Multi-wavelength label optical switching technology

Transcription

1 Multi-wavelength label optical switching technology Shilin Xiao *, Qingji Zeng, Jianxin Wang, Chun Jiang, Xudong Yang, Fengqing Liu, and Xu Zhu Center for Broadband Optical Networking Tech., Shanghai Jiaotong Univ., 3, China ABSTRACT A kind of multi-wavelength labeled optical packet switching technology is presented, in which optical header is consisted of several optical pulses in different wavelength that are in the same WDM optical channel band as optical signal payload. A probable scheme to realize such optical switching as well as an optical switching node structure is proposed. A simplify principle experiment has proved the possibility of such switching method. Key words Optical communication, optical switching, optical packet switching, multi-wavelengths label.. INTRODUCTION Optical fiber communication is becoming the main approach for modern communication transmission, especial for trunk-line transmission, whose developing direction is to enlarge communication capacity further. The dense wavelength division multiplexed (DWDM) and Erbium-doped fiber amplifier (EDFA) technology developed in recent years, called as DWDM + EDFA technology, benefits dilatation of communication so much that communication capacity of point-to-point is huge (reaching Terabit per second). But the switching equipments used in telecommunication network are still electrics whose signal process capacity is almost at the electron limit and difficult to increase. This situation seriously blocks the further development of communication to give free rein to the priority of optical fiber communication. So, optical switching technology is in its crisis to be developed. Optical switching needn t optical-electrical and electrical-optical conversion and doesn t introduce electrical bottleneck existing in electrical switchboard so that it helps much to enlarge communication network capacity to make the most use of optical communication. The optical switching technology is becoming the key of optical communication development. Optical switching models studied early are circuit switching in which the basic exchange unit is a call and the bandwidth will be reserved in a two-way process during the whole call. The main disadvantage of such technology is that wavelength routing path must be established before the data transmission and the bandwidth won t be released until the call has finished. In optical burst switching (OBS) technology,, the research highlight of late, optical signal is divided into two groups: control group * xiaoshilin@hotmail.com ; Tel: ; Fax: Optical Switching and Optical Interconnection, Lih-Yuan Lin, Shulian Zhang, Editors, Proceedings of SPIE Vol. 458, APOC, Beijing, China () SPIE X//$5. 33

2 including routing information and data group bearing service. Control information in control group must be electronic processed through router, while data group forwards directly through end to end transparent light path without O-E/E-O conversion and transmission of electronic router. The swapping granularity of OBS is prior than that of circuit switching and the bandwidth in OBS only needs be reserved on one-way process. OBS is suitable to be used in LAN and for future high burst services. The more ideal optical packet switching technology 3, 4 is the developing direction of optical switching technology, because the advantages are the little overhead, the high bandwidth utilization coefficient and the transparency of delivering frame. In optical packet switching technology, optical message is divided into a series of fixed length optical payload groups, each to be an optical message packet with fixed frame after an optical message header including routing information added, and then transmission is performed. Several kinds of technology to realize optical packet switching have been proposed, among them the solution scheme with sub-carrier multiplexing (SCM) label switching 5 has been paid much more attention in which optical packet header and payload are bearing on a suitable sub-carrier. With SCM, packet header can be easily picked up and refreshed, but normally, a narrow spectrum band of sub-carrier and a wide interval are demanded, so the number of sub-carrier is limited. Besides, broadening the spectrum band of base band will overcast sub-carrier spectrum band if the rate of payload rises. Another scheme has been proposed that optical payload and optical header are to be delivered on different wavelength channels so that reshaping header only need O-E conversion in channel header message being transmitted, but with the disadvantage of the payload and header message reserving different wavelength c hannels. A new idea is introduced in this paper to structure the optical packet header with multi-wavelength label. With this technology, optical payload in a basic switching unit is operating on a certain wavelength carrier designated, and optical header message is formed of several optical pulses with different wavelengths at the same wavelength channel pass-band. That is to say, optical header message and optical payload are delivered on a same optical WDM channel band without occupying extra wavelength resource, as well as the optical header message can be easily processed.. PRINCIPLE OF MULTI-WAVELENGTH LABEL SWITCHING In this multi-wavelength labeled switching, the structure of a basic switch unit, optical packet, is shown in figure. In time domain, header and payload are apart in early and late order. In spectrum domain, there are differences on wavelength composition between header and payload although they are carried on a same wavelength channel. If payload is delivered on a designated wavelength, i.e.,, conformed to DWDM wavelength series regulated, header carrying route information will constituted by optical pulses with different wavelengths. Different wavelength means the wavelength of each optical pulse is at a certain wavelength nearby wavelength and within the channel band interval limits ITU-T permitted. The wavelength value of optical pulse used to construct header is confined within channel pass-band, the possible 34 Proc. SPIE Vol. 458

3 values can be designated through regulating the number N ( N =, 3, 5, ) of wavelength and interval δ of wavelength, the arbitrary probable wavelength value n i can be denoted as i = ± δ, where n =,,,, (N-)/. The number M of pulse forming header and time interval T are also pre-regulated. Then the permutation and combination draft of different wavelength in header can directly denote optical route information without any extra modulating and code. Limited number M of optical pulse with limited option N of wavelength of each pulse will form a huge number of possible combination, that is, the quantity of information can be denoted by header will be huge. We can assume to form a kind of header with M equate to 5 optical pulses, like this: the first 3 pulses with carrier wavelength can be functioned not only as header identification and synchronization, also as indicating the carrier wavelength of this optical packet, the following six pulses with different wavelength can be used to denote destination address while the last six pulses to denote the source address. M Optical Packet Header : N T t i i = n Payload : Fig. The optical packet structure of multi-wavelength label switching When optical packet with such kind of multi-wavelength label header gets switch node, the carrier wavelength of payload and routing information can be got through header processor reading and translating the wave spectrum of header in order that the optical switching matrix used to control switching node selects light-path of optical payload including operation deciding whether adopting carrier wavelength conversion or not and produces a new header to ensure delivering the payload forward. Shown as figure, optical switching node are constituted by input interface part with optical demultiplexer, optical routing controlling part with header processor, optical routing switching part with optical switching matrix and -conversion, synchronizer to guarantee the co-ordinate operation on header processing and route switching and keep the information from missing, and output interface part with optical multiplexer. Proc. SPIE Vol

