We deal with roaming technologies (Handover, Band steering, IEEE 802.11k, r, v) and conduct a couple of visual experiments demonstrating their work in practice.
Introduction
Wireless networks of the IEEE 802.11 standards group are developing extremely rapidly today, new technologies, new approaches and implementations are emerging. However, as the number of standards grows, it becomes more and more difficult to understand them. Today we will try to describe some of the most common technologies that are referred to as roaming (the procedure for reconnecting to a wireless network), as well as see how seamless roaming works in practice.
Handover or "client migration"
Once connected to a wireless network, the client device (whether a smartphone with Wi-Fi, a tablet, a laptop or a 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 is moved, the signal from the access point with which the connection was originally established may weaken, which sooner or later will lead to a complete inability to transfer data. 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, yield”). 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 the subscriber to media services, it is necessary to make changes both to the core wired infrastructure (make sure that the client does not change the external and internal IP addresses) and to the handover procedure described below.
Handover between access points:
- Define a list of potential candidates (access points) for switching.
- Set the CAC (Call Admission Control) status of the new access point.
- Determine the moment to switch.
- Switch to a new hotspot:
In IEEE 802.11 wireless networks, all switching decisions are made by the client side.
Source: frankandernest.com
Band steering
Band steering technology allows the wireless network infrastructure to change the client from one frequency band to another, usually it is a forced switching of the client from the 2.4 GHz band to the 5 GHz band. 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 access points.
In which case it may be necessary to switch the client to another 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. 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 announce the SSID in the 2.4 GHz band to a client performing an active scan if activity on the 5 GHz frequency has been observed for this client for some time. That is, access points, in fact, can simply remain silent about the presence of support for the 2.4 GHz band, if it was possible to establish the presence of support for the 5 GHz frequency by the client.
There are several modes of band steering operation:
- Force connection. In this mode, in principle, the client is not informed about the presence 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 5GHz band only if the RSSI (Received Signal Strength Indicator) is above a certain threshold, otherwise the client is allowed to connect to the 2.4GHz band.
- Load balancing. Some of the clients that support both frequency bands connect to the 2.4 GHz network, and some to the 5 GHz network. This mode will not allow you to overload the 5 GHz band if all wireless clients support both frequency bands.
Of course, customers with support for only one frequency range will be able to connect to it without problems.
In the diagram below, we tried to graphically depict the essence of the band steering technology.
Technologies and standards
Let's return now to the process of switching between access points. In a standard situation, the client will maintain the existing association with the access point for as long as possible (as far as possible). Exactly as long as the signal level allows it. As soon as the situation arises that the client can no longer maintain the old association, the switching procedure described earlier will start. However, handover does not happen instantly, it usually takes more than 100 ms to complete it, and this is already a noticeable amount. There are several radio resource management standards of the IEEE 802.11 Working Group aimed at improving wireless network reconnect time: k, r, and v. In our Auranet line, 802.11k support is implemented on the CAP1200 access point, and in the Omada line, 802.11k and 802.11v protocols are implemented on the EAP225 and EAP225-Outdoor access points.
802.11k
This standard allows a wireless network to report to client devices a list of neighboring access points and channel numbers on which they operate. The generated list of neighboring points allows you to speed up the search for candidates for switching. If the signal of the current access point weakens (for example, the client moves away), the device will search 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, which allows you 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 saving encryption keys on all access points, that is, the client does not need to go through a full authentication procedure when roaming using a remote server.
802.11v
This standard (Wireless Network Management) allows wireless clients to exchange service data to improve the overall performance of a 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 loading, scheduled reboots, etc. Using BTM, the access point can send a request to the client to switch to another point with better working conditions , albeit with a slightly worse signal. Thus, the 802.11v standard is not directly aimed at speeding up the process of switching a client wireless device, however, in combination with 802.11k and 802.11r, it provides faster programs and improves the convenience of working with wireless Wi-Fi networks.
