Citation de: anaxim77 le 15 Août 2018 à 16:42:48
Hello, j'aurai une question justement, la fibre et son fonctionnement c'est pas encore très clair pour moi... Pour le débit comment ça se passe justement, est- il défini et paramétré par l'oi au niveau de l'ont ? Pour l'adsl c'était au niveau du dslam il me semble, mais la pour du Gpon, je me demande si ça ne serait pas sur l'ont...
Merci d'avance pour mon éclairage de lanterne
Tout se passe coté OLT.
Pour le trafic descendant, c'est l'OLT qui envoi, donc c'est l'OLT qui décide le maximum de donnée à envoyer.
Pour le débit montant, c'est l'OLT qui ré-alloue dynamiquement les "timeslot" toutes les X millisecondes en fonction de ce que chaque ONT a envoyé comme donnée dans le slot précédent.
CitationDynamic Bandwidth Allocation (DBA)
The OLT is responsible for allocating upstream bandwidth to the ONUs. Because the access network is shared, ONU upstream transmissions could collide if they were transmitted at random times. ONUs can be located at varying distances from the OLT, and hence the transmission delay from each ONU is unique. The OLT measures delay and sets a register in each ONU via PLOAM (Physical Layer Operations, Administration and Maintenance) messages to equalize its delay with respect to all other ONUs on the access network. This is called Ranging.
Once the delay of all ONUs have been set, the OLT transmits grants to individual ONUs. A grant is permission to use a defined interval of time for upstream transmission. The grant map is dynamically re-calculated every few milliseconds. The map allocates bandwidth to all ONUs such that each ONU receives timely bandwidth for its needs.
DBA is a methodology that allows quick adoption of users' bandwidth allocation based on current traffic requirements and it is especially good for dealing with bursty upstream traffic. GPON uses TDMA for managing upstream access by ONUs, and at any one point in time, TDMA provides unshared timeslots (upstream bandwidth over time) to each ONU for upstream transmission.
DBA allows upstream timeslots to shrink and grow based on the distribution of upstream traffic loads. DBA functions on T-CONTs, which are upstream timeslots, and each is identified by a particular ALLOC_ID. An ONU must have atleast one T-CONT, but most have several T-CONTs, each with its own priority or traffic class, and each corresponds to a particular upstream timeslot on the PON. Without DBA support on the OLT, upstream bandwidth is statically assigned to T-CONTs, which cannot be shared, and can be changed only through a management system.
There are two forms of DBA - Status Reporting DBA (SR-DBA) and Non-Status Reporting DBA (NSR-DBA).
Source: https://sites.google.com/site/amitsciscozone/home/gpon/gpon-fundamentals