ciena, Cisco link for optical networking
By STEPHEN HARDY
Declaring that circuit-switched networks will soon be obsolete, Cisco Systems Inc. (San Jose, CA) and ciena Corp. (Linthicum, MD) have joined to develop optical network architectures optimized for packet- and cell-based data traffic. The partnership envisions networks in which data switches and routers with OC-48c (2.4-Gbit/sec) interfaces deliver such traffic directly to the optical layer via dense wavelength-division multiplexing (dwdm) equipment.
The high-speed interconnections that the two companies envision will mean that the Synchronous Optical Network (sonet) multiplexers now common in today`s telephony-based networks will become increasingly unnecessary. "You`re going to see atm switches go directly to the glass through dwdm without touching sonet muxes," predicts Dennis Bilter, ciena`s director of marketing. "You`re going to see that with IP routers [as well]."
The result will be significant savings in equipment and more-efficient networks, the companies predict. In fact, Graeme Fraser, vice president and general manager of Cisco`s isp Business Unit, predicts that optical networks using packets or cells could be configured at a cost 10 times smaller than a comparable architecture based on circuit-switched time- division multiplexing.
The initial manifestation of this new network arrangement will see the Cisco 12000 Gigabit Switch Router interface directly to ciena`s dwdm equipment via an OC-48c interface that Cisco announced at the same time as the partnership (see figure on page 1). In the future, the two firms plan to support atm interfaces and define new interfaces between the data and optical layers. Some of this work may funnel through the Optical Internetworking Forum, a new industry group the two companies have founded to address optical networking issues (see "Forum to address open optical networks" on page 21). Meanwhile, Cisco plans to unveil an OC-192 (10-Gbit/sec) interface for the router late next year.
Bilter and Fraser say the new strategy reacts to the impending dominance of data services in the traffic mix carried by transport networks. Today`s topologies, which emphasize circuit-switching and time-division multiplexing (tdm), worked fine when lower-speed voice traffic predominated. But the new traffic paradigm will call for new infrastructures.
"Clearly, the tdm sonet systems were really designed for much lower levels of granularity, where they really added a lot of value," explains Fraser. However, "if you`re just simply multiplexing up a few signals at OC-48c, optical provides, I believe, a more cost-effective way of doing that. Because you`re not trying to break it down below OC-48 [2.5 Gbits/sec]."
With even higher speeds on the horizon, the advantage of optical networking becomes more pronounced, Bilter says. "The OC-48 stuff is coming out now. When they make the next jump up, to 10 Gbits/sec, what`s the point of sonet muxes? There is no point," he asserts.
Whither sonet?
While the companies` optical networking strategy removes sonet multiplexers from the high-speed network equation, sonet technology itself remains important in the early evolution of optical networks because of its ability to provide performance monitoring and restoration. "On our interface, we actually use sonet framing," Fraser concedes. "We believe that there`s such an installed base of sonet knowledge, test equipment, and procedures set up for that, that it makes sense to leverage that."
"You obviously are not going to delete one whole layer of the network by the stroke of a pen," agrees Bilter. However, the role of sonet will change, he feels, as carriers differentiate between voice and data transmission. "I would suspect what you`re going to start seeing is voice traffic being carried on sonet just like it is today--but I think you`re going to start seeing a lot of the data services and data traffic being put on [the optical-internetworking] type of solution."
With the traffic load moving toward data, sonet solutions that include the technology`s traditional multiplexing function will be pushed toward the edge of the network. "I think there`s still a lot of life in sonet in terms of access aggregation," offers Fraser.
There is also a lot of life in sonet as part of Cisco`s product strategy. "We`ll continue as internetworking providers doing more and more sonet integration into our internetworking platforms, to allow them to work seamlessly with sonet infrastructure. That includes aps [automatic protection switching] and protection schemes. It includes integrating some of the multiplexing functions so that we can have a single connection into a sonet infrastructure as opposed to having multiple lower-speed channels."
It also includes continued support for the company`s packet-over-sonet approach to transporting Internet protocol (IP) traffic across sonet-based networks. Both the IP routing scheme and the optical internetworking initiative are rooted in sonet framing, Fraser points out.
This integration of sonet into its products is part of Cisco`s five-phase strategy to bring optical internetworking to both the high and low ends of data-network architectures. The first phase involved the introduction of such high-speed platforms as the 12000 Gigabit Switch Router and the Cisco 8000 wide area networking product. The OC-48c interface and the partnership with ciena represent the second phase, in which these platforms interface directly into the optical layer. In the third phase, Cisco will continue to integrate sonet functions into its platforms, with an eye toward markets where dwdm may not be required. Phase 4 will see the company attack these markets, particularly interoffice and metropolitan applications. The fifth phase will see the company attempt to extend optical internetworking to the level of the business user at the edge of data-oriented network infrastructures.
Thus, while the company may see dwdm as the door to backbone transport networks, it will not be joining with ciena to push the technology into metropolitan applications. "For people who have access to a lot of fiber in the metro area, WDM may not be the most appropriate choice," says Fraser. "Instead of needing to use multiple wavelengths, they can just pick up multiple pieces of fiber. One of our directions is also to put long-reach optics [in Cisco`s platforms] and drive, in the metro and regional area, fiber directly for those customers." Thus, the upcoming OC-192 interface will not only enable Cisco equipment to keep pace with greater transport backbone speeds, but will allow the company to provide interoffice and metropolitan customers high capacity without resorting to dwdm.
These customers, particularly competitive local exchange carriers, are looking to extend data services to customers, says Fraser, but have had trouble getting existing point-to-point sonet infrastructures to work efficiently because of the "bursty" nature of data traffic. Optical network infrastructures that feature statistically multiplexed packets or cells offer an alternative, Cisco believes.
"I think there`s a challenge here over time to move to a slightly new mindset, which is away from a dedicated point-to-point connection to one that is statistically multiplexed right out to the edge," says Fraser. This change in thinking may already be under way. "Frame relay has done a good service there in the sense that it is one of the fastest-growing data services, apart from the Internet. And I think people are coming to grips with the notion of a statistically multiplexed infrastructure providing them with a minimum amount of bandwidth and then being able to burst up to much higher rates at very reasonable prices," Fraser reasons. q