The level of load on the network is directly proportional to the systems attached. As enterprises continue to deploy Gigabit Ethernet uplinks toward the network's edge, the demand for more bandwidth at the core will increase. For many glass-house data-center environments, this demand will emerge first on the links between the backbone and the data center.

Another significant driver for 10 Gigabit Ethernet in the enterprise is the proliferation and widespread adoption of gigabit over copper in the wiring closet. Wiring your desktops for Gigabit Ethernet may seem like overkill, but soon desktop systems will have integrated 10/100/1000Base-T LAN-on-motherboard networking interfaces. Apple Computer's G4 towers come standard with integrated 1000Base-T interfaces. And though the average desktop user may not need 1,000 Mbps all day, he or she will benefit significantly from decreased wait times on large file transfers. Such use will create bursty traffic patterns on wiring-closet uplinks, ultimately increasing backbone network load. Gigabit Ethernet will be a common item at the desktop within 18 months.

Cisco Systems and other vendors already offer 24-port 10/100/1000Base-T gigabit-over-copper modules for around $375 per port. In 1995, 10/100 Fast Ethernet interfaces cost about the same. It won't be long before desktop and edge connectivity are gigabit-enabled. This will drive the need for more bandwidth at the core.

Finally, don't underestimate the future of convergence technologies on the LAN. SAN (storage area network) technology vendors are working on iSCSI (Internet SCSI) and similar standards that will let your data network natively carry raw SCSI data between storage devices and servers. While large enterprises build out parallel storage networks today, the storage networks of tomorrow will exist on a converged LAN, which will drive the need for core bandwidth. Likewise, though voice technology doesn't use an immense amount of bandwidth in a small installation, large installations can gobble up precious bandwidth. All these technologies are on the horizon and will affect your need for bandwidth in the next two years.

Backgrounder

The 10 Gigabit Ethernet standard is significantly more complex than the previous Ethernet technologies. When 100Base-TX technology was introduced in 1993, vendors were able to leverage the copper FDDI physical interface to accelerate development. When Gigabit Ethernet was introduced in 1998, vendors leveraged the optical and electronic interfaces developed for Fibre Channel. With 10 Gigabit Ethernet, there is no comparable technology to leverage. To develop a 10-gigabit physical layer, vendors must develop a layer capable of transporting 10 billion bps.

The IEEE 802.3ae 10 Gigabit Ethernet Task Force is chartered with developing the technology's specifications. This group has set an aggressive schedule with the goal of having a ratified standard by its March 2002 meeting. The task force is now on or ahead of schedule, with many vendors planning for pre-standard products by this September.

The 802.3ae task force has outlined several key objectives that should be of interest to IT managers. The most important is that 10 Gigabit Ethernet will remain an Ethernet technology. That is, it will preserve the 802.3 Ethernet frame format, minimum and maximum frame size, and MAC (Media Access Control) client service interface. The 10 Gigabit Ethernet standard will be a full-duplex-only standard. You might recall that Gigabit Ethernet included support for a special repeater-based implementation called a buffered distributor. However, this technology never made it into widespread deployment, and as a result, 10 Gigabit Ethernet will not include a half-duplex option. This not only solves the problem of network diameter (switched networks have no inherent distance limits other than cabling limitations), but significantly simplifies the standard. Half duplex was once implemented for cost reasons; however, given that most of the cost of gigabit and 10-gigabit interfaces is in the optics, half-duplex connections no longer make sense. They won't be missed.

The 10-gigabit standard defines two physical layers (PHYs): the LAN PHY and the WAN PHY. Ten Gigabit Ethernet is being designed to support not only enterprise backbone networks but wide-area and long-haul networking applications. The LAN PHY represents the typical LAN interfaces used today, operating at a 10-Gbps data rate. The WAN PHY is designed to operate at a data rate compatible with the payload rate of OC-192c and SDH VC-4-64c (9.58 Gbps). However, unlike SONET networks, 10 Gigabit Ethernet over SONET will remain asynchronous. This will enable 10 gigabit to run over SONET networks, but the switches and routers will not need the complex and expensive stratum clocks that native SONET interfaces require. The WIS (WAN Interface Sublayer) crams 10 Gigabit Ethernet into the SONET STS-192c frame by adjusting the interpacket gap to accommodate the slightly lower data rate of OC-192c payloads.

Why two interfaces? The primary reason is to take advantage of the massive amount of existing SONET infrastructure in the public WAN. By providing a SONET-compatible interface, 10-gigabit vendors are extending the reach of the technology far outside the confines of enterprise walls. Because the WAN PHY is really just a LAN PHY with some extra components to handle simplified SONET framing, we expect many vendors will offer unified LAN-WAN interfaces in the 10- and 40-kilometer ranges.

At the physical layer, data is encoded onto fiber using 64b/66b encoding. As a refresher, 1000Base-X technology uses 8b/10b encoding to deliver a 1-Gbps data rate. Thus, for every 8 bits transmitted on a gigabit network, 10 bits of data are used to encode that data. That results in a network that is only 80 percent efficient, requiring the LAN to operate at 1.25 gigabaud to achieve a 1-Gbps data rate.

With 64/66b encoding, two additional bits are used to encode every 64 bits of data. This results in a much more efficient use of bit budget (97 percent efficient) but at the price of error correction and recovery bits. Thanks to the development of forward error-correction techniques and advanced signal-recovery techniques, however, 10 Gigabit Ethernet should be every bit as reliable as other Ethernet technologies. Ten-gigabit LAN interfaces will operate at 10.3 gigabaud.