IEEE 802.11k in detail
The standard extends the capabilities of RRM (Radio Resource Management) and allows 11k-enabled wireless clients to query the network for a list of nearby access points that are potentially candidates for switching. The access point informs clients about 802.11k support using a special flag in the Beacon. The request is sent as 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 access points of the wireless network, but only neighboring ones. That is, two wireless clients geographically located in different places will receive different lists of neighboring devices.
With such a list, the client device does not need to perform a scan (active or passive) of all wireless channels in the 2.4 and 5 GHz bands, which reduces the use of wireless channels, i.e. frees up additional bandwidth. Thus, 802.11k allows you to reduce the time spent by the client on switching, as well as improve the process of choosing an access point for connection. In addition, eliminating the need for additional scans extends the battery life of the wireless client. It is worth noting that access points operating in two bands can report information to the client about points from an adjacent frequency range.
We decided to demonstrate the work of IEEE 802.11k in our wireless equipment, for which we used the AC50 controller and CAP1200 access points. One of the popular instant messengers with support for voice calls, running on an Apple iPhone 8+ smartphone, which obviously supports 802.11k, was used as a traffic source. The voice traffic profile is presented below.
As can be seen from the diagram, the codec used generates one voice packet every 10 ms. The noticeable spikes and dips in the graph are due to the slight latency variation (jitter) that is always present in Wi-Fi based wireless networks. We set up traffic mirroring on , to which both access points participating in the experiment are connected. Frames from one access point fell into one network card of the traffic collection system, frames from the second - into the second. In the resulting dumps, only voice traffic was selected. The switching delay can be considered as the time interval that has elapsed from the moment when traffic disappears through one network interface, and 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 802.11k support enabled, the wireless client switched over on average within 120 ms, while 802.11k activation reduced this delay to 100 ms. Of course, we understand that although the switching delay has been reduced by 20%, it is still high. Further reduction in latency will be possible when using the 11k, 11r and 11v standards together, as already implemented in the home series of wireless equipment.
However, 802.11k has one more trick up its sleeve: the timing of the switch. This feature is not so obvious, so we would like to mention it separately, demonstrating its operation in real conditions. Typically, the wireless client waits until the last minute, keeping the existing association with the access point. And only when the characteristics of the wireless channel become very bad, the procedure for switching to a new access point starts. Using 802.11k, you can help the client with the switch, that is, offer to do 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 object of the customer. Two access points with 10 dBm (10 mW) radiation power, a wireless controller, and the necessary supporting wired infrastructure were installed indoors. The scheme of premises and installation locations of access points are presented below.
The wireless client moved around the room making a video call. First, we disabled 802.11k support 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.
We then enabled 802.11k support and repeated the experiment. Now the switching happened earlier, in places where the signal from the "old" access point was still quite strong. There were no lags in the voice and video. The switching point has now moved to about the middle between access points.
In this experiment, we did not set ourselves the goal of elucidating any numerical characteristics of switching, but only qualitatively demonstrate the essence of the observed differences.
Conclusion
All of the described standards and technologies are designed to improve the customer's experience of using wireless networks, make it more comfortable, reduce the impact of annoying factors, and increase the overall performance of the wireless infrastructure. We hope that we were able to clearly demonstrate the benefits that users will receive after implementing these options in wireless networks.
Is it possible to live in the 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 repeatedly repeat what was said or ask again, it will no longer be realistic to refuse.
P.S. and this is how you can make seamlessness not in the office, but at home, which we will discuss in more detail in another article.
In a corporate environment, WiFi is playing an increasingly prominent function and is playing an ever-increasing role. You can connect a smartphone or tablet to WiFi, but, more importantly, a corporate phone, a mobile data collection terminal or an online cash register for receiving payments and printing receipts. It’s good if the WiFi coverage area your business needs is small and you can get by with an ordinary inexpensive access point, but what if the wireless connection needs to cover thousands of square meters on several floors? There are definitely options.
First of all, you can "spawn" many WiFi networks on a variety of standalone access points. The option is bad because such an economy is difficult and inconvenient to manage, some mobile devices will have to switch between these networks manually as they move around the enterprise, and most importantly, all this will have to be explained to users who are not always well versed in IT, and are simply unable to absorb these wisdoms. There is only one advantage to this solution: it is cheap.
