Ch. 9 : Network Organization Concepts - PowerPoint PPT Presentation

Loading...

PPT – Ch. 9 : Network Organization Concepts PowerPoint presentation | free to view - id: 9493e-MzY0Y



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Ch. 9 : Network Organization Concepts

Description:

Sites in any networked system can be physically or logically connected to one ... Hosts are connected to one another in a linear fashion. ... – PowerPoint PPT presentation

Number of Views:170
Avg rating:3.0/5.0
Slides: 80
Provided by: Terri111
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Ch. 9 : Network Organization Concepts


1
Ch. 9 Network Organization Concepts
  • Basic Terminology
  • Network Topologies
  • Network Types
  • Software Design Issues
  • Circuit Switching
  • Packet Switching
  • Access Control Techniques
  • Medium Access Control Procedures
  • Transport Protocol Standards
  • Hardware Software
  • Connections Design
  • Many Network Designs
  • Transport Protocol Standards

2
Networks
  • When computer facilities are connected together
    by data-communication components, form network of
    automated resources.
  • Support many functions of business, education,
    healthcare, government, other organizations.
  • Provide essential infrastructure to process,
    manipulate, and distribute data information.
  • Common goal to provide a convenient way to share
    resources while controlling users access to
    them.
  • Resources include hardware (CPU, memory,
    printers, modems, disk drives) and software
    (application programs, data files).

3
General Configurations for Operating Systems for
Networks
  • Network operating system -- networking capability
    added to single-user operating system.
  • Users aware of specific computers and resources
    in the network.
  • Access via logon to/data transfer from remote
    host.
  • Distributed operating system -- users can access
    remote resources as if local resources.
  • Good control for distributed computing systems.
  • Represents total view across multiple computer
    systems for controlling managing resources
    without local dependencies.
  • Management is cooperative -- encompasses every
    resource involves every site.

4
Distributed Operating System
  • At minimum, must provide
  • Process or object management.
  • Memory management.
  • I/O management.
  • Device management.
  • Network management.
  • Easy and reliable resource sharing.
  • Improved computation performance.
  • Adequate load balancing.
  • Good reliability.
  • Dependable communications among network users.

5
Basic Terminology Network Processors
  • Network -- collection of loosely coupled
    processors, interconnected by communication
    network.
  • In distributed system each processor classifies
    other processors resources as remote and
    considers its own resources local.
  • Size, type, and identification of processors
    varies. Depending on context in which theyre
    mentioned, referred to as
  • Site -- indicates specific location in network
    with 1 computers.
  • Host -- specific computer system found at site
    whose services resources can be used from
    remote locations.
  • Node -- name assigned computer system connected
    to network to identify it to other computers in
    network..

6
Basic Terminology Client/Server
  • Host at one site (server) has resources that host
    at another site (client) wants to use.
  • Assignments arent static.
  • Actual role of client and server can alternate
    between 2 networked hosts depending on
    application and network configuration.

7
Network Topologies
  • Sites in any networked system can be physically
    or logically connected to one another in variety
    of topologies.
  • Most common geometric arrangements star, ring,
    bus, tree, hybrid.
  • Tradeoffs between need for fast communication
    among all sites, tolerance of failure at site or
    communication link, cost of long communication
    lines, and difficulty of connecting a site to
    large number of other sites.
  • Key to choosing best design is to understand
    available technology customers business
    requirements budget.

8
Criteria for Selection of a Topology
  • Basic costexpense required to link various sites
    in system.
  • Communications costtime required to send a
    message from one site to another.
  • Reliabilityassurance that many sites can
    communicate with each other even if link or site
    in system fails.
  • Users environmentcritical parameters that
    network must meet to be a successful business
    investment.

9
Star Topology (Hub, Centralized Topology)
  • All transmitted data must pass through central
    controller when going from sender to receiver.
  • Easy routing since central station knows path to
    all other sites.
  • Easily controlled access to network due to
    central control point.
  • Priority status given to selected sites.
  • Centralization of control requires that central
    site be extremely reliable able to handle all
    network traffic.

10
Ring Topology
  • All sites connected in closed loop.
  • Data transmitted in packets with source
    destination addresses.
  • Each packet is passed in one direction only.
  • Destination station copies data into local
    buffer.
  • Packet continues to circulate until it returns to
    source station, where its removed from ring.
  • Every node must be functional for network to
    perform.
  • Rings can allow failed nodes to be bypassed.

