The service mix of cable TV (MSO) operators has grown significantly in the last few years. Cable operators have gone from distributing traditional broadcast video content to providing multi-service broadband to both multiple residential and business markets. As demand for services based on Ethernet and Internet Protocol (IP) race ahead of even the boldest predictions, cable operators, along with all other service providers, must find new ways to rev up their networks to handle the requirements of data solutions and bandwidth requirements of the high performance Internet. MSOs must improve their service-enabling capabilities through cost-effective, scalable, reliable and flexible data-oriented solutions in the Local Area Network (LAN), Metropolitan Area Network (MAN) and Wide Area Network (WAN). Networks that currently exist result in bottlenecks as traffic increases in both size and volume.

The growing sophistication and robustness of LAN services, along with the expanding uses and connectivity of the Internet, create opportunities for MSOs that are well-positioned to deliver low-cost Ethernet and IP services over their optical plants. In the critical residential market, applications such as voice-over-IP (VoIP), video-on-demand (VOD), CMTS aggregation and transport, data usage for work and entertainment and home networking, etc., continue to explode as consumers take full advantage of high-speed cable modem and digital set-up box services. At the same time, the Web has created opportunities for enterprises to increase productivity and expand market presence, as well as heightened competitive pressures. As enterprises continue to outsource their networking infrastructures and non-core services, such as optical LAN services, managed optical VPN services, managed hosting, wholesale Internet access, etc., broadband service providers are well-positioned to capture these new revenue drivers, the fastest growing market sector today. Regardless of their specific infrastructure requirements, both the consumer and the enterprise need Optical Ethernet throughout LAN/ MAN/WAN. Optical Ethernet has extended LAN into a cost-effective, simple, yet robust technology for service delivery on a global scale. It now stands to do the same for MAN and WAN.

Ethernet in broadband service offerings continues to gain importance as it breaks new ground as the key technology for service providers to expand LAN services to the MAN and WAN. Ethernet, the dominant protocol in LAN, is firmly entrenched because of its simplicity, its favorable price and its value proposition. Ethernet is connectionless and possesses the capability for seamless growth through low-cost and hardware-based switches. Through dynamic bandwidth sharing, Ethernet interoperates effortlessly with widespread IP traffic of the data-concentrated applications of today.

Figure 1:  Service provider challenge and opportunity.

As more companies deploy Gigabit Ethernet and 10 Gigabit Ethernet emerges in the market, the role of Ethernet becomes even greater. Long considered a LAN/enterprise technology, Ethernet is poised to be the reliable, cost-effective and speedy workhorse of service provider networks for the MAN/WAN as well. But the MSO must provide cost-effective Ethernet services in the MAN/WAN while providing the carrier-class infrastructure that end-users demand. Optical Ethernet gives the MSO a native end-to-end Ethernet network that can unify its service delivery infrastructure for both residential and enterprise.

As bandwidth demands continue to surge, Optical Ethernet solves the access/metro bandwidth bottleneck that dominates the MSO network today. These demands impact all parts of the network, from access layers to the MAN to the backbone. Dense Wavelength Division Multiplexing (DWDM) dramatically increases available capacity in backbone and long haul networks and Gigabit Ethernet becomes the choice for the residential and enterprise networks.

Figure 2:  Today's metro network.

However, lower bandwidth connections still dominate the metropolitan and access/collector networks. Metro networks, and in turn, the access networks, need upgrading to eliminate the bandwidth bottleneck between the metro/access and long haul/backbone networks. Many consumers have reached their limits of tolerance with their current "up to 56K modems" and are moving toward 1 Megabit services. Businesses are upgrading their LANs to Fast and Gigabit Ethernet and looking to extend these services at native rates into the MAN/WAN. The true complexity begins when interconnecting these LANs across the MAN/WANs.

The traditional data transport architectures available to the service provider come in many flavors. Service providers have used Sonet and ATM for many reasons, including scalability, reliability and standards maturity. IP traffic can be mapped onto Sonet or ATM virtual circuits using well-known protocols such as packet-over-Sonet (PoS) that overlay TDM-based optical data networks. Although these approaches maintain certain advantages, they suffer from a drawback in the process of managing Layer 2 services across conventional Layer 1 WAN networks.

