Per-hop Behavior Research Articles

Bandwidth sharing under the assured forwarding Per-Hop behavior

The DiffServ’s Assured Forwarding (af) Per-Hop Behavior (phb) Group defines a differentiated forwarding of packets in four independent classes, each class having three levels of drop precedence. Specific end-to-end services based on thisphb are still being defined. A particular type of service that could assure a given rate to a traffic aggregate has been outlined elsewhere. In such a service, a fair distribution of bandwidth is one of the main concerns.

A core stateless bandwidth broker architecture for scalable support of guaranteed services

We present a novel bandwidth broker architecture for scalable support of guaranteed services that decouples the QoS control plane from the packet forwarding plane. More specifically, under this architecture, core routers do not maintain any QoS reservation states, whether per-flow or aggregate. Instead, the QoS reservation states are stored at and managed by a bandwidth broker. There are several advantages of such a bandwidth broker architecture. Among others, it avoids the problem of inconsistent QoS states faced by the conventional hop-by-hop, distributed admission control approach. Furthermore, it allows us to design efficient admission control algorithms without incurring any overhead at core routers. The proposed bandwidth broker architecture is designed based on a core stateless virtual time reference system developed recently. This virtual time reference system provides a unifying framework to characterize, in terms of their abilities to support delay guarantees, both the per-hop behaviors of core routers and the end-to-end properties of their concatenation. We focus on the design of efficient admission control algorithms under the proposed bandwidth broker architecture. We consider both per-flow end-to-end guaranteed delay services and class-based guaranteed delay services with flow aggregation. Using our bandwidth broker architecture, we demonstrate how admission control can be done on a per domain basis instead of on a hop-by-hop basis. Such an approach may significantly reduce the complexity of the admission control algorithms. In designing class-based admission control algorithms, we investigate the problem of dynamic flow aggregation in providing guaranteed delay services and devise a new apparatus to effectively circumvent this problem. We conduct detailed analyses to provide theoretical underpinning for our schemes as well as to establish their correctness. Simulations are also performed to demonstrate the efficacy of our schemes.

Providing flow-based proportional differentiated services in class-based DiffServ routers

DiffServ provides class-based differentiated quality of service (QoS). For perception of users, flow-based service differentiation is much more important than class-based. Class-based QoS per-hop behaviour (PHB) is ensured in a DiffServ router. However, a flow in a higher class may get worse QoS than a flow in a lower class due to unbalanced traffic conditions. Therefore, a novel scheme with a Bloom-filter-based estimator for number of active flows, a dynamic weighted fair queueing (WFQ) scheduler, and a queue management mechanism to provide flow-based proportional QoS differentiation is proposed. This scheme dynamically adapts the WFQ weight of each class according to estimations of numbers of active flows in each class to provide proportional bandwidth differentiation for flows in different classes. Furthermore, a queue management mechanism with estimation of numbers of active flows and queue length feedback control is employed to control the queue length of each class around a target value to achieve delay differentiation. Through detailed simulations, the proposed scheme is shown to be able to provide flow-based proportional bandwidth and delay differentiations for flows in different classes at the same time.

Adaptive provisioning of differentiated services networks based on reinforcement learning

The issue of bandwidth provisioning for Per Hop Behavior (PHB) aggregates in Differentiated Services (DiffServ) networks has received a lot of attention from researchers. However, most proposed methods need to determine the amount of bandwidth to provision at the time of connection admission. This assumes that traffic in admitted flows always conforms to predefined specifications, which would need some form of traffic shaping or admission control before reaching the ingress of the domain. This paper proposes an adaptive provisioning mechanism based on reinforcement-learning principles, which determines at regular intervals the amount of bandwidth to provision to each PHB aggregate. The mechanism adjusts to maximize the amount of revenue earned from a usage-based pricing model. The novel use of a continuous-space, gradient-based learning algorithm, enables the mechanism to require neither accurate traffic specifications nor rigid admission control. Using ns-2 simulations, we demonstrate using Weighted Fair Queuing, how our mechanism can be implemented in a DiffServ network.

Achieving proportional DiffServ per‐hop behaviour with PLQF

AbstractWe propose a novel scheme that can provide both delay and loss proportional DiffServ per‐hop behaviour. DiffServ is a framework that can provide different QoS levels to different groups of network users, and eliminate the shortcoming of the best‐effort delivery in today's Internet. The scheme employs probabilistic longest queue first (PLQF) as its forwarding and dropping mechanism. PLQF mainly reacts immediately to the queue‐length fluctuation of each service class, and then decides the probability for each QoS class, which determines the forwarding or dropping behaviour. We couple delay and loss differentiated services in one scheme. The proposed scheme is proven to achieve proportional differentiated services after detailed evaluations. Furthermore, the implementation cost of PLQF is much less than that of the previously proposed schemes, such as WTP and PLR. Copyright © 2003 John Wiley & Sons, Ltd.

