Opaque Networks Utilizing TOS
There is a potential cost, footprint and power savings by eliminating unnecessary opto-electronic conversions on a signal path in a core optical mesh network. Current networks have seen the deployment of wavelength division multiplexing (WDM) technology, followed more recently by the deployment of an optical transport layer where optical crossconnects (OXCs) are connected using WDM links .both currently deployed WDM systems and OXCs use electronics in the signal path, thereby creating an opaque network .it is very compelling to imagine an optical transport layer where signals remain in the optical domain from the time the time the enter the network until they leave the network, thereby creating a transparent network.
To carry out the assessment of opaque and transparent networks, we make the following basic assumptions on the requirements for core mesh networks:
" Network operators require a lowest cost network, not just lowest cost network elements. For example, even though optical may be cheaper than electrical network elements, a network without wavelength conversions and tunable wavelength access in the optical domain could lead to higher network cost due to inefficient capacity usage than a network with wavelength conversions in the electrical domain.
" A network operator must not be constrained to buy the entire network from a single vendor.
" In order to build a dynamic, scalable and manageable backbone network it is essential that manual configuration be eliminated as much as possible.
" An optical switching system must be easily scalable with low cost and and a small footprint as the network grows to many hundreds of wavelength channels per fiber and to a speed 40 Gb/s
Increased traffic volume due to the introduction of new broadband services is driving carriers to deployment of an optical transport layer based on WDM. The network infrastructure of existing core networks is currently undergoing a transformation from rings using synchronous optical networks (SONET) add/drop multiplexers (ADMs) to mesh topologies using OXCs. Even though the applications driving large scale deployment of transparent optical switches are not currently in place, and the traffic demand does not currently justify the the use of transparent switches that are cost effective at very high bit rates, it is possible that at some point in the future transparent switches may be deployed in the network.,
Transparent network architecture
The transparent network is as shown. Since a signal from a client network element(NE),such as a router, connected via a specific wavelength must remain on the same wavelength when there is no wavelength conversion , only a small size switch fabric is needed to interconnect the WDMs and NEs in a node. This architecture also implies end-to-end bit rate and data format transparency. Another architecture of a transparent switch in a transparent network may include a single large fabric instead of multiple switch matrices of small port counts. If one is to provide flexibility, such an architecture design would require the use of tunable lasers at the clients and wavelength conversions.