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This chapter introduces the LightStream 2020 multiservice ATM switch (LS2020 switch). It describes the structure of the LS2020 switch and presents some of its key features.
The LS2020 switch is a powerful backbone, multiservice ATM switch for local and wide area networks. As an integral part of Cisco Systems' product offerings, the LS2020 has capabilities in both ATM and fast packet switching processing, enabling it to handle Frame Relay, circuit emulation, and LAN traffic interfaces. In addition to its ATM capabilities, the LS2020 switch provides FDDI and Ethernet switching that can be easily converted to ATM. Using the LS2020 switch as a basic building block, you can create a mission-critical enterprise backbone network that provides flexible and cost-effective allocation of bandwidth, guaranteed quality of service for all running applications, interoperability with past and future devices, and scalability for future networking applications.
The LS2020 switch interoperates with Cisco Systems' family of internetworking products and can be combined with the LightStream 100 and Cisco ATM NIC cards to form an end-to-end ATM network. With the LS2020 and other Cisco Systems internetworking products, you can have end-to-end networking solutions, regardless of the type of internetworking technology you select.
Recent advances in computers and communications have begun to overburden existing network systems and technologies. For example, today's network link speeds continue to grow. In the 1970s, 1.2 kilobits per second (kbps) was considered normal speed, and 9.6 kbps was considered high speed. In the 1990s, networks using fiber optic technology are reaching speeds of 100 megabits per second (Mbps), and significant speed increases are expected in the future. Also, widespread use of applications that demand large amounts of data have overburdened existing LAN/WAN technology. These applications include distributed supercomputing, high-resolution graphics (CAD/CAM, imaging, and so on), scientific visualization, network-based client/server computing, and distributed file access.
Such advances have created the need for new network architectures and infrastructures that provide higher throughput, more usable bandwidth, and a broader range of services. The LS2020 switch was designed with these needs in mind.
In addition to being based on ATM technology, the LS2020 switch has several features that make it a reliable, cost-effective means for high-speed, broadband, open networking applications. These features are discussed in the following sections.
Most LS2020 switching and communications functions are performed at wire speed in application-specific integrated circuits (ASICs) designed specifically for and built into the LS2020 chassis. Thus, the hardware and firmware of the LS2020 eliminate much of the overhead involved when communications functions are software-based.
The entities that perform processing tasks for the LS2020 switch are divided into three general classes, based on the speed required for the task:
Today's networks feature a wide variety of applications, each with its own performance requirements. One application may need a level of service in which cell delay variation must be minimized (voice applications, for example). Another application may require service that is more cost-effective, but not as delay-sensitive. The LS2020 switch optimizes application performance by providing services appropriate to the application.
LS2020 switches provide cost savings by minimizing the transmission bandwidth needed from carriers. The extent to which an ATM switch lowers carrier costs depends primarily on the switch's congestion avoidance strategy. The LS2020 allows very high line utilization while maintaining user service guarantees.
For example, the LS2020 switch uses ControlStream, a congestion-avoidance mechanism that manages congestion by controlling traffic at the edges of the network. When an LS2020 network detects congestion, the causes of the congestion are identified and controlled individually, based on user service guarantees. Thus, congestion is eliminated at the source, link use is maximized, and mission-critical service is maintained.
The LS2020 switch provides the following mission-critical features:
You manage an LS2020 network using StreamView, which is an SNMP-based network management application that runs on a Sun SPARCstation. This Sun workstation is commonly referred to in LS2020 user documentation as the network management system (NMS). StreamView allows you to configure, monitor, and control a network of LS2020 switches. StreamView provides you with a graphical representation of your managed objects (a view of network topology) and a mouse-driven point-and-click interface.
In addition to StreamView, you may choose to run HP OpenView management software on your NMS, or you can use another network management system that is SNMP-compatible. You can perform a variety of management tasks using a simple command line interface (CLI) from a terminal attached to the console port of an LS2020 switch.
For more details on network management, see the section "Network Management Tools" in the chapter entitled "Network Management."
An LS2020 network provides a very clear migration path to ATM. The LS2020 switch is designed to let you easily migrate to ATM using your existing equipment. The LS2020 provides services that make it backward compatible with any current equipment that passes constant bit rate (CBR) traffic, Ethernet, FDDI, High-Level Data Link control (HDLC), Synchronous Data Link Control (SDLC), or Frame Relay traffic. In addition, the LS2020 switch can accept such traffic from an external device, convert it to ATM cells, and pass it through the network.
The LS2020 switch also accepts ATM cells from an external device and passes the cells through the network. The switch provides services that allow it to interface with equipment that supports ATM user-network interfaces (UNIs) and SONET interfaces. As more ATM devices become available, you can add them to your network without disrupting existing operations.
Due to the need for greater integration, an LS2020 network offers various services to carry traffic over the network. These services include the following:
The LS2020 also offers VirtualStream, a LAN internetworking feature that allows you to do the following:
The LS2020 switch is based on industry standards, allowing it to interoperate with standards-based, high-speed networking devices. The LS2020 switch adheres to the ATM specifications being developed by ITU-T, ANSI, and the ATM Forum. The LS2020 switch also complies with the SNMP specification, enabling it to be managed by any SNMP-compatible network management application.
