NETWORK SYSTEM AND OPTICAL LINE TERMINAL

• US 20090162065A1
• Filed: 12/18/2008
• Published: 06/25/2009
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Mizutani, Masahiko, Ikeda, Hiroki, Sugawara, Toshiki
• Granted Patent: US 8,331,784 B2
• Time in Patent Office: Days
• US Class Current: 398/66
• CPC Class Codes: H04J 3/0655 using timestamps
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 7/0008 Synchronisation information channels, e.g. clock distribution lines
• CPC Class Codes: H04Q 11/0067 Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
• CPC Class Codes: H04Q 2011/0064 Arbitration, scheduling or medium access control aspects
• CPC Class Codes: H04Q 2011/0079 Operation or maintenance aspects

Abstract

It is necessary to completely remove overlapping of signals between plural PONs in order to make the PONs coexist. Accordingly, it is required to share or intensively manage bandwidth use conditions over an optical fiber that serves as a common band between plural systems. Therefore, transmission clocks should be synchronized with high accuracy between plural systems. A reference clock is provided from an external device or a representative OLT to the entire systems to perform clock synchronization between plural systems, so that the overall systems are synchronized by synchronizing each OLT with the reference clock. A hierarchical management method is selected that manages ONUs under the control of each OLT by managing band use information arranged for each OLT with respect to an external device or a representative OLT for sharing of bandwidth use conditions between plural systems.

Claims

1. A network system comprising:

a first OLT (Optical Line Terminal), a second OLT, a first ONU (Optical Network Unit), and a second ONU,

wherein the first ONU and the second ONU are connected to each other through an optical fiber shared by the first OLT and the second OLT such that data is transmitted between the first OLT and the first ONU and between the second OLT and the second ONU, and

the first OLT and the second OLT supply a clock signal to the first ONU and the second ONU, respectively, at common clock timing.

2. The network system according to claim 1, wherein the first and second OLTs perform DBA (Dynamic Bandwidth Assignment) control using the common clock timing.

3. The network system according to claim 1, wherein the first and second OLTs determine timing by performing ranging using the common clock timing.

4. The network system according to claim 1, further comprising a clock synchronization control unit connected to the first OLT and the second OLT to supply the common clock timing.

5. The network system according to claim 4,

wherein each of the first OLT and the second OLT includes:

a clock oscillator;

a clock receiving unit that receives a clock signal from the clock synchronization control unit; and

a clock detecting unit that synchronizes a clock signal generated from the clock oscillator with a clock signal received by the clock receiving unit.

6. The network system according to claim 1, further comprising:

a feedback line that inputs to the clock synchronization control unit a clock signal supplied from the first OLT to the first ONU and a clock signal supplied from the second OLT to the second ONU,

wherein the clock synchronizing control unit includes;

a clock comparing unit that compares the clock signal received from the feedback line with a clock signal generated by the clock synchronization control unit; and

a clock correcting unit that corrects the clock timing based on a comparison result.

7. The network system according to claim 1, wherein communication between the first OLT and the first ONU and communication between the second OLT and the second ONU differ in bit rate from each other.

8. The network system according to claim 1, wherein a bit rate of communication between the first OLT and the first ONU is an integer multiple of a bit rate of communication between the second OLT and the second ONU, and the clock timing is a clock speed used for the first OLT and the first ONU.

9. The network system according to claim 1, wherein the first OLT and the first ONU perform communication at a higher bit rate than that of the second OLT and the second ONU.

10. The network system according to claim 1,

wherein the first OLT includes:

a clock oscillator that generates a common clock signal, and

an interface for clock signal that supplies the common clock signal to the second OLT; and

the first OLT and the second OLT supply the clock signal to the first ONU and the second ONU, respectively, at clock timing of the common clock signal that is supplied from the interface for clock signal.

11. An OLT (Optical Line Terminal) connected to an ONU (Optical Line Unit), an OLT of another system, and an ONU of another system through an optical fiber to transmit data to the ONU, the OLT comprising:

a clock oscillator that generates a common clock signal; and

an interface for clock signal that supplies the OLT of the other system with the common clock signal that determines clock timing of supplying a clock signal to the ONU of the other system,

wherein the ONU clock signal is supplied at clock timing of the common clock signal.

12. The OLT according to claim 11, wherein the OLT performs DBA control using the clock timing of the common clock signal.

13. The OLT according to claim 11, wherein the OLT performs ranging using the clock timing of the common clock signal.

14. The OLT according to claim 11, further comprising:

a feedback line that feeds back a clock signal supplied to the ONU;

a clock comparing unit that compares the clock signal received from the feedback line with a common clock signal transmitted from the clock oscillator; and

a clock correcting unit that corrects the clock timing based on a comparison result.