NetworkandTariffselection

Since the introduction of 3G, the networks have universally had three data offerings, with varying levels of service quality leading to suitability for different applications:

Voice tariff with associated data bundle

This tariff is, as it states, a voice tariff that has some data provision added to it. It is designed only for smart phones and occasional tethering of devices such as laptops to send and receive emails, browse the Internet, and then disconnect from the network.Thistariffhoweverisgenerallywhatisprocuredthroughcorporatemobile contracts. When a procurement team is required to supply data SIM’s they will contact their mobile network account manager. They oversee the mobile phone account, and will invariably be supplied with a voice SIM, with an amount of data attached.

However, use of this tariff explicitly forbids its use for anything other than within mobile phones and associated periphery's. If it is used in an IoT product, the network - under its fair use policy - will likely limit the amount of data being transmitted, throttle its speed, intermittently disconnect it from the network, or – ultimately -permanently disconnect the service. This gives the impression of unreliability.

If a voice tariff SIM is used in an IoTapplication, then to the end user it may appear as though the sim is suffering from a list of random connectivity issues. This perpetuates the perception that mobile data transmission is unreliable.

Mobile Broadband

Thistariffisdesignedto beusedby smartdevices,tablets,andcomputers.Generally, under the T&Cs of the contract, the networks specifically forbid it's use in IoT products. This tariff allows greater volumes of data to be sent and received before triggering alerts within the network (alerts are indicators to that network when the SIM may have been deployed in an inappropriate manor). The same fair use policy is used to police the tariff and the result is – as above - connectivity issues as the network temporarily forces the SIM offline, controls or throttles speeds, and potentially permanently disconnects the SIM.

M2M/IoT.

This tariff has been designed for IoT applications and the SIM is flagged to show that it is potentially going to be connected continually for days, weeks and even years. However, because it creates a higher load on the network this service does come at an additional cost over and above the previous two tariffs. This price differential often appears to be just profiteering by the network, which is far from the case. At the radio level, an IoT device is connected perpetually, regardless of whether it is sending data. This connection is a fixed resource, and as such the network places a cost on its continual use [See RAN].

Quality of Service (QoS)

There is a stark difference between the Quality of Service [QoS] which MNO’s provide for the three tariff types above.

Typically, the network’s Service Level Agreement offers 85% availability for Voice and Mobile Broadband availability. This is clearly not enough for the majority of IoT devices which, in order to provide the service as intended, require as close to 100% availability as possible.

The Mobile Network Operators (MNO) standard offer for M2M/IoT is typically 96% availability. Although this is a massive improvement on the standard Voice and Mobile Broadband, it still equates to 57 minutes off-line a day.

This is where a Mobile Virtual Network Operator (MVNO) can add value: they will build upon the 96% availability offered by the networks. Many offer 99.5% or better uptime, though noting it is worth scrutinising these claims as some of the numbers published vary widely.

Under 5G, the networks will offer additional tariffs and services to meet growing needs of Industry 4.0. These will include URLLC, narrowband IoT, higher Quality of Service as a premium offering, and lower Quality of Service for lower-cost connections, for general use. There is currently some industry discussionaround networkslicing to offer guaranteedbandwidth formission critical applications such as ‘Blue light’ services, critical infrastructure.

Technicaloperation,specificevents,and faults Mobile Cells

Mobile networks cells are constantly changing. A cell will create a donut shaped signal area and anything in that donut will get a signal, but this signal gets weaker the further away from the cell you go. As a user connects to a cell, the size of the footprint shrinks (so-called Cell Breathing). If you are at the edge of a cell and it shrinks, you will no longer have a connection to that cell and you will connect to another cell that is also serving your location if there is one, or you will drop to another technology, such as 2G/3G.

The weather affects cell performance, as do trees and buildings. Modern buildings are particularly bad for mobilenetworkreceptionasthemixofglass,steelandfoil backed insulation scatters, reflects, and absorbs the mobile signal.

Cell switching

Cell switching is the action of handing a device from one mobile cell to another. It occurs all the time when your device is moving, as you are passed from cell to cell along your journey. It can also occur when your device is static, although less frequently. For example, if you are static and connected to a cell that is suffering from network congestion, then the cell may ask your device to switch to another cell that is also serving your location in order to balance the load.