11
Double loop computer network using ring topology.
Packets of data flow in both directions. Network
can be connected to other networks via bridge or
gateway.
12
Multi-rings bridged together. Three rings
connected to each other by two bridges. This
variation of ring topology allows several
networks with same protocol to be linked
together.
13
Bus Topology
  • All sites are connected to single communication
    line running length of network.
  • Hosts are connected to one another in a linear
    fashion.
  • Data flows in both directions from host to host
    and is turned around when it reaches an end point
    controller.
  • All sites share a common communication line, so
    only one of them can successfully send messages
    at any one time .

14
Control Mechanism Is Needed to Prevent Collisions
in Bus Topology
  • Data may pass directly from one device to
    another.
  • Messages sent directly to target node without
    reaching end point controller.
  • Data may be routed to end point controller at end
    of line.
  • If data reaches end point controller without
    being accepted by host, controller turns it
    around sends it back so message can be accepted
    by appropriate node on way back.
  • With some busses each message must always go to
    end of line before going back down communication
    line to node to which its addressed.

15
Tree Topology
Data flows up and down branches of trees and is
absorbed by controllers at end points.
16
Tree Topology
  • A collection of busses.
  • Communication line is branching cable with no
    closed loops.
  • Tree layout begins at head end, where 1 cables
    start.
  • Each cable may have branches with additional
    branches.
  • Can use bridges between busses with same protocol
    and as translators to busses with different
    protocols
  • Networks can operate at speeds responsive to
    hosts in network.

17
Messages in Tree Topologies
  • Message from any site circulates through
    communication line.
  • Can be received by all other sites.
  • If message reaches end point controller without
    being accepted by host, controller absorbs it.
  • One advantage of bus and tree topologies is that
    even if single node fails, message traffic can
    still flow through network.

18
Hybrid Topology
  • Some combination of any of 4 topologies.
  • E.g., replace single host in star with ring
    (shown below).
  • E.g., star with bus topology as communication
    line feeding hub.
  • Select strong points of each topology combine
    to effectively meet systems communications
    requirements.

19
Network Types
  • Useful to group networks according to physical
    distances they cover.
  • Defining characteristics becoming increasingly
    blurred as communications technology advances.
  • Generally divided into
  • Local area networks (LAN).
  • Metropolitan area networks (MAN).
  • Wide area networks (WAN).

20
Local Area Network (LAN)
  • Configuration found within office building,
    warehouse, campus, or similarly enclosed
    computing environment.
  • E.g., cluster of personal computers located in
    same general area.
  • Usually owned, used, and operated by single
    organization.
  • Allows computers to communicate directly through
    common communication line.
  • Physically confined to well-defined local area,
    but communications arent limited to that area.
  • LAN can be a component of larger communication
    network.
  • Provide easy access to outside through bridge or
    gateway.

21
Bridges and Gateways
  • Bridge device and software that connects 2
    geographically distant LANs with same protocols.
  • E.g., simple bridge used to connect 2 Ethernet
    LANs.
  • Gateway more complex device and software used
    to connect 2 LANs or systems that use different
    protocols.
  • Translate 1 networks protocol into another,
    resolving hardware and software
    incompatibilities.
  • E.g., systems network architecture (SNA) gateway
    can connect microcomputer network to mainframe
    host.

22
Data Rates and Media for LANs
  • Data rate of high-speed LANs varies from 100 mbps
    to 1 gbps.
  • Bandwidths can support very high-speed
    transmission for fully animated, full-color
    graphics video, digital voice transmission,
    other high data-rate analog or digital signals.
  • Star, ring, bus, tree, hybrid topologies
    construct LANs.
  • Transmission medium vary among topologies.
  • Baseband coaxial cable and optical fiber are
    common to all.

23
Factors to Consider When Selecting Transmission
Medium
  • Cost.
  • Data rate.
  • Reliability.
  • Number of devices that can be supported.
  • Distance between units.
  • Technical limitations.

24
Metropolitan Area Network (MAN)
  • Configuration spanning area larger than LAN.
  • Ranges from several blocks of buildings to entire
    city but not exceeding circumference of 100
    kilometers.
  • Owned operated by a single organization.
  • Usually used by many individuals organizations.
  • May be owned operated as public utilities,
    providing means for internetworking several LANs.
  • High-speed network.

