CPET 355 Data Communications

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CPET 355Data Communications Networking

• 6. The Transport Layer
• User Datagram Protocol
• Paul I-Hai Lin, Professor
• Electrical and Computer Engineering Technology
• Purdue University, Fort Wayne Campus

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The Transport Layer

• Goals
• Provide reliable, cost effective data transport
  from source machine to destination machine
• Reside on user machine
• Service Types
• Connectionless
• UDP (User Datagram Protocol)
• Connection-oriented
• TCP (Transmission Control Protocol)

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The Transport Layer Port Number

• Port number 0 - 65536
• Internet Assigned Number Authority (IANA)
• http//www.iana.org/numbers.htm
• Well-known 0 to 1,023
• Registered 1,024 49,151
• Dynamic (private) 49,152 - 65,535

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The Transport Data Unit
From Figure 6-3, Page 485, Computer Networks, 4th
Ed, Andrew Tanenbaum, Prentice Hall
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User Datagram Protocol (UDP) RFC 768

• Connectionless, fixed port binding
• No-error control, no flow control, no
  retransmission
• Useful for Client-Server applications
• Short request
• Short reply
• Time-out, try again

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UDP Services

• Broadcast or multicast services
• Real-time data (video, audio, industrial control,
  etc)
• Short transaction time that assume implicit
  acknowledgement and tolerance on duplicate
  datagram

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TCP/UDP Services

• View Linux TCP/UDP Services
• cat /etc/services
• TCP/IP Suites
• FTP file transfer (port 21)
• Telnet remote login (port 23)

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UDP Services Examples

• Echo service (ping, port 7)
• Daytime server (port 13)
• Domain Name Server (DNS, port 53)
• Simple Network Management Protocol (SNMP, port
  161)
• Remote Procedure Call (RPC, port 111)

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UDP Services Examples

• Real-Time Transport Protocol
• Network Time Protocol (NTP)
• Bootps Server port downloading bootstrap info
• Bootpc Client port downloading bootstrap info

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UDP Header
Data

From Figure 6-23, Page 526, Computer Networks,
4th Ed, Andrew Tanenbaum, Prentice Hall
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UDP Header

• Header (8-byte)
• Source port (16-bit)
• Destination port (16-bit)
• UDP Length (16-bit)
• UDP Checksum (16-bit)
• Data (65,507 bytes 65535-20-8)
• 20-byte IP header
• 8-byte UDP header

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RTP (Real-Time Transport) Protocol RF 1889

• Real-time multimedia applications
• Internet radio
• Telephony
• Music-on-demand
• Videoconferencing
• Video-on-demand

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The Real-Time Transport Protocol
From Figure 6-25, Page 529, Computer Networks,
4th Ed, Andrew Tanenbaum, Prentice Hall
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The RTP Header
From Figure 6-26, Page 531, Computer Networks,
4th Ed, Andrew Tanenbaum, Prentice Hall
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The RTP Header

• Version (2-bit)
• P (1-bit) padded to multiple of 4-bytes
• X (1-bit) extension header present
• CC (4-bit) number of contributing sources (0 to
  15)
• M (1-bit) application-specific marker
• Payload type (7-bit) encoding algorithms
  (uncompressed 8-bit audio, MP3, etc)

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The RTP Header (continue)

• Sequence Number (16-bit)
• Packet counter
• Timestamp (32-bit)
• Synchronization source Identifier
• Stream packet (association)
• Contributing source identifier (studio mixers)

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Real-Time Control Protocol

• A sister protocol of RTP
• Handles feedback, synchronization, and user
  interface
• In-stream synchronization