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Title:
OPTICAL RESERVATION-BASED NETWORK SWITCH FABRICS
Document Type and Number:
WIPO Patent Application WO/2006/086120
Kind Code:
A2
Abstract:
A method of communicating data over a network having a plurality of nodes (0-3) thereupon is disclosed. The method includes reservin bandwidth for each node (2) of the plurality of nodes (0-3), where the data includes a destination address on the network for the data. The method also includes allocating the received data on a wavelength (Lamada 2) associated with a destination node (2) at the associated wavelength (Lamada 2). The destination node is determined based on the destination address.

Inventors:
HAMOU CLAUDE (US)
Application Number:
US2006/001579
Publication Date:
August 17, 2006
Filing Date:
January 18, 2006
Export Citation:
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Assignee:
MATISSE NETWORKS, INC. (339 North Bernardo Ave, Mountain View, California, 94043, US)
International Classes:
H04B10/20; H04J4/00; H04L12/42; H04L12/43; H04L29/12; H04Q11/00
Foreign References:
US6738582B1
Attorney, Agent or Firm:
TURNER, Kevin, F (SQUIRE, SANDERS & DEMPSEY L.L.P.8000 Towers Crescent Drive, 14th Floo, Tysons Corner Virginia, 22182, US)
Download PDF:
Claims:

CLAIMS:

1. A method of communicating data over a network having a plurality of nodes

thereupon, said method comprising the steps of:

reserving bandwidth for each node of said plurality of nodes;

receiving data at a first node of said plurality of nodes, where the data includes a

destination address on the network for the data;

allocating the received data on a wavelength associated with a destination node of

said plurality of nodes; and

directing the allocated data to the destination node at the associated wavelength;

wherein the destination node is determined based on the destination address.

2. A method as recited in claim 1, wherein said network comprises an optical fiber

ring network and said step of reserving bandwidth for each node comprises reserving

bandwidth on said optical fiber ring network for each node.

3. A method as recited in claim 2, wherein the data comprises multiple data

packets having multiple destination addresses on the network, wherein said step of

allocating the received data on a wavelength comprises allocating each data packet on a

node wavelength associated with a destination node and wherein said step of directing the

allocated data comprises directing the allocated data packets to destination nodes at

associated node wavelengths.

4. A method as recited in claim 1, wherein said step of allocating the received data

comprises tuning a fast tunable laser to the wavelength associated with a destination node.

5. A method as recited in claim 1 , wherein said step of receiving data at a first node

of said plurality of nodes comprises tuning a fast programmable receiver to a wavelength

associated with a particular node associated with a portion of the reserved bandwidth.

6. A method as recited in claim 1, further comprising receiving data at said first

node of said plurality of nodes at a wavelength associated with the first node.

7. A method as recited in claim 1 , wherein said step of allocating the received data

comprises tuning a fast tunable laser to a plurality of wavelengths associated with

destination nodes when the data includes multiple destination addresses on the network

for the data.

8. A method as recited in claim 2, further comprising achieving an integer number

of slots on the network by changing a number of time slots on the optical fiber ring

network.

9. A method as recited in claim 8, wherein the step of changing the optical number

of time slots on the optical fiber ring network comprises dynamically measuring an optical

length of the optical fiber ring and setting the number of time slots based on the measuring

of the optical length.

10. A method as recited in claim 1, wherein the step of allocating the received data

comprises managing traffic on the network based on congestion at the plurality of nodes.

11. A communications node for communicating data over a network having a

plurality of nodes thereupon, comprising:

reserving means for reserving bandwidth for each node of said plurality of nodes;

receiving means for receiving data at a first node of said plurality of nodes, where

the data includes a destination address on the network for the data;

allocating means for allocating the received data on a wavelength associated with a

destination node of said plurality of nodes; and

directing means for directing the allocated data to the destination node at the

associated wavelength;

wherein the allocating means is configured to determine the destination node based

on the destination address.

12. A communications node as recited in claim 11, wherein said network

comprises an optical fiber ring network and said reserving means comprises means for

reserving bandwidth on said optical fiber ring network for each node.

13. A communications node as recited in claim 12, wherein the data comprises

multiple data packets having multiple destination addresses on the network, wherein said

allocating means comprises means for allocating each data packet on a node wavelength

associated with a destination node and wherein said directing means comprises means for

directing the allocated data packets to destination nodes at associated node wavelengths.

14. A communications node as recited in claim 11, wherein said allocating means

comprises tuning means for tuning a fast tunable laser to the wavelength associated with a

destination node.