Secondly, can broadcast one WiFi network using the same type of standalone access points with support for WDS technology. The main disadvantage of such a solution is that the overwhelming, absolute and unconditional majority of more or less affordable (up to 300 USD) access points from popular vendors work ugly in WDS mode. Broadcasting can be lost and restored, connectivity between primary and dependent access points will be disrupted, and mobile devices will lose connection and, with it, their functionality. So it's better to leave this option for real samurai.
Ideologically and technologically, the correct option is to use a controller and dependent access points. This option is called "seamless WiFi". Its essence is that there can be many access points, and one centralized controller device is responsible for managing them and their broadcasting. Controller:
- monitors the status of slave access points, the load on them;
- regulates the signal strength and bandwidth depending on the number of clients and the nature of their work;
- independently restores areas unserved 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 fast roaming, with which you can freely move, for example, with a WiFi phone between the coverage areas of different access points, without interrupting the conversation and without observing any interruptions in communication. At the same time, the controller "sets" a signal from the closest access point to your device in a timely manner.
Modern controllers allow you to connect access points via WiFi in repeater mode (the so-called Mesh technology) without a cable connection to the network, and also provide integration with related IT systems (for example, Active Directory, geolocation services, etc.).
How to build seamless Wi-Fi
In our catalog of solutions, options for household, corporate and industry-specific WiFi solutions have already been carefully selected and described: . And if you go "on top", then the most successful options for seamless Wi-Fi on the market are represented by the following vendors:
2. Another American manufacturer reigns in the middle-end segment - . Relatively inexpensive, Cambium is also known for its reliability and high performance.
Similar to Ruckus Unleashed, Cambium can also operate in controllerless network management mode. Cambium calls this ecosystem autoPilot and supports up to 32 network access points and up to 1000 wireless clients. Functionally, it is almost as good as the version with a controller, moreover, it does not require any investment, in addition to buying the access points themselves, you do not need to buy licenses, service contracts and their updates.
Need faster, higher, stronger? You are welcome! Free cloud cnMaestro controller already supports up to 4000 access points and up to 25000 wireless clients. The software can be completely free to install on your own server if your beliefs do not allow you to use cloud solutions. With the functionality of Cambium, everything is also in order: here you have centralized management of the ecosystem, and services of geolocation, analytics, radio analysis, integration with related systems ... in general, everything your soul desires.
The disadvantage of Cambium can be considered a relatively poor line of access points: . Although everything you need is present in it: there are access points with sector antennas, supporting 802.11ac Wave 2, MU-MIMO 4x4:4, outdoor and indoor. In general, a complete gentleman's set at your service!
3. In the budget segment, the competition is much higher, but we single out TP-LINK among other daring Chinese. This is the main and most interesting competitor of Ubiquiti (which will be discussed below), although such a comparison in 2019 for TP-LINK is no longer flattering.
First, let's deal with the TP-LINK label itself: actually there are two of them. There is TP-LINK, which makes cheap home routers and plastic switches, and there is TP-LINK, which makes Enterprise line products - WiFi systems, Smart series switches, accessories for them. These are, in fact, 2 different companies, because. there are no intersection points between these two directions neither in the field of scientific developments, nor in production lines. And, for the sake of objectivity, Enterprise TP-LINK is much higher quality than its younger brother, specializing in products for SOHO.
Now to WiFi. TP-LINK has Auranet CAP line- currently in some oblivion (but this is temporary). Solution ceiling - 500 access points, 10,000 wireless clients. Controllers - only hardware, for 50 or 500 access points. Access points - in a rather old, "clumsy" design, but with support for honest seamless roaming in accordance with 802.11k / v standards, Beamforming, Band Steering, Airtime Fairness - in general, the set is completely complete. High Density on TP-LINK, of course, cannot be provided, but we have already served events for 200-300 users in one room, and this did not cause any complaints from customers.
