Introducing Digital Drift
The Digital Drift System is a high-speed, fit for purpose, access layer network for challenging industrial environments with linear topology, including:
- Uses a single coaxial cable to carry both power and data
- Provides a simple to install, affordable extension of the data network into challenging environments
- Can be installed and repaired by tradespeople on-site, using simple tools in wet, dirty and dusty conditions
- Works with all industrial devices that support Ethernet
- Delivers the performance of fibre with the simplicity of coax
The Digital Drift System
Digital Drift enables commoditised industrial Ethernet devices to be deployed to the extremities of underground mines and tunnels in a vendor neutral manner. The following slide deck provides a high level introduction to the problem statement, and explains how Digital Drift addresses the problem.
What is Digital Drift?
Digital Drift is just one element of a comprehensive underground network design. It is designed to be deployed in conjunction with fibre, with fibre typically being deployed to the underground substations and workshops, and Digital Drift extending out from those network distribution points into the working areas of the mine where conditions are more challenging. In this way, Digital Drift can make the most of each mine’s existing network infrastructure (typically fibre), but extend connectivity out into the areas where fibre is not suitable. Our recommended architecture is illustrated via project design documents that Digital Drift has submitted over the last 12 months and been successful in winning. Some of the design aspects that show Digital Drift’s role in the overall enterprise network architecture are illustrated below (with customer details redacted).
The key use cases driving the deployment of Digital Drift are digitisation and automation projects, with numerous successful deployments of control and monitoring systems, addressing primary fans, secondary fans, pumps, seismic and tele-remote from surface.
On the tele-remote front, Digital Drift has been particularly successful and is being used to backhaul RCT’s Control Master and Sandvik’s Automine systems to surface control stations. The key advantage of Digital Drift in these applications is the elimination of the need for fibre, which makes deployment simpler, cable repairs become possible, and it is faster to extend or change the network as ore drives change.
A case study of a site that used Digital Drift to enable RCT’s ControlMaster system provides a good example:
Enabling Fleet Management
Another common use of Digital Drift is to provide Wi-Fi coverage into working levels, in order to provide data connectivity to fleet management computers deployed on the mobile fleet. An example level deployment at a WA gold mine, which selected Digital Drift and Cisco Wi-Fi for their fleet management connectivity, provides an illustration of the real world network topologies and the speeds that the system achieves in practice.
Digital Drift is designed to be deployed and maintained by the underground trades, not just IT professionals. As such, it is a tactile system that provides local technician feedback as to its health without the need for complex configuration with computer software. To facilitate the ability for the underground trades to deploy, repair, and extend the system, a series of user guides are published. These guides are useful to demonstrate the ease with which the system can be deployed.
Product Data Sheets
The Digital Drift System comprises a range of active and passive devices, which work together to deliver high-speed networking and power distribution for long distances over a single coaxial cable. Data sheets for key elements of the system are included below:
Frequently Asked Questions
What frequencies are used on the coaxial cable?
- 5MHz to 98MHz
What is the power distribution capacity of the coaxial cable?
- The coaxial cable and the passive devices (power inserters, splitters, branches) are rated to 90V DC and 17A of current carrying capacity.
- The Digital Drift System is typically fed with a DC voltage of 54V through a DC splice, which is available in two variants, one with a 5A breaker and one with a 10A breaker. When the 10A breaker is selected, 540W can be delivered into the cable.
- To inject more power into the cable, the system supports multiple power insertion points to be placed along a coaxial cable segment, but care must be taken to ensure that the same voltage is used at each power insertion point on the segment.
Is the coaxial cable flame retardant, and/or low smoke, zero halogen?
- The ULR coaxial cable is both Low Smoke Zero Halogen (LSZH) and flame retardant (FR).
Does the cable survive in a corrosive environment?
- The ULR coaxial cable is primarily aluminium in construction, which has very good corrosion resistance in most environments:
- The centre conductor is copper coated aluminium (CCA);
- The shield is solid aluminium.
- Further, all junctions are advised to be wrapped in self-amalgamating tape, which reduces exposure to the environment.
What data speeds will I get?
- The top line speed offered by the system is:
- 1Gbps (physical layer)
- 750Mbps (TCP/UDP throughput)
- In practical installations, a mine can expect 300-700Mbps of actual TCP/UDP traffic throughput on coaxial cable segments, each of which can be over a thousand metres in length.
Can multiple Quadports be placed on a coaxial segment?
- A coaxial segment typically interfaces to the existing fibre-connected Ethernet network through a Digital Drift Portal. The Portal converts Gigabit Ethernet (GbE) into the coaxial data signalling format, which supports a PHY rate of 1Gbps on the coaxial cable.
- Multiple Quadports (and Portals) can then be spliced into the coaxial cable wherever Ethernet ports are required.
- Up to 16 devices with coaxial interfaces (either Portal, Quadport, or Repeater) can be connected on the coaxial segment. However, in practice approx. 10 is the maximum number of coaxial devices attached to a segment because every 1.5 – 2km a Digital Drift Repeater must be installed, which commences a new coaxial segment.
Is a headend required?
No. Simply connect a Portal and at least one Quadport to a Digital Drift coaxial segment and the devices will discover each other and begin communicating. The system does not require a headend and it does not required device addresses to be configured to know about each other.
Is the Digital Drift Portal a single point of failure?
The Digital Drift Portal interfaces between the site’s distribution network (typically an industrial Ethernet switch with fibre backhaul) and the Digital Drift coaxial cable. If a site wants to implement redundant uplinks with their Digital Drift design, then multiple Portals can be attached to a coaxial segment, with each connecting back into the site’s distribution network. However, each of the distribution switches must implement a redundancy protocol (such as Rapid Spanning Tree Protocol) to resolve the loop(s).
