Wireless mesh networks aim to provide high speed Internet service without costly network infrastructure deployment and maintenance. The main obstacle in achieving high capacity wireless mesh networks is interference between the mesh links. In this article, we analyze the carrier sensing and interference relations between two wireless links and measure the impact of these relations on link capacity on an indoor 802.11a mesh network testbed. We show that asymmetric carrier sensing and/or interference relations commonly exist in wireless mesh networks and study their impact on the link capacity and fair channel access. In addition, we investigate the effect of traffic rate on link capacity in the presence of interference.