Network Convergence for Underground Mines
Authors Mr. Matthew R. Ward, P.Eng., Varis
Ms. Anita Masuskapoe, Varis
This paper aims to describe the reasons and methods to extend enterprise networks into underground mines.
Currently mines use a number of communication networks for telephones, PLCs, two-way VHF radio and
computer networking. Each system can have different wiring, protocols, converters and interfaces all which
require expansion and maintenance. The convergence of voice, video and data using Ethernet and TCP/IP has
the very real benefit of one “wire” for underground networks. Now that the majority of underground equipment
can communicate using TCP/IP, network convergence can offer reduced network expansion and maintenance
Cost savings are good, but the truly exciting aspect of network convergence using Ethernet is the low-cost, high
speed wireless networking now available. These wireless networks offer an opportunity to facilitate mining
automation even on a small budget. How would mine operators change they way they operate if they could
gather vehicle location and data in real time? What about controlling equipment remotely? The list of
applications is long and includes traffic control, dispatching, real-time ore blending, tele-operation, automated
production reporting, vehicle health monitoring, elimination of paper forms and immediate network access for
surveyors and geologists.
An ideal converged network for underground mining would be robust, inexpensive, easy to expand, enable fast
and secure connections while keeping voice communication performance equivalent or better than what is now
provided by VHF radio.
Network Convergence – Ethernet
What could explain the fact that modern computers rely on a communication network developed in 1972?
Robert Metcalfe of Xerox was looking for a way to share printers, not define the way the world would
communicate for the next fifty years. The reason Ethernet is alive and well today is that it has become a non-
proprietary standard with readily available specifications, namely IEEE 802.3.
TCP/IP (Transmission Control Protocol/Internet Protocol) is a suite of communications standards running over
Ethernet and this combination is the basis for the Internet. Any computer connecting to the Internet is using
TCP/IP, regardless if the connection is dial-up, DSL, cable, power line or wireless. Ethernet and TCP/IP are
already used at mines for corporate networks. Some mines have introduced derivatives such as Modbus/TCP
and EtherNet/IP into their PLC networks to take advantage of the low cost of Ethernet network cards, switches,
routers and cabling. Anyone that paid $3000 to a PLC vendor for a network card knows why a $15 non-
proprietary alternative is attractive.
In addition to data communication, Ethernet and TCP/IP can be used to carry digitized voice and video signals.
Digital voice communication using TCP/IP is referred to as VoIP (Voice over Internet Protocol), and digital
video using TCP/IP is referred to as IP video. IP video equipment is significantly less expensive to deploy than
dedicated coaxial or fiber networks and opens up new monitoring possibilities for operators. This is what is
meant by convergence – a single network, Ethernet, which carries voice, video and data.
In 1999 a new standard, IEEE 802.11 was created to add wireless capability to Ethernet networks. Referred to as
Wi-Fi hotspots or WLAN, these networks consist of one or more wireless Access Points (AP) hardwired to a
Ethernet network. WLAN client devices include computers, PDA’s, bar code scanners, telephones, and cameras.
WLAN networks are optimized for high speed/short range communications. The data rate (bandwidth) that can
be attained depends on the version of 802.11, the antennas on each device, the distance between AP and the
client and how many other wireless clients are requesting bandwidth.
Table 1 - WLAN Standards, Frequencies and Data Rate (Goldhammer, 2004)
Standar Frequency Maximum Data Rate Useable Data Rate (3 m range)
802.11a 5.8 GHz 54 Mbps 23 Mbps
802.11b 2.4 GHz 11 Mbps 6 Mbps
802.11g 2.4 GHz 54 Mbps 23 Mbps
Radio propagation tests through 150 meters of underground drifts shows the 2.4 GHz 802.11b/g signal would
have 30 dB less signal loss than the 5.8 GHz 802.11a signal (Emslie, 1975). Above 1 GHz increasing
frequencies incur greater loss around corners, which eliminates 802.11a from further consideration in
The wireless data rate varies inversely with the distance between the AP and the client devices. Maximum data
rates are attainable only within a small radius from the AP. As the client device moves further from the AP the
data rate drops until the wireless connection is lost and data communication stops.
