We developed novel integrated optical packet and circuit switch-node equipment. Compared with our previous equipment, a polarization-independent 4 × 4 semiconductor optical amplifier switch subsystem, gain-controlled optical amplifiers, and one 100 Gbps optical packet transponder and seven 10 Gbps optical path transponders with 10 Gigabit Ethernet (10GbE) client-interfaces were newly installed in the present system. The switch and amplifiers can provide more stable operation without equipment adjustments for the frequent polarization-rotations and dynamic packet-rate changes of optical packets. We constructed an optical packet and circuit integrated ring network testbed consisting of two switch nodes for accelerating network development, and we demonstrated 66 km fiber transmission and switching operation of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10GbE frames. Error-free (frame error rate < 1×10−4) operation was achieved with optical packets of various packet lengths and packet rates, and stable operation of the network testbed was confirmed. In addition, 4K uncompressed video streaming over OPS links was successfully demonstrated.
©2011 Optical Society of America
Over the next ten to twenty years, the energy consumption of information and communication equipment is expected to steadily increase with the increase of Internet traffic . Because this huge energy consumption will become a major social issue, energy-efficient technologies are required for future communication networks. On the other hand, recently, various types of content, from small-data-size, low-quality content (e.g., E-mails, sensor data collection) to large-data-size, high-quality content (e.g., high-definition video distribution, remote surgery), are being transmitted on networks. To efficiently transmit these various types of content, future communication networks will need to employ a suitable communication scheme that is well-matched to the properties of the content.
We have proposed a new generation network architecture that can solve various problems in current Internet systems . One of the proposed concepts is an optical packet and circuit integrated network providing diversified services . In the integrated network, optical packet switching (OPS) links enable bandwidth-sharing and best-effort data transfer, while optical circuit switching (OCS) links enable a fully occupied bandwidth and end-to-end quality of service (QoS) guaranteed data transmission. In addition, the integrated network is expected to be highly energy-efficient by exploiting transparent optical switching technologies without optical-to-electrical-to-optical (O/E/O) conversions. By dynamically allocating wavelength resources to the OPS or OCS links, new or urgent services can be supported with efficient resource use. By multiplexing control packets for signaling and resource control on the OPS links, additional interfaces required for the control plane are reduced, simplifying the network.
We have previously developed a prototype integrated optical packet and circuit switch (OPS/OCS) as a core node and have demonstrated primitive network experiments [4–6]. Based on our latest research results, this time, we constructed a new optical packet and circuit integrated ring network testbed . The network testbed is expected to accelerate near-future network development. Previously, optical ring networks with optical add/drop multiplexers for only optical paths or optical packets have been demonstrated [8,9]. On the other hand, our network testbed has both a 100 Gbps OPS link and fourteen 10 Gbps OCS links. Moreover, novel integrated OPS/OCS node equipment was developed by introducing several key devices. To achieve more stable operation compared with the prototype [4–6], a polarization-independent semiconductor optical amplifier (SOA) switch subsystem [10,11] and gain-controlled erbium-doped fiber amplifiers (EDFA)  are installed in the node equipment. Moreover, a 100 Gbps optical packet (100G-OP) transponder and seven 10 Gbps optical transport network (10G-OTN) transponders are provided for data transmission on optical packets and paths. These transponders encapsulate the generally used 10 gigabit Ethernet (10GbE) frames coming from client networks into optical packets or OTN frames, respectively. With our network testbed, we demonstrated 66 km fiber transmission and switching operation of multiplexed 14-wavelength 10 Gbps optical paths and 100 Gbps optical packets encapsulating 10GbE frames, and we verified the performance of the network testbed. We confirmed error-free (frame error rate < 1 × 10−4) operation without equipment adjustment on OPS and OCS links of the network testbed under various routes, frame lengths, and packet rates. In addition, we demonstrated 4K uncompressed video streaming over OPS links as an example of an actual application.
2. Integrated optical packet and circuit switch-node and key technologies
Here we describe the basic architecture of an optical packet and circuit integrated network. In the integrated network, optical signals on optical paths and optical packets are multiplexed and are also transmitted on the same infrastructures by wavelength multiplexing techniques [3–6]. Wavelength resources are divided into two and allocated to OPS and OCS links. The boundary of wavelength resources between OPS and OCS links is variable, depending on the demand for optical path or packet transfers. In OPS links, at edge nodes of the integrated network, low-band signals such as Ethernet frames are en/decapsulated with wide-band optical packets. Here, we use a colored optical packet, which consists of 10 Gbps optical signals of N wavelengths . Also, control optical packets for path signaling and wavelength resource control are exchanged via OPS links. On the other hand, optical paths are provided from end to end (client to client or client to server) for high-quality services. In a core node, an integrated OPS/OCS node appropriately routes both optical signals on optical paths and optical packets.
