Design and Implementation ofGMPLS-basd Optical Slot Switching Network

with PLZT High-speed Optical SwitchTeruo Kasahara, Masahiro Hayashitani, Yutaka Arakawa, Satoru Okamoto and Naoaki Yamanaka

Dept. of Information and Computer Science, Faculty of Science and Technology,Keio University, Yokohama, 223-8522, Japan

Email: kasa@yamanaka.ics.keio.ac.jp

Abstract— In this paper, we propose a new opticalnetwork architecture, called Optical Slot Switching (OSS),suitable for large data transmission where we use PLZToptical switch controlled by GMPLS(Generalized Multi-Protocol Label Switching). PLZT ultra-high speed opticalswitch can improve the bandwidth efficiency by reducingthe guard time between data compared with the conven-tional optical switch. In OSS network, user dynamicallyestablishes the path and can transport a large size dataefficiently by using reserved slots in a moment. Throughthe experimental results, we show that our proposed OSSis suitable for large data transmission.

I. I NTRODUCTION

The IP traffic in the network increases rapidly by thespeed-up of the access network and the spread of theP2P application in recent years, and the demand for thehigh-speed mass forwarding technology has risen.

In optical network, a high technology and the controlof an optical device is important. MEMS (Micro ElectroMechanical Systems) is widely used from the viewpointof practicality in optical network such as OCS (OpticalCircuit Switching), OBS (Optical Burst Switching) [1]and so on.

On the other hand, a high-speed optical switch wasactively researched in recent years. Then, PLZT highspeed optical switch was realized by Nozomi PhotonicsCo.,Ltd. in 2005 [2]-[4]. The PLZT optical switch enableto switch its output port with under 10 nsec, and canimprove the bandwidth utilization by reducing the guardtime between data transfer unlike the MEMS switch. Itbecame possible to think about more efficient networkarchitecture by the appearance of PLZT optical switch.

In this paper, we propose quite new network archi-tecture with PLZT optical switch, named Optical SlotSwitching (OSS). One user is allocated a shared band-width in conventional architecture, on the contrary oneuser is allocated all bandwidth in a slot, which is dividedinto the slot, in proposed architecture. Using PLZT high-speed optical switch greatly decreases the guard time,and makes possible the idea of slot which was non-practicable with the MEMS switch. By allocating allbandwidth in a slot to one user, simple and transparentdata transfer is achieved. Since the multiplexing is not

done like the TDM (Time Division Multiplexing), theprotocol is free in the allocated slot.

In the proposed network, there are frames composedof two or more slots, which is a minimum unit of the datatransfer, and each link is assumed for synchronization tobe taken. One user reserves a bandwidth in slot by TDM-LSP (Time Division Multiplexing-Label Switched Path)scheme in RSVP-TE (Resource ReserVation Protocol-Traffic Engineering)[5]. Unlike TDM, GMPLS enablesthe slot switching network to reserve and release slotsdynamically, periodically and continuously, and it real-izes the distributed control of optical switches in thenetwork.

These remaining sections of this paper are organizedas follows. Section II describes the design of OSS net-work architecture, Section III shows the implementationof the experimentation of the OSS network. Section IVdescribes the demonstration of the OSS network, andSection V summarizes the current progress of the OSSnetwork.

II. OPTICAL SLOT SWITCHING (OSS)ARCHITECTURE

A. Requirement

In proposed architecture, we aim at an efficient bulkdata transmission. However, it is necessary that it doesn’tdisturb other data transfers and fill the multi user’sconnection request simultaneously.

On the other hand, it is needed that the network dealswith the multimedia data transfer. Figure 1 shows theimage of multimedia multiplexing in the Slot Switching.In proposed network, user get some number of fixedlength slot, so in the reserved slots; any data transfercan be done transparently. Our proposed architecture candeal with various types of data, Ethernet packet, TDMData and Analog signal.

B. Architecture

Figure 2 shows the proposed network. This networkconsists of two different networks, one is usual asyn-chronous optical network and the other is Optical Slot

Gb/s Ethernet packet

TDM Data Analog signal

100Mb/s Ethernet packetGb/s Ethernet packet

TDM Data Analog signal

100Mb/s Ethernet packet

Fig. 1. Multiplexing of multimedia in the Slot Switching.

Fig. 2. Proposed Slot Switching network.

Switching synchronous network. In the network there aresome users, edge routers and core routers. The user whohas connection request reserves a bandwidth by usingcontrol plane employed by GMPLS protocol betweenthe sender and the receiver before the communication.The edge router plays the role of the slot transceiver,and the core router is PLZT optical switch. The datafrom optical network is accumulated at the edge router,and transmitted as the data slot in the timing in whichsynchronization is taken. Then, the slot data is switchedto the direction which has been decided by GMPLSsignaling with the switch.

