What Is Mobility?
Mobility, or roaming, is an ability of a wireless client to maintain its association seamlessly from one access point to another securely and with as little latency as possible. To allow more flexible roaming and to minimize the need for tunnel encapsulation of traffic, Prime Infrastructure provides a robust mobility architecture that distributes mobility functionality across the network devices.
The following are the key elements of the mobility architecture:
- Mobility Controller (MC)—The MC (for example, Cisco 5700 Series Wireless Controller) is responsible for one or more MAs or switch peer groups, handling roaming within its span of control, and transiting traffic between MAs and/or MCs when co-located with MTE.
- Mobility Agent (MA)—The MA (for example, Catalyst 3650 or Catalyst 3850 Switch) resides in the access switch or edge switch that the WAP is directly connected to, and terminates at the CAPWAP tunnel for communications with the WAP.
- Mobility Oracle (MO)—The MO is a top-level control entity responsible for connecting multiple MCs or mobility subdomains in deployments of the largest scale, to enable roaming across very large physical areas.
- Mobility Domain—A roaming domain: a mobile user may roam across all of the devices in this domain (the set of WAPs and all of the control entities associated with it). This typically includes MAs and MCs, and may include a MO (to join multiple subdomains).
- Mobility Sub-Domain—The set of WAPs and associated MAs and one MC, representing a portion of a larger mobility domain (where a MO serves to coordinate roaming between multiple sub-domains).
- Switch Peer Group (SPG)—A group of switches (acting as MAs). An SPG establishes a full mesh of mobility tunnels among the group members to support efficient roaming across the WAPs associated with the switches in the group. An SPG is also intended to limit the scope of interactions between switches during handoffs. An SPG is configured by the Mobility Controller, and every switch in the switch peer group has the same view of the membership. The switches in an SPG might be interconnected by a set of direct tunnels. When a station roams from one switch to another within the same switch peer group, if the point of presence stays at the original or anchor switch, the traffic can be directly tunneled back to the anchor switch without involving the MTE. This direct tunneling mechanism is a data path optimization and is optional.
- Mobility Group—A mobility group is a set of MCs (and their associated MAs / switch peer groups)
- Mobility Tunnel Endpoint—The Mobility Tunnel Endpoint (MTE) provides data plane services for mobile devices through the use of tunneling. This minimizes the impact of roaming events on the network by keeping the user's point of presence on the network a constant. If the VLAN or subnet of the roamed client is available at the MTE, the MTE could become the point of presence; otherwise it merely functions as a tunnel switching entity that connects the roamed client to access switch or MTE that is the point of presence.