IP: Connectionless Datagram Delivery

Unreliable delivery

delivery of data is not guaranteed. A packet of data may be lost in the network, may be duplicated (ie: delivered twice) or may be delivered out of order. The IP service will not detect such conditions, nor will it notify the sender or receiver if they occur.
 

Connectionless delivery

each packet is treated entirely indpendently of all others. No information is kept as to which packets have been forwarded, and packets may travel over different routes to the same destination.
 

Best-Effort delivery

the packet delivery mechanism is engineered to always deliver packets if possible. It will not gratuitously drop packets: unreliability should only occur when underlying resources (eg buffer space) are exhausted.