25
MAN Typically Configured As a Logical Ring
  • Depending on protocol used, messages are either
  • Transmitted in 1 direction using only 1 ring.
  • Transmitted in both directions using 2
    counter-rotating rings,
  • One always carrying messages in one direction and
    other always carrying messages in opposite
    direction.

26
Wide Area Network (WAN)
  • Configuration that interconnects communication
    facilities in different parts of a country or
    world, or thats operated as part of public
    utility.
  • Uses communications lines of common carriers
    (government-regulated private companies such as
    telephone companies).
  • Uses broad range of communication media (e.g.,
    satellite, microwaves).
  • WANs are generally slower than LANs.

27
ARPAnet
  • First WAN developed by Advanced Research Projects
    Agency (ARPA) in 1969.
  • Defense Communications Agency in 1975.
  • Successor, Internet, is most widely recognized
    WAN.
  • Other commercial WANs exist (e.g Telenet).

28
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?

29
Addressing Conventions
  • Network sites need to uniquely identify users so
    can communicate access each others resources.
  • Names, addresses, routes required because sites
    arent directly connected except over
    point-to-point links.
  • Addressing protocols are closely related to
    network topology geographic location of each
    site.
  • Local name -- name by which a unit is known
    within its own system.
  • Global name -- name by which a unit is known
    outside its own system.

30
Domain Name Service (DNS) Protocol
  • Distributed data query service used to resolve
    Internet addresses.
  • Follows hierarchical organization (left to
    right) from logical user to host machine, from
    host machine to net machine, from net machine to
    cluster, and from cluster to network.
  • someone_at_icarus.lis.pitt.edu
  • someone logical user
  • icarus host for user called someone
  • lis net machine for icarus
  • pitt cluster for lis
  • edu network for University of Pittsburgh.  

31
Router
  • Router -- internetworking device, primarily
    software driven, which directs traffic between 2
    different types of LANs or 2 network segments
    with different protocol addresses.
  • Operates at Network Layer.
  • Role of routers changes as network designs
    change.
  • Used extensively for connecting sites to each
    other to Internet.
  • Used for a variety of functions including
  • Securing info generated in predefined areas.
  • Choosing the fastest route from 1 point to
    another.
  • Providing redundant network connections.

32
Routing Strategy
  • Routing protocols must consider
  • Addressing.
  • Address resolution.
  • Message format.
  • Error reporting.
  • Two of most widely used routing protocols in
    Internet
  • Routing information protocol.
  • Open shortest path first.

33
Routing Protocols
  • Most routing protocols are based on addressing
    format using network node number to identify
    each node.
  • When network is powered on, each router records
    addresses of networks that are directly
    connected.
  • At specified intervals each router in
    inter-network broadcasts copy of its entire
    routing table.
  • Eventually all routers know how to get to each of
    different destination networks.

34
Address Resolution
  • Addresses allow routers to send data from network
    to network .
  • Cant be used to get from one point in network to
    another point in same network.
  • Address resolution allows router to map original
    address to hardware address store mapping in
    table used for future transmissions.

35
Message Formats Defined by Routing Protocols
  • Messages allow protocol to perform its functions.
  • Finding new nodes on a network.
  • Testing to determine whether theyre working.
  • Reporting error conditions.
  • Exchanging routing information.
  • Establishing connections.
  • Transmitting data.

36
Problems with Data Transmission
  • Conditions may arise that cause errors such as
    inability to reach destination due to
    malfunctioning node or network.
  • Routers routing protocols report error
    condition.
  • Error correction is left to protocols at other
    levels of networks architecture.

37
Routing Information Protocol (RIP)
  • Path selection for transfer data between networks
    is based on number of intermediate nodes (hops)
    between source destination.
  • Path with smallest number of hops is always
    chosen.
  • Distance vector algorithm that is easy to
    implement.
  • Doesnt consider bandwidth, data priority, or
    type of network.
  • Can exclude faster or more reliable paths from
    being selected just because they have more hops.

38
More Problems with RIP
  • Another limitation relates to routing tables.
  • Entire table updated reissued every 30 seconds,
    whether or not changes have occurred.
  • Increases internetwork traffic negatively
    affects delivery of messages.
  • Tables propagate from one router to another.
  • Because not all routers have same info about
    internetwork, failure at any one hop can create
    unstable environment for all message traffic.

