The near future of Wi-Fi: Voice Enterprise certification

In the last article of the mini-cycle, we talked about 802.11ac , in this one we’ll talk about Voice Enterprise certification: what it is and why it is needed.

The voice in wireless networks went through about the same thorny path as in wired networks: initially, no one was going to send over something like voice and video; then the task was set, it was necessary to invent new protocols and attach additional extensions to the existing ones; in the end it all worked.
Technology more or less high-quality voice over Wi-Fi has been around for a long time, but building a quality network for VoWLAN is still a very difficult task. And not even because of the subtleties of radio planning and tuning QoS - trite, the problem is the selection of iron!

• Does the infrastructure support all the necessary technologies? Are standard or proprietary mechanisms used?
• Have standard mechanisms been tested for compatibility? What are the known shoals?
• Will we use standard or proprietary client devices?
• Do customers support all the necessary technologies? Where to get this information? (If for the infrastructure of the Enterprise class, there is always documentation, then for all Android handsets it is very difficult to find it.)
• Do voice applications support all the necessary technologies?
• And what is this "all the necessary technology" in general?

The history of the problem.

Let's start with the last item. From the point of view of voice services in the data network, we are concerned about two parameters:

• Quality : voice quality should be good throughout the entire call under any network load. In terms of services, voice quality is usually determined by the criteria of R-Value or MOS . From a network point of view, to meet this requirement, the data flow for each client should be characterized by low latency, jitter, and packet loss values.
• Coexistence with the rest of the traffic: in most corporate networks, Wi-Fi will not be used only for voice - there will be other uses. So, mechanisms of peaceful coexistence with traffic of other applications are needed, which, very likely, can be many times more.

In principle, this is enough: we need a quality service that will get along with already existing applications on the network. How does this translate into technical requirements for wireless clients and infrastructure?

• Prioritization. First of all, it is necessary to assign and take into account the priorities of different packages. Ethernet for this is 802.1p. In Wi-Fi - 802.11e, also known as WMM (Wireless MultiMedia) certification. Unlike 802.1p, where 8 classes of traffic are defined, WMM has only four: Voice, Video, Background and Best Effort. Voice traffic (AC_VO) has the highest priority. WMM is a certification of the Wi-Fi Alliance, and on their website in the database you can see which devices have been officially tested for correct support for WMM. However, prioritization alone for full QoS is not enough.
• Bandwidth management. First, as with wired QoS, functions such as reservation and / or bandwidth limiting at different levels (point, WLAN, client, etc.) may be necessary. Secondly, wireless networks are mobile and customers are moving into them. In this situation, when roaming the client, it is very important to get to a point that has enough free resources to “continue the conversation”. Otherwise, the call may end trite because we hit the overloaded point. This technology requires proper support from both the infrastructure and the client. The client should be able to poll neighboring points before roaming (think about it, while neighboring points can be on other channels!) And choose a free one (for this, the points should report their workload). However, such a scheme is quite complicated, and traditionally in Wi-Fi, no one believes in correctly working drivers on clients. Therefore, we went another way: the infrastructure must be able to understand what the client needs for full-fledged work (the client reports that he needs in the TSPEC - Traffic Specification message) and draw conclusions - allow the client to connect, or ignore it. Since these mechanisms are scattered across a number of 802.11 standards, an additional certification WMM-AC (Admission Control) was created, which verifies their correct implementation (as well as the implementation of some other things that provide load balancing in WLAN).
• Roaming Speaking of moving customers, it is important to remember that roaming itself takes some time. Depending on the network settings on the infrastructure and the client, this time can reach several seconds. Naturally, there can be no talk of any quality of voice here, since the call will simply break. To solve this problem, manufacturers have thought of a bunch of cool, but proprietary, mechanisms that had serious compatibility problems. The 802.11r standard (FT, Fast Transition), which details the fast roaming mechanism (<20ms), is intended to solve these problems. However, for a long time there was no certification confirming the correct implementation of this standard by the manufacturer. This is one of the shortcomings that Voice Enterprise is intended to fix.
• Security. Any service must be safe. The only valid Wi-Fi security certification currently in use is WPA2. Thus, our solution should work successfully within the framework of this mechanism and not break anything.
• Autonomy. We all know very well how great the difference is between the “waiting time” of a mobile phone and the “talk time”, and what tricks are used by manufacturers of mobile phones (and cellular infrastructure) to increase this time. The same thing happens in Wi-Fi. There is a separate certification WMM-PS (Power Saving), optimizing the procedure for the exchange of customer data with access points for greater energy efficiency.

