Network DOOM Traffic Analysis
----------------------------------------
Neil R. Bonner, (nrbonner@ffx.mobil.com)
        Original Release: March 28, 1995

There has been a lot of posts, discussions and misinformation regarding 
what effect playing DOOM has on a network.  The conventional thinking
is that, playing DOOM on a network will bring that network to its knees.

While it is true that the first versions (1.0 and 1.1) of DOOM used 
"broadcast" packets to communicate with other DOOM workstations, that 
method was changed in version 1.2 to use "directed" packets.  Directed
packets have less impact on LAN traffic than broadcast packets.

id Software originally used broadcast packets because this method is 
more efficient *if* all you're doing is playing DOOM on that network
segment.  However, if other workstations are on the network trying to
do real work... well then broadcast packets aren't such a good idea.

The below table illustrates exactly how much network traffic is generated
by DOOM in a 2, 3 and 4 player game.
    __________________________________________
    No. of Players   |   2   |   3   |   4   |
    ------------------------------------------
    Mb/second        |  0.04 |  0.12 |  0.24 |
    (bandwidth)      |       |       |       |
    ------------------------------------------
    Packets per Sec. |    35 |    70 |   105 |
    (per PC)         |       |       |       |
    ------------------------------------------
    Total Packets    |    70 |   210 |   420 |
    per Second       |       |       |       |
    ------------------------------------------
    Total Packets    |  4200 | 12600 | 25200 |
    per Minute       |       |       |       |
    ------------------------------------------
    Packet Size      |    72 |    72 |    72 |
    (bytes)          |       |       |       |
    ------------------------------------------

This information was gathered using a packet analyzer on an Ethernet 
(10Base-T) network with no devices other than 2 workstations running 
network DOOM.  The numbers for 3 and 4 workstations were calculated 
based on the actual observation of the 2 player game.

This network utilization chart is the same for DOOM, DOOM II and Heretic.

BOTTOM LINE: DOOM uses very little "bandwidth".  This is largely due
to the fact that DOOM packets are very small (only 72 bytes).  It is
interesting to note that there is three times more traffic generated 
going from a 2 player to a 3 player game, and six times the traffic
going from a 2 player to a 4 player game.  

Even though DOOM uses little bandwidth, it does generate a lot of packets
in a 3 and 4 player game.  Because of this, network DOOM players should
be considerate of other network users before starting a 3 or 4 player
network game.  Generally speaking, no one should be adversely impacted
by someone playing a 2 player game unless the network is already 
saturated with traffic.
+---------------------------------------------------------------+
|     Neil R. Bonner     |  Think "outside of the box".         |
| nrbonner@ffx.mobil.com |  View the world in new ways.         |
| CIS:   72254,511       |                                      |
| Voice: 703-846-4057    |      (PGP Public Key Id: 0x2CDD931)  |
+---------------------------------------------------------------+