Publication: SDN-based solutions for carrier-grade transport networks
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2020-12
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2020-12-14
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Abstract
De acuerdo con recientes predicciones [1] el tráfico de datos móviles crecerá 7 veces
entre 2017 y 2022, llegando a generar 77 exabytes de datos mensuales. Este incremento en
el consumo de datos crecerá de la mano de servicios innovadores que incluirán video 8K,
realidad virtual, realidad aumentada o juego remoto en la nube, además del gran número
de dispositivos inteligentes que formarán parte de las llamadas ciudades inteligentes,
casas inteligentes y el internet de las cosas (IoT). Por esta razón, se espera que las
redes de transporte móviles del futuro (5G y futuras generaciones) ofrezcan un gran
ancho de banda, nunca visto anteriormenente y una latencia mínima que permitan el
desarrollo de estos futuros servicios ralmente innovadores. Estas redes del futuro no sólo
evolucionarán buscando un incremento sustancial en el rendimiento, también ofrecerán una
reducción del gasto de operacion (OPEX) y el gasto de capital (CAPEX) para conseguir
un retorno de inversión (ROI) razonable. Estos estrictos requisitos no serán impulsados
únicamente por la introducción de especto radioeléctrico de ondas milimétricas, requerirá
un completo rediseño de la arquitectura actual, evolucionando hacia una arquitectura
basada en servicios.
El primer segmento de red que sufrirá este profundo rediseño será la red de acceso
(RAN), adoptando el concepto de Centralized/Cloud RAN (C-RAN), separando las distinas
funcionalidades de los puntos de acceso, situando las funcionalidades básicas de radio
de menor nivel en la capa de protocolos en una unidad remota, centralizando por otro
lado las funcionalidades de las capas superiores en unidades centralizadas. Las divisiones
funcionales (functional splits) tradicionales utilizadas en redes 4G están basadas en el
protocol Common Public Radio Interface (CPRI), este protocolo requiere de una red de
circuitos dedicada con unos requisitos de latencia y ancho de banda muy estrictos, estos
requisitos de ancho de banda son linealmente proporcionales al número de antenas, lo
que prácticamente imposibilita su uso en despliegues 5G ultra densos. Por esa razón
nuevos functional splits están siendo investigados, focalizando los esfuerzos en el uso de
Ethernet como tecnología convergente, hecho que a su vez difumina la separación entre
los segmentos de red de fronthaul y backhaul, conduciendo a una red integrada basada
en paquetes, normalmente denominada como crosshaul. Este movimiento hacia una red
totalmente paquetizada relaja extremadamente los requisitos de la red de transporte, abriendo oportunidades a soluciones virtualizadas, promoviendo el uso de tecnologías como
Software Defined Networking (SDN) y Network Function Virtualization (NFV).
SDN ha emergido como una potente herramienta para los operadores para gestionar
sus infraestructuras, este paradigma ofrece la posibilidad de ejecutar múltiples aplicaciones
inteligentes con el propósito de optimizar la red gracias a la centralización de la lógica de
la red en un controlador. Sin embargo, la propia naturaleza que permite esta gestión tan
eficiente y flexible, la centralización lógica, a su vez plantea numerosos desafíos debido
a la falta de herramienas de monitorización apropiadas para este tipo de arquitecturas
de red. Para poder ejecutar decisiones de manera correcta y precisa el controlador (y
las aplicaciones que ejecuta) necesita obtener datos y estadístacas de la red de manera
continua y actualizada. Sin embargo, esto no es posible con las soluciones de red basadas
en SDN existentes actualmente, debido a diversos problemas de escalabilidad y precisión.
Además, la centralización lógica del plano de control también presenta problemas de
fiabilidad y seguridad ya que un controlador centralizado es un punto único de fallo,
siendo un imporante foco de interés para conseguir la fiabilidad requerida en las redes de
operador.
