Characteristics of a Network
When you purchase a mobile phone or a PC, the specifications list tells you the important characteristics of the device, just as specific characteristics of a network help describe its performance and structure. When you understand what each characteristic of a network means, you can better understand how the network is designed, how it performs, and which aspects you may need to adjust to meet user expectations.
You can describe the qualities and features of a network by considering these characteristics:
- Topology: A network topology is the arrangement of its elements. Topologies give insight into physical connections and data flows among devices. In a carefully designed network, data flows are optimized and the network performs as desired.
- Bitrate or Bandwidth: Bitrate is a measure of the data rate in bits per second of a given link in the network. The unit of bitrate is bit per second (bps). This measure is often referred to as bandwidth, or speed in device configurations, which is sometimes thought of as speed. However, it is not about how fast 1 bit is transmitted over a link which is determined by the physical properties of the medium that propagates the signal it is about the number of bits transmitted in a second. Link bitrates commonly encountered today are one and 10 Gigabits per second (1 or 10 billion bits per second). 100-Gbps links are not uncommon either.
- Availability: Availability indicates how much time a network is accessible and operational. Availability is expressed in terms of the percentage of time the network is operational. This percentage is calculated as a ratio of the time in minutes that the network is actually available and the total number of minutes over an agreed period, multiplied by 100. In other words, availability is the ratio of uptime and total time, expressed in percentage. To ensure high availability, networks should be designed to limit the impact of failures and to allow quick recovery when a failure does occur. High availability design usually incorporates redundancy. The redundant design includes extra elements, which serve as back-ups to the primary elements and take over the functionality if the primary element fails. Examples include redundant links, components, and devices.
- Reliability: Reliability indicates how well the network operates. It considers the ability of a network to operate without failures and with the intended performance for a specified time period. In other words, it tells you how much you can count on the network to operate as you expect it to. For a network to be reliable, the reliability of all its components should be considered. Highly reliable networks are highly available, but a highly available network might not be highly reliable its components might operate but at lower performance levels. A common measure of reliability is the mean time between failures (MTBF), which is calculated as the ratio between the total time in service and the number of failures, where not meeting the required performance level is considered a failure. Choosing highly reliable redundant components in the network design increases both availability and reliability.
For instance, let us consider a networking device that reboots every hour. The reboot takes 5 minutes, after which the device works as expected. The figure shows the calculations of availability and reliability.
The availability percentage for the period of one day can be calculated as follows:
- Scalability: Scalability indicates how easily the network can accommodate more users and data transmission requirements, without affecting current network performance. If you design and optimize a network only for the current requirements, it can be very expensive and difficult to meet new needs when the network grows.
- Security: Security tells you how well the network is defended from potential threats. Both network infrastructure and the information that is transmitted over the network should be secured. The subject of security is important, and defense techniques and practices are constantly evolving. You should consider security whenever you take actions that affect the network.
- Quality of Service (QoS): QoS includes tools, mechanisms, and architectures, which allow you to control how and when network resources are used by applications. QoS is especially important for prioritizing traffic when the network is congested.
- Cost: Cost indicates the general expense for the initial purchase of the network components and any costs associated with the installation and ongoing maintenance of these components.
- Virtualization: Traditionally, network services and functions have only been provided via hardware. Network virtualization creates a software solution that emulates network services and functions. Virtualization solves a lot of the networking challenges in today’s networks, helping organizations centrally automate and provision the network from a central management point.