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The LightStream 1010 ATM switch is the Cisco Systems ATM switch for Enterprise and campus backbone deployment. Incorporating support for the latest ATM Forum specifications and building on Cisco IOS software, the LightStream 1010 ATM switch offers a comprehensive feature set together with the performance and scalability required for production ATM deployment.
This chapter provides an introduction to the LightStream 1010 ATM switch, and includes the following sections:
The LightStream 1010 ATM switch uses a five-slot, modular chassis featuring the option of dual, fault-tolerant, load-sharing AC or DC power supplies. The central slot (slot 2) in the LightStream 1010 ATM switch is dedicated to a single, field-replaceable ATM switch processor (ASP) module that supports both the 5-Gbps shared memory and the fully nonblocking switch fabric. The ASP also supports the feature card and high performance Reduced Instruction Set (RISC) processor that provides the central intelligence for the device. The remaining slots support up to four hot-swappable Carrier Modules (CMs). Each CM can hold up to two hot-swappable port adapter modules (PAMs) for a maximum of eight PAMs per switch, supporting a wide variety of desktop, backbone, and wide-area interfaces.
The LightStream 1010 ATM switch provides switched ATM connections to individual workstations, servers, LAN segments, or other ATM switches and routers using fiber-optic, unshielded twisted-pair (UTP), and coaxial cable.
The LightStream 1010 ATM switch provides the following software features:
The following interfaces are supported:
The following sections describe the implementation used by the LightStream 1010 ATM switch to switch cells on an ATM network:
All LightStream 1010 ATM switches are preconfigured with Cisco ATM address prefixes combined with the switch's preconfigured MAC address, generating a unique node identifier. These are used both to configure attached end systems and to automatically bring up the PNNI routing hierarchy, hence offering true plug-and-play operation. Such autoconfigured addresses suffice for a small peer group of a few dozen switches, permitting small-scale ATM internetworks to be deployed while allowing time for customers to obtain and allocate their own ATM address prefixes. If reconfiguration of addresses is required, mechanisms implemented on the LightStream 1010 ATM switch allow automatic address reassignment. This operation within the context of fully standard routing protocols is a unique capability of the LightStream 1010 ATM switch.
The LightStream 1010 ATM switch also automatically recognizes the type of PAM in a carrier module; if the new PAM is of the same type as the previous PAM, the switch will automatically restore any interface-specific configuration and PVCs saved to memory. Upon reboot, the switch also automatically restores all PVCs and any other configuration information stored within its nonvolatile memory. The LightStream 1010 ATM switch also uses the ILMI protocol to automatically recognize the nature of any new ATM interface---for example, whether it is a UNI or NNI, public or private interface---hence eliminating any manual configuration.
Such recognition and restoration mechanisms, when combined with such IP address autoconfiguration mechanisms as BOOTP, make the LightStream 1010 ATM switch fully self-configuring. Through network management applications or the text-based CLI, the network operators also can:
The LightStream 1010 ATM switch provides integrated support for ATM Forum-compliant UNI 3.0, 3.1, and 4.0 signalling. All mandatory elements of the UNI standards are supported, including the following optional features:
UNI signalling is also used by ATM end systems to inform LightStream 1010 ATM switches of the desired traffic characteristics and QoS for new connections and the acceptance or rejection of such connection requests. Fully integrating support for ATM signalling onto the ASP module ensures not only high performance, but also high reliability since no external signalling processor is required.
The LightStream 1010 ATM switch supports the routing of ATM signalling requests across a network of switches using ATM routing protocols. The ATM Forum has developed two standard routing protocols: static routing, as defined in the IISP protocol, and the PNNI routing protocol. The LightStream 1010 ATM switch supports both protocols.
The IISP protocol uses a combination of static routing and UNI signalling, and is more suitable for small networks of switches. See the section "ATM Signalling."
PNNI is based on a type of routing protocol called link-state routing. PNNI exchanges QoS routing metrics and attributes between all nodes, something that previous link-state routing protocols have not done. The metrics and attributes supported by the Cisco Systems PNNI implementation include the following:
Although the PNNI Phase1 protocol specifies the formats and types of information exchanged by the protocol, and PNNI signalling forwards signalling requests across the network, many other aspects of the protocol are left as a matter of implementation. The PNNI implementation on the LightStream 1010 ATM switch incorporates many value-added capabilities to extend beyond the base standards.
Both IISP and PNNI implementations on the LightStream 1010 ATM switch support crankback, which allows rerouting connections around nodes whose local CAC reject the connection, thus reducing setup latency. Link selection mechanisms allow for the support of redundant links, with either first-fit or load balancing selection algorithms.