Figures 1(a) and 1(b) show a photograph and a schematic illustration of our novel integrated OPS/OCS node, which mainly consists of six kinds of devices: seven 10G-OTN transponders, a 100G-OP transponder, two wavelength-selective switches (WSS), a 4 × 4 SOA switch subsystem, a switch controller, and some optical amplifiers. In OCS links, to send data on optical paths, a 10G-OTN transponder encapsulates 10GbE frames from the client side into OTN format. Because optical paths are established by control packets in advance, there is no need to read the IP destination address of incoming 10GbE frames. On the other hand, in OPS links, a 100G-OP transponder encapsulates incoming 10GbE frames from the client side into 100 Gbps optical packets, as shown in Fig. 2 . Although a number of 10GbE interfaces should be provided at each OP transponder to realize full bandwidth utilization of OPS links, in this paper, each OP transponder has one 100 Gbps optical packet interface and one 10GbE interface due to the limited number of components. We introduce 100 Gbps colored optical packets with ten 10 Gbps optical payloads, as shown at the bottom of Fig. 2. A 16-byte preamble signal is attached to each optical payload. The total size of the 10GbE frame is from 64 to 9604 bytes. The packet length of an optical packet is variable, corresponding to the length of the 10GbE frame. In parallel, a 10 Gbps, 8-byte route header including an 8-bit destination Node-ID is attached in one payload of an optical packet. The destination Node-ID is determined according to a mapping table between destination Node-IDs and the IP destination addresses of incoming 10GbE frames. Bit pattern matching of IP addresses within an arbitrary range is possible by masking and offset functions.
Wavelength resources are divided by waveband, and each of these wavebands is allocated to OPS or OCS links. In the integrated OPS/OCS node, two WSSs are used for combining or dividing OPS and OCS wavebands. In principle, the WSS can flexibly move the boundary of wavelength resources between OPS and OCS links. In addition, two WSSs also work as add/drop multiplexers for OCS links. In setting or releasing optical paths by control packets, the WSSs forward an optical signal on an optical path to the correct output port. For OPS links, a switch controller reads the destination Node-ID of a route header and controls a 4 × 4 SOA switch subsystem to forward an optical packet to the correct output port according to a switching table in each input port. A 4 × 4 SOA switch subsystem with a broadcast-and-select configuration has been developed [10,11]. The SOA has a switching speed of several nanoseconds, low polarization-dependency, and loss compensation. Previously, the switch subsystem had a minimum channel-space limitation of 400 GHz to avoid the crosstalk caused by a four-wave mixing effect. This time, the switch subsystem separates 100 GHz-spacing colored optical packets into four wavelength groups by using 100/400 GHz interleavers to switch each wavelength group. Therefore, the switch subsystem can handle 100 GHz-spacing colored optical packets without crosstalk.
To show the low polarization-dependency, we measured the spectrum of ten optical payloads of a forwarded 100 Gbps optical packet at the output of the integrated OPS/OCS node. Figure 3 shows the maximum and minimum peak-intensity when the polarization of the optical packet was randomly rotated by a polarization controller at the input of the integrated OPS/OCS node. The intensity difference of about 2 dB is due to the polarization-dependency of the integrated OPS/OCS node including one 4 × 4 SOA switch subsystem. To eliminate optical surges and gain transients for shorter packets (~100 ns), we developed a transient-suppressed erbium-doped fiber amplifier (TS-EDFA) . In addition, we improved the TS-EDFAs by optimizing the fiber length, the core diameter, and the erbium density of the EDF and adjusting the power of a pump laser-diode to suppress the wavelength-dependent gain and the output power fluctuation due to the changing packet-rate.
3. Ring network testbed and demonstration
Figure 4 shows the configuration of our optical packet and circuit integrated ring network testbed. Two integrated OPS/OCS nodes (Node 1 and Node 2) were connected by two 50 km fibers with about 12 dB loss, each consisting of a 33 km single-mode fiber (SMF) and a 17 km dispersion-compensating fiber (DCF). Each node had a unique Node-ID (Node 1 ID: “10”, Node 2 ID: “20”) and was equipped with seven 10G-OTN transponders and one 100G-OP transponder. Each node device handled 40 wavelength channels with 100 GHz channel spacing in the C-band, 1531.90–1563.05 nm (λ1–λ40). The wavelength resource for OPS links was 1547.72–1554.94 nm (λ21–λ30), and the wavelength resource for the OCS links was 1538.98–1543.73 nm (λ10–λ16) and 1558.17–1563.05 nm (λ34–λ40). Due to the limited number of components, Node 1 and Node 2 used λ10–λ16 and λ34–λ40 10G-OTN transponders, respectively. Note that a 10G-OTN transponder can receive an optical signal with a different wavelength. Each network tester (NW tester) was used as a client having a unique IP source address (IP-SA) and was connected with each node via a 10GbE interface or a layer-2 switch (L2-SW). The mapping table and the switching table of each input port in Nodes 1 and 2 are shown at the bottom of Fig. 4. In the ring network, the 4 × 4 SOA switch subsystem worked as a 2 × 2 switch by using only input ports 1 and 4 and output ports 1 and 4.
