Optical Network Structure and Terminology
An Optical Network (Fig. B) is formed by one or more Subnetworks connected by network Links, providing end-to-end service to one or more Customers.
Each subnetwork is administered by an Element Management System (EMS) and the network is administered by a Service provider. A Customer is an entity to which the service provider provides network services.
Element Management System (EMS) represents the abstraction of the subnetworks managed by EMS and the EMS itself.
Subnetwork (Fig. B) is a collection of one or more optical Network Elements (NE),
interconnected by subnetwork links, with connectivity between any pair of NE(s) (i.e., the topology is a connected graph).
A Managed Element (ME) represents the EMS view of the Network Element(NE).
Physical Termination Point (PTP) or Port is an an access point on an NE to which a link or a customer access link is attached. It is the representation of a physical port. It is defined as a source and/or sink for data transport. A good way to think about it is as a hop or (virtual) interface on a network connection. One physical TP can consist of multiple logical TPs. For instance one for each distinguishable data flow.
Connection Termination Point (CTP) represents the actual or potential endpoint of a cross-connection, link connection, or circuit. A CTP is contained within a PTP. In some cases, there is a single CTP associated with a PTP, such as with a E1 PTP. There could also be multiple CTPs, such as with vc12/VC2/VC2/VC4 CTPs contained within an STM-4 PTP. The containment relationship between ME, PTP and CTP is shown in Fig. C.
A Topological Link (TL) (Fig.B) is a physical link (for example, a fiber) between two PTPs (for example, ports), which are called aEnd TP and zEnd TP of the TL. A topological link starts in a source TP (aEnd) and ends in a sink TP (zEnd). It represents a topological relationship between two physical termination points (PTPs) for a particular layer rate. The possible set of layer rates are determined by the layer rates terminated by the PTP. The Layer rate (capacity) of TL is determined by the lowest common layer rate of the two end point TPs. Circuits/Services/Trails are provisioned through links.
A End points of a TL may belong to different subnetworks, in which case it is called a “top-level TL”, or to the same Subnetwork, and then the TL is called an “inner TL” as shown in Fig. A.