What is seamless roaming in wifi networks?

Seamless roaming is when access points in your network are controlled by a special controller wireless network. A controller in a seamless network can be either one of the routers or access points, or a separate device that monitors the general state of the air, the load on each of the wireless access points and the signal level between clients and APs. If the signal between the client and the access point deteriorates, the controller "forces" the client to a more suitable AP. The fact is that in a normal network, a client (phone, laptop, tablet) will “cling” to the MAC address of the AP (address of the WLAN interface) to the last, and not to its SSID (name), which leads to negative consequences when moving around the building. The controller will continuously - hundreds of times per second monitor the load on the access points and the quality of the signal between the base station and the client. In such networks, when moving from one end of the room to the other, the access point that is closer and not loaded will work. It is very useful for business and shopping centers, large stores, government agencies, hospitals and educational institutions. Load sharing technology will be needed when there are a lot of people in places like conference rooms or amusement parks.

Do you need a cost-effective solution with automatic client switching between them for a home for 150 bucks?

For 2020, affordable Mesh network kits appear that are no longer ashamed to install and be confident in the result. It is a pity that we are talking about several manufacturers, but there is still light at the end of the tunnel. In the budget niche there are:

Asus, TP-Link, Tenda, Ubiqiuty, Mikrotik, Zyxel and Xiaomi. Almost each of these manufacturers has several types of access points for the street and at home, for walls or ceilings, for a separate wifi network controller or one of the access points is the controller.

And now specifically with numbers. Let's go.

Seamless Wi-Fi systems from Asus.

The easiest wireless network option without controller but with automatic selection of the best access point, it can consist of several of the most common ASUS routers. Models suitable for these purposes: RT-N11P, RT-N66U, RT-AC55U RT-AC66U and newer "P" series routers. They must be connected to each other with a twisted-pair cable of category 5e and above, as shown in the picture below. On these models, it is only possible to set up Roaming Assist, which is the only way on this type of device. The following will happen: if the signal level is low, after a certain time, the router will disconnect it from the network and the client itself will reconnect to the point with the best signal. You need to understand this type of wireless network setup is not seamless, but rather voluntary-compulsory, with a short-term, but complete loss of the connection. If installed correctly, it will save a lot of money compared to even the simplest networks with an access point controller, but in practice this works with difficulties for the user, especially when he is in the area of ​​​​unreliable reception from both points, which in turn can start to “football” our a poor user and the Internet will not work properly for him. Please remember this. Routers RT-AC68U and older already have a proto-version of Mesh networks from such access points, but I don’t like the price relative to the result, it’s better to take Lear’s access points sharpened for this business. They will be discussed below.

Now let's look at the best option. MESH networks from Asus. This set is called Lyra and let's see what it can give us, but it can give us much more than our OGV, it's a joke, it can give us 350 - 450 megabits over the entire area and you can move anywhere without breaks.

Is your goal to make a high-quality wireless wifi network with roaming?

For our clients, we have professional wifi network solutions with the highest performance in terms of reliability, speed and security level. In such cases, the network consists of a number of access points interconnected by a twisted pair cable through switches and an access point controller. The functions of the wi-fi network controller include:

• tracking the load on each individual access point and its distribution.
• monitoring the quality and level of the signal between the access point and the client.
• centralized management of all access points in the network.
• providing instant switching of the client from one access point to another, without losing connection to the Internet.

Such a network can be scalable and gradually expand.

For a hotel, large office, cottage settlements, one access point, even the most productive and long-range one, is indispensable. The distribution of access points gives a much better result and has the ability to scale. The figure above clearly shows the coverage of seven access points and one controller configured for seamless roaming.

If your goal is to make sure that when moving from one access point to another, the Internet connection does not disappear, then we can help you with the search and purchase of equipment for a wifi network with roaming.

To organize a fast and loaded wireless network in the whole building, the functionality of conventional wifi routers is not enough due to the fact that the decision to "fall off" from the access point is taken by the end device itself and the router will not help here. It turns out that the same smartphone or tablet will cling to the access point to the last, given that the list of networks known to it will have an access point with a hundred percent signal.

There are two good ways to make such a grid and a lot of bad ones :) Consider the good ones, but I would not advise messing with the bad ones.

1) WiFi network with a certain number of access points interconnected by a switch and controlled by a special controller of wireless access points in the local network. This option is the most reliable, unpretentious and of course expensive. A network of this type, using Zyxel equipment as an example, will cost around $2000-3000 for an area of ​​10000m 2 (100x100m). For country houses, seamless roaming will be cheaper; $ 1000-1500 for a large house and a personal plot. Such networks are able to withstand heavy loads and evenly distribute users across access points, depending on the load on each of them. Such networks are easy to administer and are well suited for commercial real estate, hotels, restaurants, park areas and similar public places.

