Research Of Technology Relative To MAC Layer In GPON And Design Of DBA Algorithms

This paper is worked out based on the research work: 'study and applications ofpoint to point FTTH device (No. Z0005170041321) '. The research of this project isoriented to the practicable GPON system design. This paper studies the several keyissues of media access control (MAC) layer of GPON, including MAC controlsub-layer and RS sub-layer.The present dissertation focuses on study and design of the medium accesscontrol (MAC) protocol for Gigabit-Capable passive optical networks, analysis of theprotocol performance and other aspects closely correlated to the MAC protocol. TheMedia Access Control (MAC) protocol is needed for GPON to control each terminalto access the upstream channel and avoid collisions as GPON is a media-shared treenetwork. The MAC protocol plays an important role in the whole communicationssystem, and affects the system performance greatly, so it occupies the core position inthe GPON access system. ITU-T G984．1, G984．2, G984．3 and G984．4recommendation accelerates the process of standardization of GPON. But they do notspecify the MAC protocols and particular bandwidth allocation algorithms, anddeclare that it needs further studies. It's still an open problem, so our work haspractical meaning.Compared with other media-shared networks, the tree topology of PON has itsown characteristics, so some special requirements on MAC protocol are proposed.Although the method of random access is rather simple and easy to expand, it cannotsatisfy the telecommunication-class requirements of delay and throughput. So it is notavailable for PON system. Centrally controlled reservation-based bandwidthallocation algorithms are the first choice for PONs, because they display bettercharacteristics of delay and throughput.The main innovations of this paper are:①. A layered model of the uplinkbandwidth allocation system supporting more than one DBA algorithm in GPON is proposed. In the layered model, a hardware support layer is designed, including agranted-objects' queue states collection module, a tail code bandwidth mapping tableand a slot conversion module. This layered architecture separates the specific DBAalgorithms from the bandwidth management and distribution functions. Using suchlayered model and design, OLT can support multiple kinds of DBA algorithms, whichmakes the system can be used in different occasions and can satisfy the requirementsof bandwidth allocation for different services; (2) . A dynamic bandwidth allocationalgorithm for multiservice access in GPON is proposed in the case of all users in thenetwork being the same class. (3) . A novel MAC protocol in ONU is designed tosolve the fairness problem among the users in GPON, and the queue scheduler systemin ONU is designed based on the MAC protocol; (4) . On the basic of above③,another new dynamic bandwidth assignment scheme based on subscription rate andQoS in GPON is proposed in the case of the users in the system being in differentclasses. The scheme can effectively solve the problem of some malicious userseffecting others by gaining more bandwidth by over-flooding the priority queues;⑤.A new solution of implementing the multicast protocol in GPON system is proposed,including the ONU joining, leaving the multicast group and the processing method forthe downstream data by OLT.So, this paper can be summarized into the following three aspects:(1) Associating with the control system structure of the uplink bandwidthallocation, a layered model supporting the uplink bandwidth allocation function isproposed. In the model, the uplink bandwidth allocation function of OLT is dividedinto three layers: the parameter management layer, the DBA algorithm layer and thehardware support layer. It separates the DBA algorithms from the functions of dealingwith the report information and the bandwidth management and distribution. Theformer is realized by software, while the later is wholly implemented by hardwareonly. Using such layered model and design, OLT can support multiple kinds of DBAalgorithms, and the response rate of uplink bandwidth allocation will not be limited bythe performance of software or CPU, which makes GPON system can be used indifferent occasions and can satisfy the requirements of bandwidth allocation fordifferent services(2) In the aspect of dynamic bandwidth allocation (DBA), two types of DBAalgorithms based on different conditions are proposed. Firstly, when all users in aGPON network are belong to the same class, the present article designes a dynamic bandwidth allocation algorithm for multiservice. The scheme can be divided into twosteps: the first step is that the OLT will satisfy the bandwidth requirement of eachONU under an upper threshold, that is, the system set a max assured bandwidth. If therequirement bandwidth of an ONU (the fixed bandwidth is excepted) is smaller thanthe assured bandwidth, then the allocation will be implemented according to need,otherwise, the assured bandwidth will be given to the ONU. The second step is that ifthere is some surplus bandwidth, the OLT will distribute the bandwidth proportionallyfor different classe services of ONUs which did not obtain enough bandwidth forsending data according to their priorities. It is proved by theory analysis andsimulation results that the new algorithm can improve the throughput and meets thedelay requirement of all types of services and can realize the fairness for bothdifferent ONUs and services.Considering it is possible for users to request different quality of networkservices, the paper designes a novel MAC protocol in ONU, that is, users cansubscribe different network bandwidth (i.e. transmission rate), and ONU will choosethe appropriate queues for users' upstream data to be occupied according to theirsubscription rate. This MAC protocol can guarantee the fairness among users basedon a strict queue scheduling mechanism. Base on the MAC protocol, another newdynamic bandwidth assignment scheme based on subscription rate and QoS in GPONis proposed. Using this scheme, when the network load is low and the total requestbandwidth is smaller than the available uplink bandwidth, the allocation will beimplemented according to need. When the network load is high, the bandwidth isdistributed according to users' subscription rate firstly, then, if there is some surplusbandwidth, the OLT will distribute the bandwidth proportionally for ONUs which didnot obtain enough bandwidth for sending data. It is shown through OPNET simulationresults that the new algorithm can guarantee the fairness of bandwidth allocationamong users and can achieve relative small transmission delay(3) In the aspect of multicast protocol being used in Gigabit Passive OpticalNetwork, a new solution of implementing the multicast protocol in GPON system isproposed, including the method of ONU joining, leaving the multicast group and theprocessing method for the downstream data by OLT. The multicast protocol is testedon OPNET simulation platform, and the support degrees of IGMPv2 and IGMPSnooping by GPON are detected.At last, we summarize our research work and discusse the potential research topics in future...