La clara tendencia hacia la softwarización no se limita solamente a la inclusión del
paradigma SDN, va de la mano de la virtualización de funciones de red. Por esta razón
las redes móviles del futuro harán un uso intensivo de los centros de datos, ejecutando la
mayoría de los servicios de red de manera virtualizada. La ejecución de estos servicios
de manera virtualizada no se relizará exclusivamente en grandes centros de datos en la
nube (cloud), también se utilizarán pequeños centros de datos situados en el borde de
la red (edge) y en la niebla (fog), con el objetivo de reducir la latencia. Esta creciente
demanda está llevando a la infraestructura de red de los centros de datos al límite, cuyos
requisitos en términos no solo de latencia y ancho de banda, sino también de escalabilidad
y fiabilidad cada vez son más estrictos. Los algoritmos de switching tradicionales de
centros de datos basados en capa 2 utilizan lookup tables, llenas de direcciones Media
Access Control (MAC) de 48-bits donde el switch buscará el siguiente salto al que enviar el
paquete. Recientemente, Institute of Electrical and Electronics Engineers (IEEE) 802 ha
definido nuevos mecanismos para el uso estructurado del espacio local de direcciones MAC.
Esto permite introducir semántica en el espacio de dirección y utilizarlo en aplicaciones
para mejorar todo el proceso de reenvío de paquetes.
Desde esta perspectiva, esta tesis propone un conjunto de soluciones y arquitecturas
basadas en SDN para la siguiente generación de redes, incluyendo tanto el segmento
de transporte como los centros de datos. Comenzando con la red de transporte móvil,
esta tesis presenta un novedoso diseño de una red crosshaul completamente integrada,
implementada y desplegada utilizando whiteboxes. El diseño del pipeline de los elementos de
la red crosshaul ha sido cuidadosamente optimizado, elminando todas las operaciones que
impactaban negativamente en la latencia, adecuándolo para los functional splits de más bajo nivel. El diseño de la red crosshaul mostrado en esta tesis ha sido cuidadosamente evaluado,
convirtiéndose en la primera validación empírica de una red crosshaul completamente
integrada, capaz de transportar flujos de diferentes functional splits sobre la misma
infraestructura de red.
La solución de crosshaul basada en SDN detallada en este trabajo está acompañada
de un conjunto de herramientas para mejorar las funciones del plano de control. Esta
tesis presenta y evalúa un conjunto de herramientas de monitorización denotadas como
Adaptative Telemetry System (ATS), diseñadas con el objetivo de habilitar la ejecución
de tareas Operation Administration and Maintenance (OAM) localmente en los switches,
soportando la obtención de métricas de red de manera activa y precisa, incluyendo un
sistema de reporte al plano de control, cumpliendo con los requisitos exigidos por las
redes de operador. La solución propuesta está formada de una aplicación, un plugin
y un agente local ATS que permite la configuración remota de procedimientos OAM
utilizando máquinas de estado finitas, siendo completamente compatible con el estándar
de OpenFlow. Esta tesis también se centra en los problemas de fiabilidad existentes en la
propia naturaleza centralizada del paradigma SDN, presentando el diseño y la evaluación
de de una solución basada en la utilización de protocolos multipath para robustecer la
conectividad del canal de control. La solución presentada en esta tesis utiliza un protocolo
multipath para la creación de múltiples caminos redundantes a través de redes in-band
y out-of-band, permitiendo migrar la conexión de control de una ruta a otra de manera
segura y estable, sin ninguna interrupción.
Finalmente, esta tesis también investiga las oportunidades presentes en las nuevos
mecanismos de direccionamiento propuestos en IEEE 802 mencionados previamente para
su aplicación en redes de centros de datos. Esta tesis incluye un novedoso diseño basado
en Software Defined Addressing (SDA) que permite introducir semánticas en el espacio
de direccionamiento MAC, dando significado a la direcciones, eliminado por tanto la
necesidad de table lookups. Esta tesis detalla una validación unitaria, comparando la
solución propuesta con una solución SDN estándar, obteniendo unos resultados realmente
positivos. Después de la validación unitaria esta tesis detalla una evaluación completa
de un caso de uso potencial de la solución propuesta. Este caso de uso pretende separar
los flujos pequeños realmente sensibles a la latencia de los flujos de mayor tamaño que
demandan más ancho de banda. El caso de uso propuesto ha sido evaluado en una red de
centro de datos emulada, demostrando los beneficios potenciales en térmnos de congestión
de red que puede oferecer esta separación de tipos de tráfico.
