Multiplexer regulates 20 data streams on one ?ber

March 1, 1995

Multiplexer regulates 20 data streams on one ?ber


Representing a commercially viable prototype already functioning in two demanding business applications, the Muxmaster multiplexer, developed at the IBM T.J. Watson Research Center in Yorktown Heights, NY, can simultaneously deliver 20 data streams--for instance, text, video, audio and image files--over a single optical fiber.

Equally compelling, by incorporating wavelength-division multiplexing technology and point-to-point connectivity, Muxmaster can structure each data stream with a different protocol, including synchronous optical network, asynchronous transfer mode and fiber distributed data interface.

"Growth in information processing capabilities and storage capacity created a demand to link multiple users and multiple sites," says Paul E. Green Jr., manager of advanced optical networking at the IBM Research Center. "Optical technologies provide customers a cost-effective solution to their information transmission needs."

Current transmission methodologies barely tap the potential capacity of optical fiber because they are based on old technology that transmits a single stream of data at one optical wavelength through each fiber. This process means that only 0.008% to 0.02% of the total capacity of each fiber is being utilized.

As all-optical lightwave technology improves, networks should steadily encroach on the calculated 25,000-gigahert¥bandwidth of optical fiber, which can theoretically support 50,000 200-megabit-per-second channels.

Fiber-optic multiplexer

The Muxmaster fiber-optic multiplexer brings together data streams from such multiple low-speed sources as computers and associated devices, transmits them in one or more channels through an optical fiber and then redistributes the individual data streams to their appropriate destinations at the receiving end.

Using wavelength-division multiplexing technology, the multiplexer can transmit ten 200-Mbit/sec, full-duplex (simultaneous, two-way) channels over a single 50-kilometer fiber. It also transmits each channel at a different optical wavelength from 1540 to 1549 nanometers, spaced 1 nm apart, without interfering with the other channels. The optical link allows a 20-times greater usage of fiber bandwidth than previously available.

Says Jeff Jaffe, research center vice president for systems, "We view technologies such as Muxmaster as only the first step leading to all-optical networking."

The multiplexing functions are transparent to the computer equipment attached to each end of the multiplexer. Each full-duplex channel behaves as though it has two dedicated fibers.

To preserve an unimpeded optical light path so that the wavelengths do not lose their identities, the multiplexer cannot be connected to any intermediate electronic equipment. Erbium-doped optical amplifiers, however, can be interconnected between multiplexers.

The multiplexer`s transmitters use telecommunications-grade lasers capable of sending digital data at 1 gigabit per second. Bit rate per channel is limited to 200 Mbits/sec in each direction to obtain a transmission distance of 50 km. Equipment modifications can be made to achieve 622-Mbit/sec transmissions, but over shorter distances.

Applications underway

Working with Morgan Stanley in New York and Bank of Austria in Vienna, Muxmaster is currently undergoing beta testing in high-speed transaction transmission and immediate back-up environments. Both financial organizations are using the multiplexer to support rapid disaster recovery by providing nearly instant real-time mirroring, or duplication, of data between computing sites. In both applications, the multiplexer provides 24-hour/seven-day-a-week availability of up-to-the-millisecond information.

Other data-intensive applications require site-data backup for airline reservations, healthcare claims and insurance forms. In these areas, immediate access to all the available data improves operational efficiency, reduces overall costs and provides competitive advantages.

For all these applications, Muxmaster imparts a twenty-fold increase in the capacity of an optical fiber, while potentially saving 95% of the cost of a leased fiber. For example, the cost of renting a single fiber starts at $150 to $300 per mile per month. Assuming a rate cost of $150 per mile per month, a multiplexer running a 10-channel two-way link over 10 miles of fiber could save customers $362,000 per year in fiber costs.

Protocol menagerie

Protocol conversion is a serious problem for commercial networks where computer and electronics equipment from multiple vendors function under different rules and bit rates. Says Green, "Every commercial user faces a protocol zoo."

Many users face the complex problem of supporting different data-handling protocols. To accommodate, they usually have to build separate support infrastructures or do costly protocol conversions. Optical linking via Muxmaster overcomes these restrictions.

Remarks Green, "Customers save on fiber cost, can send 20 protocols and use separate channels for connecting to different vendor equipment."

The optical multiplexing/demultiplexing function is accomplished at each link end by pigtailed grating units made by Jobin-Yvon in Paris. The grating units are housed in an 8-inch square aluminum box with 21 pigtailed fibers; one fiber serves as the common fiber. They can optically multiplex 20 1-Gbit/sec streams onto the common fiber.

A temperature-controlled environment isolates the grating units at both ends of the link. A 40C temperature difference can exist between both link ends, and the system will not lose more than 1 decibel of link margin.

Online servicing

A key feature enables users to add or delete full-duplex channels by plugging or unplugging interchangeable circuit cards while Muxmaster is fully powered and operating.

The multiplexer equipment rack contains two rows of pluggable cards. The 10 laser-receiver cards in one row include a distributed-feedback laser, a photodiode receiver and a power supply, as well as safety circuits, diagnostic sensing functions, and optical and electrical interfaces to the backplane. The laser-receiver cards differ only with respect to wavelength.

An eleventh card in the laser-receiver serves as a diagnostic card. It accepts data from sensing points, processes the data and sends the data on an RS-232 connection to the user`s network management software. In one setup, a simple network management protocol subagent runs under AIX, IBM`s version of Unix. A twelfth card holds drive and diagnostic circuits for grating-unit temperature stabilization.

The other row holds 10 input/output cards, each "personalized" to the specific protocol desired.

The hot-pluggable cards contain special connectors that have different length pins. These pins engage and disengage in a certain serial order. The last pin engagement turns on the power. In unplugging, the first disengagement pin turns off the power. A chip on each card ensures a gentle transient. Users can therefore perform maintenance on one card while the other channels run unaffected.

Another available service feature includes a photonic switch at both ends of the link that will switch automatically to a backup fiber within a few milliseconds if the diagnostic card indicates failure of the primary fiber. In addition, the multiplexers can be arranged in a ring configuration so that each wavelength is transmitted clockwise and counterclockwise. Should the primary fiber fail, the backup direction is then immediately substituted.

Notes Green, "The backup fiber has not been installed in present units, but backup facilities are easily added because this option has been designed in." Actuation of the backup fiber is done via diagnostic software hooks that check laser operation, power operation and laser-receiver card functions.

Pricing is $200,000 to $250,000 per multiplexer, depending on the number of channels used. Final pricing has not been determined. q

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