Wireless Router System


Software-based Wireless Router System

Overview - A brief description of the project
Papers - DIRAC documents
Talks - Selected presentations
People - The people behind the project
Related Reseach - Interesting projects to check out


This project explores new designs for access routers that provide IP connectivity to mobile clients that use wireless links to connect to the network infrastructure. Several access points are usually connected to a single access router using wired links, and each access point provides wireless connection to every mobile client inside its cell.

The motivation for a new router design comes from the fact that the implementation and deployment of mobility-aware and channel-adaptive protocols and services on edge routers pose new requirements from the router system: they require link-layer support from the system, and in particular link-layer information about the clients. For example, mobility management protocols require knowledge on when a mobile client joined/left the network. Additionally, channel-adaptive protocols for Quality of Service, such as wireless schedulers, require periodic measurements on the quality of the channel each host perceives. Moreover, the enforcement of network-level policies often requires mechanisms that are available only at the link-layer. As an example, to deny a mobile node access to the network, some form of "physical" disconnection is needed.

Current routers though do not provide this link-layer support to services designed and developed for wireless environments, making difficult, if not impossible, their implementation and deployment.

DIRAC solves the above problem, and makes link-layer information and mechanisms available to wireless services by following a distributed design approach. It consists of two software modules:

  • Router Core (RC), which implements the main forwarding functionality, along with the (wireless) router services and protocols, and
  • Router Agents (RAs), each one of which runs on an access point, and is responsible for collecting and reporting information to the RC, and also enabling link-layer mechanisms for use by the RC..

Using the DIRAC framework, we implemented three wireless router services:

  • A micro-mobility management protocol that minimizes transient packet losses during handoffs
  • An FEC-based packet forwarding solution that solves the Head-of-Line (HoL) blocking problem over wireless links, and
  • A link-layer assisted policing mechanism that penalizes overly aggressive, wireless clients.


  • "DIRAC: A Software-based Wireless Router System". Petros Zerfos, Gary Zhong, Jerry Cheng, Haiyun Luo, Songwu Lu, Jia-Ru Li, In Proc. of ACM MOBICOM 2003 [ps]
  • "Architecture Taxonomy for Control and Provisioning of Wireless Access Points (CAPWAP)", Lily Yang, Petros Zerfos, Emek Sadot, IETF Internet Draft (work in progress) [txt]


  • "DIRAC: A Software-based Wireless Router System", presented at ACM MOBICOM, Sep. 2003 and also Nokia Research Center, Mountain View, CA, Jun. 2003 [pdf]

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