802.11R. Fast switching between points (handover)
Many Wi-Fi manufacturers promise seamless hotspot switching using their ingenious proprietary protocol.
Despite the nice promises, in practice, the delays during switching (handover) can be significantly more than the declared 50-100 ms (switching can take up to 10 seconds when using the WPA2-Enterprise protocol). The fact is that the decision to switch to another access point is always made by the client equipment. Those. Your smartphone, laptop or tablet decides when to switch it and how to do it.
Often proprietary protocols of well-known Wi-Fi manufacturers are based on forced de-authentication of a device when signal quality deteriorates. Sometimes in the Wi-Fi settings of the point, you can set "aggressiveness of roaming" - the minimum signal value at which the device will be "thrown" from the network. Often, client equipment does not respond correctly to such a kick in the ass. The TCP session is terminated, file uploading stops. The connection to the mail server, virtual machine is disconnected. Connecting to the SIP server requires re-authentication.
Quite often, a client device instead of connecting to a neighboring point with a better signal ( to this decision pushes himWi-Ficontroller) to no avail tries to reconnect to the previous point. It is even worse if the device tries to cling to another network from the list of saved ones (for example, a guest network).
But even if the switchover process goes according to plan, re-key exchange (EAP) and authorization on the Radius server (WPA-2 Enterprise) take a significant amount of time.
To solve these problems, the Wi-Fi association developed the 802.11R protocol. Most mobile devices currently support it (Apple since iPhone 4S, Samsung Galaxy S4, Sony Xperia Z5 Compact, BlackBerry Passport Silver Edition, ...)
The essence of 802.11R is that a mobile device knows its own and others' points by the mobile domain membership signal (MDIE). This signal is added to the SSID beacon.
If your iPhone sees a point from its mobile domain with a better signal-to-noise level, it pre-authorizes with another point of the mobile domain before starting the switching procedure on the existing "thread".
Secondly, authorization follows a simplified scenario - instead of a long authorization on the Radius server, the client device exchanges a PMK-R1 key with the Wi-Fi controller. (The original PMK-R0 key is transmitted only during primary authentication and is stored in the memory of the Wi-Fi controller).
At the moment when another point "retroactively" authorized the device, the actual handover takes place. Reconfiguring the frequency and channel in a smartphone takes no more than 50 milliseconds. In most cases, it goes completely unnoticed for the user.
When choosing a solution for an office Wi-Fi network, pay attention to whether the selected equipment supports the open roaming protocol 802.11R, which is understandable for client devices. For example, Edimax Pro equipment fully supports this protocol, so problems with roaming do not arise in most cases. However, if your device is old and does not understand the 802.11R protocol, it is possible to tune the aggressiveness of roaming based on signal drops below the threshold - as other Wi-Fi manufacturers do, presenting it as an "innovative solution."
802.11 K.Load balancing on a wireless network
In addition to roaming problems, corporate users often have to deal with congestion of one access point. In the classic Wi-Fi implementation, all devices tend to connect to an access point with the best signal. Sometimes, as a result of the wrong location of the point (radio planning error), all the "office inhabitants" are registered at one point, and the rest are "resting".
Due to the uneven load, the speed of the local network drops dramatically, since the radio broadcast is one big "hub" where the devices "speak in turn".
To smooth out unevenness and optimal distribution of users between points operating on different radio channels, the 802.11K protocol was developed.
802.11K works in conjunction with 802.11R (as a rule, devices that support the “R” standard also support the “K” standard).
If a mobile device “sees” a beacon signal from other points in the same mobile domain, the device sends a broadcast “Radio Measurement Request frame” request, in which it requests information about the current state of other access points within the range of visibility:
number of registered users
average channel speed (number of transmitted packets)
how many bytes were transferred in a certain time interval
In the extended specification of the standard, the client's smartphone can query the channel status from other mobile devices connected to a potentially interesting access point that support the 802.11K standard. Devices respond not only to real statistics, but also to signal / noise status.
