Compatibility test between WLAN equipment and mobile terminals

　　Before WiFi mobile phones became popular, there were already a large number of WLAN networks built, and most of them were built based on the characteristics of PCs and laptops. For practical reasons, it was impossible to build a WLAN network specifically for WiFi mobile phones. Therefore, how to maintain good compatibility with mobile phones of various brands and systems is a big challenge for WLAN manufacturers. This article mainly discusses how to perform compatibility testing on WLAN AC/AP equipment based on the characteristics of mobile phone terminals to ensure that the WLAN network has good support for mobile phones.

　　The test should cover mainstream mobile phone manufacturers and their operating systems.

　　The commonly used mobile phone operating systems covered include: Android, Apple OS, Symbian, Windows Mobile, Palm system, Blackberry system, etc.

　　Mobile phone manufacturers covered include: Nokia, Apple, Motorola, HTC, Samsung, Palm, Blackberry, Lenovo, SonyEricsson, etc.

　　In addition, actual tests show that the WLAN functions of Apple iPad and iPhone4 are basically the same, so iPad can be included in the test scope.

　　1 Basic access test

　　Testing purposes:

　　1. Clarify the support status of each mobile phone for basic WLAN functions;

　　2. Test the cooperation with H3C AC/AP.

　　According to IEEE 802.11-2007 and IEEE 802.11n-2009 protocols, the basic process of WiFi mobile phone accessing AC/AP is tested. This test takes iPhone 4/iPad (Apple OS system) and HTC A8180 (Andriod v2.2 system) as examples.

　　1.1 Supported radio modes (802.11a/b/g/n)

　　The IEEE 802.11 working group has defined the 802.11a/b/g/n standards, so it is necessary to test the WLAN radio modes supported by the mobile phone and the compatibility with the AC/AP. If multiple modes are supported at the same time, it is also necessary to test the switching between different modes (such as switching from 11g to 11n). This is the most basic test and the basis for subsequent tests. The test results are as follows

　　1.2 Multi-rate support

　　802.11-2007 defines the rate sets allowed in different radio modes and specifies the transmission rates of various wireless frames. For example, all control frames and broadcast frames are sent using the basic rate set, and unicast data frames and management frames are sent using any rate supported by both parties.

　　Multi-rate support requires testing the rate negotiation process between the mobile phone and AC/AP, and the rate selection of different wireless frames during communication. The test results are as follows.

　　1.3 WMM Capabilities

　　WMM is a subset of the 802.11e standard and is also a common WiFi standard in the industry. It provides a basic wireless QoS solution, supports the application of multimedia services such as voice and video in wireless LANs, and can achieve high-speed burst data and traffic classification. The WMM capability test can determine whether the mobile phone supports WMM capabilities and how well it cooperates with the AC/AP.

　　The test results are as follows:

　　1.4 Power-save

　　Power-save is a special feature of WLAN. Wireless terminals can choose to turn off the wireless radio when there is no message transmission to save battery power (sleep state), and wake up to receive or send messages when there is a message (active state).

　　This is an important test item in the AC/AP and mobile phone cooperation test. Because the power saving function has multiple implementation methods such as Legacy/U-APSD, if the cooperation is not tacit, it will cause continuous packet loss, seriously affecting the user experience.

　　The test results are as follows:

　　The test results show that the sleep behaviors of different mobile phones vary greatly, and AC/AP needs to be well compatible with them.

　　1.5 11g protection test

　　Since 802.11g and 11b use different modulation methods (OFDM and CCK), 802.11g is compatible with 802.11b, but 802.11b cannot recognize 802.11g frames, which will cause conflicts. The 802.11 protocol specifies protection mechanisms for 11b devices, including CTS-Self and RTS/CTS. This test is to determine whether the mobile phone supports the 11g protection function and the protection mechanism used, and its compatibility with AC/AP.

　　The test results are as follows:

　　1.6 802.11n Capability Test

　　This test item is for mobile phones that support 802.11n, and tests its basic 11n functions. 802.11n includes many test items, and here we need to focus on the following points:

　　Ø 11n mode: Determine whether the phone supports SISO (Single In-Single Out) or MIMO (Multiple Input-Multiple Output), that is, whether it uses a single antenna or multiple antennas, and the number of spatial streams supported. [page]

　　Ø 20MHz/40MHz channel and switching: 11a/b/g use 20MHz bandwidth for communication. 11n supports bundling two 20MHz frequency bands into one communication frequency band (called Channel bonding), which can double the throughput (actually more than 2 times). One of the two frequency bands will be primary and the other will be secondary.

