Datacom

The Universal Serial Bus (USB) hardware (plug-and-play) standard makes connecting peripherals to your computer easy.

USB 1.1, introduced in 1995, is the original USB standard. It has two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much lower bandwidth.

In 2002, a newer specification, USB 2.0, or Hi-Speed USB 2.0, gained wide acceptance in the industry. This version is both forward- and backward-compatible with USB 1.1. It increases the speed of the peripheral to PC connection from 12 Mbps to 480 Mbps, or 40 times faster than USB 1.1!

This increase in bandwidth enhances the use of external peripherals that require high throughput, such as CD/DVD burners, scanners, digital cameras, video equipment, and more. USB 2.0 supports demanding applications, such as Web publishing, in which multiple high-speed devices run simultaneously. USB 2.0 also supports Windows® XP through a Windows update.

An even newer USB standard, USB On-The-Go (OTG), is also in development. USB OTG enables devices other than a PC to act as a host. It enables portable equipment—such as PDAs, cell phones, digital cameras, and digital music players—to connect to each other without the need for a PC host.

USB 2.0 specifies three types of connectors: the A connector, the B connector, and the Mini B connector. A fourth type of connector, the Mini A (used for smaller peripherals such as mobile phones), was developed as part of the USB OTG specification.

While there are many applications for basic T1 rate service (1.536 Mbps), some applications require much more bandwidth. One of the most attractive features of T1 is the number of options available to accommodate these kinds of demands. The important thing to remember is that all of these higher-speed services operate with the same consistent framing formats as the standard T1 service.

T1 is a high-speed service with a clock speed of 1.544 Mbps. It’s made up of 24 64-kbps DS0 (Digital-Signal [zero]) subchannels that together can support throughput rates of up to 1.536 Mbps. But there are higher levels of T1 service that are also available. For instance, T1C service doubles the T1 rate. It supports 3.152 Mbps with a total of 48 DS0s for top-speed applications. In a T1C environment, two T1 lines are combined into one using a special T1 mux.

The next-highest level of service is called T2. It offers 6.312 Mbps over 96 DS0s by multi-plexing 4 T1 lines into a single high-speed line.

The next two levels of service are exponentially larger than T2. A high-speed T3 trunk line is 28 times larger than a standard T1 line. T3 brings 44.736 Mbps to a customer site via 672 DS0s. This tremendous capacity is made possible by multiplexing 28 T1 lines or combina?tions of T2 and T1 lines.

Finally, T4 service offers a bandwidth potential of 274.176 Mbps, made up of 4032 64-kbps DS0 subchannels. At 168 times the size of a standard 1.544-Mbps line, T4 service dwarfs T1. The physical connections require multiplexing 6 T3 lines or 168 T1 lines into a single high-speed trunk.

With so many incredibly high-speed T-level service options available, system administrators have great flexibility to configure their operations for maximum efficiency and economy.

It’s important to remember that these various levels of T1 services can be implemented simultaneously within a particularly large enterprise to support complex network configurations.

Of course, this kind of application has the potential to become somewhat overwhelming from a management standpoint. However, as long as you keep track of the individual DS0s, you should always be able to accurately gauge how much available bandwidth you have at your disposal.