39
Open Shortest Path First (OSPF)
  • Selection of transmission path made after state
    of network determined.
  • If intermediate hop is malfunctioning its
    eliminated immediately from consideration until
    its services have been restored.
  • Routing update messages sent only when changes in
    routing environment occur.
  • Reduces number of messages in internetwork.
  • Reduces size of messages by not sending entire
    routing table.

40
Problems with OSPF
  • Memory usage is increased because OSPF tracks
    more info than RIP.
  • Savings in bandwidth consumption are offset by
    higher CPU usage needed for calculation of the
    shortest path.
  • Dijkstras algorithmfind shortest paths from
    given source to all other destinations by
    proceeding in stages developing path in
    increasing lengths.
  • Computes all different paths to each destination
    in internetwork.
  • Creates topological database that is maintained
    by OSPF and is updated whenever failures occur.

41
Connection Models
  • Communication network concerned with moving data
    from one point to another.
  • Nodes are connected to communication network
    designed to minimize transmission costs provide
    full connectivity among all attached devices.
  • Data entering network at one point is routed to
    destination by being switched from node to node.
  • Circuit switching.
  • Packet switching.

42
Circuit Switching
  • Communication model in which dedicated
    communication path is established between two
    hosts.
  • Path is connected sequence of links connection
    between 2 points exists until one of them is
    disconnected.
  • E.g., Telephone system
  • Connection path must be set up before data
    transmission begin.
  • If entire path becomes unavailable, messages
    cant be transmitted because circuit would not be
    complete.
  • Delay before signal transfer begins while
    connection is set up.
  • Once circuit completed, network is transparent to
    users.
  • Info transmitted at fixed rate of speed with
    insignificant delays at intermediate nodes.

43
Packet Switching
  • Store-and-forward technique.
  • Message divided into multiple equal-sized units
    (packets).
  • Packets sent through network to their
    destination.
  • Reassembled into their original long format.
  • Does not require a dedicated connection.

44
Packet Switching Is a 3-step Procedure
  • Divide data into addressed packets.
  • Send each packet toward its destination.
  • At destination, confirm receipt of all packets,
    place them in order, reassemble data, and deliver
    it to recipient.

45
Pros Cons of Packet Switching
  • Effective for long-distance data transmission.
  • More flexible than circuit switching -- data
    transmission between devices that
    receive/transmit data at different rates.
  • No guarantee that packets all travel along same
    path or arrive in physical sequential order.
  • Packets from one message may be interspersed with
    those from other messages as travel toward
    destinations.
  • Attach header with pertinent info about packet
    before it's transmitted.
  • Info varies according to routing method used by
    network.

46
Packet Switching vs. Circuit Switching
47
Method of Selecting Path Datagrams
  • Destination sequence number of packet added to
    info uniquely identifying message to which packet
    belongs.
  • Each packet handled independently route is
    selected as each packet is accepted into network.
  • At destination, all packets of same message
    reassembled by sequence number into continuous
    message delivered.
  • Message cant be delivered until all packets
    accounted for.
  • Receiving node requests retransmission of lost or
    damaged packets.

48
Advantages of Datagram Routing
  • Helps diminish congestion by sending incoming
    packets through less heavily used paths.
  • Provides more reliability, because alternate
    paths may be set up when one node fails.

49
Method of Selecting Path Virtual Circuit
Approach
  • Complete path from sender to receiver established
    before transmission starts.
  • All packets belonging to that message use same
    route.
  • Destination packet sequence number arent
    necessary.
  • Different from dedicated path used in circuit
    switching because any node can have several
    virtual circuits to any other node.
  • Routing decision made once for all packets
    belonging to same message.
  • If node fails, all virtual circuits using that
    node become unavailable.
  • When circuit experiences heavy traffic,
    congestion is more difficult to resolve.

50
Conflict Resolution
  • Some method to control access is necessary to
    facilitate equal and fair access to network
  • Round robin.
  • Reservation. Access control techniques
  • Contention.
  • Carrier sense multiple access.
  • Token passing. Medium access
  • Distributed-queue. control protocols
  • Dual bus.