Como conclusión, se puede decir que esta tesis analiza los déficit de las futuras redes
móviles, incluyendo tanto las redes de transporte como los centros de datos, proponiendo
un conjunto de novedosas soluciones basadas en el paradigma SDN, con el claro objetivo
de mejorar la flexibilidad, el rendimiento y la robustez de la red y a su vez reduciendo el
coste para cumplir con los requisitos establecidos para los servicios de red del futuro.
According to the recent predictions [1] mobile data traffic will increase 7-fold between 2017 and 2022, generating around 77 exabites of data per month. This data traffic increase will be pushed by innovative services including 8K video, virtual reality, augmented reality or cloud gaming, in addition to the numerous devices that will enable smart cities, smart homes, and Internet of Things (IoT). For that reason, future mobile transport networks (5G and beyond) are expected to offer unprecedented bandwidth with extreme low latency to support all this kind of innovative services, but future networks are also expected to reduce the Operational Expenditure (OPEX) and Capital Expenditure (CAPEX) to a reasonable Return on Investment (ROI) range. This stringent requirements will not only be driven by the introduction of the mmWave radio spectrum, it will require a thorough redesign of the current network architecture, moving towards a new service-based mobile system. The first network segment that will undergo this redesign is the Radio Access Network (RAN), adopting the C-RAN concept, decomposing the radio access point functionality into small footprint, placing the basic radio functions of the lower levels of the protocol stack in a remote unit, and centralizing the upper levels of the stack in a Central/Cloud unit. The traditional functional split already utilized in 4G networks, based on CPRI protocol, requires a dedicated circuit-based network with stringent requirements in terms of delay and bandwidth, the bandwidth requirements are linearly dependent with the number of antennas, making this model not feasible for ultra-dense 5G deployments. For that reason new functional splits are being investigated, using Ethernet as the common factor, blurring the traditional separation between the fronthaul and backhaul network segments, driving into a converged packet based network, commonly denoted as Crosshaul. The movement towards new packet-based functional splits relax the requirements in the transport network, enabling new opportunities for softwarized solutions, focusing on SDN and NFV technologies for the future network deployments. SDN has emerged as a basic toolset for operators to manage their infrastructure, as it opens up the possibility of running a multitude of intelligent and advanced applications for network optimization purposes in a centralized network controller. However, the nature that makes possible this efficient management and operation in a flexible way, the logical centralization, also poses important challenges due to the lack of proper monitoring tools suited for SDN-based architectures. In order to take timely and right decisions while operating a network, centralized intelligence applications need to be fed with a continuous stream of up-to-date network statistics. However, this is not feasible with current SDN solutions due to scalability and accuracy issues derived from the centralized intrinsic nature of the SDN paradigm. Furthermore, the control centralization also poses resiliency, reliability and security problems since a centralized controller is a potential single point of failure and a potential bottleneck, needing special attention in order to support the demanded carrier grade requirements. The softwarization trend does not stop with the incorporation of SDN solutions, it goes hand-in-hand with the virtualization of network functions. For that reason, future mobile networks will make extensive use of Data Center Networks (DCNs), running most virtualized network services and data processing. Not only big cloud data centers will store, compute and analyze all the data, also smaller edge and fog data centers will be used, aiming to reduce the overall network latency required in the new generation of mobile networks. This increasing demand is pushing the limits of current DCNs, requiring, like mobile transport networks, higher scalability, resiliency and performance while reducing the network deployment cost. Traditional approaches for layer-2 switching in DCNs rely on table lookups, where a flat 48-bit MAC address space is searched in order to find the next hop to forward the packet to. Very recently, the IEEE 802 has defined new mechanisms for the structured use of the local MAC address space. This new flexibility enables the embedding of semantics in the MAC addresses that can be used for new applications, such as improving the standard layer-2 forwarding process. From this perspective, this thesis proposes a set of SDN-based solutions and architectures for next generation networks, including both mobile transport and DCN. Departing from the mobile transport, this thesis presents a novel design of a fully integrated Crosshaul solution, implemented and deployed using cost-efficient SDN-based forwarding elements. The pipeline design of the Crosshaul forwarding elements presented in this thesis has