Software Defined Networking (SDN) is a programmable network architecture that decouples the control plane (controller logic) from the data plane (forwarding plane) and provides flexible network management. A logically centralized control plane supports SDN feasibility. A single controller may not be capable to control the whole network. To tackle this issue, deploying multiple controllers are a necessity to handle a large network. Controller placement problem (CPP) is one of the most important issues in SDN to improve the scalability and influences the latency and performance of the whole network. Most of the previous methods only focused on latency between controllers and their associated switches but ignoring the latency between controllers and the accumulated latency of the control plane.In this paper, we define an accumulated latency to solve CPP, which takes into consideration both the latency between the controller and their associated switches and inter-controller latency. We formulate an optimization problem as a mixed-integer linear programming (MILP) under the constraint of latency. The objective of our study is to minimize the accumulated latency and minimizing the number of network controllers while optimizing their placement for achieving an optimal balance at the same time. The performance of our method is evaluated on the Internet2 OS3E real network topology. Results demonstrate that the proposed method is promising.

Concerns regarding the scalability of the interdomain routing have encouraged researchers to start elaborating a more robust Internet architecture. While consensus on the exact form of the solution is yet to be found, the need for a semantic decoupling of a node's location and identity is generally accepted as a promising way forward. However, this typically requires the use of caches that store temporal bindings between the two namespaces, to avoid hampering router packet forwarding speeds. In this article, we propose a methodology for an analytical analysis of cache performance that relies on the working-set theory. We first identify the conditions that network traffic must comply with for the theory to be applicable and then develop a model that predicts average cache miss rates relying on easily measurable traffic parameters. We validate the result by emulation, using real packet traces collected at the egress points of a campus and an academic network. To prove its versatility, we extend the model to consider cache polluting user traffic and observe that simple, low intensity attacks drastically reduce performance, whereby manufacturers should either overprovision router memory or implement more complex cache eviction policies.

The sustained growth of the global routing table is exerting an economical strain on ISPs by requiring untimely router upgrades. Notably, it has been speculated that the growth rate of router FIBs is surpassing that of its supporting technology and that the deployment of IPv6 is only to make matters worse. In this paper, we propose LISP-MPS, an architecture based on LISP, that isolates the intra-domain routing of an Autonomous System (AS) from its inter-domain routing. The resulting separation implies the decrease of backbone routing table sizes and enables an AS to control the forwarding of traffic inside its network. For a seamless, cost effective, and incremental deployment, LISP-MPS leverages iBGP to implement the LISP mapping system functionality with minimal modification to a small subset of deployed equipment. Finally, an analysis of realistic topologies shows that, despite changing how packets transit a network, the architecture does not lose resilience to failures. Moreover, we show that it can be a viable alternative to BGP/MPLS deployments due to its low implementation cost.

Current literature defines the effective capacity of a wireless link as the maximum throughput that can be supported while meeting specific Quality of Service targets on packet delay. This metric can be harnessed for a wide variety of QoS control routines within wireless networks such as traffic optimisation and delay sensitive admission control and routing. However to date, no empirical evaluation of the effective capacity of 802.11 wireless links has been carried out. We present an empirical study of the effective capacity throughput of 802.11 wireless links under a number of network scenarios. We evaluate an analytical effective capacity model and compare the result with an empirical evaluation. We find that with an accurate measurement of the channel service delay, the effective capacity model can approximate the empirical measurement quite well. We also evaluate the relationship between the effective bandwidth of multimedia traffic and demonstrate that when the effective bandwidth exceeds the effective capacity threshold of a wireless link, the probability of QoS violations increases. We conclude that the effective capacity measurement is usable within an operational setting, and can lead to optimized utilization of bandwidth in a wide range of delay sensitive control operations.

Wireless technologies are rapidly evolving and the users are demanding the possibility of changing its point of attachment to the Internet (i.e. default router) without breaking the IP communications. This can be achieved by using Mobile IP or NEMO, however mobile clients must forward its data packets through its Home Agent (HA) in order to communicate with its peers. This sub-optimal route (lack of route optimization) reduces considerably the communications performance, increases the delay and the infrastructure load. Additionally, since the HA must forward all the mobile clients' data packets, it can become the bottleneck of such networks. In this paper we present the fP2P-HN architecture, a P2P-based solution that allows deploying several HAes throughout the Internet. With this architecture a mobile client can select a closer HA to its topological position in order to reduce the delay of the paths towards its peers. Furthermore it incorporates flexible HAes that, as we will see, reduce the load at these entities. The main challenge of our solution is signaling the location of the HAes in Internet. We provide an analytical model that evaluates the costs and the benefits of the fP2P-HN architecture. The model shows that the signaling grows logarithmically with the number of HAes and that the reduction is, at least, 20% (lower bound).

