Most earlier works in the area of wireless mesh network assume a single interface being equipped in each node. In this paper, we consider the next-generation wireless mesh networks in which each node may be equipped with multiple radio interfaces, each capable of running in one of several modes (IEEE 802.11b/g 2.4 GHz or 802.11a 5 GHz mode), one of several channels, and each capable of supporting multiple modulations. We call such a network an M⁴ (multi-radio, multi-mode, multi-channel, multi-rate) wireless mesh network. For example, from off-the-shelf components, one can easily construct a mesh node with multiple IEEE 802.11a/b/g radio interfaces. Our goal is to address the resource planning and packet forwarding issues in such an environment. The proposed methodology is based on linear programming with network flow principles and radio channel access/interference models. Given a network topology, traffic requirements, and gateway capacities, we show how to allocate network interface cards and their channels to fully utilize channel bandwidths. The results can be utilized by a wireless Internet service provider to plan their networks under a hardware constraint so as to maximize their profits. To the best of our knowledge, this is the first work addressing resource planning in a wireless mesh network. Our numerical results show significant improvement in terms of aggregate network throughput with moderate network-layer fairness. The importance of network planning is further corroborated by the simulative comparisons with other multi-radio systems assuming a known and fixed number of interfaces at each mesh router.