Optical switch and protocols for use therewith

• US 6,529,301 B1
• Filed: 07/29/1999
• Issued: 03/04/2003
• Est. Priority Date: 07/29/1999
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Wang, Guo-Qiang
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/362,886
• Time in Patent Office: 1,314 Days
• Field of Search: 359/128,117,139 370/351,357,360,389,400
• US Class Current: 398/82
• CPC Class Codes: H04B 10/27 Arrangements for networking
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04Q 11/0001 using optical switching
• CPC Class Codes: H04Q 11/0003 Details
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 11/0062 Network aspects
• CPC Class Codes: H04Q 2011/0011 using wavelength conversion
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• CPC Class Codes: H04Q 2011/0039 Electrical control
• CPC Class Codes: H04Q 2011/0069 using dedicated optical channels
• CPC Class Codes: H04Q 2011/0073 Provisions for forwarding or routing, e.g. lookup tables
• CPC Class Codes: H04Q 2011/0086 Network resource allocation, dimensioning or optimisation
• CPC Class Codes: H04Q 2011/009 Topology aspects

Abstract

A method of establishing a data connection between terminal switching nodes in a network and switching nodes for implementing the method. The method involves switching nodes participating in a network layer wavelength routing (WR) protocol to determine the next hop switching node for every possible combination of terminal nodes based on the network topology. The method also involves the switching nodes participating in a network layer wavelength distribution (WD) once the data connection is to be established. The WR protocol determines the path used through the network, while the WD protocol assigns wavelengths on each link between switching nodes. The wavelengths may be different on different optical links. The switching nodes include wavelength converters with an optical switch or optoelectronic converters with a digital electronic switch. A digital electronic switch can also provide signal reformatting. Advantages of using potentially different wavelengths along various segments of a single end-to-end connection yields increased wavelength efficiency.

Claims

1. A switching node, comprising:

an optical switch fabric for switching optical signals arriving on a plurality of input optical fiber segments over to a plurality of output optical fiber segments in accordance with mapping instructions;

wavelength conversion means connected to the optical switch fabric, for modifying the wavelengths occupied by incoming or switched optical signals in accordance with conversion commands; and

a control unit connected to the optical switch fabric and to the wavelength conversion means, for exchanging control information with other switching nodes using a network layer protocol and generating said mapping instructions and said conversion commands based on said control information.

2. A switching node as claimed in claim 1, wherein said control information is exchanged using an out-of-band control channel.

3. A switching node as claimed in claim 1, wherein the out-of-band control channel is an optical supervisory channel.

4. A switching node as claimed in claim 1, wherein said control information is exchanged using an in-band control channel.

5. A switching node as claimed in claim 1, further comprising a plurality of ports for connecting the switching node to adjacent switching nodes via a respective fiber optic link and further comprising, for each port:

an optical directional coupler connected to the respective port;

an optical multiplexer connected between the respective optical directional coupler and a respective plurality of the output optical fibers; and

an optical demultiplexer connected between the respective optical directional coupler and a respective plurality of the input optical fibers.

6. A switching node as claimed in claim 5, further comprising:

at least one additional input optical fiber segment connected to each optical demultiplexer for carrying control information from the switching node connected to the respective port;

at least one additional output optical fiber segment connected to each optical multiplexer for carrying control information to the switching node connected to the respective port; and

optoelectronic conversion means connected between the control unit and the additional input and output optical fiber segments.

7. A switching node as claimed in claim 5, wherein the control unit comprises a processor and a memory element accessible by the processor.

8. A switching node as claimed in claim 7, wherein the memory element stores a routing table and a wavelength availability table, wherein the routing table contains a next hop switching node field associated with every possible pair of terminal switching nodes and wherein the wavelength availability table contains the identity of the switching nodes connected to any of the ports by a respective multi-wavelength fiber optic link and, for each wavelength, an indication of whether that wavelength is occupied or available.

9. A switching node as claimed in claim 8, wherein the next hop switching node field is generated by the control unit executing a routing algorithm.

10. A switching node as claimed in claim 9, wherein the routing algorithm is the Dijkstra algorithm.

11. A switching node as claimed in claim 8, wherein the switching node is connected to a previous switching node in a path identified by a first terminal switching node and a second terminal switching node, and wherein the control unit is operable to:

a) receive messages from the previous switching node;

b) if the message is a CONNECTION_REQUEST message, then;

access the wavelength availability table to identify an available wavelength on the link between the current and previous switching nodes, said available wavelength being associated with one of the input optical fiber segments; and

if the current switching node is the second terminal switching node;

generate mapping commands for establishing a connection using said available wavelength between the input optical fiber segment associated with said available wavelength and one of the output optical fiber segments; and

send a CONNECTION_CONFIRM message to the previous switching node;

otherwise;

access the routing table to determine the contents of the next hop switching node field associated with the first and second terminal switching nodes; and

forward the CONNECTION_REQUEST message to the switching node identified by the next hop switching node field; and

c) if the message is a CONNECTION_CONFIRM message, then;

generate mapping commands for establishing a connection using said available wavelength between the input optical fiber segment associated with said available wavelength and one of the output optical fiber segments; and

send a CONNECTION_CONFIRM message to the previous switching node.

12. A switching node as claimed in claim 11, wherein said conversion commands are sent to the wavelength conversion means if the available wavelength used by an input optical fiber segment differs from the wavelength associated with the output optical fiber segment to which the input optical fiber is connected by the optical switch fabric.

13. A switching node as claimed in claim 1, wherein the control information includes topology information about the network and wherein the mapping instructions and conversion commands are automatically reconfigurable as a function of changes in the topology information.

