + (Transport header + data)
- Version (IPv4/IPv6), source and destination IP addresses, length flags, TTL, protocol, checksum
- Structure: Transport header (e.g. TCP) + data
- Source and destination ports, sequence number, ack number, data offsets, flags, checksum
- Internet Protocol
- No concept of connection.
- Packets are passed from one computer to the next, until reaching the destination.
- No delivery guarantee, no receiving ack.
- Sometimes multiple copies of the same packet are passes, taking different paths, and thus arriving at different times.
- Designed to be able to route around connectivity problems.
- Transmission Control Protocol
- Built on-top of IP.
- Once a connection has been made between two parties, sending data between the two is much like writing to a file on one side and reading from a file on the other.
- Reliable and ordered, i.e., arrival and ordering are guaranteed.
- Takes care of splitting your data info packets and sending those across the network, so you can write bytes as a stream of data.
- Makes sure it doesn't send data too fast for the Internet connection to handle (flow control).
- Hides all complexities of packets and unreliability.
- Sends an ack for every packet received.
- Queues up data until there's enough to send as a packet.
- TCP tends to induce packet loss for UDP packets whenever they share a bottleneck node (same LAN/WAN).
- User Datagram Protocol
- Built on-top of IP, very thin layer over it.
- Unreliable protocol, usually around 1-5% packet loss.
- No guarantee of ordering.
- Minimizes transmission delay.
- Send a packet to destination IP address and port; the packet will get passed from computer to computer and arrive at destination or get lost.
- Receiver simply listens on specific port and gets notified when a packet arrives, with the sender address:port, and packet size.
- One guarantee over IP – a packet will either arrive as a whole (all of it) at destination or not at all (no partial delivery).
- You need to manually break your data up into packets and send them.
- You need to make sure you don't send data too fast for your Internet connection to handle.
- Good for when you want data to get as quickly as possible from client to server without having to wait for lost data to be resent, usually real-time data.
- Examples: real-time gaming, metrics reporting, video/audio streaming.