IP switches deliver broadband over cable
By Holland Young
Network World, 05/06/02
Today's broadband options include standard T-1 services, DSL or access to Ethernet-based metropolitan-area networks. T-1 services can be pricey, DSL isn't available everywhere, especially if your location is too far away from the central office, and metropolitan Ethernet is limited to major cities. A new technology is making it possible for companies to obtain dedicated, IP-based broadband connections over standard coaxial cable lines.
Typical cable networks have several limitations that make them unsuitable for corporate access. Bandwidth is shared among end users, which means service slows drastically during periods of peak usage. The cable architecture also forces each user to wait for permission to transmit, causing latency that is problematic for telephone conversations, video transmissions or other real-time services. Until now, cable operators could only offer "best-effort" service in the 1M to 3M bit/sec range, which may be a reasonable solution for home users, but corporations depend on reliable, robust connectivity to enable routine daily business communications.
The one advantage of cable is that the hybrid fiber coaxial (HFC) network is ubiquitous in the U.S. During the past few years, operators have upgraded their HFC networks, reducing the number of customers on a given fiber node, improving performance and increasing bandwidth capability.
In combination with the upgraded HFC plant, new technology lets cable operators provide dedicated bandwidth to each enterprise subscriber. With this system, each company is allotted its own switched, dedicated IP connection that is scalable from 5M to 40M bit/sec downstream and 500K to 8M bit/sec upstream. As bandwidth is "locked up" for each user, it is available to that user in the same manner that a T-1 is dedicated to a user 24 hours a day, 7 days a week. The dedicated IP channel system consists of an IP switch router located at the cable system head-end facility and a gateway IP router located at the customer premises. This requires no changes to the HFC network and therefore no capital expenditures to pass on to the subscriber.
The heart of this service delivery platform is the switch router that resides at the cable system head end. The device interfaces with the cable system routers and switching systems for data, voice and video services via Gigabit Ethernet. From there, it delivers IP packets over the cable plant to enterprise subscribers utilizing Quadrature Amplitude Modulation.
At the enterprise location, an access gateway demodulates the transmissions and extracts the IP packets, delivering them to users via 100Base-T Ethernet. The system is designed to support Internet access and all WAN traffic, including e-mail and mission-critical applications.
The switch router provides IP quality of service (QoS) and traffic management capabilities based on industry-standard mechanisms such as Differentiated Services and Multi-protocol Label Switching. Because the switch router combines IP QoS with a transport technology that provides deterministic bandwidth between network and customer premises, there is no need to implement latency-causing extensions that focus on arbitrating shared bandwidth. By leveraging the Internet Engineering Task Force QoS standards, traffic flows are handed off seamlessly from the backbone to the network edge, across the last mile and to the customer's physical interface using a common QoS signaling protocol.
With this level of bandwidth, enterprise services such as videoconferencing, remote security monitoring, off-site backup, VPN and voice-over-IP service are possible. Dedicated bandwidth eliminates the latency inherent in contention-based architectures, improving QoS and en-abling telephone-company-grade service-level agreements. Network reliability is maintained, as the switch router is a carrier-class design with 99.999% reliability, including automatic failover to standby modules.
Bandwidth is also dynamically scalable by the operator at any time and can be increased up to 40M bit/sec to match the changing needs of enterprise subscribers. |