14. A switching node as claimed in claim 1, wherein each input optical signal consists of a sequence of packets, with each packet containing of a header and a payload, the switching node further comprising:

means connected to the input optical fiber segments and to the control unit, for extracting the header of each packet;

wherein the mapping instructions and the conversion commands are further dependent on the information contained in the header.

15. A switching node, comprising:

a first plurality of optoelectronic converters, for converting input optical signals occupying respective wavelengths into electronic signals;

a second plurality of optoelectronic converters, for converting output electronic signals into output optical signals occupying respective wavelengths;

a digital switch fabric connected to the optoelectronic converters, for switching the input electronic signals over to the output electronic signals in accordance with mapping instructions; and

a control unit connected to the digital switch fabric and to the optoelectronic converters, for exchanging control information with other switching nodes using a network layer protocol and generating said mapping instructions based on said control information.

16. A switching node as claimed in claim 15, wherein said control information is exchanged by means of an out-of-band control channel.

17. A switching node as claimed in claim 15, wherein said control information is exchanged by means of an in-band control channel.

18. A switching node as claimed in claim 15, further comprising a plurality of ports for connecting the switching node to adjacent switching nodes and further comprising, for each port:

an optical directional coupler connected to the respective port;

an optical demultiplexer connected between the respective optical directional coupler and respective ones of the first plurality of optoelectronic converters; and

an optical multiplexer connected between the respective optical directional coupler and respective ones of the second plurality of optoelectronic converters.

19. A switching node as claimed in claim 18, further comprising:

at least one input optical fiber segment connected to each optical demultiplexer for carrying incoming control information;

optoelectronic conversion means connected between the input optical fiber segments and the control unit;

at least one output optical fiber segment connected to each optical multiplexer for carrying outgoing control information; and

optoelectronic conversion means connected between the control unit and the output optical fiber segments.

20. A switching node as claimed in claim 15, wherein the digital switch fabric comprises means for re-formatting the input electronic signals prior to switching.

21. A switching node as claimed in claim 15, wherein the digital switch fabric comprises means for re-formatting the output electronic signals after switching.

22. A method of establishing a data connection between first and second terminal switching nodes in an optical network, the network comprising said terminal switching nodes and a plurality of other switching nodes interconnected by multi-wavelength optical links, the method comprising:

identifying a path comprising a set of links and wavelengths for transporting data between the first and second terminal switching nodes via zero or more intermediate switching nodes; and

at each intermediate switching node connected to a respective ingress link and a respective egress link in the identified path, switching the optical signals arriving on the respective ingress link over to the respective egress link and performing wavelength conversion if the wavelengths occupied on the respective ingress and egress links are different.

23. A method as claimed in claim 22, wherein the step of identifying a path comprises:

a) at each switching node, associating a respective next hop switching node with every possible pair of switching nodes;

b) the first terminal switching node forwarding a data connection request message to the next hop switching node associated with the instant combination of the first and second terminal switching nodes;

c) upon receipt of the connection request message, the next hop switching node reserving a wavelength on the link connecting the next hop switching node to the first terminal switching node;

d) renaming the next hop switching node as the current switching node;

e) if the current switching node does not correspond to the second terminal switching node, the current switching node forwarding the data connection request message to the next hop switching node corresponding to the instant combination of the two first and second terminal nodes;

f) upon receipt of the connection request message, the next hop switching node reserving a wavelength on the link connecting the next hop switching node to the current terminal switching node;

g) repeating step d), e) and f) until the current switching node corresponds to the second terminal switching node.

24. A method as claimed in claim 23, wherein step a) comprises executing a routing algorithm based on topology information about the network.

25. A method as claimed in claim 24, wherein said topology information is exchanged among the switching nodes using a control channel.

26. A method as claimed in claim 25, wherein the control channel is an in-band control channel.

27. A method as claimed in claim 25, wherein the control channel is an out-of-band control channel occupying at least one wavelength along each link.

28. A method as claimed in claim 22, wherein switching the optical signals comprises:

at the intermediate switching node connected to the second terminal switching node;

switching the optical signal occupying the reserved wavelength on the respective ingress link over to the reserved wavelength on the respective egress link and forwarding a connection confirmation message to the switching node connected to the ingress link; and

at every other intermediate switching node;

upon receipt of a connection confirmation message, switching the optical signal occupying the reserved wavelength on the respective ingress link over to the reserved wavelength on the respective egress link and forwarding a connection confirmation message to the switching node connected to the ingress link.

29. A wavelength distribution protocol for enabling the establishment of a data connection between a first terminal switching node and a second terminal switching node via zero or more intermediate switching nodes along a path in a network, wherein an initial CONNECTION_REQUEST message is sent to the first terminal switching node upon initially requesting said data connection, the protocol comprising, at each current switching node connected in said path between a previous switching node and/or a next switching node by respective optical links:

receiving messages from the previous or next switching node;

if the message is a CONNECTION_REQUEST message, then;

if the current switching node is not the first terminal switching node, identifying and storing an available wavelength on the link between the current and previous switching nodes; and

if the current switching node is the second terminal switching node, establishing a connection using the available wavelength and sending a CONNECTION_CONFIRM message to the previous switching node, otherwise forwarding the CONNECTION_REQUEST message to the next switching node; and

if the message is a CONNECTION_CONFIRM message, then;

establishing a connection using the previously stored available wavelength; and

if the current switching node is not the first terminal switching node, sending a CONNECTION_CONFIRM message to the previous switching node.