ISO - OSI 
  International Standards Organization
  Open System Interconnection (1983?)
    Standard driven by phone companies (AT&T and European).

  7 layers - 
    Physical Layer - sending of bits.
      Mechanical, electrical, timing interfaces, and physical trans. medium.

      Voltage and timing, Establishment and termination of connections, 
        uni or bidirectional, connector pin count.
    
    Data Link Layer - successful transmission of bits.
      Breaking data stream up into checkable frames of bits.
  
      Hanling speed differences at different nodes of network.

      Deals with individual packets or frames.

    Network Layer - successful delivery of individual frames across network.
      Routing of frames.
     
      Conversion of addressing of packets on disimilar sub-nets.  
   
      Control of congestion on network.

      Still working at node to node level.

    Transport Layer - parses data into packets of workable size for network
      layer.

      Basically, interface between individual system/software and network.

      Responsible for sequencing created packets and rebuilding them on 
        delivery with minimal errors.

      Level at which communicating machines interact. 

    Session Layer - provides a specific transaction between machines.
      Establishes task definition and control.
        FTP - connect, login, transfer data, close.

        And guarantees that the file transmitted was correctly reassembled,
         i.e; if connection lost and re-established, 
           transfer continues at interruption.

    Presentation Layer - guarantees common syntax of data transmitted.
      When submitting a program to MVS, convert ASCII text to EBCDIC. 

    Application Layer - defines protocols and actions.
      Http, telnet, ftp, etc.

      Defines server an available services.

   

   

   
 
IPv4 - Internet Protocol packet (datagram packet).
  Address
  4 octet current protocol - 2^32.
  (IPv6) - 6 octets - 2^48 - however it must be backwards compatible. 

  Pactet details.
  Minimum of 40 bytes and up to 65535 bytes.  
    Packet size independent of lan protocols.

  Besides data being transmitted, some information it contains:
    Total Length of packet up to 65535. 

    Packet ID - serial number combined with Host ID results in a unique id.
 
    Fragment Offset - used if datagram needs to be broken down for a 
    particular network.

    TTL - time to live, used to guard against a lost and wandering packet.

    Protocol number - type of packet: control, UDP, or TCP

    Source and destination IPs.

  Error checking - at the IP level, just check that the packet been delivered 
  in an uncorrupted form.

TCP - Transmission Control Protocol packet
  Generated by the application.
 
  Source and destination ports - used to destinguish which application
  or service is being communicated with on a particular machine.

  Sequence number - offset from beginning of whole payload. Used to 
  rebulid the whole block of data being transfered. 

  A variety of control/condition flags.

  Data being transmitted.

  Error checking - has all the data for the session or activity been 
  delivered, is it re-assembled in the right order, and there is no
  duplication of packets. 


Handshaking.

Establish a connection.

Client sends SYNC to server
Server responds with a SYNC/ACK back to client
Client completes connection with an ACK back to server.

Data is now transmitted in multiple packets.

Termination

One of the devices sends a FIN packet. It may also include the last 
packet of data.

The other device responds with an ACK. 

The two devices then switch places with the 2nd device sending a FIN and
the 1st responding with an ACK.

Which device initiates a termination depends on particular task.

* If first device wishes to terminate a connection but the second device has
some final business to do (data transmission), this 2 step termination allows
this to take place.

see : 
 http://www.tcpipguide.com/free/t_TCPConnectionTermination-2.htm


UDP - User Datagram Protocol packet
  A simpler version of a TCP packet - single unit of communication. Often
  used for communicating control information.

  Source and destination ports, Size, checksum - all 16 bit

  Data. allowable size 2^32-1

  * Ureliable - no check to see if reached destination. 
  * Not ordered - each UDP datagram is its own package. 
  * Lightweight - one packet just sent all alone in the world.
  * Checksum only check of data integrity. 
  * No congestion control.


ICMP - Internet Control Message Protocol

  8 byte heacder
  Bits 
  0-7   Type - type of info, also specifies size of data payload.
  8-15  Code
  16-31 Checksum
  32-63 Rest of header. Contents determined by type flag.
  64-   data - depending on type, may even be empty.