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 Convergence in the Wireless World — Voice, Video and Data with the Axxcelera AB-Access
For years we have been hearing about converged networks, that elusive nirvana of telecommunications, the vision of one network that does it all voice, video and data equally well. While there are claims and counter claims in the wired world as to whether or not this has been truly accomplished, quietly and with great success around the world Axxcelera has delivered on this promise with its Broadband Wireless Access (BWA) system, AB-Access™.
A Difficult Challenge
The reason why the converged network has been so elusive is simple: the transport requirements for these very different traffic types are far ranging and complex. The challenge is not just to support all three on a single network, but to do it efficiently and cost effectively. It would be simple, for example, to provide a fiber link between two branch offices of a company and deliver everything desired voice, video conferencing, high speed data transfer etc.. However this is neither efficient nor cost effective. Throwing excess capacity at the problem is not an approach any profit minded service provider can follow.
The AB-Access has been designed from the ground up to deliver on the promise of converged transport. The system has the features and inherent engineering base necessary to satisfy the unique needs of voice, video, and data simultaneously. Below, each traffic type and its transport needs is examined, followed by a brief discussion of how the AB-Access meets these needs.
Data
Delivering data is not a challenge in and of itself. The Internet Protocol (IP) as an accepted standard world wide means that interoperability and basic transport are simple and easy to support. The challenge focuses more on how to deliver lots of data efficiently. Data traffic is by its very nature very tolerant of delays or latencies in a network. A single file transfer can take seconds with no impact on the information. On the other hand, data packets are intolerant of errors in the bits being transmitted. While there are higher layer protocols for addressing corrupted bits, these can have a large impact on the throughput performance. The other inherent feature of data transmissions lies in the bursty nature of the traffic. Thus a data traffic stream needs widely varying levels of capacity, must be error free or at a minimum a very low error rate, but can tolerate wide ranging latencies.
AB-Access delivers on all these fronts. Each AP delivers 25Mbps to its wireless network, with each SU supporting up to 15.5Mbps in ATM mode or when configured as an Ethernet bridge or IP router. In addition, the AB-Access has built into it's over the air protocol error detection and correction, keeping the error rates at a minimum and ensuring optimal throughput performance.
With some systems, this is accomplished by dedicating pipes to each Subscriber Unit, a very inefficient design for data traffic. The AB-Access employs Bandwidth on Demand technology, thus increasing the amount of effective bandwidth available at any given moment. AB-Access divides the available bandwidth between only the SU's that have traffic to send, thus transporting bursty traffic flows at maximum efficiency.
Voice
Historically voice has been delivered, either wireless or wire line, in a dedicated, one-to-one circuit switched manner. This is because of the unique requirements voice traffic places on a network. While voice traffic is typically at a relatively low bit rate, 64kbps in the PSTN, and as low as 15kbps in the cellular world, it is especially intolerant of latency, and even more intolerant of changing latency rates or jitter. Industry practice for wire line phone calls mandates no more than 200 to 250ms (1/5th to 1/4th of a second) one way latency for acceptable voice quality.
In addition with a voice call, error rates are not as critical. Dropped or corrupted bits in a voice stream results in hiss or pops, not pleasant but it does not prevent the call from taking place. AB-Access handles the latency sensitive voice traffic at several layers. First, the system offers two methods of voice transmission, native ATM and Permanent Virtual Circuits (PVC) designed to integrate to the PSTN easily. The product also supports Voice over IP when configured as a bridge or a router. Both of these methods rely upon the basic feature of the AB-Access system – the ability to introduce approximately 1ms of latency in the wireless network portion of the system.
For VoIP, AB-Access goes a step further. Typically, VoIP packets are short in nature, but plentiful in volume. Many BWA systems are limited in the number of simultaneous VoIP calls they can support because of the massive amount of small packets to be processed. AB-Access has taken this into account and has been designed to support up to 20 simultaneous VoIP calls from a single SU.
Video
Video is probably the one of the most difficult types of traffic to support. It requires the low latency and jitter performance of a voice call, but places high demands on the data capacity at the same time. In addition, it is also intolerant of errors. It can be argued that video takes the most stringent requirements of both voice and data traffic.
Thus the successful video transport system will combine low latency with high capacity and low bit error rates. Again, this can be done easily if money is not a concern. The challenge is to design a system that addresses these requirements and can be done at a cost that supports the business plan of the service provider.
AB-Access does this elegantly and cost effectively. With its low latency, approximately 1ms, and its high capacity, 25Mbps per AP with a net throughput of up to 15.5Mbps per SU, the system delivers on both of these requirements. Coupled with it's over the air protocol addressing error rates, AB-Access has the ability to transport video like no other BWA system available.
Converged - Data, Voice, and Video
While it is certainly impressive, the capability of the AB-Access to support these disparate transmissions, if the system could only do one at a time it would be much less useful. To be truly converged, the network must be able to support all three major traffic types in a single network, at the same time.
This can and is accomplished with the Axxcelera AB-Access BWA system. No other product has been deployed in real world environments, actively supporting data, voice and video simultaneously on one network. No matter the applications and services to be delivered, Service Providers can rest easy knowing their solution choice is simple and clear - AB-Access from Axxcelera Broadband for all your wireless network deployments.
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