Product Technology

This chapter presents the general system technology and the available protection architectures for Cisco's dense wavelength division multiplexing (DWDM) metro system, the Cisco ONS 15200.

1.1 Optical System Description

The ONS 15200 DWDM metro system transports data over wavelengths using fiber-optic cables. The ONS 15200 operates in the 1550-nm transmission window. Over a single optical fiber pair, the ONS 15200 can carry up to 32 channels of data in the following bit rates and formats:

155 Mbps—SONET OC-3 or SDH STM-1
622 Mbps—SONET OC-12 or SDH STM-4
2.5 Gbps—SONET OC-48 or SDH STM-16
100 Mbps—1.25 Gbps, pass-through mode with 2R operation

Protected or unprotected data can transmit over the ONS 15200.

The optical layer is independent of the electronic protocol that is external to the ONS 15200 system. You can use any higher-level protocol, including proprietary products, within the ONS 15200 system. Any protocol used must fulfill the requirements listed in this book, including the bit rates listed in this section.

1.2 Optical Channels

In the ONS 15200 system, optical channels transport information between two client-layer interface ports. All optical channels in the ONS 15200 system are duplex channels, which means that traffic flows in both directions. The optical channels can be unprotected, as described in the "Unprotected Channels" section, or protected, as described in the "Protected Channels" section.

1.2.1 Unprotected Channels

In an unprotected channel, protection fiber is not available. Only one fiber sends traffic to the client layer of the receiving node. You can use unprotected channels where protection is not needed or if the client layer provides protection. Cisco recommends that you only use protection in one layer and avoid potentially conflicting protection schemes. You can add protection in the client layer described in the "Physical Layout" section. Figure 1-1 displays an example of ONS 15200 unprotected channels.

Figure 1-1: Unprotected Channels in an ONS 15200 System

1.2.2 Protected Channels

In optically protected channels, data traffic flows in two physically separated streams to the receiving node. The configuration of the receiving node determines which traffic flow is transferred to the client layer of the receiving node. Figure 1-2 displays an example of optical fiber-protected channels in an ONS 15200 system. This form of optical channel protection is rapid and provides continued system coverage in case of fiber breaks between nodes.

Figure 1-2: Optically-fiber protected channels in an ONS 15200 system

Client-layer protection schemes for the ONS 15200 are:

SONET/SDH add/drop multiplexer (ADM) rings—Traffic travels in two directions between any two nodes. If one route fails, the alternate route continues to transport the traffic.

Client-layer 1+1 automatic protection switching (APS)—Two separate connections exist between two client-layer interfaces. One of the connections is standby and is used only when the active connection fails.

Layer 3 load sharing—Two routes transport traffic from one client to a dual home node. (See "Product Configurations." for a description of the dual home node configuration.) The routes are used below their maximum capacity. If one of the two routes fails, the traffic shifts to the other route.

1.2.3 Software Configurable Protection

In Release 1.1 and later, the 2R/3R (unclocked/clocked) Client Layer Interface Port (CLIP) module is user configurable for unprotected or fiber protected operation. (See Cisco ONS 15200 Command Line Interface Manual, R1.1).