WLAN devices based on CSMA/CA access schemes have become a fundamental component of network deployments. In such wireless scenarios, traditional networking applications, tools, and protocols, with their built-in measurement techniques, are usually run unchanged. However, their actual interaction with the dynamics of underlying wireless systems is not yet fully understood. A relevant example of such built-in techniques is bandwidth measurement. When considering WLAN environments, various preliminary studies have shown that the application of results obtained in wired setups is not straightforward. Indeed, the contention for medium sharing among multiple users inherent to CSMA/CA access schemes has remarkable consequences on the behavior of and results obtained by bandwidth measurement techniques. In this paper, we focus on evaluating the effect of CSMA/CA-based contention on active bandwidth measurement techniques. As a result, it presents the rate response curve in steady state of a system with both FIFO and CSMA/CA-based contending cross-traffic. We also find out that the distribution of access delay shows a transient regime before reaching a stationary state. The duration of such transient regime is characterized and bounded. We also show how dispersion-based measurements that use a short number of probing packets are biased measurements of the achievable throughput, the origin of this bias lying on the transient detected in the access delay of probing packets. Overall, the results presented in this paper have several consequences that are expected to influence the design of bandwidth measurement tools as well as to better understand the results obtained with them in CSMA/CA links.

On-line end-to-end Service Level Agreement (SLA) monitoring is of key importance nowadays. For this purpose, past recent researches focused on measuring (when possible) or estimating (most of the times) network QoS or performance parameters. Up to now, attempts to provide accurate techniques for estimating such parameters have failed. In addition, live reporting of the estimated network status requires a huge amount of resources, and lead to unscalable systems. The originality of the contribution presented in this paper, relies on the statement that the accurate estimation of network QoS parameters is absolutely not required in most cases: specifically it is sufficient to be aware of service disruptions, i.e. when the QoS provided by the network collapses. For this purpose, we propose an algorithm for disruption detection of network services. The proposed solution is based on the use of the well-known Kullback-Leibler Divergence algorithm. More specifically, we work on simple to measure time series, i.e. received inter-packet arrival times. In addition of efficiently detecting network QoS disruptions, the algorithm, also drastically reduces the required resources, and the overhead produced by the traffic collection for scalable SLA monitoring systems. The validity of the proposal is verified both in terms of accuracy and consumed resources in a real testbed, using different traffic profiles.

Wireless technologies have rapidly evolved and are becoming ubiquitous. An increasing number of users attach to the Internet using these technologies; hence the performance of these wireless access links is a key point when considering the performance of the whole Internet. In this paper we present a measurement-based analysis of the performance of an IEEE 802.16 (WiMAX) client and an UMTS client. The measurements were carried out in a controlled laboratory. The wireless access links were loaded with traffic from a multi-point videoconferencing application and we measured three layer-3 metrics (one-way-delay, IP-delay-variation and packet loss ratio). Additionally we estimate the performance of a WiFi and Ethernet client as a reference. Our results show that Ethernet and WiFi have comparable performances. Both the WiMAX and the UMTS links exhibited an asymmetric behavior, with the uplink showing an inferior performance. We also assessed the causes of the discretization which appears in the jitter distributions of these links.

New business infrastructures over the Internet pose a new set of traffic constraints. In particular, multimedia and interactive contents require guarantees of bandwidth and delivery time. The broad deployment and real-time nature of this class of applications require the provisioning of specific resources in the network to guarantee a certain level of quality of service (QoS). QoS techniques need ways of obtaining feedback about the status of the QoS enabled paths, for example, for checking the fulfilment of service level agreements (SLA). A possible technique for obtaining such feedback is by passively monitoring the network traffic. The issue with traffic monitoring is the additional bandwidth needed by the control traffic generated by the different collection points in order to synchronise its acquired QoS metrics. Moreover, passive monitoring at line speed is an expensive process both in terms of resource consumption and price. However, some of these requirements can be significantly reduced by using traffic sampling. This paper presents a novel methodology for intra-domain on-line distributed QoS monitoring, which makes an efficient use of the network resources by employing distributed sampling mechanisms. The proposal is validated by performing real tests on an European-wide testbed. Our results show that the sampling technique can significantly reduce the traffic overhead, while obtaining very accurate estimations of the One Way Delay performance metric.

A foreseeable scenario is where on the Internet mobile IPv6 is deployed and a large percentage of the clients are mobile nodes. These mobile clients will communicate with large servers, which under the mobile IPv6's point of view, will be correspondent nodes. Usually large servers operate in servers farms with a load balancer device. Mobile clients can communicate with these servers through their home agent (a sub-optimal path) or directly by using the built-in mechanisms of mobile IPv6 route optimization. In this paper we detail an important incompatibility between the mobile IPv6's route optimization and several load balancing techniques. This means that mobile clients need to revert to the sub-optimal path when communicating with these server farms. This issue reduces considerably the communications performance increasing the delay and the infrastructure load. Moreover it may be an important drawback when considering mobile IPv6's deployment. In this paper we show which load balancing techniques are incompatible with route optimization and we propose a novel mobile entity that solves this issue for several load balancing techniques.

