To support bursty traffic on the Internet (and especially WWW) efficiently, optical burst switching (OBS) is proposed as a way to streamline both protocols and hardware in building the future gener...

Optical burst switching (OBS) - a new paradigm for an optical Internet

Optical Packet Switching (OPS) is the promising switching technique to utilize the huge bandwidth offered by all-optical networks using the DWDM (Dense Wavelength Division Multiplexing) technology. However, optical packet contention is the major problem in an OPS network. Resolution and avoidance are two schemes to deal with the contention problem. A resolution scheme resolves collisions, while an avoidance scheme tries to reduce the number of potential collision events. Many OPS architectures rely on optical buffers to resolve contention. Unfortunately, optical buffering technology is still immature as it relies on bulky optical fiber delay lines. Furthermore, it requires a complex control. Therefore, a bufferless OPS network could still be the most straightforward implementation in the near future. In this article, we survey the contention resolution and avoidance schemes proposed for bufferless OPS networks. We also review the resolution and avoidance schemes that can handle the Quality of Service (QoS) issue in a QoS-capable bufferless OPS network.

Contention avoidance and resolution schemes in bufferless all-optical packet-switched networks: a survey

Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained.

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Benchmarking and viability assessment of optical packet switching for metro networks

This paper presents an architecture for an all optical switching node. The architecture is suitable for optical packet and optical burst switching and provides appropriate contention resolution schemes and QoS guarantees. A concept, called virtual memory, is developed to allow controllable and reasonable periods for delaying optical traffics. Related to its implementation, several engineering issues are discussed, including the use of loopbased optical delay lines, fiber Bragg gratings, and limited number of signal amplifications. In particular, two implementations using optical flip-flop and laser neuron network based control units are analyzed. This paper also discusses the implementation and performance of an alloptical synchronizer that is able to synchronize arriving data units to be aligned on the clock signal associated with the beginning time of slots, in the node, with an acceptable error.

A New All-Optical Switching Node Including Virtual Memory and Synchronizer

We address the problem of congestion resolution in optical packet switching (OPS). We consider a fairly generic all-optical packet switch architecture with a feedback optical buffer constituted of fiber delay lines (FDL). Two alternatives of switching granularity are addressed for a switch operating in a slotted transfer mode: switching at the slot level (i.e., fixed length packets of a single slot) or at the burst level (variable length packets that are integer multiples of the slot length). For both cases, we show that in spite of the limited queuing resources, acceptable performance in terms of packet loss can be achieved for reasonable hardware resources with an appropriate design of the time/wavelength scheduling algorithms. Depending on the switching units (slots or bursts), an adapted scheduling algorithm needs to be deployed to exploit the bandwidth and buffer resources most efficiently.

http://users.atlantis.ugent.be/cdvelder/publications/papers/journals/callegati__scheduling_OPS_var_and_fixed__pnet_sep_2004.pdf

Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

Future network should be able to efficiently serve packet-based networks, such as the Internet. In this paper, based on results from COST 266, we explore characteristics of optical burst switching (OBS) and optical packet switching (OPS). Both node design and metropolitan area network (MAN) are discussed. A unique joint comparative performance evaluation of contention resolution in OBS and OPS are presented, as well as methods of quality of service (QoS) differentiation in OBS/OPS networks, and their performance.

Optical burst and packet switching: node and network design, contention resolution and quality of service

Optical burst and packet switching: node and network design, contention resolution and quality of service, Results from the study in COST 266

Optical Packet Switching (OPS) and Optical Burst Switching (OBS) are optical networking concepts based on fully exploiting fast dynamic allocation of (D)WDM channels. Compared to more static approaches focussing on providing end-toend optical channels, OPS and OBS aim at providing greater bandwidth efficiency, granularity and flexibility. In this paper we give an overview of the issues arising when designing an optical switch for either OPS or OBS, including packet formats, contention resolution techniques, and switching fabrics.

Node architectures for optical packet and burst switching.

Most existing wide area telecommunication networks (WAN) have an SDH based, electronically circuit switched transport core. Connection setup or tear down may require days or weeks and multiplexing/demultiplexing always require complex optical/electro/optical (O/E/O) conversions. Nowadays, the operators and vendors are working on an optical control plane, which should control setup and tear down of connections. Work on automatically switched optical network (ASON) and generalised multi-protocol label switching (GMPLS) takes place within ITU and IETF, respectively. Resulting optically circuit switched (OCS) networks can offer explicit transfer guarantees, since circuit establishments are confirmed. However, this generates a delay equal at least to the round-trip time, typically several ms. Even though OCS networks will offer more flexibility than today's solution, the access to the optical bandwidth will still be provided with fibre/wavelength granularity. Future networks should be able to serve a client layer that includes packet-based networks, such as the Internet, which may have a highly dynamic connection pattern with a significant portion of bursty traffic between the communicating pairs. In this case, OCS transport may not be flexible enough. It would require over-dimensioning of the number of connections and of the bandwidth reservation of each connection, to avoid excessive delay and extensive buffering at the ingress router. Here is when Optical Packet Switching (OPS) and Optical Burst Switching (OBS) come into play, with the goal of reducing delays and improving the utilisation of the network's resources through statistical multiplexing. This comes at the expense of not being able to offer explicit transfer guarantees. However, suitable node design and proper dimensioning of network resources may enable support of most services over the same network. OPS and OBS logical performance in relation to contention resolution and quality of service (QoS) differentiation will be discussed in 4.3 and 4.4. Moreover, hybrid schemes are possible where OPS and OBS share the WDM layer with an OCS scheme, serving applications with the need for explicit transfer guarantees. Europe has been very active in OPS research, especially through projects like RACE ATMOS [1], ACTS KEOPS [2], IST DAVID [3], IST STOLAS [4] and COST 266. OBS was proposed very recently [5], but different research groups in Europe have already made significant contributions to this field, as later sections in this chapter show. Inevitably, there are some differences in terminology within the research community; we here explicitly describe some concepts and terms used in this chapter. Both optical packet …

Elise Baert

Papers

Optical burst and packet switching: node and network design, contention resolution and quality of service

Optical burst and packet switching: node and network design, contention resolution and quality of service, Results from the study in COST 266

Node architectures for optical packet and burst switching.

Optical burst switching and optical packet switching

Architectures for optical packet and burst switches (Invited)