Frequently Asked Questions about Gigabit Ethernet
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What type of presence does the Gigabit Ethernet Alliance have at NetWorld+Interop, Fall 1998? The Gigabit Ethernet Alliance has decided not to conduct booth demonstrations because customers are deploying Gigabit Ethernet in production networks. The NetWorld+Interop also has an operational parallel Gigabit Ethernet/ATM backbone across the show floor at the Georgia World Congress Center. This InteropNet Gigabit Ethernet Backbone is built with products from multiple vendors and demonstrating interoperability and actual application, supporting the aggregate traffic from all vendor booths with 10/100/1000 Mbps Ethernet connections. According to Dell'Oro Group, Over 54,000 Gigabit Ethernet ports have been installed in the first half of 1998. Whereas the first group demonstration of Gigabit Ethernet was back in May, 1997, today it is becoming a widely used, fully interoperable standard for enterprise backbones. What other activities is the Gigabit Ethernet Alliance focusing on? The Gigabit Ethernet Alliance continues to work on two primary aspects focusing on the Gigabit Ethernet Technology; 1000BASE-T and communicating standards and technology/market status to press/analysts and end users.
What is the current status of IEEE 802.3z? The IEEE 802.3z was officially approved by the IEEE standards board in June, 1998. The completion of the standard is the culmination of two-and-a-half years of intense effort within the IEEE 802.3 Working Group. What is the current status of IEEE 802.3ab? The IEEE 802.3ab 1000BASE-T draft received working group ballot approval in September, 1998, the first step in the standards approval process. Sponsor ballot or LMSC (LAN MAN Standards Committee) ballot is expected to start as planned in November, 1998. Final approval is still targeted for March, 1999. What is the cabling requirement for supporting 1000BASE-T? The IEEE 802.3ab Task Force has always targeted the installed-base Cat. 5 UTP as the wiring required to support Gigabit Ethernet, and there has been no deviation from that objective. It is expected that any Cat. 5 UTP installation that are able to support 100BASE-TX will successfully be able to support Gigabit Ethernet on Copper (1000BASE-T). For more information, please reference the two document that Gigabit Ethernet Alliance has published: the 1000BASE-T cabling technical brief and the 1000BASE-T white paper (available on the Gigabit Ethernet Alliance web site). Will speeding up Ethernet, yet again, really serve the needs of applications in the next 5 years? Yes. And when the time comes, we will probably have 10x Gigabit Ethernet, with switches and buffered repeaters much as we know them today. Is Gigabit Ethernet really Ethernet? Yes. Ethernet is defined by the frame format, the use of CSMA/CD, use of full duplex, the use of flow control and the management objects defined by the IEEE 802.3 group. Gigabit Ethernet will employ all of these. Thus, it is Ethernet, only faster. For starters, the same management staff that ran Fast Ethernet is running this standards project and, with this experience, understand the details of standards development and approval. Geoff Thompson is the chair of all of Ethernet (IEEE 802.3); Howard Frazier is chair of the Gigabit Ethernet standard (IEEE 802.3z). Dr. Howard Johnson is serving as chief technical editor of the standard. This is a seasoned team. Other factors that build confidence and accelerated the project schedule include:
What physical media options (PHYs) will Gigabit Ethernet support? A variety of PHY types are specified in the IEEE 802.3z standard. This includes support for a broad range of distances including various options optimized for important cost/distance design points. PHYs incorporated into the standard include 1000BASE-CX, which will support interconnection of equipment clusters; 1000BASE-SX, which is targeted for horizontal building cabling; and 1000BASE-LX, which will support backbone building, cabling and campus interconnections. Additionally the IEEE 802.3ab task force is developing the standard for 1000BASE-T, which will provide 1 Gb/s Ethernet over 4-pair Category 5 cabling up to 100 meters. The task force has special expertise in Digital Signal Processing (DSP) technology. This group is building on the technical foundation developed by the 802.3z Task Force for 1000BASE-X, but is working on a longer timeline. Will Gigabit Ethernet be available over copper media? Yes. There are two distance goals: 25m and 100m. 25m is already defined in the 1000BASE-CX specification (part of IEEE 802.3z where IEEE Standards Board approval was received in June, 1998). 1000BASE-CX is a standard intended for use in a switching closet or computer room as a short jumper. This standard uses 8B/10B coding at a serial line rate of 1.25 GB/s, and will run over a 150-ohm balanced cabling with somewhat better specifications than IBM type-I STP. The advantage of a short copper link standard is that it could be quickly generated and inexpensive. The 100m (Cat 5 UTP) spec has been assigned to the IEEE 802.3ab Task Force (IEEE Standards Board approval targeted for March, 1999). The 1000BASE-T standard is intended for use at distances of up to 100 meters over ordinary category-5 unshielded twisted pair cabling (four pairs required). Obviously, this is a more demanding and difficult application. As a result, the 802.3ab standard has a different timetable from the remainder of Gigabit Ethernet, which was specified by the 802.3z Task Force. What applications are envisioned for copper media versus fiber? We expect that early customers will focus on the use of Gigabit Ethernet as a backbone technology and for server connections. The first installations will require fiber, for long connections between buildings, and short copper links, for connections between servers and hubs. Over time, as the market for workgroup and desktop Gigabit Ethernet services develops, customers will demand Gigabit links that are compliant with the installed base of Cat-5 UTP wiring.
Will routers have trouble keeping up with Gigabit Ethernet data rates? Routers typically utilize processors for packet-switching. All major router vendors have technology and product development in place to address the Gigabit throughput challenge. A new category of routing switches has also emerged in the marketplace which provides both routing and switching functions. Is Gigabit Ethernet compatible with layer 3 switching? Yes. Layer 3 switching makes use of a known packet format to make forwarding decisions. The Ethernet packet format delivers a basis for Layer 3 switching by providing a consistent format to identify the necessary data fields for making switching decisions. The switching decision is based on information beyond (i.e. after) the destination and source MAC addresses in the Ethernet frame. Ethernet is dominant as the LAN of choice for desktop and campus backbones. According to IDC, it is used in over 80% of installations. There is no question that wide deployment of Fast Ethernet hardware to the desktop, whether in use or not, sets the stage for successful Gigabit intranet applications which will create the need for Gigabit Ethernet. In addition, the use of high-density Fast Ethernet in wiring closets and data centers drives the need for Gigabit Ethernet links for backbone applications. Thus, the growth of Fast Ethernet will positively influence the Gigabit Ethernet market. What modifications to TCP/IP stacks will be required to keep up with Gigabit Ethernet? CPUs are getting faster and, thus, network throughput will continue to grow. On the software side, Sun, SGI, HP and others, have already made TCP/IP stack and operating-system efficiency improvements which enable higher TCP/IP throughput for their systems. We expect these vendors to continue to deliver performance improvements as Gigabit Ethernet is developed and deployed. In fact, several are active in Alliance activities, based on customer demands for higher throughput servers to meet Intranet application demands. Absolutely. Today, a 32-bit PCI implementation already pumps out data in the multi-hundred megabits range. A 64-bit PCI bus will handle Gigabit Ethernet throughput
How many vendors are working on silicon to support Gigabit Ethernet? There are approximately 25 semiconductor vendors participating in Alliance activities. This includes all the major suppliers of standard product, semi-custom, and custom ASICs. Are end users represented in the Gigabit Ethernet Alliance? The Alliance steering committee has discussed the benefits of having end users become members. Since the IEEE standards process is driven by individual contributors, we have felt the best way for users to get involved at this time is to participate in the IEEE 802.3z activities. The Alliance has sparked some interests from the end user community, as represented by the addition of Duke Energy as a member. Who's missing from the list of members? Currently, there are over 110 member companies in the Alliance. All the major suppliers from the networking, computer, semiconductor, test equipment, component and consulting industries are represented. The current membership shows broad industry support for Gigabit Ethernet and the Gigabit Ethernet Alliance.
