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ICSA 411: Week 4 Protocol Architectures

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Not an actual architecture, but a model for how they work ... Open Systems Interconnection (OSI) 7-Layer Model. TCP/IP. Systems Network Architecture (SNA) ... – PowerPoint PPT presentation

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Title: ICSA 411: Week 4 Protocol Architectures


1
ICSA 411 Week 4Protocol Architectures
  • Elizabeth Lane Lawley, Instructor

2
Simple Protocol Architecture
  • Not an actual architecture, but a model for how
    they work
  • Similar to pseudocode, used for teaching
    programming
  • Once we understand the building blocks, we can
    look at specific examples
  • Open Systems Interconnection (OSI) 7-Layer Model
  • TCP/IP
  • Systems Network Architecture (SNA)

3
Why Use Protocol Architecture?
  • Data communications requires complex procedures
  • Sender identifies data path/receiver
  • Systems negotiate preparedness
  • Applications negotiate preparedness
  • Translation of file formats
  • For all tasks to occur, high level of cooperation
    is required

4
Modular Approach
  • Break tasks into subtasks
  • Each module handles specific subset of tasks
  • Communication occurs
  • between different modules on the same system
  • between similar modules on different systems

5
Simple Modular Example
  • File transfer facility
  • Three modules
  • File transfer module could handle translation and
    inter-application communication
  • Communication service module could handle
    negotiation of preparedness, data flow
  • Network access module could handle data path

6
Advantages of Modularity
  • Easier application development
  • Network can change without all programs being
    modified

7
Three-Layer Model
  • Distributed data communications involves three
    primary components
  • Applications
  • Computers
  • Networks
  • Three corresponding layers
  • Network access layer
  • Transport layer
  • Application layer

8
Network Access Layer
  • Concerned with exchange of data between computer
    and network
  • Includes addressing, routing, prioritizing, etc
  • Different networks require different software at
    this layer
  • Example X.25 standard for network access
    procedures on packet-switching networks

9
Transport Layer
  • Concerned with reliable transfer of information
    between applications
  • Independent of the nature of the application
  • Includes aspects like flow control and error
    checking

10
Application Layer
  • Logic needed to support various applications
  • Each type of application (file transfer, remote
    access) requires different software on this layer

11
Addressing
  • Each computer on a network requires a unique
    address on that network
  • Each application on the computer must have a
    unique address within the computer to allow the
    transport layer to support multiple applications
  • Data units must include network and application
    addresses

12
Standardized Protocol Architectures
  • Vendors like standards because they make their
    products more marketable
  • Customers like standards because they enable
    products from different vendors to interoperate
  • Two protocol standards are well-known
  • TCP/IP widely implemented
  • OSI well-known, less used, still useful for
    modeling/conceptualizing

13
OSI
  • Application
  • Presentation
  • Session
  • Transport
  • Network
  • Data Link
  • Physical
  • Open Systems Interconnection
  • Developed by ISO
  • Contains seven layers(see page 358)

14
OSI Lower Layers
  • Physical
  • Data Link
  • Network

15
OSI Physical Layer
  • Responsible for transmission of bits
  • Always implemented through hardware
  • Encompasses mechanical, electrical, and
    functional interfaces
  • e.g. RS-232

16
OSI Data Link Layer
  • Responsible for error-free, reliable transmission
    of data
  • Flow control, error correction
  • e.g. HDLC

17
OSI Network Layer
  • Responsible for routing of messages through
    network
  • Concerned with type of switching used
  • Handles routing between networks, as well as
    through packet-switching networks

18
OSI Upper Layers
  • Transport
  • Session
  • Presentation
  • Application

19
OSI Transport Layer
  • Isolates messages from lower and upper layers
  • Breaks down message size
  • Monitors quality of communications channel
  • Selects most efficient communication service
    necessary for a given transmission

20
OSI Session Layer
  • Establishes connections between systems
  • Manages log-ons, password exchange, log-offs
  • Tracks physical location of files on both sides
    of a transfer

21
OSI Presentation Layer
  • Provides format and code conversion services
  • Examples
  • File conversion from ASCII to EBDIC
  • Invoking character sequences to generate bold,
    italics, etc on a printer

22
OSI Application Layer
  • Provides access to network for end-user
  • Users capabilities are determined by what items
    are available on this layer

23
OSI in Action Outgoing File Transfer
  • FTP program issues command to Application Layer
  • Application passes it to Presentation, which may
    reformat, passes to Session
  • Session requests a connection, passes to
    Transport
  • Transport breaks file into chunks, passes to
    Network
  • Network selects the datas route, passes to Data
    Link
  • Data Link adds error-checking info, passes to
    Physical
  • Physical transmits data, which includes
    information added by each layer

24
OSI in Action Incoming File Transfer
  • Physical receives bits, passes to Data Link
  • Data Link checks for errors, passes to Network
  • Network verifies routing, passes to Transport
  • Transport reassembles data, passes to Session
  • Session determines if transfer is complete, may
    end session, passes to Presentation
  • Presentation may reformat, perform conversions,
    pass to Application layer
  • Application presents results to user (e.g.
    updates FTP program display)

25
TCP/IP v. OSI
  • See diagram page 359 for relationships
  • Most production software uses TCP/IP rather
    than OSI
  • Why has OSI lost the war? Two primary reasons
  • Not as mature as TCP/IP
  • Unnecessarily complex (seven layers rather than
    five)

26
Why Study OSI?
  • Still the best model for conceptualizing and
    understanding protocol architectures
  • Later ICSA networking classes expect you to know
    and understand this model
  • Key points
  • Modular
  • Hierarchical
  • Boundaries between layersinterfaces

27
TCP/IP
  • Transmission Control Protocol/Internet Protocol
  • Developed by DARPA
  • No official protocol standard
  • Can identify five layers
  • Application
  • Host-to-Host (transport)
  • Internet
  • Network Access
  • Physical

28
TCP/IP Physical Layer
  • Physical interface between a DTE (e.g. computer
    or terminal) and a transmission medium
  • Specifies
  • Characteristics of medium
  • Nature of signals
  • Data rate
  • Similar to mechanical aspects of RS-232

29
TCP/IP Network Access
  • Exchange of data between end system and network
  • Address of host and destination
  • Prioritization of transmission
  • Software at this layer depends on network (e.g.
    packet-switching vs. Ethernet)
  • Segregation means that no other software needs to
    be concerned about net specifics

30
TCP/IP Internet Layer
  • An Internet is an interconnection of two or more
    networks
  • Internet layer handles tasks similar to network
    access layer, but between networks rather than
    between nodes on a network
  • Uses IP for addressing
  • Implemented in workstations and routers

31
TCP/IP Transport Layer
  • Also called host-to-host layer
  • Reliable exchange of data between applications
  • Uses TCP protocols for transmission

32
TCP/IP Application Layer
  • Logic needed to support variety of applications
  • Separate module supports each type of application
    (e.g. file transfer)
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