Connectionless services need a unit of data that is self-contained with all necessary addressing, so it can be routed independently without connection state.
A self-contained, independent packet in a connectionless service that carries its own addressing and can take any path to the destination.
- Application data is encapsulated in a datagram with source and destination addresses/ports
- Each datagram is treated independently by the network
- Datagrams may take different paths and arrive out of order
- No relationship between consecutive datagrams (no connection state)
- UDP packets are datagrams; IP packets are also datagrams
- Self-contained with full addressing
- No connection state maintained
- Can arrive out of order or not at all
- Used by UDP and IP (connectionless protocols)
- Built from: Connectionless Service — datagrams are the unit of transfer
- Built from: UDP — uses datagrams
- Built from: IP Protocol — IP packets are datagrams
- Contrasts with: Virtual Circuit — independent vs stateful path
- No delivery guarantees — applications must handle loss
- Datagram size limits (UDP: 65,507 bytes minus IP header; practical limit often 1,500 bytes due to MTU)
- Fragmentation at IP layer if datagram exceeds MTU