TP-LINK's second ecosystem is called Omada, it introduces the EAP series access points. The controller - Omada Controller - is available in hardware version (with a limit of 50 access points in the 1st network), but there is also a software version that can be installed on a server running Windows or Linux. EAPs look modern and, of course, do everything that a self-respecting access point needs to be able to do in 2019.
4. Our next patient is Ubiquiti of the UniFi series. This is when you want beautiful and cheap. And "beautiful" with Ubiquiti will be constantly, tk. they have everything subject to design: from packaging to design of control interfaces. And the design is truly one of the best in the industry. In general, Ubiquiti products are characterized by an extremely low price with a fairly high quality of the product as a whole.
The main disadvantage of Ubiquiti is that it still does not support truly seamless WiFi roaming in accordance with IEEE standards, offering its proprietary implementation instead. Which works, well, let's say, so-so. So if you need to get your WiFi clients to roam seamlessly with voice or video applications, then Ubiquiti, sadly, is no longer the right choice for you. The same goes for High Density - it's not about Ubiquiti. In general, Ubiquiti is far from ideal in the radio part, but thanks to a powerful component base, a very wide range of equipment and the right marketing policy, they are still one of the most popular manufacturers of WiFi solutions. In Russia, Ubiquiti reveals 2 more significant drawbacks: the lack of an official service and representation. The first means that the guarantee on the territory of the Russian Federation works a little better than nothing, and the second means that you will not have technical support or certificates for equipment (which closes its way to state-owned enterprises and telecom operators).
The advantage of Ubiquiti is in their UniFi ecosystem, which now includes not only WiFi equipment, but also switches, routers, video surveillance, telephony, and more recently even some smart home components. Moreover, the management of all this economy is available through very beautiful and convenient applications (including mobile ones) that integrate with the Ubiquiti "cloud", i.е. You can "steer" the UniFi ecosystem from anywhere in the world, and this is without any dancing with port forwarding, static IP addresses and other leapfrog. All in all, it's really convenient.
5. Mikrotik, Edimax, Wisnetworks, TG-NET, etc. We add the 5th item in this list only because the number 5 is more beautiful than 4. Well, or it has a better reputation. Objectively, the vendors listed here still do not even reach the level of Ubiquiti (they may not be worse, but by the combination of factors of their perception by the market they are still not so significant), but they still occupy some niche in the market and enjoy some popularity.
Let's boldly brag: we have accumulated extensive experience in deploying large Wi-Fi networks, we managed to "feel" the most diverse solutions of most specialized vendors live, and we know their strengths and pitfalls. We are ready to apply our experience for the design and installation of wireless networks in your enterprise. - save your time and money!
A new version of the OS 2.13.C0 operating system was released on 09/20/2018. This version adds support for IEEE 802.11k / 802.11r standards in manual configuration mode.
Thanks to the new mechanism "Seamless Wi-Fi Roaming" switching from one access point to another on a mobile phone, instead of five seconds, is now only 100 ms. With seamless roaming, clients connected via Wi-Fi, when moving from the coverage area of one kinetic router to another, will not notice how quickly the switching between devices takes place. Thus, even Voice over Wi-Fi telephone conversations will be uninterrupted.
How does seamless roaming for Wi-Fi Keenetic work?
As it was before?
In a large room, for example, in a country house or a two-story apartment, two devices are installed. On the first floor, there is an Internet center, the second device on the top floor is connected to the first cable and operates in the "access point" mode. If the user wants to communicate via video communication, for example, in Skype, while moving from the first floor to the second, at some point he will leave the coverage area of the first device and, accordingly, disconnect from the WiFi network.
Even if your smartphone of the latest model, knowing the network of the second device, connects to it in just seconds, the skype call will still be interrupted. The same will happen if you download files or send them. In any case, the action will be interrupted due to reconnection to the Wi-Fi network and a short pause in the data exchange.
As it is now?
