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The Warning Signs Your Network Needs Replaced

atlanticstormIf you think lightning can’t strike twice, think again. It can strike twice, thrice or even quarce. (Is that really a protologism?) A well known ferry operator on the West Of Scotland has the blown out network equipment to prove it. The coastal ferry terminals of Scotland are long standing facilities. Surprising to some, in the winter in Scotland, the seemingly constant procession of Atlantic storms frequently bring intense atmospheric instability with them as the UK’s TORnado and storm Research Organisation (TORRO for short) can testify. Lightning frequently is a major problem for many businesses in this area and it can have a devastating effect on their sensitive IT infrastructure. As Doug Rask, an IT manager in the area put it, “We would take an occasional lightning strike and the equipment would be fine initially, but after some days or weeks, they’d start falling over, and we’d have to analyse the problem and quickly get things replaced.” Lightning strikes are admittedly a bit of an extreme example, well concede, but they do qualify the problem of the constant environmental stresses and strains that your static sensitive network hardware has to face almost constantly.

When systems begin to show signs of this wear and tear, it can manifest itself in the shape of chronic network niggles such as poor throughput or frequent hangs, crashes and outages. The hardware may simply be coming to the end of its natural life, or perhaps the user enterprise has simply grown beyond the maximum capabilities of the network, says Pete Macsorley, IT manager at Corpach Pumps. Other factors that can cause an agency to consider a network refresh could be the deployment of new applications such as anti virus systems or phased migration and collaborative services. Usually the real world reason for a network overhaul is not just a single warning sign but a combination of multiple elements of the above.

CONSISTENT EQUIPMENT FAILURE

When lightning strikes a building, the earthing systems should and almost always will protect the systems but every now and again a strike of ferocious magnitude can overwhelm these safety systems to the point that damage is caused to the network  and IT equipment. “When we get strikes on our sites, it typically doesn’t kill of our systems there and then. It does however initiate a collapsing system which culminates in the eventual hard failure of equipment. This can take 3-6 months,” said Mark Forrest, IT engineer for a well known salmon farming company.

At some time in the next 6 months, the kit would begin to play up. Users would notice a badly performing network, intermittent hangs and patchy access to servers, forcing Forrest to carry out systematic fault finding and replace the failing kit. “Atmospherics and particularly lightning places a cost burden of 3 to 4 switches per hit” says Marks boss, Joe McGarry.

AGEING HARDWARE

headerAgeing or end-of-life networking gear can compel organisations to replace their systems, especially when the initial warranty expires and/or support organisations place a premium on their support due to the increased likelihood of call out and expensive engineering time. “Sometimes this cost uplift is so great that there is no option left but to replace new for old and enjoy the more relaxed maintenance landscape that ensues,” says Dan McDougall, CTO at a major food manufacturing company.

“Networks are there for one reason, to serve the business. Unless they’re failing too frequently, the main reason we would decide to upgrade the network is the cost of their support,” McDougall says. “Sometimes the kit on your business network is just so old that the cost of the warranty dwarfs the cost of new for old.”

For example, the salmon farming company mentioned previously recently needed to move their regional offices in Oban. It made perfect sense to look at equipping the new premises with a new network and servers because most of the kit at the old office was 5-9 years old and EOL (End Of Life), Forrest says “I was sure I didn’t want to be moving any of my old equipment that had been through the lightning hits more than once. I wanted new for old.”

They had also decided to move some services to the cloud such as their voice network services and had enhanced the resolution with which they remotely monitored the underwater salmon pens. They purchased 2 Cisco UCS servers, three new routers, eight switches and upgraded their WIFI network using Cisco Meraki, Furthermore in addition to moving to hosted voice, they improved the storage of their IP video inputs from the farm cages as well as a new access and building control system which also used the network. This network upgrade brought with it gigabit networking to the desktop and has markedly increased the performance and efficiency of the business unit.