Thus, if your smartphone sees 2 or more points within the same mobile domain, it will choose the point not with the best signal, but the point that will provide a faster connection to the local network (less busy).
The reception conditions, the number of users and the load at the point can change dynamically, but using the 802.11K and 802.11R protocols, devices will switch seamlessly and the load on the network will always be evenly distributed.
Many vendors using proprietary protocols implement a semblance of 802.11K, where a congested point forcibly disconnects clients with worse reception conditions or limits the maximum number of simultaneously registered devices and disables registration if the number of clients exceeds acceptable limits. These proprietary protocols are not as effective, but still prevent the Wi-Fi network from collapsing at all.
How to save money on radio planning with802.11K
The use of equipment supporting 802.11R and 802.11K protocols partly corrects mistakes made during radio planning. Dynamic protocols with roaming support help avoid congestion of individual points and distribute the load between points evenly across the network.
The WiFi-solutions team recommends to always do radio planning, but sometimes in small networks, you can dot chaotically. Dynamic protocols will improve Wi-Fi quality and load balancing between adjacent hotspots.
The use of dynamic protocols for seamless roaming can reduce the coverage area. Thus, you can provide high-quality coverage with fewer dots. Savings on equipment - up to 25%.
I need a consultation. Get in touch with me.
We understand roaming technologies (Handover, Band steering, IEEE 802.11k, r, v) and conduct a couple of visual experiments that demonstrate their work in practice.
Introduction
Wireless networks of the IEEE 802.11 group of standards today are developing extremely rapidly, new technologies, new approaches and implementations appear. However, as the number of standards grows, it becomes more and more difficult to understand them. Today we will try to describe several of the most common technologies that are referred to as roaming (the procedure for reconnecting to a wireless network), and also see how seamless roaming works in practice.
Handover or "client migration"
Once connected to a wireless network, a client device (be it a smartphone with Wi-Fi, a tablet, laptop or PC equipped with a wireless card) will maintain a wireless connection if the signal parameters remain at an acceptable level. However, when the client device moves, the signal from the access point with which the connection was originally established may weaken, which sooner or later will lead to a complete impossibility of data transmission. Having lost connection with the access point, the client equipment will select a new access point (of course, if it is within reach) and connect to it. This process is called handover. Formally, handover is a migration procedure between access points, initiated and performed by the client itself (hand over - "transfer, give, give up"). In this case, the SSIDs of the old and new points do not even have to match. Moreover, the client can fall into a completely different IP subnet.
To minimize the time spent on reconnecting a subscriber to media services, it is necessary to make changes both to the backbone wired infrastructure (make sure that the client's external and internal IP addresses do not change) and to the handover procedure described below.
Handover between access points:
- Determine the list of potential candidates (access points) for switching.
- Set the CAC-status (Call Admission Control - call availability control, that is, in fact, the degree of congestion of the device) of the new access point.
- Determine the moment to switch.
- Switch to new access point:
In IEEE 802.11 wireless networks, all handover decisions are made by the client side.
Source: frankandernest.com
Band steering
Band steering technology allows a wireless network infrastructure to transfer a client from one frequency band to another, usually a forced client switch from 2.4 GHz to 5 GHz. Although band steering is not directly related to roaming, we decided to mention it here anyway, as it is related to client device switching and is supported by all of our dual-band APs.
When can it be necessary to switch a client to a different frequency range? For example, such a need may be associated with the transfer of a client from an overloaded 2.4 GHz band to a more free and high-speed 5 GHz band. But there are other reasons as well.
It should be noted that at the moment there is no standard that strictly regulates the operation of the described technology, so each manufacturer implements it in its own way. However, the general idea remains roughly the same: access points do not advertise the SSID in the 2.4 GHz band to a client performing an active scan, if activity of this client at a 5 GHz frequency has been noticed for some time. That is, access points, in fact, can simply keep silent about the presence of support for the 2.4 GHz band, if it was possible to establish the availability of client support for the 5 GHz frequency.