Real-time traffic is an important issue when designing networks. The growth in the deployment of voice applications in packet switched networks requires that the network can guarantee a minimum level of quality. At the same time, customers want guaranties that the proper quality of service is provided for their contracted services. In this environment service providers need means of reporting the quality level of their networks. Standardisation bodies define general metrics, such as delay, jitter or losses without giving detailed information regarding the actual user's perception of the traffic. Other approaches such as the mean opinion score (MOS), are too coarse to be significant on best-effort based environments such as the Internet. This work is motivated by the potential change in the quality of service (QoS) parameters found in packet switched networks. Which highlights the inaccuracy of metrics such as MOS, since they were designed for the stable circuit switched networks. This paper proposes a novel approach to on-line voice quality measurement which is more suitable for packet switched networks than the classical alternatives, while keeping the subjective approach of MOS. Moreover, our solution permits the real-time reporting of the voice communication's quality. Along with the specification of this metric, the paper provides an experimental validation of the proposal using a real testbed with real applications. The results show the higher accuracy in reporting using this proposal over the standard metrics currently used.

A foreseeable scenario is where, on the Internet, mobile IPv6 is deployed and a large percentage of the clients are mobile nodes. These mobile clients will communicate with large servers, which under the point of view of mobile IPv6 will be correspondent nodes. In mobile IPv6 if a mobile node wants to communicate with a correspondent node directly (route optimization) it must perform the return routability procedure which includes sending and receiving signaling messages, cryptographic calculations and storing a state. This procedure must be performed for each mobile client connection and for each handover. The return routability procedure would introduce a very significant load on these servers. Moreover the servers must be modified in order to support the route optimization of mobile IPv6. These issues may be a drawback for the deployment of mobile IPv6. In this paper we propose mobility agents, a centralized solution that performs route optimization on behalf the correspondent nodes. Mobility Agents reduce the deployment cost, do not require modifying the servers, they are compatible with NEMO and other mobility protocols. Moreover they allow deploying different extensions of mobile IPv6 such as optimized MIPv6 without modifying the correspondent nodes.

This paper presents a RWA strategy based on the stochastic estimation of the effective number of available wavelengths (ENAW) along interdomain paths. We propose an approximate model to roughly estimate the ENAW on the paths across multiple domains, and then refine this estimation by means of observations and an adaptive prediction-correction Kalman filtering process. Unlike traditional Kalman filters, which use noisy measurements as their observations, we use the information contained in the routing updates as noisy measurements of the existent wavelength occupancy along the paths. Based on these observations, we estimate the ENAW on the candidate paths, and use this information to influence the RWA decision when the number of available wavelengths makes a lightpath request prone to be blocked. The approximate model we are proposing in this paper is based on a noisy extension of a simplified model derived for two domains. Our results validate the usefulness of the model, and confirm that by estimating the wavelength occupancy prior to the RWA decision the blocking ratio can be considerably reduced.

Usual QoS routing algorithms involve the periodic update of network state information in all the network nodes. Based on this knowledge the QoS routing algorithms select the `best' route. It has been shown in the literature that the performance of these QoS routing algorithms strongly depends on the frequency of updating. We propose a new QoS routing mechanism called Prediction-Based Routing based on predicting the availability of links and routes regardless from the network state information. Consequently, update messages are not required, hence reducing signalling overhead and providing a major enhancement in terms of scalability. We show that the PBR is a viable option compared with usual QoS routing algorithms from the point of view of performance, complexity ad signalling overhead.

A hierarchical network architecture is one of the hard recommendations stated at the automatically switched optical networks (ASON) specifications. This paper focuses on providing ASON with a hierarchical routing in order to ensure the scalability for large worldwide networks, mainly focusing on the functionality expected from GMPLS routing, such as aggregation schemes and routing algorithms, targeting to optimize the global network performance while guaranteeing scalability. Simulation results indeed show the benefits obtained owing to harder overhead reduction without impacting on the blocking probability.

