2. Learning Objectives
⢠Several different network topologies - including the
star, ring, bus, tree, and hybrid - and how they
connect numerous hosts to the network
⢠Several types of networks: LAN, MAN, WAN, and
wireless LAN
⢠The difference between circuit switching and packet
switching, and examples of everyday use that favor
each
Understanding Operating Systems, Fifth Edition 2
3. Learning Objectives (continued)
⢠Conflict resolution procedures that allow a network
to share common transmission hardware and
software effectively
⢠The two transport protocol models (OSI and TCP/IP)
and how the layers of each one compare
Understanding Operating Systems, Fifth Edition 3
4. Basic Terminology
⢠Network
â Collection of loosely coupled processors
â Interconnected by communication links
⢠Using cables, wireless technology, both
⢠Common goal
â Provide convenient resource sharing
â Control access
⢠General network configurations
â Network operating system (NOS)
â Distributed operating system (D/OS)
Understanding Operating Systems, Fifth Edition 4
5. Basic Terminology (continued)
⢠Network operating system (NOS)
â Networking capability
⢠Added to single-user operating system
â Users aware of specific computers and resources in
network
â Access resources
⢠Log on to remote host
⢠Data transfer from remote host
Understanding Operating Systems, Fifth Edition 5
6. Basic Terminology (continued)
⢠Distributed operating system (D/OS)
â Users not aware of specific computers and resources
in network
⢠Access remote resources as if local
â Good control: distributed computing systems
⢠Allows unified resource access
â Total view across multiple computer systems
⢠No local dependencies for controlling and managing
resources
â Cooperative management
Understanding Operating Systems, Fifth Edition 6
7. Basic Terminology (continued)
⢠Distributed operating system (D/OS) (continued)
â Comprised of four managers with a wider scope
Understanding Operating Systems, Fifth Edition 7
8. Basic Terminology (continued)
⢠Distributed operating system (D/OS) (continued)
â Advantages over traditional systems
⢠Easy and reliable resource sharing
⢠Faster computation
⢠Adequate load balancing
⢠Good reliability
⢠Dependable communications among network users
Understanding Operating Systems, Fifth Edition 8
9. Basic Terminology (continued)
⢠Remote
â Other processors and resources
⢠Local
â Processorâs own resources
⢠Site
â Specific location in network
⢠One or more computers
⢠Host
â Specific computer system at site
⢠Services and resources used from remote locations
Understanding Operating Systems, Fifth Edition 9
10. Basic Terminology (continued)
⢠Node
â Name assigned to computer system
⢠Provides identification
Understanding Operating Systems, Fifth Edition 10
11. Network Topologies
⢠Physically or logically connected sites
⢠Star, ring, bus, tree, hybrid
⢠Topology tradeoffs
â Need for fast communication among all sites
â Tolerance of failure at a site or communication link
â Cost of long communication lines
â Difficulty connecting one site to large number of other
sites
Understanding Operating Systems, Fifth Edition 11
12. Network Topologies (continued)
⢠Four basic criteria
â Basic cost
⢠Expense required to link various sites in system
â Communications cost
⢠Time required to send message from one site to
another
â Reliability
⢠Assurance of site communication if link or site fails
â User environment
⢠Critical parameters for successful business investment
Understanding Operating Systems, Fifth Edition 12
13. Star
⢠Transmitted data from sender to receiver
â Passes through central controller
⢠Hub or centralized topology
⢠Advantages
â Permits easy routing
â Easy access control to network
⢠Disadvantages
â Requires extremely reliable central site
â Requires ability to handle all network traffic
⢠No matter how heavy
Understanding Operating Systems, Fifth Edition 13
15. Ring
⢠Sites connected in closed loop
⢠May connect to other networks
â Using bridge (same protocols)
