Best effort is lame! what to do? It's the job of our Transport (layer 4)protocols to build services our apps need out of IP's modest layer-3 service #1 workhorse: TCP(Transmission Control Protocol) Service provided by TCP Connection oriented (explicit set-up /tear-down o End hosts(processes)can have multiple concurrent long-lived communication Reliable, in-order, byte-stream delivery o Robust detection retransmission of lost data 37“ B e s t Effort” is Lame! What to do? 37 • It’s the job of our Transport (layer 4) protocols to build services our apps need out of IP’s modest layer-3 service • #1 workhorse: TCP (Transmission Control Protocol) • Service provided by TCP: – Connection oriented (explicit set-up / tear-down) o End hosts (processes) can have multiple concurrent long-lived communication – Reliable, in-order, byte-stream delivery o Robust detection & retransmission of lost data