GIGABIT ETHERNET



Supervisor:         Dr. Steve Vickers

Student:            Lim Ming Hai

Course:             Information Systems Engineering II

Coursework:         Article 2 of SURPRISE '97

Date of submission: 27th May 1997

Abstract

Today's desktop computers have 10-Mbs or 100-Mbs connections that allow data to be transferred at incredible speeds, but still there are complaints of bottlenecks. This is due mainly to the changing applications of computers. As data warehousing, medical imaging, video conferencing and CAD/CAM become more commonplace, stopgap measures like centralized servers with multiple 100-Mbs network connections will quickly become saturated. One highly touted proposed solution is Gigabit Ethernet.

Origins

To examine the future direction of high-speed networking, the IEEE 802.3 committee formed a High-Speed Study Group in November 1995. In March 1996, the IEEE approved the 802.3z Task Force which focused solely on Gigabit Ethernet and developing the standard for it. The following goals have been defined by the Task Force:

Operations

Gigabit Ethernet uses a combination of protocol technologies from the original Ethernet specification and the ANSI X3T11 Fibre Channel specification. These two standards are joined as shown in the figure below:

  • Connector
    The lowest layer of the initial fiber version of the Gigabit Ethernet protocol stack uses layer FC-0 from the Fiber Channel specification. This defines the physical characteristics of the interface and media, including the cables, drivers, transmitters and receivers.

  • Serializer/Deserializer
    This lies on top of the Physical layer and supports multiple encoding schemes. Encoding is media dependent. 8B/10B encoding was designed for fiber optic media so when support for twisted pair cabling is added to the Gigabit Ethernet specification, this layer will have to provide an encoding scheme for twisted pair to work with Gigabit Ethernet.

  • 8B/10B Encode/Decode
    This layer describes the byte synchronization and the encode/decode scheme which transmits 8 bits as a 10-bit code group. The features of this scheme are low-cost component design and good transition density for easy clock recovery.

  • Media Access Control (MAC)
    Gigabit Ethernet supports both full-duplex and half-duplex transmission systems. In full-duplex mode, signals can travel in both directions simultaneously. In half-duplex mode, the MAC supports the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method as specified in Ethernet. The flow control mechanisms for the two modes will be described in more detail later.

  • Upper Layers
    Above the MAC layer, Gigabit Ethernet supports both Ethernet and IEEE 802.2 Logical Link Control (LLC) which allows multiple upper layer protocols (e.g. TCP/IP) to run over Gigabit Ethernet.

    Flow Control

    Full-Duplex Transmission
    When Gigabit Ethernet uses full-duplex transmission, signals travel in both directions on the same connection simultaneously. This allows the aggregate data rate of an Ethernet network to be doubled. In the case of Gigabit Ethernet, the network can achieve 2-Gbs data rate. With full-duplex, CSMA/CD access control mechanism need not be invoked as collisions are not possible. However, full-duplex can only be used for point-to-point connections and cannot be used for shared port connections. This means full-duplex can be used between two workstations but not between multiple workstations and a repeater. The full-duplex standard can also be used for Ethernet and Fast Ethernet.

    Half-Duplex Transmission
    In half-duplex transmission, signals can again travel in both directions on a wire but not simultaneously. To gain access to the network, Gigabit Ethernet needs to use CSMA/CD which waits for a clear channel before transmitting frames down the wire. Should two stations send frames at the same time, a collision will result and only after a random interval of time will both stations attempt to transmit again. This method is most commonly used on shared Ethernet segments. If a switch port is front-ended with a repeater or hub, it can be shared as shown in the figure below.

    Carrier Extension
    The amount of time needed for a station to send an Ethernet frame the full length of a wire and have the jam signal caused by a collision travel back to the station is the slot-time. With frames as small as 64 bytes travelling at speeds of 1000-Mbs, the normal slot-time of Ethernet is not long enough to accommodate a 100 meter cable. This means the station finishes transmitting the frame before it is aware of any collision.

