Seamless Wi-Fi roaming. Seamless WiFi network Wireless roaming

Seamless wifi roaming - effectively combining multiple access points to wireless network Internet into a continuous system under the control of their broadcasting 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

To cover large area With access to the wireless Internet, a large number of stand-alone points can be set up. 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 directs exactly to specific device signal 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 the 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.

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 initially 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"). V this case The SSIDs of the old and new sites 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 - control of the availability of calls, 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 it comes about 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 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 approximately the same: access points do not advertise the SSID in the 2.4 GHz band to the client performing an active scan if activity has been noticed for some time this client at 5 GHz. That is, access points, in fact, can simply remain silent about the availability 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 communicate to 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 at 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 the BTM, the access point can send a request to the client to switch to another point with better working conditions , even with a few worst signal... Thus, the 802.11v standard is not directly aimed at speeding up the switching process of a client wireless device, but in combination with 802.11k and 802.11r provides more fast work programs and improves the convenience of working with wireless networks Wi-Fi.

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 peer-to-peer access points. 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 contains not all possible access points of the wireless network, 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. One of the popular messengers with support for voice calls, running on a smartphone, was used as a traffic source Apple iPhone 8+, known to support 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 traffic collection systems, frames from the second to 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 with the combined use of the 11k, 11r and 11v standards, 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 clearly demonstrate 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 corporate environment, WiFi is playing an increasingly prominent role and is playing an increasingly important role. You can connect a smartphone or tablet to WiFi, but, more importantly, a corporate phone, a mobile data collection terminal or an online cashier for accepting payments and printing checks. 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 wireless need to cover thousands of square meters on multiple floors? There are certainly options.

At first, it is possible to spawn multiple WiFi networks on multiple autonomous access points. The bad option is that such an economy is difficult and inconvenient to manage, when moving around the territory of the enterprise, some mobile devices will have to be switched between these networks manually, and, most importantly, all this will have to be explained to users who do not always understand IT well, and are simply unable to absorb these wisdom. There is only one plus for such a solution: it is cheap.

Secondly, can broadcast one WiFi network using the same type of autonomous 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 of popular vendors operate 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 functional characteristics. So it's better to leave this option for real samurai.

Ideologically and technologically correct option is the use of 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 engaged in managing them and their broadcasting. Controller:

monitors the status of subordinate access points, the load on them;
adjusts 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" (for some controllers options like printers are available to generate and print temporary user credentials);
provides fast roaming, with which you can freely roam, for example, with a WiFi phone, between the coverage areas of different access points, without interrupting the conversation and without observing any interruptions in connection. At the same time, the controller in a timely manner "sets" on your device a signal from the closest access point.

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 adjacent IT systems (for example, Active Directory, geolocation services, etc.).

What to build seamless Wi-Fi on

Our solution catalog has already carefully selected and described options for household, corporate and industry WiFi solutions:. And if you go "to the top", then the most successful options for seamless Wi-Fi on the market are presented by the following vendors:

2. In the middle-end segment, another American manufacturer reigns. Relatively inexpensive, Cambium is also reliable and powerful.

Similar to Ruckus Unleashed, Cambium can also operate in network management mode without a controller. Cambium calls this ecosystem autoPilot and supports up to 32 access points on the network and up to 1000 wireless clients. Functionally, it is almost not inferior to the version with a controller, moreover, it does not require any investment, in addition to purchasing the access points themselves, there is no need to buy licenses, service contracts and their updates.

Need faster, higher, stronger? Please! Free cloud the cnMaestro controller already supports up to 4000 access points and up to 25000 wireless clients. The software can be installed completely free of charge on your own server, if beliefs do not allow using cloud solutions. Cambium's functionality is also all right: here you have centralized ecosystem management, geolocation services, analytics, airtime analysis, integration with related systems ... in general, everything your heart 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, with support for 802.11ac Wave 2, MU-MIMO 4x4: 4, outdoor and indoor. In general, a complete gentleman's set is at your service!

3. In the budget segment, the competition is much higher, but we distinguish TP-LINK from other daring Chinese. This is the main and most interesting competitor to Ubiquiti (which will be discussed below), although such a comparison in 2019 for TP-LINK is not at all flattering.

