Communications

The IMS seismic system is designed around modern, digital communication networks.

All the communication technologies used by the IMS system are 100% compliant with standard networking protocols. This makes for seamless integration of the IMS system with existing telecommunications networks.

Ethernet for flexibility

Most IMS hardware products, including netADC and netSP are Ethernet enabled. Other IMS devices, such as UPS and GPS-timer, can be accessed over Ethernet using Ethernet-enabled devices as a transparent bridge. Therefore, most networking equipment providing an Ethernet interface can be used to implement the communications network used for telemetry, monitoring and control of IMS equipment. Examples include standard copper Ethernet switches, GSM/GPRS, WiFi, fibre optic Ethernet, xDSL and satellite modem. This flexibility of communications options makes even the most remote locations suitable for the IMS system.

Waveforms over Ethernet (WoE)

Waveforms over Ethernet (WoE) is IMS’s digital streaming data transfer protocol, designed to be carried by Ethernet-compatible networks. Via reliable Ethernet links, WoE conveys digitised, uncompressed seismic data from the point of digitisation (i.e. the netADC/sensor interface) to a seismic processor (i.e.netSP). Monitoring and control information is also transported in this manner.

WoE is fully compliant with the IEEE 803.2u Ethernet standards. This means WoE networks are built from standard, commercial off-the-shelf (COTS) networking components. Examples of COTS components are cables, Network Interface Cards (NICs), media converters and switches.

WoE is a low-overhead protocol, ensuring very low latency and maximum data throughput. Unlike higher-level protocols, such as the Transport Control Protocol (TCP) commonly used to browse the internet, WoE is designed to run exclusively over reliable, switched network segments (LANs). Where a less reliable and/or lower-bandwidth network segment exists, or network boundaries are crossed (e.g. via a router), higher-level connection-based protocols are used.

Because WoE is standards compliant, it comfortably co-exists on existing local networks (e.g. business LANs). As the amount of data streamed over WoE increases due to increased number of stations and/or higher composite sampling rates, a dedicated LAN or VLAN is recommended.

xDSL (Ethernet extension)

DSL technology enables Ethernet links to be extended over a single pair of standard telephone-grade copper wires. This is especially attractive at sites where copper infrastructure already exists, and the significant additional cost of installing fibre is not feasible.

IMS DSL modems operate at speeds of up to 5,4 Mbps over distances of up to 7 km. They integrate the timing signal required for synchronisation of digitisers without a view of GPS satellites (e.g. at underground stations) into the DSL-encoded data. This is a significant advantage over standard DSL communications, as it eliminates the need for a separate communications channel for timing. This keeps the number of copper pairs and/or fibre down to one per link.

Precision Time Protocol (PTP)

Keeping the clocks of all data acquisition nodes accurately synchronised is of utmost importance in a distributed seismic-monitoring network. Traditionally this has been achieved using dedicated timing networks. However, now IMS offers PTP-enabled (PTPv2: IEEE 1588-2008) devices as a cost-effective and simple means of achieving this over standard business LANs.

PTP devices distributed across a network are capable of synchronising their clocks with sub-microsecond accuracy, using mostly pre-existing networking infrastructure. A PTP network operates with one grandmaster providing timing-update information to multiple PTP slaves.

IMS currently produces four PTP-enabled devices to build your PTP-synchronised seismic monitoring network:

  • a standalone, rack-mount PTP grandmaster, with GPS receiver. This device receives timing information from GPS satellites and distributes it to the PTP network.
  • a standalone, rack-mount PTP slave. This device receives timing updates over the network from the PTP grandmaster, and provides non-PTP IMS devices with the standard IMS time-synchronisation signal.
  • a PTP slave integrated into a netSP. This device receives timing updates over the network from the PTP grandmaster, and provides connected netADCs with the standard IMS time-synchronisation signal.
  • a DIN-rail mounted PTP slave. This device receives timing updates over the network from the PTP grandmaster, and provides non-PTP IMS devices with the standard IMS time-synchronisation signal.

The PTP network has built-in redundancy thanks to the Best Master Clock Algorithm, which allows the devices on the network to automatically select between grandmaster devices in the event of a communication or power interruption to any one grandmaster.

IMS PTP devices are fully compatible with popular third-party PTP equipment, such as Cisco, Microsemi and Meinberg.

For best performance, a dedicated VLAN or LAN for PTP traffic may be recommended. On sufficiently busy or complex networks, dedicated PTP network infrastructure (IEEE1588-enabled switches) can be recommended.

TCP/IP

TCP and IP are the ubiquitous technologies that enable the internet and the World Wide Web. Their widespread use is leveraged by the IMS system to ensure maximum compatibility with existing networks.

TCP provides reliable, ordered delivery of data streams between hosts. IP handles the addressing and routing of data across networks. Together, TCP and IP provide the services required to reliably deliver data across complex networks, be it a mine, wide area network (WAN) or the internet.

TCP/IP is used by the IMS system wherever reliable, ordered data transfer services are required (for example, the transfer of seismic events from netSP to the seismic server [Synapse]or central database).

It should be noted that the increased reliability of TCP/IP comes at the cost of increased latency, which limits its real-time performance. This is why WoE is preferred to transfer seismic data over smaller, more reliable and faster networks.

Web Technology

Apart from the transfer of raw seismic data from remote stations, the IMS stable includes a number of routine seismological and technical support services, all of which require 24/7 reliable connectivity to sites across the globe.

In today’s corporate environment, security breaches in IT networks pose a very real threat, with potentially serious consequences. Therefore, it is not surprising that often the most challenging part of establishing a data-transfer service is meeting the site-specific IT requirements. Furthermore, every network is different, with different security requirements, which can mean time-consuming and expensive setups and maintenance procedures. IMS has extensive experience in working with corporate IT departments and meeting their stringent security requirements.

Fortunately, most corporate networks have capabilities for effortlessly allowing secure and controlled web access to specified hosts (i.e. web browsing). IMS capitalises on this, by using custom, in-house tools based on web technologies that are fully compliant with standard IT security requirements, such as authenticating proxy servers. Therefore, web access is the sole requirement to securely transfer the requisite data for around-the-clock.