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

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

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

Communication channels are multiplexed

Data flow on an isochronous link

A data communication network

Asynchronously multiplexed link

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

Packet forwarding (store and forward) networks

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

Queuing delays versus utilization.