Fast rerouting mechanisms are being studied in order to provide fault tolerance for LSP in an MPLS network in case of node or link failure. For QoS provision, protected LSP are handled apart from non-protected LSP. Rerouting mechanisms when applied on protected LSP must take into account QoS requirements. This paper presents a mechanism that is able to handle multiple failures along an LSP while using an optimal alternative LSP. The rerouting decision is taken close to the point of failure that reduces the restoration time. The use of pre-established alternative LSP also reduces the restoration time and avoids blocking when looking for an alternative path. The proposal is based on a hybrid approach of segment repair and path repair and provides a new alternative LSP using dynamic rerouting once the protected one has been rerouted. In this way, there is always an alternative LSP for each protected LSP. The over all performance (recovery time, end-to-end delay, packet losses, and network resource utilization) is compared with existing protection mechanisms by simulation. The proposed hybrid approach, optimal and guaranteed alternative path (OGAP), avoids the possible use of a non-optimal alternative LSP to reroute the protected traffic and provides the flexibility of alternative route selection and setup as well as better resource utilization. Moreover, our proposal guarantees at least one alternative LSF at any time for the traffic on the protected LSP

Multiprotocol label switching and traffic engineering are proposed by the IETF to improve the network performance. Moreover, some QoS routing algorithms must be added in order to optimize the path selection process. However, in highly dynamic large networks, existing QoS routing algorithms suffer from a blocking probability, which in part is due to the existence of inaccuracy in the network state information used to select the path. This paper deals with the BYPASS based routing mechanism, which was introduced in the previous paper to overcome this routing inaccuracy effect in IP/MPLS scenarios. We suggest an enhancement of the BBR mechanism to optimize the bandwidth allocation by balancing the path length and the residual bandwidth, and its performance is evaluated by simulation.

We present a reliable, fast and efficient mechanism for rerouting traffic when there is a link/node failure or congestion problem in multiprotocol label switching (MPLS) networks. This proposal is able to guarantee rigorous QoS criteria for high-priority data traffic by eliminating packet loss and disorder, and minimizing packet delay. This directly translates into an improvement of important quality measure attributes, such as performance, reliability and fault tolerance, in MPLS-based networks. We use a predefined, alternative label switched path (LSP) in order to restore traffic (protection switching or fast rerouting). A theoretical model is formulated for the failure scenario in a protected LSP segment and we validate it through simulations using the MPLS network simulator (MNS). Further simulations show that our mechanism is able to eliminate packet loss and disorder completely while reducing the full restoration time. The potential cost in terms of the important issue of buffer requirements is also studied. Even for the worst case, buffer requirements are well within justifiable limits for guaranteeing QoS for high-priority data traffic in protected LSPs. The combination of these improvements helps to minimize the effects of link failure. This facilitates satisfying rigorous QoS requirements, increasing the throughput, rapid release of network resources and enhancement of the end-to-end performance of MPLS networks.

VC merge has been presented as the most likely implementation to offer multicast forwarding in MPLS environments when ATM is used as data link layer. But it presents some characteristics that may not be desirable, like extra buffering and delay, and modification of traffic characteristics. Other types of mechanisms are presented in the literature to solve these problems. Compound VC (CVC) is one of these mechanisms. This paper presents a general comparison of VC merge and CVC. It finally discusses the implementation issues of a CVC switch. Though its implementation is more complex, it is shown that CVC forwarding could be carried out by using state-of-the-art ATM hardware.

Multiprotocol label switching (MPLS) is an advanced forwarding scheme, which allows the network to achieve the traffic engineering (TE) objectives. When two or more MPLS nodes are connected via an ATM backbone merely composed of ATM switches, it is necessary to add some mechanisms to allow the label distribution and allocation between both nodes. In this paper a solution is proposed to integrate ATM and MPLS, so that the ATM backbone will be seen as a unique MPLS node from the MPLS domain and as a consequence of that the end-to-end LSP establishment can be carried out.

This paper presents a fast and efficient mechanism for rerouting traffic when there is a link failure or congestion problem in multiprotocol label switching (MPLS) networks. Our method uses a predefined, alternative label switched path (LSP) in order to restore traffic and significantly improves the performance in comparison to similar, existing proposals. We show that our proposal is not only able to reduce the average traffic delay due to path restoration, but also eliminates the problem of packet disorder. The latter-as is well known-can have significant impact on the overall, end-to-end performance. We have simulated our mechanism using the MPLS network simulator (MNS) and the performance metrics were compared to other proposals. The simulation results show that our new mechanism provides a significant improvement on average delay while eliminating packet disorder. The combination of these two improvements helps to minimize the effects of link failure and/or congestion. This facilitates the rapid release of network resources and improves the end-to-end performance of MPLS networks.

One of the problems to deal with when offering multicasting at the ATM level is forwarding. When using ATM adaptation layer 5 (AAL5), the cell-interleaving problem must be solved to be able to properly reassemble AAL5 packets at end-systems. Compound VC (CVC) is one of the solutions that have been proposed. Its main characteristic is the utilization of dynamically assigned packet identifiers to allow multiplexing. The convenience of this approach is validated through simulation. This paper also presents some preliminary results on the behavior of the packet loss probability due to running out of identifiers. The curves obtained will help in providing some dimensioning rules for the number of identifiers required for a given multicast group according to its traffic characteristics and a negotiated packet loss probability.