Reconfigurable Optically Interconnected Systems

With the immense growth of data consumption in today's data centers and high-performance computing systems driven by the constant influx of new applications, the network infrastructure supporting this demand is under increasing pressure to enable higher bandwidth, latency, and flexibility requirements. Optical interconnects, able to support high bandwidth wavelength division multiplexed signals with extreme energy efficiency, have become the basis for long-haul and metro-scale networks around the world, while photonic components are being rapidly integrated within rack and chip-scale systems. However, optical and photonic interconnects are not a direct replacement for electronic-based components. Rather, the integration of optical interconnects with electronic peripherals allows for unique functionalities that can improve the capacity, compute performance and flexibility of current state-of-the-art computing systems. This requires physical layer methodologies for their integration with electronic components, as well as system level control planes that incorporates the optical layer characteristics. This thesis explores various network architectures and the associated control plane, hardware infrastructure, and other supporting software modules needed to integrate silicon photonics and MEMS based optical switching into conventional datacom network systems ranging from intra-data center and high-performance computing systems to the metro-scale layer networks between data centers. In each of these systems, we demonstrate dynamic bandwidth steering and compute resource allocation capabilities to enable significant performance improvements. The key accomplishments of this thesis are as follows. In Part 1, we present high-performance computing network architectures that integrate silicon photonic switches for optical bandwidth steering, enabling multiple reconfigurable topologies that results in significant system performance improvements. As high-performance systems rely on increased parallelism by scaling up to greater numbers of processor nodes, communication between these nodes grows rapidly and the interconnection network becomes a bottleneck to the overall performance of the system. It has been observed that many scientific applications operating on high-performance computing systems cause highly skewed traffic over the network, congesting only a small percentage of the total available links while other links are underutilized. This mismatch of the traffic and the bandwidth allocation of the physical layer network presents the opportunity to optimize the bandwidth resource utilization of the system by using silicon photonic switches to perform bandwidth steering. This allows the individual processors to perform at their maximum compute potential and thereby improving the overall system performance. We show various testbeds that integrates both microring resonator and Mach-Zehnder based silicon photonic switches within Dragonfly and Fat-Tree topology networks built with conventional equipment, and demonstrate 30-60% reduction in execution time of real high-performance benchmark applications. Part 2 presents a flexible network architecture and control plane that enables autonomous bandwidth steering and IT resource provisioning capabilities between metro-scale geographically distributed data centers. It uses a software-defined control plane to autonomously provision both network and IT resources to support different quality of service requirements and optimizes resource utilization under dynamically changing load variations. By actively monitoring both the bandwidth utilization of the network and CPU or memory resources of the end hosts, the control plane autonomously provisions background or dynamic connections with different levels of quality of service using optical MEMS switching, as well as initializing live migrations of virtual machines to consolidate or distribute workload. Together these functionalities provide flexibility and maximize efficiency in processing and transferring data, and enables energy and cost savings by scaling down the system when resources are not needed. An experimental testbed of three data center nodes was built to demonstrate the feasibility of these capabilities. Part 3 presents Lightbridge, a communications platform specifically designed to provide a more seamless integration between processor nodes and an optically switched network. It addresses some of the crucial issues faced by the works presented in the previous chapters related to optical switching. When optical switches perform switching operations, they change the physical topology of the network, and they lack the capability to buffer packets, resulting in certain optical circuits being unavailable. This prompts the question of whether it is safe to transmit packets by end hosts at any given time. Lightbridge was developed to coordinate switching and routing of optical circuits across the network, by having the processors gain information about the current state of the optical network before transmitting packets, and being able to buffer packets when the optical circuit is not available. This part describes details of Lightbridge which is constituted by a loadable Linux kernel module along with other supporting modifications to the Linux kernel in order to achieve the necessary functionalities

The 5G era of mobile networks: a comprehensive study of the related technologies accompanied by an experimentation framework