There are several modes of band steering operation:
- Force connection. In this mode, the client, in principle, is not informed about the availability of support for the 2.4 GHz band, of course, if the client has support for the 5 GHz frequency.
- Preferred connection. The client is forced to connect in the 5 GHz band only if the RSSI (Received Signal Strength Indicator) is above a certain threshold, otherwise the client is allowed to connect to the 2.4 GHz band.
- Load balancing. Some clients that support both frequency bands connect to the 2.4 GHz network, and some to the 5 GHz network. This mode will not overload the 5 GHz band if all wireless clients support both frequency bands.
Of course, customers with support for only one frequency band will be able to connect to it without any problems.
In the diagram below, we tried to graphically depict the essence of the band steering technology.
Technologies and standards
Let's now return to the very process of switching between access points. In a typical situation, the client will maintain the existing association with the access point as long as possible. Exactly as long as the signal level allows it to be done. As soon as a situation arises that the client can no longer maintain the old association, the switch procedure described earlier will start. However, handover does not happen instantly, it usually takes more than 100 ms to complete, which is already a noticeable amount. There are several radio resource management standards of the IEEE 802.11 working group aimed at improving wireless reconnection times: k, r, and v. In our Auranet line, 802.11k support is implemented on the CAP1200 access point, and in the Omada line on the EAP225 and EAP225-Outdoor access points, the 802.11k and 802.11v protocols are implemented.
802.11k
This standard allows a wireless network to tell client devices a list of neighboring access points and channel numbers on which they operate. The generated list of neighboring points makes it possible to speed up the search for candidates for switching. If the signal of the current access point weakens (for example, the client is removed), the device will look for neighboring access points from this list.
802.11r
Version r of the standard defines the FT - Fast Transition (Fast Basic Service Set Transition) function to speed up the client authentication procedure. FT can be used when switching a wireless client from one access point to another within the same network. Both authentication methods can be supported: PSK (Preshared Key) and IEEE 802.1X. Acceleration is carried out by storing encryption keys on all access points, that is, the client does not need to go through the full authentication procedure when roaming with the involvement of a remote server.
802.11v
This standard (Wireless Network Management) allows wireless clients to exchange service data to improve the overall performance of the wireless network. One of the most used options is BTM (BSS Transition Management).
Typically, a wireless client measures its connection to an access point to make a roaming decision. This means that the client has no information about what is happening with the access point itself: the number of connected clients, device boot, scheduled reboots, etc. Using BTM, the access point can send a request to the client to switch to another point with better working conditions , even with a slightly worse signal. Thus, the 802.11v standard is not directly aimed at speeding up the switching process of a client wireless device, but when combined with 802.11k and 802.11r, it provides faster program performance and improves the convenience of working with Wi-Fi wireless networks.
IEEE 802.11k in detail
The standard extends the capabilities of Radio Resource Management (RRM) and allows 11k-enabled wireless clients to query the network for a list of potential candidate hotspots. The access point informs clients of 802.11k support through a special flag in the Beacon. The request is sent in the form of a management frame called an action frame. The access point also responds with an action frame containing a list of neighboring points and their wireless channel numbers. The list itself is not stored on the controller, but is generated automatically upon request. It is also worth noting that this list depends on the location of the client and does not contain all possible wireless access points, but only neighboring ones. That is, two wireless clients geographically located in different locations will receive different lists of neighboring devices.
With such a list, the client device does not need to scan (active or passive) all wireless channels in the 2.4 and 5 GHz bands, which reduces the use of wireless channels, that is, free up additional bandwidth. Thus, 802.11k allows you to reduce the time spent by the client for switching, as well as improve the process of choosing an access point for connection. Plus, eliminating the need for additional scans helps extend the battery life of the wireless client. It is worth noting that access points operating in two bands can inform the client about points from an adjacent frequency band.
