UDP: User Datagram Protocol

What Can IP Do? Deliver datagrams to hosts – The IP address in a datagram header identify a host – treats a computer as an endpoint of communication Best effort delivery -- no guarantees

What Do Your Applications Need? Individual packets go to their own applications – Your machine may run multiple applications simultaneously Outlook, Firefox, Windows Media Player. Different levels of services – Every bit of information should be received correctly. – Can tolerate some information loss Streamed media

Transport Layer Services Transport layer provides end-to-end connectivity across the network – Virtual communications via TCP software

Layer 4 Packet: Segment Segments carry application data across the network Segments are carried within IP datagrams within frames App, e.g., HTTPIPTCP Frame Segment Datagram

Endpoint Identification with Protocol Port Numbers Port numbers – Independent of the OS Well-known port numbers: – 22: SSH – 25: SMTP – 80: HTTP – and more:

Transport Layer Services TCP/IP suite contains two transport protocols. – User Datagram Protocol (UDP) – Transmission Control Protocol (TCP) UnreliableReliable MessagesUDP StreamTCP

Comparison of Transport Protocols TCP is full-featured, UDP is a glorified packet TCP (Stream)UDP (Message) ConnectionsConnectionless Point-to-point communicationArbitrary Interaction Bytes are delivered once, reliably, and in order Message may be lost, reordered, duplicated Arbitrary length contentLimited message size Flow control matches sender to receiver Can send regardless of receiver state Congestion control matches sender to network Can send regardless of network state

Why using UDP service? No connection establishment – Get straight to the point No connection state – A server can support more active clients simultaneously Fine application-level control over what data is sent, and when – Faster if application can tolerate some data loss – Avoid overly delayed segments

Some Examples ApplicationTCP or UDP? TCP Remote terminal accessTCP WebTCP File transferTCP Streaming multimediaUDP, TCP Internet telephonyUDP, TCP Name translationTypically UDP Remote file serverTypically UDP TCP today: >95% Internet traffic ~75% on-demand and live streaming

Discussion Why is it that 75% video traffic is sent over TCP rather than UDP in today’s network?