For example, in the past, bandwidth contention had sometimes resulted in the live video from the pens squeezing out the traffic for the very control systems which were used to enable the application of feed to the pens. The upgraded network, using 802.1q VLAN trunking was able to segment the traffic and ensure that the requirements of each business process were safeguarded. Bandwidth contention had become a thing of the past. Finally and perhaps ironically, they also installed a new earthing system and new earthing cable, which should protect the new locations sensitive electronic equipment more effectively from future lightning strikes.

CREATING BANDWIDTH

Sometimes, the introduction of new applications on the network necessitates a network upgrade. For example, VoIP (hosted or owned) or realtime video services can place very specific demands on a network and if it isn’t up to the job, a refresh can prove inevitable,

An increased rollout of virtualisation and thin client technology can also drive cost savings in terms of network user hardware which may be partially offset by the costs of the new network to support it.

CONTINUOUS PHASED APPROACH

tick-tock-google-searchSome agencies adopt what is best described as a continuous phased approach to keeping the network at the cutting edge. This can prove to be a useful mitigation to the sometimes problematic expense of replacing the whole network every few years as well as enabling financial planners to smooth the requirement for capital across many financial years. It’s a cost-effective way of keeping the network stable and up to date.

DB Refrigeration in Ayr, for example, has gradually upgraded most of its 15 wiring-closet switches since 2012 and will replace a few more this year, says IT manager, Connor Piacentini.

This autumn however, it was the core routers turn to be replaced. The IT department upgraded its Gigabit Ethernet Cisco Catalyst 6509 core switch to a 6509-E which could support 10 Gigabit Ethernet. “It was 8 years old, so we knew we had to upgrade it finally,” Piacentini says.

SHARED SERVICES

Consolidation by agencies of the use of their expensive network resources seems to be a popular way to save costs these days. For example in the Public Sector, many regional councils share some of the higher end networked resources making the burden on each organisation smaller. This can however mean that the new network  must be far more capable than any of the incumbents.

Police Scotland, following its recent merger has to build regional backup emergency operations facilities, so if disaster strikes and one goes down, another can take over. The investment requires new network equipment to build the WAN. It is speculated at this time that they are also negotiating with infrastructure providers to build a proprietary fibre ring.

Upgrade Advice

1. Plan for future needs. When deciding how much bandwidth you need and what equipment to buy, don’t assess for your current needs. Spec it out for five years from now. A good rule of thumb is to plan for a 50 percent increase in bandwidth usage and a 30 percent increase in the number of employees.

2. Pair a network upgrade with a larger technology project. It’s often easier to prove return on investment and get a network upgrade funded if it’s tied to a bigger project. When IT administrators propose a private-cloud deployment, for example, they can argue that a network upgrade is critical for good cloud performance.

3. Purchase maintenance contracts only on the most critical equipment, such as main routers and switches. Purchasing contracts on all equipment can be cost-prohibitive. It can be cheaper to purchase one backup wiring closet switch and use that if a switch fails instead of purchasing contracts for each switch.

Designing Commercial WIFI Networks.

wifiWhen designing commercial WiFi networks, a wireless survey is an essential part of the design process. This can come in many forms but they can be broadly grouped into two main groupings, namely, the more conventional “walk around” style of survey or one done purely on the strength of detailed schematics of the location. It is easy to focus in on the prominent questions of signal strength and bandwidth however this should always be done in the context of the user experience at a given point on a given day with the network in full operational use.

Context

It is almost always the case that designing a commercial grade wifi network involves a good deal of groundwork including asking the users some fairly detailed questions about the location, the structure of the building, existing physical cable plant and associated infrastructure as well as local administrative practices. This information as well as detailed information about the required functionality of the new WIFI network including the key questions of coverage and capacity is fundamental to the creation of an effective rollout plan. It is important too at this stage to bear close account of the types of clients to be used on the eventual production network.

Performing the Survey

wisurvWhen designing a WiFi network, you have to consider how the network is going to look from the point of view of your WiFi clients – all of your clients. Clients come in a very wide variety of shapes, sizes and capabilities. Some may have good quality RF hardware and decent gain antennas, ensuring that they will have few issues in a reasonably well designed network. They should easily be able to connect to deployed APs and achieve SNR levels that ensure low error rates and good throughput.

