Layered Optical Networks -Implications to switching and transmission

With the aim of supporting and enhancing high-capacity communication networks, such as telephony, Internet and others, this work has investigated: • transmission gains with time-slotted optical communication, • performance of optical add/drop multiplexers (OADMs) and optical crossconnects (OXCs), • OXC networks serving Internet Protocol (IP)-routers, • packet hop reductions in IP-controlled optical networks, • a simple optical neighbour discovery method, • economics of complementing a client network with an optical express layer. Time-slotting was shown to enable bi-directional transmission at the same frequency and multiwavelength transmission over dispersion-shifted fibre. The cascadability of fixed and reconfigurable OADMs of various technologies was investigated using re-circulating loop experiments. The fixed OADMs could allow more than 20 hops of DWDM signals while the reconfigurable OADMs displayed somewhat poorer performance. A similar study where done for OXCs with electrical switch matrices (OEXC) and an experimental model of an optical matrix. The OEXC in 2R mode could allow 7 cascades within 2dB powerpenalty given that the signal bandwidth was substantially lower than the bandwidth of the electrical switch (in the order of 1⁄4 to 1⁄2). An experimental network, “Winchester”, consisting of OEXC, IP-routers with Gigabit Ethernet ports, and DWDM links, was built and investigated in the Stockholm area. This work investigated cost-effective IP-over-optical networks and the possibilities and difficulties of wavelength configurable IP backbones from an operator’s perspective. A management systems based on IP, Java and CORBA was also developed and evaluated. It was concluded that a cost-effective IP/Gigabit Ethernet network is well enhanced by OEXCs to achieve a well-operated network. Computer simulations showed the possibility to reduce IP-traffic hop-count by adjusting the reconfigurable network to the traffic characteristics. Up to 25% reduction is achievable. A simple method for automatic neighbour discovery was proposed and evaluated. Eliminating the need for costly electronics to read/write channel overhead information, the method make use of functions already supported by common optical ports. Finally, the cost-benefit of complementing a client network with an optical (reconfigurable) express layer was analytically investigated. With appropriate port and common equipment cost of the optical elements, the total network cost can be substantially reduced: around 30% for medium size networks (30 nodes) and up to 60% for large networks (100 nodes). ISBN 91-7283-663-6 • ISRN KTH/MVT/FR-03/9-SE • ISSN 0348-446 • TRITA-MVT Report 2003:9