Οι συνεχώς αυξανόμενες απαιτήσεις από τα δίκτυα κινητών επικοινωνιών για τη παροχή καλύτερων υπηρεσιών και τη διασύνδεση όλων και περισσότερων συσκευών, ωθούν τη κοινότητα του κλάδου στην ανάπτυξη νέων μεθόδων και τεχνολογιών οργάνωσης των δικτύων προκειμένου να αντιμετωπιστεί αποτελεσματικά αυτή η πρόκληση. Δεδομένου ότι η παρούσα τεχνολογία έχει φτάσει στα όρια της από άποψη ικανότητας διαχείρισης της κίνησης, απαιτείται η ανάπτυξη ενός νέου πλαισίου λειτουργίας το οποίο θα μπορεί να ανταποκριθεί αποτελεσματικά στις νέες συνθήκες που διαμορφώνονται από τη τηλεπικοινωνιακή αγορά. Η 5 η γενιά των δικτύων κινητών επικοινωνιών (5G) αποσκοπεί στην επίλυση ακριβώς αυτού του ζητήματος, μέσα από την ανάπτυξη ενός νέου μοντέλου λειτουργίας. Το μοντέλο αυτό αναδιαρθρώνοντας εκ βάθρων τον τρόπο λειτουργίας του δικτύου σε όλα τα επίπεδα, σχηματίζει ένα νέο οικοσύστημα δικτυακών υποδομών και λειτουργιών το οποίο επιτρέπει τη παροχή στους χρήστες υπηρεσιών υψηλού επιπέδου, προσαρμοσμένες στις εκάστοτε ανάγκες τους. Στα πλαίσια της παρούσας εργασίας μελετήθηκαν εκτενώς οι θεμελιώδεις αρχές και οι κυριότερες τεχνολογίες που διέπουν τη λειτουργία ενός δικτύου νέας γενιάς καθ’ όλο το μήκος του. Ξεκινώντας από τις καινοτομίες που αφορούν τη δομή των 5G δικτύων σε επίπεδο αρχιτεκτονικής, η ανάλυση επεκτείνεται με μία προσέγγιση από κάτω προς τα πάνω· στα επίπεδα εκπομπής και πρόσβασης στο δίκτυο (C-RAN & MAC), στους μηχανισμούς που είναι υπεύθυνοι για παροχή των λειτουργιών και υπηρεσιών του δικτύου (NFV), ενώ εν συνεχεία γίνεται αναφορά στο νέο μοντέλο δρομολόγησης και διαχείρισης της κίνησης συνολικά στο δίκτυο (SDN) και σε επόμενο στάδιο παρουσιάζεται η τεχνολογία που αφορά την ικανότητα παροχής διακριτών υπηρεσιών στους χρήστες (E2E Slicing). Ακόμα, παρουσιάζονται ορισμένοι χαρακτηριστικοί δείκτες και μετρικές που σχετίζονται με τη προτυποποίηση των τεχνολογιών του δικτύου καθώς και όλες οι τρέχουσες εξελίξεις που αφορούν την ανάπτυξη του 5G στην Ευρώπη. Στη συνέχεια παρουσιάζονται τα δεδομένα του πειράματος που διεξήχθη για τους σκοπούς της εργασίας και αφορά αφενός τη μοντελοποίηση ενός υφιστάμενου δικτύου με βάση τα νέα πρότυπα του 5G και αφετέρου την αξιολόγηση της απόδοσης του με βάση ορισμένα σενάρια σχετικά με τη τοπολογία και το πλήθος των δεδομένων που ανταλλάσσονται κάθε στιγμή στο δίκτυο. Η εξέταση των παραμέτρων αποδοτικότητας εστιάζει στην ικανότητα του ONOS SDN Controller να διαχειρίζεται τη κίνηση των δεδομένων όταν προκύπτουν ορισμένα συμβάντα που επηρεάζουν την αρχική δομή του δικτύου. Ως προς τα αποτελέσματα των μετρήσεων που διεξάγονται, παρόλο που φαίνεται το θετικό αντίκτυπο που θα έχει η ενσωμάτωση των νέων τεχνολογιών στην απόδοση των δικτύων κινητών επικοινωνιών, υπάρχουν ακόμα ορισμένα επιμέρους ανοικτά ζητήματα τα οποία χρήζουν περαιτέρω έρευνας από τη πλευρά των μελών της τηλεπικοινωνιακής κοινότητας ώστε να μην υποσκαφθεί τελικά το αρχικό όραμα της καθολικής λειτουργίας όλων των κινητών συσκευών υπό μία ενιαία ομπρέλα.The ever-increasing demand from mobile communications networks for the provision of better services and interconnection of more devices is pushing the industry's community to develop new network organization methods and technologies in order to effectively address this challenge. As the current technology has reached its limits in terms of traffic management capability, it is necessary to develop a new operating framework that can effectively respond to the new conditions created by the telecommunications market. The 5th generation of mobile communication networks (5G) aims to solve this exact issue by developing a new operating model. This model, by thoroughly restructuring the way the network operates at all levels, forms a new ecosystem of network infrastructures and functions that enables the provision of high-level services to users, tailored to their particular needs. The fundamental principles and key technologies that govern the operation of a new generation network throughout its entire length were extensively studied in the context of this paper. Starting with the innovations regarding the structure of 5G networks at the architectural level, the analysis extends to a bottom-up approach: from the broadcast and access levels to the network (C-RAN & MAC) to the mechanisms responsible for delivering the network's functions and services (NFV). Then, the new network-based routing and traffic management (SDN) model is introduced, and the technology for providing distinctive services to users (E2E Slicing) is presented. Furthermore, some characteristic indicators and metrics related to the standardization of the network's technologies are presented, as well as all the current developments related to the development of 5G in Europe. Then, the data of the experiment carried out for the purposes of the paper is presented. On the one hand, this data concerns the modeling of an existing network based on the new 5G standards and, on the other hand, the evaluation of its performance based on some scenarios regarding the topology and the amount of data exchanged at any time on the network. The examination of the efficiency parameters focuses on the ability of the ONOS SDN controller to manage the traffic of the data when certain events affecting the original network structure occur. In terms of the results of the measurements being carried out, although the positive impact of the incorporation of new technologies on the performance of mobile communications networks appears to be positive, there are still some individual open issues that need further research by members of the telecommunications community in order for the original vision of the universal operation of all mobile devices under one single umbrella not to be ultimately undermined