Frequently Asked Questions

The BigAir network is a non-terrestrial network, which does not rely on Telstra for the provision of any of its services. Unlike most other carriers in Australia, the BigAir network bypasses all Telstra exchanges and legacy PSTN (copper) networks with our "Fibre in the Sky" wireless connections. Each basestation (transmission tower) is typically a tall or medium height building which has good line of sight over a region. Every basestation comprises:

• Redundant power systems
• Networking equipment
• Point to Point (PTP) backhaul radios "feeding" the basestation with Internet connectivity.
• Point to Multi-Point (PTMP) radios (sector radios) which distribute the service to customers. Typically, a sector radio will service 60-80 degrees using directional antennas.

A client site typically contains a subscriber radio with built-in antenna. This unit establishes the wireless connection with the respective sector radio on a nearby basestation. A sector radio can be thought of as the master while the client can be thought of as the slave. Each master can talk to many slaves at the same time. The BigAir wireless broadband network will allow complete bypass of the copper networks, and eventually the mobile phone networks can also be bypassed using wireless data networks.

Non-line-of-sight (NLOS) or near-line-of-sight is a term used to describe radio transmission across a path that is partially obstructed, usually by a physical object in the Fresnel zone (see diagram below).

Many types of radio transmissions depend, to varying degrees, on line of sight between the transmitter and receiver. Obstacles that commonly cause NLOS conditions include buildings, trees, hills, mountains, and, in some cases, high voltage electric power lines. Some of these obstructions reflect certain radio frequencies, while some simply absorb or garble the signals; but, in either case, they limit the signal strength and quality of radio transmissions, affecting the speed and performance of the service.

The BigAir wireless network works most effectively with clear line of sight (LOS), this allows BigAir to provide guaranteed speeds, latency and availability at all times. Near line of sight refers to implementations in which the Fresnel zone 'touches' buildings or trees, but can still send a signal to the receiver from the basestation.

Line of Sight

When a user is connected to the Internet using DSL broadband technology they are sharing the connection infrastructure with other users. The term contention is simply a ratio used to measure the extent of this sharing. The typical contention ratio for DSL services is between 20:1 and 100:1. For example on a package with a contention of 50:1, up to 50 other Broadband users may share the equipment and bandwidth in the local telephone exchange. An analogy would be driving a car in peak (rush-hour) and off-peak traffic. During the rush hour you contend the road with everybody else and it may take you longer to get to your destination than during off-peak. This industry-wide method is used by all broadband providers.

The BigAir network operates with a maximum contention ratio of 5:1 which is very low by industry standards. The average contention ratio across the BigAir network in reality is an extremely low 2:1. Since we own and operate our own network, upgrading capacity on a sector to maintain a guaranteed contention ratio is relatively simple and this enables BigAir to guarantee its services levels.

In a network, latency, a synonym for delay, is an expression of how much time it takes for a packet of data to get from one designated point to another. The unit for Latency is measured in milliseconds. Latency is measured by sending a packet from one location to another and the round-trip time is considered the latency.

Typical latency range

BigAir Fixed Wireless latency

15-25ms (typical for sites within 5 km's of the CBD)
25-40ms (typical for sites in outer metro areas such as Baulkham Hills)

Quoted latency figures is the round trip time taken for a packet of data to travel from a customer to the core of the BigAir network (and back again).

The BigAir network is designed to support WiMAX. WiMAX is an Institute of Electrical and Electronics Engineers (IEEE, see www.ieee.org ) standard designated 802.16-2004 (fixed wireless applications) and 802.16e-2005 (mobile wireless). The industry trade group WiMAX Forum (www.wimaxforum.org) has defined WiMAX as a "last mile" broadband wireless access (WIRELESS BROADBAND) alternative to cable modem service, Digital Subscriber Line (DSL) or T1/E1 service. WiMAX is also an acronym for World-wide Interoperability for Microwave Access.