been carefully optimized, eliminating the latency-impacting operations, making it suitable for lower layer functional splits. The Crosshaul design introduced in this thesis has been extensively evaluated, being the first empirical validation of a fully integrated Crosshaul network, transporting flows from various functional split options over the same switching infrastructure. The presented SDN-based Crosshaul solution is accompanied by a set of tools devoted to enrich the control plane functions. This thesis presents and evaluates a set of monitoring tools denoted as ATS, that enables the local execution of OAM procedures directly on the switches, supporting the active and precise measurements and reporting of strategic metrics, needed for the correct operation of carrier grade networks. The proposed ATS solution is formed by an ATS application, an ATS plugin and an ATS agent, allowing the remote configuration of OAM procedures by using Finite State Machine (FSMs) modelling, being fully compatible with the current OpenFlow standard. This thesis also focuses on the reliability issues present in the SDN centralized nature, presenting the design and evaluation of a multipath-based solution that aims to secure and robustize the control channel. The presented multipath solution creates several disjoint redundant paths over the out-of-band and in-band management networks allowing to seamless migrate the OpenFlow control connection from a failing path to an available one without traffic interruption. Finally, this thesis also investigates the opportunities present in the aforementioned IEEE 802 mechanisms for the structured use of the local MAC address space, and its applicability to current DCNs L2 switching schemas. This thesis includes a novel SDA solution that allows to embed semantics into the MAC addresses, giving meaning to the address structure, eliminating the need of look-up tables. This thesis incorporates a unit testing validation of the proposed SDA solution, comparing it with a baseline switching method. Due to the positive results obtained in the unit testing validation, the presented contribution also evaluates the flexibility of SDA illustrating a potential application for segregating the latency-sensitive small-frame flows from the large data-intensive large flows, evaluating it in an emulated DCN, demonstrating the potential benefits of this traffic segregation in terms of network congestion. As a conclusion, it can be said that this thesis analyzes some technical gaps of the future generation of mobile networks, ranging from mobile transport to data center networks, proposing novel SDN-based solutions aiming to increase the overall flexibility, performance and robustness while reducing the cost in order to match the stringent requirements of future network services.
According to the recent predictions [1] mobile data traffic will increase 7-fold between 2017 and 2022, generating around 77 exabites of data per month. This data traffic increase will be pushed by innovative services including 8K video, virtual reality, augmented reality or cloud gaming, in addition to the numerous devices that will enable smart cities, smart homes, and Internet of Things (IoT). For that reason, future mobile transport networks (5G and beyond) are expected to offer unprecedented bandwidth with extreme low latency to support all this kind of innovative services, but future networks are also expected to reduce the Operational Expenditure (OPEX) and Capital Expenditure (CAPEX) to a reasonable Return on Investment (ROI) range. This stringent requirements will not only be driven by the introduction of the mmWave radio spectrum, it will require a thorough redesign of the current network architecture, moving towards a new service-based mobile system. The first network segment that will undergo this redesign is the Radio Access Network (RAN), adopting the C-RAN concept, decomposing the radio access point functionality into small footprint, placing the basic radio functions of the lower levels of the protocol stack in a remote unit, and centralizing the upper levels of the stack in a Central/Cloud unit. The traditional functional split already utilized in 4G networks, based on CPRI protocol, requires a dedicated circuit-based network with stringent requirements in terms of delay and bandwidth, the bandwidth requirements are linearly dependent with the number of antennas, making this model not feasible for ultra-dense 5G deployments. For that reason new functional splits are being investigated, using Ethernet as the common factor, blurring the traditional separation between the fronthaul and backhaul network segments, driving into a converged packet based network, commonly denoted as Crosshaul. The movement towards new packet-based functional splits relax the requirements in the transport network, enabling new opportunities for softwarized solutions, focusing on SDN and NFV technologies for the future network deployments. SDN has emerged as a basic toolset for operators to manage their infrastructure, as it opens up the possibility of running a multitude of intelligent and advanced applications for network optimization purposes in a centralized network controller. However, the nature that makes possible this efficient management and operation in a flexible way, the logical