â Using gateway (different protocols)
⢠Data transmitted in packets
â Source and destination address fields
⢠Packet passed from node to node
â One direction only
⢠Every node must be functional
â Bypass failed node needed for proper operation
Understanding Operating Systems, Fifth Edition 15
19. Bus
⢠Sites connect to single communication line
⢠Messages circulate in both directions
⢠One site sends messages at a time successfully
⢠Need control mechanism
â Prevent collision
⢠Data passes directly from one device to another
â Data may be routed to end point controller at end of
the line
Understanding Operating Systems, Fifth Edition 19
21. Tree
⢠Collection of buses connected by branching cable
â No closed loops
⢠Designers create networks using bridges
⢠Message from any site
â Received by all other sites until reaching end point
⢠Reaches end point controller without acceptance
â Host absorbs message
⢠Advantage
â Message traffic still flows even if single node fails
Understanding Operating Systems, Fifth Edition 21
25. Network Types
⢠Grouping
â According to physical distances covered
⢠Characteristics blurring
⢠Network types
â Local area networks (LAN)
â Metropolitan area networks (MAN)
â Wide area networks (WAN)
Understanding Operating Systems, Fifth Edition 25
26. Local Area Network
⢠Single office building, campus, similarly enclosed
environment
â Single organization owns/operates
⢠Communicate through common communication line
⢠Communications not limited to local area only
â Component of larger communication network
â Easy access to outside
⢠Through bridge or gateway
Understanding Operating Systems, Fifth Edition 26
27. Local Area Network (continued)
⢠Bridge
â Connects two or more geographically distant LANs
â Same protocols
⢠Bridge connecting two LANs using Ethernet
⢠Gateway
â Connects two or more LANs or systems
â Different protocols
⢠Translates one network protocol into another
⢠Resolves hardware and software incompatibilities
⢠SNA gateway connecting microcomputer network to
mainframe host
Understanding Operating Systems, Fifth Edition 27
28. Local Area Network (continued)
⢠Data rates: 100 Mbps to more than 40 Gbps
⢠Close physical proximity
â Very high-speed transmission
⢠Star, ring, bus, tree, and hybrid
â Normally used
⢠Transmission medium: varies
⢠Factors determining transmission medium
â Cost, data rate, reliability, number of devices
supported, distance between units
Understanding Operating Systems, Fifth Edition 28
29. Metropolitan Area Network
⢠Configuration spanning area larger than LAN
â Several blocks of buildings to entire city
⢠Not exceeding 100 km circumference
⢠Owned and operated by a single organization
â Used by many individuals and organizations
â May be owned and operated as public utilities
⢠Means for internetworking several LANs
⢠High-speed network often configured as a logical
ring
Understanding Operating Systems, Fifth Edition 29
30. Wide Area Network
⢠Interconnects communication facilities in different
parts of a country or world
â Operated as part of public utility
⢠Uses common carriersâ communications lines
â Telephone companies
⢠Uses broad range of communication media
â Satellite, microwaves
⢠WANs generally slower than LANs
â Examples: ARPAnet (first WAN), Internet (most
widely recognized WAN)
Understanding Operating Systems, Fifth Edition 30
31. Wireless Local Area Network
⢠LAN using wireless technology to connect
computers or workstations
â Located within range of network
⢠Security vulnerabilities
â Open architecture; difficulty keeping intruders out
Understanding Operating Systems, Fifth Edition 31
32. Wireless Local Area Network
(continued)
⢠WiMAX standard 802.16
â High bandwidth, long distances
Understanding Operating Systems, Fifth Edition 32
33. Software Design Issues
⢠How do sites use addresses to locate other sites?
⢠How are messages routed and how are they sent?
⢠How do processes communicate with each other?
⢠How are conflicting demands for resources
resolved?
