A Probe-based And Measurement-based Admission Control Scheme For DiffServ Network: Design And Implementation

In recent years, with the rapid development of Internet, network Quality of Services(QoS) is brought out,which can meet the new requirements of some new application, such as "High Bandwidth, Low Delay, Low jitter and Low packets Loss Ratio". QoS researches how to do the best to guarantee the transmitting quality of network applications within the limited resources. The transmitting quality or requirements include limited end-to-end delay, jitter, packets loss ratio, bandwidth guarantee, etc. now, IP QoS research includes packet scheduling algorithm, connection admission control, traffic shaping and policing, queue management, etc. Connection Admission Control (CAC) is, when receive a request for access network by some flows, network decides if accept the request at the same time the requirements of other flow is guaranteed, and decides if return the result of admission control. In this paper, the author researches an enhanced admission control scheme in DiffServ network. The aim of admission control is to decide if can come forth a catastrophic result which lead to other flow's QoS requirements can't guarantee, when accept a new flow's access network. Currently, the successful CAC schemes include Time Windows policy, Management-based policy, Probe-based policy, etc. Time Windows methods are based on the notion that a source is only allowed to transmit up to a maximum number of bits within a fixed period of time. The Management-based admission control can avoid resources waste by shifting part of the task of traffic specifications from the user to the network. Instead of the user explicitly specifying his traffic, the network attempts to "learn"the statistics of existing flows by making on-line measurement. The Probe-based methods is before flows transmitting data, the source sends a series of probing packets to probe the network congestion conditions, then decide the next actions. Our keystone is the Management-based and Probe-based policy. Based on the existing schemes, this paper brings forward a new end-to-end QoS guarantee method, which is called "Probe-and-Measurement-based"admission control schemes. Its characteristic is "Once probes, all path measures, sub-domain admission controls, centralize decision". The method can assure the flows'QoS which have been accepted by network, and at the same time, can't admit overabundance flows. Some have existed technologies such as probing, packets traffic measuring, packets classifying and marking, routers PHB queue length threshold limiting, parallel probe flows number threshold limiting, etc. The admission control method in this paper includes three sub-procedures: Probe and Measuring phase, Intra-Domain Admission Control phase, Inter-Domain Admission Control phase. In Probe and measuring phase, when a host wishes to set up a new flow, it starts by sending a constant bit rate probe at the maximum rate that the data flow will require. The probe packet's ACT field is marked ACR. The probing time is chosen by the sender from a range of values defined in the service contract. The probe packet size should be small enough so that we get sufficient number of packets in our probing period to perform the acceptance decision. When the host sends the first probe packet, it includes the peak bit rate and length of the probe, as well as a flow sequence number in the data field of the packet. With this information we allow the end host to perform an early rejection, based on the expected number of packets that it should receive not to surpass the target loss probability. The sender starts a timer, which value should be over the probe length plus the expected round trip time. This timer will go off in case the sender does not receive an acknowledgement to the probe. The timer will also allow the sender to infer that none of the probe packets went through and to give up further attempts to setup a connection. Upon receiving the first probe packet for a probe flow, the ingress routers, the core routers, the egress routers in a DiffServ domain and the end host starts counting the number of received packets and the number of lost packets or other QoS information. When the probing period finishes and the end host receives the last probe packet, it compares the probe loss measured with the target loss and sends back a packet accepting or rejecting the incoming flow. These accept/reject packet is sent back at high priority to minimize the risk of loss. Then the system of admission control enters the Intra-Domain phase. In Intra-Domain Admission Control phase, the end point and the egress routers of each domain sends back an Intra-Domain admission RR packet accepting or rejecting the incoming flow according to the measured result to its upstream routers going against the coming path. The core routers transmit...