Protocol Hierarchy - PowerPoint PPT Presentation


PPT – Protocol Hierarchy PowerPoint presentation | free to view - id: aa571-MDQyN


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

Protocol Hierarchy


... header to each piece, but also a trailer, and gives the resulting unit to layer ... be set up before any communication takes place over which all packets travel ... – PowerPoint PPT presentation

Number of Views:1186
Avg rating:3.0/5.0
Slides: 29
Provided by: FordhamUn5


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

Title: Protocol Hierarchy

Lesson 5
Protocol Hierarchy
  • Question How can communication be provided to
    the top layer of the five-layer network of the
    following figure?

Providing communication to Top Layer of 5-Layer
Destination Machine
Source Machine
Important thing about the Figure
  • The peer process on layer 4, for example,
    conceptually think of their communication as
    being horizontal, using the layer 4 protocol
  • Each layer is likely to have a procedure called
    something like SendToOtherSide and
    GetFromOtherSide, even though these procedures
    actually communicate with lower layers across the
    3/4 interface, not with the other side.

Providing communication to Top Layer of a 5-Layer
  • A message M is produced by an application running
    in layer 5 and given to layer 4 for transmission
  • Layer 4 puts a header in front of the message to
    identify the message and passes the result to
    layer 3

The Header
  • Headers contain control information, such as
    sequence numbers, to allow layer 4 on the
    destination machine to deliver messages in the
    right order if the lower layer do not maintain
  • In some layers, headers can also contain sizes,
    times, and other control information.

Providing communication to Top Layer of a 5-Layer
  • In many networks, there is no limit to the size
    of messages transmitted in the layer 4 protocol,
    but there is always a limit impose by the layer 3
    protocol. Consequently, layer 3 must break up the
    incoming messages into smaller units, packets,
    attaching a layer 3 header to each packet. In
    this example, M is split into two parts M1 and

Providing communication to Top Layer of a 5-Layer
  • Layer 3 decides which of the outgoing lines to
    use and passes the message to layer 2.
  • Layer 2 adds not only a header to each piece, but
    also a trailer, and gives the resulting unit to
    layer 1 for physical transmission.

Providing communication to Top Layer of a 5-Layer
  • At the receiving machine the message moves
    upward, from layer to layer, with headers being
    stripped off as it progresses.
  • None of the headers below n are passed up to
    layer n.

  • The peer process abstraction is crucial to all
    network design. Using it, the unmanageable task
    of designing the complete network can be broken
    down into several smaller, manageable design
    problems, namely, the design of individual
  • The lower layers of a protocol hierarchy are
    frequently implemented in hardware or firmware.

Connection-Oriented Service and Connectionless
  • Connection-oriented service means that a
    connection must be set up before any
    communication takes place over which all packets
  • Example Telephone system
  • Connectionless service packets are routed
  • Example Snail mail

The OSI Model
  • The Open Systems Interconnection (OSI) model was
    developed by the International Standards
    Organization (IS0).
  • Called the ISO OSI model because it deals with
    connecting open systemsthat is, systems that are
    open for communication with other systems. Will
    use OSI for short.
  • Has seven layers

Principles on which the Seven Layers are Based
  • A layer should be created where a different
    abstraction is needed
  • Each layer should perform a well-defined function
  • The function of each layer should be chosen with
    an eye toward defining internationally
    standardized protocols.
  • The layer boundaries should be chosen to minimize
    the information flow across the interfaces
  • The number of layers should be large enough that
    distinct functions need not be thrown together in
    the same layer out of necessity and small enough
    that the architecture does not become unwieldly.

The Seven Layers
  • Layer 1 Physical Layer
  • Layer 2 Data Link Layer
  • Layer 3 Network Layer
  • Layer 4 Transport Layer
  • Layer 5 Session Layer
  • Layer 6 Presentation Layer
  • Layer 7 Application Layer

Layer 1 Physical Layer
  • Deals with basic network hardware.
  • Design issues have to do with making sure that
    when one side sends a 1 bit, it is received by
    the other side as a 1 bit, and not a 0 bit

Layer 2 Data Link Layer
  • Specify how to organize data into frames
  • Specify how to transmit frames over a network

Layer 3 Network
  • Specify how addresses are assigned
  • Specify how packets are forwarded from one end of
    a network to the other

Layer 4 Transport Layer
  • Specify how to handle details of reliable transfer

Session Layer
  • Specify how to establish a communication session
    with a remote system (e.g. how to login to a
    remote time-sharing computer).
  • Gives specification for security details such
    authentication using passwords.

Layer 6 Presentation Layer
  • Specify how to present data.
  • Such protocols needed because different brands of
    computers use different internal representations
    for integers and characters
  • In other words
  • Layer 6 protocols needed to translate from the
    representation on one computer to the
    representation on another

Layer 7 Application Layer
  • Each layer 7 protocol specify how a particular
    application uses a network
  • Example specification for an application that
    transfers files from one computer to the other

TCP/IP Reference Model
Internet Layer
  • Connectionless
  • Permits hosts to insert packets into any network
    and have them travel independently to the
    destination (potentially on different networks)
  • Packets may arrive out of orderhigher layers
    deal with ordering
  • Official packet format protocol Internet
    Protocol (IP)
  • Internet layers job
  • deliver IP packets to their destination (packet
    routing and congestion are major issues here)
  • Similar to OSI network layer

The Transport Layer
  • Allow peer entities on the source and destination
    machines to carry on a conversation
  • Two end-to-end protocols defined here
  • TCP (transmission control protocol)
  • UDP (User datagram protocol)

Transmission Control Protocol (TCP)
  • Reliable connectionless-oriented protocol
  • Allows byte streams originating on one machine to
    be delivered without error to another machine in
    the internet
  • Fragments incoming byte stream into discrete
    messages and passes each one to the internet
  • At destination receiving TCP process reassembles
    the receive messages into the output stream.
  • Handles flow control fast sender wont swamp
    slow receiver with more messages than it can

UDP (User Datagram Protocol)
  • Unreliable, connectionless protocol no
    sequencing or flow control

The Application Layer
  • Protocols
  • telnet virtual terminal
  • ftp File transfer
  • smtp electronic mail
  • Domain Name System (DNS) maps hosts names onto
    their network addresses
  • NNTP the protocol for moving USENET news
    articles around
  • HTTP protocol for fetching pages on the www
  • Etc.

Host-to-Network Layer
  • Not well defined
  • Varies from host to host and network to network
  • Host must connect to network using some protocol
    so it can send IP packets to it