However, other clients may have miniscule, poorly designed antennas, with low-cost, low quality RF circuitry. Their antennas may often be in a housing partially made of metal. They may have limited power available due to the power demands of a smartphone handset on a very limited battery. The explosion of mobile devices such as tablets and smartphone means that the majority of clients on a network may suffer these limitations . With the proliferation of these ‘less able’ clients, it is often best to be pessimistic about client capabilities when designing a wireless network and design for your ‘worst case’ clients.
We need to take a step back and think about the survey to be performed. What are we measuring? Are signal levels and SNR actually measured with a smartphone or tablet? The answer is: no. We will actually be measuring (in all likelihood) using a laptop with a USB wireless dongle that has very good RF capabilities. Will this survey ‘client’ see the network in the same way as a less capable tablet or smartphone? (The answer is no.)

An Alternative Point of View

In order to understand if this network is going to meet the design criteria laid down, we need to look at the survey data gathered from the point of view of the clients that will be using the network. As mentioned previously, we have to assume the worst, and design for our less able clients.

Back to the Drawing Board

Unfortunately, we now see huge holes in our coverage. We simply cannot meet the design criteria for our agreed limitations for less able devices in this network. We certainly have to add in enough access points, repositioning APs and perhaps winding up our AP transmit powers. There are other considerations that also need to be considered. These include factors such as client transmit power, client sensitivity and the varying CCI view of each client type. The key takeaway from this is that client capabilities need to factored in to design considerations – a survey using raw measurements is generally an invalid approach on today’s “support everything” networks.

Summary

cheaptabIn summary, we’ve taken a look at how we need to define design criteria for the type of wireless network that will meet customer requirements. Although we may be able to measure the design criteria using a professional survey tool, we need to be mindful of how the measurements are collected. Survey data gathered with a high-spec wireless NIC is generally going to see RF signals at higher levels than a lower spec mobile device.
When considering how effective our design will be in meeting the design criteria, we have to consider how the gathered RF data will look from the point of view of a actual clients that will use the network. Only then can we be sure of whether we can meet the design criteria and the customers’ requirements.

Mobile Satellite Broadband for Events

Events come in all shapes and sizes from little cosy gatherings to gigantic extravaganzas. They also take place in allsorts of locations from city centres to remote mountaintops. Often they will be arranged in ad hoc places which do not have any existing telephone or internet access infrastructure.

Unfortunately this can present a problem for today’s event organisers with the modern day requirement for connectivity everywhere. Go to any country festival nowadays and you will be dazzled with a wide array of items for sale from clothing to foodstuffs to souvenirs. Event organisers have so many ways these days to engage with audiences far beyond the immediate vicinity of the event and this can often be the key element that define their success.

So whether its up to the minute twitter feeds, broadcast access to seminars or demonstrations, live web radio streams, guest wireless internet access or credit card transaction processing, the many and varied ways which telecommunications access to the rest of the world can enhance an event offer opportunities galore for event organisers and attendees alike.

 

At Apogee Internet, we have it all covered wherever your event may be. On a boat in the middle of the Irish Sea or at the top of Ben Nevis we can provide your event with high speed Internet access at the core of our offering provisioned across the Astra fleet of spacecraft. This service can be provisioned to cover any location in Europe, the Middle East  or Africa. We can provide the service with Engineers to set up and manage the equipment or, if preferred, as an equipment only service for your own technicians to take care of. Our comprehensive and easy to follow instructions make the set up achievable by anybody with extremely rudimentary knowledge of networks and we can provide remote support too if required.

Once the connection is established, the additional services can be applied so whether its point of sale machines or simply providing wireless network access to be made available to the area, we have the equipment available for hire to facilitate any eventuality. We would be so bold as to say that if you can imagine it, we can very probably make it happen. If you have an event coming up and you would like to enhance the facilities and engage with an audience from afar, give us a call today.

 

If you are in the UK, you can call us free on 0800 012 1090. If you are elsewhere in Europe, the Middle East or Africa, call us on +44 1560 321349.