Understanding Operating Systems, Fifth Edition 33
34. Addressing Conventions
⢠Addressing protocols
â Fulfill need to uniquely identify users
â Closely related to site network topology and
geographic location
⢠Distinction between local and global name
â Local name within its own system
â Global name outside its own system
⢠Must follow standard name conventions (length,
formats)
Understanding Operating Systems, Fifth Edition 34
35. Addressing Conventions (continued)
⢠Example: Internet address
â someone@icarus.lis.pitt.edu
â Uses Domain Name Service (DNS) protocol
⢠General-purpose data query service
⢠Hierarchical
⢠Domain names read left to right
â Logical user to host machine
â Host machine to net machine
â Net machine to cluster
â Cluster to network
⢠Periods separate components
Understanding Operating Systems, Fifth Edition 35
36. Routing Strategies
⢠Router
â Internetworking device (primarily software driven)
â Directs traffic
⢠Between two different types of LANs
⢠Between two network segments (different protocol
addresses)
â Network layer operation
â Role changes (network designs changes)
⢠Connects sites
â To other sites and Internet
Understanding Operating Systems, Fifth Edition 36
37. Routing Strategies (continued)
⢠Router functions
â Securing information
⢠Generated in predefined areas
â Choosing fastest route
⢠From one point to another
â Providing redundant network connections
⢠Routing protocol considerations
â Addressing, address resolution, message format,
error reporting
⢠Address resolution
â Maps hardware address
Understanding Operating Systems, Fifth Edition 37
38. Routing Strategies (continued)
⢠Message formats
â Allow performance of protocol functions
⢠Finding new network nodes
⢠Determine whether they work (testing)
⢠Reporting error conditions
⢠Exchanging routing information
⢠Establishing connections (transmit data)
⢠Most widely used Internet routing protocols
â Routing information protocol (RIP)
â Open shortest path first (OSPF)
Understanding Operating Systems, Fifth Edition 38
39. Routing Strategies (continued)
⢠Routing information protocol (RIP)
â Path selection based on node and hop number
⢠Between source and destination
â Path with smallest number of hops chosen (always)
â Advantage
⢠Easy to implement
â Disadvantages
⢠No consideration: bandwidth, data priority, network type
⢠Update and reissue routing table: changes or not
⢠Tables propagate (router to router)
Understanding Operating Systems, Fifth Edition 39
40. Routing Strategies (continued)
⢠Open shortest path first (OSPF)
â Network state determined first
â Transmission path selected
â Update messages sent when changes in routing
environment occur
⢠Reduces number of messages in internetwork
⢠Reduces message size: not sending entire table
â Disadvantages
⢠Increased memory usage
⢠Bandwidth savings offset by higher CPU usage
⢠Shortest path calculation
Understanding Operating Systems, Fifth Edition 40
41. Connection Models
⢠Communication network concern
â Moving data from one point to another
â Minimizing transmission costs
â Providing full connectivity
⢠Circuit switching
â Dedicated communication path
⢠Established between two hosts before transmission
begins
â Example: telephone system
â Disadvantage
⢠Delay before signal transfer begins
Understanding Operating Systems, Fifth Edition 41
42. Connection Models (continued)
⢠Packet switching
⢠Store-and-forward technique
â Before sending message
⢠Divide into multiple equal-sized units (packets)
â At destination
⢠Packets reassembled into original long format
⢠Header contains pertinent packet information
⢠Advantages
â More flexible, reliable
â Greater line efficiency
â Users allocate message priority
Understanding Operating Systems, Fifth Edition 42
45. Connection Models (continued)
⢠Datagrams
â Packet destination and sequence number added to
information
⢠Uniquely identifying message to owning packet
â Each packet handled independently
â Route selected as each packet accepted
â At destination
⢠All packets of same message reassembled
â Advantages
⢠Diminishes congestion and provides reliability
Understanding Operating Systems, Fifth Edition 45
