Transcript Intro to UDP and TCP

2004.4.29.
 UDP
 TCP
1
My computer
Bridge
Router
Data
Your computer
Data
Application
Application
Transport
Transport
Network
Network
Network
Link
Link
Link
Link
Physical
Physical
Physical
Physical
2
My computer
Bridge
Router
Data
Data
Data
Your computer
Application layer PDU
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
3
Rise of the Stupid Network
 Voice network
Intelligence
inside the network
• encoding/decoding
• echo cancellling
• conference bridges
• etc.
 Internet: idiot savant’s network
Just
deliver the bits
4
Is IP going to take over the world?
 Not yet
Only
a small portion of the comm market
• Compared to TV/cable/radio/movie market
Link
utilization low
• less than 50% compared to 80+% of telephone
Robust
• troubling problems of routing protocols
Simple
Real-time
application support
5
Multiplexing/Demultiplexing
 To extend IP’s delivery service
Between
Web
Email
2 end systems to 2 processes
SoriBada
Web
Email
SoriBada
Application
Application
Transport
Transport
Network
Network
Link
Link
Physical
Physical
6
UDP Message Queues
Lineage
VoD Player
MP3 player
UDP
7
Connectionless Transport: UDP
 User Datagram Protocol
Provides
only mux/demux and light error control
No initial connection setup overhead
No connection state
Small packet header overhead
Finer application-level control
source port #
length
destination port #
UDP header
= Total 8 bytes
checksum
8
UDP Checksum
 For error detection
No
recovery, only detection
What happens if an error is detected?
Why does UDP have a checksum?
 Checksum calculation
Over
UDP header and UDP data (+ some of IP
header)
16-bit-long 1’s complement of the sum
odd-numbered UDP data -> padded with 0
9
Connection-oriented: TCP
 Transmission Control Protocol
For
reliable data transfer
3-way handshaking for connection setup
Error checking
Flow control
Congestion control
Error-free, in-order delivery of data to
application layer
10
TCP Header
15
0
Source Port Number
16
31
Destination Port Number
Sequence Number
Acknowledgement Number
Header
Reserved
Length
TCP Flags
TCP Checksum
Window Size
Urgent Pointer
11
TCP Connection Tear-Down:
2-Army Problem
Attack!
OK!
??
OK!
??
12
Closing a TCP Connection
Client
Server
FIN
ACK
FIN
Time-wait
ACK
Closed
13
TCP Congestion Control
 Window size
function
of
• receiver buffer size
• delay x bandwidth
 Several flavors
Reno/Tahoe/Vegas
14
Rethinking the design of the Internet:
The end to end arguments vs. the
brave new world
15