WiMAX uses microwave radio technology to connect computers to the Internet in place of wired connections such as DSL or cable modems. WiMAX works very much like cell phone technology in that reasonable proximity to a base station is required to establish a data link to the Internet. Users within 5 to 8 kilometres of the base station will be able to establish a link using non-line-of-sight (NLOS) technology with typical data rates of 30Mbps. Users at typical distances of up to 20 kilometres from the base station with an antenna mounted for line-of-sight (LOS) to the base station will be able to connect at data rates as high as 100Mbps.

One of the most often heard descriptions of WiMAX in the press is that it is "Wi-Fi on steroids". In truth, it is considerably more than that. Not only does WiMAX offer exponentially greater range and throughput than Wi-Fi (technically speaking 802.11b, although new variants of 802.11 offer substantial improvements over the "b" variant of 802.11), it also offers carrier grade quality of service (QoS) and security. Wi-Fi has been notorious for its lack of security. The "b" variant of 802.11 offered no prioritization of traffic making it less than ideal for voice or video.

The key message here is that the BigAir network is NOT using WLAN equipment. WLANs (eg. WiFi access points) use a contention based MAC (media access control) which means that every client has to "fight" for its bandwidth and share of the spectrum.

WiMax is not Wi-Fi

BigAir instead uses sophisticated equipment based on WiMAX which uses an OFDM (Orthogonal Frequency Division Multiple Access) based MAC. It uses a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations.

With OFDM BigAir is able to maximise distance and throughput and build resistance to interference in to the wireless broadband network. The spectrum is also divided into multiple sub-carriers and modulation (throughput) declines with distance.

BigAir uses 'Licensed Spectrum'

The other important point in relation to spectrum is that ALL spectrum is licensed and regulated by the ACMA (Australian Communications Media Authority). There is no such thing as unlicensed spectrum. BigAir makes use of "Class License" spectrum. This spectrum is designed for co-existence of multiple users, so the maximum transmit power levels are restricted and wireless carriers like BigAir have designed the network for these power conditions. The amount of spectrum BigAir has available for BigAir's use is enormous - roughly 4 times as much spectrum as Unwired, and 30-50 times as much as the mobile carriers. This enables BigAir to offer much higher data rates than mobile phone networks.

The speed and stability of DSL on any given line in the access network is a function of the signal to noise ratio at the end of that line, which in turn depends on –

• the length, quality and dimensions of the copper cable
• the amount of crosstalk (directly related to "cable fill", the proportion of pairs in the cables carrying DSL)
• noise from sources in the business premises (including wiring)
• noise picked up from the environment eg radio frequency interference
• any faults that might be present

Geographic coverage achieved at a given headline speed also depends on -

• the topology of the access network
• the statistical distribution of line lengths

These factors are based on physical science and are identical for anyone operating DSL on an access network. The speed delivered to the end user also can depend on retail and wholesale product definitions, the makes of DSLAM and modem (as standard specifications can be implemented by different designs) and other decisions on how the network operates the chosen DSL technology. In addition, the end user throughput depends on operational decisions on backhaul and contention ratios. The line data available to end users from modems is highly variable in extent and quality and is not a reliable guide to DSL performance.

Wireless communications devices provide considerable flexibility by sending signals over airwaves instead of over wires or fiber. However, sending signals over airwaves can create the opportunity for a security risk in the form of data interception. Using the following five techniques, which provide protection at the physical, network and application layers of the network, BigAir is able to provide a highly secure and robust system to keep out wireless eavesdropping and malicious user attacks.

The BigAir Networks security infrastructure has the following features:

