1.
UDP
TCP

2. Application
Transport
Network
Link
Physical
My computer
Your computer
Bridge
Router
Data

3. My computer Your computer Bridge Router Data Application layer PDU
Here Introduce PDU - protocol data unit.

4. 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

5. 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

6. Multiplexing/Demultiplexing
To extend IP’s delivery service
Between 2 end systems to 2 processes
Web
SoriBada
Web
SoriBada
Application
Application
What does it use to demultiplex? PORT NUMBERS
Transport
Transport
Network
Network
Link
Link
Physical
Physical

7. UDP Message Queues
Lineage
VoD Player
MP3 player
UDP

8. 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
See how you can bring down the Internet??
No connection state either at the end host or inside the network
Length = UDP header + payload
source port #
destination port #
UDP header
= Total 8 bytes
length
checksum

9. UDP Checksum For error detection Checksum calculation
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

10. 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

11. TCP Header 15 16 31 Source Port Number Destination Port Number15 16 31
Source Port Number
Destination Port Number
Sequence Number
Acknowledgement Number
Header
Length
Reserved
TCP Flags
Window Size
TCP Checksum
Urgent Pointer

12. TCP Connection Tear-Down: 2-Army Problem
Attack!
OK! ?? ??
OK!
Symmetric or Asymmetric disconnect?
Telephone = symmetric, can cause data loss.

13. Closing a TCP Connection
Client
Server
FIN
ACK
FIN
Time-wait period is to wait around just in case the last ACK is lost.
ACK
Time-wait
Closed

14. TCP Congestion Control
Window size
function of
receiver buffer size
delay x bandwidth
Several flavors
Reno/Tahoe/Vegas

15. Rethinking the design of the Internet: The end to end arguments vs
Rethinking the design of the Internet: The end to end arguments vs. the brave new world