The LS2020 switch conforms to all the standards listed in Table 2-1; however, not every detail of each standard has been implemented. Compliance with standards ensures that LS2020 switches can interoperate with a wide range of network devices.
| Document Number | Title |
|---|---|
| ANSI T1.403 | ATM UNI DS1 interface |
| ANSI T1.618 (LAP-F) and ITU-T Q. 922 Annex A | Frame Relay (for Frame Format) |
| ANSI T1.617 Annex D and ITU-T Q.933 Annex D | Frame Relay (for LMI1 and PVC management) |
| ANSI T1.627-1993 B-ISDN | ATM Layer Functionality and Specification |
| ANSI T1.606 and ITUT-T I.233 | Frame Relay (for UNI) |
| ANSI X3T9.5 | FDDI Standard for I/O interfaces |
| ATM Forum UNI Specification V2.0, 3.0, 3.1 | ATM UNI Service |
| FRF.2 | Frame Relay (for NNI) |
| IEEE802.1g | Translation Bridging |
| IEEE802.3 | Ethernet |
| IEEE802.3 | Fiber Ethernet (for 10Base-FL) |
| IEEE802.1d | Spanning Tree Protocol |
| ATMF94-003397 | Circuit Emulation Service |
| Internet RFC #1157 | Simple Network Management Protocol |
| Internet RFC #1213 | Management Information Base (MIB-II) |
| Internet RFC #1248 | Ethernet Interface Type MIB |
| Internet RFC #1406 | DS1/E1 Interface Type MIB |
| Internet RFC #1407 | DS3/E3 Interface Type MIB |
| Internet RFC #1493 | Definition of Managed Objects for Bridges |
| Internet RFC #1512 | FDDI Interface Type MIB |
| Internet RFC #1595 | SONET Interface Type MIB |
| ITU-T I.150 | BISDN Asynchronous Transfer Mode Functional Characteristics |
| ITU-T I.311 | BISDN General Network Aspects |
| ITU-T I.361 | BISDN ATM Layer Specification |
| ITU-T I.363 | BISDN ATM Adaptation Layer (AAL) Specification (AAL 5 only) |
| ITU-T I.371 | Traffic Control and Congestion Control in B-ISDN |
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Figure 2-1 shows the key components of an LS2020 switch.
The LS2020 architecture includes the following major elements:
Together, these modules provide the functions needed to receive frames, bits, or ATM cells from external devices and transfer ATM cells across a network.
The following sections describe these modules.
In an LS2020 switch, the concurrent cell switch module consists of a switch card and a console/modem assembly. The switch card contains the concurrent cell switch, which interconnects all interface and NP modules. The console/modem assembly provides the physical interfaces for the console and modem ports on the switch card.
Figure 2-2 shows the architecture of the concurrent cell switch module.
In a concurrent cell switch, each interface module or NP module is interconnected with every other interface module or NP module through a concurrent cell switch that allows multiple transactions to occur among all modules simultaneously.
The use of many parallel paths allows the aggregate throughput of an LS2020 switch to be extremely high, without requiring that the speed of each individual interface match the aggregate speed.
The concurrent cell switch on the switch card has ten input ports and ten output ports. Each output port has two channels to reduce the probability that data passing through the switch will be blocked. The total bandwidth on each port is 200 Mbps in full-duplex mode. Allowing for cell headers and switch contention (more than two switch input lines contending for the same output line), this bandwidth capability provides a sustained payload throughput of approximately 160 Mbps in full-duplex mode. All switch ports can pass traffic simultaneously, resulting in a peak transfer rate of 2 Gbps and an aggregate sustained payload throughput of 1.6 Gbps.
The NP module contains an NP card and an NP access card. The NP module supports RouteStream, a highly sophisticated distributed network routing protocol.
NP tasks include the following:
The NP access card houses an Ethernet interface for the NP module, making it possible for a network management station to attach to the LS2020 network that has no LAN interface modules. Each NP module also has an associated disk assembly. The disk assembly contains a floppy disk drive and a hard disk drive. The floppy disk drive is used to load new NP and interface module software. The hard drive contains operational software, boot and configuration information, and storage for statistics.
Two types of interface modules are present in an LS2020 switch:
LS2020 switches carry traffic received from external devices in frames, ATM cells, or constant bit rate streams. If the traffic is in frames, the edge module parses incoming frames and determines the connection on which the traffic should be sent. The edge module segments the frames into ATM cells and transmits the cells across the LS2020 network. The edge module also reassembles ATM cells received from the LS2020 network into the original frames and transmits them from the edge interface to external devices.
If the traffic from external devices is in ATM cells, the edge module examines incoming cells and determines the connection on which the traffic should be sent. It then transmits the cells across the LS2020 network; no cell segmentation or reassembly is needed. The edge module also receives ATM cells from the LS2020 network and transmits them from the module to external devices.
If the traffic is a constant bit stream, the edge module segments the stream into cells. The edge module also reassembles the cells into the original bit stream (preserving the original bit timing) and transmits the stream from the edge module interface to external devices.
Each edge module contains an onboard control processor that works with the NP to set up new connections and provide low-level information required by the network management system.
The edge modules for the LS2020 switch are as follows:
Trunk modules connect one LS2020 switch to another LS2020 switch to form an LS2020 backbone network. All traffic passed between trunk modules is packaged as ATM cells. The trunk module receives cells from a trunk line, recognizes the connection on which the cells arrived, and routes the cells to the next LS2020 switch in the connection.
The trunk modules for the LS2020 switch are as follows:
The Test and Control System (TCS) is a fully integrated, yet autonomous, computer system within the LS2020 chassis. A TCS microcomputer is located on each NP, interface, and switch module in an LS2020 chassis. The TCS communications path is completely separate from the LS2020 switch. As long as the TCS components have power and are themselves operational, the TCS can function independently.
The TCS has two primary functions:
Figure 2-3 shows three LS2020 switches connected in an LS2020 network. As shown in the figure, external devices are connected to the LS2020 switches by edge modules, and traffic passing between the external devices and the edge modules is packaged as frames or ATM cells. Trunk modules connect LS2020 switches to each other. Traffic passing between LS2020 switches (or between any two cards within an LS2020 switch) is passed as ATM cells.
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