What will be the first applications for Gigabit Ethernet? Based on a series of user and VAR surveys conducted by the Dell'Oro Group, server-to-switch and switch-to-switch applications will be most popular for early deployment of Gigabit Ethernet. No. We feel there are a sufficient number of server and workstation vendors participating in the standard to address the software, throughput and redundancy issues.
Will Gigabit Ethernet equipment offer both shared and switched implementations? Yes. Switched Gigabit Ethernet will be available in precisely the same form as that used by Ethernet and Fast Ethernet today - using full-duplex physical-layer connections. Shared-bandwidth hubs will be available in two types: a simple repeater, and a new type called a buffered distributor or full-duplex repeater (a.k.a. full duplex distributor or repeater). What changes are being made to CSMA/CD? In order to maintain a roughly 200-meter topology at Gigabit speeds, both the minimum CSMA/CD carrier time and the Ethernet slot time have been extended from their present value of 512 bits to a new value of 512 bytes (4096 bits). Note that the minimum packet length of 64 bytes has not been affected. All packets will still be padded out by the MAC to a minimum of 64 bytes. What's new is the carrier event time. The carrier signal on the wire will be extended to build each packet out to a minimum carrier length of 512 bytes. Packets longer than 512 bytes are not extended. The carrier extension feature, used only in half-duplex links, fixes the timing problems inherent in CSMA/CD without changing the minimum packet size perceived at the MAC service interface. These changes, which can impact small-packet performance, have been offset by incorporating a new feature, called packet bursting, into the CSMA/CD algorithm. Packet bursting will allow servers, switches, and other devices to send bursts of small packets without relinquishing control of the network. Devices that operate in full duplex mode (switches and buffered distributors) are not subject to any of the carrier extension, slot time extension, or packet bursting changes. Full-duplex devices will continue to use the regular Ethernet 96-bit IPG and 512-bit minimum packet size. Note that all Gigabit Ethernet products announced so far support full-duplex connections, so there is no sacrifice of bandwidth for any size packets in the current generation of products. A buffered distributor is a new type of 802.3 hub having the following properties:
How will buffered repeaters implement flow control? Refer to the previous answer.
What is the status of the 802.3x flow control standard?
The 802.3x is an IEEE standard as of March,1997.
How does Gigabit Ethernet compare to ATM?
Gigabit Ethernet and ATM are complementary technologies, each has its place
in the LAN. However, Ethernet and Fast Ethernet have been demonstrated to be
the most popular and dominant LAN technology ever, and the advent of GbE
will simply extend that dominance. Ethernet, now scalable from 10, to 100,
to 1000 Mbps, can be deployed in the backbone for high-speed connections to
server farms, power workgroups, or just regular clients on the desktop.
Gigabit Ethernet is the enabling technology, allowing Ethernet to have a
native backbone for the first time and enabling Ethernet to go from desktop
to the backbone with absolute ease.
When and where should users deploy ATM versus deploying Gigabit Ethernet?
ATM is ideal for use in wide area network (WAN) connections, where the need
for support of integrated services (i.e. voice, video, image, data and text)
and real-time applications are especially strong. ATM can also be used
within LANs where integration to an ATM WAN is crucial and the cost and
complexity are warranted. Gigabit Ethernet completes the Ethernet offering
by providing high-speed connections for servers and a natural backbone
extension for the huge installed base of Ethernet and Fast Ethernet.
How will Gigabit Ethernet support applications such as multimedia, where QoS
is important?
