TCOM 509 – Internet Protocols (TCP/IP) Lecture 04_a Transport Protocols - UDP Instructor: Dr. Li-Chuan Chen Date: 09/22/2003 Based in part upon slides of Prof. J. Kurose (U Mass), Prof. K. Fall (UC-Bekeley)

Internet Layer Internet Net interface/ Physical Transport Application IP LAN Packet radio TCPUDP TelnetFTPDNS Transport Layer: UDP TCP

Internetworking Protocols

Transport Protocols Provides an end-to-end transfer services. Sits on top of IP layer and below the application layer. The less the network services, the more the transport protocol must do. Two types –Connection-Oriented: TCP (Transmission Control Protocol) RFC 793 –Connectionless: UDP (User Datagram Protocol) RFC 768

Transport services and protocols provide logical communication between application processes running on different hosts transport protocols run in end systems –send side: breaks application messages into segments, passes to network layer –receiving side: reassembles segments into messages, passes to application layer more than one transport protocol available to apps –Internet: TCP and UDP application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport

Transport vs. network layer network layer: logical communication between hosts transport layer: logical communication between processes (allow multiple applications to run simultaneously on a given host)

Internet transport-layer protocols TCP –reliable delivery –congestion control –flow control –connection setup UDP –unreliable delivery –“best-effort” IP – packets are independent – no flow control – no re-order of datagram – no acknowledgement –packet may be lost, delayed, out of order services not available: –delay guarantees –bandwidth guarantees application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport

UDP often used for streaming multimedia apps –loss tolerant (VoIP) –rate sensitive other UDP uses –DNS –SNMP reliable transfer over UDP: add reliability at application layer –application-specific error recovery!

UDP Format UDP message = user datagram Source port: optional if not used, set to 0. UDP header size = 8 bytes Checksum: optional. Use 1’s complement to detect transmission errors. source port # dest port # 32 bits Application data (message) UDP segment format length checksum Length, in bytes of UDP segment, including header

UDP Pseudo-Header UDP pseudo-header: 12 octets Prepends UDP datagram with a pseudo-header and appends an octet of 0s to multiple of 16-bit. Stores all 0s in the checksum field. Compute 1’s complement of sum of the resulting datagram. Source IP Address Destination IP Address ZeroProtoUDP Length PROTO: IP protocol type code (17 for UDP)

UDP – Port Assignment Port (decimal) KeywordDescriptio n 7ECHOEcho 53DOMAINDomain Name Server 67BOOTPSBOOTP or DHCP Server 68BOOTPCBOOTP or DHCP Client 69TFTPTrivial File Transfer Two computers need to agree on port numbers before they can interoperate. Well-known port assignments (see table) Dynamic binding: need to request for port number on the remote computer.

Homework 2 ChapterProblem 127 Due Monday 09/29/2003, 7:20 p.m.