51
Access Control Techniques Round Robin
  • Allows each node on network to use communication
    medium.
  • If node has data to send, its given certain
    amount of time to complete transmission, at end
    of which opportunity is passed to next node.
  • If node has no data to send or completes
    transmission before time is up, then next node
    begins its turn.
  • Efficient technique with many nodes transmitting
    over long periods.
  • When few nodes transmit over long periods of
    time, substantial overhead to pass turns from
    node to node.
  • Other techniques preferable depending on whether
    transmissions are short intermittent (e.g.,
    interactive terminal-host sessions), or lengthy
    continuous (e.g., massive file transfer
    sessions).

52
Access Control Techniques Reservation
  • Well suited for lengthy continuous traffic.
  • Access time on medium is divided into slots
    node can reserve future time slots for its use.
  • Similar to synchronous time-division multiplexing
    (used for multiplexing digitized voice streams)
    where time slots are fixed in length
    preassigned to each node.
  • Good for configuration with several terminals
    connected to host computer through single I/O
    port.

53
Access Control Techniques Contention
  • Better for short and intermittent traffic.
  • No attempt is made to determine whose turn it is
    to transmit so nodes compete for access to
    medium.
  • Works well under light to moderate traffic.
  • Performance tends to break down under heavy
    loads.
  • Major advantage -- easy to implement.

54
Medium Access Control Procedures Carrier Sense
Multiple Access (CSMA)
  • Contention-based protocol thats easy to
    implement.
  • Network node listens to (tests) communication
    medium before transmitting any messages.
  • Prevents collision with another node thats
    currently transmitting.
  • Multiple access -- several nodes connected to
    same communication line as peers, on same level,
    and with equal privileges.

55
Collisions In CSMA
  • 2 nodes could transmit at same instant,
    creating collision.
  • Data from all transmissions damaged line
    remains unusable while damaged messages are
    dissipated.
  • When receiving nodes fail to acknowledge
    transmission, senders know it didnt reach
    destinations.
  • Both retransmit.
  • Probability of collisions increases if nodes
    farther apart.
  • CSMA less appealing access protocol for large or
    complex networks.

56
Carrier Sense Multiple Access With Collision
Detection (CSMA/CD).
  • CSMA algorithm was modified to include collision
    detection.
  • E.g., Ethernet.
  • Collision detection does not eliminate collisions
    but it does reduce them.
  • When collision occurs, jamming signal sent
    immediately to both senders, which wait random
    period before retrying.
  • With this protocol amount of wasted transmission
    capacity is reduced to time it takes to detect
    collision.

57
Collision Avoidance (CSMA/CA).
  • Collision avoidance -- access method prevents
    multiple nodes from colliding during
    transmission.
  • Efficiency is questionable.
  • Implemented in LocalTalk, Apples cabling system,
    which uses a protocol called LocalTalk link
    access protocol.
  • If collisions occur, involve only 3-byte packets,
    not actual data.
  • Protocol does not guarantee data will reach its
    destination, but it ensures that any data thats
    delivered will be error free.

58
Token-Passing Networks
  • Special electronic message (token) is generated
    when network is turned on and passed along from
    node to node.
  • Only node with the token allowed to transmit, and
    after it has done so, it must pass token on to
    another node.
  • Popular because access is fast and collisions are
    nonexistent.
  • Typical topologies bus or ring.

59
Token-Bus Network
  • Token is passed to each node in turn.
  • Upon receipt of token, node attaches data to it
    and sends packet with token data to its
    destination.
  • Receiving node copies data, adds acknowledgment,
    returns packet to sending node.
  • Sending node passes token on to next node in
    logical sequence.
  • Initial node order determined by cooperative
    decentralized algorithm.
  • Once network is running, turns determined by
    priority based on node activity.
  • Higher overhead at each node than CSMA/CD.
  • Nodes may have long waits under certain
    conditions before receiving token.

60
Token Ring
  • Most widely used protocol for ring topology.
  • Based on use of free/busy token that moves
    between nodes in turn one direction only.
  • If node wants to send message,waits free token
    to come by.
  • Changes token from free to busy sends its
    message immediately following busy token.
  • All other nodes must wait for free token to come
    to them again.
  • Receiving node copies message in packet sets
    copied bit to indicate it was successfully
    received.
  • Packet continues, making complete round trip back
    to sender.
  • Sending node releases new free token on network..

