OSPF Design: 1 – Networking and Routing Fundamentals

  1. The application layer essentially acts as the end-user interface. This is the layer where inter-action between the mail application (cc:Mail, MS Outlook, and so on) or communications package (SecureCRT for Telnet or FTP Voyager for FTP) and the user occurs.
  2. The presentation layer is responsible for the agreement and translation of the communication format (syntax) between applications.
  3. The session layer responsibilities range from managing the application layer’s transfer of information to the data transport portion of the OSI reference model. An example is Sun’s or Novell’s Remote Procedure Call (RPC), which uses Layer 5.
  4. The transport layer is responsible for the logical transport mechanism, which includes functions conforming to the mechanisms characteristics.
    Provides a level of error checking and reliability (through sequence numbers) to the transmission of user data to the lower layers of the OSI reference model. This is the only layer that provides true source-to-destination, end-to-end connectivity through the use of routing protocols such as open shortest path first (OSPF) or the file transfer protocol (FTP) application as examples of TCP.
    The most common usage of UDP is streaming media solutions, such as Real Audio.
  1. The data link layer provides framing, error, and flow control across the network media being used. An important characteristic of this layer is that the information that is applied to it is used by devices to determine if the packet needs to be acted upon by this layer (that is, proceed to Layer 3 or discard).
    Serial interfaces do not normally require unique Layer 2 station addresses, such as MAC addresses, unless it is necessary to identify the receiving end in a multipoint network.
    24 bits are dedicated for Organization Unique Identification (OUI) and 24 bits are for unique identification.
    First 3 bytes of an Ethernet address are the company ID, and the last 3 bytes are assigned by the manufacturer.
  1. Physical layer is responsible for defining information regarding the physical media, such as electrical, mechanical, and functional specifications to connect two systems.
    The physical layer is composed of three main areas: wires, connectors, and encoding.

The data portion of an information unit at a given OSI layer can potentially contain headers, trailers, and data from all the higher layers. This is known as  encapsulation.  Continue reading “OSPF Design: 1 – Networking and Routing Fundamentals”

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