switch delivers more services at access layer other than merely providing increased speeds and feeds. Wireless services is now integrated with the switch, which ensures that the access layer switch terminates the wireless users data plane, thereby delivering on the promise of Cisco's unified architecture. Unification implies that mobility services are provided to both wireless and wired stations.
The switch provides seamless roaming, which requires transparency of the network configuration and deployment options to the client.
From the end user's perspective, any mobility event must not change its IP address, its default router or DHCP server. This means that as stations roam, they must be able to
Send an ARP to their default router, or
Transmit a DHCP request to the server that had previously assigned their address.
From the infrastructure's perspective, as mobility events occur, the station's traffic must follow its current point of attachment, which can either be a mobility agent (MA) or mobility controller (MC). This must be true regardless of whether the station has moved to a network that is configured for a different subnet. The period from which the station is not receiving traffic following its mobility event must be as short as possible, even below 40 ms whenever possible, which includes any authentication procedures that are required.
From the infrastructure's perspective, the mobility management solution must have four main components, and all of these functions must be performed within the constraints of roaming:
Initial Association—This function is used to identify the user's new point of attachment in the network.
Context Transfer—This function is used to transfer state information associated with the station. This ensures that the station's static and real-time policies, including security and application ACLs, and services, remain the same across handoffs.
Handoff—This function is used to signal that the station's point of attachment has changed, and control of the station should be relinquished by the previous access switch.
Data Plane—This function is typically tied to the handoff process, and ensures that the station's traffic continues to be delivered and received from the station without any noticeable performance degradation.