Figure 1 - 802.11g Data Rate vs. Distance, PC Magazine, November 2004
Data Rate (Mbps)
0 20 40 50
Each wireless client connected to the same Access Point must share its bandwidth. There is documented
degradation in speed for all clients when one client is far away from the AP (Duda, 2003). When this happens
the AP lowers its bit rate in order to work with the weak signal of the distant client. The unintended
consequence of this is that the data rate for all other clients slows to the speed of the distant client.
As powerful as these new WLANs are, there are problems as described above. They can be avoided by limiting
the number of clients in each hotspot, and avoiding distant communication where possible.
Wireless Data Applications
WLAN high speed data can be used in any number of applications underground. Vehicles can be fitted with
WLAN modems and controllers to report load weighing and vehicle health (Dasys, 2003). Tele-operation
becomes a practical option with real data rates over 5 Mbps enabling high quality IP video streaming. Wireless
enabled hand held computers or PDAs can be used to eliminate paper forms within WLAN hotspots. Surveyors
and geologists would be able to access the corporate network from hotspots located at the working face.
Not all areas of the mine require high speed data access. Probable hotspot locations are garages, lunchrooms,
refuge stations and production areas. WLAN hotspots could be easily moved to follow the mining activity.
Production monitoring could be accomplished with APs at the draw and dump points.
Adding resource tracking capabilities would enable dispatching, traffic control and real time ore blending.
Varis’ Smart Tag readers plug directly into the Ethernet network and can detect up to 50 tags traveling at 50 km/
The mining industry has been talking about these applications for years, but Ethernet WLAN will make their
implementation much easier.
Conventional video transmission uses dedicated fiber optic or coaxial cable. Leaky feeder can also be used to
transmit up to 8 channels of video. In the case of a dedicated network the expense is in the installation and
maintenance of the cabling. With leaky feeder the expense is the modulator and where required, PTZ (Pan, Tilt,
Zoom) controls. IP video eliminates the cabling, modulator and PTZ control costs. PoE (Power over Ethernet)
can also be used to power IP cameras, which enables cameras to be located up to 100 meters from the nearest
AC source. Sony PTZ IP video cameras cost approximately $1600, which is less than half of the conventional
IP video quality is dependent on lighting, encoding/compression scheme and the image update rate. MPEG-4
encoding provides a high quality image while using less than 1 Mbps bandwidth. As the image size and update
rate are reduced the required bandwidth drops significantly so that several dozen low and medium quality
images can be transmitted.
Extending Ethernet Underground
Several methods can be used to extend Ethernet networks, however this paper will only consider three as they
are the best suited for implementation in underground mines and tunnels:
• Twisted pair cabling
• Fiber optic cabling
• Cable modem
Inexpensive twisted pair cabling can support Ethernet up to 100 Mbps (Cat 5) or 1000 Mbps (Cat 6) however
the maximum length of the cable is limited to 100 meters. To extend Ethernet over twisted pair beyond this
distance requires an Ethernet switch to be installed and powered every 100 meters which increases the system
cost, complexity and IT support requirements. Voice communication is attained with overlapping WLAN
hotspots and wired or wireless VoIP phones.
Figure 2 – Ethernet over Twisted Pair Cabling on Mine Level Plan
Fiber has almost unlimited bandwidth/speed and is immune to noise. Multi mode fiber can run 2000 meters
between Ethernet switches and single mode fiber can run 5000 meters. Fiber optic cabling can be armored and
composite fiber/copper cables can provide AC/DC power to network devices. Fiber optic Ethernet switches and
routers are commercially available from several vendors. Drawbacks with fiber include cost and that its fragile
nature requires trained installers. Voice communication is attained with overlapping WLAN hotspots and wired
or wireless VoIP phones.
Figure 3 – Ethernet over Fiber Optic Cabling on Mine Level Plan
Cable modems carry TCP/IP over cable TV networks to deliver high speed networking, Internet access and
VoIP services. DOCSIS 2.0, the current standard for cable modems provides 54 Mbps downstream and 41 Mbps
upstream. Mines with an existing Varis Smart Com leaky feeder network can be configured to carry Ethernet by
adding the CMTS (Cable Modem Termination Service) controller, cable modems and frequency translators. The
frequency translators are required as leaky feeder networks have a different bandsplit than cable TV networks.
Cable modem and frequency translators are installed wherever a high speed wireless network is required. Voice
communication is attained using two-way VHF radios and optionally, wired or wireless VoIP phones.