Spread Spectrum Modulation Techniques

Wireless Local Area Networking technology today exploits a technology which was thitherto mostly hidden inside the shadowy domain of military communications and radar. This technology comprises a collection of ideas which are termed Spread Spectrum Techniques (SST). Spread Spectrum techniques have some powerful properties which make them an excellent candidate for networking applications. To better understand why, we will take a closer look at this fascinating area, and its implications for networking.

Spreading the Spectrum

The first major application of Spread Spectrum Techniques (SST) arose during the mid-sixties, when NASA employed the method to precisely measure the range to deep space probes. In the following years, the US military became a fan of SST due to its ability to withstand jamming (ie intentional interference), and its ability to resist eavesdropping.

Today this technology forms the basis for the ubiquitous Global Positioning System (GPS), the not so ubiquitous NMIDS (Nato Multifunction Information Distribution System/AWACS) datalink (used between aircraft, ships and land vehicles), and last but not least, the virtually undetectable bombing and navigation radar on the bat-winged B-2 bomber. If you ever get asked what technology your home shares with a stealth bomber (excluding astronomical cost), you can state without fear of contradiction that it uses the same class of modulation algorithm.

How is this black magic achieved? The starting point is Claude Shannon’s information theory, a topic beloved by diehard communications engineers. Shannon’s formula for channel capacity is a relationship between achievable bit rate, signal bandwidth and signal to noise ratio.

Shannons theory states that channel capacity is proportional to bandwidth and the logarithm to the base of two of one plus the signal to noise ratio, or:

Capacity = Bandwidth*log2 (1 + SNR).

What this means is that the more bandwidth and the better the signal to noise ratio, the more bits per second you can push through a channel. This is indeed common sense. However, let us consider a situation where the signal is weaker than the noise which is trashing it. Under these conditions this relationship becomes much simpler, and can be approximated by a ratio of Capacity/Bandwidth = 1.44* SNR.

What this says is that we can trade signal to noise ratio for bandwidth, or vice versa. If we can find a way of encoding our data into a large signal bandwidth, then we can get error free transmission under conditions where the noise is much more powerful than the signal we are using. This very simple idea is the secret behind spread spectrum techniques.

Consider the example of a 3 kHz voice signal which we wish to send through a channel with a noise level 100 times as powerful as the signal. Manipulating the preceding equation, we soon find that we require a bandwidth of 208 kHz, which is about 70 times greater than the voice signal we wish to carry. Readers with a knowledge of radio will note here that this idea of spreading is a central part of FM radio and the reason why it produces better sound quality compared to the simpler AM scheme.

Other than punching through large levels of background noise, why would we otherwise consider using spread spectrum techniques ? There are a number of good practical reasons why spread spectrum modulation is technically superior to the intuitively more obvious techniques such as AM and FM, and all of the hybrids which lie in between.

  • The Ability to Selectively Address. If we are clever about how we spread the signal, and use the proper encoding method, then the signal can only be decoded by a receiver which knows the transmitter’s code. Therefore by setting the transmitter’s code, we can target a specific receiver in a group, or vice versa. This is termed Code Division Multiple Access. or CDMA
  • Bandwidth Sharing. If we are clever about selecting our modulation codes, it is entirely feasible to have multiple pairs of receivers and transmitters occupying the same bandwidth. This would be equivalent to having say ten TV channels all operating at the same frequency. In a world where the radio spectrum is being busily carved up for commercial broadcast users, the ability to share bandwidth is a valuable capability.
  • Security from Eavesdropping. If an eavesdropper does not know the modulation code of a spread spectrum transmission, all the eavesdropper will see is random electrical noise rather than something to eavesdrop. If done properly, this can provide almost perfect immunity to interception.
  • Immunity to Interference. If an external radio signal interferes with a spread spectrum transmission, it will be rejected by the demodulation mechanism in a fashion similar to noise. Therefore we return to the starting point of this discussion, which is that spread spectrum methods can provide excellent error rates even with very faint signals.
  • Difficulty in Detection. Because a spread spectrum link puts out much less power per bandwidth than a conventional radio, this means that they can coexist with other more conventional signals without causing catastrophic interference to narrowband links.

