Cisco Systems manual Cisco 7401ASR Installation and Configuration Guide

Chapter 2 Rack-Mounting, Tabletop Installation, and Cabling

Connecting I/O Cables

This degradation results in a decrease in the link span (the distance between a transmitter and a receiver) that can be supported reliably. The effect of DMD can be overcome by conditioning the launch characteristics of a laser source. A practical means of performing this conditioning is to use a device called a mode-conditioning patch cord.

A mode-conditioning patch cord is an optical fiber cable assembly that consists of a pair of optical fibers terminated with connector hardware. Specifically, the mode-conditioning patch cord is composed of a single-mode optical fiber permanently coupled off-center (see Offset in Figure 2-14) to a graded-index multimode optical fiber. Figure 2-14shows a diagram of the mode-conditioning patch cord assembly.

A mode-conditioning patch cord assembly is composed of duplex optical fibers, including a single-mode-to-multimode offset launch fiber connected to the transmitter, and a second conventional graded-index multimode optical fiber connected to the receiver. The use of a plug-to-plug patch cord maximizes the power budget of multimode 1000BASELX and 1000BASELH links.

Note The mode-conditioning patch cord is required to comply with IEEE standards. The IEEE found that link distances could not be met with certain types of fiber-optic cable cores. The solution is to launch light from the laser at a precise offset from the center, which is accomplished by using the mode-conditioning patch cord. At the output of the patch cord, the GBIC is compliant with the IEEE 802.3z standard for 1000BASELX.

	Cisco 7401ASR Installation and Configuration Guide
2-20	OL-5419-01 B0