Network reliability is a measurement of the dependability of the networking equipment. Will the equipment operate in different environments? Can it recover from most types of failures? Is it easily repaired without taking the network down? The networking device must be physically sturdy, and it must be well engineered to support standard reliability features like redundant power, hot swappability, and other failover mechanisms. Without those functions, a switch would not be able to recover from most failures on its own and would require manual repairs, which can be expensive, not to mention the cost of network downtime to day-to-day business.

Availability, on the other hand, is the ability of a device to provide network services if and when they are needed without delay. Availability is based more on a network device's intelligence. For example, a switch or router could be functioning perfectly, but if time-sensitive traffic, such as video or VoIP, is bogged down by web surfing, the traffic becomes useless by the time it reaches the destination. Without traffic management, congestion will reduce performance to a crawl, giving the perception of a network outage and costing money in lost productivity. The availability intelligence of a switch is based on its traffic-shaping functions, such as quality of service, routing services, queuing, and other bandwidth management functions. By shaping the traffic on the network, high priority traffic will reach its destination ahead of lower priority traffic, congestion will be eliminated, and services will be available across the network.

Even though reliability and availability are separate, you cannot have one without the other. If the network is not reliable, then it is not functioning and services will not be available. Conversely, if the network is running but is congested, then the network is perceived to be unreliable because you cannot access its services. It is an important balancing act to have both qualities in a network device. When designing a network it is desirable to have a switch with high degrees of reliability and availability to ensure the network will be operating and able to pass traffic effectively, averting costly network downtime.