15. A communications node as recited in claim 11, wherein said receiving means

comprises tuning means for tuning a fast programmable receiver to a wavelength

associated with a particular node associated with a portion of the reserved bandwidth.

16. A communications node as recited in claim 11, further comprising second

receiving means for receiving data at said first node of said plurality of nodes at a

wavelength associated with the first node.

17. A communications node as recited in claim 11, wherein said allocating means

comprises tuning means for tuning a fast tunable laser to a plurality of wavelengths

associated with destination nodes when the data includes multiple destination addresses

on the network for the data.

18. A Communications node as recited in claim 12, further comprising means for

achieving an integer number of slots on the network by means for changing a number of

time slots on the optical fiber ring network.

19. A communications node as recited in claim 18, wherein the means for

changing the optical number of time slots on the optical fiber ring network comprises

means for comprises means for dynamically measuring an optical length of the optical

fiber ring and means for setting the number of time slots based on the measuring of the

optical length.

20. A communications node as recited in claim 11, wherein the allocating means

comprises traffic managing means for managing traffic on the network based on

congestion at the plurality of nodes.

21. A communications node for an optical fiber network, said communications

node comprising:

a receiver for receiving optical data from source nodes;

a transmitter for transmitting optical data to destination nodes; and

a media access controller which determines a slot clock based on a system clock

signal received by the receiver;

wherein the receiver is of a first type that is one of a fixed wavelength type and a

tunable wavelength type, the transmitter is of a second type that is one of the fixed

wavelength type and the tunable wavelength type, where the first and second types are not

the same; and

wherein the media access controller is configured to allocates and direct data,

received from a plurality of nodes on the optical fiber network, on a wavelength associated

with a destination node determined for the data.

22. A communications node as recited in claim 21, wherein said network

comprises an optical fiber ring network.

23. A communications node as recited in claim 22, wherein the data comprises

multiple data packets having multiple destination addresses on the network and wherein

the media access controller allocates and directs each data packet on a node wavelength

associated with the destination.

24. A communications node as recited in claim 21, wherein said transmitter is of

the tunable wavelength type and said transmitter is configured to be tuned to the

wavelength associated with a destination node.

25. A communications node as recited in claim 21, wherein said receiver is of the

tunable wavelength type and said receiver is configured to be tuned to a wavelength

associated with a particular node associated with a portion of the reserved bandwidth.

26. A communications node as recited in claim 22, wherein the media access

controller determines a slot clock based on a system clock signal achieving an integer

number of slots on the network by changing the optical length of the optical fiber ring

network.

Description:

OPTICAL RESERVATION-BASED NETWORK SWITCH FABRICS

BACKGROUND OF THE INVENTION

FIELD OF INVENTION

[0001] The present invention relates to networks, such as Local Area Networks

(LANs) and access optical networks. Such networks can occur within an enterprise and

the present invention is also directed to fabrics coordinating traffic on those networks.

In particular, the present invention for direct all-optical routing that allows for data to be

switched between nodes.

DESCRIPTION OF RELATED ART

[0002] Fiber-optic infrastructure is a vital part of today ' s rapidly changing worldwide

networks. The drive for interconnectivity as well as the exponential growth in data

traffic, as a result of new applications, requires the adoption of new optical solutions.

Carriers and service providers are looking to increase their revenue by delivering new

services such as storage area networks and IP based services to their customers. New

technologies that can leverage the existing network, as well as increase the economic

viability of new network applications, are needed. New market opportunities and the

recent advances in optical technologies (such as wavelength division multiplexing,

tunable lasers and high speed optical/electronic components) have yielded new

developments in the optical networks area.

[0003] Traditionally, optical networks were used mainly in long-haul area networks.

Today, however, new optical networks are being introduced in the regional,

metropolitan and the local access area networks, including in enterprises. The

long-haul area networks use a fiber-optic infrastructure to create large data pipes

between two distanced points. Contrastingly, the new optical networks are facing

different demands.

[0004] Optical networks in the regional, metropolitan and the access area networks

require a sustained, high bandwidth, while maintaining mesh connectivity and

supporting multiple services and multiple classes of service. For example, metropolitan

area networks can transport voice traffic, SAN traffic and other IP traffic. Voice traffic

demands low bandwidth, with a guaranteed bandwidth, while SAN traffic is delay

sensitive and is burst traffic. An IP traffic class of service is application dependent.

Optical network are required to aggregate multiple types of data and transport while

keeping the required quality of service.

