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ITEC 1000 “Introduction to Information Technology” Lecture 11: Computer Systems and Networks 1 Lecture Template: System Performance Improvement Multiprocessing Computer Interconnection OSI model and TCP/IP Network Topologies Protocols Wide Area Network High Performance Computing 2 System Performance Improvements Multiple CPUs Sharing memory and I/O facilities Conflict among the CPUs for shared resources Faster clock speed, buses and circuits Improving technology to design faster CPU circuits and buses Wider instruction and data paths Wider interface between the CPU and memory allows to fetch more data in a single operation Faster disk access Smaller discs, more density packed, increased storage RAID: data on different discs, multiple access simultaneously More and faster memory Reduces the time to access instructions and data 3 Multiprocessing Reasons Increase the processing power of a system Parallel processing Types of multiprocessor systems Tightly coupled systems Loosely coupled systems 4 Tightly Coupled Systems Also called multiprocessor systems Identical access to programs, data, shared memory, I/O, etc. Easily extends multi-tasking, and redundant program execution Two ways to configure Master-slave multiprocessing Symmetrical multiprocessing (SMP) 5 Tightly Coupled Systems 6 Master-Slave Multiprocessing Master CPU Manages the system Controls all resources and scheduling Assigns tasks to slave CPUs Advantages Simplicity Protection of system and data Disadvantages Master CPU becomes a bottleneck Reliability issues – if master CPU fails entire system fails 7 Symmetrical Multiprocessing Each CPU has equal access to resources Each CPU determines what to run using a standard algorithm Disadvantages Resource conflicts – memory, i/o, etc. Complex implementation Advantages High reliability Fault tolerant support is straightforward Balanced workload 8 Loosely Coupled Systems Clusters or multi-computer systems Each system has its own CPU, memory, and I/O facilities Each system is known as a node of the cluster Advantages Fault-tolerant, scalable, well balanced, distance is not an issue Two ways to configure Shared-nothing model Shared-disk model 9 Shared-Nothing Model High speed link between nodes No sharing of resources Partitioning of work through division of data Advantage Reduced communication between nodes Disadvantage Can result in inefficient division of work 10 Shared-Disk Model High speed link between nodes Disk drives are shared between nodes Advantage Better load balancing Disadvantage Complex software required for transactional processing (lock, commit phases) 11 Cluster Models 12 Computer Interconnection Communication channel – pathway for data movement between computers Point-to-Point connectivity Communication channel that passes data directly between two computers Serial connection Telephone modem Terminal controller – handles multiple point-topoint connections for a host computer Multipoint connectivity Multidrop channel or shared communication channel 13 Example: Point-to-Point 14 Definitions Topology: the way in which loosely coupled computers are interconnected Synonym: configuration Protocol: a set of rules and standards for communications between computers 15 Client-Server Architecture Computer server provides services File storage, databases, printing services, login services, web services Client computers Execute programs in its own memory Access files either locally or can request files from a server 16 Client-Server Network F server 17 A typical data packet 18 The layers of the OSI model 19 Passing a message through an intermediate node 20 A comparison of OSI and TCP/IP 21 Beowulf Clusters Simple and highly configurable Low cost Networked Computers connected to one another by a private Ethernet network Connection to an external network is through a single gateway computer Configuration COTS – Commodity-off-the-shelf components such as inexpensive computers Blade components – computers mounted on a motherboard that are plugged into connectors on a rack Either shared-disk or shared-nothing model 22 Blade and Rack of Beowulf Cluster 23 LAN Topology Arrangement of workstations in a shared medium environment Logical arrangement (data flow) Physical arrangement (cabling scheme) 24 Network Topologies Bus: Nodes are connected to a common bus with a terminator on each end. Ring: Similar to bus, but bus is closed - no ends. Star: A central node does most of the processing. Remote nodes are connected point-to-point with it. Loop: Similar to ring but nodes are directly in communication path. Hierarchical: A tree-like structure emanating from a central or root node. Web: