Figure 2 is the conceptual configuration of the KJJVC (Oh et al. 2010). There are several VLBI data playback systems which will be used in our combined VLBI network, such as Mark5B, VERA2000, K-5/OCTADISK and some kind of optical fiber which shall be introduced in near future. Some of them have the VSI-H compatible interface, but the others take the different interface for the data transmission. And also they have their own maximum data recording/play back rates respectively.
To absorb all of these differences and in homogeneity among these existing VLBI data playback systems, the Raw VLBI Data Buffer (RVDB) was introduced, which is in fact a big data server with many large RAID disks and several kind of VLBI data interfaces. The VLBI Correlation Subsystem (VCS) shall receive the VLBI data from the RVDB system, shall calculate the correlation between the every possible pairs of data inputs with proper control parameters given from the correlator control and operation computer, and then shall dump the correlation results into the data archive system. Data archive system, is also a kind of data server, which is used to capture the correlated data output from the VCS, to save them as a structured file system. Finally there is also the correlator control and operation software for overall system. The KJJVC development is a joint project in close collaboration with the KASI and the NAOJ based on the MOU (Memorandum of Understanding) in 2005. The VERA2000 and other playback, RVDB development is responsible for NAOJ. The Mark5B, VCS, Data archive system development are responsible for KASI. And the control and operation software development are cooperated with KASI and NAOJ.
In May 2010, the Korea-Japan Correlation Center (KJCC) (see figure 3)was established at Yonsei University (KVN headquarter) in Seoul and the KJCC joint operation is now proceeding by the MOA (Memorandum of Agreement) for joint operation between KASI and NAOJ on July 2011. The KJCC will move to Daejeon (KASI headquarter) in 2012.
Figure 2. The conceptual design of KJJVC
2. Playback Systems
The KVN is now using the Mark5B system for recording and playback the observed data. The KASI participated in Mark5B development with Haystack Observatory as a member of international consortium. It can support the VSI compatible and RAID-based HDD storage system. The Recording and playing back speed is 1024-Mbps. The VERA is now extensively using the DIR2000 system for recording and playback with 1024-Mbps. Recently the manufacturer of DIR2000 had been stopped to make, so the NAOJ developed new playing back system named VERA2000, which is modified by DIR1000H system for only playing back.
3. RVDB (Raw VLBI Data Buffer) system
The RVDB system, which was developed by NAOJ, consists of Data Input Output (DIO), 10GbE switch, and Disk Data Buffer (DDB) (Oyama et al. 2008). It is able to record the data with maximum 2048-Mbps data rate, and can play back the data to correlator with nominal 2048-Mbps data rate. So, it has a function such as 2048-Mbps recorder and playback. As shown in figure 3, the different type of playback systems is used in KJJVC. So, the purpose of the RVDB system is that it can adjust the data format and easily synchronize the data during playback and maintain the buffering between recorder speed and correlation speed.
4. VLBI Correlation Subsystem (VCS)
The main specification of VCS was described in table 2. The VCS has a capability to process the total 120 cross-correlation and 16 auto-correlation intended for maximum 16 stations, maximum 8192-Mbps (4-streams × 1 Gsps/2-bit/64-MHz clock) input data rates per station. Correlation architecture is FX-based and it will use the variable length of FFT (Fast Fourier Transform) to maintain the 0.05 km/sec resolution of velocity at 22-GHz. Maximum delay rate is ±36,000-km and maximum fringe tracking is 1.075-kHz. The number of frequency channel per correlation output is 8,192.
5. Data Archive System
The basic architecture is infiniband. For KVN and KJJVN (Korea-Japan Joint VLBI Network), the first phase of data archive system with about 100TB capacity was implemented. It has 4 10Gbit Ethernet input port to connect with VCS output and 1 10GbE Ethernet port is connected with data file system for share the disk. We have a plan to increase the system capacity in accordance with EAVN in near future.
Figure 3. Korea-Japan Correlation Center
Table 2. The specification of Korea-Japan Joint VLBI Correlator (KJJVC)
References
http://kvn-web.kasi.re.kr (written in Korean)
Han, S.-T., Lee, J.-W., Kang, J.M., Je, D.-H., Chung, M.-H., Wi, S.-O., Sasao, T, & Wylde, R. 2008, Int. J. Infrared Milli. Waves, 29, 1
Iguchi, S. et al. 2005, PASJ, 57, 259
Kobayashi, H., et al. 2003, in ASP Conf. Ser., 306, in New Technologies in VLBI, ed. Y.C. Minh (San Francisco: ASP), 367
Nakajima, J. et al. 2000, IVS CRL-TDC News, 17, 18
Oh, S.-J. et al. 2011, PASJ, 63(6) will be published.
Oh, S.-J. et al. 2010, GM proceedings
Oyama, T., Y. Kono, T. Hara, N. Kawaguchi, 2008, General Meeting Abstract Book, 68.
Whitney, A. R. 2003, in ASP Conf. Ser., 306, New Technologies in VLBI, ed. Y.C. Minh (San Francisco: ASP), 123
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