We decided to visually demonstrate the operation of IEEE 802.11k in our wireless equipment, for which we used an AC50 controller and CAP1200 access points. As a source of traffic, we used one of the popular instant messengers with support for voice calls, running on an Apple iPhone 8+ smartphone, knowingly supporting 802.11k. The voice traffic profile is shown below.
As you can see from the diagram, the used codec generates one voice packet every 10 ms. The noticeable spikes and dips in the graph are due to the slight variation in latency (jitter) always present in Wi-Fi based wireless networks. We configured traffic mirroring to which both access points participating in the experiment are connected to. Frames from one access point fell into one network card of the traffic collection system, frames from the second - into the second. In the received dumps, only voice traffic was sampled. Switching delay can be considered the time interval from the moment of traffic loss through one network interface until it appears on the second interface. Of course, the measurement accuracy cannot exceed 10 ms, which is due to the structure of the traffic itself.
So, without enabling support for the 802.11k standard, switching the wireless client took an average of 120 ms, while activating 802.11k allowed this delay to be reduced to 100 ms. Of course, we understand that although the switching latency was reduced by 20%, it still remains high. A further reduction in latency will be possible when the 11k, 11r and 11v standards are used together, as is already implemented in the home series of wireless equipment.
However, 802.11k has another up its sleeve: timing to switch. This possibility is not so obvious, so we would like to mention it separately, demonstrating its work in real conditions. Typically, the wireless client waits until the last, maintaining the existing association with the access point. And only when the characteristics of the wireless channel become completely bad, the procedure for switching to a new access point is started. With the help of 802.11k, you can help the client with the switch, that is, offer to make it earlier, without waiting for significant signal degradation (of course, we are talking about a mobile client). Our next experiment is devoted to the moment of switching.
Qualitative experiment
Let's move from the sterile laboratory to the real customer's site. The room installed two 10 dBm (10 mW) APs, a wireless controller and the necessary supporting wired infrastructure. The layout of the premises and the locations of the access points are presented below.
The wireless client moved around the room making a video call. First, we turned off support for the 802.11k standard in the controller and set the places where the switch took place. As you can see from the picture below, this happened at a considerable distance from the "old" access point, near the "new" one; in these places the signal became very weak, and the speed was barely enough to transmit video content. There were noticeable lags in voice and video when switching.
Then we turned on 802.11k support and repeated the experiment. The switchover now took place earlier, in places where the signal from the "old" access point was still strong enough. There were no lags in the voice or video. The switching point has now moved approximately halfway between the access points.
In this experiment, we did not set ourselves the goal of elucidating any numerical characteristics of switching, but only qualitatively demonstrating the essence of the observed differences.
Conclusion
All described standards and technologies are designed to improve the client's experience of using wireless networks, make it more comfortable to work, reduce the influence of annoying factors, and increase the overall performance of the wireless infrastructure. We hope that we were able to demonstrate clearly the benefits that users will receive after implementing these options in wireless networks.
Is it possible to live in an office without roaming in 2018? In our opinion, this is quite possible. But, having tried once to move between offices and floors without losing the connection, without having to re-establish a voice or video call, without being forced to repeat what was said or ask again, it will no longer be realistic to refuse.
P.S. but this is how you can make seamlessness not in the office, but at home, which will be discussed in more detail in another article.
In the modern business environment of almost any enterprise, it is difficult to overestimate the role of information technology, and more recently, especially WiFi networks. Wireless communication becomes an excellent assistant when you need to connect a smartphone or tablet, a manager's corporate phone, a data collection terminal for a warehouse employee, or, for example, a device for accepting payments in a restaurant hall, to the Internet. If the territory of your office or enterprise is small, and the load by the number of connected devices does not exceed one dozen - everything is extremely simple, you need to install and configure a WiFi router.
