Inverse Multiplexing for Reliable Transport in Wide-Area Wireless Networks

The limited bandwidth of current wide-area wireless access networks (WWANs) is often insuff icient for demanding applications, such as streaming audio or video, data mining applications, or high-resolution imaging. Inverse multiplexing is a standard method for achieving higher end-to-end bandwidth by splitt ing traffic across multiple physical li nks creating a single logical channel. This technique is commonly used today in ISDN and analog dialup installations. Current implementations, however, are designed for private links with stable channel characteristics. Unfortunately, most WWAN technologies use shared channels that display highly variable link characteristics, including bandwidth, latency, and loss rates. This paper presents a novel inverse multiplexing method for WWAN environments, termed Link Quality Balancing, which uses relative performance metrics to adjust traff ic scheduling between bundled links. By exchanging loss rate information, we compute relative short-term available bandwidths for each link. We discuss the challenges of adaptation in a WWAN network, CDPD in particular, and present performance measurements of our current implementation of Wide-Area Multi -Link PPP (WAMP) for CDPD modems under both Constant Bit Rate (CBR) and TCP loads.