Summarize. Even just to simply select the appropriate access points and client devices for VoWLAN, you need to check them for the presence of five certifications (Wi-Fi, WMM, WMM-AC, WMM-PS, WPA2), and also for compliance with certain parts of the 802.11 standard r, there is simply no certification for it. In addition, really fast 802.11r operation requires the implementation of some of the 802.11k (RRM - Radio Resource Management) and 802.11v (WNM - Wireless Network Management) specifications that also need to be tested. Then carry out compatibility tests and hope for the best, since none of these certifications and specifications imposes special requirements on the client roaming algorithm itself ( “Yes, I support 802.11r and can quickly be installed, but I ’ll be roaming only when the percentage lost packages will reach 80% " ).
Unfortunately, historically, the roaming logic of wireless clients is entirely determined by their manufacturer. And well, if no glitches!
Thus, the construction of VoWLAN was a risky business, there was little confidence in them, as a result, low prevalence and demand. Having described the scale of the disaster, I think you can proceed to a solution.

Decision

The solution is designed to be a single certification “ Wi-Fi CERTIFIED Voice Enterprise ” (in this register), which imposes requirements on the radio part, on protocol support, on compatibility, and on the performance and overall performance of the client. Consider what is checked in certification:

• The correctness of the implementation of protocols. Provides compatibility.
  • RRM: parts of the 802.11k specification. Required for infrastructure and customers.
  • FT: parts of the 802.11r specification. Required for infrastructure and customers.
  • WNM: part of the “BSS Transition Management” specification 802.11v. Optional for infrastructure and customers. If there is support, the point will inform the client about its neighbors, allowing it to plan in advance at what point to go further.
• Compliance with performance requirements. Provides quality. It is tested according to a specific set of scenarios, simulating various situations in an almost fully loaded network. Required for infrastructure and customers.
  • Delay (including roaming parts): <50ms one way
  • Jitter : <50ms
  • Packet loss : <1%
  • Sequentially lost packets : no more than three.
• Availability of other certifications. To simplify life.
  • Basic certification : one or more of Wi-Fi certifications (a / b / g / n). Required for infrastructure and customers.
  • Security : Voice Enterprise requires WPA2-Enterprise, which means support for RADIUS and certain types of EAP. There is also Voice Personal, the requirements are simpler there.
  • QoS and bandwidth control: WMM and WMM-AC respectively. Required for infrastructure and customers.
  • Energy efficiency : WMM-PS. Required for infrastructure, optional for clients (for example, if the client is
    Wi-Fi-powered microcomputer mounted on a forklift

    
    ).

Thus, with the advent of this certification, the work on network design, selection, testing and configuration of devices (clients and infrastructure) is greatly facilitated, since A certain set of generally applicable criteria and principles appears.
Further details of certification can be found in the official WFA document , which was used as a source for this article.
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Why is the "near future"?

So, there appeared a solution to a rather serious problem, which allows VoWLAN to be taken out of the semi-experimental phase into the mainstream, and to deliver a lot of good profit to all. The decision is important and necessary. Why is the "near future"?
Like the other two key Wi-Fi specifications, 802.11i and 802.11n, the Voice Enterprise output was regularly migrated. It was originally planned to start in November 2007. However, as a result of various perturbations, the official press release about the launch of certification and the “early start of testing and issuing certificates” was released only in May 2012. And even now, a year later, it is very difficult to find certified products on the WFA website . In fact, most of the first and second tier Enterprise WLAN vendors have long supported all the necessary technologies, but they do not seem to be in a hurry with “official” certification (perhaps, resources are being transferred to the struggle for 802.11ac leadership, as long as it's hot). So, for now, Voice Enterprise for us is “the near future.”
But I think next year (or even at the end of it) the “official” support of Voice Enterprise will be announced for most access points, and, most importantly, for client devices, and this will allow the voice to be registered in wireless networks as firmly as and wired.

Your opinion?