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ATM-focused supplement to Packet Magazine
Volume 1 Number 1, Second Quarter
While Asynchronous Transfer Mode (ATM) offers great advantages, not all ATM implementations are created equal. The challenges inherent in the management and control of traffic congestion, bursty LAN environments, and migration from the predominant shared-media networking paradigm are not trivial. The Cisco Systems LightStream[tm] 2020 enterprise ATM switch provides the advantages -- and meets the challenges -- of the migration to switched internetworking environments that are based on Asynchronous Transfer Mode (ATM).
ATM enterprise switches play a pivotal role, performing at the core of large-scale networks. These devices differ sharply from workgroup ATM switches by meeting the following requirements:
The LightStream 2020 enterprise ATM switch addresses each of these points with its innovative architecture and advanced ATM functionality.
LightStream (TM) 2020 enterprise ATM switches operate at the core of ATM networks
With ATM cell throughput of 3.2 million cells per second, Fiber Distributed Data Interface (FDDI) forwarding at the rate of 1.53 million packets per second, and Frame Relay throughput of 126,000 frames per second, the LightStream 2020 offers more than enough bandwidth to build campus backbone networks and public or private WANs.
Achieving high utilization rates without congestion requires powerful and sophisticated traffic management capabilities. The LightStream 2020 uses ControlStream traffic management, a set of advanced quality-of-service and congestion avoidance capabilities, to achieve utilization rates that otherwise would be unattainable.
ControlStream's quality-of-service functions allow network managers to guarantee bandwidth and assign high queuing priorities to mission-critical or time-sensitive traffic flows. Less demanding flows are allotted bandwidth on an equitable, as-available basis, so that all traffic types get the service levels they need.
Another way that the LightStream 2020 avoids congestion -- and the resulting data loss and retransmission -- is through the Early Packet Discard mechanism, which regularly reports trunk utilization rates to the edge of the network, thereby allowing the switch to detect congestion points before they become critical. When congestion begins, the ControlStream application reports the problem, then limits excess traffic at the edge of the network. Using Early Packet Discard, the switch drops entire packets before they can enter the network, rather than allowing just cells to drop. If a switch drops just one cell out of a 30-cell packet, it must retransmit all 30 cells. Early Packet Discard prevents this waste of time and bandwidth by enabling the LightStream 2020's intelligent LAN interfaces to retain the packet until there is enough bandwidth available. This self-regulating congestion-avoidance mechanism results in extremely high utilization without any degradation in quality of service.
The LightStream 2020 provides the reliability and versatility crucial for switching engines at the core of large, mission-critical internetworks. Redundant components on the LightStream 2020 include power, switching, network processors, and automatic rerouting around trunk failures to prevent downtime and avoid the risks associated with single points of failure.
The bursty nature of LAN traffic causes huge variations in throughput requirements for ATM switches. One solution to this problem is to provide buffers for the excess traffic. However, the way that buffers are configured and deployed can have a significant impact on overall system price and performance. Simply adding enough buffers to each port to handle the anticipated maximum throughput is very expensive and can create a situation in which delay-sensitive traffic is buried in very large buffers, denying it adequate quality of service. The LightStream 2020 uses a unique "elastic buffers" architecture to resolve these issues. For example, an eight-port line card has a dedicated buffer of 4000 cells -- but it also has a large buffer pool of 32,000 cells that can be shared dynamically among all ports on the card. Thus, each port has a minimum buffer of 4000 cells available at any time, and a virtual buffer of 36,000 cells for peak periods. No port is ever completely without buffering, and every port can accommodate extremely large traffic bursts. To keep delay-sensitive traffic from getting "buried," the LightStream switch has input and output cell processors to determine the priority levels of various traffic types and ensure that traffic entering the network connection is duly prioritized.
The LightStream 2020 provides an unparalleled degree of service integration, together with a wide range of LAN and WAN interfaces to connect to existing networks. While it can act as a pure ATM switch, it also provides FDDI and Ethernet switching capabilities. Thus the LightStream 2020 can serve as an immediate, high-powered switching solution for end-to-end ATM, or as a scalable migration path to ATM using today's LAN environments.
The LightStream 2020 rises to the challenges facing IS professionals in enterprise networking -- reducing total cost of ownership, increasing reliability and performance, as well as providing excellent functionality for core ATM enterprise internetworks. It reduces costs by minimizing recurring leased-line charges. The ability to intermix all types of traffic -- including data, voice, and video -- onto a single leased line allows the LightStream 2020 to amortize costs more efficiently. In addition, it can keep utilization rates as high as possible on each leased line, so users pay only for the leased-line capacity they need. A LightStream-based network can achieve 90 percent utilization rates and still provide the quality of service demanded by even the most demanding application types.
The LightStream 2020's unique architecture is based on four key elements: a concurrent cell-switch matrix, a network processor, function cards, and access cards. This scalable design provides hardware-based switching, ATM connection routing, cell buffer management, ATM adaptation, and data-link bridging -- which give users the power and performance they need, plus the scalability required for growing networks.
The concurrent cell-switch matrix implements a low-latency crosspoint in hardware for extremely high-performance enterprise switching. The network processor and function cards perform hardware-based bridging internetworking services, including Institute of Electrical and Electronic Engineers (IEEE) 802.1d (spanning tree) and 802.1h (translational) bridging and IP fragmentation on Ethernet and FDDI. Future releases will enhance these features and bring new interfaces and services. The fourth element, the access cards, mate function cards with the desired network types.
Through powerful, graphics-based system management and configuration capabilities, the LightStream 2020 takes on the real world of heterogeneous networks that incur frequent topology changes. StreamView, a graphical network management application written for the HP OpenView platform, offers powerful tools for configuring and monitoring a LightStream ATM network.
Cisco's LightStream 2020 ATM enterprise switch provides a key enabling technology for the migration to the ATM future. The blueprint for that migration is the CiscoFusion[tm] architecture for switched internetworking, which specifies ATM as the ultimate building, campus, and enterprise backbone. The LightStream 2020 switch's ability to intermix multiple traffic types and still provide the quality of service demanded by each makes it the ideal ATM engine for core support of large numbers of disparate LAN and WAN types.
With its large and growing collection of integrated interface engines, the LightStream 2020 switch provides a smooth migration path from today's shared-media networking paradigm to the coming future of switched internetworking. The LightStream 2020 has solidified Cisco's leadership in today's transitional networking environment, where an ATM core with high performance, scalability, and sophisticated traffic management is a critical component in successful building enterprise-wide networks.
To highlight the different roles these products play, LAN interfaces on a LightStream 2020 might be used to connect an existing Ethernet or FDDI backbone to a new ATM backbone. But only a router that supports ATM, such as the Cisco 7000, can perform such diverse tasks as routing AppleTalk across an ATM backbone, filtering traffic from a public ATM network to allow e-mail but block file transfers, and connecting an IBM mainframe channel to an ATM network. Note that the LightStream 2020 can act as a pure ATM switch or a hybrid Ethernet or FDDI switch, leading many organizations to use the LightStream 2020 today as a migration path from shared LANs to ATM backbones.
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