First, let's take a look at the TP-LINK label itself: there are actually 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, since there are no intersection points between these two directions neither in R&D, nor in production lines. And, for the sake of objectivity, Enterprise TP-LINK is significantly higher in quality than its younger brother, which specializes in products for SOHO.

Now to WiFi. TP-LINK has Auranet CAP line- currently in some oblivion (but this is temporary). The ceiling of the solution is 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 the support of an honest seamless roaming in accordance with the standards 802.11k / v, 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 hall, and this did not cause complaints from customers.

TP-LINK's second ecosystem is called Omada, it introduces the EAP series access points. The controller - Omada Controller - is produced in hardware (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 under Windows control or Linux. EAPs look modern and, of course, can do everything a self-respecting access point needs to be able to do in 2019.

4. Our next patient is Ubiquiti UniFi series. This is when you want beautiful and cheap. Moreover, it will be "beautiful" with Ubiquiti all the time, tk. they have everything subordinate to design: from packaging to design of management 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 the IEEE standards, offering a proprietary implementation instead. Which works, well, let's say so-so. Therefore, if you need to organize flawless roaming of WiFi clients with voice or video applications, then Ubiquiti, sadly, is no longer for you. The same goes for High Density - this is not about Ubiquiti. In general, in the radio part, Ubiquiti is far from ideal, 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 shortcomings: the lack of 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 - that you will not have either technical support or certificates for equipment (which closes his way to state enterprises and to telecom operators).

Ubiquiti's advantage lies in their UniFi ecosystem, which now includes not only WiFi equipment, but also switches, routers, video surveillance, telephony, and more recently even some components of a smart home. Moreover, the management of this entire economy is available through very beautiful and convenient applications(including mobile), integrating with the Ubiquiti "cloud", i.e. You can "steer" the UniFi ecosystem from anywhere in the world, and this is without any dances 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 on this list only because the number 5 is prettier than 4. Or he has a better reputation. Objectively, the vendors listed here do not yet even reach the level of Ubiquiti (they may not be worse, but by the totality 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.

We brag about it: we have extensive experience in deploying large Wi-Fi networks, we managed to "touch" live the most diverse solutions of the majority of specialized vendors, and we know their strengths and pitfalls. We are ready to apply our experience to the design and installation of wireless networks in your enterprise. - save your time and money!

Modern principles of building infocommunication networks are focused not only on providing high-speed access, but also on the convenience of users. Roaming in Wi-Fi networks is the very component that is more related to the convenience of subscribers. In radio networks, roaming is the process of switching a subscriber of a wireless network from one base station(access point, from the service area of which the subscriber leaves) to another (into the service area of which this subscriber enters).

A fairly common situation in the offices of large companies with a Wi-Fi network is the absence of roaming or its incorrect configuration. This leads to the fact that, despite the presence of uniform radio coverage throughout the building, when the subscriber moves through it, SSH sessions are interrupted, file downloads stop, not to mention the interruptions of communication sessions when using WatsApp, Skype and other similar applications.

The easiest, cheapest and most common way to organize roaming is to configure a radio network from access points with the same SSID. When the power of the radio signal from the subscriber weakens (SNR decreases - signal-to-noise ratio), this leads to a decrease in the connection speed, and if the SNR falls below a critical level, then the connection is completely disconnected. In the event that a wireless subscriber device "sees" equipment with the same SSID on the network, it connects to it.

Many manufacturers of wireless equipment use proprietary protocols for roaming, but even in this case, handover delays can reach several seconds, for example, when using the WPA2-Enterprise protocol, when access points need to be connected to a RADIUS server:

The stumbling block in the organization of Wi-Fi roaming is that the decision to switch from one access point to another is made by the subscriber (more precisely, the client equipment). Most protocols for switching a subscriber from one Wi-Fi device to another use forced disconnection of the user from the access point when the signal quality deteriorates. In the settings of most access points that support roaming, you can set the minimum signal level at which the subscriber will be disconnected from the network. This is not the best way to implement roaming, because the TCP session is also broken, and the client device may unsuccessfully try to continue trying to establish a connection with the device that has impudently kicked it out of the network.

802.11r and 802.11k- "Mobile"Wi-Fi

To solve the problems described above, in 2008 the 802.11r specification was published (and later an amendment to it - 802.11k), which is an addition to the 802.11 standard and serves to provide seamless radio coverage and switch subscribers from one access point to another. So if you are going to solve a similar problem of organizing seamless Wi-Fi roaming, then you need to choose equipment that supports these standard specifications.

