Belle of the N+I Ball.
Tour the recent Networld+Interop floor, and one thing was evident: Gigabit Ethernet has truly arrived. A little more than a year after products began shipping; and six months after the standard for optical fiber was ratified, Gigabit Ethernet has become a mature technology ready to take on a variety of enterprise roles.
Initially, Gigabit Ethernet is finding use mainly as an upgrade for FDDI (Fiber Distributed Data Interface) find Fast Ethernet backbones. However, it's expected to quickly follow the same migration path taken by Fast Ethernet, starting with switch-to-switch links before moving down the network hierarchy to switch-to-server connections. Once the standard for unshielded twisted-pair wiring is ratified (see sidebar), Gigabit Ethernet may even be deployed to the desktop.
Dataquest, the San Jose, Calif., market research firm, expects Gigabit Ethernet sales to soar from $19.8 million last year to about $1.36 billion by 2001, with the number of ports shipped rising from 8,100 last year to 1.55 million in 2001.
The Dell' Oro Group of Portola Valley, Calif., a research firm that tracks the Gigabit Ethernet market, predicts even stronger growth, based on early indications that users are embracing the technology more aggressively than expected. Dell'Oro expects shipments to reach 7.8 million ports annually by 2001 and is projecting sales in excess of $3 billion by 2002.
More than 40 vendors now supply Gigabit Ethernet products, ranging from Layer 2 and Layer 3 (routing) switches, uplink/downlink modules, and network interface cards (NICs) to router interfaces and a new device called a full-duplex repeater or buffered distributor. This hub-like device interconnects two or more Ethernet links operating at 1 Gbps or faster and forwards all incoming packets to the connected links, except the originating one, providing a shared-bandwidth domain. Unlike a repeater, it can buffer incoming frames before forwarding them. It is useful for connecting server farms to a Gigabit Ethernet backbone.
About 70 percent of today's network backbones use FDDI, which is limited to 100 Mbps. This may have been adequate before organizations began using the Internet and corporate intranets, when 80 percent of traffic was contained within workgroups and departments. Today, 80 percent of the traffic is on the backbone, pressuring network managers to find faster alternatives.
Shared FDDI backbones can be upgraded to Gigabit Ethernet by replacing the backbone FDDI concentrator with a Gigabit Ethernet switch and installing Gigabit Ethernet NICs in the routers attached to the backbone. If the network includes a ring of FDDI concentrators or routers, as in a campus configuration, a Gigabit Ethernet switch or repeater can be installed as the core of the network, with the routers attached to the switch.
Similarly, a Fast Ethernet backbone switch that aggregates multiple 10- and 100-Mbps switches can be easily upgraded with a gigabit version.
As a backbone technology, Gigabit Ethernet is expected to face stiff competition from Asynchronous Transfer Mode (ATM) technology, especially where voice or video accounts for a large portion of the traffic. Gigabit Ethernet proponents argue that it is faster and cheaper than ATM and is easier to implement and manage, since the underlying technology is widely deployed and well understood.
Gigabit Ethernet also integrates smoothly into existing Ethernet networks, since it uses the same frame structure and protocol. In addition, most Gigabit Ethernet switches include 10- and 100-Mbps Ethernet ports and can operate with the same network management systems.
Even so, ATM is a more mature technology, with established quality-of-service (QoS) standards, and it integrates well with Token-Ring networks and the ATM-based carrier networks used for WAN access. The IEEE 802 committee has established QoS standards for Ethernet, but these have yet to be universally embraced by Gigabit Ethernet vendors. Implementing QoS over a WAN link can also be difficult.
Where QoS is important--say for giving priority to video streams or determining which traffic will get the most bandwidth from relatively slow WAN links--ATM may have the edge. Otherwise, Gigabit Ethernet generally wins on the basis of speed, cost, ease of installation and configuration, and staff familiarity with the technology.
Gigabit Ethernet also provides a simple upgrade path for Fast Ethernet switches and links, since it uses the same frame formats and flow control methods, eliminating the need to translate between different types of Ethernet traffic. In addition, the same network management systems and troubleshooting techniques can often be used.
As a rule of thumb, wherever Fast Ethernet runs today, Gigabit Ethernet could well run tomorrow. According to a recent study by the Cahners In-Stat research firm, 34 percent of enterprises currently use Fast Ethernet to link switches, while 46 percent use it to link servers. Much of Gigabit Ethernet's growth will come from upgrading these links to 1 Gbps.
Before using Gigabit Ethernet to link servers, though, network managers need to make sure the servers can handle its blazing speed. Many high-end Unix servers are up to the challenge, but Windows NT 4.0 is questionnable, and users may have to wait for NT 5.0 before proceeding with the 1-Gbps connection.
