Case Study

3 Toplogies of Fiber Optic Modems

Buenoptic,as a manufacturer of various fieldbus/ethernet/serial to fiber optic converters,in recent years is engaged in both products markting and fiber optic converter products' knowledge propaganda,which helps customers know better about the application of fiber optic converter products.

Currently,the fiber opticconverter products mainly include 3 link ways:

  • Point to point:

In telecommunications, a point-to-point connection refers to a communications connection between two nodes or endpoints. An example is a telephone call, in which one telephone is connected with one other, and what is said by one caller can only be heard by the other. This is contrasted with a point-to-multipoint or broadcast communication topology, in which many nodes can receive information transmitted by one node. Other examples of point-to-point communications links are leased lines, microwave relay links, and two way radio. Examples of point-to-multipoint communications systems are radio and television broadcasting.The term is also used in computer networking and computer architecture to refer to a wire or other connection that links only two computers or circuits, as opposed to other network topologies such as buses or crossbar switches which can connect many communications devices.

  • Multi-drio Bus(MDB,Multi-point or Line):

A multidrop bus (MDB) is a computer bus in which all components are connected to the same set of electrical wires. A process of arbitration determines which device gets the right to be the sender of information at any point in time. The other devices must listen for the data that is intended to be received by them.

Multidrop buses have the advantage of simplicity and extensibility, but electronically are limited to around 200–400 MHz (because of reflections on the wire from the printed circuit board (PCB) onto the die) and 10–20 cm distance (SCSI-1 has 6 metres). ODT (On-die termination) circuits in modern SDRAM chips are examples of facing such a problem of electrical impedance discontinuity. Fully Buffered DIMM is a totally different approach of not using the multidrop bus architecture to connect multiple DRAM modules to a memory controller. Multidrop standards such as PCI are therefore being replaced by point-to-point systems such as PCI Express.

Multidrop buses are also used by vending machine controllers to communicate with the vending machine's components, such as a currency detector (coin or note reader). Not surprisingly, these MDB buses communicate with the MDB protocol, a 8-bit serial protocol with an additional mode bit. The mode bit differentiates between ADDRESS and DATA bytes.

  • Redundant Ring(In USA,aslo called Dual Self-healing ring SHR,or DSHR):

A self-healing ring, or SHR, is a telecommunications term for loop network topology, a common configuration in telecommunications transmission systems. Like roadway and water distribution systems, a loop or ring is used to provide redundancy. SDH, SONET and WDM systems are often configured in self-healing rings.

The system consists of a ring of bidirectional links between a set of stations, typically using optical fiber communications. In normal use, traffic is dispatched in the direction of the shortest path towards its destination. In the event of the loss of a link, or of an entire station, the two nearest surviving stations "loop back" their ends of the ring. In this way, traffic can still travel to all surviving parts of the ring, even if it has to travel "the long way round".

A second break in the ring may divide it into two sub-rings, but in such a case each sub-ring will remain functional.

Advantages:Self-healing rings offer high levels of resilience at low cost, since it is often geographically easy to take multiple paths across the landscape and link them up into a ring with very little extra fibre length.

Recent submarine communications cables are typically built in pairs, to function as a self-healing ring.

Very high resilience systems are typically built on interconnected meshes of self-healing rings.

Another example of a self-healing ring network technology is the FDDI local-area network.

Resilient Packet Ring is a new technology for packet-switched self-healing ring networks.

These types of rings mainly used for saving high rate traffic flowing in Telecom networks.

See also

Picture Diagrams for the 3 link ways: