3Com 3C63311 Reference Guide - Page 225

OC3/STM-1 Port 213 n The cells are passed to a line HEC framer to synchronize to the line speed. n The T1/E1 chip adds the T1/E1 overhead and converts the digital data into a bipolar format suitable for transmission. An 8 KHz clock is extracted from the T1/E1 clock (on all T1's/E1s) and is used for system synchronization. The system uses this clock or other clocks to generate a stable 8 KHz clock for all other modules and interfaces. OC3/STM-1 Port The OC3/STM-1 port supports either a multi-mode fiber interface-used mostly for local workgroup switch connection-or a single-mode fiber interface-used for intermediate range operation (up to 15 kilometers). The PathBuilder S310 does not include an OC3/STM-1 port. On the OC3/STM-1 receive side, the data flow is as follows: n A fiber interface module converts the light to electrical data. n The data is fed to a chip where the clock is recovered. The PHY chip also provides all the line functions and cell framing. n The chip interfaces directly to the CTX, which performs address translation and output buffering. n The data is placed in the corresponding output buffer. On the OC3/STM-1 transmit side, the data flow is as follows: n Cells received from the CTX are passed directly to the transmitter. Four buffers are supported for the OC3/STM-1. n The output of the chip feeds into the fiber interface module. An 8 KHz clock is extracted from the OC3/STM-1 clock, and the system uses the OC3/STM-1 clock or other line clocks to generate a stable 8 KHz clock to be used for system synchronization. DS3/E3 UNI Modules The optional DS3 module is compatible with AT&T Publication 54014 specifications, uses the unchannelized format, and is compliant to M23 or the C-bit parity ANSI-107a, 1991 specifications. It performs the following key functions: n Provides line interface functions and terminates the FEAC and MDL for the C-bit format n Performs ATM to physical layer mapping and adds PLCP according to UNI 3.0 n Performs peak traffic shaping on the transmit (14 bulk shapers) The optional E3 UNI module is typically used for terminating/accessing public or private WAN services. However, depending on your local applications, you can also use this module in the port slot for taking local traffic across the WAN. The E3 UNI module performs the following key functions: n Performs ATM to physical layer mapping and adds PLCP according to UNI 3.0 n Performs peak traffic shaping on the transmit (14 bulk shapers)