There are three problems to realize the proposed SlotSwitching network. First, end-to-end slot reservation isneeded. We would like to solve it by extending theTDM-LSP scheme in RSVP-TE and realizing OpticalSlot reservation. RSVP-TE is the one standardized as asignaling protocol of GMPLS.

Second, we transmit the fixed size data slot at theedge router. The various types of data including Ethernetpacket, analog data and TDM data would arrive atthe edge router asynchronously, so it is necessary toaccumulate the data at the edge router and to transmitthe data slot in the timing of taken synchronization.

Third, we should take synchronization in all nodessince the unit of data transfer is Slot in proposednetwork. We explain each item by the remainder of thischapter.

Data Data Data

Slot Guard Time

(Switching Time)

Data Data Data

Slot

(b) PLZT Switch

=msec order

Guard Time = 10ns

(a) MEMS Switch

Fig. 3. Influence by the guard time between slots.

Ban

dw

idth

Eff

icie

ncy

(%)

Guard Time (Switching Time 2)

1nsec 1 sec 1msec

100

75

25

50

Slot Size = 1msec

PLZT

20nsec

MEMS

200msec

Band width Efficiency

= slot size / (slot size + guard time)

Suitable for the OSS network

Fig. 4. Bandwidth efficiency to guard time.

C. PLZT optical switch

In proposed architecture, we apply PLZT opticalswitch to reduce the guard time between slots. FigureII-C shows the comparison of influence by the guardtime of MEMS and PLZT. As shown in fig.II-C(a),conventional MEMS switch needs the guard time ofmsec order, on the other hand, PLZT optical switchcan shorten the guard time down to 10nsec as shownin fig.II-C(b). Because of reduction of the guard time,data transfer with Time Division method is efficient andrealistic.

Figure 4 illustrates the bandwidth efficiency of theswitch of MEMS and PLZT. it is assumed that theguard time is twice at the switching time. The bandwidthefficiency is ratio of the slot length to the length inwhich the guard time is added to the slot length. Asshown fig.4, PLZT optical switch is suitable for the OSSnetwork compared with MEMS switch in terms of bandwidth efficiency.

D. control and reservation

The slot switching network consists of a control planeand a data plane, and it synchronizes the devices inthe network. In the control plane, we employ GMPLS

t

n0 n1 n2 n3 n4

slot1

slot2

slot1

slot2

slot1

Frame1

Frame2

Frame3

path

resv

slot2

Frame4slot1

Fig. 5. An example of slot reservation by signaling in proposednetwork.

extension protocol as the slot reservation scheme. UnlikeTDM, GMPLS enables the slot switching network toreserve and release slots dynamically, and it realizes thedistributed control of optical switches in the network.The data plane is based on an all optical network in-cluding PLZT optical switches manufactured by NozomiPhotonics. This product is the result of collaborationbetween Keio Univ. and Nozomi Photonics. Before thedata transfer, an optical path is setup between senderand receiver, including intermediate core PLZT opticalswitch.

Figure 5 shows an example of slot reservation signal-ing in proposed network. Each time line is divided intoframes consisting of several slots. In fig.5, the numberof slots in a frame is 2. If connection request fromnode n0 to node n2 arrives, noden0 sends a PATHmessage to noden2 to collect slot use information ofeach link. Since data is transferred with several slots,PATH message collect slot use information of severalslots. Each intermediate node maintains informationabout the reserved slots. Intermediate node receiving thePATH message checks whether there are vacant slots. Ifthere are vacant slots, intermediate nodes send a PATHmessage to next node. As destination noden2 receivea PATH message, it selects the earliest a series of slotsand sends a RESV message to reserve that slots. In fig.5,intermediate node which receives the RESV messagereserve the slot 2 in Frame 2 and 3, and transfer thedata.

We will describe the slot reservation method in nextsubsection. The slot reservation is classified into somemethods.

3

1

4

2

0

#3#2#1#0

3

1

4

2

0

#3#2#1#0

Slot number

Th

e n

um

ber

of

Fra

me

(3)(4)

(2)

future

(1)

Fig. 6. An example of slot assignment scheduling.

E. scheduling

In proposed architecture, there are 4 types of slot as-signment scheduling, single-slot, multi-slot, multi-frameand multi-slot multi-frame. Figure 6 shows an exampleof slot assignment scheduling in proposed network.Each user can select desired slot assignment schedulingaccording to their data size, dead line and other QoS.We introduce each scheduling method here since theselection of the best slot assignment is under evaluatingnow. It is necessary to use the scheduling methodproperly by the data size and the dead-line.