2) A well-established way is to use the Roaming asist function. This method is the most budgetary. With four ASUS RT-AC66U routers, you can get an analogue of seamless wifi roaming and a wireless network speed throughout the house and adjacent territory of 300-500 megabits per second on the 802.11ac standard. with automatic switching between access points. In both cases, wifi routers are connected to each other by a wire.

Budget and professional solutions in our store with installation and configuration.

Seamless wifi roaming is an effective combination of several access points to a wireless Internet network into a continuous system controlled by their broadcasting by one central controller device. Properly 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, purchase the necessary technical equipment, install and configure seamless Wi-Fi at any facility in Moscow.

Working principle of seamless WIFI

To cover a large area with access to the wireless Internet, you can install a large number of autonomous points. However, in this version, you will have to constantly switch, moving around the territory. This is not at all practical and inconvenient. 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 is 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 identify the following types of equipment, which is the most successful modern option for equipping private houses, offices, shopping malls and other types of facilities:

1. Seamless roaming wifi Mikrotik CAPsMAN is a very reliable and relatively inexpensive equipment option that can handle almost any task.
2. Seamless wifi roaming Ubiquiti UniFi is the most versatile, uninterrupted solution that provides a consistent level of connectivity in any area.
3. Seamless Zyxel wifi roaming is a more expensive equipment option, which, in addition to the standard controller, is also represented by special access points with controller functions.

Regardless of the area of ​​the object 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 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:

1. Define a list of potential candidates (access points) for switching.
2. Set the CAC (Call Admission Control) status of the new access point.
3. Determine the moment to switch.
4. 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 chose 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:

1. 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.
2. 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.
3. 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.

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 wireless network subscriber from one base station (access point, from whose service area the subscriber leaves) to another (in whose service area this subscriber enters).

A fairly common situation in the offices of large companies with a Wi-Fi network is the lack of roaming or its incorrect settings. This leads to the fact that, despite the presence of uniform radio coverage throughout the building, when a subscriber moves through it, SSH sessions are interrupted, file downloads stop, not to mention disconnected 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 of access points with the same SSID. When the power of the radio signal from the subscriber weakens (SNR - signal-to-noise ratio decreases), 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, then 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 organizing Wi-Fi roaming is that the decision to switch from one access point to another is made by the subscriber (more precisely, client equipment). Most protocols for switching a subscriber from one Wi-Fi device to another use a 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 option for implementing roaming, because the TCP session is still disconnected, and the client device may unsuccessfully try to continue trying to establish a connection with the device that brazenly 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 (and later also an amendment to it - 802.11k) was published, 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 the encryption keys from all access points are stored in one place, which allows the subscriber to reduce the authentication procedure to the exchange of four short messages. The 11k correction allows you to reduce the discovery time of access points with better signal levels. This is realized due to the fact that packets with information about neighboring access points and their status begin to "fly" over the wireless network.

The general principle of the 802.11r standard is that the user terminal has a list of available access points. Accessible 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 performs pre-authorization with another access point from MDIE using the still active wireless connection.

To speed up the connection, authentication occurs 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 another access point has authorized the subscriber does handover occur. Further, the switching speed will no longer depend on how fast the packets fly over the network, but only on how quickly the subscriber device can change the frequency to a new channel. With this algorithm, the subscriber switching occurs imperceptibly for the user.

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

Ready-made solutions for seamless roaming

You can organize wireless roaming using conventional access points that support the above specifications. And this option is more suitable for cases where 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 need to set up a separate controller that manages the entire network, but there are others that do not 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 on 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, and recognizing devices on the network. In the future, with the growth of the network, these points can be transferred to the mode of operation with a physical controller, abandoning the virtual one.

Motorolla is famous for its intelligent Wing 5 solution, which is "endowed" with wireless equipment. Thanks to this solution, all equipment (both local and remote) is combined 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 can intelligently control bandwidth and load balance between access points, thereby distributing network traffic evenly among all access points. In addition, the equipment can dynamically reconfigure itself if interference is detected (for example, if a microwave oven is nearby). Also, the equipment has the function of adaptive coverage, which allows you to increase the signal strength for devices in the network with a low signal-to-noise ratio (SNR). And of course, an important function is the self-healing of neighboring access points in case they freeze.

Cisco also has a similar solution called the Cisco Mobility Express Solution. The policy of Cisco in terms of software approach is somewhat reminiscent of Apple - easy to deploy and configure (setup takes less than 10 minutes). Therefore, it is suitable for companies with a small staff of IT specialists or without it at all. 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 a regular 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 on the network, it can be configured through any Cisco Aironet equipment operating on 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

Setting up roaming in the network without using specialized solutions from leading manufacturers of network equipment is possible, but it is always useful to use not only the "bare standard". Therefore, implementing seamless roaming with enterprise-class virtual or physical WLAN controller solutions from vendors such as Cisco, Motorola, Juniper, and Aruba makes it easy to manage other access points without the need for additional hardware. This means that with their help, any company, both small and medium-sized businesses, can offer its wireless customers the same high level of service as large enterprises, without any additional costs and complex software.