CIS 212 Microcomputer Architecture Day 21 Rhys Eric

CIS 212 Microcomputer Architecture Day 21 Rhys Eric Rosholt Office: Office Phone: Web Site: Email Address: Gillet Hall - Room 304 718 -960 -8663 http: //comet. lehman. cuny. edu/rosholt/ rhys. rosholt @ lehman. cuny. edu

Chapter 8 Data and Network Communication Technology

Chapter 8 Data and Network Communication Technology Chapter Outline Communication Protocols Encoding and Transmitting Bits Transmission Media Channel Organization Focus – Serial and Parallel Storage Connections Focus – Infiniband Clock Synchronization Error Detection and Correction Focus – 802. 11 Wireless Network Standards Focus - Upgrading Storage and Network Capacity (Part I)

Communication Protocol Components

Channel Organization • Configuration and organization issues – Number of transmission wires or bandwidth assigned to each channel – Assignment of those wires or frequencies to carry specific signals – Sharing, or lack thereof, of channels among multiple senders and receivers • Three types: simple, half-duplex, full duplex

Channel Organization Type Function Example Simple Uses one optical fiber or copper wire pair to transmit data in one direction only Halfduplex Identical to a simplex channel but sends a control signal to reverse transmission direction CB Radios Full duplex Uses two fibers or wire pairs to support simultaneous transmission in both directions Telephone Broadcast Radio & TV

Channel Sharing • Uses available capacity by combining traffic of multiple users • For use when no single user or application needs a continuous supply of data transfer data capacity • Techniques – Circuit switching – Packet switching – Frequency division multiplexing (FDM)

Channel Sharing Techniques Circuit switching Packet switching FDM • Allocates an entire channel to a single user for duration of one data transfer operation • Only used where data transfer delay and available data transfer capacity must be within precise and predictable limits (e. g. , telephone service) • Allocates time on the channel by dividing many message streams into smaller units (packets) and intermixing them during transmission • Divides a broadband channel into several baseband channels (e. g. , cable television)

Packet Switching, or TDM (Time Division Multiplexing) Packets are sent to their destination as channel capacity becomes available.

Channel Sharing, or FDM (Frequency Division Multiplexing) Signals are transmitted within each subchannel at a fixed frequency or narrow frequency range.

Technology Focus Infiniband • A data interconnection standard developed by a consortium of digital communications companies. • Uses a switched fabric which interconnects multiple devices with multiple transmission pathways and a mesh of switches – A matrix-like interconnection – Allows any sender and any receiver to connect – Supports many simultaneous connections

Communication Protocol Components

Communication Protocol Components

Communication Protocol Components

Clock Synchronization • Ensures that sender/receiver use same time periods and boundaries to encode/decode bit values • Asynchronous transmission – Relies on specific start and stop signals to indicate beginning and end of a message unit • Synchronous transmission – Ensures that sender/receiver clocks are always synchronized by sending continuous data streams

Unsynchronized Clocks If bit time boundaries are misaligned, the receiver is unable to interpret bits correctly because they contain two different signal levels.

Synchronous Transmission Messages are transmitted in fixed-size byte groups called blocks.

Asynchronous Transmission

Communication Protocol Components

Error Detection and Correction • Error detection – A form of redundant transmission – Increasing redundancy increases chances of error detection at the expense of reducing channel throughput • Common error detection methods – Parity checking – Block checking – Cyclical redundancy checking

How Methods of Error Detection and Correction Vary • Size and content of redundant transmission • Efficient use of the communication channel • Probability that an error will be detected – Failure is a Type I error • potentially disasterous • Probability that an error-free message will be identified as an error – Failure is a Type II error • wasteful • Complexity of the error detection method

Parity Checking • Also called VRC – Vertical Redundancy Checking • Can be based on even or odd bit counts • Has a high Type I error rate • Reliability issues – Unreliable in channels subject to error bursts affecting many adjacent bits – More reliable in channels with rare errors that are usually confined to widely spaced bits

Parity Checking

Block Checking Horizontal Redundancy Checking • Also called Longitudinal Redundancy Checking (LRC) • Sending device counts number of 1 -valued bits at each bit position within a block • Sender combines parity bits for each position into a Block Check Character (BCC) and appends it to the end of the block • Receiver counts 1 -valued bits in each position and derives its own BCC to compare with that transmitted by sender

Block Checking Longitudinal Redunancy Checking An even parity bit is computed for each position of a block of 8 bytes. The set of parity bits forms a BCC that is appended to the block for error detection.

CRC Cyclic Redundancy Checking • Most widely used error detection technique • Produces a BCC usually more than 8 bits long; can be as large as 128 bits • Much lower Type I and Type II error rates than VRC (parity) checking and LRC checking

Technology Focus – 802. 11 Wireless Network Standards • The first 802. 11 standard defined two RF transmission methods – FHSS Frequency Hopping Spread Spectrum – DSSS Direct Sequence Spread Spectrum • The 802. 11 a standard divides the bands between 5 and 6 GHz into 22 channels and uses OFDM to encode data. • The 802. 11 b standard enhances DSSS by creating more high bandwidth channels • The 802. 11 g standard updates the 802. 11 b standard with narrower bands using OFDM.

Business Focus – Upgrading Network and Storage Capacity • • Bradley Advertising Agency The trade-off between short and long-range benefits of copper and fiber optic wiring Copper is installed in most buildings, works well for current needs, and can be upgraded – Current technology pushes copper to its maximum Fiber optic cable has far greater theoretical capacity than copper – Current optical products are expensive and not yet perfected Fiber optic cable is the future – But when is it cost effective for a particular organization or need?

Summary • Communication protocols • How bits are represented and transported among computer systems and hardware components • Transmission media • Channel organization • Clock synchronization • Detecting and correcting errors in data transmission, reception, or interpretation

Chapter Goals • Explain communication protocols • Describe signals and the media used to transmit digital signals • Compare and contrast methods of encoding and transmitting data using analog or digital signals • Describe methods for efficiently using communication channels • Describe methods for detecting and correcting data transmission errors

Chapter 9 Computer Networks

Chapter 9 Computer Networks Chapter Outline Network Topology Addressing and Routing Media Access Control Network Hardware OSI Network Layers TCP/IP Focus – Voice over IP Network Standards Focus - Ethernet Focus - Upgrading Network Capacity (Part II)

Chapter Goals • Compare and contrast bus, ring, and star network topologies • Describe packet routing across local and wide area networks • Describe the CSMA/CD media access control protocol • Describe network hardware devices, including network interface units, routers, and switches • Describe the OSI network model, the TCP/IP protocol suite, and IEEE network standards

Chapter 9 Computer Networks

Network Topology • Spatial organization of network devices, physical routing of network cabling, and flow of messages from one network node to another • Can be physical or logical • Three types – star, bus, ring – differentiated by – Length and routing of network cable – Type of node connections – Data transfer performance – Susceptibility of network to failure

Point-to-Point Network Topology Impractical for all but very small networks

Point-to-Point Network Topology Impractical for all but very small networks

Point-to-Point Network Topology Impractical for all but very small networks

Advanced Network Topologies Improve practicality for most networks

Store and Forward System Centralizes the work of networking

Next Class Tuesday April 24, 2012 Rhys Eric Rosholt Office: Office Phone: Web Site: Email Address: Gillet Hall - Room 304 718 -960 -8663 http: //comet. lehman. cuny. edu/rosholt/ rhys. rosholt @ lehman. cuny. edu