1) single-slot reservation:It is illustrated the slot as-signment scheduling of single-slot reservation in fig.6(1).In fig.6(1), slot # 3 in frame # 1 is assigned to user (1). Inthe case of small size data transfer, user can be assignedfreely one slot shown as fig.7(a). As a result, high-speedand low-blocking data transfer is possible.

2) multi-slot reservation:In fig.6(2), it is illustratedthe assignment scheduling of multi-slot reservation. Infig.6(2), slot # 1, # 2 and # 3 in frame # 0 are assigned touser (2). If the data size is large to some degree and thedata transfer in a short time is needed, this schedulingis applied. Figure 7(b) shows a image of data transfer inmulti-slot scheduling. This scheduling will need a lot ofslots in a frame, so other data transfer will be blocked.

3) multi-frame reservation:We show the assignmentscheduling of multi-frame reservation in fig.6(3). Infig.6(3), slot # 0 from frame # 0 to # 4 are assignedto user (3). When the data size is large to some degreeand the data transfer doesn’t have the strict dead-line,this type of scheduling is used. The Dead-line meansthe time which data transfer must be finished. Figure7(c) illustrate a image of data transfer in multi-framescheduling. Using multi-frame scheduling, it is possibleto assign some slots without influencing other datatransfer, but it take a long time.

4) multi-slot multi-frame reservation: Figure6(4)shows the slot assignment of multi-slot multi-framereservation. In fig.6(4), slot # 1 and # 2 from frame # 1to # 4 are assigned to user (4). This method enables

The number of Slot in a frame is 4Data

Slot

Frame0 Frame1 Frame2

Frame

Frame

Frame

(d) multi -slot multi -frame

(c) multi -frame

(b) multi -slot

(a) single -slot

Frame3 Frame4

Fig. 7. Comparison for slot reservation method.

Ethernet

-

RAM

Speed converter

Ethernet

-

RAM

Speed converter

Fig. 8. Composition of transmitter.

to transfer the data speedy in the case of large sizedata such as contents delivery. However, since a lot ofslots are needed in a frame, other data transfers maybe interrupted. In fig.7(d), we show the image of datatransfer in this method.

F. slot transceiver

Since data is transferred with data slot in proposednetwork, it is needed to accumulate the data and sendwith synchronous timing at edge router. Furthermore, thetransceiver must deal with the data of different protocolin each slot, special transceiver is needed in each edgerouter. Figure 8 shows a composition of transmitterused in proposed network. In fig.8, the transmitter canaccept the Ethernet data, the data from RAM and thespeed converted data. In next section, we describe theimplementation of slot transceiver.

At the ingress node, data is divided into queuesaccording to its destination address. The packet is readfrom the queue by the signal from outside according tothe timing of a slot concerned. In the turning point ofthe slot, the guard time is set if necessary. On the otherhand, the slot data is returned to former type of data atthe egress node and transferred to desired destination.

Optical Slot Switching network (synchronous)

Ethernet (Asynchrounous)

Ethernet

100Mbps

Ethernet

100Mbps

sender

receiver

Edge router

Edge router

PLZT Optical Switch

GMPLS Control Plane Supporting Slot Switching

with RSVP-TE signaling

Fig. 9. Implemented Slot Switching network.

III. I MPLEMENTATION

Figure 9 shows the network that we would liketo implement. This network consists of two differentnetwork, one is asynchronous Ethernet and the other isOptical Slot Switching synchronous network. There aretwo PC in Ethernet layer, and two edge router and oneoptical switch in OSS layer.

There are three problems to implement proposedSlot Switching network. First, before data transfer, slotreservation signaling between sender and receiver isneeded. We would like to solve it by extending theTDM-LSP scheme in RSVP-TE and realizing OpticalSlot reservation.

Second, the transceiver to send the fixed size slotdata is needed. Since Ethernet packet arrive at the edgerouter asynchronously, it is necessary to accumulate andtransmit the data at the edge router in the timing thatsynchronization is taken.

Third, we must take synchronization in the network.In OSS network, data is transferred in the slot which isµsec order. It is necessary to take synchronization strictlyto make the best use of the PLZT high-speed switching,and to decrease the guard time.

Control Unit

Optical Switch Unit

Srial Port

Optical Input

To GMPLS NetworkController

Control Unit

Optical

Switch Unit

Serial Communication

Controller BoardFPGA

4000 2Memory banksFast Driver

Optical Switch

FPGA

(Linux PC)

Rx Tx

FPGA

To GMPLS

Optical Output

Fig. 10. The PLZT optical switch system with the GMPLS-basedcontroller.

Ethernet

Optical Slot Switching

Buffering

According to

Destination address

Output

ABC BAA C

A

A B C

BAC

Reconfigurable

processor

Input

Frame

Slot

Electric signal

Fig. 11. Slot transceiver.

