Download Overview of Computer Networks

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
1
The Transport Layer
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Goals
• Provide reliable, cost –effective data transport
from source machine to destination machine
• Reside on user machine
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Service Types
• Connectionless
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UDP (User Datagram Protocol)
• Connection-oriented
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April 5, 2004
TCP (Transmission Control Protocol)
Prof. Paul Lin
2
The Transport Layer – Port
Number
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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
April 5, 2004
Prof. Paul Lin
3
The Transport Data Unit
From Figure 6-3, Page 485, Computer Networks, 4th Ed,
Andrew Tanenbaum, Prentice Hall
April 5, 2004
Prof. Paul Lin
4
User Datagram Protocol
(UDP) – RFC 768
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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
April 5, 2004
Prof. Paul Lin
5
UDP Services
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Broadcast or multicast services
Real-time data (video, audio, industrial
control, etc)
Short transaction time that assume
implicit acknowledgement and
tolerance on duplicate datagram
April 5, 2004
Prof. Paul Lin
6
TCP/UDP Services
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View Linux TCP/UDP Services
$cat /etc/services
TCP/IP Suites
• FTP – file transfer (port 21)
• Telnet – remote login (port 23)
April 5, 2004
Prof. Paul Lin
7
UDP Services Examples
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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)
April 5, 2004
Prof. Paul Lin
8
UDP Services Examples
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Real-Time Transport Protocol
Network Time Protocol (NTP)
Bootps – Server port downloading
bootstrap info
Bootpc – Client port downloading
bootstrap info
April 5, 2004
Prof. Paul Lin
9
UDP Header
Data
……
From Figure 6-23, Page 526, Computer Networks, 4th Ed,
Andrew Tanenbaum, Prentice Hall
April 5, 2004
Prof. Paul Lin
10
UDP Header

Header (8-byte)
• Source port (16-bit)
• Destination port (16-bit)
• UDP Length (16-bit)
• UDP Checksum (16-bit)
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Data (65,507 bytes = 65535-20-8)
• 20-byte IP header
• 8-byte UDP header
April 5, 2004
Prof. Paul Lin
11
RTP (Real-Time Transport)
Protocol – RF 1889

Real-time multimedia applications
• Internet radio
• Telephony
• Music-on-demand
• Videoconferencing
• Video-on-demand
April 5, 2004
Prof. Paul Lin
12
The Real-Time Transport Protocol
From Figure 6-25, Page 529, Computer Networks, 4th Ed,
Andrew Tanenbaum, Prentice Hall
April 5, 2004
Prof. Paul Lin
13
The RTP Header
From Figure 6-26, Page 531, Computer Networks, 4th Ed,
Andrew Tanenbaum, Prentice Hall
April 5, 2004
Prof. Paul Lin
14
The RTP Header
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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)
April 5, 2004
Prof. Paul Lin
15
The RTP Header
(continue)
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Sequence Number (16-bit)
• Packet counter
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Timestamp (32-bit)
Synchronization source Identifier
• Stream – packet (association)
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Contributing source identifier (studio
mixers)
April 5, 2004
Prof. Paul Lin
16
Real-Time Control Protocol
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A sister protocol of RTP
Handles feedback, synchronization,
and user interface
In-stream synchronization
April 5, 2004
Prof. Paul Lin
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