Availability Guide for Problem Management

Problem Management Tools
Availability Guide for Problem Management–125509
9-20
NonStop Access for Networking (NSAN)
NonStop Access for Networking (NSAN)
NSAN is a joint Tandem and Ungermann-Bass networking solution that delivers fault
tolerance from the server out to the desktop by creating primary and alternate paths
between PCs, networking hubs, and Tandem NonStop and Integrity servers. NSAN
provides fault tolerance to client and server applications by using fully redundant local
area networks (LANs) and LAN connections.
The Tandem server connection is achieved through software that supports the use of two
3615 Ethernet controllers, paired to support a single LAN communications line. The PC
client connection is achieved through the use of the UB Networking MasterLAN II-T2
dual port LAN adapter and associated drivers.
NSAN improves availability by providing a primary and backup Ethernet path from the
server to the network and from the network to the client. It also lowers networking costs
caused by scheduled or unscheduled downtime. NSAN also provides:
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Configurable and scalable levels of availability
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Compatibility with 10BaseT Ethernet networks
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Automatic switching between alternative Ethernet paths
How NSAN Works
NSAN works with existing UB Networking 10BaseT LAN hubs. To take advantage of
NSAN features, two UB Networking hubs are internetworked in redundant fashion to
provide primary and backup 10BaseT Ethernet paths to Tandem 3615 controllers.
Standard UB Networking dual Ethernet backbone LANs provide backup paths between
the hubs.
The UB Networking MasterLAN II-T2 network interface card (NIC) provides dual paths
from each LAN-attached PC to dual networking hubs. The MasterLAN II-T2 software
drivers sense both paths and automatically switch from the active path to the backup
path in the event of failure.
“I Am Alive” Status Packets
Each 3615 controller is assigned three media access control (MAC) addresses. The
Tandem LAN Access Method (TLAM) subsystem uses both the group address and the
unique MAC address assigned to each controller to exchange “I am alive” status packets
between members of the controller pair.
Each 3615 controller has a network management timer that operates at intervals of one
second. If a status change occurs, the controller sends TLAM a message. Status
messages can indicate that the controller has started or stopped receiving
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“I am alive” status packets from its twin
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Media packets from the network
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Link-pulses from the network (Link-pulse changes are not issued at one second
intervals.)