[0005] Communication networks can be divided into two general types:

circuit-switched networks (typically used for telephony traffic) and packet-switched

networks (typically used for data traffic). Circuit-switched networks (like SONET or

SDH) are networks wherein connections between nodes are fixed, whether data are

crossing the connection or not. Each connection in a circuit-switched network has a

constant-bandwidth. Packet-switched networks, on the other hand, are connectionless

networks, wherein data is transmitted in a burst mode. The benefit of packet-switched

networks is that bandwidth is used more optimally. However the connectionless

networks lack the ability to reserve bandwidth, and support a hard quality of service.

Moreover the statistic aggregation of packets can create an overload situation, in which

packets may suffer large delays or even data loss.

[0006] AU optical networks are basically packet-switched networks, in which routing

packets from a source node to a destination node is done optically, without the need for

optical-electrical conversions outside the source and destination nodes. A sub-group of

the all-optical networks is the all-optical multi-ring networks. Optical multi-ring

networks are based on a fiber ring topology, in which the fiber-ring is a shared optical

medium. Nodes, located around the fiber-ring, are equipped with optical receiver, fixed

to a unique wavelength, and with an ultra-fast tunable transmitter. In a multi-ring

optical network each wavelength is associated with a specific node. Transmitting

packets to destination node is done by a tunable-laser tuned to the destination

wavelength. Logically the network is a multi-ring topology, which allows any node to

address any other node simply by changing its transmitter wavelength to the target's

receiver wavelength without electrical routing.

[0007] As in other shared media topologies, in the packet switched multi-ring

topology, the problem of collisions when accessing the fiber must be addressed. There

are two main approaches to resolve packets collision problems: 1) an Ethernet-like

scheme where carrier detection is applied or 2) a synchronous system where collision

can't happen since each participant (node) has a reserved time when it can use the

media. By giving each node a required time or time frame in which it can use the media,

a synchronizing scheme between all the nodes needs to be implemented. In the case of

optical slotted ring dynamic networks, packets can be transmitted to the fiber in

dedicated time slot boundaries. The optical media poses special problems that need to

be overcome with respect to the slot synchronization.

[0008] Furthermore, since packets can be transmitted from any one node to any other

node on the fiber ring, frequency, phase and the position of the payload inside the time

slot cannot be guaranteed. Synchronizing on the signal frequency and phase, and

recognizing the payload should be done within a fraction time of the packet duration

and calls for fast synchronization solutions. In addition, in many networks that utilize

optical fiber, the optical signals must be "translated" into electrical signals in order for

the packet data to be switched. Such a process can slow down the throughput of the

switching system.

[0010] Thus, there is a need for a synchronization scheme that addresses the

problems discussed above for use in dynamic optical networks. There is also a need for

a process and system that overcomes the problem of time slot synchronization between

the nodes on the fiber ring so it is possible for each node to access the fiber without

collisions. Furthermore, in the context of this synchronization method, there is also a

need to define a method to recover the packet's data and clock in an ultra-fast recovery

time. Also, there is a need for a switching system that can take the place of a

semiconductor-based switch.

SUMMARY OF THE INVENTION

[0011] This invention seeks to overcome the drawbacks of the above-described

conventional network devices and methods. The present invention provides for a new

synchronization method for an optical slotted ring dynamic network. With this

approach, nodes that send packets to the same destination node must access the fiber at

a designated time-slot. The synchronizing signal is sent from a master node to the other

nodes. The present invention also provides for a burst mode receiver used to receive

and process an optical signal. Additionally, the use of a fiber providing the functions of

a switch fabric is also disclosed.

[0012] According to one aspect of this invention, a method of communicating

data over a network having a plurality of nodes thereupon. The method includes reserving

bandwidth for each node of the plurality of nodes and receiving data at a first node of the

plurality of nodes, where the data includes a destination address on the network for the

data. The method also includes allocating the received data on a wavelength associated

with a destination node of the plurality of nodes and directing the allocated data to the

destination node at the associated wavelength. The destination node is determined based

on the destination address.

[0013] Additionally, the method may be applicable to an optical fiber ring

network and the bandwidth is resolved on the optical fiber ring network for each node.

Also, the data may be multiple data packets having multiple destination addresses on the

network, each data packet may be allocated on a node wavelength associated with a

destination node and the allocated data packets are directed to destination nodes at

associated node wavelengths. Also, the step of allocating the received data may include

tuning a fast tunable laser to the wavelength associated with a destination node.

Additionally, the step of receiving data at a first node of the plurality of nodes includes

tuning a fast programmable receiver to a wavelength associated with a particular node

associated with a portion of the reserved bandwidth.