These implementations have the inherent drawback of a "leased line" view of transport facilities. Bandwidth, allocated in terms of circuits, must be predetermined and remain relatively static. When new nodes are provisioned on this type of architecture, it requires extensive traffic engineering, which causes operational costs to soar. As traffic enters the MAN in the form of leased pipes at a DS-1/3 or OC-3/12 granularity, this mapping of dynamic data traffic onto static, circuit-based optical connections results in extremely low bandwidth utilization, inefficiency and waste. This lack of granularity adds challenges to implementing anything above the simplest service level agreements (SLA). As real bandwidth demand continues to increase, fiber routes will exhaust and require costly capacity upgrades.

Figure 3:  Optical Ethernet with resilient packet ring.

Innovative service providers implement IP-based networks using Optical Ethernet. Service providers can build the network as Optical Ethernet over dark fiber, Optical Ethernet over Resilient Packet Ring (RPR), Optical Ethernet over DWDM, or a hybrid solution of these three architectures. The most robust solution involves creating virtual packet rings over Sonet infrastructures.

This approach, referred to as Resilient Packet Ring, is implemented by integrating Ethernet interfaces and capabilities on optical network elements (NEs). This allows all or part of a ring's bandwidth to be shared among all RPR-equipped NEs. This truly optimizes RPRs for carrying connectionless Ethernet frames in both point-to-point and multicast applications. As a result of deploying Optical Ethernet over RPR, MSOs can increase service velocity to their cable modem and enterprise fiber-based customers, since RPR-enabled network elements auto-discover their network topology and primary/secondary switching routes.

MSOs can also realize cost savings by not converting native customer premise Ethernet to ATM and TDM. Because the network needs of residential and enterprise customers are fundamentally different, Optical Ethernet over RPR can be provisioned with distinct tiered services for different QoS needs. The Standards Board of the Institute of Electrical and Electronic Engineers (IEEE) Standards Association has approved 802.17 to create a new standard for RPRs.

RPR protocol possesses many values, including bandwidth flexibility and utilization, scalable ubiquity, spatial re-use, statistical multiplexing, tunable bandwidth, auto-discovery capabilities and carrier class reliability. The combination of the simplicity of the Layer 2 cloud with the capacity, bandwidth efficiency and lower overhead protocol of the optical network provides RPR its greatest value. In effect, the entire optical ring becomes a distributed learning bridge, extending the LAN switching model to the MAN/WAN scale. The edge nodes of the Ethernet connection view the ring as a simple Ethernet segment. The RPR architecture remains unaffected by the Layer 3 protocol that may be employed, whether IP, Internet packet exchange, AppleTalk or other legacy protocols.

The sheer ubiquity of Ethernet provides advantages, as most of the installed LAN connections are already Ethernet. Optical Ethernet via RPR provides a scalable and flexible solution to connect these LANs. Without traditional routers in the path for enterprise intranet traffic, Ethernet bridging can be deployed transparently while supporting any protocol with very low latency and jitter. By providing Optical Ethernet over RPR, MSOs can provide native end-to-end Ethernet tunnels throughout an entire network, without packaging Ethernet, native to the end user, into much more complex ATM and TDM, and unpackaging it to Ethernet at the receiving customer premise.

MSOs with Optical Ethernet using RPR immediately see improvement in network performance to support VoIP and other latency/jitter sensitive applications. Furthermore, MSOs can establish an end-to-end SLA with a native Ethernet network due to the simplicity of networking processing within the network.

RPR also creates more efficient bandwidth utilization. As Ethernet frames arrive at the Network Element port, they are mapped to the portion of the ring bandwidth allocated for RPR service. TDM services with Sonet protection may use the remaining bandwidth with the automatic protection switching mechanism intact.

