Lecture 11:

1. ITEC 1000 “Introduction to Information Technology” Lecture 11: Computer Systems and Networks

2. Lecture Template: • System Performance Improvement • Multiprocessing • Computer Interconnection • OSI model and TCP/IP • Network Topologies • Protocols • Wide Area Network • High Performance Computing

3. 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

4. Multiprocessing • Reasons • Increase the processing power of a system • Parallel processing • Types of multiprocessor systems • Tightly coupled systems • Loosely coupled systems

5. 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)

6. Tightly Coupled Systems

7. 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

8. 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

9. 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

10. 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

11. 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)

12. Cluster Models

13. 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-to-point connections for a host computer • Multipoint connectivity • Multidrop channel or shared communication channel

14. Example: Point-to-Point

15. Definitions Topology: the way in which loosely coupled computers are interconnected Synonym: configuration Protocol: a set of rules and standards for communications between computers

16. 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

17. Client-Server Network F server

18. A typical data packet

19. The layers of the OSI model

20. Passing a message through an intermediate node

21. A comparison of OSI and TCP/IP

22. 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

23. Blade and Rack of Beowulf Cluster

24. LAN Topology • Arrangement of workstations in a shared medium environment • Logical arrangement (data flow) • Physical arrangement (cabling scheme)

25. 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.

26. 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

27. Ring LAN Diagram

28. Ring Topology

29. 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

30. Bus LAN Diagram

31. Bus Topology

32. 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

33. 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

34. Star LAN Diagram

35. Star Topology Guy in the Middle

36. Loop Topology

37. Hierarchical Topology Big Guy at Top

38. Web Topology

39. 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

40. 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

41. 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

42. Ethernet Frame

43. Switched Ethernet

44. 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

45. 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

46. 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

47. 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

48. 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

49. A Switched Wide Area Network

50. 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 load-balancing software • Network workload cannot be controlled using the above method