[0014] In addition, data may be received at the first node of the plurality of nodes at

a wavelength associated with the first node. Also, the step of allocating the received data

may include tuning a fast tunable laser to a plurality of wavelengths associated with

destination nodes when the data includes multiple destination addresses on the network

for the data. Also, an integer number of slots may be achieved on the network by

changing the optical length of the optical fiber ring network, where that change may occur

by adjusting an optical delay line. Additionally, the step of allocating the received data

may include managing traffic on the network based on congestion at the plurality of

nodes.

[0015] In another aspect of the invention, a communications node for

communicating data over a network having a plurality of nodes thereupon is disclosed.

The node includes reserving means for reserving bandwidth for each node of the plurality

of nodes and receiving means for receiving data at a first node of the plurality of nodes,

where the data includes a destination address on the network for the data. The node also

includes allocating means for allocating the received data on a wavelength associated with

a destination node of the plurality of nodes and directing means for directing the allocated

data to the destination node at the associated wavelength. The allocating means is

configured to determine the destination node based on the destination address.

[0016] In another aspect of the invention, a communications node for an optical

fiber network is disclosed. The node includes a receiver for receiving optical data from

source nodes, a transmitter for transmitting optical data to destination nodes and a media

access controller which determines a slot clock based on a system clock signal received by

the receiver. The receiver is of a first type that is one of a fixed wavelength type and a

tunable wavelength type, the transmitter is of a second type that is one of the fixed

wavelength type and the tunable wavelength type, where the first and second types are not

the same. Also, the media access controller is configured to allocates and direct data,

received from a plurality of nodes on the optical fiber network, on a wavelength associated

with a destination node determined for the data.

[0017] These and other objects of the present invention will be described in or be

apparent from the following description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For the present invention to be easily understood and readily practiced,

preferred embodiments will now be described, for purposes of illustration and not

limitation, in conjunction with the following figures:

[0019] Fig. 1 illustrates all-optical multi-ring network with four nodes, and a

schematic implementation of node #2, where node #2 drops wavelength #2, while other

wavelengths pass thru the node;

[0020] Fig. 2 illustrates the slots on the slotted network over an optical ring,

where the slots are rotating in the ring at one direction;

[0021] Fig. 3 shows the packet position inside the time slot;

[0022] Fig. 4 illustrates the case where the number of slot on the ring is not of an

integer number of slots, the tail slot overlap the head slot;

[0023] Fig. 5 illustrates the master node PHY 5 according to one embodiment of

the present invention, responsible of the synchronization channel, and the slots locking

mechanism;

[0024] Figs. 6a and 6b illustrate optical delay lines (ODL), with Fig. 6(a)

illustrating schematically a parallel ODL and Fig. 6(b) illustrating schematically a serial

ODL;

[0025] Fig. 7 illustrates a regular node PHY, according to one embodiment of the

present invention, responsible of the synchronization channel, and the slots locking

mechanism;

[0026] Fig. 8 illustrates a delay control process that compensates accumulated

delay for the broadcast wavelength;

[0027] Fig. 9 illustrates a Synchronous burst mode receiver diagram, according

to one embodiment of the present invention;

[0028] Fig. 10 illustrates one implementation of a 10GHz clock phase shifter

according to one aspect of the present invention;

[0029] Fig. 11a illustrates an all-optical multi-ring network with four nodes,

where Fig. l ib illustrates that both the receiver and the laser at each node are tunable,

according to one embodiment of the invention; and

[0030] Fig. 12 illustrates the use of an optical fiber ring as a switch fabric,

according to one aspect of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0031] The invention is directed, in part, to a synchronization scheme for an

all-optical network, in which nodes are equipped with an ultra-fast tunable laser

transmitter and a fixed receiver. As shown in Fig. 1, each node station has a receiver

101 tuned to a specific wavelength and a tunable laser 102 for transmitting to the other

nodes. Both the laser and receiver are in communication with the Media Access

Control (MAC) 103. According to the present invention, the synchronization scheme

defines any one of the nodes as a master-node (or referred to as the origin-node). The

master-node can be any of the network nodes and may perform additional tasks such as

synchronization signal distribution and reservation algorithm execution.

[0032] As discussed above, optical packet networks can be divided into two

types: slotted networks and unslotted networks. Slotted networks are synchronous

networks in which all the packets have the same fixed size and are transmitted inside

fixed time slots. On some systems, the time slot's duration can be larger then the packet

transmission duration due to guard times and headers. Unslotted networks are

asynchronous networks in which the packets can have a variable size and are not

transmitted within a time slot. The present application has particular relevance to

optical slotted packet networks based on an optical ring topology and proposes a

method to synchronize such a network.

