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Photonic IP routing using optical codes: lOGbit/s optical packet transfer experiment Naoya Wada Communications Research Laboratory, MP7: 4-2-1, Nukui-Kita, Koganei, Tokyo 184-8795,Japan Phone: T81-42-327-6371,Fax: +81-42-327-7035, ,!-mail:
[email protected]
Ken-ichi Kitayama Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan Phone: +81-6-6879-7692, Fax: +81-6-6879-7688,E-mail: kita;
[email protected]
1. Introduction An explosive increase in Intemet Protocol (IP) traffic demands new classes of high-speed distributed IP router. The current IP backbone systems are being realized using SDH/ATM networks. IP packets are transported via electrical IP router between optical line terminals (OLT) in both the core and edge networks. SDH/WDM network could replace the OLT by the wavelength division multiplexing line terminal (WDM-LT), however, the electrical IP router is still remain in the core network. The electrical IP router shows a performance bottleneck because of limited throughput, and it also causes end-to-end transmission delay. In IP over photonic network.,photonic IP roui:ers are located in the edge networks as the IP backbone routers and only the wavelength routers are located in the core network. The photonic IP routers can communicate with each other through a full-mesh WDM core network [ 13. This will minimize transfer delay and support the high throughput of the nodes.
In current electrical IP routers, routing-table lookup is the worst bottleneck of routing-speed because of its complex lookup algorithm. The maximum routing speed of electrical IP routers is around lo7 packets par second (pps). Therefore, to remove the bottleneck of electrical table lookup, high performance router having lookup speed close to the transmission rate is required. Only the photonic IP router will be able to satisfy this requirement. Its target speed is; around 10'opps [:2]. A novel photonic IP routing based on parallel processing for IP addresses has been proposed [2]. In this IP routing, each IP address is mapped onto an optical code, and the optical correlations in the time domain between an incoming optical code and those in the address bank are performed in a parallel manner. The proof-of-principle experiment has shown that it has a processing speed of 6.5x109pps. However, data transport experiment has not been done. In this paper, packets consisting of 8-chip-long header and 64bit-long burst payload data at 10GWs are generated and routed optical domain, based upon photonic processings of the optically coded address. All-optical .packet address inspection and 1OGbit/s burst payload data transportation are demonstrate:dexperimentally for the first time. Photonic IP router
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2. Photonic IP routing Suppose that an IP packet is encapsulated in such an optical frame as data link layer of OS1 Reference Model and carried as shown in Fig. 1. The optical path overhead contains wavelength routing information, and the IP packet is accommodated in the optical path payload [3]. The IP header is composed of the optical code. The block diagram of proposed photonic IP router is represented in Fig. 1. It consists of wavelength demultiplexer and photonic processor. To individually process IP packets on different wavelength paths, there has to be an array of photonic processors as many as the number of wavelengths paths. The photonic processor consists of a header processor, 1xN optical switch, and optical delay. The header processor includes an address processor, which is composed of optical amplifiers, optical correlators, and optical pulse reshapers, and an address encoder. A set of optical correlaters works as an address bank, which stores optical codes correspond to the addresses in the routing table. Address recognition is based on optical correlation in the time domain between the input optical code and the codes in the address bank. The controller decodes the addressing code of each IP header and outputs the signal, which controls the 1xN optical switch. The optical switch obeys the control signal and selects the route of each packet. O~tical . .Dacket transmitter ..............................................
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3. Experimental set-up Fig.2 represents the experimental set-up of distributed photonic IP routing with two ports. Set-up consists of optical packet transmitter and photonic processor composed of address processor, 1x2 optical gate switch, and optical delay. An optical packet transmitter consists of 2ps-1OGHz-MLLD, Limo3intensity modulators (IM), optical encoder, and optical delay. Optical encoder consists of tapped delay-lines with thermo-controlled optical phase shifters as shown in Fig. 2. All elements are monolithically fabricated by using planar lightwave circuit (PLC) technology. The optical carrier phase of each chip pulse is shifted either 0 or n: by the phase shifter to generate the 8-chip binary phase shift keying (BPSK)-codes [4]. Address processor is comporsed of optical correlaters, photo detectors (PD), low-pass filters (LPF), and gain-clamped RF amplifier. The 1x2 optical gate switch consists of two IMs with 40GHz bandwidth.
In the optical packet transmitter, IM 2 generates 64bit-long burst data signal at lOGbit/s. IM 1 and optical encoder generate optical header which is 8-chip BPSK optical codes with a time interval of 5ps. Generated optical code and payload data signal are combined to form a packet. In the address processor, if the input code matches with the code of a correlater, the output (correlated signal) takes a high value. On the other hand, in unmatched case, the correlated signal takes lower value. In matched case, the correlation signal is converted to the electrical signal, and its waveform is elongated to gate and hold open the IM gate switch. While in the unmatched case, the bias is not changed, then the gate switch still close. The header processor can open an objective gate switch and reads the matched packet to the target port. 4. Results Fig. 3(a) is a streak camera trace of a generated packet with an optical code #1: “0.nxn:n:n:n:O”.Figs. 3(b) and (c) represent streak camera trace of correlater outputs to the packets with a header of code #1:
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“Onnnnnn0” (matched code) and a code #2: “0~;OnOnOn”(unmatched code), respectively. In both cases, each bit of payload data of the packet is time spread by passing through the correlater and takes so small value in comparison with the decoded header that it. does not operate mistakenly with gate switch.
Figs.4 (a) and (b) represent the measured payload data of Port 1 and Port 2 to the two different input packet having header of “OnnnnnnO” matched with correlater 1 and “OnOnOnOn” matched with correlater 2, respectively. These clearly show that the address processor ;alternatively switches two optical gate switches as the input optical code switches between #1 and #2. It means that the header processor distinguish the 8-chip long optical codes at the h.eader of packets ,and control the optical switch. Fig.5 (a) and (b) are measured bit error rates (BER) of routed 64bit-long payload data with code #1 and #2, respectively, in each corresponding port. The measured BERs are less than lo-’’, which confirms the proper packet routing operation. Thses results guarantee the high speed photonic IP routing. 5. Conclusion
Packets consisting of 8-chip-long header and 64bit-long burst payload data at 10Gbit/s have been generated and routed optical domain, based upon photonic processings of the optically coded address. All-optical packet address inspection and 1OGbit/s burst paryload data transportation have been demonstrated experimentally for the first time. ,411-optical contrcll scheme for optical gate switch would be one of the subject to be studied. 6. References [ 13 H. Yoshimura, K. Sato, and N. Takachio, “Future photonic transport networks based on WDM technologies,” IEEE Commun. Magazine, pp.74-81, Feb. 1999. [Z] K. Kitayama and N.Wada, “Photonic IP routing,” to appear in ZEEE Photon. Technol. Lett..
[3] A. Watanabe, S. Okamoto, and K. Sato, “WDM optical path-based robust IP backbone network,” 1999 Optical Fiber Communication Conference (OFC’99), TuFl(San Diego, 1!>99). [4] N. Wada, H. Sotobayashi, and K. Kitayama, “Error-free lOOkm transmission of 10Gbitk optical code division multiplexing using BPSK picoseconds-pulse code sequence with novel time-gating detection.” Electron. Lett., vo1.35, pp.833-834, 1999.
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Fig. 3. Streak camera trace of (a) generated packet and correlated signah i n (b) matched and (c) unmatched cases lo.>[I_
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Fig. 4. Routed data with code (a) #1 and (b) #:2
Fig. 5. Measured BER at (a) Port 1 and (b) Port 2
