Ulaanbaatar has close ties to cities like Seoul ( from UB), Hong Kong ( from UB), Tokyo ( from UB) and Moscow ( from UB). The Zamyn Uud-Erenhot and Altanbulag-Kyakhta borders are the only places where sustained interaction occurs between Mongolia and its neighbors. Other ports are much smaller. For now Ulaanbaatar remains the main, and almost only, point of contact between Mongolia and its neighbors. Beijing remains the closest global city to Ulaanbaatar (). The UB-Peking corridor is served by busy air, rail and road links.