István Moldován

Performance of rapid spanning tree protocol in access and metro networks

Ethernet provides a simple and low-cost solution at high bandwidth for access and metropolitan networks. The failover performance of bridges is indispensable of their applicability. Therefore, new IEEE protocols were developed and deployed in support of fast recovery. Rapid Spanning Tree Protocol (RSTP) is the current fault handling mechanism for generic topologies, which is included in the standards and implemented in each Ethernet bridge nowadays. There are many different statements about the recovery time of RSTP from the order of seconds down to the order of ten milliseconds. Most of these analyses only rely on simulation results assuming ideal conditions. This paper reports on the performance of RSTP in real environment. It presents an experimental performance analysis of RSTP based on measurement results from test networks comprising Ethernet bridges from various vendors. Basic processing times and hardware delays are deeply analyzed for small topologies and the performance of RSTP is then characterized for larger network topologies.

Bandwidth guarantees for resilient Ethernet networks through RSTP port cost optimization

Ethernet protocol is the most wide-spread protocol in the local area network (LAN) environment. It is cost effective, simple, and provides high speeds, exactly what is needed in the provider network. However, deployment in the provider network imposes carrier-grade requirements. Standardization bodies realized this, and they are extending its capabilities: QoS support and traffic management by 802.1Q virtual LANs (VLANs), traffic engineering by 802.1s multiple spanning tree protocol (MSTP), administration and management issues by 802.1 ag connectivity fault management (CFM). However, with carrier-grade extensions Ethernet started to lose an important property: simplicity. Often the topology of the Ethernet aggregation is simple, tree-like, so complex protocols like MSTP are not required even when resilience is supported by adding several links. In most cases the plain rapid spanning tree protocol (RSTP) can provide the necessary restoration and loop protection capability. However, the default settings of the RSTP protocol may not provide optimal network utilization, and it is difficult to predict its behavior after a failure. In this paper we present a tool for RSTP optimization, which engineers the network for best utilization while also ensures that optimal paths will be selected after a link failure. The result of the optimization is a port cost set for all bridge interfaces. The optimization is performed off-line using an integer linear program (ILP). We show that compared to the default settings higher throughput can be achieved, while the required bandwidth is guaranteed in case of any link failure.

Optimizing QoS aware Ethernet spanning trees

Ethernet is gaining in importance in both access and metro networks. As a layer 2 technology, Ethernet gives a basic framework for routing, QoS and traffic engineering (TE), as well as a protocol for building up trees. IEEE 802.1 standards define default configuration parameters considering the topology only. We propose methods for resource management in Ethernet networks through spanning tree optimization for both STP (spanning-tree protocol) (IEEE 802.1D) and MSTP (multiple spanning-tree protocol) (IEEE 802.1s). As a result of optimization, we assign costs to the bridge ports in the network to build trees based on these costs via STP and MSTP. These trees yield optimized routing, TE and support for different QoS classes. We show on typical metro-access networks that, through optimization, the total network throughput can be significantly increased for both enforcing fairness or allowing starvation of some demands. This gain can be realized by simultaneously assigning demands to trees and routing these trees.

Optimized QoS protection of Ethernet trees

Ethernet is being increasingly employed in metro networks. Ethernet gives routing schemes and protocols for building up trees, for instance STP, RSTP and MSTP. It also implies simple restoration mechanisms. In this paper we propose an optimization framework, where the Ethernet MSTP trees are protected and QoS is guaranteed even after a failure. The optimization is based not only on the topology, but it also takes traffic conditions and QoS constraints into account. The numerical results show that the proposed optimization significantly increases the throughput of the network. The best result can be achieved when preemption is assumed, i.e., when the best effort traffic may remain unprotected, but not the high priority one. This way high throughput can be realized at normal operation, while it still protects prioritized traffic in case of a failure. Furthermore, protection mechanisms act faster than the standard restoration mechanism resulting shorter out-of-service times, and therefore higher availability.

Scalable Tree Optimization for QoS Ethernet

The low cost and the wide availability make Ethernet the dominant networking technique of access networks. Standardization further extends the capabilities of Ethernet by adding traffic separation and prioritization (802.1Q) and by allowing use of multiple spanning trees (802.1s). In this paper we present an Ethernet based QoS architecture for broadband services with triple play support. We propose an optimization framework with Traffic Engineering where the MSTP trees are spanned taking both the traffic conditions and the QoS requirements into account. The optimization is based on our previously presented formal model. Here we propose a novel decomposition based tree constructing heuristic with high scalability. We conduct simulations to evaluate the performance of the heuristic method that provides nearly optimal solutions within acceptable time constraints.