Gigabit Ethernet provides one of the most important mechanisms needed for
"Campus Scaled" multimedia applications, and that is very high-capacity,
low-latency links. Many multimedia applications are running today over
Ethernet at 10 Mb/s or 100 Mb/s. Ethernet's capabilities to support "Class
of Service" (CoS) are being enhanced at Layer 2 by work completed in IEEE
802.1p. This work specifically focuses on setting up Multicast Groups within
a switched IEEE 802 to reduce the scope of flooding when traffic such as IP
Multicast is used for multimedia applications. Further, IEEE 802.1p
specifies the use of priority queuing mechanisms to support traffic which
may need lower or higher priority than normal, best-effort, traffic. Today,
the most typical use of RSVP from an end system is over unprioritized
Ethernet links (at least in the last 100 Meters), to Layer 3 routers, and
then out into the Wide Area Network. The work in IEEE 802.1, when combined
with RSVP, enhances the ability of end systems and switches to deliver
high-quality, low-latency bandwidth on a campus scale.
Other new protocols under development that will contribute to QoS and CoS
over ANY version of Ethernet include the IP type of service fields: RTP,
RTCP, and IGMP. These new tools will provide type of service, multicast and
control of real-time information as they become available and deployed over
the next few years. Gigabit Ethernet will take advantage of these new
protocols for delivery of QoS and CoS services.
When will RSVP, 802.1Q and 802.1p be ready?
RSVP is being worked on in the IETF. IEEE 802.1Q is expected to be approved
as a standard by end of 1998. IEEE 802.1p is already a standard, a part of
IEEE 802.1D-1998.
What is the status of the 1000BASE-T Gigabit Ethernet over copper Draft Standard (802.3ab)?
The draft has successfully completed Working Group and Sponsor ballots and is currently undergoing procedural approvals in preparation for submission to REVCOM and the Standards Board for approval as a standard.
When will the IEEE 1000BASE-T standard be ratified?
All technical work on the Draft Standard has been finished since 1998. The GEA expects that the outcome of a procedural IEEE 802 electronic ballot will be to forward the 1000BASE-T IEEE 802.3ab Draft to the IEEE Standards Board for ratification in June 1999.
What is your response to the argument that ratification of the IEEE 803.2ab standard in September 1999 and not the original target of March indicates that it is not possible to achieve Gigabit speeds over copper?
First, the 1000BASE-T Standard is expected to be ratified in June not September. There are no technical issues with the standard and all technical work on the Draft Standard was completed last year (CY98). The slip that the GEA announced in March of the expected target date for ratification involved technical editing requirements and procedural operations of the IEEE standards process, in other words "red tape." Second, very early prototype chips have shown that Gigabit speed over copper is possible.
Does the expected ratification date in September of the IEEE 803.2ab standard mean that customers should investigate alternative cable solutions, e.g. Cat 6?
No. Category 6 is not an alternative to 1000BASE-T, it is an alternative to Cat 5e. 1000BASE-T will run over Cat 5, Cat 5e, and proposed Cat 6. All copper cable plant will have to be tested for return loss and far-end cross talk (see below) to be certified for 1000BASE-T operation. Network managers or planners should not consider replacing Cat 5 with a higher-performance cable until they have tested the installed Category 5 links.
There is NO standards effort underway for a Category 6-only physical layer for Gigabit Ethernet.
Will GbE run over the installed base of Cat 5 cabling?
Yes. 1000BASE-T IEEE 802.3ab committee has designed and specified 1000BASE-T to run over four pairs of Category 5 balanced cabling. The four pairs of Category 5 balanced cabling used by 1000BASE-T are specified in ANSI/EIA/TIA-568-A (1995) and ISO/IEC 11801:1995 the international building wiring standard. Some specific link performance parameters to be met are covered in a document called TIA-TSB95.
Category 5 systems installed before 1995 (namely before the completion of ANSI/TIA/EIA568-A in 1995) may contain connecting hardware that does not comply with the Category 5 standard and might not be able to run 1000BASE-T. Note that 100BASE-TX is also not specified to support such links that include non-Cat 5 components. According to the industry experts that make up the IEEE 1000BASE-T Task Force, any link that is currently using 100BASE-TX should easily run 1000BASE-T.
How can a customer be sure GbE will run over his or her installed Cat 5?
