Assured Forwarding PHB Group

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.

RIO is the primary active queue management technology for handling AF(assured forwarding) class traffic for services that have minimum bandwidth guarantees. However, RIO unfairly allocates the excess AF bandwidth among LSPs(label-switched paths) which have TCP flows aggregated as AF class in a DiffServ-Capable MPLS Network. This issue obstructs the business model in which ISPs promote LSP users to expand the LSP-required bandwidth for enriching the quality of AF traffic. In this paper, we propose a way, called weighted fair RIO (WF-RIO), to resolve this issue. WF-RIO can allocate the excess AF bandwidth among LSPs in proportion to their AF minimum guaranteed bandwidth by multiplying the dropping probability of RIO by an LSP-specific weight which is simply calculated from the traffic rates for the individual LSPs. We evaluate the proposed method by computer simulation and demonstrate its effectiveness.

The differentiated services (DiffServ) architecture for provisioning quality of service (QoS) in the Internet provides a flexible framework for supporting a variety of services in heterogeneous environments. The assured forwarding (AF) per hop behaviour is a means of providing differential treatment of various DiffServ classes through achieving higher forwarding probabilities for higher priority classes. Extending the AF model to support fine grain QoS specification in W-CDMA environments allows mobile users in third-generation systems to benefit from the economical savings made possible by resource sharing among different classes of aggregated traffic. We consider extending the AF model to support the delivery of quasi constant bit-rate (QCBR) traffic streams on the downlink. In our study, each QCBR stream is assumed to have a prescribed average bit-rate and time duration, and is expected to be transmitted to completion without interruption at the requested bit-rate. The availability of such a service is beneficial for transmitting real-time traffic to mobile devices with limited power and buffering resources. The proposed mechanisms are based on integrating a suitable power-sharing structure for achieving differential treatment between classes with a crude power prediction algorithm for estimating the probability that no forced termination will occur at certain instants in the future. We compare the performance of a non-predictive scheme with a predictive scheme for different AF classes and source information bit-rates. Our results show that significant improvement in the forwarding probability, throughput, and power utilization for the DiffServ classes can be attained using the predictive scheme.

Loss differentiation is recommended as a service differentiation provided by an assured forwarding (AF) per-fop behavior (PHB) in differentiated service (DiffServ) architecture. An active queue management (AQM) technique is addressed as a suitable alternative to realize the service differentiation because the AF PHB should attempt to minimize long-term congestion while permitting short-term congestion in order to accommodate traffic bursts. In order to realize the AF PHB using an AQM scheme, it is desirable that the AQM scheme has DVO properties of sheltering and load tolerance in order to protect low drop precedence traffic and to prevent starvation of high drop precedence traffic. In this paper, we introduce another desirable property of assured drop probability. We modify an existing AQM algorithm for the property so that it assures a target drop probability in a properly provisioned network. Other properties of sheltering and load tolerance still hold for the modified AQM scheme. We evaluate it with other comparable schemes, i.e., WRED and RIO through simulation.

We define an analytical approach and a methodology to determine the set of service level agreements (SLA) that can be effectively supported by a DiffServ IP network. We consider the assured forwarding (AF) per hop behavior (PHB), and, based on the SLA probabilistic description, we derive a worst-case mathematical formulation for the overbooking probability, i.e., the probability that the traffic crossing any link of a source-destination path exceeds the link capacity. We then compare analytical results with simulation of different traffic models.

The differentiated services (DS) architecture provides a framework for the scalable provisioning of multiple service levels in the Internet. Its definition and initial work have concentrated mainly on per-hop behaviors (PHB) and mechanisms at each DS domain. Equally important is what happens between DS domains. Thanks to the flexibility of the architecture, it is the providers’ choice how to interconnect with peers. In principle, traditional, static peering agreements work together with DS, but they do not offer the flexibility and dynamics needed in an electronic market for network capacity. Therefore, we look at dynamic service level agreements at the interdomain level. Such agreements are established by software entities called traders. These traders follow market-based principles to decide which contracts will be beneficial. In particular, traders compare the offers made by neighbor providers and select the most interesting ones. This selection of peer services creates competition among providers and integrates route selection based on service level and destination. We describe and implement a framework for service level agreement trading. We show the basic workings and first performance results of SLA trading using specific traders and an experimentally defined PHB in a simulation environment. Keywords— Network architecture, differentiated services architecture, service level agreement, pricing, trading, interdomain QoS routing.

