Event:
Passive optical networking (PON) chip company, Broadlight, has been awarded a patent by the US Patent Office entitled: ‘Method and grant scheduler for cyclically allocating time slots to optical network units’.
Why is this important?
Dynamic bandwidth allocation (DBA) performs a key role in point-to-multipoint PON networks. A PON comprises an optical line terminal (OLT) at an operator’s central office connected to several optical network units (ONUs) via fibre. An ONU typically resides in the building basement or in a home.
The OLT broadcasts data downstream to the ONUs. In a gigabit PON (GPON), the downstream data rate is 2.5Gbps. Each ONU identifying the data meant for it using a unique packet header. In the upstream path – for GPON it is 1.25Gbps - only one ONU broadcasts at a time.
DBA is needed to make efficient use of the uplink capacity by assigning slots when each ONU can transmit its data. DBA must also take into account quality of service (QoS) requirements associated with the various traffic types (video, voice and data). “DBA increases revenue for the network provider by ensuring that bandwidth is not wasted,” says Eli Elmoalem, a system architect at Broadlight.
Method used:
Broadlight’s patent implements two approaches to DBA. The first, dubbed status reporting DBA, involves periodically polling the ONUs to determine their latest traffic needs. The second approach - traffic monitoring DBA – requires the OLT to run an algorithm that predicts the ONUs’ bandwidth needs based on their traffic bandwidth usage history.
Broadlight’s patented technique for GPON runs either or both approaches to determine how much bandwidth to allocate to each ONU. The patent also details how best to partition the tasks between the OLT silicon and software executed on the chip.
This is Broadlight’s second DBA patent award. The first, entitled “Method of providing QoS and bandwidth allocation in a point to multi-point network” is a generic DBA approach, says Eli Weitz, Broadlight’s CTO, applicable to any point-to-multipoint network whether it is cable, Broadband PON (BPON), GPON or Ethernet PON (EPON).
What next?
Developing DBA for 10G GPON. The development work for 10G PON is being undertaken by Full Service Access Network (FSAN) and will be standardised by the ITU-T.
DBA for 10G GPON will be more demanding: the split ratio - the number of ONUs served by one OLT – is higher with as many as 512 ONUs per PON, as is the upstream bandwidth. For 10G GPON, two upstream rates are being proposed: 2.5Gbps and 10Gbps.
References:
[1] “Predictive DBA: The ‘Right’ Method for Dynamic Bandwidth Allocation in Point-to-MultiPoint FTTH Networks”, a white paper by Broadlight
[2] “The Importance of Dynamic Bandwidth Allocation in GPON Networks,” a white paper by PMC-Sierra.
[3] “A Comparison of Dynamic Bandwidth Allocation for EPON, GPON and Next Generation TDM PON.” IEEE Communications Magazine, March 2009