[0033] In a slotted network topology over an optical ring, slots are rotating in the

ring in one direction, as shown by the circular arrow in Fig. 2. Nodes add packets to the

rotating slots in the transmission direction and drop packets from the slots on the

receiving direction.

[0034] In this access method, a global synchronization scheme is needed in order

for nodes to be synchronized on the slots boundaries. In a synchronous slotted ring the

number of slots on the ring must be an integer number. In the case where the number of

slot on the ring is not of an integer number of slots, the tail slot will overlap the head

slot, as shown in Fig. 4. Overlapping makes it impossible for the scheme to be collision

free.

[0035] Since all the nodes are synchronized on a global slot clock, a

synchronization jitter between nodes can be created. Moreover, when the slot is used to

transmit packets with different wavelengths, a "walk-off between packets is created,

due to the chromatic dispersion. In order to avoid packet overlap, guard times are

required. Fig.4 shows the packet 301 positioned inside the time slot. A guard time 302

is placed before and after the data packet payload inside a time slot.

[0036] Since each node receives packets from different destinations, the packet

phase and the position of the packet inside the slots is not precisely known. A burst

receiver is needed at the receiving node for phase locking and to determine the packet's

position in the slot. The burst receiver uses a preamble header, which each packet has;

where the preamble header contains a "barker" to mark the beginning of the payload.

[0037] The system can be implemented with or without a single system clock.

On a synchronized ring operating with a single system clock, one node (master node)

broadcasts a system-clock signal that is locked onto by all the other nodes. The

system-clock is used, by each node, for transmitting data to other nodes, for sampling

the received data signals and for slot synchronization. When the system is implemented

with no single system clock, the broadcast channel can be used for slot synchronization

alone.

[0038] In order to keep the slots from overlapping, slots boundaries can be

determined by a single source. In the case where the system is implemented using a

single system clock, the master node transmits the time-slot clock by transmitting a

cyclic series with the slots-clock cycle. At the slave nodes, a correlator tuned to this

series can be used for recovering the time-slot clock. The transmitted series propagates

around the ring and returns to the master node. A locking mechanism at the master node

then changes the time-slot duration to eliminate the slots overlapping. The time-slot

duration is controlled through the change in the series sequence phase. This is done by

changing the sequencer reset times.

[0039] In order to achieve an integer number of time slots on the ring, the size of

the physical ring can be changed (by using a configurable optical delay line), or the

packet size could be changed. On rings having large lengths, where there is a high

number of slots on a ring, a small change in the packet size is multiplied by the number

of slots. In this case, a higher guard time could absorb the packet size change. On

shorter rings, changing the guard time is not enough, and the payload size must be

changed in order to keep a constant bit rate. In this embodiment, the Master node is

responsible of measuring the ring length and then to determine the optical delay line

configuration and the time-slot size.

[0040] In addition to the regular PHY tasks, the PHY at the master node should

maintain an integer number of slots on the fiber. The PHY at the master node has a

locking mechanism to accomplish this task. Fig. 5 illustrates the master node PHY,

according to one embodiment of the present invention. The first stage provides for a

rough adjustment of the ring length, where the adjustment is performed through a

tunable optical delay line (ODL) 501. The second stage is for small adjustment and is

done by a Phase Locked Loop (PLL) that is locked to the slot clock signal. The PLL is

made up of, in this embodiment, of a drop component 502 that takes part of the signal

that is processed by the Clock and Data Recovery (CDR) component. The output from

the CDR is sent to the correlator 504 and to the sequencer 505. The correlator 504

produces a slot clock signal and provides this signal to a phase detector where it is

multiplied with the output of a voltage control oscillator (VCO). The output of the

phase detector is sent to a low pass filter 508 and then to a controller 509 to produce a

clean slot clock without the jitter that may be present in the derived slot clock signal.

The clean slot clock and the bit clock are input into a sequencer and the sequencer

outputs a signal to the add/drop multiplexer 506 (ADM). The multiplexer allows for a

signal specific to that node to be extracted or added. The multiplexed signal is sent to a

modulator along with a signal from the light source tuned to the broadcast wavelength.

The new signal is added back to the ring to be received by the next node.

[0041] Sending the time-slot clock on the same phase as the received signal

assures that slots are not overlapping. The PLL adjustments are used to set the time-slot

duration. The duration of the time-slot clock is changed by changing the series

sequence phase (by resetting the sequence). A signaling channel can be added over the

broadcast wavelength as well using an electrical add and drop.

