Egress Nodes Research Articles

Optical Transparency of a Heterogeneous Pan-European Network

We have experimentally shown that the physical design of a transparent network should be tailored to both the network topology and the network traffic matrix. For a pan-European network for which 85% of the traffic was shorter than 2000 km, almost all connections may be transparent; with very simple engineering rules (erbium-doped fiber amplifiers only, no power equalization except for the per-band equalization in the node, constant static dispersion management whatever the ingress and egress nodes, and whatever the wavelength...). We have also experimentally shown how dispersion management should take into account unavoidable inaccuracies that are to be found in the field.

DCAP

This paper proposes a detection mechanism called DCAP for a network provider to monitor incoming traffic and identify misbehaving flows without having to keep per-flow accounting at any of its routers. Misbehaving flows refer to flows that exceed their stipulated bandwidth limit. Through collaborative aggregate policing at both ingress and egress nodes, DCAP is able to quickly narrow the search to a candidate group that contains the misbehaving flows, and eventually identify the individual culprits. In comparison to per-flow policing, the amount of state maintained at an edge router is reduced from O ( n ) to O (√ n ), where n is the number of admitted flows. Simulation results show that DCAP can successfully detect a majority (64--83%) of the misbehaving flows with almost zero false alarms. Packet losses suffered by innocent flows due to undetected misbehaving activity are insignificant (0.02--0.9%). We also successfully build a prototype that demonstrates how DCAP can be deployed with minimal processing overhead in a soft-QoS architecture.

Dynamic Routing of Bandwidth Guaranteed Connections in MPLS Networks

Finding a path in the network for a new incoming connection able to guarantee some quality parameters such as bandwidth and delay is the task of QoS routing techniques developed for new IP optical networks based on label forwarding techniques such as Generalized Multiprotocol Label Switching (GMPLS). In this paper we focus on the routing of bandwidth guaranteed flows in a dynamic scenario where new connection requests arrive at the network edge nodes. When more than one path satisfying the bandwidth demand exists, the selection of the path aims at minimizing the blocking probability of future requests. We propose a new routing algorithm named Virtual Flow Deviation (VFD) which exploits the information of the ingress and egress nodes of the network and the traffic statistics. This new algorithm, in most scenarios, achieves remarkable reduction in the blocking probability with respect to previously proposed schemes.

Bandwidth–delay constrained routing algorithms

The development of technologies like Multi-Protocol Label Switching (MPLS) and Differentiated Services has laid the foundation for Internet to support multimedia applications like Voice over IP. Although much work has been done on laying MPLS paths to optimize performance, most has focused on satisfying bandwidth requirements. Relatively little research has been done on laying paths with both bandwidth and delay constraints. In this paper, we present bandwidth–delay constrained routing algorithms that use knowledge of the ingress–egress node pairs in the network in reducing the rejection rates for setting up new paths. Simulation is used to evaluate the algorithms and compare their performance against some existing algorithms for bandwidth constraints that have been modified to handle delay constraints. The results show that the proposed algorithms outperform all others under a wide range of workload, topology and system parameters.

The structure and management of service level agreements in networks

The paper proposes a structure for quality-of-service (QoS)-centered service level agreements (SLA), and a framework for their real-time management in multiservice packet networks. The SLA is structured to be fair to both parties, the service provider and their customer. The SLA considered here are for QoS assured delivery of aggregate bandwidth from ingress to egress nodes; however, the control and signaling is for the more granular flows or calls. A SLA monitoring scheme is presented in which revenue is generated by the admission of flows into the network, and penalty incurred when flows are lost in periods when the service provider is not SLA compliant. In the SLA management scheme proposed, the results of a prior off-line design are used, in conjunction with measurements taken locally at ingress nodes, to classify the loading status of routes. The routing and resource management are based on virtual partitioning and its supporting mechanism of bandwidth protection. The effectiveness of SLA management is measured by the robustness in performance in the presence of substantial diversity in actual traffic conditions. A simulation testbed called D'ARTAGNAN has been built from which we report numerical results for a case study. The results show that the SLA management scheme is robust, fair and efficient over a broad range of traffic conditions.

