Cooperative Roaming 2.0 Technology White Paper

Contents

Introduction· 1

Background· 1

Benefits· 2

Technical implementation· 2

Roaming timing· 2

Roaming guidance based on static policy· 2

AI-driven roaming guidance based on network features and client profiles· 3

Roaming target 6

Roaming execution· 6

Mutual awareness network· 6

Fast service switchover 7

Intelligent roaming cache· 7

Roaming calibration· 8

Application scenarios· 9

Typical applications of cooperative roaming· 9

Introduction

Background

Roaming refers to the process where a wireless client moves from accessing one AP to another within a zone where different APs provide the same Service Set Identifier (SSID). In traditional roaming, clients control their roaming behaviors independently. The access controller (AC) lacks collaborative interaction with clients in roaming detection and decision-making processes, resulting in suboptimal roaming performance.

The main issues with current roaming include:

·     Client stickiness: Some client roaming algorithms prioritize persistence with the already connected AP. In this case, a client will not actively switchover to a better AP nearby unless the signal strength of the currently connected AP degrades to nearly unusable levels. The client cannot quickly connect to the nearest AP wherever the user goes.

·     Time-consuming roaming: Clients must detect the communication quality, scan the wireless environment, select the appropriate AP, and perform a service switchover to complete a roaming process. Since the client lacks a full network perspective, it cannot quickly scan for available services. It must scan each channel individually and select an available service, resulting in a time-consuming process with severe packet loss.

·     Frequent roaming: Clients roam autonomously based on their own roaming policies and also under the guidance of the AC. However, this might cause clients to roam repeatedly between two APs, preventing persistence on an appropriate AP.

·     Roaming delays: This issue might occur due to varying network conditions, such as AP deployment in high-density setups or complex environments like building corners. Different clients also have unique characteristics, such as protocol support, transmit power, and roaming response capabilities. A unified roaming policy cannot ensure users always quickly connect to the best AP when they move to different locations.

To optimize the roaming experience, cooperative roaming combining IEEE 802.11k, 802.11v, and 802.11r protocols has emerged. Cooperative roaming refers to the cooperation among AP, AC, and clients to facilitate roaming. APs and clients can detect each other's network status. The AC comprehensively calculates client data collected by APs. Based on client roaming big data, the system forms roaming characteristics (network features) for specific air interface environments through AI learning and creates client profiles for individual devices. The system can combine network features with device profiles to create personalized roaming guidance policies. This approach ensures applying the unique policy for each specific device in one network, which significantly improves user experience, as shown in Figure 1.

Figure 1 Cooperative roaming

Benefits

Cooperative roaming offers the following advantages:

·     Detect client movement (such as moving or stationary) to dynamically adjust roaming policies. This effectively eliminates unnecessary switchovers caused by environmental fluctuations and improves user roaming experience.

·     Build detailed client profiles at the individual device level (not vendor or brand), and dynamically learn and generate roaming network features based on these profiles, ensuring applying the unique policy for each specific device in one network

·     The AC and wireless clients mutually perceive the network topology from their respective perspectives, enabling the wireless clients to quickly discover the optimal wireless service.

·     The AC calculates the neighboring APs around the current access AP of a client and actively guides the client to roam to the best neighboring AP, reducing client stickiness.

·     This reduces the number of key negotiation packets required during roaming to shorten the delay in the roaming process.

·     Use intelligent roaming cache to reduce packet loss during roaming and effectively prevent out of service.

·     The AC analyzes data from clients that roam repeatedly and stops prompting the client to roam once the client connects to the optimal AP, reducing the occurrence of repeated roaming.

Technical implementation

Roaming timing

Roaming guidance based on static policy

The AP periodically checks the client RSSI and flexibly adjusts the roaming sensitivity, allowing the AC to guide client roaming at the most appropriate time. When one of the following conditions is met, the AC actively guides client roaming to reduce client stickiness:

·     The average RSSI weakens during two consecutive detection cycles and drops far below the cooperative roaming threshold.