[0042] In the case where the bit clock is not distributed, the time-slot clock is

transmitted directly over the broadcast wavelength and a simple PLL can be used to

recover the clock.

[0043] The ring length and the slot size determine the slot clock adjustments.

Given that the residue (the excess partial time slot on the ring) is divided between all of

the slots on the ring, a clock adjustment is needed, where the residue is divided between

each of the number of slots. Since on small rings the needed adjustment might be too

large for the system needs, it is possible to artificially change the original ring size. This

can be done, for example, at the master node using a tunable optical delay line.

[0044] An example of a tunable optical delay line illustrated in Fig. 6(a) has four

delays positions: none, 1 A slot, Vz slot and 3 A slot. This delay line can be used to reduce

the residue. By changing the source clock, the remaining residue will be then

eliminated. Hence, the maximum clock adjustment can be reduced by a factor of four.

[0045] In one embodiment, a Parallel Optical Delay Line may be used, as

illustrated in Fig. 6(a). The Parallel Optical Delay Line two 1 :N optical switches switch

between N fibers of 0 to 1 time slot lengths. The two switches have to get the same

control. The granularity of this ODL is dependent on the number of ports each optical

switch has.

[0046] In another embodiment, a Serial Optical Delay Line may be used. A

Serial Optical Delay Line, as illustrated in Fig. 6(b), can have N stages; each stage can

include a 1 :2 switch, a delay line and a combiner. By changing the state of each of the N

switches, 2 N different delays are possible. A relatively high Insertion Loss, however, is

one penalty in this configuration.

[0047] The system can be implemented with or without a globally synchronized

bit clock. When the bit clock is distributed, slot synchronization is accomplished by

transmitting a repeating sequence over the broadcast bit clock channel, onto which each

node locks. In the case the bit clock is not distributed, the slot clock is transmitted

directly over the broadcasted channel. In both cases, the broadcast wavelength is

dropped at each node, reconstructed and transmitted again in a daisy chain manner.

[0048] The PHY at the regular nodes is illustrated in Fig. 7. In the first stage the

System Clock and the Slot Clock are recovered. The signal is received at the drop 702

and a conventional CDR 703 extracts the Data & the CLK from the broadcasted

wavelength. The clock extracted is used as the system clock, and the data is used to

extract the Slot clock. The data transmitted over the broadcast wavelength is a cyclic

series with a cycle of the Slot Clock rate. A correlator 704 tuned to this series is used for

recovering the slot clock.

[0049] In the next stage, the node's specific wavelength is dropped 705 and

sampled using a Synchronous burst mode receiver (SB-CDR) 706. The SB-CDR

generates a clock synchronous to the data received using a phase shifter. The use of a

phase shifter assures a fast locking time. Next, packets are added 708 to the fiber using

the tunable laser, and on the last stage, the broadcast wavelength is retransmitted 707

after it has passed through an O-E-O conversion and signaling data is added and

dropped 709 & 710.

[0050] As can be seen, the broadcast wavelength is recovered at each node, and

retransmitted in a daisy-chain manner. Since the data is recovered and retransmitted,

the internal delay of the electronics might cause a phase shift of up to one broadcast

wavelength clock. This delay is accumulated at each node on the ring, and should be

considered in the packet guard time. Alternatively, this delay can be minimized

through the use of an appropriate delay control, either by optics or an electrical delay, as

shown in Fig.8.

[0051 ] In the case where the Slot Clock is transmitted directly over the broadcast

wavelength, a simple PLL can be locked over the returning signal. The slot clock,

transmitted by the master node, propagates around the ring to all the nodes. Each node

drops the clock signal wavelength, and converts the optical signal to electrical. Since

the slot clock needs to have low jitter/noise characteristics, a phase-lock-loop (PLL) can

be used to recover a clean clock. In any of the methods, the recovered slot clock is used

to time the node transmitter and receiver, and thus avoid overlapping between slots.

[0052] Since the system bit clock is distributed and each node transmits the

packet bits using a clock derived from the system clock, the receiver doesn't need a

frequency lock. Bit synchronization can be achieved by merely shifting the clock phase

using a phase shifter based burst receiver. Shifting the phase alone can be done much

faster than the frequency and phase locking that the traditional PLL receiver does.

[0053] An example of a Synchronous burst mode receiver is illustrated in Fig. 9.

Since the system clock is known, the data frequency is known as well. The SB-CDR

uses the system clock as a reference for the phase deviation measurement. The phase

deviation measurement is used in adjusting the phase shifter and the phase-shifted clock

is then used for sampling the data. The SB-CDR phase locking is done in two stages. In

the first stage the phase shifter is shifted directly to the calculated phase. In the second

stage the correct phase is kept during the packet transmission by slower corrections.

