Information Technology Reference
In-Depth Information
Figure 3. Application port map
Figure 4. Domain name map
Domain Name
IP
Application
Port
FTP
21
George.edu
10.4.2.1
SMTP
25
thomas.gov
10.4.2.3
DHCP
67
john.org
10.4.5.6
HTTP
80
martha.edu
10.7.8.9
Oracle
1525
martha.org
10.10.0.11
nected” by six to 10 foot long pieces of wire held at each end by the player playing the “NIC.”
(One player can play two NICs by using one hand for each.)
The operation is summarized in Figures 6 and 7. Column 2 describes the actions of each
layer, and Column 3 describes how this is handled in the simulation. [An equals sign (=)
indicates that the player follows the instruction in Column 2.] The sending application writes
the message on the message form which has only 10 characters per line. TCP then cuts the
message into 10 character chunks, adds a sequence number, and appends to each a header.
Each of these combinations becomes a packet. TCP adds to each the port number of the
sending and receiving applications to the packet and sends it to IP.
IP gets the destination IP address from DNS and appends it along with its own IP address
to each packet. IP looks in the routing table and determines the IP address of the first hop.
It also calculates a “time to live” and adds it to the packet as well. The packet is sent to NAL.
NAL determines the first hop MAC address and appends it to the packet, which is then
sent to the correct NIC. It also calculates a CRC, which is added to the header. The packet
is passed to the physical layer.
The physical layer is represented by a six to 10 foot long piece of wire that has been
threaded through a hole in an envelope. One end is held by each of the two linked devices.
The sending end lifts the wire, and the packet runs down the wire to the next computer. While
this may sound silly, it introduces some fun and seems to help actively involve the class in
the simulation.
Figure 5. Packet header and data forms
Header
DATA
1
2
3
4
5
6
7
8
9
10
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