The astonishing versatility of the Cisco 2600, 3600 and 3700 router series is highlighted by its broad support of Integrated Services Digital Network Primary Rate Interface (ISDN PRI) connectivity. The available Cisco 2600/3600/3700 PRI network modules provide various port densities to meet customer requirements at various price points. The optional, integrated CSU lets customers consolidate customer premises equipment (CPE) to provide multifunction dial access server, router, and other capabilities within the Cisco 2600/3600/3700 series in power branch office environments. The balanced and unbalanced serial connectivity options enable conformity to a customer's specific application.