The input signal is limited by a limiting amplifier 901 and the output is sent to both the

phase detector and the sample unit 902. The phase detector operates on a clock signal

from the phase shifter 904 with the input signal. The output of the phase detector is sent

to a low pass filter 903 and to a controller 905 for the phase shifter. The phase-shifted

clock is also sent to the sample unit 902 to sample the data.

[0054] Normally, a source node transmits a packet within the time-slot

boundaries, using the appropriate guard times. However, due to the fact that destination

node receives packets from multiple source nodes; the packet's position inside the

time-slots is not known. In order to recognize the packet payload, a "barker" is placed

between the preamble and the packet payload. The digital receiver recognizes the

barker, and extracts the payload.

[0055] On a synchronized ring operating with a single system clock, one node

(master node) broadcasts a system-clock signal that is locked onto by all of the other

nodes. The system-clock is used, at each node, for transmitting data to other nodes and

for sampling the received data signals. However, the nodes are located at different

distances from each other and have different electrical/optical inner-delays; this means

that although all the source nodes transmit signals using the same clock, the destination

node gets a phase shifted signal depending on the source node location/delay.

[0056] In order to handle the shift delays and avoid the need for a burst receiver

and/or the penalty of a PLL locking time, the receiving nodes can use a phase-shifter

scheme. In the phase-shifter scheme, the bit clock frequency is known. The known

frequency clock is shifted by the phase shifter to the correct bit clock phase. The phase

shift needed is determined from a phase detector. The correct phase is kept during the

packet transmission by slow corrections.

[0057] An embodiment of a 10GHz clock phase shifter implementation is

illustrated in Fig. 10: One Direct Digital Synthesizer (DDS) 1004 is used as a VCO in a

Phase Locked Loop. Its frequency and phase are locked to the 622 MHz system-clock.

A second DDS 1006 receives the same control words, from the controller 1005, as the

first DDS so its output is the same as the first DDS. By adding a constant value to the

control words, the second DDS keeps track of the input frequency, but with a different

phase. The phase-shifted output is then multiplied with a 15 x system clock, creating a

phase controlled lOGbit clock.

[0058] Dense Wavelength Division Multiplexing (DWDM) is an optical

technology used to increase bandwidth over existing fiber optic backbones. DWDM

works by combining and transmitting multiple signals simultaneously at different

wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual

fibers. Therefore, eight optical carrier-48 signals may be multiplexed into one fiber, to

increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s.

[0059] One advantage to DWDM is that it is protocol and bit-rate independent.

DWDM-based networks can transmit data in Internet Protocol (IP), Asynchronous

Transfer Mode (ATM), Synchronous Optical Network / Synchronous Digital Hierarchy

(SONET /SDH), and Ethernet. Therefore, DWDM-based networks can carry different

types of traffic at different speeds over an optical channel. From a QoS (Quality of

Service) stand point, DWDM-based networks create a lower cost way to quickly

respond to customers' bandwidth demands and protocol changes.

[0060] In one embodiment of the present invention, the use of Reservation Based

method, as discussed above, a DWDM fiber optical ring may be used to achieve the

functionality of a switch. The present invention uses fast tunable lasers and/or fast

programmable receivers to convert the optical fiber ring into a switch fabric.

[0061] All the nodes in the system are connected through the optical fiber, each

node has a dedicated wavelength assigned to it or programmed while connected to the

fabric. Using the reservation based method, bandwidth is reserved to each node in the

fabric and the direction of traffic on separate wavelength intended to different nodes is

resolved. Thus, the present invention has the ability to direct traffic simultaneously

from different sources to different destination nodes by the allocation of the appropriate

data on the wavelengths assigned to each nodes in the system is achieved.

[0062] The reservation-based method provides a scheduling mechanism to

control the transmission of the appropriate wavelengths while using a tunable laser

and/or the reception of the correct wavelength while using programmable receivers.

Such a system is illustrated in Figs. 1 Ia and 1 Ib. The invention is therefore directed, in

the embodiments discussed below, to a system and method for all-optical switching

system such as network or fabric- switch, in which optical elements 111 are equipped

with tunable laser transmitter 112 and/or tunable receiver 113, as shown in Fig. 17B.

Both tunable elements are controlled by the electrical layer 114.

[0063] Although using two tunable elements does not improve the system

dynamic allocation it simplifies the system deployment. Systems which are based on

fixed elements (transmitters or receivers) are required to be designed in a way that no

two elements with the same configuration will be connected to the same network. By

using only tunable elements the network can configure itself during the initialization

process avoiding the pre-design.