The two markers system for TCP and UDP flows in a differentiated services network

There are two cruxes of issues identified in differentiated services (Diffserv) networks: one is TCP dynamics, and the other is the interaction of TCP and UDP flows for assured forwarding per hop behaviour (PHB). The saw-tooth like behaviours of TCP prevent each flow from realising its target rate, and congestion insensitive flows such as UDP penalise for TCP flows when both are given same AF class. Therefore, we argue the use of TCP-friendly building blocks and fairness modules in the Diffserv architecture regarding these issues, and propose two markers system (TMS) that is able to properly mark packets and fairly share the bandwidth to each flow for their targeted sending rates. TMS has two marking modules that are placed on the source and the edge of a Diffserv network, respectively. For sources of the network, TCP-source making module plays important roles of reducing TCP impacts in the assured services and adequately marking packets. Next, in the edge of the network, the edge-embedded marking module conducts new fairness policy based on the marking rate of flows from sources, so-called ‘marking rate-based fairness’. Finally, we present simulation results to illustrate the effectiveness of TMS scheme over several parameters. That is, TMS alleviates TCP impacts over assured service and the issue of unfair distribution of excess bandwidth in an over-provisioned networks as well as unfair degradation in an under-provisioned network for TCP and UDP flows.

Delay jitter bounds and packet scale rate guarantee for expedited forwarding

We consider the definition of the expedited forwarding per-hop behavior (EF PHB) as given in RFC 2598 and its impact on worst case end-to-end delay jitter. On the one hand, the definition in RFC 2598 can be used to predict extremely low end-to-end delay jitter, independent of the network scale. On the other hand, we find that the worst case delay jitter can be made arbitrarily large, while each flow traverses at most a specified number of hops, if we allow networks to become arbitrarily large; this is in contradiction with the previous statement. We analyze where the contradiction originates and find the explanation. It resides in the fact that the definition in RFC 2598 is not easily implementable in schedulers we know of, mainly because it is not formal enough, and also because it does not contain an error term. We propose a new definition for the EF PHB, called packet scale rate guarantee (PSRG) that preserves the spirit of RFC 2598 while allowing a number of reasonable implementations and has very useful properties for per-node and end-to-end network engineering. We show that this definition implies a rate-latency service curve property. We also show that it is equivalent, in some sense, to the stronger concept of adaptive service guarantee. Then we propose some proven bounds on delay jitter for networks implementing this new definition, both in cases without loss and with loss.

Equivalent differentiated services for AODVng

A well-known research challenge is the establishment of some quality of service in an ad hoc network. Such a fluid and dynamic environment does not lend itself to extensive state-building approachess like Intserv. Diffserv, in which packets are treated according to some class aggregation seems to be a better match. Diffserv provides strong guarantees to applications by being mainly based on admission control, policing and provisioning. In this paper, we present the "Equivalent Differentiated Services" (EDS) per-hop behavior. EDS provides a set of best-effort services with differentiated performances. We show how EDS could benefit ad hoc networks.

QUIPS-II: a simulation tool for the design and performance evaluation of Diffserv-based networks

This article presents a discrete event simulator, called Queen's University IP Simulator-II, which can be used for the design and performance evaluation of Diffserv-based networks. The simulator implements both the expedited and the assured forwarding per-hop forwarding behaviors in Diffserv networks, sharing many features of the IETF proposals. By setting up a network model with variable parameters, simulation can be carried out to observe the Diffserv behavior. Some performance evaluations of both forwarding mechanisms are provided as examples.

A probabilistic priority scheduling discipline for multi-service networks

This paper proposes a novel scheduling discipline for service differentiation among traffic classes in multi-service networks, which is referred to as the Probabilistic Priority (PP) discipline. The PP discipline is based on the Strict Priority (SP) discipline with the difference that each priority queue is assigned a parameter as in Weighted Fair Queueing (WFQ) and Weighted Round Robin (WRR) disciplines. The parameter determines the probability with which its corresponding queue is served when it is polled by the server. Similar to WFQ and WRR, service differentiation as well as fairness among traffic classes can be achieved in PP by setting the assigned parameters properly. In addition, the PP discipline can be easily reduced to the ordinary SP discipline or to the reverse SP discipline. Moreover, the PP discipline can provide service segregation among groups of traffic classes while at the same time provide service differentiation among classes within each group. The proposed PP discipline may be used in controlling per-hop behavior in differentiated services networks.