These characteristics endeared spread spectrum comms to the military community, who are understandably paranoid about being eavesdropped and jammed. However, the same properties are no less useful for local area networking over radio links. Indeed these are the reasons why the current IEEE draft specification for radio LANs is written around spread spectrum modulations. To better understand the inner workings of this fascinating area, we will now more closely examine the various choices we have for spread spectrum designs. The two basic methods are indeed both used in LAN equipment.

Direct Sequence Systems 

Direct Sequence (DS) methods are the most frequently used spread spectrum technique, and also the conceptually simplest to understand. DS modulation is achieved by modulating the carrier wave with a digital code sequence which has a bit rate much higher than that of the message to be sent. This code sequence is typically a pseudorandom binary code (often termed “pseudo-noise” or PN), specifically chosen for desirable statistical properties. In effect we are transmitting a wideband noise like signal which contains embedded message data. The time period of a single bit in the PN code is termed a chip, and the bit rate of the PN code is termed the chip rate.

A wide range of pseudorandom codes exist which can be applied to this task. These codes should ideally be balanced, with an equal number of ones and zeroes over the length of the sequence (also termed the code run), as well as being cryptographically secure. This is necessary because a spread spectrum system which uses a cryptographically insecure code will still possess the properties previously discussed, but if an eavesdropper can synchronise on to the signal they will eventually be able to crack it and extract the data. Using a secure code prevents this. The mechanics of generating pseudorandom codes is a fascinating area within itself. The most commonly used approach for producing a wide range of code types is the use of a tapped register with feedback as well as a modulo 2 adder. These are very simple to implement in hardware.

A PN code generator of this type uses a register with taps between selected stages. These taps are logically ORed and then fed back in to the input stage of the register. The state machine produced in this fashion will periodically cycle through the same PN sequence as the clock is applied.

Significantly, code sequence lengths of up to thousands of bits in length can be produced with about a dozen register stages. With modern VLSI techniques it is feasible to build generators with clock speeds up to hundreds of MHz on any die, moreover recent high speed Emitter Coupled Logic (ECL) devices allow the creation of generators with clock speeds into the GHz region.

Having produced a black box which generates a PN code with the required characteristics, the process of combining the PN modulation with the data to be transmitted, and modulating this upon a carrier is not technically difficult at all. The simplest technique, one of many, is to invert the PN code when a ‘0’ bit of message data is to be sent, and to transmit the PN code unchanged when a ‘1’ bit of message data is to be sent. This technique is termed Bit Inversion Modulation. The result is a PN code with an embedded data message.

The simplest form of carrier modulation which can be used is AM, however in practice one or another form of Phase Shift Keying (PSK) is usually employed. PSK schemes are commonly used in modems, and involve the modulation of the carrier phase with the data signal. In a DS transmitter using Binary PSK, the carrier wave is phase shifted back and forth 180 degrees with each 1 or 0 in the PN code chip stream being sent. The process of modulating the carrier with the PN code is often termed spreading.

The internals of a DS receiver are somewhat more complex than those of the transmitter, but not vastly so. The central idea in all SST receivers is the use of the correlation operation.

Correlation, a favourite method of our friends in the statistics community, is a mathematical operation which determines a measure of likeness or similarity between two sets of data or two time processes. In an SST receiver, the correlation operation is use to measure the similarity of a received PN code sequence to an internally generated PN code sequence. Ideally, if these PN sequences are the same, a high correlation will be detected, whereas if the codes are different, a low correlation is detected.

Mathematically the correlation operation, in its simplest form, is the integral of the product of two time varying functions. In a DS receiver of the simplest kind, the hardware maps directly onto the basic maths. The correlator is built by combining a multiplier with a low pass filter (ie integrator in a control engineer’s language).

One of the two time varying functions is the received PN modulated signal, the other is the PN sequence produced by a PN generator internal to the receiver. In the simplest situation, the receiver’s PN generator is a clone of the PN generator in the transmitter.

The multiplier can be one of many designs, importantly it multiplies in effect two single numbers and is therefore trivially simple. Classical textbooks cite the analogue doubly balanced mixer as the standard multiplier. The output from the multiplier is a time varying measure of the similarity between the two codes, blended with the remnants of uncorrelated (ie real) noise and interfering signals.