centralization, also poses important challenges due to the lack of proper monitoring tools suited for SDN-based architectures. In order to take timely and right decisions while operating a network, centralized intelligence applications need to be fed with a continuous stream of up-to-date network statistics. However, this is not feasible with current SDN solutions due to scalability and accuracy issues derived from the centralized intrinsic nature of the SDN paradigm. Furthermore, the control centralization also poses resiliency, reliability and security problems since a centralized controller is a potential single point of failure and a potential bottleneck, needing special attention in order to support the demanded carrier grade requirements. The softwarization trend does not stop with the incorporation of SDN solutions, it goes hand-in-hand with the virtualization of network functions. For that reason, future mobile networks will make extensive use of Data Center Networks (DCNs), running most virtualized network services and data processing. Not only big cloud data centers will store, compute and analyze all the data, also smaller edge and fog data centers will be used, aiming to reduce the overall network latency required in the new generation of mobile networks. This increasing demand is pushing the limits of current DCNs, requiring, like mobile transport networks, higher scalability, resiliency and performance while reducing the network deployment cost. Traditional approaches for layer-2 switching in DCNs rely on table lookups, where a flat 48-bit MAC address space is searched in order to find the next hop to forward the packet to. Very recently, the IEEE 802 has defined new mechanisms for the structured use of the local MAC address space. This new flexibility enables the embedding of semantics in the MAC addresses that can be used for new applications, such as improving the standard layer-2 forwarding process. From this perspective, this thesis proposes a set of SDN-based solutions and architectures for next generation networks, including both mobile transport and DCN. Departing from the mobile transport, this thesis presents a novel design of a fully integrated Crosshaul solution, implemented and deployed using cost-efficient SDN-based forwarding elements. The pipeline design of the Crosshaul forwarding elements presented in this thesis has been carefully optimized, eliminating the latency-impacting operations, making it suitable for lower layer functional splits. The Crosshaul design introduced in this thesis has been extensively evaluated, being the first empirical validation of a fully integrated Crosshaul network, transporting flows from various functional split options over the same switching infrastructure. The presented SDN-based Crosshaul solution is accompanied by a set of tools devoted to enrich the control plane functions. This thesis presents and evaluates a set of monitoring tools denoted as ATS, that enables the local execution of OAM procedures directly on the switches, supporting the active and precise measurements and reporting of strategic metrics, needed for the correct operation of carrier grade networks. The proposed ATS solution is formed by an ATS application, an ATS plugin and an ATS agent, allowing the remote configuration of OAM procedures by using Finite State Machine (FSMs) modelling, being fully compatible with the current OpenFlow standard. This thesis also focuses on the reliability issues present in the SDN centralized nature, presenting the design and evaluation of a multipath-based solution that aims to secure and robustize the control channel. The presented multipath solution creates several disjoint redundant paths over the out-of-band and in-band management networks allowing to seamless migrate the OpenFlow control connection from a failing path to an available one without traffic interruption. Finally, this thesis also investigates the opportunities present in the aforementioned IEEE 802 mechanisms for the structured use of the local MAC address space, and its applicability to current DCNs L2 switching schemas. This thesis includes a novel SDA solution that allows to embed semantics into the MAC addresses, giving meaning to the address structure, eliminating the need of look-up tables. This thesis incorporates a unit testing validation of the proposed SDA solution, comparing it with a baseline switching method. Due to the positive results obtained in the unit testing validation, the presented contribution also evaluates the flexibility of SDA illustrating a potential application for segregating the latency-sensitive small-frame flows from the large data-intensive large flows, evaluating it in an emulated DCN, demonstrating the potential benefits of this traffic segregation in terms of network congestion. As a conclusion, it can be said that this thesis analyzes some technical gaps of the future generation of mobile networks, ranging from mobile transport to data center networks, proposing novel SDN-based solutions aiming to increase the overall flexibility, performance and robustness while reducing the cost in order to match the stringent requirements of future network services.
Description
Keywords
Software Defined Networking, SDN, Adaptative Telemetry System, ATS, Operation Administration and Maintenance, OAM, 5G-crosshaul