The IETF Differentiated Service (DiffServ) architecture can allow for establishing a modern large scale network which guarantees the quality of service. In order to realize the multiple levels of packet drop precedence required for the Assured Forwarding (AF) framework of DiffServ, a multi-level RED algorithm is needed. RIO (RED with In/Out) is suitable for the AF scheme, and two major RIO variants such as RIO-D and RIO-C have been proposed and widely used. Both use the average lengths of virtual queues to determine the multiple levels of drop precedence and have different coupling strengths between virtual queues. The key difference between RIO-C and RIO-D lies with the fact that RIO-C takes full coupling and RIO-D has zero coupling. In this paper, a novel algorithm called RIO-FEC (RIO based on Fractional Exponent Coupling for determining the coupling strength) is proposed, and can achieve partial coupling with a controllable coupling power for calculating each average virtual queue length. The effects of the fractional exponent based coupling on the drop rates and throughputs of color-labeled virtual queues are analyzed, and a fractional power 1/3 is found to be optimal. The queue weight factor for calculating the EWMAs (Exponential Weighted Moving Averages) of virtual queue lengths, thus affecting the drop probability, is also presented. The results show that the proposed algorithm can achieve a total drop rate and a total throughput as good as RIO-D. Furthermore, RIO-FEC outperforms RIO-C and RIO-D in terms of preventing the lowest-priority virtual queue from bandwidth starvation, and can effectively adjudge the coupling strengths to gain the desired control on the allocation of priority and fairness.

TPOT: translucent proxying of TCP

M2I2tswTCM: A new efficient optimization marker algorithm to improve fairness bandwidth in DiffServ networks

This paper presents the performance evaluation of per-hop forwarding behavior in the differentiated services Internet. Both the expedited forwarding and the assured forwarding behaviors are observed and investigated in terms of packet delay and packet drop rate. This investigation was carried out using Queen's University IP Simulator v2.0 (QUIPS-II). A significant amount of results have been obtained under various parameter settings. The results show that the Diffserv per-hop forwarding mechanisms can provide good service differentiation on the Internet.

This paper addresses a new approach of IP/MPLS to provide QoS in radio access networks (RANs) that satisfies the diverse QoS requirements while efficiently utilizing network resources in the RANs. Two levels of service differentiation are denned, namely MPLS-level and DiffServ-level. At MPLS-level, separate label switched paths (LSPs) are established for control plane traffic and user plane traffic. At DiffServ-level, control plane traffic (network control and signaling) and real-time user plane traffic are mapped to DiffServ expedited forwarding (EF); non-real-time user plane traffic is mapped to DiffServ assured forwarding (AF). Combining QoS routing with dynamic resource allocation, simulation results show that this approach does provides a framework of QoS support in IP/MPLS-based radio access networks.

This paper addresses the issue of QoS internetwork-operability when an ISP's or MSO's native IP network serves as transit or backbone to business customers whose sites span various geographic regions. The QoS interworking mechanism described in this paper is also applicable for VoIP peering among MSOs and/or ISPs. In addition, a mechanism is proposed in this paper to obtain appropriate QoS treatment in an egress router (egress PE4) when the ISP/MSO has an MPLS-enabled network. Due to penultimate hop popping (PHP), packets arrive at the egress PE of a MPLS network as native IP packets. Because of this a mechanism to preserve original QoS information of a packet across a network boundary, while allowing the ISP/MSO to key on its own marking for PHB (per hop behavior) determination, is clearly needed

In the current routing mechanism for Mobile Ad hoc Networks, service differentiation is not realized completely, resulting in resources wastage for best-effort (BE) traffic and deficiency for real-time traffic, such as voice and video. A novel service differentiated multi-path routing mechanism is proposed, in which service differentiation is realized in network layer based on multi-path routing. Multiple paths found in the route discovery procedure are evaluated, sorted and chosen according to the packet service type. Simulations show that the resource requirement of real-time traffic is better satisfied and the overall performance is improved effectively, that is, the end-to-end delay is decreased and the packet delivery ratio is increased evidently.

A weakness of the current structure of the Internet is that it does not provide the capability to support a wide range of QoS. This problem will worsen as wireless services become more popular and need to be supported using the Internet. A new model, known as differentiated service (DiffServ), has been proposed by IETF to extend the Internet to be a QoS-capable, scaleable and efficient network. Whereas DiffServ has received considerable attention from researchers, few analytical studies on supporting a wireless DiffServ have been published. The authors formulate a simple analytical model for the assured forwarding class of differentiated service over wireless links. Based on the assumption of a slowly fading channel and the use of a RIO queue management policy, they obtain expressions for performance measures that characterise the service provided to different kinds of packets. Although the model is simple, it is computationally efficient and numerical results generated using the model closely match those obtained using simulation.

This paper presents results from performance measurements carried out in a differentiated services WAN connecting three major cities in southern Finland. The target of the measurements was to collect precise information about the level of service experienced by a user transmitting files with FTP in a network that implements service differentiation by using drop precedence levels and separate classes for real time and non-real time traffic. Special attention was paid to the behaviour of competing TCP flows produced by users with different service level specifications. Background traffic from ISPs network was injected into our test network in order to create traffic profiles which are typical in a core network. The results show clearly that the SIMA model used for the implementation of the DS mechanisms in the network nodes can provide service differentiation in a useful and fair manner in traffic conditions varying from light load to severe overload.