·     The average RSSI weakens during two consecutive detection cycles and drops close to the cooperative roaming threshold, and the latest RSSI collected during the cycle is much lower than the threshold.

·     The average RSSI fluctuates well below the cooperative roaming threshold during the detection cycle.

Different clients have different transmit power levels. Using the same roaming threshold affects roaming timeliness. Setting different roaming policies for different clients can better meet the roaming timeliness requirements.

AI-driven roaming guidance based on network features and client profiles

Motion state identification based on client signal characteristics

Due to the characteristics of the air interface environment, the signal strength of a stationary client may fluctuate unpredictably. Conventional signal detection algorithms may misinterpret this fluctuation as movement, causing unnecessary roaming for wireless clients.

APs periodically check the RSSIs of clients and determine their movement status based on RSSI variation patterns. This ensures that clients promptly roam when moving, but avoid roaming when stationary with good signal quality, effectively reducing unnecessary roaming.

Roaming thresholds based on network features and client profiles

As shown in Figure 2, Client 1, Client 2, and Client 3 roam in the wireless network. The system uses AI reinforcement learning to analyze roaming data and generate individual client profiles. It also learns roaming characteristics (network features) of each AP.

Figure 2 Network features and client profiles generated through AI learning

As shown in Figure 3, when Client 2 roams from AP 1 to AP 2, the system provides roaming guidance based on AP 1's network features and Client 2's profile in the current network environment. By continuously collecting and analyzing Client 2's actual roaming data, the system optimizes roaming guidance policies.

When Client 4 roams from AP 3 to AP 4, the system uses AP 3's network features as the initial reference to guide the roaming process for Client 4. During subsequent use, the system continuously collects Client 4's roaming data. Based on its behavioral patterns, the system gradually adjusts and optimizes roaming guidance conditions. This ultimately creates a roaming policy that better aligns with the client's actual needs.

Figure 3 Accurate roaming guidance based on network features and client profiles

As shown in Figure 4, take the roaming threshold as an example. When APs have the same transmit power, the system can analyze statistics from actual roaming data of multiple clients to calculate a group roaming threshold. The group roaming threshold reflects the average roaming behavior of all clients and represents their overall roaming characteristics. However, since hardware capabilities, antenna performance, and usage environments vary across devices, each client forms its own unique roaming threshold during actual roaming. The individual roaming threshold for a client is the optimal threshold calculated based on the historical roaming behavior and characteristics of the client. The difference between group roaming thresholds and individual roaming thresholds defines the key characteristics of client profiles.

Figure 4 Varying client roaming thresholds in environments with different density levels

As shown in Figure 5, the roaming threshold for the same client varies by network deployment density. In high-density AP deployment environments, the client roaming threshold is usually higher than the threshold in low-density deployment environments. Variations in roaming thresholds due to differences in network deployment density also reflect key network features.

Figure 5 Illustration of roaming thresholds in different deployment scenarios

As shown in Figure 6, in certain scenarios such as edge APs or conference room APs, the transmit power of an AP may differ from the transmit power of surrounding APs. At this point, the clients' roaming threshold remains unchanged. However, because the APs have different transmit power levels, the clients must move closer to the low-power AP. Roaming thresholds vary slightly depending on the trigger location, which also reflects key network features.

Figure 6 Client roaming between APs with different transmit power levels

Roaming target

The AC actively negotiates with clients to help clients switchover to the nearest suitable AP, reducing client stickiness.

·     The AC combines the network environment information of APs and each client to perform a comprehensive calculation. This enables the AC to find more suitable client access locations and optimizes the roaming experience of each client.