Each node can send a data on an optical path and an optical packet not only to an opposite node but also to itself via the ring network for an external loopback test. We transmitted both data on optical paths and optical packets through various routes of the ring network. For example, we tested an OPS loop route from NW tester 1 to NW tester 2 through Node 1 and Node 2. At NW tester 1, the frame length, the frame interval, and the bit-rate of 10GbE frames were set to 1518 bytes, 232 bytes, and 8.6 Gbps, respectively. A 10GbE frame from NW tester 1 with the IP destination address 10.100.1.12 of NW tester 2 was encapsulated into a 100 Gbps colored optical packet by a 100G-OP transponder at Node 1. The destination Node-ID of “10” was given to the optical packet according to a mapping table with a 24-bit mask (/24), as shown at the bottom of Fig. 4. A switch controller outputted a control signal to the SOA switch subsystem and forwarded the optical packet to the output port 1 according to the switching table in the input port 4. A WSS for adding outputted the optical packet to the network side. The optical packet was transmitted through a 50 km fiber. At the same time, data on each 7-channel optical path from Nodes 1 and 2 was transmitted around ring networks and multiplexed with optical packets. In Node 2, the optical packet with the destination Node-ID of “10” was sent to an SOA switch subsystem by a WSS for dropping and was forwarded from the input port 1 to the output port 1 at the switch subsystem. Again, the optical packet was transmitted through another 50 km fiber. Only optical packets with the destination Node-ID of “20” were forwarded to the output port 4 and dropped into a 100G-OP transponder at Node 2. Finally, after going around, the optical packet with the destination Node-ID of “10” was dropped at the output port 4 of the SOA switch subsystem in Node 1. The 10GbE frame was recovered from the optical packet and sent to NW tester 2. Figures 5(a) –5(d) show the eye-diagrams of an optical payload of 1549.8 nm measured at the output of each EDFA in the loop route from Node 1. The measured points are (a)–(d) in Fig. 4. The Q-factors in Figs. 5(a)–5(d) were 10.4, 9.90, 8.73, and 8.51, respectively. Figure 5(e) shows the spectrum of the multiplexed optical packets and optical paths at the output of Node 1. Figure 5(f) shows the temporal waveform of the multiplexed optical packets and optical paths, in which the optical packet rate was 10%, and Fig. 5(g) is the temporal waveform of only an optical packet extracted by a band-pass filter.
We measured the error rate of 10GbE frames through various routes on the ring network, such as loop routes from Node 1 or 2 and one-way routes from Node 1 or 2 to Node 2 or 1, by using OPS or OCS links. The frame lengths (FLs) of the 10GbE frames were set at 64 bytes, 1518 bytes, or 9000 bytes when using OPS links, and 1518 bytes or 9000 bytes when using OCS links. In addition, we changed the frame interval of the 10GbE frames and set the optical packet rate (PR) at 1% or 10%. Figures 6(a) and 6(b) show a measured frame error rate of less than 1 × 10−4 under various conditions for the OPS and OCS links, respectively. Because an error rate of below 1 × 10−4 is regarded as high quality , error-free operation of OPS and OCS links was achieved without equipment adjustments. Additionally, four-copied optical packets with the packet rate of 10% were generated by the copy function of the 100G-OP transponder and were transmitted around the ring network from Node 1. Figure 7 shows the temporal waveform of the original and four-copied optical packets with a packet rate of 50%. The measured error rate of the original frames was also less than 1 × 10−4, and the throughput per port of the OPS links in the integrated OPS/OCS node was estimated at more than 43 Gbps. These results demonstrate the stable operation of the network testbed under the conditions described above.
Finally, for an actual application, we demonstrated 4K uncompressed video streaming over OPS links. At a 4K video transmitter (4K video Tx.), as shown in Fig. 4, 6.4 Gbps 10GbE frames including uncompressed 4K video were generated and launched into Node 1. Optical packets encapsulating the 10GbE frames were transferred from Node 1 to Node 2 over OPS links. The 10GbE frames were sent to a 4K video receiver (4K video Rx.), and 4K video was displayed. Figure 8 shows the clearly displayed 4K video after transmission.
We built a novel optical packet and circuit integrated ring network testbed with two OPS/OCS nodes and verified the performance. We demonstrated 66 km transmission and switching of 100 Gbps colored optical packets and 14-wavelength 10 Gbps optical paths. We achieved error-free operation and confirmed basic functions on the network testbed. The testbed can contribute to accelerating network development.
The authors would like to thank Takeshi Makino, Wei Ping Ren, and Tomoji Tomuro of the National Institute of Information and Communications Technology for their support in the experiments.
References and links
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