46. Connection Models (continued)
⢠Datagrams (continued)
â Message not delivered until all packets accounted for
â Receiving node requests retransmission
⢠Lost or damaged packets
â Advantages
⢠Diminishes congestion
⢠Sends incoming packets through less heavily used
paths
⢠More reliability
⢠Alternate paths set up upon node failure
Understanding Operating Systems, Fifth Edition 46
47. Connection Models (continued)
⢠Virtual circuit
â Complete path sender to receiver
⢠Established before transmission starts
â All message packets use same route
â Several virtual circuits to any other node
â Advantages
⢠Routing decision made once
⢠Speeds up transmission
â Disadvantages
⢠All virtual circuits fail upon one failure
⢠Difficult to resolve congestion (in heavy traffic)
Understanding Operating Systems, Fifth Edition 47
48. Conflict Resolution
⢠Device sharing requires access control methods
â Facilitates equal and fair network access
⢠Access control techniques
â Round robin
â Reservation
â Contention
⢠Medium access control protocols
â Carrier sense multiple access (CSMA)
â Token passing
â Distributed-queue, dual bus
Understanding Operating Systems, Fifth Edition 48
49. Conflict Resolution (continued)
⢠Round robin
â Node given certain time to complete transmission
â Efficient
⢠If many nodes transmitting over long time periods
â Substantial overhead
⢠If few nodes transmit over long time periods
⢠Reservation
â Good if lengthy and continuous traffic
â Access time on medium divided into slots
â Node reserves future time slots
Understanding Operating Systems, Fifth Edition 49
50. Conflict Resolution (continued)
⢠Reservation (continued)
â Good configuration
⢠Several terminals connected to host through single I/O
port
⢠Contention
â No attempt to determine transmission turn
â Nodes compete for medium access
â Advantages and disadvantages
⢠Easy implementation; works well under light to
moderate traffic; better for short and intermittent traffic
⢠Performance breaks down under heavy loads
Understanding Operating Systems, Fifth Edition 50
51. Conflict Resolution (continued)
⢠Carrier sense multiple access (CSMA)
â Contention-based protocol
â Easy implementation (Ethernet)
â Carrier sense
⢠Node listens to/tests communication medium before
transmitting messages
⢠Prevents collision with node currently transmitting
â Multiple access
⢠Several nodes connected to same communication line
as peers
⢠Same level and equal privileges
Understanding Operating Systems, Fifth Edition 51
52. Conflict Resolution (continued)
⢠CSMA Disadvantages
â Collision
⢠Two or more nodes transmit at same instant
â Probability of collision increases
⢠As nodes get further apart
â Large or complex networks
⢠Less appealing access protocol
Understanding Operating Systems, Fifth Edition 52
53. Conflict Resolution (continued)
⢠CSMA/CD
â Modification of CSMA
â Includes collision detection (Ethernet)
â Reduces wasted transmission capacity
â Prevents multiple nodes from colliding
⢠Collisions not completely eliminated (reduced)
â Implemented in Appleâs cabling system: LocalTalk
â Collision occurrence involves small packet
⢠Not actual data (in case of Apple CSMA/CA)
⢠No guarantee data will reach destination
â Ensures error free data delivery
Understanding Operating Systems, Fifth Edition 53
54. Conflict Resolution (continued)
⢠Token Passing
â Special electronic message (token)
⢠Generated and passed node to node
â Only node with token allowed to transmit
⢠Then passes token
â Fast access
â Collisions nonexistent
â Typical topologies
⢠Bus
⢠Ring
Understanding Operating Systems, Fifth Edition 54
55. Conflict Resolution (continued)
⢠Token-bus
â Token passed to node in turn
⢠Data attached; sent to destination
â Receiving node
⢠Copies data; adds acknowledgment; returns packet to
sending node
â Sending node passes token to next node in sequence
â Initial node order determination
⢠Cooperative decentralized algorithm
⢠Then determined by priority based on node activity
Understanding Operating Systems, Fifth Edition 55
56. Conflict Resolution (continued)
⢠Token-bus (continued)
â Higher overhead at each node (than CSMA/CD)