Can Digital Drift operate on a flexible coaxial cable?
The Digital Drift System is optimised to operate on the Ultra Low Resistance (ULR) coaxial cable, which is a half inch diameter, trunk coaxial cable with a Low Smoke Zero Halogen (LSZH) flame retardant jacket. This cable provides an engineered balance between cost, power distribution capacity and data communication distance. However, some deployment scenarios require a more flexible cable (e.g. temporary installation on re-reelable spools). In these circumstances, the following cable types can be used:
- RG11, with solid copper centre conductor;
When deploying the system flexible coaxial cable, the power distribution capacity is reduced considerably and the data communication distance is reduced slightly. Contact your Digital Drift technical sales support contact to verify if your target application will operate on flexible coaxial cable.
Can Digital Drift operate on my existing leaky feeder system?
- The Digital Drift System can work over the standard yellow leaky feeder cable that is installed in many underground mines. The frequencies used by the Digital Drift system propagate down the yellow cable and high-speed data networking and power distribution can be achieved over it. However, the incumbent bi-directional line amplifiers (placed every 350m or 500m along the cable) do not pass the Digital Drift data communications signal through them. As a result, it is necessary to remove the existing bi-directional line amplifiers from the leaky feeder cable in order to operate Digital Drift over it. Unfortunately this would cause the 2-way radio system to stop working, which is not acceptable to most mines. It is recommended that the Digital Drift System be deployed for data networking (i.e. tele-remote, environmental monitoring, asset tracking, video & VoIP) on a dedicated high capacity coaxial cable, using the same concepts and skills as used on leaky feeder radio systems.
How is the available bandwidth shared by the Digital Drift devices on each coaxial segment?
- The media access control is based on a time division multiple access (TDMA) architecture. A ‘domain master’ schedules the transmission opportunities. Within the Digital Drift System, Portals and Repeaters operate as the ‘domain master’.
- There are two types of transmission opportunity:
- Contention-Free Transmission Opportunities, which have a fixed duration and are allocated to a specific pair of transmitter and receiver. These are used for implementing TDMA Channel Access for specific applications that require quality of service (QoS) guarantees.
- Shared Transmission Opportunities, which are shared among multiple devices in the network. These are divided into Time Slots with two types:
- Contention-Free Time Slots, which implement implicit token passing and allow each device contention free access to the medium in its time slot.
- Contention-Based Time Slots, which are used for implementing CSMA/CARP Channel Access.
- The default configuration dynamically adjusts the TX / RX time slots among the devices and bursts up and down to the device that needs the bandwidth most. Typically no fine tuning of this behaviour is required as the available bandwidth on the coaxial cable typically exceeds the traffic requirements. However, when it does need to be fine tuned, the Digital Drift Config Tool provides the mechanism to configure the devices, thus allocating time slots to specific traffic classes and guaranteeing QoS for particularly critical traffic.
How is the Digital Drift network monitored?
- Each active device in the Digital Drift System contains at least one coaxial interface. The coaxial interface operates as a Layer 2 bridge and does not require an IP address to operate. However, it can optionally be given an IP address, which can be used by a Network Monitoring System (NMS) to monitor the availability of the device.
- Further, managed Quadports have an embedded Ethernet switch, which is fully managed. This enables it to be assigned an IP address for the purpose of network monitoring, with a comprehensive SNMP MIB available for remotely monitoring:
- RJ45 Ethernet interface status;
- PoE power delivery status;
- VLAN configuration;
- MAC address table;
- Traffic throughput.
- In addition to the continual monitoring that an NMS provides, the Digital Drift Config Tool can be executed from a computer to scan a coaxial segment for more advanced troubleshooting. The Config Tool is used by a technician to:
- Verify that the active devices on a coaxial segment have established communications with each other;
- Verify which node is acting as the domain master;
- Assign / modify the IP address of the coaxial interface of an active device;
- View the effective throughput between pairs of active devices on the coaxial segment;
- View the signal to noise ratio between pairs of active devices on the coaxial segment.
Is the Digital Drift network and switch configuration similar to the rest of the mine network? Is significant training required for network technicians?
- The embedded switch inside each QuadPort (managed or unmanaged) behaves just like a standard industrial Layer 2 Ethernet switch. There is a small amount of training required for technicians to become familiar with the configuration interface. However, this is primarily a familiarity matter, rather than a new technical learning curve.
- The aspect of Digital Drift that is different to conventional network training is the Point to Multi-point (P2MP) nature of the coaxial medium. From a networking perspective this is atypical because the ‘uplink switch’ (i.e. the switch upstream of the Digital Drift coaxial segment) will see multiple downstream switches on a port. The implications on the uplink switch’s port is that:
- Port security needs to be opened up to allow multiple downstream MAC addresses;
- Multiple LLDP devices will be seen on that downstream port. (Note that LLDP works perfectly and the IEEE standard caters for this – it is just that this scenario is not often seen in a corporate network)
- Bridge Protocol Data Units (BPDUs) used by various redundancy protocols (STP, RSTP, REP) will traverse this Point to Multi-Point medium and arrive at multiple downstream switches. (Note that redundancy protocols can be used with Digital Drift. However, it is important to be mindful of its P2MP nature to avoid loops)
- Once this Point to Multi-Point nature is comprehended, the various Layer 2 Ethernet standards can be readily applied to a Digital Drift coaxial network segment. This includes VLANs, QoS and redundancy protocols (such as RSTP).