Alex C. Snoeren
© Massachusetts Institute of Technology. December 12, 2002.
The proliferation of mobile computing devices and wireless networking products over the past decade has led to an increasingly nomadic computing lifestyle. A computer is no longer an immobile, gargantuan machine that remains in one place for the lifetime of its operation. Today's personal computing devices are portable, and Internet access is becoming ubiquitous. A well-traveled laptop user might use half a dozen different networks throughout the course of a day: a cable modem from home, wide-area wireless on the commute, wired Ethernet at the office, a Bluetooth network in the car, and a wireless, local-area network at the airport or the neighborhood coffee shop.
Mobile hosts are prone to frequent, unexpected disconnections that vary greatly in duration. Despite the prevalence of these multi-homed mobile devices, today's operating systems on both mobile hosts and fixed Internet servers lack fine-grained support for network applications on intermittently connected hosts. We argue that network communication is well-modeled by a session abstraction, and present Migrate, an architecture based on system support for a flexible session primitive. Migrate works with application-selected naming services to enable seamless, mobile ``suspend/resume'' operation of legacy applications and provide enhanced functionality for mobile-aware, session-based network applications, enabling adaptive operation of mobile clients and allowing Internet servers to support large numbers of intermittently connected sessions.
We describe our UNIX-based implementation of Migrate and show that sessions are a flexible, robust, and efficient way to manage mobile end points, even for legacy applications. In addition, we demonstrate two popular Internet servers that have been extended to leverage our novel notion of session continuations to enable support for large numbers of suspended clients with only minimal resource impact. Experimental results show that Migrate introduces only minor throughput degradation (less than 2% for moderate block sizes) when used over popular access link technologies, gracefully detects and suspends disconnected sessions, rapidly resumes from suspension, and integrates well with existing applications.
This thesis recieved the 2003 MIT EECS George M. Sprowls Doctoral Dissertation Award (Honorable mention).
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