No abstract

We analyze the link-layer handoff process in wireless LANs based on the IEEE 802.11b standard and suggest how to reduce its duration. Firstly, we divide the process into three phases: detection, search and execution. Our performance measurements indicate that the detection and search phases are the main contributors to the handoff time. We show that the linklayer detection time can be reduced to three consecutive lost frames. We also show that the search time can be reduced at least by 20% using active scanning with the two timers that control its duration set to 1 ms and 10.24 ms. Several simulations illustrate the achieved reduction in handoff time.

There has recently been a notable interest in the organization of routing information to enable fast lookup of IP addresses. The interest is primarily motivated by the goal of building multigigabit routers for the Internet, without having to rely on multilayer switching techniques. We address this problem by using an LC-trie, a trie structure with combined path and level compression. This data structure enables us to build efficient, compact, and easily searchable implementations of an IP-routing table. The structure can store both unicast and multicast addresses with the same average search times. The search depth increases as 2(log log n) (log log n) (log log n) with the number of entries in the table for a large class of distributions, and it is independent of the length of the addresses. A node in the trie can be coded with four bytes. Only the size of the base vector, which contains the search strings, grows linearly with the length of the addresses when extended from 4 to 16 bytes, as mandated by the shift from IP version 4 to IP version 6. We present the basic structure as well as an adaptive version that roughly doubles the number of lookups/s. More general classifications of packets that are needed for link sharing, qualityof-service provisioning, and multicast and multipath routing are also discussed. Our experimental results compare favorably with those reported previously in the research literature.

We propose a load-balancing scheme for overlapping wireless LAN cells. Agents running in each access point broadcast periodically the local load level via the Ethernet backbone and determine whether the access point is overloaded, balanced or under-loaded by comparing it with received reports. The load metric is the access point throughput. Overloaded access points force the handoff of some stations to balance the load. Only under-loaded access points accept roaming stations to minimize the number of handoffs. We show via experimental evaluation that our balancing scheme increases the total wireless network throughput and decreases the cell delay.

Podcasting has become a very popular and successful Internet service in a short time. This success illustrates the interest for participatory broadcasting, in its actual form however, podcasting is only available with fixed infrastructure support to retrieve publicized episodes. We aim at releasing this limitation and present herein our podcasting system architecture together with a prototype implementation based on opportunistic wireless networking that allows us to extend podcasting to ad hoc domains.