61
Distributed-Queue, Dual Bus (DQDB) Protocol
  • Intended for use with dual-bus configuration.
  • Where each bus transports data in only one
    direction.
  • Standardized by IEEE as part of MAN standards.
  • Transmission on each bus consists of steady
    stream of fixed-size slots.
  • Slots generated at end of each bus marked free
    sent downstream, where theyre marked busy
    written to by nodes ready to transmit.
  • Nodes read and copy data from slots, which then
    continue to travel toward end of bus, where they
    dissipate.

62
Transport Protocol Standards
  • Network usage quickly grew in 1980s along with
    need to integrate dissimilar network devices from
    different vendors.
  • Increasingly difficult as number complexity of
    network devices increased.
  • Users pressured industry to create single
    universally adopted network architecture for true
    multi-vendor interoperability.
  • Two competing standards
  • OSI.
  • TCP/IP.

63
Open Systems Interconnection (OSI) Reference
Model from ISO
  • International Standards Organization (ISO)
    created open systems interconnection reference
    model.
  • Serves as framework for defining services that
    network should provide to its users.
  • Provides basis for connecting open systems for
    distributed applications processing.
  • Open means that any 2 systems that conform to
    reference model related standards can be
    connected, regardless of vendor.

64
OSI Layers and Protocols
  • Similar functions collected together into 7
    logical clusters (layers).
  • Group easily localized functions so each layer
    could be redesigned its protocols changed
    without changing services expected from/provided
    to, adjacent layers.
  • Boundaries between layers were selected at points
    that past experience had revealed to be
    effective.
  • Software handles data transmission from one
    terminal or application program to another.

65
Layer 1The Physical Layer
  • Bottom of model where mechanical, electrical,
    functional specifications for connecting device
    to particular network described.
  • Primarily concerned with transmitting bits over
    communication lines.
  • Voltages of electricity timing factors
    important.
  • Only layer concerned with hardware.
  • All data must be passed down to it for actual
    data transfer between units to occur.
  • E.g., 10Base-T, RS449, and CCITT V.35.

66
Layer 2The Data Link Layer
  • Software is needed to implement Layer 2 is
    stored in some type of programmable device (e.g.,
    front end processor, network node).
  • Bridging between 2 homogeneous networks occurs
    here.
  • On one side, DLL establishes controls physical
    path of communications before sending data to
    physical layer below it.
  • Takes data packets assembles it for
    transmission by completing its frame.
  • Frames contain data combined with control error
    detection characters.
  • On other side, DLL checks for transmission errors
    resolves problems caused by damaged, lost, or
    duplicate message frames.
  • E.g., High-Level Data Link Control (HDLC) and
    Synchronous Data Link Control (SDLC).

67
Layer 3The Network Layer
  • Provides services such as addressing routing
    that move data through network to its
    destination.
  • Software at this level accepts blocks of data
    from Layer 4, resizes them into shorter packets,
    routes them to proper destination.
  • Addressing methods that allow a node and its
    network to be identified, algorithms to handle
    address resolution are specified here.
  • Database of routing tables keeps track of all
    possible routes a packet may take determines
    how many different circuits exist between any 2
    packet switching nodes.

68
Layer 4The Transport Layer
  • Host-to-host or end-to-end layer -- maintains
    reliable data transmission between end users.
  • Program at source computer can send virtual
    communication to similar program at destination
    via message headers control messages.
  • Physical path goes to Layer 1 across to
    destination computer.
  • Software handles user addressing ensures that
    all packets of data received none lost.
  • Stored in front end processors, packet switching
    nodes, or host computers.
  • Has mechanism to regulate info flow so fast host
    cant overrun slower terminal or overloaded host.
  • E.g., Transmission Control Protocol (TCP).

69
  • Layer 5The Session Layer
  • Layer 5 is responsible for providing a
    user-oriented connection service and transferring
    data over the communication lines. The transport
    layer is responsible for creating and maintaining
    a logical connection between end points. The
    session layer provides a user interface that adds
    value to the transport layer in the form of
    dialogue management and error recovery. Sometimes
    the session layer is known as the data flow
    control layer because it establishes the
    connection between two applications or processes,
    enforces the regulations for carrying on the
    session, controls the flow of data, and resets
    the connection if it fails. This layer may also
    perform some accounting functions to ensure that
    users receive their bills. The functions of the
    transport layer and session layer are very
    similar, and because the operating system of the
    host computer generally handles the session
    layer, it would be natural to combine both layers
    into one, as does TCP/IP.

