Metro Edge Solution for Wireline Carriers

SONET and SDH networks are a mainstay for wide-area and metropolitan-area communications worldwide. Deployed in the 1980s, they were designed specifically to manage TDM characteristics associated with voice- and connection-oriented point-to-point, or highly delay-sensitive point-to-network traffic. IP data traffic, on the other hand, has somewhat different characteristics. Most notably, data traffic is "burst" oriented and considered nondeterministic, because of its unpredictable traffic patterns. Because of this bursty nature, data services are more efficiently delivered using a different strategy than traditional voice services. Networks can transport data traffic more efficiently using virtual, private, or shared services offering a constant rate of speed as well as a peak rate of speed. Typically, the constant requirements are only 35 percent of the peak requirements. So without shared bandwidth (fixed rate data service), typically more than 65 percent of the bandwidth is not used the majority of time.

Today, one of the most common Ethernet services offered over SONET/SDH networks is Ethernet Private Line (EPL). Because it operates much like a dedicated private voice line, it features a fixed-in-size, point-to-point and exclusive connection that cannot be shared. This results in the inefficient use of SONET and SDH networks for the delivery of data services.

For example, if an enterprise customer has five downtown locations it wishes to interconnect and provide Internet access using a 100-Mbps EPL service. Under most existing deployments, each location would require a dedicated OC-3 circuit consuming 155 Mbps of bandwidth over a SONET network. An additional 155 Mbps per location is required for protection bandwidth. Therefore, using a traditional SONET EPL solution, these five circuits will consume aggregate ring capacity totaling 1.5 Gbps of bandwidth to deliver the requested 100-Mbps service.

Now if the customer wanted to deploy an advanced data application over this network, it would not be possible because most advanced data applications require features such as QoS, which most EPL services do not support. EPL typically does not support bandwidth on demand or the ability to share one service between all locations, using oversubscription for efficiency.

These scenarios suggest it is time to rethink how we deploy Ethernet over SONET-based networks.

To overcome these limitations and efficiently and effectively carry data traffic on SONET networks, industry groups and carriers are turning to an evolving IP Transport standard called Resilient Packet Ring (RPR). In fact, a standards based RPR movement is currently being driven by the IEEE 802.17 working group. RPR enables the efficient transport of IP traffic through statistical multiplexing and spatial reuse of core capacity.

RPR can operate over multiple physical media, including SONET and SDH, enabling the efficient transport of data traffic. By using statistical multiplexing and spatial reuse of idle transport capacity, RPR allows for the optimization of virtual tributary and synchronous transport signal (STS) frame capacity up to 100 percent of the available payload in bandwidth assignable to a particular frame. RPR helps ensure that all customers have secure separation, as well as reliable segregation of all IP traffic, even where sub-multiplexed VLAN tags are transported on the same physical circuit paths. RPR uses Layer 3 features such as QoS to prioritize data traffic. Now the customer can choose from differing classes of service ranging from best effort through guaranteed circuit availability. For the service provider, this means the ability to offer differentiated services including "Platinum" services for jitter- and latency-sensitive applications, such as VoIP, or "Silver" and "Bronze" services to meet specific customer needs and requirements.

By offering statistical multiplexing and QoS features, in conjunction with RPR, the Cisco ONS 15454 ML-Series Line Card facilitates the efficient and effective delivery of multipoint data traffic over highly resilient SONET networks. Now the features required to support the advanced data service demanded by business customers are readily available to service providers.

Using the previous example, with the ML-Series card, the business customer can interconnect all five of its locations via a single 100-Mbps shared ring. In addition, the service provider can offer service-level agreements (SLA) for peak rates and committed rates to meet the specific requirements of each location within that customer network. This offers significant advantages to the service provider because the service uses only 100 Mbps of bandwidth resources to deliver the service. The customer gains an economic advantage, because the multipoint service would typically cost less than the five private-line point-to-point services otherwise required. Furthermore, customers can deploy advanced data applications and now have the flexibility to immediately add bandwidth and features to their services on demand.

The Cisco ONS 15454 ML-Series Line Card's advanced set of QoS features, statistical multiplexing, and robust support for RPR allows flexibility in service choices and the efficient use of network resources so that the customer and the provider can use their resources competitively.