IBM is addressing the issue by using larger-than-standard Ethernet frames, which are easier for servers to handle on high-speed networks. Developed by Alteon Networks, the so-called jumbo frames contain 9,018 bytes, compared to the Ethernet limit of 1,518 bytes. They improve performance by requiring the server CPU to handle fewer frames and deal with fewer interruptions.
IBM will initially support jumbo frames on its RS/6000 servers, and is expected to add support for its AS/400 mid-range systems and Netfinity PC server. While jumbo frames is not a standard, it may be soon if Alteon can make its case with the IEEE committee. IBM's endorsement may help.
RELATED ARTICLE: Standards continue torrid pace
As with the other Ethernet standards, the ones or Gigabit Ethernet appear to be on a fast track. Fast Ethernet took only 13 months to go from first draft to final approval, and Gigabit Ethernet required about the same time. Last June, the 802.3z task force created by the IEEE standards committee to develop the 1-Gbps specifications was successful in ratifying the standard for Gigabit Ethernet operation over optical fiber. A companion 802.3ab task force expects to ratify the standard for operation over Category 5 unshielded twisted pair (UTP) next March. After that, the next major development will be the 802.3ad standard for link aggregation. An IEEE task force was formed in July to develop and approve the standard by March 2000.
The 802.3z standard defines two basic modes: the 1000Base-LX uses long-wavelength laser transceivers to support links of up to 550 meters with multi-mode fiber and 5 km with single-mode fiber; 1000Base-SX employs short-wavelength laser transceivers to support links of 220 to 550 meters with multimode fiber, depending on its bandwidth. The task force targeted 1000Base-SX at low-cost multimode fiber runs in horizontal and shorter backbone applications. The 1000Base-LX is intended for longer multimode building fiber backbones and single-mode campus backbones.
For copper cabling, the 1000Base-CX standard supports short-haul jumpers made from shielded twisted-pair for interconnecting equipment clusters or for links within a switching closet or computer room of less than 25 meters. The 1000Base-T standard for Category 5 UTP cable being developed by the 802.3ab task force will utilize all four twisted pairs to extend operation to a distance of 100 meters.
Given the high percentage of copper wiring in corporate networks, development of the 1000Base-T standard is considered critical to Gigabit Ethernet's adoption and growth. The draft standard calls for five-level pulse amplitude modulation for transmission at 125 Mbaud over each wire pair. Two data bits are encoded into a four-level signal, with the fifth level for control. This results in 250 Mbps of data transmitted over each of the four pairs.
The IEEE 802.3z task force is also working on a media-independent interface that decouples the access protocol from the lower layer, enabling separate development of additional physical layers based on future advances in silicon technology and digital signal processing.
Backward compatibility with the huge installed base of 10- and 100-Mbps Ethernet nodes was one of the objectives set by the IEEE 802.3 committee when it authorized the 802.3z task force to develop the 1-Gbps specifications in July, 1996. Among the goals were use of the Ethernet frame format and CSMA/CD (Carrier Sense Multiple Access/Collision Detection) access method, and support for both half- and full-duplex operation.
To make shared-media Gigabit Ethernet practical, however, the task force had to modify the access method, which would otherwise have limited implementations to spans of a few meters.
This limit is imposed by the CSMA/CD algorithm, which requires the worst-case round-trip delay of the network to be less than or equal to the transmission time of the shortest frame. With the 64-byte minimum frame size used by 10- and 100-Mbps Ethernet, the network size for 1-Gbps operation would have to be less than 20 meters.
One solution, called carrier extension, increases the minimum frame size to 512 bytes, lengthening the range to more than 150 meters but causing inefficiencies when there is little data to send. Also, the longer frame causes more collisions, reducing the efficiency even more.
To compensate, the IEEE 802.3z committee has adopted a further enhancement, called packet bursting, that improves bandwidth utilization for short frames and decreases the probability of collisions. With this technique, a burst of short frames is appended to the channel-extended, 512-byte frame so that it avoids a collision. The overhead is shared among several short frames.
Gigabit Ethernet supports new full-duplex operating modes for switch-to-switch and switch-to-workstation connections. Full-duplex operation requires no change in the minimum frame size since CSMA/CD is suspended on such links to allow traffic to travel in both directions at once. Its operation will be identical to that of Fast Ethernet.
Gigabit Ethernet has no provision for the quality of service (QoS) needs of time-sensitive traffic, such as voice or video, but other standards bodies are addressing these issues.
The IEEE 802.1p and 802.1q standards groups, for instance, provide QoS over all forms of Ethernet by "tagging" packets with an indication of their class of service so applications can communicate each packet's priority to the internetworking devices. Also, the Internet Engineering Task Force has issued a standard, called Resource Reservation Protocol (RSVP), that lets end stations reserve bandwidth for high-priority traffic.
Edwards is a datacommunications consultant who writes about network computing technology and its business uses.