Table of Contents

1.1  Optical System Description
1.2  Optical Channels

1.2.1  Unprotected Channels
1.2.2  Fiber-Optically Protected Channels

1.2.2.1  Client Layer Protection Schemes

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 optics. The ONS 15200 operates in the 1550 nm transmission window. Over a single optical fiber pair, the ONS 15200 can carry up to sixteen channels of data in the following bit rates and formats:

• 155 Mbps - synchronous optical network (SONET) optical channel 3 (OC-3) or synchronous digital hierarchy (SDH) synchronous transfer mode 1 (STM-1)
  
  
• 622 Mbps - SONET OC-12 or SDH STM-4
  
  
• 2.5 Gbps - SONET OC-48 or SDH STM-16
  
  
• 1.25 Gbps - Gigabit Ethernet
  
  

The data transmitted over the ONS 15200 can be protected or unprotected.

The optical layer is independent of the electronic protocol external to the ONS 15200 system. Any higher-level protocol, including proprietary products, can be used within the ONS 15200 system, provided it fulfills the requirements listed in this book, including 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 "Fiber-Optically Protected Channels" section.

1.2.1  Unprotected Channels

In an unprotected channel, no protection fiber is available. Only one fiber sends traffic to the client layer of the receiving node. However, protection can be added in the client layer described in the "Physical Layout" section. Figure 1-1 displays an example of ONS 15200 unprotected channels.

1.2.2  Fiber-Optically 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 ONS 15200 system optical fiber-protected channels. This form of optical channel protection is rapid and provides continued system coverage in case of fiber breaks between nodes.

1.2.2.1  Client Layer Protection Schemes

Client-layer protection schemes for the ONS 15200 are:

• SONET/SDH ADM rings — traffic is transmitted in two directions between any two nodes. If one route fails, the alternate route continues to transport the traffic.
  
  
• Client-layer 1+1 APS — two separate connections are established between two client-layer interfaces. One of the connections is standby and 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.
  
  

Posted: Mon Sep 30 20:42:57 PDT 2002
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