The Cisco 3600 platform with digital modem network modules offers high-performance branch office dial access - -the most flexible, scalable, and manageable solutions available.The digital modem module is bundled with the High Speed Serial Interface (HSSI), network module interface that supports speeds up to 52 Mbps over a Wide Area Network. The HSSI network module for the 3600 requires an external T3/E3 CSU for connectivity to the WAN, or can be used in a back-to-back configuration, without the requirement for an external CSU. For use in the Enterprise or Service Provider environment; the HSSI network module can be used for point-to-point connections, Frame-Relay services, or used with inverse multiplexers to distribute your bandwidth over multiple T1/E1 lines.Cisco offers a 3620 PRI Dial Bundle: 1FE2CT1-CSU, 24DM and IP IOS.