4 Header recognition, Payload Header Synchronizer processing, and generation New header Incoming fibers Optical Outgoing fibers switching matrix Demux with conversion Mux Fig. The optical switching node of multi-wavelength label switching In this switching mode, header can be generated through optical-electrical modulate technology. Optical pulses forming header with an interval of n δ to can be achieved through tunable laser or directly modulating carrier wave with frequency-shift keying (FSK). Such header can be processed in electrical domain through optical-electrical conversion method. One way is to change the difference of wavelength into the interval in space through grating demultiplxer, then to receive with a detector array. Another way is that optical pulses of header couples local laser with wavelength of first, and be changed into electrical intermediate frequently signal through optical coherent detection, then the electrical pulses with different wavelengths can be identified and processed with frequently discrimination technique. Wavelength is an easily recognized optical parameter. Header consisted of pulses with different wavelengths can be processed comparatively easy and is of powerful anti-interference ability. Especially with the development of the optical process techniques (such as optical selection, optical storage, optical cross-connection and denser wavelength division multiplexing technology), this kind of optical signal header adopted can be possibly erased and replaced all in optical domain, and the optical switching adopting multi-wavelength labeled header technique can possibly realizes optical wavelength routing identification and other optical message process all in optical domain. 3. A SIMPLIFIED PRINCIPLE EXPERIMENT Figure 3 shows a simplified optical multi-wavelength label switching principle experiment. Figure 3(a) is the structure diagram of this experiment. Four terminations are connected with an optical switching node OXC (optical cross connects) through the optical transmitter (Tx) and the optical receiver (Rx) respectively to accomplish data switching. The fundamental of switching is explained in figure 3(b). In order to simplify the process of procedure, optical 36 Proc. SPIE Vol. 458

5 transmitter of each terminator adopts a same optical carrier wavelength. Between the optical header and optical payload in each packet exits a delay time, which is not shorter than the process duration of header, and then the optical storages can be left out. The header is composed of optical pulses, whose wavelengths are nearby the carrier wavelength of payload (these two pulses and payload carrier are still in a same communication channel), and the different composition of whose wavelengths can be used to distinguish these 4 different terminators. Header Processing Tx4 Rx4 Payload Header WDM D D Fiber S Tx Rx OXC Tx3 Rx3 Tx Tx Tx3 4 4 Switching Tx4 Tx Rx Rx Rx4 a (b) Fig. 3 A principle experiment of multi-wavelength label switching In the experiment, the reality working wavelength of optical payload is the 33rd channel wavelength, = 55.9 nm, belongs to DWDM series regulated by ITU-T, and the rate of signal is 6 Mbit/s; the operating wavelength of optical header pulse are two wavelengths within the 33rd channel, = nm and = 55.7 nm; (, ), (, ), (, ), (, ) denote the address, from the first to the fourth terminator respectively. Taking Tx transmitting optical signal as an example, when the optical header enters wavelength division multiplexer WDM in processor through optical switch s, two wavelengths of pulses in header can be separated. After received by optical detector D and D respectively, address can be identified. Then, processor controls S to lead the optical payload to a 4 4 optical switching matrix, at the same time controls the 4 4 matrix to select optical routing and forwards the payload to pre-determined receiving terminator. 4. CONCLUSION It s the inevitable trend of the development in communication technology to substitute electronic switching with optical switching. The key to carry out optical switching is to establish a rational switching mechanism of routing and switching optical signals based on their wavelengths A kind of multi-wavelengths label optical switching is proposed in this paper, in which the head of an optical Proc. SPIE Vol

6 packet is composed of several optical pulses with different wavelengths that are in the same wavelength channel band as the optical payload, and the permutation and combination draft of different wavelength in the header are used to indicate optical route information. This switching idea is of the advantages of header not occupying extra wavelength channel alone, transmitting a great deal of routing information and easy to be normalized. With the progress on optical signal processing technology, this kind of optical switching technology is a promising sort of optical switching technology really in all -optical processing with higher speed. ACKNOWLEDEGMENTS The work was jointly supported by the Science Technology Development Fund of Shanghai, the National 863 Plan, the National Nature Science Fund, and the Engineering Plan of China. REFERENCE. C.Qiao and M.Yoo, Optical Burst Switching(OBS)-A New Paradigm for an Optical Internet, J. High Speed Network, 8, pp , C.Qiao and M.Yoo, Choices, Features and Issues in Optical Burst Switching (OBS), Optical Net. Mag.,, pp ,. 3. C.Guillemot et al., Transparent Optical Packet Switching: The European ACTS KEOPS project Approach, IEEE J. Lightwave Tech.,, PP. 7-34, David K. Hunter and Ivan Andonovic, Approaches to Optical Internet Packet Switching, IEEE Commun. Mag., 9, pp. 6-,. 5. Winston I. Way et al., A Novel Optical Label Swapping Technique Using Erasable Optical Single-Sideband Subcarrier Label, OFC, paper WD6,. 38 Proc. SPIE Vol. 458