The integration operation disposes of the latter, and we are then left with the data which we intended to extract. This series of operations is often termed despreading. In practice, we often need to synchronise our receiver’s PN generator to the incoming SST signal, therefore there is often much additional complexity required to produce an internal reference PN sequence in proper sync with the incoming message PN sequence.

At this point it is worth reflecting upon what we have. We can generate either cryptographically secure or insecure codes. We can embed a digital data stream in one or another fashion into the code stream. All of this can be performed with pure digital logic. Once we have a combined data/code stream, we can use a very simple analogue modulation to put the message upon a carrier.

The resulting radio signal looks like white noise to a third party who doesn’t know the code. Our receiver shares similar hardware design with our transmitter. It uses a trivial demodulation scheme, and extracts digital data from the incoming PN data/code stream. Other radio signals occupying our bandwidth are largely ignored. Whilst an SST transmitter-receiver pair may be conceptually more complex to understand than most classical analogue schemes, it is well suited to implementation in digital logic because most of the smarts at either end of the link are purely digital. This means that such hardware can be made much more compact than many classical narrowband analogue schemes, which often require a lot of analogue hardware which may or may not be easy to squeeze into Silicon.

Consider a narrowband 16 or 64 level QAM scheme, which is not only vulnerable to interference and noise, but also requires a digital signal processing chip to demodulate. For those readers with a bent toward radio engineering, the spectral envelope of a DS system is typically a sine function, with suppressed outer sidebands beyond the first null, and often a suppressed carrier. A parameter which radio types will appreciate is process gain, a measure of signal to noise ratio improvement achieved by despreading the received signal. For a DS system it is typically about twice the ratio of RF bandwidth to message bandwidth. Therefore to improve your ability to reject interference by 20 dB, you need to increase your chip rate by a factor of 100.

Frequency Hopping Systems 

Frequency Hoppers (FH) are a more sophisticated and arguably better family of spread spectrum techniques than the simpler DS systems. However, performance comes with a price tag here, and FH systems are significantly more complex than DS systems. The central idea behind a FH system is to retune the transmitter RF carrier frequency to a pseudorandomly determined frequency value. In this fashion the carrier keeps popping up a different frequencies, in a pseudorandom pattern. The carrier itself can be modulated directly with the data using one of many possible schemes. The available radio spectrum is thus split up into a discrete number of frequency channels, which are occupied by the RF carrier pseudorandomly in time.

Unless you know the PN code used, you have no idea where the carrier wave is likely to pop up next, therefore eavesdropping will be quite difficult. Frequency hoppers are typically divided into fast and slow hoppers. A slow frequency hopper will change carrier frequency pseudorandomly at a frequency which is much slower than the data bit rate on the carrier. A fast frequency hopper will do so at a frequency which is faster than that of the data message.

Hybrid (FH/DS) Systems

If we are really paranoid about being eavesdropped, we can take further steps to make our signal difficult to find. A commonly used example is that of a hybrid spread spectrum system using both FH and DS techniques. Such schemes will typically employ frequency hopping of the carrier wave, while concurrently using a DS modulation technique to modulate the data upon the carrier.

In this way an essentially DS modulated message is hopped about the spectrum. To successfully intercept such a signal you must first crack the FH code, and then crack the DS code. If you want to be even more secure, you encrypt your data stream with a very secure crypto code before you feed it into your DS modulator, and employ cryptographically secure PN codes for the DS and FH operations. Your eavesdropper then has to chew his way through three levels of encoding. Such a scheme is used in the NMIDS (Nato Multifunction Information Distribution System/AWACS) datalink.

Summary 

Spread Spectrum techniques are technologically superior to conventional narrowband modulation techniques in a number of important areas. They form the datalink layer of todays WLANs in operation in most households in the UK as well as in most offices. Their ubiquity belies their complexity and without SST the modern day advantages of mobile telephony as well as wireless LAN networking would not be possible. If your organisation needs assistance with its radio communications in the field of wireless networking, give us a call free today on 0800 012 1090. We look forward to your call.