802.11r uses Fast Basic Service Set Transition technology, thanks to which encryption keys from all access points are stored in one place, which allows the subscriber to reduce the authentication procedure to four short messages. Amendment 11k reduces the time it takes to find access points with better signal strengths. This is realized due to the fact that packets with information about neighboring access points and their state begin to "fly" over the wireless network.

The general principle of operation of the 802.11r standard is that the subscriber terminal has a list of available access points. The available points belong to the same MDIE mobile domain, MDIE membership information is broadcast along with the SSID. If the subscriber sees an available access point from MDIE with the best SNR level, then the subscriber through the still active wireless connection pre-authorizes with another access point from MDIE.

To speed up the connection, authentication takes place according to a simplified scheme, instead of authorization on the RADIUS server, the subscriber terminal exchanges a PMK key with the Wi-Fi controller. The PKM key is transmitted only during the first authentication and is stored in the Wi-Fi controller's memory.

Only after the other access point has authorized the subscriber is the handover performed. Further, the switching speed will no longer depend on how fast packets fly through the network, but only on how quickly the subscriber device can reorganize the frequency to new channel... With this algorithm, the switching of the subscriber occurs imperceptibly for the user.

Despite the fact that the overwhelming majority of modern Wi-Fi devices support 802.11r, you should always leave a fallback, so it would not be superfluous to configure "aggressive roaming", which works on the principle of disconnecting the subscriber when SNR drops below a predetermined threshold.

Ready-made solutions for seamless roaming

Roaming in a wireless network can be organized using conventional access points that support the above specifications. And this option is more suitable for those cases when the network consists of a small number of access points. But if your network has a dozen wireless points, then for such a network it is more expedient to consider specialized solutions from Cisco, Motorola, Juniper Aruba, etc.

Some solutions require setting up a separate controller that manages the entire network, but there are some that don't need a controller. For example, Aruba Networks has Instant points that do not work without a physical controller, but there is a virtual one that rises at one of the points. At the same time, most of the services for which such networks are created work: seamless roaming, scanning the radio spectrum and space, recognizing devices in the network. In the future, with the growth of the network, these points can be switched to the mode of operation with a physical controller, abandoning the virtual one.

Motorolla is famous for its Wing 5 smart solution, which is "endowed" with wireless equipment. Thanks to this solution, all equipment (both local and remote) is united into a single distributed network, which reduces the number of switches in the network, and access points can work more synchronously and efficiently.

With the Wing 5 solution, Motorolla equipment can intelligently control bandwidth and load balancing between APs, thereby distributing network traffic evenly across all APs. In addition, the equipment can dynamically reconfigure itself in case of interference detection (for example, if there is a microwave oven nearby). The equipment also has an adaptive coverage function that allows you to increase the signal power for devices in a network with a low signal-to-noise ratio (SNR). And, of course, an important function is the self-healing of neighboring access points in the event of a freeze.

Cisco also has a similar solution, and it is called the Cisco Mobility Express Solution. Cisco Policy on Approaching software somewhat reminiscent of Apple - ease of deployment and configuration (setup takes less than 10 minutes). Therefore, it is suitable for companies with little or no IT staff. Mobility Express Solution is deployed on the basis of Cisco Aironet access points, which also have a virtual controller and there is no need to purchase a separate device for this. Aironet can be connected and configured even from an ordinary smartphone, you just need to connect to an access point using a known SSID with a standard factory password:

When connecting to an access point using a known IP address, the user will be prompted to complete the configuration using the Cisco WLAN Express Setup Wizard. Regardless of how many access points there are in the network, its configuration can be done through any Cisco Aironet equipment operating in the network. By the way, when setting up a network from a smartphone, you can download a separate Cisco Wireless application, available both on Google Play and App Sore.

Conclusion

Configuring roaming in the network without using specialized solutions from leading manufacturers network equipment it is possible, but always beneficial, to use more than just the "bare standard". Therefore, the implementation of seamless roaming using enterprise-class virtual or physical WLAN controller solutions from manufacturers such as Cisco, Motorola, Juniper and Aruba allows you to easily manage other access points without the need for additional equipment. This means that with their help, any company, both small and medium-sized businesses, can offer their wireless clients the same high level service, like large enterprises, without any additional costs and complex software.