Sub10 white paper denial of service

1 60 GHz - Denial of Service - 200112

60GHz POINT TO POINT NETWORKS – DENIAL OF SERVICE

INTRODUCTION

Sub10 Systems define the phrase ‘denial of service’ for circumstances when radio link traffic is

disrupted or corrupted, temporarily or permanently, by physical or electronic means.

We have looked at the issue from a practical viewpoint, taking into consideration link locations,

probable RF propagation conditions and likely network topography.

It will be shown later that the probability of accidental denial of service due to RF ‘pollution’ at

60GHz is very low, owing to propagation characteristics in the band and antenna design of the Sub10

Liberator.

Deliberate denial of service does present a slightly higher risk, with physical damage or disruption of

link equipment most likely. Attempting to use a 60GHz radio ‘jammer’ to interrupt link

communication is seen as complex to do and unlikely to succeed.

LINK LOCATIONS AND PHYSICAL SECURITY

In order to achieve optimum performance in the network, all links should be mounted on rooftops

or high points of buildings. Either on poles fixed to a high point on the roof, or on stand-off

mountings fixed to an outside wall, just below a parapet. In most cases we expect that access to the

roof of any building, used for an element of the network, will be strictly controlled, ensuring good

physical security, requiring keys and or passes to get onto the roof at all.

Sub10 Liberator Outdoor Units (ODU) on the roof top will be mounted in positions requiring

equipment such as a ladder to reach them; alternatively, ODU fixed to the outside wall of a building,

below the parapet, will be hard to reach without specialist equipment and the correct level of

training in climbing techniques.

Combine good physical security with relatively inaccessible mounting points and it can be seen

someone with malicious intent would find it difficult to interfere with one or more of the Sub10

Liberator links. In this sense, “interfere” is used in the physical, rather than electronic sense. After

discussion with our specialist RF team, the general consensus is that someone wanting to sabotage a

network could do this very easily by simply cutting one or more of the power/data ‘drop’ cables

feeding an ODU. The recommendation? If the access to a rooftop is not secure and strictly

controlled, put procedures into place to make it so. Additionally, run power and data drop cables

inside steel conduit in order to protect them from accidental or deliberate damage.

2 60 GHz - Denial of Service - 200112

ACCIDENTAL ‘DENIAL OF SERVICE’

Considering the accidental situation. The propagation of radio-waves at 60GHz is affected very

significantly by oxygen absorption. Figure 1 illustrates that the oxygen absorption peak, of 16dB/Km,

is coincident with virtually the whole 60GHz band.

Fig 1 –Oxygen Absorption Peak of 16dB/km over 60GHz Band

The principle effect of high levels of attenuation, due to oxygen absorption, is to restrict ranges of

60GHz radio systems to below 2km. Add the effects of this range limitation to the very narrow radio

beam produced by a Sub10 Liberator as shown in Figure 2 and it can be seen the 60GHz band is very

resistant to interference, regardless of how many 60GHz radios are deployed in a small geographic

area.

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Fig. 2 – Narrow antenna beam significantly reduces chances of interference

A practical illustration of excellent frequency reuse, with no adverse interference, is in Vienna,

Austria, where a mobile telephone service provider planned to deploy 90 Sub10 Liberator links in

support of a city wide mobile telephone network; using the links to transport data from mobile

telephone base-stations back into the network. Prior to the roll-out, a detailed interference analysis

was conducted; the analysis showed, theoretically, there would be no interference despite, in many

cases, little physical separation between radio units.

Fig 3. Vienna – (Light Blue & Green showing some Liberator paths)

This study gave the integrator and operator sufficient confidence to go ahead with the deployment

and prove that theory and practice were one and the same. The 60GHz element of the whole

network has been operating, interference free, providing carrier grade levels of service, for well over

2 years. The diagram at Figure 3 above illustrates the extensive use of various types of radio links in

one area of the network. The light blue paths are a small proportion of the total of 90 Liberator links

deployed in the network.

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DELIBERATE ‘DENIAL OF SERVICE’

Moving on to a scenario where, despite your best efforts to secure the roof of a building, someone

with malicious intent is able to gain access to it. As stated earlier, the simplest thing for them to do

would be to tamper with the drop-cable providing power and data to each ODU. Alternatively, they

could obstruct the antenna face with cardboard or some similar material. Actions of this type

should immediately alert those monitoring the network that service had ceased and would trigger an

inspection and rectification visit.

The Sub10 RF team have considered the challenge of building a device able to ‘jam’ radio signals at

60GHz. In order for this jammer to be effective, it would need a relatively large (60cm) directional

antenna, the transmitter itself and a portable power supply. There is then the difficulty of getting

this whole device onto a rooftop without attracting suspicion. Once there, the only way an

individual link could be affected is to focus the jamming signal directly into the operating beam.

Considering the link ODU are going to be well above head height, or on the outside wall of a

building, above a sheer drop, this would be extremely difficult.

Using the same device to try to ‘attack’ a remote Liberator ODU positioned on another building

some hundreds of metres away would be defeated owing to the significant degradation of the

transmitted signal caused by oxygen absorption coupled with losses due to free space. Effectively,

the jamming signal once it had travelled a few hundred metres, even if pointed directly at the

antenna of the Sub10 Liberator ODU, would be of insufficient strength to disrupt service.

SUMMARY

Accidental denial of service has, through deployments such as those in Vienna, been shown to be

unlikely.

Deliberate denial of service is possible and would most likely be via physical damage to drop cables

or ODU. The best protection against this is to ensure best in class security for those rooftops where

the Sub10 Liberator will be deployed.

The probability of disruption using a 60GHz ‘jammer’ is perceived to be very low.