Optical packet transmission
A burst mode optical signal is transported as payload of a framed continuous bit-stream optical signal through an optical transport network. The optical bursts are all generated at a common nominal bitrate which equals substantially the payload bitrate of the continuous bit-stream optical signal. The bursts are converted into a continuous bit stream by filling gaps between the bursts with a predefined pattern. The continuous bit stream thus created is then mapped into frames to generate the framed continuous bit-stream optical signal for transmission.
1. A method of transporting a burst mode optical signal as a payload of a framed continuous bit-stream optical signal over an optical transport network, the method comprising the steps of:
generating optical bursts at a common nominal bitrate equal to a payload bitrate of the continuous bitstream optical signal;
converting said bursts into a continuous bit stream by filling gaps between the bursts with a predefined pattern; and
mapping said continuous bit stream into frames to generate said framed continuous bitstream optical signal for transmission.
2. A method according to claim 1 , wherein said optical bursts comprising a payload and a header section and wherein said payload section is generated with said payload bitrate of the continuous bit-stream optical signal and wherein said header section is generated with a lower bitrate than said payload bitrate.
3. A method according to claim 2 , wherein the bitrate of the header is lower as said payload bitrate by an integer factor, preferably by a power of 2.
4. A method according to claim 1 , wherein the nominal bitrate of the burst mode optical signal is either of the three payload bitrates defined in International Telecommunicationn Union Telecommunication Standardization Sector (ITU-T) G.709.
5. A method according to claim 1 , wherein the burst mode optical signal has a nominal bitrate prior to said mapping.
6. A method according to claim 5 , wherein the nominal bitrate of the burst mode optical signal is either of the three payload bitrates defined in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) G.709.
7. A network element interfacing an optical packet network and an optical transport network, said network element comprising
a first interface which receives a burst mode optical signal from said optical packet network;
a second interface which transmits a framed continuous bit-stream optical signal towards the optical transport network;
a detector for detecting pauses between bursts of said burst mode optical signal;
a pattern generator for inserting a filling pattern into said pauses detected by said detector to generate a continuous bitstream;
and a mapper for mapping said continuous bit stream into frames to generate said framed continuous bit-stream optical signal for transmission.
8. A network element interfacing an optical packet network and an optical transport network, said network element comprising
a first interface which receives a framed continuous bitstream optical signal from the optical transport network, said continuous bitstream optical signal carrying as payload a burst mode optical signal with pauses between gaps being filled with a filling pattern;
a second interface which transmits a burst mode optical signal towards said optical packet network;
a detector for detecting sequences filled with said fixed pattern in said payload; and
a zero-bit generator for replacing said filling pattern by pauses to recover said burst mode optical signal.
9. A system comprising a terminal for an optical packet network and a network element interfacing said optical packet network to an optical transport network, wherein said network element comprises:
a first interface which receives a burst mode optical signal from said optical packet network;
a second interface which transmits a framed continuous bit-stream optical signal towards said optical transport network;
a detector for detecting pauses between bursts of said burst mode optical signal;
a pattern generator for inserting a filling pattern into said pauses detected by said detector to generate a continuous bitstream; and
a mapper for mapping said continuous bit stream into frames to generate said framed continuous bit-stream optical signal for transmission,
and wherein said terminal is adapted to create a burst mode optical signal with a nominal bitrate of either of the three payload bitrates defined in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) G.709.
10. The system according to claim 9 , wherein said terminal has a clock accuracy of less than 20 parts per million (ppm).
11. The system according to claim 9 , further comprising an optical switch for said optical packet network, wherein said optical switch processes headers of optical packets of received burst mode optical signals with a tolerance against clock deviations in the header bitrate of substantially 500 parts per million (ppm) at a nominal bitrate of 624,705 Mbit/s.
12. The system according to claim 9 , further comprising a second network element for interfacing said optical transport network to a second optical packet network, said second network element comprising
a first interface which receives said framed continuous bitstream optical signal from said optical transport network, said continuous bitstream optical signal carrying as payload said burst mode optical signal with pauses between gaps being filled with a filling pattern;
a second interface which transmits a recovered burst mode optical signal towards said second optical packet network;
a detector for detecting sequences filled with said fixed pattern in said payload; and
a zero-bit generator for replacing said filling pattern by pauses to recover said burst mode optical signal.