algorithm to determine the path for any data that arrives and needs to be switched through the network. The routing algorithm calculates the minimum distance path through the network, verifies the availability of bandwidth, and then sets up a connection between the two ATM endpoints in the network. The routing algorithm can use metrics to determine the least−cost route for setting up a virtual connection.

A route that is selected through the route generation function is based on the smallest number of hops to the destination. If two equal paths exist, the routing algorithm uses the bandwidth of the links as the tie−breaker: It uses the fastest link with the most available bandwidth.

When a route needs to be generated, the routing algorithm creates the most efficient route based on the following information:

∙Source and destination addresses (the internal addresses used to designate the VCC endpoints in the network)

∙Bandwidth type (indicates the pool to be used for allocation, data, or control purposes)

∙Service specification of the desired bandwidth or a minimum acceptable bandwidth

Scaling factors allow for a partial allocation of bandwidth for certain types of data traffic. The primary scaling factor is not definable and is always set to 1. A secondary scaling factor can be defined by an administrator; it’s typically set to a range of 1 to 2 percent.

When identifying a minimum acceptable bandwidth, you must set a parameter that will be an enforced rate for the VCC. This parameter will make the routing algorithm choose a link that has bandwidth equal to or greater than the assigned minimum acceptable bandwidth value. Doing so prevents the possibility of an output port sending data at a greater rate than an intermediate link can handle and guarantees a certain amount of bandwidth for those applications that require it.

LightStream Troubleshooting Tools

The LightStream series of Cisco switches has many troubleshooting and monitoring tools. The boot process can be used to find hardware or software problems, certain protocols can be used for troubleshooting, and a unique tool called a snooping mechanism allows all or some of the connections to be transparently mirrored to a port. Let’s take a better look at these troubleshooting tools in the following sections.

LightStream Boot Process

When you power−on a LightStream for the first time, you should be able to access the console port. Within the first few seconds of turning on the power, you should see the following three lines:

System Bootstrp, Version 201 (1025), SOFTWARE

Copyright (c) 1986−1996 by Cisco Systems

ASP processor with 16384 Kbytes of main memory

These lines indicate how much memory is installed in the switch. Checking the amount of memory installed in the switch against the amount displayed here can identify a hardware problem. If the bootstrap fails to load, the boot ROM could have a problem. If the switch has no configuration, it will default to setup mode.

If you see the following notice during the boot process and you’re prompted to set up the switch, then the installed nonvolatile RAM (NVRAM) may have a problem—particularly if a saved configuration existed when the power was recycled. Let’s take a look:

Notice: NVRAM invalid, possibly due to a write erase.

— System Configuration Dialog —

At any point you may enter a question mark ’?’ for help. Use ctrl−c to abort configuration dialog at any prompt.

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Default settings are in square brackets ’[]’

Would you like to enter the initial configuration dialog? [yes]

From this prompt, you can enter the initial configuration dialog or decline and manually enter the configuration. This choice allows an administrator to use the Command Line Interface (CLI) on the LightStream switch. If you are not familiar with configuring a LightStream switch, you may want to continue using the System Configuration Dialog screen.

Supported Troubleshooting Protocols

LightStream switches support many protocols, such as Bootstrap Protocol (BOOTP) and Telnet, for remote access to the switch and autoconfiguration. In−band management access is possible through the ATM interfaces or the Ethernet port. Out−of−band management can be handled by the console port or either of the two serial ports. One serial port allows a dedicated port to attach a local terminal, and one can be used to attach an external modem for dial−in access through an analog telephone line.

Trivial File Transfer Protocol (TFTP) can be used for remote access to upload new firmware upgrades, save configurations, or upload configurations.

Snooping Mechanisms

Snooping mechanisms used by the LightStream 1010’s ports allow a mirrored connection from one or more ports to be mirrored to another port. As a result, any data on a selected mirrored port will be copied and sent to the mirror port. This process is completely transparent to the end devices connected to the port or ports being monitored, and the data can be analyzed by an external ATM analyzer attached to the mirrored port.

Snooping mechanisms are one of the most important monitoring and troubleshooting tools used in ATM switches. ATM analyzers can be used to monitor the traffic flows in and out of the selected ports. No external devices can be connected to monitored ports to easily identify problems associated with ATM.

Multiprotocol Over ATM

Multiprotocol Over ATM (MPOA) enables the fast routing of internetwork−layer packets across a nonbroadcast, multiaccess (NBMA) network. MPOA replaces multihop routing with point−to−point routing using a direct VCC between ingress and egress edge devices or hosts.

Two components will be discussed here:

∙MPOA Server (MPS)

∙MPOA Client (MPC)

The MPS

The MPS supplies the forwarding information used by MPCs. Once the MPS receives a query from a client, it responds with forwarding information. MPOA uses Next Hop Resolution Protocol (NHRP) to support the query and response. The MPS on the router can also terminate shortcuts.

Although, a router is usually designated as an MPS, it can also be designated as an MPC.

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