Joe Jupin
CIS 617
3/1/04

1. Name the layers of the TCP/IP reference model and 
   answer the following questions.
   a. Which layer is responsible for reliability?
   b. Which layer is responsible for addressing?
   c. Which layer is responsible for flow control?
   d. Which layer is responsible for multiple users
      per computer?
   e. Which layer is responsible for routing?

   Ans: Application, transport, network and host-to-network.
        a. Transport
        b. Host-to-network
        c. Transport
        d. Transport
        e. Network


2. Define a communication channel and discuss the methods
   for sharing or multiplexing it.

   Ans: A communication channel is a single logical point-to-point
        connection between source and destination.

        Frequency division multiplexing divides a channel into
        different frequencies, which can be used to send
        multiple messages, simultaneously, over a single
        channel.

        Time division multiplexing time-shares a channel between
        multiple sources and destinations by giving each source
        a time slice of the channel at full bandwidth.


3. What is a carrier sense protocol? Name and describe three
   CSMA protocols.

   Ans: A protocol in which stations listen for a carrier
        or transmission.

   a. 1-persistant - Listens until channel is clear. Sends a
      transmission. If collision occurs, waits a random amount
      of time and retransmits.
   b. Nonpersistent - Checks to see if channel is clear. If so,
      it starts sending. If not, it waits a random amount of time
      and repeats from the beginning.
   c. N-persistent - When the station is ready to send, it senses
      the channel. If the channel is free, it transmits with
      a probability p. With a probability q = 1-p, it defers until
      the next slot. This is repeated until the frame is sent.

4. What is a virtual LAN and what is the differences and are the
   benefits over a non-virtual LAN?

   A virtual LAN is a collection of computers in a network that are
   grouped logically, as opposed to geographically in a non-VLAN.
   All machines in one logical group (like a department) can 
   be on one LAN even if their in different physical locations.
   This allows better security and distribution of capacity between
   logical groups than in a non-VLAN. 

5. Compare and contrast connection-oriented and connectionless
   protocols, name one of each.

   A connection-oriented service is modeled after a telephone system.
   The connection is a path through a network, similar to a tube,
   where the sender pushes bits in one end and the receiver takes
   them from the other.

   A connectionless protocol is similar to the postal system.
   Each message carries the destination address and may take one
   of many paths through the network independent of the other messages.


   TCP is connection-oriented.
   UDP is connectionless.