70
Layer 6The Presentation Layer
  • Responsible for data manipulation functions
    common to many applications.
  • E.g., formatting, compression, encryption, data
    conversion, syntax conversion, protocol
    conversion.
  • Gateways connecting networks with different
    protocols are presentation layer devices.
  • Accommodate totally different interfaces as seen
    by terminal in one node expected by application
    program at host computer.
  • E.g., IBM's Customer Information Control System
    (CICS) teleprocessing monitor is presentation
    layer service located in host mainframe.

71
Layer 7The Application Layer
  • Application program's, terminals, and computers
    access network.
  • Provides interface to users
  • Responsible for formatting user data before
    passing it to lower layers for transmission to a
    remote host.
  • Contains network management functions tools to
    support distributed applications.
  • E.g., File transfer and electronic mail.
  • Once OSI model is assembled, it allows nodes to
    communicate with each other.
  • Each layer provides completely different array of
    functions to network.
  • All layers work in unison to ensure that network
    provides reliable transparent service to users.

72
Transmission Control Protocol/ Internet Protocol
(TCP/IP)
  • Oldest transport protocol standard.
  • Basis for Internet communications..
  • Developed for U.S. Department of Defenses
    ARPAnet.
  • Provides reasonably efficient error-free
    transmission between different systems.
  • Large info files can be sent across sometimes
    unreliable networks with high probability that
    data will arrive error free.
  • TCP/IP emphasizes internetworking and providing
    connectionless services.

73
TCP/IP
  • Organizes a communication system with 3 main
    components
  • Processes
  • Hosts.
  • Networks.
  • Processes execute on hosts, which can support
    multiple simultaneous processes that are defined
    as primary units that need to communicate.
  • Processes communicate across networks where hosts
    connected.
  • Based on hierarchy, model roughly partitioned
    into 2 major tasks
  • Manages transfer of info to host in which process
    resides.
  • Ensures it gets to correct process within host.
  • Network needs to be concerned only with routing
    data between hosts, as long as hosts can then
    direct data to appropriate processes.

74
Network Access Layer
  • Equivalent to physical, data link, and part of
    network layers of OSI model.
  • Protocols at this layer provide access to
    communication network.
  • Some functions performed here
  • Flow control.
  • Error control between hosts.
  • Security.
  • Priority implementation.

75
Internet Layer
  • Equivalent to portion of network layer of OSI
    model that isnt already included in previous
    layer.
  • Specifically mechanism that performs routing
    functions.
  • Protocol is usually implemented within gateways
    hosts.
  • Example of a standard set by DoD is Internet
    Protocol (IP).
  • Provides connectionless service for end systems
    to communicate across 1 networks.

76
Host-Host Layer
  • Equivalent to transport and session layers of the
    OSI model.
  • Supports mechanisms to transfer data between 2
    processes on different host computers.
  • Services provided include
  • Error checking.
  • Flow control.
  • Ability to manipulate connection control signals.
  • Example of a standard set by DoD is Transmission
    Control Protocol (TCP).
  • Provides a reliable end-to-end data transfer
    service.

77
Process/Application Layer
  • Equivalent to presentation application layers
    of OSI model.
  • Protocols for computer-to-computer resource
    sharing terminal-to-computer remote access.
  • Specific examples of standards set by the DoD
  • File Transfer Protocol (FTP)-- simple application
    for transfer of ASCII, EBCDIC, binary files.
  • Simple Mail Transfer Protocol (SMTP) -- simple
    electronic mail facility.
  • TELNET -- simple asynchronous terminal capability
    that provides remote log-on capabilities to users
    working at terminal or PC.

78
Terminology
  • ARPAnet
  • bridge
  • bus topology
  • distance vector algorithm
  • distributed operating system (DOS)
  • Domain Name Service (DNS)
  • Ethernet
  • gateway
  • hosts
  • hybrid topology
  • Internet
  • ISO
  • local
  • local area network (LAN)
  • metropolitan area network (MAN)
  • network operating system (NOS)
  • nodes
  • open shortest path first (OSPF)
  • OSI reference model
  • packets
  • protocol

79
Terminology -2
  • remote
  • ring topology
  • router
  • routing information protocol (RIP)
  • sites
  • star topology
  • TCP/IP model
  • token ring
  • token-bus
  • topological database
  • tree topology
  • wide area network (WAN)
About PowerShow.com