Project3 - Congestion Control
Outline
• Overview
• Project Specification and Tasks
• Tools and Time Table
Overview
• BitTorrent-like file transfer application
• Reliability and congestion control protocol
similar to TCP
• UDP based and C programming
• Allow regroup up to 3 members
Project Specification
• Intro to BitTorrent file transfer protocol
• Congestion control mechanism to ensure fair
and efficient network utilization.
• Smart optimizations to get the best possible
transfer time (extra credit).
Intro to BitTorrent
Hash(
)=
= .torrent
•
•
•
•
•
A fixed-size chunk of 512Kbytes in pro3
Verification by rehashing
Flooding, no tracker server
Single master-file, different ownership
BT = TCP, Project3 = UDP
Terminology
master-data-file
1e 34 b4 27
master-chunk-file
1e 34
haschunk-file
GET b4
Peer A
hasb4 27
chunk-file
Peer A
Peer B
GET 34
Peer B
Node.map
File Transfer
•
•
•
•
Requesting peer send “WHOHAS <list>”
Responding peer send “IHAVE <list>”
Decide, and send “GET <chunk-hash>”
Responding peer send multiple “DATA”
Packet Format
Packet Header
Packet Type
Code
WHOHAS
0
IHAVE
1
Seq Num
GET
2
Ack Num
DATA
3
ACK
4
DENIED
5
Magic
Version
Header Len
Type
Packet Len
Payload
= hash list or data
SPLIT PACKET
LONGER THAN
1500 BYTES!
Provided Files
hupsim.pl – Emulates network topology using
topo.map
sha.[ch] - The SHA-1 hash generator
input buffer.[ch]+bt parse.[ch] - Handle user
input
debug.[ch] - helpful utilities for debugging
output
peer.c - A skeleton peer file
nodes.map+topo.map - the hidden network
topology
Project Tasks
• 100% Reliability & Sliding Window
• Congestion control
• *Intelligent Peer Selection and Caching
100% Reliability & Sliding window
SENDER
Last Available
Last ACKed Last Sent
• Cumulative ACK
• Duplicate ACK
RECEIVER
Last Received
Next Expected
Congestion control
• Slow start : ACK received => window++
• Congestion Avoidance : Window size = 1 after
a loss (Simple Version)
• Fast Retransmit : Retransmit after 3 duplicate
ACK
• Fast Recovery : No need to implement (But
you may need it in Task3)
Tools
• Spiffy: Simulating Networks with Loss &
Congestion
sendto() => spiffy_sendto()
• Gnuplot and etc
TimeTable
Date
Event
Description
5/23
Project3 released
START EARLY
5/27
CheckPoint1 (NO
Hand in)
WHOHAS flooding and IHAVE response
6/3
CheckPoint2 (Hand
in)
Simple Chunk Download with stop-and-wait
6/8
CheckPoint3 (NO
Hand in)
Sliding window flow-control with reliability
6/15
CheckPoint4(Hand
in)
Simple Congestion Avoidance, with cwnd =
1 after any loss
6/19
Early bird deadline
Required functionality (+10 bonus points)
6/26
Deadline
No penalty
Thanks
Good Luck & START EARLY!