TCP-friendly traffic conditioning in DiffServ networks: a memory-based approach

Recently, there has been a considerable research interest in designing intelligent markers, tailored for TCP traffic. Markers, one of the building blocks of a traffic conditioner play a major role for resource allocation in a Differentiated Services (DiffServ) network. The TCP dynamics make the design of a marker difficult in many respects. In this paper, we list out the issues related to designing a TCP-friendly marker and propose an intelligent two-colour marker, namely, memory-based marker (MBM) to address those issues. We then extend this concept for a three-colour marker, memory-based three-colour marker (MBTCM), to be deployed for the assured forwarding per-hop behaviour in a DiffServ network. We illustrate the benefits of the MBTCM over time sliding window three-colour marker. The markers were implemented in NS simulator and extensive simulations were done to study their behaviours. Our results show significant improvement in TCP performance, especially in achieving fairness among priority flows with distinct round trip times, windows, and target rates. The markers are capable of protecting TCP flows in cases of congestion caused by the unruly UDP flows. We also investigate the impact of coexisting assured service UDP flows on the assurance to the TCP flows. The major benefits of our markers are its simplicity, least sensitivity to parameters and transparency to the end hosts.

Experimental TCP Performance Evaluation on Diffserv AF PHBs over ATM SBR Service

In these days, IP network customers become sensitive to the QoS guarantee provided by the network. Amongst many QoS guarantee schemes, Diffserv (Differentiated Services) is the one of the most practical candidates for the next generation IP networks. Under these circumstances, the commercial network venders have already provided the Diffserv routers that support EF (Expedited Forwarding) PHB (Per Hop Behavior). However, AF (Assured Forwarding) PHB in Diffserv still has not been provided by commercial routers. Therefore, it is a realistic solution that SBR3 (Statistical Bit Rate 3) of ATM emulates AF PHB, but it is not clear whether TCP traffic over AF PHB emulated by ATM is differentiated from the best effort TCP traffic over DF (Default Forwarding) PHB. To confirm the differentiation, we have experimentally studied TCP performance through the link into which TCP connections over AF PHB and DF PHB are aggregated. This paper describes the experimental results and discusses the possibility of the TCP performance differentiation between AF PHB and DF PHB over ATM.

Internet design for SLA delivery from service level agreement to per-hop behavior: a report on the 1st TEQUILA workshop

Internet design for SLA delivery from service level agreement to per-hop behavior: a report on the 1st TEQUILA workshop

A QoS service for IP video applications on demand over DTM

The Differentiated Services model (DiffServ) provides a great flexibility in defining a variety of services through PHBs ( Per Hop Behaviors ) and traffic conditioners. It fits in well with the Integrated Services model (IntServ), jointly offering features such as: QoS signaling; admission control; channel management; assignment of resources (buffer and bandwidth); sorter configuration; and establishment of traffic agreements. With this integration you can have a scalable, flexible, and dynamic QoS environment in networks of the Internet core.This article describes and analyzes the DGF ( DTM Guaranteed Forwarding ) service that guarantees a minimum rate of retransmission of packets, based on RSVP signaling and traffic agreements (SLA), as well as losses close to the error rate of the physical medium, which are ideal features for video applications on demand.When this service is provided, the aforementioned QoS models are integrated with the transport and switching solution called DTM ( Dynamic Synchronous Transfer Mode ), a fast circuit switching technology. DTM is simple, cost-effective, provides QoS features, and is naturally dynamic in supplying bandwidth as well as flexible in fitting in with other IETF QoS models.Thus in the proposed architecture, IPoDQoS ( IP over DTM QoS ), we make use of the dynamism of network protocols and we offer managed VBR traffic in the IP layer (i.e.: DGF service) not originally offered in DTM technology.

Aggregation and conformance in differentiated service networks

The Differentiated Service (Diff-Serv) architecture [1] advocates a model based on different “granularity” at network edges and within the network. In particular, core routers are only required to act on a few aggregates that are meant to offer a pre-defined set of service levels. The use of aggregation raises a number of questions for end-to-end services, in particular when crossing domain boundaries where policing actions may be applied. This paper focuses on the impact of such policing actions in the context of individual and the bulk services built on top of the Expedited Forwarding (EF) [7] per-hop-behavior (PHB). The findings of this investigation confirm and quantify the expected need for reshaping at network boundaries, and identify a number of somewhat unexpected behaviors. Recommendations are also made for when reshaping is not available.

