Optical Burst Switch as a New Switching Paradigm for High-Speed Internet

Optical Burst Switch as a New Switching Paradigm for High-Speed Internet

Joel J.P.C. Rodrigues (Instituto de Telecomunicações, University of Beira Interior, Portugal), Mário M. Freire (Institute of Telecommunications, Portugal), Paulo P. Monteiro (University of Beira Interior, Portugal) and Pascal Lorenz (Institute of Telecommunications, Portugal)
DOI: 10.4018/978-1-60566-014-1.ch152
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Abstract

The concept of burst switching was initially proposed in the context of voice communications by Haselton (1983) and Amstutz (1983, 1989) in the early 1980s. More recently, in the late 1990s, optical burst switching (OBS) has been proposed as a new switching paradigm for the so-called optical Internet, in order to overcome the technical limitations of optical packet switching, namely the lack of optical random access memory (optical RAM) and to the problems with synchronization (Baldine, Rouskas, Perros, & Stevenson, 2002; Chen, Qiao, & Yu, 2004; Qiao & Yoo, 1999; Turner, 1999; Yoo & Qiao, 1997; Xu, Perros, & Rouskas, 2001). OBS is a technical compromise between wavelength routing and optical packet switching, since it does not require optical buffering or packet-level processing as in optical packet switching, and it is more efficient than circuit switching if the traffic volume does not require a full wavelength channel. According to Dolzer, Gauger, Späth, and Bodamer (2001), OBS has the following characteristics: • Granularity—the transmission unit size (burst) of OBS is between the optical circuit switching and optical packet switching; • Separation between control and data—control information (header) and data are transmitted on a different wavelengths (or channels) with some time interval; • Allocation of resources—resources are allocated using mainly one-way reservation schemes. A source node does not need to wait for the acknowledge message from destination node to start transmitting the burst; • Variable burst length—the burst size is variable; • No optical buffering—burst switching does not require optical buffering at the intermediate nodes (without any delay).
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Introduction

The concept of burst switching was initially proposed in the context of voice communications by Haselton (1983) and Amstutz (1983, 1989) in the early 1980s. More recently, in the late 1990s, optical burst switching (OBS) has been proposed as a new switching paradigm for the so-called optical Internet, in order to overcome the technical limitations of optical packet switching, namely the lack of optical random access memory (optical RAM) and to the problems with synchronization (Baldine, Rouskas, Perros, & Stevenson, 2002; Chen, Qiao, & Yu, 2004; Qiao & Yoo, 1999; Turner, 1999; Yoo & Qiao, 1997; Xu, Perros, & Rouskas, 2001). OBS is a technical compromise between wavelength routing and optical packet switching, since it does not require optical buffering or packet-level processing as in optical packet switching, and it is more efficient than circuit switching if the traffic volume does not require a full wavelength channel. According to Dolzer, Gauger, Späth, and Bodamer (2001), OBS has the following characteristics:

  • Granularity—the transmission unit size (burst) of OBS is between the optical circuit switching and optical packet switching;

  • Separation between control and data—control information (header) and data are transmitted on a different wavelengths (or channels) with some time interval;

  • Allocation of resources—resources are allocated using mainly one-way reservation schemes. A source node does not need to wait for the acknowledge message from destination node to start transmitting the burst;

  • Variable burst length—the burst size is variable;

  • No optical buffering—burst switching does not require optical buffering at the intermediate nodes (without any delay).

In OBS networks, IP packets (datagrams) are assembled into very large size packets called data bursts. These bursts are transmitted after a burst header packet (also called by setup message or control packet), with a delay of some offset time in a given data channel. The burst offset is the interval of time, at the source node, between the processing of the first bit of the setup message and the transmission of the first bit of the data burst. Each control packet contains routing and scheduling information and is processed in core routers at the electronic level, before the arrival of the corresponding data burst (Baldine et al., 2002; Qiao & Yoo, 1999; Verma, Chaskar, & Ravikanth, 2000; White, Zukerman, & Vu, 2002). The transmission of control packets forms a control network that controls the routing of data bursts in the optical network (Xiong, Vandenhoute, & Cankaya, 2000). Details about OBS network architecture are given in the next section.

Key Terms in this Chapter

Bursts: In OBS networks, IP packets (datagrams) are assembled into very large size data packets called bursts.

Network Architecture: Defines the structure and the behavior of the real subsystem that is visible for other interconnected systems, while they are involved in the processing and transfer of information sets.

SCU: Switch control unit or signaling engine. The SCU implements the OBS signaling protocol, and creates and maintains the forwarding table and configures the optical cross connect.

One-Way Reservation Schemes: These schemes may be classified, regarding the way in which output wavelengths are reserved for bursts, as immediate and delayed reservation. JIT and JIT+ are examples of immediate wavelength reservation, while JET and Horizon are examples of delayed reservation schemes.

Burst Offset: The interval of time, at the source node, between the processing of the first bit of the setup message and the transmission of the first bit of the data burst.

Control Packet (or burst header packet or setup message): a control packet is sent in a separated channel and contains routing and scheduling information to be processed at the electronic level, before the arrival of the corresponding data burst.

Burst Assembly: Basically the process of aggregating and assembling packets into bursts at the ingress edge node of an OBS network.

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