　　Ø Short Guard Interval (Short GI): Since the signal propagates along multiple paths, the latest information symbol received at the receiving side may collide with the information symbol of the previous reception process that has not yet ended, resulting in ISI interference. For this reason, the 802.11a/g standard requires that when sending information symbols, an 800 ns time interval must be ensured between information symbols. This interval is called Guard Interval (GI). 11n still uses the default 800 ns GI, but when the multipath effect is not serious, the interval can be configured to 400 ns, which can increase the throughput by nearly 10%.

　　Ø Frame Aggregation (frame aggregation, divided into A-MSDU and A-MPDU): In the past, 802.11a/b/g frame processing had a relatively large overhead, such as Preamble, FCS, waiting time for ACK, etc., which affected the operating efficiency of the MAC layer. Frame aggregation technology reduces overhead and frame collision opportunities by sending multiple frames together at once, thereby improving MAC efficiency. Depending on the number and length of aggregated frames supported, throughput can be greatly improved.

　　Ø Block Ack: According to the 11n protocol, for MSDU aggregate frames, they can be acknowledged as a frame, but for MPDU aggregate frames, each frame that constitutes the aggregate frame needs to be acknowledged separately. In order to improve the efficiency of the MAC layer, the protocol defines a block acknowledgement mechanism, which can use a Block Ack frame to acknowledge the entire MPDU aggregate frame. Frame Aggregation + Block Ack can increase the throughput of traffic such as file transfer by 100%.

　　Ø 11n Protection: The 11n protocol defines four operating modes: no protection, non-member protection, 20MHz protection, and non-HT mixed. The four modes are defined so that 11n APs and terminals can reasonably select the rate according to the network conditions, provide backward compatibility, and reduce frame conflicts.

　　The test results are as follows (since HTC A8180 does not support 11n, only iPhone 4 is used as an example):

　　The test results show that although the iPhone 4 and iPad support 802.11n, since they only support SISO (spatial single stream) with a single antenna, the highest negotiated rate is only 65Mbps, which is far from the 300Mbps that can be achieved by the 2x2 MIMO commonly used in PC-type wireless network cards.

　　2 Authentication and encryption testing

　　Using authentication and encryption mechanisms in WLAN networks is conducive to improving network security and protecting user data from theft. H3C AC/AP fully supports various wireless authentication and encryption technologies. The purpose of this test: 1. Clarify the support of each mobile phone for authentication and encryption; 2. Test the cooperation with H3C AC/AP.

　　Since some WLAN networks that have been built have deployed authentication methods such as Portal, which were originally designed for PC terminals. The principle is to redirect the web pages opened by PC browsers such as IE/Firefox through HTTP to the Portal server for authentication. Therefore, whether mobile terminals can complete Portal authentication after connecting to the WLAN network is an important item in the compatibility test with such networks.

　　In addition, some WLAN networks use highly flexible settings such as hybrid encryption, and whether they can be adapted to mobile terminals also requires attention.

　　This test takes iPhone 4/iPad as an example.

　　2.1 Certification Test

　　Depending on the location of the authentication server, authentication methods can be divided into the following two types:

　　Ø Remote authentication: AC acts as a NAS device and forwards the terminal's authentication message to a remote server for centralized authentication.

　　Ø Local authentication: H3C AC supports local EAP Server and local Portal Server. Dot1x-EAP and Portal authentication can be completed directly on AC without installing other servers.

　　Common authentication types include Preshared key, Dot1x-PEAP, Dot1x-TLS, WAPI, Portal, etc.

　　The test results are as follows:

　　The test results show that: for the original WLAN network using Portal authentication, iPhone 4/iPad can use its built-in Safari browser to support it well and has good compatibility with H3C AC/AP.

　　2.2 Encryption Test

　　With the development of WLAN, the supported encryption methods have evolved from the original WEP defined by 802.11, to TKIP of the WiFi Alliance, to the current coexistence of CCMP defined by 802.11i and WAPI with China's own intellectual property rights.

　　The cooperation between AC/AP and mobile phones in encryption is related to the distribution and management of keys, as well as whether data can be correctly encrypted and decrypted.

　　The test results are as follows:

　　From the test results, we can see that: except for WEP128, iPhone 4 can well support various encryption methods, and can also adapt well to each other in the H3C WLAN network that adopts hybrid encryption.

　　2.3 Key Update

　　In WLAN networks with high security requirements, the key update function is often configured to regularly update user keys to reduce the risk of key cracking. 802.11i defines two types of key updates: Pairwise Transient Key (PTK) and Group Temporal Key (GTK). The WAPI protocol defines three types of key updates: Base Key (BK), Unicast Session Key (USK) and Multicast Session Key (MSK). [page]

　　During the key update process, the mobile terminal should remain connected to the AC/AP and should not be disconnected.

