Building Multiservice Transport Networks - page 87

Traditionally, dense wavelength-division multiplexing (DWDM) has been used to relieve congested fiber networks when the option of deploying additional fiber cable strands is cost-prohibitive. An example of the "fiber relief" strategy is the deployment of point-to-point DWDM within a fiber transmission section to create "virtual" fiber strands in the network. These virtual fiber strands are then deployed as fiber sections for Synchronous Optical Network (SONET) rings or for point-to-point optical fiber systems.

As DWDM systems become more intelligent , DWDM system deployment is becoming more expansive to include optical service drops , such as storage protocol extension and high-bandwidth Ethernet. These types of services are bandwidth- intensive and tend to strain the limits of typical SONET OC-48/192 system deployments. Therefore, the most optimal method for offering these and other services is with dedicated wavelengths .

This chapter examines the tenets of offering such "wavelength services" over the ONS 15454 Multiservice Transport Platform (MSTP) and explores the different categories and characteristics of wavelength services as they relate to ONS 15454 MSTP features/functions. The chapter concludes with a discussion on the management capabilities of ONS 15454 MSTP wavelength services.

SONET/SDH Services

One of the key aspects of providing this type of service over DWDM is transparency. In effect, the DWDM system must operate as a virtual optical fiber extension, in that the SONET/SDH communications overhead bytes and performance-monitoring data should be preserved during transmissions. Both the 2.5-Gbps and 10-Gbps multirate transponder interfaces for the ONS 15454 MSTP allow for SONET/SDH services to operate transparently . The client SONET/SDH communications overhead bytes are not terminated on the transponder interface card in this mode of operation. This feature is also present on the 4x2.5-Gbps enhanced muxponder interface. To preserve end-to-end client SONET/SDH performance monitoring and fault isolation, key overhead bytes, such as the B1 overhead and the J0 overhead bytes, are also passed across the ONS 15454 MSTP system from end to end. In this manner, client-to-client unidirectional path -switched ring (UPSR)/subnetwork connection protection (SNCP), or bidirectional line-switched ring (BLSR)/ multiplex section shared protection rings (MS-SPR) can be deployed over ONS 15454 MSTP DWDM wavelength channels.

Storage-Area Networking Services

Characteristics for storage interconnect interfaces vary, depending on the type of storage protocols being distributed across the network. Where real-time data replication is required, full line-rate throughput for protocols such as Fibre Channel (FC) are essential. Consequently, distance-extension techniques such as buffer-to-buffer credits and flow control must be incorporated into the DWDM client interface. Conversely, asynchronous, non-real -time storage requirements are less demanding on bandwidth use and distance extension.

A wide range of storage interconnect protocols can be supported using the ONS 15454 MSTP transponder interfaces. The 2.5-Gbps multirate transponder can support industry-standard 1- or 2-Gb FC or fiber connection (FICON), in addition to lower-bit-rate protocols such as Enterprise Systems Connection (ESCON) or geographically dispersed parallel sysplex (GDPS). The interface card is Small Form Factor Pluggable (SFP)based, so each of these channel varieties can exist simultaneously on a single interface, with each port operating independently of the others. Optionally, the 2.5-Gbps multiservice aggregation interface can be used to provide the FC/FICON extension services. Where higher-bit-rate storage services are required, the 10-Gbps multirate transponder provides the option for 10-Gbps FC extension over the ONS 15454 MSTP network.

Ethernet Services

Ethernet interfaces are quickly becoming the predominant growth engine for transport networks. Because of its ubiquitous interface parameters and low-cost equipment, Ethernet is replacing services that time-division multiplexing (TDM) rates such as T1/T3 and OC-n typically served . As Ethernet services become more reliable, tremendous growth in Gigabit, fractional Gigabit, and 10-Gbps Ethernet services will dominate the market place.

The ONS 15454 MSTP provides a full suite of transponder interfaces to effectively extend Ethernet networks across a DWDM transport network. Both the 2.5-Gbps multiservice aggregation card and the 2.5-Gbps multirate transponder provide SFP interfaces for native Gigabit Ethernet (GigE) transport. Both cards allow for low latency and packet loss, in that Ethernet Layer 2 source/destination switching is not required for transport. Additionally, Ethernet performance monitoring is available through frame/packet counters on the client interface ports.

For high-bit-rate Ethernet transmissions, the 10-Gbps multirate transponder can be utilized to support 10-GigE service extensions. The Ethernet services marketplace is experiencing a high rate of growth for 10-Gbps Ethernet capability to effectively trunk data between high-traffic Ethernet switching devices. These data rates cannot be supported with SONET/SDH because they exceed the maximum SONET OC-192/STM-64 line-rate capacity of 9.9532 Gbps. Thus, aside from direct fiber transport, wavelength-division multiplexing (WDM) transmission provides the only viable alternative for 10-GigE port extensions.

Variable Bit-Rate Services

A critical aspect of DWDM wavelength services is flexibility and transparency. Some customer transport requirements don't easily fall into a well-known category or bit-rate scheme, such as SONET/SDH or Ethernet. For those cases, the DWDM wavelength system must exhibit the flexibility to interface with a variety of nonstandard or seldom-used transport technologies.

For the ONS 15454 MSTP DWDM system, the 2.5-Gbps multirate transponder allows for 2R provisioning. In this mode, the incoming client signal is transparently passed through the DWDM system without specific bit-rate or formatting requirements. As such, the ONS 15454 DWDM system does not provide performance-monitoring capability for 2R-transported signals. However, the 2R mode enables the carrier to offer DWDM wavelength transport of asynchronous signals, such as video and asynchronous transfer mode (ATM).