Methods and apparatus for achieving multiple bit rates in passive optical networks
Systems and techniques for multiple bit rate optical data transmission. A passive optical network includes an optical line termination unit (OLT) connected to one or more optical network units (ONUs) by optical elements. The OLT is capable of performing downstream transmission to the ONUs at each of a variety of different bit rates, and each ONU performs upstream transmission at one or more bit rates. The OLT can sense a bit rate of a received transmission and change its operation so as to receive and process the transmission exhibiting the sensed bit rate. Each of the ONUs receives and processes downstream transmissions at one or more bit rates, but each ONU is capable of maintaining a phase and frequency lock to downstream transmissions at all bit rates supported by the OLT. One or more of the ONUs may also receive and process downstream transmissions exhibiting different or changed bit rates.
1. An optical network unit (ONU) for use in a passive optical network employing multiple downstream bit rates, comprising:
a media access control and data processing and operational control circuit;
a serializer/deserializer operating at a clock rate compatible with a highest bit rate used in the passive optical network and producing deserialized output and comprising a clock data recovery circuit employing a bit rate detection circuit to detect bit rates of downstream transmissions based on sensing phase and frequency of the downstream transmissions, the clock data recovery circuit utilizing the detected bit rates to synchronize the serializer/deserializer with downstream transmissions having different bit rates; and
a downsampling module for translating the output of the serializer/deserializer to a lower bit rate data stream and providing the lower bit rate data stream to the media access control and data processing and operational control circuit.
2. The optical network unit of claim 1 , wherein the ONU operates under dual gigabit passive optical network (GPON) standards and broadband passive optical network BPON) standards, wherein the serializer/deserializer operates at a clock rate compatible with a GPON standard bit rate and wherein the downsampling module translates the output of the serializer/deserializer to a BPON standard bit rate data stream.
3. The optical network unit of claim 1 , wherein the ONU transmits upstream data at two or more upstream transmission rates and the upstream transmission rate is selectively changed to accommodate a transmission path quality of an available transmission path.
4. The network of claim 1 , wherein the ONU is operative to receive and process downstream data transmissions at more than one bit rate, transmission path quality is indicated by an upstream transmission from the ONU, and the ONU adapts for changes in a downstream transmission rate to the ONU to accommodate the quality of the transmission path.
5. The optical network unit of claim 1 , further comprising:
a multilongitudinal laser for data transmission and said media access and data processing and operational control circuit changes the bit rate employed for upstream data transmission depending on the capabilities of the laser used under conditions prevailing at the time of transmission.
6. The optical network unit of claim 1 further comprising:
a clock and data recovery circuit operative to achieve a phase and frequency lock to a highest bit rate downstream transmission.
7. The optical network unit of claim 6 wherein the clock and data recovery circuit is operative to maintain the phase and frequency lock when the bit rate of downstream transmission changes.