[0064] Converting wavelengths to specific nodes addresses provides the needed

mechanism to solve the addressing process, while the synchronization allows the use of

optical fibers at different length. Thus, the method of using reservation map to control

tunable lasers to transmit and fixed receivers, or programmable receivers and fixed

lasers to transmit, combined with a synchronization mechanism are used to achieve the

functions of a switch fabric. These functions may include bandwidth allocation per

node and the simultaneous transmission and reception of data on different node in a

system which includes a plurality of nodes. The switch fabric also provides for the

ability to replace a pre-determined routing table, which defined the traffic source and

destination digital addresses, with wavelengths, where this is used as an alternative to

traditional implementation of this function in switches using digital solid state

semiconductors .

[0065] A reservation-based optical switch fabric is generally illustrated in Fig.

12. All the nodes 1210 in the system are connected through the optical fiber 1200, with

each node having a dedicated wavelength assigned to it or programmed while

connected to the fabric. As illustrated in Fig. 12, node 3 has assigned thereto a

wavelength λ 3 , such that node 3 need only be concerned with signals a wavelength the

same as its assigned wavelength. Using the reservation based method, bandwidth is

reserved to each node in the fabric and the direction of traffic on separate wavelength

intended to different nodes is resolved.

[0066] Thus, the present invention has the ability to direct traffic simultaneously

from different sources to different destination nodes by the allocation of the appropriate

data on the wavelengths assigned to each nodes in the system is achieved. Such

functionality has import for data that arrives at a node and needs to be multicast or

broadcast to other nodes. In each case, a tunable laser is used to send out the received

data on a plurality of wavelengths corresponding to the proper destination nodes.

[0067] Traditional implementation of the functions described above using

solid-state semiconductors consist of combining the functions of switching traffic based

on source and destination addressing, traffic management and traffic scheduling. In the

present embodiment of the invention, the tunable lasers and receivers, together with the

synchronizing process, provide the equivalent to layer 2 scheduling, forwarding and

linking of data.

[0068] Usually a crossbar function is implemented to cover directing traffic from

different sources to different destination and the traffic scheduler combined with the

traffic management function, are the functions need to deliver traffic based on priority

and demand of bandwidth. The implementation is based on separate solid state

semiconductors or having these some of all of these functions integrated in one of more

semiconductor devices. These functions can also include the dropping of packets

because of congestion at ports of the switch, on a priority or non-priority basis.

Traditional switch fabrics also allow for traffic arriving or departing from a port to be

monitored by mirroring packets to another port where the monitoring occurs.

[0069] The approach of the present embodiment of the invention is the ability to

direct wavelengths within a single fiber optic wire to different destinations. The present

embodiment also allows for the use of the reservation map algorithm, which provides

the control mechanism to the fast tunable laser to select the appropriate wavelength.

[0070] The monitoring of data through mirroring of data to another node can be

easily accomplished through the system provided by the present invention. As an

example, suppose that packets received by node 4, in Fig. 12, are to be monitored by

mirroring those packets to node 5 also. In a traditional semiconductor system, extra

copies of the packets destined for node 4 would need to be replicated and forwarded to

node 5. In the present invention, the receiver in node 5 would merely need to be tuned

to λ 4 such that it can also receive the same packets that are received by node 4.

[0071] This embodiment provides for a completely new approach for the

implementation of these switch fabrics, achieving a new level of distribution over long

and short distances and a cost efficiency advantage due to the ability of building the

switch in a scalable manner. Implementation using semiconductor-based switches

forces the centralization of the fabric into one specific rigid location. With the optical

fiber switch mechanism of the present invention, the switching need not occur in a

central location and can be spread out to portions of the network where the switching

functions may be most appropriate.

[0072] In summary, the invention is directed to a reservation-based media access

controller which is capable of providing a full reservation optical network. The

invention is also directed to an optical network which implements the full reservation

algorithm, and methods of providing full reservation optical communication utilizing

reservation of time-slots and wavelengths. Various configurations of an optical

network and the nodes thereof can be provided, as discussed herein, and the media

access controller can be created based upon a plurality of discrete components

configured to form a functioning unit, and can also be formed on a single semiconductor

substrate.

[0073] Although the invention has been described based upon these preferred

embodiments, it would be apparent to those of skilled in the art that certain

modifications, variations, and alternative constructions would be apparent, while

remaining within the spirit and scope of the invention. In order to determine the metes

and bounds of the invention, therefore, reference should be made to the appended

claims.