A. PLZT Optical Switch System with GMPLS-basedController

In order to realize the proposed slot switching net-work, we developed a PLZT optical switch system witha GMPLS-based controller. Figure10(b) shows a blockdiagram of the system. Figure10(a) shows the switchsystem with the controller. The system consists of acontrol unit and an optical switch unit. The controlunit is a Linux-based PC with GMPLS software andis connected to the optical switch unit via a serial cable.The optical switch unit consists of an ultra-high speedcontroller board, a fast driver and an optical switch body.The controller board includes an FPGA that has a pairof 4000 pattern memory banks. It reads and writes thebanks based on signals from the controller and sends theappropriate switching pattern signal to the fast driver.The fast driver sends switch signals to the switch bodyupon receiving signals from the controller board. Thesystem can activate the switch by slot according to aRESV message from the GMPLS control plane.

B. data slot transceiver

In this paper, we would like to use the packet-capture accelerator manufactured by U10 Networks.Figure 11 shows a data slot transceiver and image ofdata slot generation in proposed network. The Ether-net data which comes from input port are processedat Reconfigurable processor, and buffered into DRAMaccording to destination address of each packet. With theelectric signal from outside, the transceiver takes somedata from DRAM, and sends a data slot which size isdecided beforehand.

ServerClient3

Client2Client1

PLZT SW1 PLZT SW2

Control PC

61.86.20.261.86.20.3

192.168.20.3 192.168.20.2

192.168.20.5

61.86.20.10 61.86.20.561.86.20.1 61.86.20.20

192.168.20.1

GMPLS Control Plane Supporting Slot Switching

with RSVP-TE signaling

Fig. 12. A experimental network of the slot switching network.

IV. EXPERIMENTAL NETWORK

We experimented on the slot reservation that useGMPLS control plane. Figure 12 shows the setup used toimplement slot switching network. In the network, thereare one Server PC, Client PCs and two PLZT opticalswitches controlled by GMPLS. 192.168.20.X meansan address in the data plane, and 61.86.20.X means anaddress in the control plane. The number of slots in aframe is 2, and slot size can be changed as needed. OneServer and three Clients all use a newly developed 1.5µm optical NIC (Network Interface Card). Each controlPC is a control unit of the switch system. Each opticalswitch, which is the optical switch unit of the switchsystem, is a 1× 8 switch. The network synchronizesthe switch systems by connecting the systems via asynchronization cable.

It is assumed that Client1 or Client2 requires thestreaming data from Server and Client3 requires thecontents download from Server. And contents downloadis prior to streaming transfer here. When the contentsdownload request from Client3 is occurred, Client3sends a PATH message to Server correcting the in-formation of slot use. If there are any other opticalpaths to the Server, the path is released. Server sendsa RESV message to Client3 to reserve all slots in allframes to transfer a contents data. Due to using all slots,the contents download is finished earlier than the caseof using one slot. At the same time as the ending ofcontents download, all the slots are released and newslot assignment is done for streaming transfer ahead.

This contents delivery using Slot Switching is demon-strated at KEIO TECHNO-MALL, which is held inTokyo International Forum in December, 2006.

V. CONCLUSION

We have designed and implemented an optical slotswitching network. We will examine the suitable slotsize, number of slot in a frame and reservation methodfor efficient data transfer. Furthermore, we would like toimplement the slot generator and other item in proposednetwork.

ACKNOWLEDGMENT

This work is partly supported by National Institute ofInformation and Communications Technology, NozomiPhotonics, and Keio University 21 century COE programon “Optical and Electronic Device for Access Network”.

REFERENCES

[1] C. Qiao and M. Yoo, “Optical Burst Switching (OBS)-A NewParadigm for an Optical Internet,”J.High Speed Networks, vol.8,no.1, pp.69-84, Jan.1999.

[2] K. Nashimoto, et. al., “High-Speed PLZT optical Switchesfor Burst and Packet Switching, ” Proc. Broadband Networks,pp195-200, Oct. 2005.

[3] R. Inohara, et. al., “First demonstration of synchronization-freenanosecond label switching node utilizing 1×8 PLZT switch, ”Proc. OFC, OWP7, Mar. 2006.

[4] T. Nomura, et. al., “Novel Optical Packet Switched AccessNetwork Architecture, ” Proc. OFC, OTuJ6, Mar. 2006.

[5] L. Berger, ed., “Generalized Multi-Protocol Label Switch-ing(GMPLS) Signaling Resource ReserVation Protocol-TrafficEngineering(RSVP-TE) Extentions,” IETF RFC 3473, Jan. 2003.