Asynchronous/Synchronous interfaces are the most versatile serial connections that Cisco offers. These interfaces support a wide variety of protocols and applications, including WAN concentration, transport of SDLC and Bi-sync data, and asynchronous terminal connections. Cisco announces the availability of the NM-16A/S that has double the interface density of the NM-8A/S. - See more at: http://network-guarantee.co.uk/network/products-page/cisco-router/cisco-3800-series/cisco-routers-nm-16as/#sthash.NilKksMv.dpuf