# Network Criteria ## Introduction For a network to be effective and reliable, it must meet certain standards and criteria. These criteria define the quality and capability of a network. Network engineers and designers use these criteria when planning, building, and evaluating networks. The three most important criteria for evaluating a network are performance, reliability, and security. ## Performance Performance refers to how well a network delivers data from one device to another. There are several ways to measure network performance. Bandwidth is the maximum amount of data that can be transmitted over a network connection in a given period of time, usually measured in bits per second. Higher bandwidth means more data can be transmitted simultaneously. Throughput is the actual amount of data successfully transmitted over the network in practice, which is often lower than the theoretical bandwidth due to network congestion, protocol overhead, and errors. Latency is the time it takes for a single packet of data to travel from the source to the destination, measured in milliseconds. Low latency is critical for applications like video calls and online gaming. Jitter is the variation in latency over time. Consistent latency is important for real-time applications because unpredictable delays cause degraded audio and video quality. Packet loss occurs when packets fail to reach their destination and must be retransmitted, which reduces throughput and increases latency. ## Reliability Reliability refers to the ability of a network to consistently deliver data without failure. A reliable network should be available whenever users need it. Availability is usually expressed as a percentage of uptime. A network with 99.9 percent availability is down for less than nine hours per year, while a network with 99.999 percent availability is down for less than six minutes per year. Fault tolerance is the ability of a network to continue operating even when some of its components fail. Networks achieve fault tolerance through redundancy, which means having backup components that can take over when primary components fail. Recovery time is how quickly a network can restore full operation after a failure. Networks use protocols like Spanning Tree Protocol and routing failover mechanisms to minimize recovery time. ## Security Security refers to the protection of the network and its data from unauthorized access, misuse, and attack. Authentication ensures that only authorized users and devices can access the network. This is typically achieved through usernames and passwords, digital certificates, or multi-factor authentication. Authorization defines what each authenticated user is allowed to do on the network, limiting access to only the resources each user needs. Encryption protects data by encoding it so that only authorized recipients can read it. This prevents eavesdroppers from understanding intercepted data. Data integrity ensures that data has not been modified during transmission. Hashing algorithms are used to verify that received data is identical to what was sent. Non-repudiation ensures that a sender cannot later deny having sent a message, which is important for legal and business transactions. ## Scalability Scalability refers to the ability of a network to grow and handle increased demand without significant degradation in performance or reliability. A scalable network can accommodate more users, more devices, and more traffic as the organization grows. Poor scalability can lead to performance problems as a network expands beyond what its original design can support. Good network design anticipates future growth and builds in the capacity to expand. ## Manageability Manageability refers to how easy it is to monitor, configure, and maintain the network. A network that is difficult to manage will consume excessive IT staff time and resources. Good manageability requires clear network documentation, standardized configurations, centralized monitoring tools, and easy-to-use management interfaces. Network management protocols such as SNMP allow administrators to monitor device status, collect performance data, and receive alerts when problems occur. ## Quality of Service Quality of Service refers to the ability to prioritize different types of network traffic to ensure that critical or time-sensitive applications receive the resources they need. For example, a network with Quality of Service configured will prioritize voice call packets over file download packets so that voice calls remain clear even when the network is congested. Quality of Service is especially important in networks that carry a mix of time-sensitive traffic like video and less time-sensitive traffic like large file transfers.