The LightStream 1010 ATM switch supports the most advanced traffic management and ATM signalling and routing capabilities. In addition to ATM Forum-compliant ABR congestion control, the LightStream 1010 ATM switch supports the following mechanisms required to deliver QoS on demand to all ATM traffic classes and ATM adaptation layer (AAL) types:
Many of these capabilities are supported on the field-replaceable feature card on the ASP module. The LightStream 1010 ATM switch also supports the UNI signalling protocols and the ILMI, both required for full support of both signaled and permanent ATM connections (PVC/SVC). Soft PVC support facilitates PVC setup by using signalling protocols across the network; VP tunneling enables signalling across public networks.
The LightStream 1010 ATM switch supports guaranteed QoS for the CBR and VBR classes and best-effort for the UBR and ABR classes.
Since only UNI 4.0 allows you to explicitly specify both individual QoS parameters and request traffic classes, the LightStream 1010 ATM switch maps UNI 3.0/3.1 service classes into the appropriate UNI 4.0 class and parameter.
Sophisticated connection admission control (CAC) algorithms, based upon the particular architecture of the LightStream 1010 ATM switch, allow maximization of switch and link utilization, while precluding the possibility of violating preestablished guarantees. These algorithms, together with the ATM Forum specific generic CAC (GCAC) algorithm, permit the rapid, accurate determination of source routes across a network of LightStream 1010 ATM switches. User controls allow regulation of strictness or looseness of the CAC algorithm, providing either greater network utilization or stricter control over guarantees.
Once the traffic descriptor is derived, the source switch first performs a CAC function to determine whether local resources exist to support the requested connection. If this is positive, the LightStream 1010 ATM switch uses the PNNI 1.0 protocols to determine a source route through the network that its GCAC algorithms suggest is able to support the requested connection, and then forwards the request using PNNI 1.0 signalling. If and when the connection is routed through to the final destination, and is accepted, then the LightStream 1010 ATM switch completes the connection and informs the requesting end system.
In order to deliver such guarantees, the LightStream 1010 ATM switch implements the following four configurable levels of delay priority into which the various traffic classes are mapped:
By supporting so many levels of priority, the LightStream 1010 ATM switch can ensure full separation of the various traffic classes, and hence ensure absolute priority for the guaranteed services over the best-effort services.
The buffering of the LightStream 1010 ATM switch can be flexibly allocated between each of the traffic classes and output ports to ensure that the switch can be tuned for any particular traffic profile or deployment scenario. The following configurable buffer controls are available:
The maximum buffer controls on the service classes can be modified to adjust the oversubscription factor. This controls the degree of random multiplexing---and hence of the amount of effective buffering---within the switch fabric. Fixed minimum buffer limits preclude the possibility of buffer starvation where high priority traffic consumes all available switch buffers, leading to the possibility of head-of-line blocking.
In addition to using CAC, delay priority, and buffer controls to deliver QoS guarantees, the LightStream 1010 ATM switch also uses traffic policing, or usage parameter control (UPC), to monitor the compliance of ATM end systems to agreed traffic contracts. As per the ATM Forum UNI specification, the LightStream 1010 ATM switch supports a dual mode leaky bucket algorithm, a highly flexible algorithm that permits the automatic policing of the most important parameters for each of the traffic classes---for instance, the peak cell rate and cell delay variation of CBR connections, the burst size and sustainable cell rate of VBR connections, and the peak cell rate and burst size for UBR/ABR connections. Such traffic policing parameters are extracted automatically from UNI signalling and programmed into the switch fabric.
Cells found to be noncompliant by the UPC function with their stated traffic contracts can either be dropped or, if buffer resources permit, passed but tagged for preferential dropping by having their Cell Loss Priority (CLP) bits set to 1. Correspondingly, the LightStream 1010 ATM switch also implements two levels of CLP. A configurable threshold can be set on each of the per-service class port buffers; beyond the threshold the switch accepts only cells with the CLP bit not set, favoring conformance traffic. Cells with the CLP bit set to 1 are preferentially dropped. However, such cells, are not dropped arbitrarily, particularly for the best-effort services; dropped cells are selected by intelligent packet discard mechanisms of the LightStream 1010 ATM switch.
The ATM Forum UNI signalling protocols allow end systems to designate which particular connections carrying packet-based traffic are eligible for packet drop; the LightStream 1010 ATM switch interprets such signalling and automatically identifies the connections. These connections are typically used to carry traffic from protocols such as TCP/IP, which analysis has shown to yield far higher throughput in networks employing packet rather than cell-based discard policies. The LightStream 1010 ATM switch builds upon such analysis with its intelligent packet-discard mechanisms, ensuring that any event that might cause a cell drop---exceeded cell-tagging threshold, or buffer overflow---invokes the packet-dropping mechanisms.
