IP Router Architecture: IP Routers are becoming increasingly complex to build and manage. Typical lines of code in a router rival that of a 5ESS telephony switch today (5-10 million lines of code). The basic idea behind this project is to separate the router control plane from the transport plane, define a standardized interface between the two planes, and aggregate the numerous points of control in today's IP network to a few servers that manage the entire network. An overview of this project was presented at HotNets 2004 and is available here
Hybrid wireless architectures: We have been investigating how different wireless technologies interact and complement one another? For example, WiMAX appears to be a good technology to "backhaul" traffic from 3G base stations serving high speed data users. We examine a number of interesting design problems in this 3G/WiMAX hybrid network in a paper presented at Infocom 2005. Another architecture that we have investigated in detail is the use of 3G and WiFi networks in a complementary manner. In third generation (3G) wireless data networks, mobile users experiencing poor channel quality usually have low data-rate connection to the base station. Providing service to low data-rate users is required for maintaining fairness, but results in reducing the cell's aggregate throughput. We designed the Unified Cellular and Ad-hoc Network (UCAN) architecture for enhancing cell throughput, while maintaining fairness. In UCAN, mobile clients have both 3G cellular links as well as IEEE 802.11-based peer-to-peer links. The 3G base station forwards packets for destination clients with poor channel quality to proxy mobile clients with better channel quality. The proxy clients then use an ad-hoc network composed of other mobile clients and IEEE 802.11 wireless links to forward the packets to the appropriate destinations, thereby improving cell throughput while maintaining fairness. As part of this architecture, we examine greedy and on-demand protocols for proxy and ad-hoc route discovery and maintenance, secure crediting, and multicast performance enhancements. Performance improvements of several hundred percent can be achieved using UCAN.
TCP: 3G Wireless links exihibit a great degree of rate and delay variation since they have incorporated extensive local retransmission mechanisms (to reduce loss) and intelligent channel state based scheduling (to increase throughput). We performed a comprehensive evaluation of the impact of variable rate and delay on long-lived TCP performance and developed several network-based solutions to mitigate this impact. The details of our work on TCP performance over 3G Wireless Links was presented at ACM/IEEE Mobicom'02 and work on further enhancements for short and long-lived flows will appear in IEEE Infocom'04 . In another related project, we examined TCP fairness issues over wireless LAN. In the presence of both mobile senders and receivers, we identify four different regions of TCP unfairness (depending on the buffer size at the base station). We developed a simple solution that can be implemented at the base station above the MAC layer that ensures that the different TCP flows share the 802.11 bandwidth equitably. TCP Fairness over Wireless LAN will be presented at IEEE Infocom'03 .
HAWAII: The vision behind this project is to specialize IP routers with new protocols that specifically cater to wireless mobile users. We designed a novel protocol, called HAWAII, that adds hierarchy and scalability to Mobile IP by localizing mobility management. HAWAII acts in a complementary manner to Mobile IP similar to how OSPF, the intra-domain routing protocol works with BGP, the inter-domain routing protocol. HAWAII results in minimized handoff disruption for application traffic and increased scalability. We also developed IP-based paging protocols that enhance the network to locate and awaken IP hosts (that are in standby state, conserving battery power) before delivering data packets. For details on the implementation and simulation results, please refer to the papers on HAWAII in IEEE/ACM Transactions on Networking and IP Paging in the proceedings of ACM/IEEE Mobicom'2001 .
RIMA: The goal was to have an IP router (with additional software and hardware) serving as an integrated network element that supports both voice and data transport in 3G wireless networks. We built a prototype of this system that performs the functionality of the Mobile Switching Center, MSC, and the data service nodes, SGSN/GGSN. This system uses IP-based mobility management and performs integrated call control for both circuit and packet voice. This work was presented at PIMRC'00 as an invited paper. In a related project, we developed a prototype of the MSC with over 100K lines of code, running on a cluster of Sparcstations connected by an ATM switch. The challenge was to ensure that the MSC software was scalable, reliable, and manageable. We achieved scalability of about 1 million busy hour calls and reliability of 99.995% on a 8 Ultra Sparc II cluster. Papers detailing performance , reliability and signaling results are available.