Once stationary usage of the applications is working satisfactorily, run tests to verify that users moving throughout the coverage areas are able to continue operating the applications successfully. When testing, be certain to move about the coverage area at typical and maximum speeds that users will operate the applications. This is necessary because roaming tends to break down at higher speeds. Also, run a wireless packet sniffer to record packet transmissions between the client device and the network. This will help you better understand the underlying issues if you run into problems. For example, you might see significant delays when the system is re-establishing the flow of packets when the client device radio hands off from one access point to another. By looking at the packet trace, you may also see that a client device is experiencing significant retransmissions with a particular access point before handing off to another access point with better signal quality, which would point to issues with the client radio’s ability to roam. For wireless IP applications, place a call and walk through the facility while talking to someone on a wired phone. As you walk, monitor the voice quality. If everything is working okay, you should hear consistent quality as you traverse the facility and the phone roams from one access point to another. If you detect poor sound quality at any point, check the signal strength indicator on the phone. A reduction of sound quality may occur when the signal strength is low. To make roaming phone call tests easier to perform, wear an earpiece for listening to the voice quality and monitoring the signal strength indicator on the phone at the same time. When performing the roaming tests, ensure that the phone can “see” at least two access points (each on nonoverlapping channels) from anywhere within the covered area. This can often be done by observing the phone’s wireless connection utility. If two or more access points cannot be seen on nonoverlapping channels, a phone roaming from one access point to another may not be smooth enough to maintain good voice quality. To make voice quality consistent, you might need to reengineer the wireless network by moving access points or adding additional access point. If the phone is connected to a particular access point and does not roam even if located directly under another access point, there may be more than one access point having relatively high signal strengths on overlapping RF channels. In this case, you may be able to fix the problem by adjusting the transmit power of one of the access points. Or, you might need to reengineer the WLAN. Another reason that the phone may not be roaming in this scenario is that the nearby access point is not operating. So, check the status of the access point. Another problem with roaming is that the phone may roam from one access point to the other too slowly. In this case, check the phone wireless utility to ensure that there is indeed another acceptable access point to roam to. The problem could be that there are no other access points having strong enough signal strength for the phone to roam. If the phone appears to roaming promptly to the next access point, there might still be excessive delay problems on the wired network infrastructure.
Sometimes the phone may roam okay with regard to the network, but the phone loses connection with the call manager. In this case, check to be certain that the phone is not traversing different IP subnets, which can cause a Layer 3 connection loss and disconnection from the call manager. In addition, if using Cisco LEAP, make certain that some of the access points are not blocking TCP ports associated with the LEAP protocol.
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