Elsevier

Computer Communications

Volume 28, Issue 15, 15 September 2005, Pages 1770-1777
Computer Communications

Fair intelligent admission control over resource-feedback DiffServ network

https://doi.org/10.1016/j.comcom.2004.12.022Get rights and content

Abstract

The basic DiffServ model lacks mechanisms to prevent itself from being overloaded and to inform its internal capability to the external world. This paper addresses the problem by presenting a Fair Intelligent Admission Control (FIAC) over an enhanced-DiffServ architecture. The central idea is to make admission decision based on both informed internal network QoS states and the external traffic QoS requirements at the edge node. This model has several advantages: (1) it is backward compatible with DiffServ, (2) it adapts to traffic load and network QoS state changes, and (3) it provides interactive communication between the external QoS requirements and the internal DiffServ network capability. In this paper, we use simulation to evaluate the performance of DiffServ with or without FIAC. The performance demonstrates that the new scheme is able to admit traffic fairly and achieve edge-to-edge QoS under heavy traffic conditions and network state changes.

Introduction

Efforts to provide Quality of Service (QoS) for the Internet have led to two distinct approaches: the Integrated Service (IntServ) and the Differentiated Service (DiffServ).

The goal of IntServ is to provide per-flow end-to-end QoS [8]. The IntServ architecture needs an explicit setup mechanism to convey information to routers so that they can provision resources to the requested services. The resource requirements for running per-flow resource reservations on routers increase proportionally to the number of separate reservations that need to be accommodated. The use of per-flow state and per-flow processing is thus not feasible across the high-speed core of a network.

In contrast, the DiffServ architecture [9] achieves scalability by limiting QoS functionalities to class-based priority mechanisms. DiffServ makes a distinction between operations performed in the core of the network, and operations at the edges of the network, scheduling and queue management only deal with a few classes of traffic, and can thus remain relatively simple. The DiffServ architecture is composed of a number of functional elements: packet classifier, traffic conditioner and per-hop forwarding behaviors (PHB). The PHB determines the priority in terms of DiffServ codepoint (DSCP). There are two types of PHBs besides the default best-effort service: expedited forwarding (EF) PHB and assured forwarding (AF) PHB [10]. The Assured Forwarding service provides qualitative differentiation among the AF classes. Expedited Forwarding service is intended to provide low-delay, low-jitter, and low-loss services by ensuring that EF aggregate is served at a certain configured rate.

However, it has been observed that traditional DiffServ, e.g. RIO-based scheme [1], exposes the unfair allocation of the network bandwidth among the Assured Forwarding services in case of different Round Trip Time (RTT), UDP/TCP interaction, network provision state changes, and unfair for micro flows inside the aggregate. This is because the traditional DiffServ is unaware of its internal network QoS states. Even if the ‘internal’ network is in congestion state, the DiffServ still forwards the overloading traffic into the network, worsening the congestion situation.

To address the above problems and provide stronger QoS without sacrificing scalability, we have designed Fair Intelligent Admission Control (FIAC) over DiffServ architecture. In this scheme, admission control decisions are performed at the edge router based on QoS requirement and the feedback of the current network capability state which is provided by the enhanced DiffServ [4]. The admission control decisions are made solely at the ingress edge router; per-flow state is not maintained in the network core router, and there is no coordination of state with core nodes. Therefore, admission control is performed in a scalable way. Second, the admission control over DiffServ is fully compatible with the DiffServ framework without any change in DiffServ domain. The most advantage of this approach is that it is able to make predictable admission control to converge to the optimum point which satisfies the ‘external’ traffic requirements and the internal network capability. Furthermore, FIAC over DiffServ allows DiffServ domain administrator to adjust policy to meet end-to-end QoS requirements.

The paper is organized as follows. Section 2 discusses some related work. Section 3 introduces the FIAC over DiffServ network model. Section 4 presents the Resource Discovery Protocol over DiffServ. In Section 5, we introduce Fair Intelligent Admission Control Module. In Section 6, we simulate FIAC over DiffServ to assess its performance against traditional DiffServ model. Section 7 concludes with suggestions for future work.

Section snippets

Related work

Over the last 2 years, several research efforts have been made to find ideal service architecture, that is, the service architecture which combines the advantages of DiffServ and IntServ

De Meer et al. [2] provided an analysis of existing IP quality of service solutions and the implied signaling issues. It is pointed out that an improvement to the QoS DiffServ architecture could be achieved by providing congestion signaling from within a DiffServ domain to the boundary between the two

FIAC over extended DiffServ network model

The problem of traffic overloading and network state changes for DiffServ is due to DiffServ being unaware of internal network capability. The aims of FIAC over DiffServ are: (a) to setup a communication channel between internal (the network capability) and external (the traffic QoS requirements), (b) to make admission decision based on internal (network capability) and external (the traffic QoS requirements).

We developed two additional modules to implement the above two goals: (a) Resource

Resource discovery protocol over DiffServ

Basically, the Resource Discovery Protocol is used to generate Resource Discovery (RD) packets for collecting the current network QoS states. The DiffServ domain administrator can assign the DSCP (e.g. EF class) to RD traffic. The DiffServ router is extended to include the QoS state monitoring function. Upon receiving a RD packet, the router consults its QoS state and modifies the fields of the RD packets accordingly and then forwards the RD packet to other router along the path to the egress

Fair intelligent admission control module

After receiving QoS report from Resource Discovery Protocol, the Admission Control Module estimates the incoming class traffic and applies Fair Intelligent Admission Control (FIAC) algorithm to make admission decision The philosophy behind FIAC is to handle the overloading traffic as early as possible. In turn, the congestion could be prevented as early as possible. The objective of FIAC is to guarantee a fair amount of the network bandwidth allocation among classes according to relative

Fair intelligent admission control over DiffServ evaluation

In this section, we evaluate the performance of FIAC over DiffServ design. All simulations were performed in NS-2 [12], and are based on FIAC-DiffServ architecture, which we developed as an enhanced DiffServ module. The parking-lot configuration (see Fig. 4) is set up to study the behavior with overloading traffic. Some traffic traverses Ingress1→CoreEgressD1, and other traffic traverses Ingress2→CoreEgressD2. The inter-router link (CoreEgress) is the bottleneck link. The bandwidth of

Discussion and conclusion

The paper proposes FIAC over DiffServ scheme for providing tighter edge-to-edge QoS responses under heavy traffic loads in the underlying network. It intelligently resolves the mismatches between QoS requirements of traffic class and network capacity at an edge node. The scheme relies on a capability discovery loop between ingress edge and egress edge. With our approach the QoS parameters discovered are not global since the loop only has a partial view of the network. Global information can be

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