When a cell-dropping threshold is exceeded for a cell of a particular packet flow, the LightStream 1010 ATM switch puts the associated connection into a tail-drop mode, dropping all the other cells that might arrive for that packet. The only cell that remains is the final cell in the packet, which is forwarded with the CLP bit reset to 0. This setting ensures that the cell reaches the final destination, and allows completion of any packet reassembly that may have started. A second, higher threshold is defined for each port buffer that defines the intelligent packet discard (PD) point. Beyond this threshold, the switch begins the discarding all packets along a particular connection, with future enhancements to allow for connections to be picked for discard based upon various policies (for example, highest volume) to increase fairness in throughput.
These mechanisms act together to make the LightStream 1010 ATM switch essentially emulate a packet switch such as a LAN switch or router, which also acts upon and drops entire packets. These packet discard mechanisms work closely with higher layer protocols such as TCP, which are designed to rapidly adjust packet flow rates in response to network congestion, as signaled by packet discards, or, conversely, rapidly increase packet throughputs so as to take advantage of network bandwidth availability.
The LightStream 1010 ATM switch can also go beyond current packet based mechanisms for greater scalability and faster network convergence, through its support of the ATM Forum available bit rate (ABR) congestion control mechanisms.
The ABR specifications define a series of congestion control mechanisms that switches and ATM end systems can use to regulate the amount of traffic sent across ABR connections, and hence minimize cell loss.
ABR is a sophisticated specification with multiple possible modes of operation, specifying the behavior of both source and destination end systems, and of intermediate switches. Source end systems periodically generate inline Resource Management (RMs) cells that are sent intermixed with data cells along all connections. These are then received by destination end-systems and returned along the backward connection to the source indicating whether or not intermediate switches had experienced congestion. Switches can indicate congestion in three ways:
1. In explicit forward congestion indication (EFCI) marking mode, switches can set a bit in the headers of forward cells to indicate congestion; these are then turned around at the destination and sent back to the source.
2. In relative rate marking mode, switches can set a bit within forward, backward, or both; forward and backward RM cells indicate congestion.
3. In explicit rate marking mode, switches can indicate within forward, backward, or both; forward and backward RM cells indicate exactly which rate they are willing to receive along a particular path.
The source end system uses specified algorithms to control the allowed cell rate (ACR) depending upon the type of feedback received. In general, this list of mechanisms is ranked in order of both sophistication and complexity. In general terms, EFCI marking, though widely available particularly on wide area switches, can give only minor improvements in performance because of the latency of turning around the forward congestion indication. As with any feedback mechanism, congestion control schemes operate optimally when the latency of the feedback path is minimized---indeed, excessive latencies can be counterproductive, since they might cause sources to slow down unnecessarily after the network congestion has already eased.
The LightStream 1010 ATM switch allows individual thresholds to be set for EFCI or Relative Rate marking, and a higher threshold for Early Packet and CLP discard. Any occasion on which a cell is dropped, however, including UPC, triggers the Tail Packet Discard mechanism. This intelligent packet discard, in which no cell is ever arbitrarily dropped, is a unique, patented capability of the LightStream 1010 ATM switch.
In addition to traffic policing and congestion control mechanisms, the LightStream 1010 ATM switch also supports a unique traffic pacing mechanism that allows the rate at which traffic is sent across a port to be limited to any of a wide variety of peak traffic rates. This capability is particularly important when connecting across a public UNI to a public network, since many such networks base their tariffs to a particular aggregate bandwidth. Future enhancements to the LightStream 1010 ATM switch, implemented on the next version of the feature card, will implement even greater traffic shaping capabilities, such as on a per-connection or virtual path basis.
The LightStream 1010 ATM switch has full support for ATM Operations, Administration, and Management (OAM) cell flows---F4 flows used within virtual paths and F5 flows used within virtual channels. The LightStream 1010 ATM switch can be configured either for end-to-end or segment loopback F4 and F5 flows; cells can be sent either on demand, or periodically, in order to verify link and connection integrity. Alarm indication signal (AIS) and remote defect indication (RDI) functions are also supported on both F4 and F5 flows.
In addition to the standard OAM functions, the LightStream 1010 ATM switch has the unique value added capability to send OAM pings (OAM cells that contain the ATM node prefixes or IP addresses of intermediate switches). This feature allows network administrators to determine the integrity of a chosen connection at any intermediate point, from any other point along the connection, hence greatly easing network debugging and troubleshooting.
The LightStream 1010 ATM switch provides an interface to switched LANs across an ATM network, providing LAN users with access to ATM-based services. LAN emulation extends virtual LAN (VLANs) throughout the network by establishing point-to-point ATM virtual circuit connections between switches on the same VLAN.
A LANE client or server can be configured for the ASP CPU for in-band management (Telnet and SNMP).
The LightStream 1010 ATM switch LAN emulation capabilities include:
Cisco implements classical IP and ARP over ATM as described in RFC 1577. RFC 1577 defines this application configured as a logical IP subnetwork (LIS). It also describes the functions of an ATM ARP server and ATM ARP clients in requesting and providing destination IP addresses and ATM addresses in situations when one or both are unknown. Cisco switches can be configured to act as an ARP client or ARP server.