·     The AC accurately predicts the roaming destination AP for clients based on their historical roaming data and real-time statistics of the entire wireless network. The advantages of prediction based on historical roaming trajectories are as follows:

¡     Client roaming does not rely on client response. Although the traditional 802.11k protocol allows clients to measure data from surrounding neighbors, different clients respond differently to measurement requests. Issues such as non-support for measurements, no response, or erroneous neighbor responses make it difficult to obtain accurate neighbor information.

¡     By predicting the roaming destination APs based on the common trajectories of wireless clients within an area in different directions, the recommended neighbors are more accurate and align with client habits.

Roaming execution

Mutual awareness network

The AP interacts with the client to perceive network topology, improving the efficiency and quality of roaming.

·     The AP periodically provides the client with channel and wireless service information of neighbor APs. The client does not need to scan each channel individually. This reduces the time it takes for the client to discover APs.

·     The AP periodically sends requests to the client to collect BSS information detected on the current working channel. The AC generates a candidate BSS list based on the reported information from the client and uses the list to guide client roaming. This makes the AC roaming decision more in line with the client network quality assessment criteria.

Fast service switchover

This feature allows key negotiation and installation during the wireless link association phase. This reduces the number of key negotiation packets exchanged during roaming, shortens the roaming delay, and allows clients to complete authentication more quickly when roaming to a new AP. This function primarily uses two working mechanisms: Over-the-DS and Over-the-Air. The Over-the-Air mechanism is more widely used. It suits scenarios that require high roaming compatibility. The workflow is as follows:

Clients communicate directly with the destination AP for pre-roaming authentication. This method is suitable for scenarios with high roaming compatibility requirements. When a client roams between APs (from AP 1 to AP 2), the information exchange process is shown in Figure 7.

1.     The client comes online from AP 1 and requests to roam to AP 2.

2.     The client sends an authentication request to AP 2.

3.     The client receives an authentication response from AP 2.

4.     The client sends a reassociation request to AP 2.

5.     The client receives a reassociation response from AP 2.

6.     The client completed roaming from AP 1 to AP 2.

Figure 7 Over-the-air roaming

Intelligent roaming cache

The intelligent roaming cache function identifies roaming behaviors of different clients. For clients with a clear target AP, it enables seamless cross-device switchover during movement. This function reduces packet loss during roaming and prevents out of service by pre-creating client forwarding entries on target APs. It caches downstream traffic in advance and delivers it to clients after they come online. The specific process is shown in Figure 8.

1.     The wireless network guides the client to roam to another AP.

2.     The client replies with a BSS Transition Management (BTM) response that carries the target neighbor information.

3.     The client roams from AP 1 to AP 2 and comes online.

4.     The AC creates a client forwarding entry on AP 2.

5.     The downlink service traffic is sent to the client through AP 2, and the cached traffic is delivered promptly.

Figure 8 Intelligent roaming cache

Roaming calibration

As shown in Figure 9, when clients frequently roam in a specific area, the AC collects roaming data and selects the best AP for them. When a client roams back to an AP, the AC stops steering the client to roam and dynamically fine-tunes the client's roaming threshold on this AP. When a superior access location is available, the AC can continue to guide client roaming.

Figure 9 Roaming calibration

Application scenarios

Typical applications of cooperative roaming

As shown in Figure 10, most clients in the network support 802.11k, 802.11v, and 802.11r protocols. You can configure cooperative roaming to enable seamless roaming for clients within an Extended Service Set (ESS) area and optimize the roaming experience. The specific configuration for the AC is as follows:

1.     Enable BSS switchover management for the wireless service template, so that the AC can notify clients to access a more suitable BSS.

2.     (Optional.) Enable intelligent roaming cache under the wireless service template.

3.     Enable radio resource measurement in radio view to inform clients about the channel quality and available resources measured by APs.

4.     Enable client profiling in system view and enable smart calculation of the roaming threshold in radio view.

5.     (Optional.) Enable fast BSS transition for the wireless service template to shorten the roaming delay.

Figure 10 Cooperative roaming