Rapid Mobility via Type Indirection

Economies of scale and advancements in wide-area wireless networking are leading to the widespread availability and use of millions of wirelessly-enabled mobile computers, Personal Digital Assistants (PDAs), and other portable devices. The same trends are also resulting in the large-scale deployment of publically acessible wireless access points in both fixed (e.g., hotel, coffee shop, etc.) and mobile (e.g., train, subway, etc.)

We consider two rapid mobility scenarios. The first is rapid individual mobility across network cells (e.g., a mobile user on an inter-city bus travelling on a highway with cell sizes of half a mile). This scenario requires fast handoff handling to maintain connectivity. A second, more problematic scenario is a bullet train with hundreds of mobile users. With cell sizes of half a mile, there are frequent, huge bursts of cell crossings that will overwhelm most mobility and application-level protocols.

The challenge is to provide fast handoff across frequent cell crossings for a large number of users, potentially traveling in clusters (mobile crowds).  Handled naively, the delay in processing handoffs will be exacerbated by the large volume of users moving in unison, creating congestion and adding scheduling and processing delays and disrupting the timely delivery of packets to the mobile hosts.

Previous works propose to minimize handoff delay using incremental route reestablishment and hierarchical foreign agents or switches, by organizing the wireless infrastructure as a static hierarchy or collection of clusters.  A proposal also exists for Mobile IP to adopt a simplified version of hierarchical handoff management. These approaches specify separate mechanisms to handle handoffs at different levels of the hierarchy. Also, since they statically define aggregation boundaries in the infrastructure, foreign agents or switches are prone to overloading by spikes in handoff traffic, such as those generated by the movement of large mobile crowds.

To address these issues, we introduce Warp, a mobility infrastructure leveraging flexible points of indirection in a peer-to-peer overlay.  Warp uses a mobile node's unique name to choose the members of a virtual hierarchy of indirection nodes. These nodes act as hierarchical foreign agents to support fast handover operations. Warp also supports hierarchical types, where mobile crowds can redirect traffic through single indirection points and aggregate handoffs as a single entity.  For example, an access point on the train can then perform handoffs as a single node while forwarding traffic to local mobile nodes. Although our techniques are applicable to most decentralized object location and routing (DOLR) networks, we discuss Warp in the context of the Tapestry peer-to-peer overlay.


Rapid Mobility via Type Indirection
Ben Y. Zhao, Ling Huang, Anthony D. Joseph and John D. Kubiatowicz
Third International Workshop on Peer-to-Peer Systems (IPTPS)
San Diego, CA. February 2004.
[Abstract, PDF (120KB), ps.gz (70KB)]

Supporting Rapid Mobility via Locality in an Overlay Network
Ben Y. Zhao, Anthony D. Joseph and John Kubiatowicz
U. C. Berkeley Technical Report UCB/CSD-02-1216, November 2002
[PDF(257KB), Compressed Postscript(228KB)]


Rapid Mobility via Type Indirection
Presented at IPTPS, San Diego, CA. February 2004.
[Talk: PDF(580KB), PowerpointShow(405KB)]


Ben Y. Zhao, February 18, 2004