But what if you need to wirelessly cover an entire building of a multi-storey hotel, a factory workshop, several halls of a large restaurant, a large office or, for example, a recreation area with an area of \u200b\u200bseveral hectares?
What are the ways to solve this problem?
The company website offers the most advanced solution for large corporate and private WiFi networks - Seamless WiFi
With the help of our equipment, you can build a modern seamless wireless network at home, in the enterprise, indoors or outdoors.
How it works?
In fact, you have a single WiFi network under the control of one controller and dependent access points. This is called seamless WiFi. The point is that there can be from several access points to several hundred, while one centralized controller device or specialized software is engaged in traffic management and broadcasting.What is a controller for:
- constant monitoring of the status of access points, the load on them;
- controls signal strength and bandwidth depending on the number of clients and the nature of their work;
- independently restores areas unattended due to equipment failures by increasing the coverage area from nearby access points;
- provides web authentication and dynamic accounts for the implementation of the so-called. "guest access" (some controllers have options like printers to generate and print temporary user credentials);
- provides a continuous WiFi signal with which you can freely move, for example, with a WiFi phone, between the coverage areas of different access points, without interrupting the conversation or observing any interruptions in the connection. At the same time, the controller in a timely manner "sets" on your device a signal from the closest access point.
- give access to the Internet to the end client (for example, a mobile phone or tablet)
- under the control of the controller, the peak load is removed from one point to another
Convenient and beautiful graphical interface
If you have a plan of the premises / area where the wireless network will be deployed, then it can be used in a useful way to maintain the network. In the settings menu of the wireless controller, you can create or download a room map.
Radio frequency map. Monitor and analyze the surrounding radio environment.
The dashboard provides a visual representation of the status of your network and displays basic information about each of its segments. 
Great functionality of settings. You can select WiFi channels, frequency spectrum and transmitter power, etc. 
You can buy two types of sets of equipment from us for creating seamless WiFi networks
Networks in the range of WiFi 2.4 + 5 GHz with support for up to 50 users per access point
These kits are presented on the equipment of the Ubiquity company and are fully compatible with routers and switches of the Mikrotik brand. It acts as a controller, which, firstly, is convenient in terms of management, and secondly, it removes the load from the main router and is fully responsible for the wireless network at the facility. The number of access points is programmatically limited to 20. Wireless points of the Ubiquity Unifi AP series are presented in two versions - for indoor, indoor and outdoor. The recommended number of users is up to 50 clients per 1 access point. Depending on the scale of the task, we offer the following options for sale:
| Number of users (max) | WiFi coverage m2 | User work mode | Placement of WiFi equipment | Kit Contents |
| 100 | up to 200 | Internet surfing social networks IP telephony |
Indoors | Controller - 1 pc. Access point / - 2 pcs. |
| 100 | up to 200 | Internet surfing social networks IP telephony watching video online |
Outside | Controller - 1 pc. Access point - 2 pcs. |
| 200+ | up to 400 | Internet surfing social networks IP telephony watching video online |
Indoors | Controller - Supports WiFi 802.11ac protocol with a maximum speed of up to 1200 Mbs - Modern and intuitive graphical controller interface for managing access points - Kits with Ubiquity Unifi AP Mesh equipment support Wireless Uplink technology, which makes it possible, if necessary, not to connect access points directly to the controller via wires
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Nowadays, various wireless devices are gaining popularity, for which high-speed access to the network is possible only via WiFi. These are Ipad / Iphone, and other mobile gadgets. When you want to organize WiFi access on an area of \u200b\u200b30 sq. m., then installing a regular Dlink for 1200 rubles will solve all your problems, but if you have an area\u003e 500 sq. m. and this is only one floor, this solution will not work. If you use ordinary access points or routers, then each router will have its own network name (unique SSID), or the routers will need to be spread far away so that the coverage areas do not overlap, and this will lead to the appearance of areas with very poor reception quality, or, generally, absent signal. About six months ago, I faced the same problem, the solution was found quickly enough - UniFi.
