When XNET first begins, the above window, called the console, is displayed. This console provides the primary
interface for the operation of XNET. Assuming that the preferences have been configured correctly for the system, the
user may hit START to begin monitoring the network. The main console provides minimal information. Its primary purpose
is to allow the user to select additional desired features (i.e., MAP, TERM, NODES, and GRAPH), as well as setting
preferences (i.e., SIMUL, PORT, and PREFS).
Introduction
XNET is a network analyzer designed specifically to monitor AX.25 packet radio networks. It will collect and
display network data allowing the user to understand network traffic and channel utilization. XNET is written in Tcl/Tk
and can operate on any computer system supporting the language and UNIX. The hardware necessary to operate XNET is a
radio receiver and a Terminal Node Controller (TNC) which connects to the computer system through an RS-232 port. XNET
provides many features that are useful to both the casual packet user as well as a network administrator and the packet
radio BBS sysop wishing to better understand a packet network.
REQUIREMENTS Other than packet radio equipment such as the receiver and TNC, the following additional
computer components are required.
Any computer system supporting Tcl/Tk (typically a UNIX workstation)
Tcl version 7.5
Tk version 4.1
FEATURES
Counts packet traffic
Collects node statistics
Graphical representation of network utilization
Displays raw network traffic
Includes example simulations of network traffic
Visual display of network connections
Extensive use of color and GUI to display information
DISTRIBUTION POLICY XNET is a freeware program. It may be freely distributed on BBS's and the Internet.
DOWNLOAD SOFTWARE The distribution consists of two files. The "readme" file provides history and the
abstract. A "tar" file contains the application program which consists of many files. The hexidecimal value following
md5sum below was generated by the md5sum UNIX command. It is provided as a checksum verification of the
download.
The map window gives the Big Picture of the network. It is intended to be a graphical representation of a heard
node on the network sending packets to a destination node. The map displays only heard stations and stations that have
been sent a packet.
If a node sends a packet to another node, a line is drawn from the source (left side of MAP window) to the
destination node (right side of the MAP window). Each node is drawn twice, once as a source (left side) and once as a
destination (right side). The number next to the node name is the number of connections (i.e., lines) for this node.
The line always represents packet traffic from source to destination (i.e., left to right).
APRS
Below is another Network Map example. This is a Network Map of an APRS (Automatic Packet Reporting System). As you
might expect, there are no AX.25 connections as shown vividly by the lack of "blue X" connections on the map. All the
stations in a APRS merely transmit at intervals (i.e., 10 to 60 minutes) a UI (Unnumbered Information) frame. These UI
frames contain the latitude and longitude of the station. They do not listen, they only speak and say, in essence, "If
anyone is listening, here I am!"
DX PACKET CLUSTER
Here is a DX Packet Cluster Network Map. In this type of network, a central station (usually a BBS) acts as a
clearing house for information and deseminates it. Therefore, as you would expect, the central node sends many packets
to remote stations and those stations are not connected as witnessed again by the absence of "Blue X" lines
which denote a connection.
This window shows all currently active nodes. Other network statistics include the number of packets transmitted by
that station, the network utilization in percent, and the elapsed time since a packet was last received from that
station.
XNET does not monitor disconnect packets to detect a node disconnect. It determines if a node is active from the
age of the last packet transmitted by that node. Detecting disconnect packets could be useful, however, many nodes
leave the network, without sending a proper disconnect frame. Therefore another mechanism needs to be used by XNET to
ascertain connect status. That mechanism is to age the packets and remove nodes that have exceeded the time-out period.
The PREFS menu is provided to allow the user to specify the time-out period, if exceeded, the node is assumed to be
disconnected.
The GRAPH window provides channel utilization information. This window shows channel utilization for 1, 5, and 25
hour periods. The user may freely move from graph to graph to obtain more or less resolution as desired. The graph
should be used as a relative rather than absolute value of network utilization.
XNET computes channel utilization based on the number of characters received during a one minute sampling period.
The height of the vertical line is also based on the RADIO BAUD rate selected in the PREFS menu. Note that this value
is used for computational purposes only and represents the baud rate of transmission over the radio link (not the data
rate between the computer and the TNC).
The TERM window displays raw network traffic. However, the packet is truncated if it exceeds the width of the
window. This window was intended to allow the user to see packets as they are received by XNET. Truncating the packets
was performed to allow the user to easily see the header of each packet, since that is the information of most
interest.
The simulation preferences is actually one of three preference windows. The windows are: SIMUL, PORT, and PREFS. In
each of these windows the user is allowed to configure and select preferences. These preferences are saved in a text
file (prefs) which is used each time XNET is STARTed.
This SIMUL window allows the user to select between the serial port or one of the simulations. If a serial port is
selected, the PORT parameters preference's window should be configured for the desired port parameters such as the baud
rate, stop bits, parity, etc.
Selecting a simulation is ideal for testing and educational purposes. Most of the simulations are actual
prerecorded off the air network traffic. However, the traffic is not played back in real time.
The serial PORT configuration window is provided to allow the user to specify port parameters. All information that
XNET uses comes from the TNC which provides the information over an RS-232 link. It is therefore imperative that the
two devices use the same transfer protocol.
This window is provided to allow the user to specify miscellaneous XNET preferences.
RADIO BAUD RATE The radio baud rate is the transfer rate of data over the radio link. This value does not
affect the physical rate of the serial port. The value is used only in the computation of network utilization as
displayed in the GRAPH window.
HEARD STATION TIME-OUT The NODES window displays all active nodes. These nodes are defined as being either
heard (blue) or unheard (brown). The time-out specified here is used to determine when the heard station is assumed to
have left the network and therefore is dropped from the list.
UNHEARD STATION TIME-OUT This time-out period performs a similar function as the heard time-out, but the
period is for the unheard stations.
CONNECTION TIME-OUT Like the two time-out periods discussed, the connection time-out determines when nodes
are removed. However, this time-out is used to update the MAP window.
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