Published In March 2001
Let’s begin this series on Gigabit Ethernet by recognizing the state of local area networks (LAN) wiring today. (My Gigabit Ethernet article in the September 2000 issue of Electrical Contractor provides background.) Most office networks are now installed with 10/100 Ethernet adapters in the desktop computers, simply because most users and software applications can’t use more bandwidth. Today, only the most demanding office applications can strain the Fast Ethernet (100 Base T) bandwidth, unless they are carelessly programmed. (For example, this could mean pulling each record of a large database on the server across an overloaded, shared-media LAN instead of asking a server program to prescreen the records or to calculate a required input.) Nevertheless, Gigabit Ethernet is clearly already being deployed in the cores of high-performance networks, particularly in and around server farms and Internet-connected routers. Furthermore, many more (desktop) computers will need Gigabit soon as the demand for bandwidth continues to chase the supply. New demands will come from many sources, including Inter-net/intranet applications, streaming audio and video, data warehousing, interactive conferencing, publishing, medical imaging, and scientific modeling. Prices now have dropped, as predicted, so that Gigabit Ethernet adapter cards are advertised in the range of $340 to $699, quantity one, in a recent network catalog sampling. However, these catalogs obviously show that the industry’s bread-and-butter products are 10/100 Ethernet adapters: there are only one or two Gigabit adapters advertised in each competing catalog, and one even goes further by labeling it a Gigabit Server Adapter. Each catalog lists dozens of 10/100 Ethernet adapters, ranging in price from $14.99 (after rebate) to $159.95, quantity one. Gigabit Ethernet hub prices are decreasing rapidly as well, although pure Gigabit hubs are rarely advertised in catalogs. Instead, the high-end offering is usually a hub with multiple 10/10 ports but only one or two Gigabit fiber uplinks for about $80 to $100 per port. One pure four-port1000 Base T switched hub with uplink was listed at $305/port. When these prices are compared with 24-port 10/100 dual-speed hubs ranging from $15 to $20+ per port, it is obvious why Gigabit links are reserved for only those niche (core) applications where they are needed. However, as the prices continue to come down, more power users are expected to find use even these blistering speeds productively. Gigabit Ethernet transmission may use both fiber optic (single-mode and multimode) and metal cables [coax, shielded twisted pair (STP), and unshielded twisted pair (UTP)]. This series will concentrate on UTP copper as the most popular because of its current lower price and easier installation. However, glass cable prices are constantly coming closer to copper cable prices. And, as Jim Hayes argued in his April 2000 column, copper is not always the least expensive cable today; it depends upon the application. Later in this series, we will delve into more details of the best installation practices for Gigabit Ethernet, but here is a quick summary. Consistently use compliant components throughout each cable run. For example, if the runs are 5e compliant, then the patch cords should also be Cat 5e! Maintain minimum bend radius everywhere. Minimum bend radius is no less than eight times for UTP during installation, and four times after installation. Long before the conductors suffer physical damage, excessive bending brings them too close to each other and crosstalk causes signal degradation. Minimize untwisting of pairs. Less than 1/2 inch is allowed before excessive crosstalk degrades signal integrity again. Use minimum pulling force on cables. Cable weight itself will damage conductor integrity if too long a length is moved without intermediate help. Don’t pinch the cable with staples or other positioning mechanisms. Again, minimum inter-conductor spacing is crucial. As always, maximum length must be respected. Typical maximum for horizontal runs is 90m, with an additional 10m of patch cables allowed. Avoid electromagnetic interference (EMI). Low-voltage, high-speed data signals are especially vulnerable to corruption by any kind of competing energy. Terminations must be carefully selected and installed. Once again, the “weak-link” effect overwhelms an otherwise perfect installation if, for instance, a Cat 3 patch panel is used in the middle of a Cat 5 wire run. After-install tests must be run with accurate, appropriate qualification tools to ensure that the entire wiring system will achieve the expected results. Later articles in this six-part series will deal with the following topics: * detailed installation procedures, * selection of appropriate tools, * troubleshooting Gigabit installations, * basic physics involved, and * challenges of 10 Gigabit Ethernet, the new frontier of LAN connectivity. SHINN is principal of Compututor. He can be reached via e-mail at firstname.lastname@example.org.