End-to-end relative Differentiated Services for IP networks

In the last decade two major solutions, namely IntServ and DiffServ have been introduced to empower IP networks with quality of service (QoS) capabilities. Among these two the DiffServ, which exhibits a better scalability and is the starting point for this paper is based on a per hop shaping of the traffic. The nodes control independently the flows without knowledge about the network state or/and the limitations suffered by the flows at other hops. Thus, violation of service differentiation can also occur. To correct this inefficiency a network-wide proportional service model is proposed. After presenting the theoretical argumentation and the architecture, we also provide an algorithm that computes the shaping factor needed to sustain our architecture. We use simulation experiments to validate our proposal.

A flexible switch-router with reconfigurable forwarding and Linux-based Control Element

The practical validation of investigating new router architectures and control algorithms is troublesome. It is partially due to the lack of programmable architectures that are fast enough for current networking, widely programmable, and equipped with the great variety of protocols that routers and switches has to handle. The idea of open, software-based routers running on commodity hardware have spread in recent years, resulting several practical implementations of so called soft-routers. Beside the economic advantages of having the Forwarding Element functions tackled by commodity Network Interface Cards (NICs), this approach suffers from issues of sub-optimal performance. This is partly due to the fact that all forwarding decisions are made by the main CPU instead of involving local processors at the NICs. Separating the functions into Forwarding Element and Control Element by the ForCES framework enabled the development of new control algorithms and protocol implementations for routers, however there are no widely available implementations. This paper describes a solution that is utilizing programmable hardware accelerators at the Forwarding Element, while keeping the advantages of open, Linux-based software-based router implementations. The hardware accelerators are implemented in the C-board, a reconfigurable, FPGA-based networking platform. The interoperability with existing Control Elements are described together with an analysis of features and capabilities of this combined solution.

Ethernet over WDM: Optimization for resilience and scalability

The emerging Ethernet technologies deployed in metro networks provide services based on pure Ethernet. Low cost optical Ethernet interfaces are used to interconnect different sites. Then, the use of wavelength division multiplexing technology with optical Ethernet is clearly the next step in building cost efficient metro networks. In this paper we propose a novel architecture and configuration methods that make metro Ethernet better scale to larger traffic and to covering larger areas that consist of more nodes promising significantly lower costs. The idea is to utilize wavelength paths optimally for bypassing certain Ethernet nodes and by employing traffic grooming according to different strategies we propose and compare. The result is always a tradeoff between the cost of the solution and the achievable throughput. Our methods are based on integer linear program and combinatorial heuristics. The proposed architecture and the optimization framework support very fast recovery upon a failure. Furthermore, it handles the shared risk link groups to ensure that the working and the backup paths should be physically disjoint. The method also supports traffic engineering goals: network utilization and resilience. Furthermore, it can be well used to enforce limitations on the depth and diameter of the obtained logical topology that allows scalability.

A Low Power, Programmable Networking Platform and Development Environment

Programmable networking platforms are getting widely used for customized traffic manipulation, analysis and network management. This propagates the need for exceptional development flexibility, for wide variety of high-speed interfaces and for the usage of high performance, yet low power technologies. This paper presents an FPGA-based programmable platform, capable of real-time processing, filtering and manipulating 10Gbps traffic. In order to expand its potential, besides the two 10GbE interfaces, the platform contains extension slots for COM express, mini PCI-e, and it has 16 onboard SFP connectors, towards which the fraction of the traffic, or even the full traffic can be forwarded to. The design is modular, programmable in both hardware (firmware) and software, aiming low power consumption. The full potential of the hardware can only be exploited with an easy-to-use development environment, with simple design customization and support for creating new applications. To fulfill this, a development environment is also presented, including a modeling framework that provides an easy way to create new networking applications on the platform. This framework allows modeling applications in SystemC, and eases the development of the hardware description code.

On the optimal configuration of metro Ethernet for triple play

Triple Play requires cost-effective implementation of three services that are different in both traffic and QoS requirements. The methods applied for optimization of Ethernet trees must support not only point-to-point pipes but also point-to-multipoint connections for multicast and statistical multiplexing models for better resource allocation. In this paper we present a QoS architecture for Triple Play service over metro Ethernet networks. Based on the architecture we propose an optimization framework and a novel scalable heuristic algorithm that supports optimal off-line configuration of trees and optimal VLAN assignment to these trees. The optimized configuration considers traffic engineering (TE) objectives and can be performed via centralized management plane. The obtained results show, that the performance of the proposed optimization framework can be further improved if the aggregation pipes are statistically multiplexed. Meanwhile, the proposed algorithm remains scalable, i.e. its complexity does not increase at all