â Nodes have long waits before receiving token
⢠Token-ring
â Token moves between nodes in turn
⢠One direction only
â To send message
⢠Node must wait for free token
â Receiving node copies packet message
⢠Sets copied bit indicating successful receipt
Understanding Operating Systems, Fifth Edition 56
57. Conflict Resolution (continued)
⢠Distributed-queue, dual bus (DQDB)
⢠Dual-bus configuration
â Each bus transports data one direction only
â Steady stream of fixed-size slots
⢠Slots generated at end of each bus
â Marked as free and sent downstream
⢠Marked busy and written to
⢠Written by nodes ready to transmit
â Nodes read and copy data from slots
â Continue travel toward end of bus: dissipate
Understanding Operating Systems, Fifth Edition 57
59. Conflict Resolution (continued)
⢠DQDB advantages
â Negligible delays under light loads
â Predictable queuing under heavy loads
â Suitable for MANs managing large file transfers
â Satisfy interactive usersâ needs
Understanding Operating Systems, Fifth Edition 59
60. Transport Protocol Standards
⢠Network usage grew quickly (1980s)
⢠Need to integrate dissimilar network devices
â Different vendors
⢠Creation of single universally adopted architecture
â OSI reference model
â TCP/IP
Understanding Operating Systems, Fifth Edition 60
61. OSI Reference Model
⢠Basis for connecting open systems
â Distributed applications processing
⢠âOpenâ
â Connect any two systems conforming to reference
model and related standards
⢠Vendor independent
⢠Similar functions collected together
â Seven logical clusters (layers)
Understanding Operating Systems, Fifth Edition 61
63. OSI Reference Model (continued)
⢠Layer 1: The Physical Layer
â Describes mechanical, electrical, functional
specifications
â Transmits bits over communication line
⢠Examples: 100Base-T, RS449, CCITT V.35
⢠Layer 2: The Data Link Layer
â Establishes and controls physical communications
path before data sent
â Transmission error checking
â Problem resolution (on other side)
⢠Examples: HDLC and SDLC
Understanding Operating Systems, Fifth Edition 63
64. OSI Reference Model (continued)
⢠Layer 3: The Network Layer
â Addressing and routing services moving data through
network to destination
⢠Layer 4: The Transport Layer
â Maintains reliable data transmission between end
users
⢠Example: Transmission Control Protocol (TCP)
⢠Layer 5: The Session Layer
â Provides user-oriented connection service
â Transfers data over communication lines
⢠Example: TCP/IP
Understanding Operating Systems, Fifth Edition 64
65. OSI Reference Model (continued)
⢠Layer 6: The Presentation Layer
â Data manipulation functions common to many
applications
⢠Formatting, compression, encryption
⢠Layer 7: The Application Layer
â Application programs, terminals, computers
⢠Access network
â Provides user interface
â Formats user data before passing to lower layers
Understanding Operating Systems, Fifth Edition 65
66. TCP/IP Model
⢠Transmission Control Protocol/Internet Protocol
(TCP/IP)
â Oldest transport protocol standard
â Internet communications basis
â File-transfer protocol: send large files error free
â TCP/IP
⢠Emphasizes internetworking
⢠Provides connectionless services
â Organizes communication system
â Three components: processes, hosts, networks
â Four layers
Understanding Operating Systems, Fifth Edition 66
68. TCP/IP Model (continued)
⢠Network Access Layer
â Protocols provide access to communication network
â Flow control, error control between hosts, security,
and priority implementation performed
⢠Internet Layer
â Equivalent to OSI model network layer performing
routing functions
â Implemented within gateways and hosts
â Example: Internet Protocol (IP)
Understanding Operating Systems, Fifth Edition 68
69. TCP/IP Model (continued)
⢠Host-Host Layer
â Transfer data between two processes
⢠Different host computers
â Error checking, flow control, manipulate connection
control signals
â Example: Transmission Control Protocol (TCP)
⢠Process/Application Layer
â Protocols for computer-to-computer resource sharing
and terminal-to-computer remote access
â Examples: FTP, SMTP, Telnet
Understanding Operating Systems, Fifth Edition 69