Optical Multiplex Section Termination

The following processes are the responsibility of the optical multiplex section (OMS) trail termination, I.E the processes initiate at the point of trail termination:  

•validation of connectivity integrity 

•assessment of transmission quality 

•transmission defect detection and indication 

 As was the case with the optical channel, the optical multiplex section (OMS) consists of a pair of bidirectional but co-located optical channel termination source and sinks functions.  

•Optical multiplex section termination source: accepts the adapted information from a client layer network at its input inserts the OMS overhead and presents the characteristic information of the OMS layer network at its output.  

•Optical multiplex section termination sink: accepts the characteristic information of the OMS layer network at its input extracts the OMS overhead and presents the adapted information at its output.  

Point-to-Point with Optical Regenerator

In this topology we will consider a straightforward point-to-point topology but with a regenerator (3R) inline. What we can see happening here is that all three layers have their respective trails terminated at the regenerator. This is because the regenerator is affecting the individual signals at the highest optical channel layer. By doing 2R or 3R regeneration on the entire signal requires disturbance and manipulation of the individual client signals at the OC layer. Consequently, these changes to the client signals require subsequent changes to be made at the lower OMS and OTC layers.

In this regeneration example, we can see that the trails in all of the layers are affected by performing, 2R or 3R regeneration of the signal. Consequently, all the OCh and OMS trails sink at the regenerator and new trails are spawned and sourced again at the regenerator’s line output. 

Again, if this equipment is going to be OTH (G.709) compliant it must have the capability to understand, process, analyze the OTH OH, and to act accordingly. 

Optical Multiplexor Section Layer

The Optical Multiplexor Section layer will be responsible for handling the preparation, grooming, and signal equalization of client signals prior to and during the multiplexor process. The OMS layer provides the path for the transport of client signals that the transponders in the optical client layer have transformed to wavelengths in preparation for their travel through the optical multiplex section trail. 

The characteristic information that exists in the optical multiplex section layer comprises two distinct logical signals:  

1.       A data stream that represents the adapted client data stream produced by the transponders in the optical channel layer 

2.       A data stream that represents the optical multiplexor section overhead (OMS)  The Optical Multiplexor Section provides the functionality for processing and networking multi-wavelength optical signals. In OTH parlance multi-wavelength can also represent a single wavelength. 

The Optical Multiplexor Section layer capabilities include the following functionality:  

• ·       Overhead processes that ensure the integrity of the multiplexor section information that has been used to adapt the original client signal 

• ·       Processes that enable the section level  operation and management functions such as section survivability  

The process for obtaining an OMS signal consists of the following steps:  

1.       The modulation of a clients signal by the optical signal section 

2.       Allocation of a specific wavelength or frequency to the optical carrier signal 

3.       Generation of the OMS overhead 

HORIZONTAL CABLING (CABLING SUBSYSTEM 1)

Horizontal cabling includes horizontal cable, telecommunications outlet/connectors in the work area (WA), mechanical terminations and patch cords or jumpers located in a telecommunications room (TR) or telecommunications enclosure (TE) and may incorporate multi-user telecommunications outlet assemblies (MUTOAs) and consolidation points (CPs). The pathways and spaces to support horizontal cabling shall be designed and installed in accordance with the requirements of TIA-569-B.

Some networks or services require applications-specific electrical components (such as impedance matching devices). These application-specific electrical components shall not be installed as part of the horizontal cabling. When needed, such electrical components shall be placed external to the telecommunications outlet/connector. Keeping application-specific components external to the telecommunications outlet/connector will facilitate the use of the horizontal cabling for varying network and service requirements. 

A minimum of two permanent links shall be provided for each work area. The cabling should beplanned to accommodate future equipment needs, diverse user applications, ongoing maintenance, relocation and service changes. Indeed, horizontal cabling is often less accessible than backbone cabling and adding or changing horizontal cabling may cause disruption to occupants and their work once the building walls and ceilings are closed after the initial installation. The time, effort, and skills required for these subsequent changes are significant and make the choice and design layout of the horizontal cabling very important to the building occupants and to the maintenance of the telecommunications infrastructure. Therefore, it is incumbent on the designer to accommodate user needs and to reduce or eliminate the probability of requiring changes to the horizontal cabling as user requirements evolve.

Each 4-pair cable at the equipment outlet shall be terminated in an eight-position modular jack. The telecommunications outlet/connector for 100-ohm balanced twisted-pair cable shall meet the requirements of ANSI/TIA/EIA-568-B.2.

Optical fibers at the equipment outlet shall be terminated to a duplex optical fiber outlet/connector meeting the requirements of ANSI/TIA-568-C.3

Wiring for Tomorrow: Undersea Fiber Cables

The first undersea cable, which was laid for telegraph, was laid in 1851 between England and France. In 1956 the first coax cable—called transatlantic link (TAT-1)—went in. TAT-1 had the capacity to carry 35 conversations over 64Kbps channels.

The first fiber undersea cable, laid in 1988, was called TAT-8 and could support 4,000 voice channels. But undersea use of fiber didn't take off until 1994, when optical amplifiers were introduced. By the end of 1998, some 23 million miles of fiber-optic cable had been laid through out the world, by dozens of companies, at tremendous cost. By mid-1999 the total transatlantic bandwidth was 3Tbps, compared to just 100Gbps in 1998. By the end of 2001, we are likely to reach6Tbps. Between Asia and Europe, in 1997, we had bandwidth of 11Gbps; by 1999, we had 21Gbps;and by 2003, we should have 321Gbps. You can see that a great deal of spending has been done on fiber-optic cable, all over the world.

Fiber technology breakthroughs are having a profound impact on service providers, and that's witnessed by the constantly changing prices for intercontinental capacity. The construction cost of 64Kbps circuits has dropped from almost US$1,500 in 1988, to US$300 in 1995, to just a couple dollars per line today. When operators purchase undersea capacity, they pay two charges. The first isa one-time charge for the bandwidth—the indefeasible right of use. The second is an ongoing operations, administration, and maintenance charge that's recurring for the maintenance vessels that service the cable, and this is typically 3% to 5% of the total purchase cost.

The economic shifts look like this for a capacity of 155Mbps: At the start of 1997, it would have costUS$20 million; in 1998, it was down to US$10 million; in early 2000, it was down to US$2 to US$3million; and in 2001, it's expected to be at US$1 million. The operations, administration, and maintenance charges have remained the same because the contracts originally called for the calculation of those charges based on the cable length as well as the bandwidth, so as you increased your bandwidth, your operations, administration, and maintenance charges increased. Those agreements were recently changed so that you are only charged the operations, administration, and maintenance costs for the length of the cable. Hence, as you expand capacity, the maintenance charge is dropped.