Figure 4 – Overview of Ethernet over Leaky Feeder
Figure 5 – Ethernet over Leaky Feeder System
Router ports each
Rx RFOUT O
Network connection Cable Modem, IN OUT
through CAT5 cable Router, Frequency Leaky Feeder
or wireless network Access Point
card Translator CAT5 Cable
To decide which method of extending Ethernet is best we also need to consider the quality of the voice
communication that each method provides.
Stationary Voice Communication
POTS (Plain Old Telephone Service) telephones require a separate fiber and/or copper network. Over time these
networks become maintenance intensive due to cable damage and corrosion. Telephone wiring repair is
eliminated with VoIP, as proven by the 90+% maintenance cost decrease at Kidd Creek Mine (Nortel, 2003).
VoIP systems can call sister sites that also have VoIP without incurring toll charges. It is quite possible to
reduce the number of incoming lines leased from telephone service providers (Nortel, 2003) as the inter-site
calls are no longer routed over leased lines. VoIP requires a sizable amount of technology investment but there
is a potential to realize a reasonable payback.
All three methods of Ethernet network extension will support desktop VoIP telephones. The network must be
designed and maintained properly for VoIP to function properly. VoIP is a digital system which has specific
network requirements for voice prioritization, bandwidth, packet loss, latency, jitter and end-to-end delay. These
requirements must be addressed when designing the Ethernet network and the network must be monitored and
maintained to ensure acceptable VoIP performance.
Mobile Voice Communication
Mobile voice communication is a very important service in underground mining. Mobile voice networks are
used for dispatch, traffic control, emergency response, worker safety verification and general production
communication. The quality, coverage and ease of use of mobile voice services are important considerations in
determining how to extend Ethernet underground.
Fiber optic and twisted pair networks provide mobile voice service using multiple WLAN Access Points and
wireless VoIP handsets. Each Access Point installation requires trained technicians to determine its location,
antenna configuration, range and speed. In order to roam between Access Points without dropping calls there
needs to be overlapping WLAN coverage between Access Points. There is a maximum number of voice calls
that any AP can support and will vary with several factors with the most critical being distance between AP and
handset. Voice applications need traffic consistency as voice packets need to arrive relatively quickly together in
order to prevent jitter and drop-offs. Wireless VoIP will improve once the IEEE 802.11e Quality of Service
standard is ratified and implemented so that wireless voice data will have priority over asynchronous functions
like file transfer. Handset maker Spectralink SVP protocol currently performs this function in the absence of the
802.11e standard however only for 11 Mbps 802.11b Access Points. There are currently no wireless VoIP
handset manufacturers delivering industrial-grade equipment.
In contrast leaky feeder is an analog radio system specifically designed for mining and tunneling
communication and is used at over 300 sites worldwide. It is a radiating cable network that provides continuous
mobile voice coverage regardless of mine size, drift size, wall and support adsorption properties and mobile
obstacles such as trucks. Leaky feeder can be installed by miners and its maintenance is facilitated by effective
local and remote diagnostics. Either conventional or trunked VHF radios can be used and industrial-grade
portable and vehicular (mobile) radios are available from several vendors. Accessories to facilitate radio use in
industrial environments include cases, speaker microphones, headsets and throat microphones.
Both VoIP and VHF radio can be equipped with PTT (push to talk) to effectively coordinate tasks. VoIP phones
and VHF trunking radio with keypads provide private conversations between parties. VoIP phones have some
features that radios do not including voice mail and SMS messaging.
The widespread adoption of Ethernet and TCP/IP is a powerful driver in “one wire” convergence. This one wire
can be a new fiber optic or twisted pair cable or an existing leaky feeder network, or a combination of all three.
Underground mine operators need to understand the cost saving and productivity benefits that can be attained
with an underground converged network that supports high speed wireless networking. Hotspots can be
strategically located to gather vehicle data and provide wireless networking at the face. Location systems
coupled with vehicle data can be used to improve processes and reporting.
The decision on how to provide mobile voice communications is critical to safety and productivity. Wireless
VoIP systems are still in their infancy and require expert installation and tight control of the network traffic to
provide equivalent voice capabilities to VHF radios and leaky feeder. The durability of wireless VoIP handsets
is a question mark and there is a lack of handset accessories to suit the underground environment.
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