19-09-2012, 01:41 PM
A Comprehensible GloMoSim Tutorial
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Abstract
The following document intends to present an easy tutorial to use and simulate wireless networks
in GloMoSim, as well as the basic structure of the simulator. We have tried to gather in a consistent
manner, information from several sources: white papers, On-Line Site information, README ¯les from
the software and mails from the glomosim mail-list. The software version discussed in this document
is 2.03 for Unix platforms, although many concepts are in general applied to other platforms (windows
2000).
GloMoSim
Global Mobile Information System Simulator (GloMoSim) is a scalable simulation environment for large
wireless and wireline communication networks [1]. GloMoSim uses a parallel discrete-event simulation
capability provided by Parsec. 1
GloMoSim simulates networks with up to thousand nodes linked by a heterogeneous communications
capability that includes multicast, asymmetric communications using direct satellite broadcasts, multi-hop
wireless communications using ad-hoc networking, and traditional Internet protocols.
The Visualization Tool
GloMoSim has a Visualization Tool that is platform independent because it is coded in Java. To initialize the
Visualization Tool, we must execute from the java gui directory the following: java GlomoMain. This tool
allows to debug and verify models and scenarios; stop, resume and step execution; show packet transmissions,
show mobility groups in di®erent colors and show statistics.
The radio layer is displayed in the Visualization Tool as follows: When a node transmits a packet, a
yellow link is drawn from this node to all nodes within it's power range. As each node receives the packet,
the link is erased and a green line is drawn for successful reception and a red line is drawn for unsuccessful
reception. No distinction is made between di®erent packet types (ie: control packets vs. regular pacekts,
etc) [3].
Setting up the Transmission Range
Because of the way radio transmissions are a®ected by the environment in such a complex way, it is quite
di±cult to predict the comportment of a system and to de¯ne a radio transmission range of a node. The
radio range is the average maximum distance in usual operating conditions between two nodes. There is no
standard and common operating procedure to measure a range (except in free space, which is useless), so we can't really compare di®erent products from the ranges as indicated in the mobile devices data-sheets.
If we want to compare mobile nodes in term of range performance, we must look closely at the transmitted
power and sensitivity values. These are some measurable characteristics of the hardware which indicate
the performance of the products in that respect. The transmitted power is the strength of the emissions
measured in Watts (or milliWatts). Government regulations limit this power, but also having a high transmit
power will also be likely to drain the batteries faster. Nevertheless, having a high transmit power will help to
emit signals stronger than the interferers in the band. The sensitivity is the measure of the weakest signal
that may be reliably heard on the channel by the receiver (it is able to read the bits from the antenna with
a low error probability). This indicates the performance of the receiver, and the lower the value the better
the hardware. Usual values are around -80 dBm (the lowest, the better, for example -90 dBm is better).
Con¯guring Mobility
The only available mobility model in GloMoSim v2.03 is the Random Waypoint Mobility Model (RWPM) [7].
In this model a node randomly selects a destination from the physical terrain, and moves in the direction of
that destination in a speed uniformly chosen between MOBILITY-WP-MIN-SPEED and MOBILITY-WP-
MAX-SPEED parameters (de¯ned in meter/sec). After it reaches its destination, the node stays there for a
MOBILITY-WP-PAUSE time period.
If we want to use mobility patterns other than RWPM, then we must specify the parameter MOBILITY
TRACE in order to indicate GloMoSim that individual movements for nodes will be taken from a ¯le speci¯ed
by MOBILITY-TRACE-FILE. The MOBILITY-INTERVAL parameter is used to indicate nodes to update
their position every MOBILITY-INTERVAL time period, while MOBILITY-D-UPDATE is used when a
node updates its position based on the distance (in meters). The philosophy in GloMoSim is somehow
di®erent to NS-2 [8]. In NS-2, we indicate the destination point and a constant velocity, with this the
node arrives at a certain time. In GloMoSim we specify the destination point and the time the node will
arrive there, the tool determines the constant velocity to do this.
Some Simulation Examples
MAC protocols Simulation
Glomosim has several MAC protocols to be used in a simulation, such as CSMA, MACA and 802.11. In
CSMA (Carrier Sense Multiple Access) protocol, a station wishing to transmit, ¯rst listen to the medium
in order to determine if another transmission is in progress (carrier sense). If the transmission medium is
in use, the station waits, otherwise it may transmit. Unfortunately, CSMA is limited by two interference
mechanisms: the hidden and the exposed terminal problems. The hidden terminal problem occurs because
the radio network, as opposed to other networks, such as a LAN, does not guarantee high degree of con-
nectivity. Thus, two nodes, which maintain connectivity to a third node, do not necessarily, can hear each
other. In Fig. [ 2] node A is in communication with node B where A is currently transmitting. Node C
wishes to communicate with node B as well. Following the CSMA protocol, node C listens to the medium,
but since C does not detect node's A transmission, it declares the medium free. Consequently, C accesses
the medium, causing collisions at B.