1. COP 5611 Operating Systems Spring 2010
Dan C. Marinescu
Office: HEC 439 B
Office hours: M-Wd 2:00-3:00 PM

2. Lecture 9 Reading Assignment: Chapter 7 from the online textbook
HW1 due today.
Remember: A progress report for the project is due on every Monday till week 12.
Last time: Thread coordination and scheduling
Multi-level memories
I/O bottleneck
Today:
Network properties
Layering
Data link layer
Next time
Network layer 2 2 2 2 2

3. Properties of Networks
Physical limitations:
Speed of light  finite communication latency
Hostile environments
Limited channel capacity  limited bandwidth
Channels are shared - multiplexed
Why:
Support any-to-any communication
Share costs
How
Isochronous multiplexing – scheduled access
TDM
FDM
Asynchronous multiplexing

4. Communication channels are multiplexed

5. Data flow on an isochronous link

6. A data communication network

7. Asynchronously multiplexed link

8. Communication Continuous versus bursty
The old phone network versus data networks
Human versus computer communication
Connection-oriented versus connectionless communication
Packet-forwarding networks
Routing problem
Delays

10. Packet forwarding (store and forward) networks

11. Problems in packet forwarding networks
Delay
Propagation delay
Transmission delay
Processing delay
Queuing delay
Resources are finite and a worst case design is not feasible  heavy tail distributions of resource needs
Buffer overflow and discarded packets
Adaptive rate modulated by information regarding network congestion
Timers and packet retransmission
Duplicate packets

12. Queuing delays versus utilization.