Everything connected to everything else. 25 LAN Topologies: Ring Repeaters are joined by unidirectional point-to-point links in a ring As data circulates past a receiver, the receiver checks its address, and copies those intended for it into a local buffer Data circulates until it returns to source, which removes it from network Better performance at high levels of usage 26 Ring LAN Diagram 27 Ring Topology 28 LAN Topologies: Bus Multipoint medium Stations attach to linear medium (bus) using tap Transmission from any stations travels entire medium (both directions) Termination required at ends of bus to prevent the signal from bouncing Break in cable brings down entire bus 29 Bus LAN Diagram 30 Bus Topology 31 LAN Topologies: Tree Generalization of bus topology Branching cable with no closed loops Cable(s) begin at headend, travel to branches which may have branches of their own Each transmission propagates through network, can be received by any station 32 LAN Topologies: Star Each station connected point-to-point to a central station, usually with two unidirectional links Switching in the central station connects pairs of nodes together Central node can broadcast info, or can switch frames among stations Failure of central station causes entire network to go down 33 Star LAN Diagram 34 Star Topology Guy in the Middle 35 Loop Topology 36 Hierarchical Topology Big Guy at Top 37 Web Topology 38 Topology Selection: Factors Distances between stations Layout of the room/building Overall size of the network Distance between the most remote nodes Speed requirements Network traffic Total number of stations 39 Medium Access Control (MAC) Protocols Characteristics of the channels, data rate, voltage levels, etc. Node access to the channel (medium access control protocol) Steer data to its destination Detect errors Prevent multiple nodes from accessing the network simultaneously (collision) Ethernet and token ring Implemented in hardware 40 Ethernet MAC Protocol MAC – Medium Access Control Ethernet and CSMA/CD Carrier sense multiple access with collision detection Four step procedure If medium is idle, transmit If medium is busy, listen until idle and then transmit If collision is detected, cease transmitting After a collision, wait a random amount of time before retransmitting 41 Ethernet Frame 42 Switched Ethernet 43 Token Ring MAC Protocol Token “seized” by changing a bit on the circulating frame to indicate start of frame rather than token Default configuration requires sender to complete transmission and begin receiving transmitted frame before releasing the token “Early token release” allows release of token after transmission but before receipt of frame 44 Hubs The active central element of the star layout When a single station transmits, the hub repeats the signal on the outgoing line to each station Hubs can be cascaded in a hierarchical configuration Ethernet hubs are physically a star but logically a bus 45 Bridges Allow connections between LANs and to WANs Used between similar networks Read all frames from each network Accept frames from sender on one network that are addressed to a receiver on the other network Retransmit frames from sender using MAC protocol for receiver 46 Gateways Similar to bridges but connect dissimilar networks Convert format of the message to correspond to the protocol of the other network Network traffic is specifically addressed to the router 47 Wide Area Network Circuit switching Dedicated channel between source and destination for duration of connection Message switching Dedicated channel for an entire message Packet switching An independent path is created for each datagram Virtual circuit switching A route is created from source to destination before transmission begins and all datagrams are sent using the same route 48 A Switched Wide Area Network 49 Networks vs. Clusters Externally, clusters appear as a single computing unit Network nodes are individually identifiable Workload on a cluster is determined by cluster administration and loadbalancing software Network workload cannot be controlled using the above method 50 High Performance Computing Massively parallel processor architectures (MPP) Clusters of power machines or larger Beowulf blade clusters Well suited for problems that can be broken into subtasks Grid computing Supercomputer performance through distributing CPU processing to the spare CPU cycles of personal computers connected to a network 51 Parallel Computers Massively parallel architectures Hundreds to millions of CPUs CPUs have small amounts of local memory All CPUs have access to global shared memory Pipelined CPUs Results from one CPU flow to the next CPU for additional processing 52