Pricing, provisioning and peering: dynamic markets for differentiated Internet services and implications for network interconnections

This paper presents a decentralized auction-based approach to pricing of edge-allocated bandwidth in a differentiated services Internet. The players in our network economy model are one raw-capacity seller per network, one broker per service per network, and users, to play the roles of whole-sellers, retailers, and end-buyers, respectively, in a two-tier wholeseller/retailer market, which is best interpreted as a "sender-pay" model. With the progressive second price auction mechanism as the basic building block, we conduct a game theoretic analysis, deriving optimal strategies for buyers and brokers, and show the existence of networkwide market equilibria. In addition to pricing, another key consideration in building differentiated network services is the feasibility of maintaining stable and consistent service level agreements across multiple networks where demand-driven dynamic allocations are made only at the edges. Based on the proposed game-theoretic model, we are able to construct an explicit necessary and sufficient condition for the stability of the game, which determines the sustainability of any set of service level agreement configurations between Internet service providers. These analytical results are validated with simulations of user and broker dynamics, using the distributed progressive second price auction as the spot market mechanism in a scenario with three interconnected networks, and two services based on the proposed standard expedited forwarding and assured forwarding per-hop behavior.

Virtual time reference system: a unifying scheduling framework for scalable support of guaranteed services

We propose and develop a novel virtual time reference system as a unifying scheduling framework to provide scalable support for guaranteed services. This virtual time reference system is designed as a conceptual framework upon which guaranteed services can be implemented in a scalable manner using the DiffServ paradigm. The key construct in the proposed virtual time reference system is the notion of packet virtual time stamps, whose computation is core stateless, i.e., no per-flow states are required for its computation. We lay the theoretical foundation for the definition and construction of packet virtual time stamps. We describe how per-hop behavior of a core router (or rather its scheduling mechanism) can be characterized via packet virtual time stamps, and based on this characterization establish end-to-end per-flow delay bounds. Consequently, we demonstrate that, in terms of its ability to support guaranteed services, the proposed virtual time reference system has the same expressive power and generality as the IntServ model. Furthermore, we show that the notion of packet virtual time stamps leads to the design of new core stateless scheduling algorithms, especially work-conserving ones. In addition, our framework does not exclude the use of existing scheduling algorithms such as stateful fair queuing algorithms to support guaranteed services.

A random early demotion and promotion marker for assured services

The differentiated services (DiffServ) model, proposed to evolve the current best-effort Internet to a quality-of-service-aware Internet, provides packet level service differentiation on a per-hop basis. The end-to-end service differentiation may be provided by extending the per-hop behavior over multiple network domains through service level agreements between domains. The edge routers of each of the domains monitor the aggregate flow of the incoming packets and demote packets when the aggregate incoming traffic exceeds the negotiated interdomain service agreement. A demoted packet may encounter other edge routers on its path that have sufficient resources to route the packet with its original marking. In this paper, we propose a random early demotion and promotion (REDP) technique that works at the aggregate traffic level and allows (1) fair demotion of packets belonging to different flows, and (2) easy and fair detection and promotion of the demoted packets. Using early and random decisions on packets REDP ensures fairness in promotion and demotion. It uses a three color marking mechanism, reserving one color fur differentiating between a demoted packet and a packet with the original out-of-profile marking. We experiment with the proposed REDP scheme using the ns2 simulator for both TCP and UDP streams. The results demonstrate the fairness of REDP scheme in demoting and promoting packets. Furthermore, we show a variety of results that demonstrates that REDP provides better assured services compared to the previously proposed RIO scheme with or without the provision of promotion.

A differentiated services architecture for multimedia streaming in next generation Internet

This paper presents a Differentiated Services (Diffserv or DS) architecture for multimedia streaming applications. Specifically, we define two types of services in the context of Assured Forwarding (AF) per hop behavior (PHB) that are differentiated in terms of reliability of packet delivery: the High Reliable (HR) service and the Less Assured (LA) service. We propose a novel node mechanism called Selective Pushout with Random Early Detection (SPRED) that is capable of simultaneously achieving the following four objectives: (1) a core router does not maintain any state information for each flow (i.e., core-stateless); (2) the packet sequence within each flow is not re-ordered at a node; (3) packets from HR service are delivered more reliably than packets from LA service at a node during congestion; and (4) packets from TCP traffic are dropped randomly to avoid global synchronization during congestion. We show that SPRED is a generalized buffer management algorithm of both tail-dropping and Random Early Detection (RED), and combines the best features of pushout (PO), RED and RED with In/Out (RIO) mechanisms. Simulation results demonstrate that under the same link speed and network topology, network nodes employing our Diffserv architecture have substantial performance improvement over the current Best Effort (BE) Internet architecture for multimedia streaming applications.