Flexgrid technology is now considered to be a promising solution for future high-speed network design. In this context, we need a tutorial that covers the key aspects of elastic optical networks. This tutorial paper starts with a brief introduction of the elastic optical network and its unique characteristics. The paper then moves to the architecture of the elastic optical network and its operation principle. To complete the discussion of network architecture, this paper focuses on the different node architectures, and compares their performance in terms of scalability and flexibility. Thereafter, this paper reviews and classifies routing and spectrum allocation (RSA) approaches including their pros and cons. Furthermore, various aspects, namely -fragmentation, modulation, quality-of-transmission, traffic grooming, survivability, energy saving, and networking cost related to RSA, are presented. Finally, the paper explores the experimental demonstrations that have tested the functionality of the elastic optical network, and follows that with the research challenges and open issues posed by flexible networks.Index Terms-Elastic optical networks, node architecture, spectrum management, routing and spectrum allocation, and sliceable bandwidth-variable transponder.

Buffered crossbars have been considered as an alternative for non-buffered crossbars to improve switching throughput. The drawback of a buffered crossbar is the memory amount that is proportional to the square of the number of ports (O N 2 ). This is not the main limitation when the buffer size is kept to a minimum size such that implementation is feasible. For a small buffer size, the number of ports of a switch module is not limited by the memory amount but by the pin count. We propose a novel architecture: a Combined Input-One-cell-Crosspoint Buffer crossbar (CIXB-1) with Virtual Output Queues (VOQs) at the inputs and round-robin arbitration. We show that the proposed architecture can provide 100% throughput under uniform traffic. A CIXB-1 offers several advantages for a feasible implementation such as scalability and timing relaxation. With the currently available memory technology, a one-cell crosspoint buffered switch is feasible for a 32 32 fabric module.

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