Layered optical networks : implications to switching and transmission

Author: Stefan Larsson; Kth; []

Keywords: ;

Abstract: With the aim of supporting and enhancing high-capacitycommunication networks, such as telephony, Internet and others,this work has investigated:· transmission gains withtime-slotted optical communication, · performance ofoptical add/drop multiplexers (OADMs) and optical crossconnects(OXCs), · OXC networks serving Internet Protocol(IP)-routers, · packet hop reductions in IP-controlledoptical networks, · a simple optical neighbour discoverymethod, · economics of complementing a client network withan optical express layer.Time-slotting was shown to enable bi-directionaltransmission at the same frequency and multiwavelengthtransmission over dispersion-shifted fibre. The cascadabilityof fixed and reconfigurable OADMs of various technologies wasinvestigated using re-circulating loop experiments. The fixedOADMs could allow more than 20 hops of DWDM signals while thereconfigurable OADMs displayed somewhat poorer performance. Asimilar study where done for OXCs with electrical switchmatrices (OEXC) and an experimental model of an optical matrix.The OEXC in 2R mode could allow 7 cascades within 2dBpowerpenalty given that the signal bandwidth was substantiallylower than the bandwidth of the electrical switch (in the orderof ¼ to ½).An experimental network,“Winchester”, consistingof OEXC, IP-routers with Gigabit Ethernet ports, and DWDMlinks, was built and investigated in the Stockholm area. Thiswork investigated cost-effective IP-over-optical networks andthe possibilities and difficulties of wavelength configurableIP backbones from an operator’s perspective. A managementsystems based on IP, Java and CORBA was also developed andevaluated. It was concluded that a cost-effective IP/GigabitEthernet network is well enhanced by OEXCs to achieve awell-operated network. Computer simulations showed thepossibility to reduce IP-traffic hop-count by adjusting thereconfigurable network to the traffic characteristics. Up to25% reduction is achievable. A simple method for automaticneighbour discovery was proposed and evaluated. Eliminating theneed for costly electronics to read/write channel overheadinformation, the method make use of functions already supportedby common optical ports.Finally, the cost-benefit of complementing a client networkwith an optical (reconfigurable) express layer was analyticallyinvestigated. With appropriate port and common equipment costof the optical elements, the totalnetwork cost can besubstantially reduced: around 30% for medium size networks (30nodes) and up to 60% for large networks (100 nodes).