　　The test results are as follows:

　　From the test results, we can see that the GTK update message of iPhone 4 does not comply with the provisions of the 802.11i protocol, and the key length field of group message 2 is incorrectly assigned a value. H3C devices can be well compatible because they adopt the principle of lenient entry and strict exit. This also reflects the importance of mobile terminal compatibility testing.

　　3 Actual transmission rate test

　　Due to the WLAN protocol's own overhead and the characteristics of WLAN shared bandwidth, the actual data transmission rate between WLAN terminals and AC/APs and the negotiated rate can differ greatly. Taking the highest negotiated rate of 54Mbps for 802.11g as an example, the actual PC download rate is often difficult to exceed 30Mbps or even lower.

　　Since mobile phones cannot be installed with accurate performance testing tools like IxChariot like PCs, most of the time the only way to approximately evaluate the actual transmission rate is to share files between the mobile phone and PC via WLAN.

　　Taking iPad downloading files as an example, the test results are as follows (Note: Considering the actual environment, this test data is for reference only):

　　From the test results, we can see that the download rate of mobile terminals from the same WLAN network is much lower than that of PC terminals, indicating that the performance bottleneck is mainly in the processing power of the mobile phone itself. However, considering the usage scenario, this rate can already meet its usage requirements. Mobile terminals often browse the web, use instant messaging tools (such as QQ), or watch videos through WLAN. The traffic of such applications is unlikely to exceed 1Mbps.

　　4 Roaming test

　　In a WLAN network, the coverage of each AP is limited. When a mobile phone moves, it is likely to move from the coverage of one AP to the coverage of another AP. In this process, roaming technology is needed to ensure the continuity of wireless connection. Compared with PC terminals, mobile phones have stronger mobility and higher requirements for WLAN network roaming.

　　There are many forms of roaming, which can be divided into the following two types according to the roaming speed.

　　Ø Non-fast roaming: The terminal goes offline from one AP and then goes online again on another AP. If there is authentication, such as Dot1x (WPA) authentication, it must be re-authenticated after roaming. The terminal will be offline for a short time during non-fast roaming.

　　Ø Fast roaming: WLAN network and terminals support Dot1x (RSN), and the terminal carries PMKID information in the reassociation frame sent to the new AP during roaming, and then enters the fast roaming process. At this time, no re-authentication is required, and key negotiation is performed directly. The terminal will not be disconnected during the fast roaming process. The time for H3C AC/AP to achieve fast roaming switching is less than 50ms, and users will not feel it.

　　Roaming can be divided into the following two types according to the different roaming destinations.

　　Ø Intra-AC roaming: When a wireless terminal roams from one AP in an AC to another AP in the same AC, it is called intra-AC roaming, as shown in Figure 1.

　　Figure 1 Intra-AC roaming

　　Ø Inter-AC roaming: When a wireless terminal roams from an AP in one AC to an AP in another AC, it is called inter-AC roaming, as shown in Figure 2.

　　Figure 2 Inter-AC roaming

　　It should be noted that the active initiator of roaming is the terminal, which is the dominant factor in roaming. The terminal determines the conditions for roaming according to its own settings, and the AP cannot intervene. If some terminals do not accurately judge the conditions for roaming, and do not initiate roaming to access a new AP with a better signal when the signal of the original AP is already very poor, the message transmission rate will continue to decrease and the user experience will deteriorate. Similarly, if the AC/AP equipment does not cooperate well with the terminal when it initiates roaming, it will also affect the user experience. [page]

　　Taking iPhone 4 as an example, the test results are as follows:

　　5 Actual business experience test

　　The purpose of any underlying test is to obtain a better actual service experience. Mobile terminals have a variety of application services, and connecting to a WLAN network for service experience testing is essential. This test can help you understand the typical applications of mobile phones.

　　Taking iPhone 4 as an example, the test results are as follows:

　　From the test results, we can see that H3C AC/AP works well with iPhone 4 and provides a good experience in various applications. The only drawback is that iPhone 4 Apple OS system does not support flash video playback due to its own limitations.

　　6 Conclusion

　　This article introduces the basic ideas and testing methods for compatibility testing between WLAN access devices (AC/AP) and mobile terminals. In fact, there are many other items that can be tested, such as the relationship between the WiFi signal strength displayed by the mobile phone and the negotiation rate, the impact of the mobile phone Bluetooth function on the WiFi connection, etc. In this type of compatibility test, first, it is necessary to ensure the diversity of mobile terminal types, and second, to combine the characteristics of the mobile terminal itself and the application for testing to ensure a good experience for users.

　　Note: The test results in this article only represent the compatibility between WiFi mobile phones/terminals and H3C WLAN devices, and are not used as a basis for performance/function evaluation of mobile phones/terminals.