The RPR service employs its own failure recovery mechanism more suited for packet-oriented traffic. This Layer 2 protection scheme provides Sonet-like protection at less than 50 milliseconds. The Sonet bandwidth otherwise reserved for protection can be used for live traffic, which effectively doubles the bandwidth capacity without any traffic engineering. To the MSO, true Gigabit Ethernet connectivity can be established through an OC-12 channel using RPR versus traditional Sonet.

Figure 4:  Resilient packet ring (not just Ethernet over Sonet).

Bandwidth utilization is also more flexible with RPR. Optical Ethernet solutions allow flexible bandwidth management from the port level down to the packet level. Service providers can deliver bandwidth by demand with possible metro services scaling from 1 to 1000 million bits per second (bps) in 1 Mbps increments. Through the use of optical management software, service providers can provision guaranteed bandwidth as little as 1 Mbps with the ability to burst up to 10 Mbps. This allows for offerings to meet the momentary higher-bandwidth needs in addition to the budgeted needs of the customer. This creates flexible bandwidth offerings more closely aligned with the requirements of each customer, which in turn, creates efficiency and provides the service provider with a competitive edge. MSOs deploying with Optical Ethernet using RPR can now provide service to Fortune-100 companies with Gigabit Ethernet as easily as SOHO VPN customers requiring 1 Mbps. To cable modem subscribers, a flexible CMTS connection in the headend can ensure bandwidth availability as bandwidth needs increase.

RPR also enables scalable SLAs. The amount of traffic added or dropped at a given node is provisioned in 1 million bps increments and is based on the service level subscribed to by each node and customer. Four priority queues that map to IEEE 802.1p priority levels are provided. Thus, even within an Ethernet pipe, various service-level packages can be offered. Because RPR incurs much less network processing penalty in both latency and jitter than traditional Layer 3 routing, true end-to-end SLAs can be established with end users for various types of traffic. IEEE 802.1Q support allows the end user to divide traffic into Virtual LANs (VLANs). This allocation reduces the need for broadcasting frames around the entire network.

Spatial re-use provides another significant value proposition for RPR. A topology discovery protocol determines how many nodes exist in the ring and the shortest path to reach each of those nodes. Unlike Sonet, RPR will not lock out an entire ring for the duration of a transfer. The only portion of the ring used is the section between the source and destination nodes. This feature allows simultaneous transfers to take place between other nodes on the ring. Unlike some traditional MAN solutions that do not remove the packet from the ring until it reaches the originating source node, packets are extracted from the optical ring once they reach the destination node. This capability effectively increases the capacity of the optical ring bandwidth by several levels. Spatial re-use dramatically increases the efficiency of the ring operations, reduces complexity and maintains Sonet's carrier-class reliability.

Another prominent feature of RPR protocols revolves around the transportation of data for multiple customers in a single Sonet payload envelope. Point-to-any-other-point connectivity is achieved by deploying metropolitan optical rings for the physical transport layer with the customer premises as part of the ring. This allows for the statistical sharing of optical bandwidth among different data groupings, achieving a cost-effective implementation of virtually meshed networks. This also eliminates the exploding requirement for private lines or private virtual connections through the traditional MAN architectures. A single Ethernet port replaces the T-1/3s that enterprises have used for WAN connectivity. At the same time, TDM and ATM-based voice and video traffic can be multiplexed into the same Sonet payload envelope while maintaining the deterministic service requirements of these offerings. This statistical multiplexing offers another important role in efficiency of the Optical Ethernet system.

In summary, the demand for a variety of data services in the MSO environment of today provides opportunity for the service providers to increase both their revenues and customer base by offering granular and true multi-tiered services to residential and enterprise customers. Optical Ethernet and the use of RPR technology allow native Ethernet connectivity over optical networks without converting to a less efficient protocol such as ATM and TDM. Optical Ethernet alleviates the access bandwidth bottleneck between today's enterprise LANs and backbone networks by leveraging the simplicity of Ethernet with the reach and reliability of optics. This allows the cable operator/service provider to cost-effectively implement and operate a flexible and scalable MAN, while still addressing the needs of residential and enterprise customers.