Example of Installing WiFi UniFi in a car wash with multiple buildings.
UniFi Provides Wireless Coverage to Arcadia California School District.
UniFi Provides Wireless Access to Upscale Hotels in Peru.
UniFi WiFi hotspots capabilities:
One network for all WiFi points.
Attractive design.
Easy to install, PoE.
Shows the coverage area and the location of the access points on the administrator display.
Centralized wireless network management.
Guest networks, no LAN access.
Creation of temporary passwords for guest users.
Automatic software updates on access points.
High scalability: up to 100 or more points.
Multiple wireless networks with differentiated access rights.
Separation of traffic of network users by VLAN.
Fast on-net roaming when switching between access points.
Tracking user traffic, identifying sources of increased network load.
Large coverage area.
The ability to generate one-time temporary passwords (relevant for public places: hotels, cafes, etc.)
Connecting points in repeater mode.
An overview of the features of the UniFi Controller is here.
Implementation of WiFi from Ubiquity in Peru hotels here (translation).
Hardware controller for Ubiquiti UniFi. UniFi Cloud Key.
How it looks in practice:
A software controller is installed on one of the computers in the network, on which all the settings of the wireless network are made.
All settings of points and network parameters are subsequently made through this controller. Below are a couple of screenshots of the settings and appearance.
This is a building plan showing the locations of the points.
Setting up a guest network without access to corporate resources.
Monitoring of active clients.
Access point monitoring.
View from above.
The installation and configuration process is extremely simple:
1. Place the dots and connect them to the local network, UniFi supports PoE so that only an ethernet socket is needed to connect them.
2. Install the software controller on any computer in the network, configure the parameters of WiFi networks, initialize the points, after initialization, the settings from the controller will be applied to the point, and the point will be ready for operation. Even when the controller is turned off, the settings on the points are saved.
Seamless wifi roaming is an effective combination of several access points to the wireless Internet into a continuous system under the control of their broadcast by one central device-controller. Correctly installed and configured equipment allows you to use the global network in any area on an ongoing basis without partial or complete signal interruption. Depending on the goals set, UmkaPro is always ready to design, buy the necessary technical means, mount and configure seamless Wi-Fi at any facility in Moscow.
Seamless WIFI working principle
Multiple stand-alone points can be set up to cover a large area with wireless Internet access. However, in this version, you will have to constantly switch, moving around the territory. This is not practical and inconvenient at all. It was to create a single network in which the signal is not lost when switching between access points, and seamless wifi roaming was developed.
The essence of its work lies in the simultaneous operation of several access points. At the same time, their broadcasting is controlled by one controller, which:
- monitors the load on each access point;
- adjusts the signal, as well as the bandwidth, depending on the number of users;
- guarantees high-speed roaming, through which you can freely move around the territory without interrupting data transmission. The controller constantly sends a signal to a specific device from those access points that are closest.
What is seamless wifi built on
Years of work in this direction allow us to single out the following types of equipment, which is the most successful modern option for equipping private houses, offices, shopping malls and other types of facilities:
- Seamless roaming wifi Mikrotik CAPsMAN is a very reliable and relatively inexpensive piece of equipment that can cope with almost any task.
- Seamless wifi roaming Ubiquiti UniFi is the most versatile, uninterrupted solution that provides a consistent level of connectivity in any area.
- Seamless roaming wifi Zyxel is a more expensive option of equipment, which, in addition to the standard controller, is also represented by special access points with controller functions.
Regardless of the area of \u200b\u200bthe facility being equipped, our company's specialists are always ready to design and install Ubiquiti, Zyxel or Mikrotik wifi roaming with high quality. Years of work in this direction allow us to guarantee the impeccable quality and efficiency of the installed system.