The ATM ARP mechanism is applicable to networks that use SVCs in a pure PVC environment. It requires that a network administrator configure only the device's own ATM address and that of a single or multiple ATM ARP server into each client device. When the client makes a connection to the ATM ARP server, the server sends ATM Inverse ARP requests to learn the IP network address and ATM address of the client on the network. It uses the addresses to resolve future ATM ARP requests from clients. Static configuration of the server is required.
In Cisco's implementation, the ATM ARP client tries to maintain a connection to the ATM ARP server. The ATM ARP server can tear down the connection, but the client attempts once each minute to bring the connection back up. No error messages are generated for a failed connection, but the client will not send packets until the ATM ARP server is connected and translates IP network addresses.
For each packet with an unknown IP address, the client sends an ATM ARP request to the server. Until that address is resolved, any IP packet sent to the ATM interface will cause the client to send another ATM ARP request. When the ARP server responds, the client opens a connection to the new destination so that any additional packets can be sent to it.
The LightStream 1010 ATM switch may be configured as an ATM ARP Client to work with any ATM ARP server conforming to RFC 1577, or as an ARP server.
Since ATM is a cell-oriented transmission technology, circuit emulation services (CES) circuits in an ATM network must be emulated in order to provide required support for user voice and video traffic. Hence, CES in an ATM network must be comparable in functionality to that currently provided by today's existing time division multiplexing (TDM) telephony devices.
For example, consider a situation in which you are currently employing physical telephone circuits connected to PBXs (Private Branch eXchanges) as the primary means of CBR data transmission. For a variety of reasons, you may wish to have equivalent CBR functionality available within an ATM network.
A CES module, together with appropriate software, is the solution. A CES module provides the means to emulate your current telephony technology and, more importantly, to migrate that functionality into an operational ATM network.
This configuration allows you to reduce networking costs by consolidating separate voice, data, and video facilities into a single, reliable, multivendor ATM network. With equivalent CBR technology thus available within the ATM network, your view of CBR traffic does not change in any fundamental way---CBR data is still introduced into a circuit, and CBR data still emanates from a circuit.
The essential distinction, however, is that an emulated CBR circuit employs a different medium for data transport, namely, the ATM network. Nevertheless, an emulated circuit behaves logically as though the communicating entities are actually physically connected by wires.
The CES modules provide connectivity to other LightStream 1010 ATM switch interface modules and to the ATM network.
You can manage your LightStream 1010 ATM switch through the administrative interface which connects directly to a console terminal, or through a modem that connects to the EIA/TIA-232 interface on the ASP. (See the chapter "Configuring Terminal Lines and Modem Support.") Alternatively, you can access the administrative interface using Simple Network Management Protocol (SNMP), Telnet, Serial Line Internet Protocol (SLIP), and Point-to-Point Protocol (PPP).
Instead of defining a large set of commands, SNMP places all operations in a get-request, get-next-request, and set-request format. For example, an SNMP manager can get a value from an SNMP agent or store a value into that SNMP agent. The SNMP manager can be part of a network management system (NMS), and the SNMP agent can reside on a networking device such as a switch. The SNMP agent can respond to MIB-related queries being sent by the NMS.
SNMP agents support the following functions:
The CiscoView application for the LightStream 1010 ATM switch is a graphical user interface (GUI)-based device management application that provides dynamic status, statistics, and configuration information. This application is a subset of the CiscoView application that offers similar feature for the other switched internetworking products such as Catalyst LAN switches and Cisco routers.
With the CiscoView application for the LightStream 1010 ATM switch, users can more easily understand the complex management data and configuration parameters available for ATM switches. It organizes this information into a graphical representation in a clear, consistent format.
Users can integrate the CiscoView application for the LightStream 1010 ATM switch with several of the leading network management platforms to provide management application integration. You can run CiscoView on UNIX workstations as a fully functional, independent LightStream 1010 ATM switch management application. In addition, you can launch it from the AtmDirector topology map by simply double-clicking on a LightStream 1010 ATM switch icon.
ATM is defined by a large number of cross-referenced specifications from a variety of standards bodies, including the ATM Forum, the ANSI T1S1 Committee, Bellcore, ETSI, and the ITU-T. The ATM Forum specifications can be regarded as preeminent since they build upon, and refer to, specifications from all other ATM standards bodies; compliance with ATM Forum specifications implies compliance with all referenced specifications. The LightStream 1010 ATM switch supports the following general standards:
The LightStream 1010 ATM switch uses the following standard Internet protocols:
The LightStream 1010 ATM switch supports standard and enterprise-specific MIBs. The following MIBs are supported:
Posted: Tue Jun 22 13:46:04 PDT 1999
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