The Ethernet PON (EPON) is using 1 gigabit per second Ethernet transport, which is suitable to very high-speed data applications, as well as to converged system support (telephone, video, etc.). The unprecedented amount of bandwidth is directed toward, and arriving from a single entity, the Optical Network Unit (ONU).
An EPON network can be viewed as a distributed switch. An Optical Line Terminal (OLT) manages remotely the transmission of each ONU. The OLT and the ONUs exchange messages. In each cycle of such an exchange, the OLT grants a grant to each ONU, which is answered by a report message from the ONU. The ONU has a queue manager that prepares queue status information, which is transmitted using MPCP messages to the OLT to enable smart management. In other words, the ONU “informs its internal queues status” to the OLT. The OLT management is executed using a Dynamic Bandwidth Allocation (DBA) algorithm. An efficient algorithm is essential to guarantee Quality of Service (QoS), required to fulfill a Service Level Agreement (SLA). Operator revenues will increase from selling sophisticated SLAs to customers. High bandwidth utilization allows adding more customers to the network. Thus, a queue manager in an ONU is an enabler for any DBA algorithm executed by the OLT.
One of the key causes for low bandwidth utilization is the packet fragmentation loss. A fragmentation loss occurs when a grant does not match precisely the amount of bytes to be transmitted by the ONU. An ONU is not allowed to fragment packets, causing the remaining portion of a grant to be wasted. FIG. 1 shows a grant with a grant length 102. If for example three packets, marked #1, #2, and #3, are to be included in the grant, packets, #1 and #2 will fit, while packet #3 will not. There will be a fragmentation loss 104 given by the grant length minus the sum (in bytes) of the packets transmitted.
FIG. 2 shows a prior art EPON system comprising an OLT 200 and a plurality of ONUs 202. The OLT and the ONUs exchange messages. In each cycle of such an exchange, the OLT grants a grant G to each ONU, which is answered by a report message REP from the ONU to the OLT. For example, the reporting by the ONU to a grant received in a cycle N−1 at a grant message time tG(N−1) occurs at a report message transmission time tR(N−1). Regardless of the particular algorithm be used to differentiate between ONUs, the basic granting scheme is identical. An ONU must have a deterministic behavior in the time period between report message transmission and grant message reception, i.e. tG(N−1)−tR(N−1). The information of the OLT is updated only up to tR(N−1). The transmission order depends on packet priority, which can be any arbitrary value (e.g. 0. 7 in EPON). In this case, 0.7 means that there are 8 priorities, numbered from 0 to 7, with 0 being the lowest and 7 being the highest. Whenever a packet of a higher priority exists in the queue, it will be transmitted before any packet of a lower priority.
The ONU reports the total number of bytes (“total bytes”) existing in any of the sub-queues. The IEEE802.3 standard allows reporting additional information per sub-queue, the additional information based on defining a programmable threshold per sub-queue. The threshold is set by the OLT using a proprietary message. For example, in a sub-queue with 5 packages of priority 0.5, the threshold in bytes may be 1600, 4000, 3000, 3000, 4000 and 2000, respectively. The ONU reports the total number of bytes below the programmable threshold. In the example above, this number could be 1500, 0, 2800, 0, 3900 and 1500, and it is a result of the actual queue occupancy. Utilizing this information will help to reduce the grant size, which can be used for finer granting.
FIG. 3 shows a flow chart of the steps in the reception of a packet to a queue by the ONU, as occurring in prior art systems. The packet is written in step 300, and the priority of the packet is extracted in step 302. The length of the new packet is added to the content (“total bytes”) of the appropriate (same priority) packet sub-queue in step 304, to yield a new “total bytes” value. If the combined value of “bytes below threshold” and packet length is still smaller than the threshold of the sub-queue, the value of the “bytes below threshold” of the particular sub-queue is incremented with the packet length in step 306. Else, the value of the “bytes below threshold” remains unchanged. For example, a packet with a length of X bytes is added to the relevant sub-queue that has a threshold T and a value of “bytes below threshold” M. If X+M<T, M=M+X. Else, M remains unchanged.
The methods used in prior art result in packet fragmentation losses and therefore low bandwidth utilization. It is thus desirable to provide a new set of efficient management methods and algorithms that will eliminate packet fragmentation losses, enable efficient full bandwidth utilization and guarantee QoS.