Performance Analysis Of EPON Registration Protocol

The Ethernet passive optical network (EPON) has become one of the mostpromising candidates for the fiber-to-the-home (FTTH) applications, in which theresidential users may frequently turn on and off the optical network unit (ONU) forthe sake of power saving. After turning on, an ONU need register to the optical lineterminal (OLT) in order to access the network. In the registration protocol defined bythe IEEE802.3av standard, an offline ONU randomly sends its registration requestmessage in the given discovery window. Due to collisions among registration requestmessages, an ONU may have to make several attempts before its successfulregistration, which will induce probems such as the probability of success registration,registration delay, and stability of the registration protocol. This paper models andanalyzes the registration protocol, aiming at providing evidences for selecting asuitable size of the discovery window.Firstly, this paper presents the analysis about the registration throughput and theregisgtration efficiency of the protocol. When a registration request messages overlapwith other registration request messages in time, there occurs a collision. Therefore,the collision of the registration request message is modeled as an isolation problem inthis paper. Based on this model, the conditional probability of success registration fora given number of registering ONUs is first obtained, and then the closed-formexpressions of registration throughput and registration efficiency are derived.Analytical results show that the discovery window size has a direct effect on theregistration throughput and the registration efficiency. If the discovery window forregistration process is set properly, the registration efficiency can achive its maximumvalue. Further, simulation results verify the correctness of the proposed model.On the basis of the above results, this paper further analyzes the stability and theregistration delay of the registration protocol. As time gose on, an ONU shifts amongthe following three states: online state, registration state, and offline state. Accordingto the state transition of a tagged ONU, a discrete-time Markov chain is establishedfor the registration process, from which the characteristic function of the registrationprotocol is formulated. By solving this characteristic function, the stable region andthe mean registration delay of the registration protocol are derived. When thediscovery window is larger than a critical value, the registration protocol stays at thestable steady-state, and the registration delay experienced by a regisgering ONU isbounded, and the EPON network can function well. In the stable region, our results show that further enlarging the discovery window reduces the registration delaymarginally but yet lowers the registration efficiency significantly.In sum, this paper reaches the following conclusions:(1) As repect to its throughput and stability, the EPON registration protocol showssimilar characteristics to the medium access control (MAC) protocol in wirelessnetworks, e.g. ALOHA and CSMA.(2) In the future FTTH applications, the random delay mechanism in the EPONregistration protocol can effectively improve the registration throughput and theregistration efficiency.(3) The stability of the registration protocol is revelant to the discovery window size.(4) In the stable region, the registration protocol has not only a stable throughput butalso a bounded registration delay experienced by the ONU.(5) When the registration protocol is strictly stable, its discovery window need not tobe overly large.