Keenetic 802.11k/r seamless roaming allows you to avoid completely reconnecting the device in two steps. When using the 802.11k communication standard, the client device does not spend time completely scanning the air and searching for access points, the device knows in advance which networks are preferable. Thanks to the 802.11r communication standard, the authentication time in the new network is greatly reduced. As a result, the process of reconnecting to the network is reduced to one hundred microseconds, which is not at all noticeable to the user.
This seamless connectivity is especially relevant to ensure a stable connection in IP telephony.
What devices support seamless Wi-Fi?
"Seamless Wi-Fi roaming" is supported by all models of Keenetic routers (dual-band and single-band), all devices for which a new version of the Keenetic OS 2.13 operating system has been released. These include all kinetics of the previous and latest generation, most of those that are on sale.
How to set up Keenetic seamless roaming?
A detailed setup guide can be found in Keenetic database . Here we will focus only on the main points:
Easy to set up Keenetic seamless roaming for the main segment "Home network" can be done using the web interface. To set up the same options for "Gbackbone network» or other arbitrary segments, you must resort to the command line;
On dual-band kinetics, both one network and both 2.4 and 5 GHz Wi-Fi networks can be enabled with the same settings (name, key, work schedule);
IDs for one segment must be the same across all devices;
The keys and SSID of the mobile domain must be the same.
You can configure the kinetics via the web interface only if it works in the "Basic" or "Access Point" modes. For the “Amplifier” mode, setting is possible only using the command line.
Which clients support seamless Wi-Fi roaming?
Smartphones and tablets must also support seamless Wi-Fi roaming according to IEEE 802.11k/r standards. You can find out exactly whether a particular model supports this standard in the technical documentation from the manufacturer. Note that most modern Apple and Samsung devices support this standard.
In the modern business environment of almost any enterprise, it is difficult to overestimate the role of information technology, and recently especially WiFi networks. Wireless communication becomes a great helper when you need to connect a smartphone or tablet to the Internet, 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. 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 to do if you need to cover the whole 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 several hectares with a wireless connection?
What are the ways to solve such a problem?
The company site 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, at the enterprise, indoors or outdoors.
How it works?
In fact, you have a single WiFi network running under the control of one controller and dependent access points. This is called "seamless WiFi". The point is that there can be from several to several hundred access points, while one centralized controller device or specialized software is responsible for managing and broadcasting traffic.What is the controller for:
- constant monitoring of the status of access points, the load on them;
- manages signal strength and bandwidth depending on the number of clients and the nature of their work;
- independently restores areas unserved 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 and without observing any interruptions in communication. At the same time, the controller "sets" a signal from the closest access point to your device in a timely manner.
- give Internet access to the end client (for example, a mobile phone or tablet)
- under the control of the controller, they remove the peak load 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 wireless controller settings menu, you can create or download a room map.
Radio frequency map. Monitor and analyze the radio environment around you.
The dashboard provides a visual representation of the status of your network and displays basic information about each network segment. 
Great functionality of settings. You can select WiFi channels, frequency spectrum and transmitter power, etc. 
Here you can purchase two types of equipment kits for creating seamless WiFi networks
Networks in the WiFi 2.4 + 5 GHz range with support for up to 50 users per 1 access point
These kits are presented on Ubiquity equipment and are fully compatible with Mikrotik brand routers and switches. 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 placement indoors, indoors and outdoors. 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 area m2 | User mode | Placement of WiFi equipment | Kit contents |
| 100 | up to 200 | Internet surfing social media IP telephony |
indoors | Controller - 1 pc. Access point / - 2 pcs. |
| 100 | up to 200 | Internet surfing social media IP telephony watching video online |
On the street | Controller - 1 pc. Access point - 2 pcs. |
| 200+ | up to 400 | Internet surfing social media IP telephony watching video online |
indoors | Controller - WiFi protocol support 802.11ac with maximum speed up to 1200 Mbs - Modern and intuitive graphical interface of the controller for managing access points - Kits with equipment Ubiquity Unifi AP Mesh support Wireless Uplink technology, which allows, if necessary, not to connect access points directly to the controller by wire
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