The safest way to ensure that 1000BASE-T will run on an installed Cat 5 cable plant is to test the links. The IEEE together with the TIA has developed two simple tests for return loss (echo) and far-end cross talk to qualify links for 1000BASE-T operation. These tests can be conducted with test tools from Fluke, Hewlett Packard, Microtest, and others. The tests themselves have been defined in several ANSI/TIA/EIA documents. NOTE: Basic cable testing information is provided by ANSI/TIA/EIA-TSB-67- "Transmission Performance Specifications for Field Testing of Twisted Pair Cabling System." The additional test parameters for FEXT (ELFEXT) and return loss will be published as ANSI/TIA/EIA-TSB 95.
For new installations deploying 1000BASE-T what cabling type should be implemented?
The Gigabit Ethernet Alliance recommends that all new cable installations should be Cat 5e. Because the Cat 5e standard includes performance measures for return loss and far-end cross talk, cable installers who certify their Cat 5e installations to be ANSI/TIA/EIA 568A compliant incorporate return loss and far end cross talk performance in their certification. Network planners might want to consider Category 6 cabling because it promises greater headroom. However, they should be aware that proposed Category 6 connectors from different vendors may not interoperate. NOTE: Far-end cross talk (FEXT) is measured as equal level FEXT or ELFEXT and power sum ELFEXT or PSELFEXT.
How do network managers and planners know whether to test or not?
New installations: For new installations, the GEA recommends the installation of Cat 5e cabling. The Cat 5e specification includes the two tests for return loss (echo) and FEXT. Cat 6 is a proposed TIA (Telecommunications Industry Association) specification, which also includes the two tests and is in the process of standardization. Any customers evaluating Cat 6 should be aware that components labeled Cat 6 today from different vendors may not interoperate. In theory, a network planner could install Category 5 cabling but would have to include performance tests as part of the installation contract and specify return loss and FEXT testing as per TIA TSB95. In practice, all new installations should be Cat 5e or better.
Existing installations: The IEEE together with the TIA has developed two simple tests for return loss (echo) and far end cross talk (ELFEXT, PSELFEXT) to qualify links for 1000BASE-T operation. These tests can be conducted with test tools from Fluke, Hewlett Packard, Microtest, and others. All existing Category 5 links can be tested for return loss and FEXT by applying the tests. If the tests uncover problems, because the performance of the patch cords was not specified in Cat 5, such problems are most likely to occur in the easily accessible patch cords in the equipment room and work area. Most of the time, the solution involves an upgrade to Category 5e patch cords.
When can customers expect standards-based 1000BASE-T products?
The standard should be complete by June 1999. 1000BASE-T NICs, switches and other equipment are expected to begin shipping after approval of the standard. The goal of the whole Ethernet industry is to create a solid standard so that 1000BASE-T products from multiple vendors can interoperate.
Why is 1000BASE-T so important?
1000BASE-T is important for three reasons: First, most of the cabling installed inside buildings today is Cat 5 UTP, and 1000BASE-T will enable Gigabit Ethernet operation over this installed base. This enables the deployment of GbE onto horizontal copper runs as well as Into smaller networks that do not have fiber backbones or fiber in the vertical risers.
Second, 1000BASE-T, on a per-connection is expected to be very cost effective. Such cost-effectiveness will stimulate market demand.
Finally, 1000BASE-T allows auto-negotiation between 100 and 1000 Mbps, This will allow customers to easily migrate from Fast Ethernet to Gigabit Ethernet. Network managers do not have to conduct forklift upgrades of both edge and core devices simultaneously, but can deploy GbE incrementally with devices that support both FE and GbE.
Where can I get more information about 1000BASE-T and cabling?
A11: For more information on Gigabit Ethernet, or 1000BASE-T, see the GEA web page at: http://www.gigabit-ethernet.org/. For specific white papers, see:
http://www.gigabit-ethernet.org/technology/whitepapers/.
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