• TCP and UDP
  • TCP forms a connection between two elements in a communication.
    • This consists of a logical mapping between ports and ip addresses on two machines.
    • It provides reliable transfer, ie if a packet is dropped, a new one is requested.
    • This is accomplished via sequence number of packets
    • It also provides flow control
    • This is somewhat expensive however.
  • UDP or User Datagram Protocol is an alternative
    • This is at the same level as TCP
    • There is not guarantee of delivery
    • Or in-order delivery
    • The header is much smaller, and the overhead much lower.
    • And much less processing
    • In the case of SNMP this is an ideal solution
    • Look at the two headers on page 39.
    • 
    • Note, even the checksum is optional.
• IPV6
  • The payload, plus the transport layer header, plus the IP header is an IP Packet or an IP Datagram
  • In IPv4 this included 32 bit source and destination addresses.
  • There was some thought that we would run out of addresses in the near future.
    • There are 2³² or 4.3 billion addresses possible with this setup.
    • But at the time we were assigning big chunks of addresses to single sites.
    • For example Edinboro has 147.64._._ or 2¹⁶ 65,536 addresses assigned to us.
    • in fact, in MCS we have 147.64.242.___ and 147.64.243.___ or 512 addresses assigned to us.
  • The IETF (Internet Engineering Task Force) decided in 1995 that we would soon run out with IPv4 addresses so they created IPv6.
  • This has a address size of 128 bits.
  • or 3.4x10³⁸ addresses.
    • This is not completely unreasonable.
    • Some day your watch may have an ip address.
    • And your mp3 player
    • and your refrigerator
    • ...
  • The process of moving to IPv6 is expected to take decades.
  • 
• Some Applications
  • SMTP - Simple Mail Transfer Protocol
    • This is a file transfer protocol (RFC 821).
    • That also involves source and destination users
    • Which has become far more complex in recent years.
    • There is an ability to act as a relay, in case the source and destination are
  • FTP as we have discussed (RFC 959)
  • TELNET as we have discussed (RFC 854).
  • All of these use TCP/IP
  • Even SSH (RFC 4251).
• MIME - Multipurpose Internet Mail Extension (RFC 2045)
  • Built on top of SMTP
• Look at the picture on page 42
•