Dynamic transition matrix generation for topology aggregation

In large networks nodes are clustered into groups for the purpose of simplifying routing. Each group has a set of ingress–egress nodes, and routing information is conveyed to the outside world in the form of a transition matrix that gives the cost of traversing the network between each ingress–egress node pair. In a dynamic environment where costs are subject to change, the cost for traversing a group, and consequently the transition matrix is affected. In this paper, we present a novel graph-coloring method for computing and consistently maintaining in a dynamic environment the transition matrix corresponding to a group of nodes. This method is applicable in the case where path selection is based on restrictive costs, such as bandwidth, and it considers the symmetric case. A key characteristic of the method is its ability to distinguish between topology or link-cost changes that necessarily leave the transition matrix unchanged and those that may not; that is, a correct transition matrix is maintained at all times without recomputing it every time a cost change occurs. Numerical results illustrate the efficiency of the method, expressed in terms of the percentage of time that the transition matrix needs to be recomputed.

Design and implementation of scalable edge-based admission control

While the integrated services (IntServ) solution to Internet QoS can achieve a strong service model that guarantees flow throughputs and loss rates, it places excessive burdens on high-speed core routers to signal, schedule, and manage state for individual flows. Alternatively, the differentiated services solution achieves scalability via aggregate control, yet cannot ensure a particular QoS to individual flows. To simultaneously achieve scalability and a strong service model, we have designed and implemented a novel architecture and admission control algorithm termed egress admission control. In our approach, the available service on a network path is passively monitored, and admission control is performed only at egress nodes, incorporating the effects of cross traffic with implicit measurements rather than with explicit signaling. In this paper, we describe our implementation of the scheme on a network of prototype routers enhanced with ingress–egress path monitoring and edge admission control. We report the results of testbed experiments and demonstrate the feasibility of an edge-based architecture for providing IntServ-like services in a scalable way.

Smoothing variable-bit-rate video in an internetwork

The burstiness of compressed video complicates the provisioning of network resources for emerging multimedia services. For stored video applications, the server can smooth the variable-bit-rate stream by transmitting frames into the client playback buffer in advance of each burst. Drawing on prior knowledge of the frame lengths and client buffer size, such bandwidth-smoothing techniques can minimize the peak and variability of the rate requirements while avoiding underflow and overflow of the playback buffer. However, in an internetworking environment, a single service provider typically does not control the entire path from the stored-video server to the client buffer. This paper presents efficient techniques for transmitting variable-bit-rate video across a portion of the route, from an ingress node to an egress node. We develop efficient techniques for minimizing the network bandwidth requirements by characterizing how the peak transmission rate varies as a function of the playback delay and the buffer allocation at the two nodes. We present an efficient algorithm for minimizing both the playback delay and the buffer allocation, subject to a constraint on the peak transmission rate. We then describe how to compute an optimal transmission schedule for a sequence of nodes by solving a collection of independent single-link problems, and show that the optimal resource allocation places all buffers at the ingress and egress nodes. Experiments with motion-JPEG and MPEG traces show the interplay between buffer space, playback delay, and bandwidth requirements for a collection of full-length video traces.

Dynamic burst transfer time-slot-base network

This article proposes a new high-speed network architecture called dynamic burst transfer time-slot-base network (DBTN). The DBTN network is based on circuit-switched network technology. A routing tag is attached to a burst at an ingress edge node and the burst is self-routed in a DBTN network, the circuit of which is created dynamically by the routing tag. The routing tag, which is called time-slots-relay, consists of link identifiers from the ingress to the egress nodes and is used to create the circuit. Subsequent data is switched over the circuit being created in an on-the-fly fashion. Each link identifier is loaded into the address control memory (ACM) of each circuit switching node, and thereby the circuit to the destination is created dynamically. Subsequent user data follows immediately after the time-slots-relay and is sent over the established circuit. Thus short-lived fairly large data transfers such as WWW traffic are efficiently carried. A circuit between adjacent nodes is created and released dynamically so bandwidth efficiency is improved compared with conventional circuit-switched networks. Time division multiplexing of the circuit-switched network is utilized so there is no delay jitter or loss within a burst. We address the performance of DBTN switches and report the experimental system.