This paper discusses merits and drawbacks of the Optical Burst Switching (OBS) paradigm, which received so much attention by the academic research community. Since the topic is hot, and given the several flavors of OBS available in the literature, we first define what we mean by OBS. Then, we carefully design a reference scenario and a set of evaluation experiments that can be used to obtain quantitative answers to interesting questions in a repeatable way. Within this framework, we motivate our skepticism towards two frequent assertions about the OBS paradigm: its ability to (i) exploit the network bandwidth more efficiently than Optical Circuit Switching (OCS) alternatives, and (ii) to efficiently solve contentions without optical buffers.

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On the Myths of Optical Burst Switching

Optical networking paradigms based on statistical multiplexing, such as Optical Burst Switching or Optical Packet Switching, require the adoption of suitable contention resolution mechanisms at the optical nodes due to packets/bursts attempting to get access to the shared output channel at the same time. In the most general case of multi-fiber output links, contentions are tried to be solved by exploiting different domains — namely space, wavelength and time — and by applying an optimal scheduling policy. This paper focuses on the key parameters that can be used to design and optimize an optical packet/burst contention resolution scheme and shows how such parameters should be correlated for a correct performance assessment, taking into account feasibility trade-offs due to limited optical buffering and wavelength conversion capability.

Key parameters for contention resolution in multi-fiber Optical Burst/Packet Switching nodes

This paper proposes a methodology to compare scheduling algorithms for congestion resolution in optical burst switching or optical packet switching networks, focusing on the issue of wavelength conversion capabilities. The performance of such algorithms when full wavelength conversion is available at the switching nodes are compared with the case of conversion capabilities over a limited range of wavelengths. The results presented show that limited range wavelength conversion is not necessarily performing worse than full wavelength conversion, as long as the correct terms of comparison are considered.

OPN06-6: Congestion Resolution in Optical Burst/Packet Switching with Limited Wavelength Conversion

The WASPNET project proposed a packet sequence criterion to preserve end-to-end packet order in optical packet switching (OPS) networks controlled by the scattered wavelength path (SCWP) operational mode. This paper shows that this packet ordering methodology causes performance impairments, related to unbalanced wavelength usage in fibre links. This skewed usage is inherent to the WASPNET sequencing criterion. As a solution, a round-robin sequence criterion is proposed. The presented technique eliminates non-uniform wavelength utilisation in fibre links for any traffic pattern, as well as the performance impairments associated. We also propose an optimum scheduling algorithm for OPS output-buffered switch fabrics, which preserves packet order by following the new sequencing criterion. Copyright © 2005 AEIT.

Round-robin wavelength assignment: a new packet sequence criterion in optical packet switching SCWP networks

We present a novel non-conventional approach to the future optical and wireless hybrid transport network that is capable of supporting the dominating kinds of traffic, i.e., voice/real-time, wireless and packet traffic, in a single transport network. The proposed model combines different technologies as connection and connectionless networks, optical cable and wireless (microwave/millimetre wave or optical wireless) and it is suitable for a variety of purposes and services in order to achieve global broadband networking features. Our new networking model contains an extension to the wireless world in order to achieve mobility and personalisation of the connection. It consists of an upgrade of real-time traffic with a microwave modulated optical wave, in order to carry out conventional mobile wireless via optical fibres though long distances and without a significant distortion. The whole available bandwidth can be fully exploited in the hybrid network. In the IP part of the network, quality of service can be differentiated for various classes of packets and network reliability/survivability can be categorised for the whole hybrid network. This substitutes the complete and revolutionary shifting to packet traffic, that many promote, with smooth evolutionary upgrades.

Towards broadband global optical and wireless networking

https://www.cba.upc.edu/downloads/category/11-articles?download=412:[ARTICLE]OSN_UNIBO-UPC.pdf

Keeping the packet sequence in optical packet-switched networks

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 …

Optical burst switching and optical packet switching

https://cba.upc.edu/downloads/category/11-articles?download=413:[article]comnet2005_careglio.pdf

J. Solé Pareta

Papers

Keeping the packet sequence in optical packet-switched networks

Optical burst switching and optical packet switching

Service category-to-wavelength selection technique for QoS support in connection-oriented optical packet switching

Keeping the Packet Sequence in Optical Packet-Switched Networks