Lectures

  Network Layer - successful delivery of individual packets or data-grams
    across network.

    Routing of individual data packets.
     
    Logical (virtual) addressing such as Internet Protocol.

    Transferring of packets across dissimilar sub-nets.  
      Re-Framing of packet to traverse a particular sub-net.
   
    Control of congestion on network.

    Still working at node to node level.

    Not concerned with getting whole transmission to final destination.
      Just moving individual packets along to destination.

    Failure to deliver all packets of transmission NOT part of this layer.
  
    IP, ICMP*

  Data Link Layer - successful transmission of bits between individual nodes.

    Electronic/logical side of the connection. zeros and ones.

    Breaking data stream up into check-able frames of bits.
  
    Handling speed differences at different nodes of network.

    Deals with individual packets or frames.

    Data destination addressable only to other nodes on particular network.
      * Specialized node called gateway router provides access on/off local
        network.

    Physical address of interface.

    Negotiates access to network.

    Bit/frame-level error correction.

  Physical Layer - sending of bits.
    Equivalent of a physical bus.

    Mechanical, electrical, and physical transmission medium.

    Voltage and timing, Establishment and termination of connections, 
      uni or bidirectional, connector design and pin count.
 
    Network topology - bus, tree, mesh, ring

    Also interface design - hubs, repeaters, etc. 
    
  The OSI architecture was proposed in the mid-80s when small, complex,
    fast monolithic processors were just beginning to appear.
.  
  In practice, 
    Several of these layers were merged when current protocols and 
    electronics are implemented.
 
    Ethernet protocol combines physical and data link layers.
      And delegates some aspects to the network layer and takes over some 
      others from the network layer.

    Network is now generally handled by IP, (Internet Protocol) 
  
    Transport and part of the session layer are handle by TCP (