Due to organic cell switching and operational changes to networks, it is important to note that the network coverage pattern observed at device installation can change substantially.

‘Network is down’

It is true that mobile networks and cells do go ‘down’ from time to time. However, this is planned and generally takes place overnight, in very specific locations and for specific reasons such as hardware maintenance. When things come back up, it is always the devices that are poorly set-up that prevent these events passing seamlessly. Unfortunately, the poorly configured devices may still regard their last session prior to the disruption as active. Unless the device has been set up to monitor its connection, the device is unable to recover from this state without human intervention – usually a manual reboot.

Mobile Network Operators have invested heavily in their networks, improving cell densities within towns and cities. This has increased further with the rollout of 5G. Within most urban environments itiscommonforamobile devicetoseeupto50cellsitcanconnectto,andeveninquiterurallocations the ability to see a handful of cells is the norm. Therefore, for whatever the reason a cell may be offline, there are usually other cells which can handle the data.

A poorly configured device may fail to reconnect after a disconnection, giving the impression the network is permanently down when there was only a momentary loss of a single cell, and/or when other cells are still available. This is, of course, an issue if the device in question is a remote IoT monitoring station!

Wise data plan selection alongside correct device configuration can help alleviate these occurrences.

Mobile ‘Black holes’

‘Black holes’ are when the connection simply disappears. If you have deployed a mobile solution, you will probably have come across these without knowingwhat they are, or what causes them.

When adevicehas been connected to amobile networkforaperiod, the network sleeps the radio layer of the RAN if no data has been transmitted. The period this takes varies depending on the usage of the cell you are connected to. This has no impact on the IP layer which stays ‘connected’.

When your device wishes to send data again, the radio layer wakes, and your sessioncarrieson.Thisisexhibitedasthefirstpacketofdatatakingabitlongerthan the packets that follow it.Occasionally, the radio layer does not wake correctly, but because you still have an IP layer the software still believes it is connected, and the packets effectively go ‘into a black hole’. This can cause software hang-ups and glitches.

Tip: Black Holes can be resolved by simply as sending a ‘ping’ now and again - though this increases the data volume used - and rebooting the device if it fails to receive a reply ‘ping’. An alternative is to monitor the Transmission Control Protocol (TCP) session, and restart the session if the TCP connection fails.

Antennae (Aerials)

The placement and design of antennae are some of the most important considerations of any deployment using mobile radio.

It is commonplace for antennae to be mounted on the side of cabinets that house the router. It is thought, bymounting the antennaon the side insteadof the top of the cabinet, there will be reduced chance of water ingress. However, antennae procured from reputable manufacturers will have a series of neoprene washers and membranes that, if the fitting instructions are followed and any nuts not over tightened, will provide a stable watertight seal for the life of the equipment.

By placing the antenna on the side of the cabinet – especially a metal cabinet - the signal reception is effectively shielded by at least 180 degrees. If the antenna is placed on top of the cabinet, it will have full 360 degrees sight of any mast.

Cutting corners with the antenna – whether location or specification - can cause huge dips in the performance of the connected device.

A word of caution about using a directional antenna to get a better signal. Whilst this may help if the location will only ever be served by a single cell site, if the location is served by multiple cells, then using a directional antenna will be counterproductive as the device cannot switch to another cell. It is likely that installation of a directional antenna will limit flexibility in the longer term.

Tip: Even low-loss cabling loses ½ dB per meter.Thismeans if an antenna with 3 dB gain is fitted to 3 metres of cable, half the gain/performance of the antenna is lost.

Keeping the cable length between the antenna on the router/modem as short as possible will therefore enhance the overall performance of the connection.

In rural locations or smaller towns, cell towers are a regular sight and can often be visible for miles around. In dense urban environments, the equipment is instead mounted at strategic locations in, around, and upon existing buildings.

Routers

Mobilephonemanufactureshavespenthundredsofmillionsofpoundsonresearchanddevelopment, and on software to optimise the way the modern cell phones connect and participate in an expensive approval process with Mobile Networks, ensuring that connectivity is flawless.

