Seamless roaming
The Cisco UWN solution supports seamless client roaming across lightweight access points managed by the same controller, between controllers in the same mobility group on the same subnet, and across controllers in the same mobility group on different subnets. Also, in controller software release 4.1 or later releases, client roaming with multicast packets is supported.
802.11 voice-over-IP (VoIP) telephones actively seek out associations with the strongest RF signal to ensure the best quality of service (QoS) and the maximum throughput. The minimum VoIP telephone requirement of 20-millisecond or shorter latency time for the roaming handover is easily met by the Cisco Wireless solution, which has an average handover latency of 5 or fewer milliseconds when open authentication is used. This short latency period is controlled by controllers rather than allowing independent access points to negotiate roaming handovers.
The Cisco Wireless solution supports 802.11 VoIP telephone roaming across lightweight access points managed by controllers on different subnets, as long as the controllers are in the same mobility group. This roaming is transparent to the VoIP telephone because the session is sustained and a tunnel between controllers allows the VoIP telephone to continue using the same DHCP-assigned IP address as long as the session remains active. The tunnel is torn down, and the VoIP client must reauthenticate when the VoIP telephone sends a DHCP Discover with a 0.0.0.0 VoIP telephone IP address or a 169.254.*.* VoIP telephone auto-IP address or when the operator-set user timeout is exceeded.
Nomadic Roaming
Seamless roaming is best analogized to a cellular phone call. For example, suppose you are using your cellular phone as you drive your car on the freeway. A typical global system for mobile (GSM) communications or time-division multiple access (TDMA) cell provides a few miles of coverage area, so it is safe to assume that you are roaming between cellular base stations as you drive. Yet as you roam, you do not hear any degradation to the voice call (that is what the cellular providers keep telling us). There is no noticeable period of network unavailability because of roaming. This type of roaming is deemed seamlessbecause the network application requires constant network connectivity during the roaming process.
Nomadic roaming is different from seamless roaming. Nomadic roaming is best described as the use of an 802.11-enabled laptop in an office environment. As an example, suppose a user of this laptop has network connectivity while seated at his desk and maintains connec-tivity to a single AP. When the user decides to roam, he undocks his laptop and walks over to a conference room. Once in the conference room, he resumes his work. In the back-ground, the 802.11 client has roamed from the AP near the user's desk to an AP near the conference room. This type of roaming is deemed nomadic because the user is not using network services when he roams, but only when he reach his destination.