1. Proprietary Wireless and Data Formats
   Unlike a WiFi based Wireless LAN such as 802.11b or 802.11a/g where the standard is "open," BigAir uses proprietary communications signaling and data-link protocols. Unless a customer has a BigAir Subscriber Unit, it would be almost impossible to intercept or spoof the wireless data streams.
2. Pseudo-random Transmission Scrambling and Encryption
   The proprietary signaling scheme used by BigAir pseudo-randomly scrambles the transmissions with one of over 500,000 scrambling sequences, thus increasing the difficulty of intercepting a transmission. Using another BigAir Subscriber Unit, it would take more than one year to search through all the scrambling codes. Encryption is also employed on every wireless link, typically at 128 bit.
3. MAC Address Authentication
   The BigAir Base Stations maintain a user-configurable and password controlled table of authorized BigAir subscriber unit MAC addresses. Subscriber units cannot talk to the network unless the BigAir Base Station Unit authenticates its MAC address and "adds" it to the network.
4. MAC Address Filtering
   The BigAir Subscriber Units are configured to filter the downlink traffic stream to prevent a BigAir Subscriber Unit from outputting traffic that is destined to another BigAir Subscriber Unit. The filtering restrictions can be based upon Ethernet addresses, VLAN addresses, or IP addresses. Only the BigAir network operations centre (NOC) can configure the filtering controls. This prevents unauthorized access of another user's data.
5. Theft Protection
   BigAir Base Stations measure the distance of the connection to each BigAir Subscriber Unit. If one of the BigAir Subscriber Units is physically moved to another location, the BigAir Base Station will detect that the distance is different and will signal an alarm to the BigAir NOC. This protects against someone stealing a Subscriber Unit and using its valid MAC address to enter the network. Subscriber Units will not listen to a Base Station Unit unless they are "added" to the network via the Base Station Unit.

Fibre is recognised as an excellent high bandwidth solution. Additionally, when properly installed, fiber is very reliable. But even fiber is subject to cuts, building fires and floods, earthquakes, etc.  Excellent reliability, but not perfect by any means.

The problems associated with fiber deployment include:

Upfront Cost: The problem with new fiber is the cost to deploy it is often prohibitive. The dominant portions of the costs are not the glass itself, or the electronics-it is the cost of laying the fiber, and especially the cost of trenching or other methods of protecting the strands.

Installation Lead-time: In addition to the large upfront costs, there is the long lead time to install fiber networks. Fiber can take anywhere from 6 weeks to 6 months to 'light up' once it has been ordered which can mean costly delays.

The advantages of Wireless broadband versus Fiber:

1. Reliability: Up to 99.999% availability can be achieved with wireless equipment. In addition to this it is normally very easy to install a second backup wireless link connected to a different basestation, which provides even higher levels of availability. In contrast the cost to install a second fiber connection using different street duct access is normally prohibitive expensive.
2. Wireless is non-terrestrial: The BigAir wireless network has been designed to completely bypass terrestrial networks for both last mile access and also backhaul links, which means the network is completely insulated from breaks in fiber-optic and copper networks which are often caused by civil works and other unexpected activities.
3. Rapid deployment: Wireless connections can be installed in just hours.
4. Ease of relocation: Temporary locations or businesses that relocate frequently can take advantage of wireless broadband and relocations are normally simple and not expensive. In most situations the wireless equipment can be quickly redeployed. In contrast once fiber has been laid it is a sunk cost that cannot be relocated.
5. Scalability: The upgrade costs for wireless broadband services are typically much lower than legacy networks. Therefore, a business can start with just the required capacity and add to it as its requirements grow.

DSL – Digital Subscriber Line
A technology that allows digital signals to be transferred on standard telephone lines. There are different types of DSL, with the newer being faster.

ADSL / ADSL2+ – Asymmetric DSL
A technology that allows a maximum 1.5Mbps download and 256kbps upload speed for version 1.

The newer 2+ variant is rated at 24Mbps download and 1Mbps upload. However you must be very close to the exchange to achieve max speed. Hence, a more realistic speed for the majority of the population should average at 10Mbps download and 600kbps upload.

SHDSL – Symmetric High Bit-Rate DSL
This variant of DSL allows much a symmetric experience where the upload speed and download speed is the same at 2Mbps. Circuits may be bonded to create a 4Mbps link. However, to achieve 2Mbps the distance of the circuit must be no greater than 3km. Once the circuit exceeds this distance, the circuit will run at slower speeds. Maximum distance from exchange is 6km where the speed will fall down to 192kbps.

VDSL / VDSL2 – Very High Bit-rate DSL
A high speed, short distance DSL technology which allows speed of upto 18Mbps download and 16Mbps upload within the high rise building. The second variants of VDSL will allow speeds of 50Mbps to 100Mbps within the same building. This technology is very popular in countries like Korea where the internet is used for mass distribution of video and TV.