Contrast this to the modem and routers available for industrial use. Although many have a degree of built-in intelligence, they rely heavily on being set up correctly for their location and traffic profile by a skilled engineer. Unfortunately, the skill set neededtodothisiscurrently inshortsupplyandmostfieldengineersandcomputer network specialists leave the default settings ‘as-is’. This in turn degrades the hardware’s potential performance and ultimately the performance of the delivery of the data.

There are suppliers of SIMs and Hardware who can ship preconfigured devices that have been set-up correctly to optimise the performance of the device and the connection to the mobile network. However, it is still important to think of the interaction between the firmware, software, and application layer within the router and how that is expecting to react with the local devices and the network.

Dongles vs Routers

So-called ‘dongles’, which connect via USB, are not designed for permanent installations. Power control is difficult, and there is no connection management, as the user is expected to disconnect the dongle and reconnect it if there is an issue. Also, since the USB port can stay live in a power cycle then the standard ‘turn it off and turn it back on again’ process often has no effect. The radio module versionsarealso constantlychanging,whichcancauseincompatibilityissueswithdeployedhardware. Large estates of devices quickly become impossible to manage. USB dongles are not designed to manage black holes, and radio performance can be poor.

In general, dongles are designed for light domestic/office use. When they are used constantly, they have a Mean Time Between Failure (MTBF) of six to eight months. The devices become unreliable rather than fail completely resulting in an increase of expensive site visits.

With routers, the hardware platform is stable and any changes to the radio modules are controlled and tested before they are released. The MTBF is commonly five years. The manufacturers have connection management to prevent mobile ‘black holes’ (if the device is configured correctly). Hours of engineering time out in the field can be saved by bench testing the manufacturer’s default settings against what is configurable and observing the net result. However, a lack of knowledge about the router’s capabilities is often where projects fail to deliver the performance required by the end user.

Multi IMSI

Multi IMSI is used to switch between the identities of the SIM on a single SIM. For example, the SIM could hold an O2 IMSI and a Vodafone IMSI(or up to 10 IMSIs) and be told which to use by sending an Over the Air (OTA) command. Multi IMSI technology is aimed at providing a cheaper service to the end user - instead of using a roaming SIM with its associated costs generated by their international interconnects needed to provide the roaming service. The multi IMSI uses an IMSI of a national operator and accesses local prices instead of roaming prices. This would seem to be the ideal solution: low-cost multi-network connectivity.

However, Multi IMSI brings additional complexity which is worth understanding before adopting this option. The software and operating system that supplies the OTA command is bespoke to the MVNO that supplied the SIM. At present, no MNO supports the Multi IMSI deployment on their back office. As the solution is bespoke, this leaves the end user with a question mark over the longevity of the Multi IMSI solution. An MVNO could cease trading or change their back-office platform, leaving the SIMs dead and the end user with no choice but to exchange the physical SIMs in their devices.

The SIMs could also be stranded if the process of an OTA command is not received by the SIM or if there is an interruption during application of the changeover applet. The SIM may have been told to change from a Vodafone IMSI to say, a Three IMSI, which for amyriad of reasons does not take effect, and the Bootstrap network is not available in that location. Again, the SIM can become either temporarily or permanently stranded.

Tip: No Network covers 100% of the UK land mass. Ask vendors of Multi IMSI systems to demonstrate how they recover a stranded SIM where there is no Bootstrap network coverage. More importantly, ask for a written guarantee that the SIM platform will be supportedforthe life oftheproject. Thinkabout theexpected lifeofthe projectfromwhen the last SIM is deployed, rather than from the first.

SIM Faults

IoT SIMs rarely go faulty, as they have solid state construction without moving parts. The primary reasontheymaynotworkisoftenthewaythattheyaresetuponthenetwork,withthemostcommon problems being:

• Wrong IP addressing

• Duplicate IP addressing

• Wrong APN input into set-up of device

• SIMs being shipped but not activated

• SIMs being enabled for WAP not WEB

• Too large a current applied to contacts

Tip: Use of an MNO or MVNO with a BSI 9001 system in place can eliminate most ‘SIM faults’ from SIM shipment and set-up.