This module provides connectivity to an OC-3/STM-1fiber for high-bandwidth data applications and voice-data integration applications. The circuit emulation service deck enables the network module to carry voice traffic, such as telephone calls and faxes, video, or any other legacy TDM traffic over an ATM network simultaneously with data traffic. The circuit emulation service deck supports ATM AAL1 structured and unstructured Circuit Emulation Service (CES). The circuit emulation service deck also supports echo cancellation for a full T1/E1 trunk, allowing digital ISDN calls and analog modem calls over a single digital network interface.You need both an OC-3/STM-1 ATM Circuit Emulation Service network module and a 1 or 2-port T1 or E1 multiflex trunk interface card (VWIC-1MFT-T1=, VWIC-1MFT-E1=, VWIC-2MFT-T1=, VWIC-2MFT-E1=, VWIC-2MFT-T1-DI=, VWIC-2MFT-E1-DI=) for a voice connection. You can install one multiflex trunk interface card (providing up to two voice ports) in the circuit emulation service deck on the OC-3/STM-1 ATM Circuit Emulation Service network module.Circuit emulation is a service based on ATM Forum standards that allows communications to occur between AAL1 CES and ATM UNI interfaces, that is, between non-ATM telephony devices (such as classic PBXs or TDMs) and ATM devices (such as Cisco 3600 series routers). Thus, a Cisco 3600 series router equipped with an OC-3/STM-1 ATM Circuit Emulation Service network module offers a migration path from classic T1/E1 data communications service to emulated CES T1/E1 unstructured (clear channel) services or structured (N x 64) services in an ATM network.The OC-3/STM-1 ATM Circuit Emulation Service network module is capable of using three clocking modes to meet the timing requirements of CBR data.Synchronous is the default clocking mode for CES. If you have a single PRS, such as a clock signal from a telephone company, you should use synchronous mode. If you are using structured CES, you must use synchronous mode. In the event that the priority 1 PRS fails for any reason, the network clock synchronization service automatically recovers network timing by using a priority 2 PRS available from another source. Synchronous residual time stamp (SRTS) allows equipment at the edges of a network to use a clocking signal that is different (and completely independent) from the clocking signal being used in the ATM network. SRTS mode also allows two CPEs to have different clocks. Adaptive - typically used when it is not possible to implement either synchronous or SRTS mode. This is the least precise and least recommended method. Adaptive clocking requires neither the network clock synchronization service nor a global PRS for effective handling of CES traffic. Rather than using a clocking signal to convey CES traffic through an ATM network, adaptive clocking infers appropriate timing for data transport by calculating an average data rate for the CES traffic.