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| 6.1 |  | Characteristics of Transport Layer Technologies |
| 6.1.2 |  | User Datagram Protocol |

UDP is connectionless and is considered unreliable because it does not guarantee packet delivery. UDP operates on ‘best effort delivery’ basis and does not use packet sequencing, acknowledgment or retransmission mechanisms for flow control and error detection/correction. If flow control and error detection/correction features are required for a UDP-based data flow, these features must be implemented in higher layer protocols or applications. -

Because UDP does not retransmit lost packets and does not consume bandwidth with acknowledgments, it is relatively light-weight, fast, and is suitable for both one-to-one and one-to-many communications. Over congestion-free and error-free networks, UDP is ideal for transferring small amounts of data, and for supporting streaming applications such as voice communications and video multicasts. However, using UDP over congested or error-prone networks often results in high degrees of data loss with higher-layer protocols, applications, or even users having to initiate data retransmission.

Many higher-layer protocols and applications make use of UDP, including:

- Trivial File Transfer Protocol (TFTP)
- Domain Name Service (DNS)
- NetBIOS Name Resolution (NetBIOS-NS)
- Windows Internet Name Service (WINS)
- Bootstrap Protocol (BootP)
- Dynamic Host Configuration Protocol (DHCP)
- Network Time Protocol (NTP)
- Remote Authentication Dial-In User Service (RADIUS)
- Terminal Access Control Access Control Server (TACACS)

| Web Links Protocol Numbers http://www.iana.org/assignments/protocol-numbers