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UBR + MCR A unique Cisco class for best−effort data traffic
delivery with a specified minimum bandwidth. This
class is used in a LAN for high−end resource
applications or in a WAN with an ATM for a
guarantee of a certain amount of bandwidth (also
called a committed information rate [CIR]).
One of the great features of the LightStream 1010 switch is its ability to use the same interface modules as the
Cisco Catalyst 5500 series of switches. This feature allows the LS1010 to be controlled in the same way as the
Catalyst 5500 series, with the AtmDirector, CiscoView, and CiscoWorks for Switched Internetworks (CWSI)
software available from Cisco.
LightStream 2020
The LS2020 is one of Cisco’s most powerful LAN, WAN, backbone, campus, and multiservice−type ATM
switches. This switch offers cost−effective bandwidth coupled with superior QoS handling in the network.
Several other features make this switch a perfect solution for ATM: This switch works well with existing
devices and will scale well with future technologies and applications. The switch supports not only ATM but
also fastpacket switching applications, which means that it can support Frame Relay, circuit emulation, and
LAN technologies such as Fiber Distributed Data Interface (FDDI) and Ethernet.
Switching and communications on the LS2020 are performed at wire speed, so no noticeable latency is caused
by the switch processor or the Application−Specific Integrated Circuits (ASICs) used to switch data traffic
from one interface to another. Processing tasks are handled by three components based solely on the speed
required for each task. Let’s take a look at these three components:
Line card—Used when a particular function must be completed in a tenth of a millisecond or less.
Such functions include implementing traffic policies and cell forwarding.
•
Line card control processor—Performs complex tasks that must be completed in a tenth of a
millisecond or less. These functions include interface management, error handling, and line−up and
line−down protocol processing.
•
Network processor software—Performs less critical processing that can be handled in more than a
tenth of a millisecond, such as cell processing and network management request processing.
•
The LightStream 2020 processor card is shown in Figure 9.3.
Figure 9.3: The LightStream 2020 processor card.
The LS2020 switch can use a software package called ControlStream, which is a traffic management
application used to control data traffic. This software allows very high line utilization while at the same time
maintaining users’ QoS guarantees. ControlStream software employs congestion avoidance and traffic control
techniques that allow network links to operate at high levels of utilization by scaling back data that has a
much lower priority, including data traffic that is tolerant to traffic delays in the network. As a result, traffic
selection can occur at congestion points in the network.
The LightStream 2020 uses an internal routing mechanism to provide a path through an ATM virtual channel
connection (VCC). These routing mechanisms allow the LS2020 network to provide paths through permanent
virtual connections (PVCs) and switched virtual connections (SVCs). Through these virtual connections, the
LS2020 supports synchronous connections over ATM user−network interface (UNI) PVCs, Frame Relay
PVCs, and circuit emulation PVCs. The switch also provides connections over physical LAN medias such as
Ethernet and FDDI.
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