April 5, 2004 Prof. Paul Lin 1 CPET 355 Data Communications & Networking 6. The Transport Layer User Datagram Protocol Paul I-Hai Lin, Professor Electrical and Computer Engineering Technology Purdue University, Fort Wayne Campus

April 5, 2004 Prof. Paul Lin 2 The Transport Layer Goals Goals Provide reliable, cost –effective data transport from source machine to destination machineProvide reliable, cost –effective data transport from source machine to destination machine Reside on user machineReside on user machine Service Types Service Types ConnectionlessConnectionless UDP (User Datagram Protocol) UDP (User Datagram Protocol) Connection-orientedConnection-oriented TCP (Transmission Control Protocol) TCP (Transmission Control Protocol)

April 5, 2004 Prof. Paul Lin 3 The Transport Layer – Port Number Port number: Port number: Internet Assigned Number Authority (IANA) Internet Assigned Number Authority (IANA) Well-known: 0 to 1,023Well-known: 0 to 1,023 Registered: 1,024 – 49,151Registered: 1,024 – 49,151 Dynamic (private): 49, ,535Dynamic (private): 49, ,535

April 5, 2004 Prof. Paul Lin 4 The Transport Data Unit From Figure 6-3, Page 485, Computer Networks, 4 th Ed, Andrew Tanenbaum, Prentice Hall

April 5, 2004 Prof. Paul Lin 5 User Datagram Protocol (UDP) – RFC 768 Connectionless, fixed port binding Connectionless, fixed port binding No-error control, no flow control, no retransmission No-error control, no flow control, no retransmission Useful for Client-Server applications Useful for Client-Server applications Short requestShort request Short replyShort reply Time-out, try againTime-out, try again

April 5, 2004 Prof. Paul Lin 6 UDP Services Broadcast or multicast services Broadcast or multicast services Real-time data (video, audio, industrial control, etc) Real-time data (video, audio, industrial control, etc) Short transaction time that assume implicit acknowledgement and tolerance on duplicate datagram Short transaction time that assume implicit acknowledgement and tolerance on duplicate datagram

April 5, 2004 Prof. Paul Lin 7 TCP/UDP Services View Linux TCP/UDP Services View Linux TCP/UDP Services $cat /etc/services $cat /etc/services TCP/IP Suites TCP/IP Suites FTP – file transfer (port 21)FTP – file transfer (port 21) Telnet – remote login (port 23)Telnet – remote login (port 23)

April 5, 2004 Prof. Paul Lin 8 UDP Services Examples Echo service (ping, port 7) Echo service (ping, port 7) Daytime server (port 13) Daytime server (port 13) Domain Name Server (DNS, port 53) Domain Name Server (DNS, port 53) Simple Network Management Protocol (SNMP, port 161) Simple Network Management Protocol (SNMP, port 161) Remote Procedure Call (RPC, port 111) Remote Procedure Call (RPC, port 111)

April 5, 2004 Prof. Paul Lin 9 UDP Services Examples Real-Time Transport Protocol Real-Time Transport Protocol Network Time Protocol (NTP) Network Time Protocol (NTP) Bootps – Server port downloading bootstrap info Bootps – Server port downloading bootstrap info Bootpc – Client port downloading bootstrap info Bootpc – Client port downloading bootstrap info

April 5, 2004 Prof. Paul Lin 10 UDP Header From Figure 6-23, Page 526, Computer Networks, 4 th Ed, Andrew Tanenbaum, Prentice Hall Data ……

April 5, 2004 Prof. Paul Lin 11 UDP Header Header (8-byte) Header (8-byte) Source port (16-bit)Source port (16-bit) Destination port (16-bit)Destination port (16-bit) UDP Length (16-bit)UDP Length (16-bit) UDP Checksum (16-bit)UDP Checksum (16-bit) Data (65,507 bytes = ) Data (65,507 bytes = ) 20-byte IP header20-byte IP header 8-byte UDP header8-byte UDP header

April 5, 2004 Prof. Paul Lin 12 RTP (Real-Time Transport) Protocol – RF 1889 Real-time multimedia applications Real-time multimedia applications Internet radioInternet radio TelephonyTelephony Music-on-demandMusic-on-demand VideoconferencingVideoconferencing Video-on-demandVideo-on-demand

April 5, 2004 Prof. Paul Lin 13 The Real-Time Transport Protocol From Figure 6-25, Page 529, Computer Networks, 4 th Ed, Andrew Tanenbaum, Prentice Hall

April 5, 2004 Prof. Paul Lin 14 The RTP Header From Figure 6-26, Page 531, Computer Networks, 4 th Ed, Andrew Tanenbaum, Prentice Hall

April 5, 2004 Prof. Paul Lin 15 The RTP Header Version (2-bit) Version (2-bit) P (1-bit) – padded to multiple of 4-bytes P (1-bit) – padded to multiple of 4-bytes X (1-bit) – extension header present X (1-bit) – extension header present CC (4-bit) – number of contributing sources (0 to 15) CC (4-bit) – number of contributing sources (0 to 15) M (1-bit) – application-specific marker M (1-bit) – application-specific marker Payload type (7-bit) – encoding algorithms (uncompressed 8-bit audio, MP3, etc) Payload type (7-bit) – encoding algorithms (uncompressed 8-bit audio, MP3, etc)

April 5, 2004 Prof. Paul Lin 16 The RTP Header (continue) Sequence Number (16-bit) Sequence Number (16-bit) Packet counterPacket counter Timestamp (32-bit) Timestamp (32-bit) Synchronization source Identifier Synchronization source Identifier Stream – packet (association)Stream – packet (association) Contributing source identifier (studio mixers) Contributing source identifier (studio mixers)

April 5, 2004 Prof. Paul Lin 17 Real-Time Control Protocol A sister protocol of RTP A sister protocol of RTP Handles feedback, synchronization, and user interface Handles feedback, synchronization, and user interface In-stream synchronization In-stream synchronization