    To create a longer slot-time, Gigabit Ethernet uses a technique called carrier extension. The frame size of an Ethernet packet is not changed but the time used on the wire is extended to guarantee at least a 512-byte slot-time.

    Applications

    There are numerous applications which will benefit greatly from the widespread use of Gigabit Ethernet. The most obvious ones are those that require large files to be transferred over networks.

    Large files like those created by scientific applications dealing with 3D models of molecules or desktop publishing applications which produce full colour magazines. In the case of complex medical images like CAT scans and detailed architecture plans, the file sizes are in the region of hundreds of gigabytes.

    Intranets are becoming very popular within companies that want to employ Internet technologies to allow internal users to access critical data through web browsers. Current networks can handle data and images relatively easily but with the introduction of audio and video, they will need to be upgraded.

    Data warehousing has become increasingly popular with the result being a large strain placed on networks as these warehouses may have terabytes of data stored over hundreds of platforms. The data must be updated regularly so that decision makers can have real time data on which to base critical business reports and analyses.

    Video conferencing will become commonplace as computers offer native MPEG decoding capability and as low-cost encoding chip sets become widely available. To cope with all these applications and their demands on network bandwidth, critical sections of networks can be migrated to Gigabit Ethernet.

    Migration

    Many reasons have been touted for a migration from Ethernet and Fast Ethernet to Gigabit Ethernet and some of the most compelling are:

    Cost
    Gigabit Ethernet connections will cost less than other technologies of comparable speed (e.g. 622-Mbs ATM). Still, initial costs are normally overshadowed by the costs of supporting a network. Gigabit Ethernet provides a management environment that is similar to Ethernet. With Ethernet being the most common network connection in the world, most LAN administrators and end users will require minimal re-training. Also, there is no need to invest in additional protocol stacks or middleware.

    Interoperability and backward compatibility
    Gigabit Ethernet is fully compatible with the installed base of over 70 million Ethernet nodes and provides seamless interoperability with Ethernet and Fast Ethernet. It also supports existing applications, network operating systems and network management. This means Gigabit Ethernet connections can be added to provide increased bandwidth only in those portions of the network where it is needed.

    Performance
    The raw speed of data transfer (one gigabit per second) is unmatched by any technology available now. Because Gigabit Ethernet uses the same frame format as Ethernet and Fast Ethernet, it avoids the cost, complexity and performance penalty found when translating between Ethernet and Asynchronous Transfer Mode (ATM) or any other network technology.

    References

    Charles Spurgeon
    Ethernet Configuration Guidelines
    Peer-to-Peer Communications, Inc.
    ISBN: 1-57398-012-9

    John E. McNamara
    Local Area Networks, An introduction to the technology
    Digital Press, 1985
    ISBN 0-932376-79-7

    Digital Equipment Corporation
    Network Troubleshooting Guide
    Digital Press, August 1990

    http://www8.zdnet.com/macweek/mw_1040/gw_gigabit.html
    Macweek Gateways
    October 21, 1996 / Volume 10 Number 40
    Focus on Networking
    New Gigabit Ethernet gains industry support
    By April Streeter

    http://www.cisco.com/warp/public/729/gigabit/index.html
    Cisco Systems Gigabyte ethernet solutions

    http://www8.zdnet.com/pcweek/sr/0916/18mgiga.html
    PC Week Online
    September 18, 1996
    Gigabit Ethernet technology gets real

    http://www8.zdnet.com/pcmag/issues/1603/pcmg0057.htm
    PC Magazine
    February 4, 1997
    Fast Routes to the Net
    ISDN routers offer fast, multiuser connections for telecommuting and Internet access

    http://www.zdnet.com/intweek/daily/960822a.html
    INTER@CTIVE WEEK
    August 22, 1996
    The Ascent Of Gigabit Ethernet
    By Joe McGarvey

    http://www8.zdnet.com/pcmag/issues/1603/pcmg0077.htm
    PC Magazine
    February 4, 1997
    Get into the Fast Lane: Fast Ethernet Solutions
    By Sarah L. Roberts