We report VLBI observing performance of the Korean VLBI Network (KVN). The KVN is
the first millimeter-dedicated VLBI network in East Asia. The KVN consists of three 21-m radio
telescopes with the baseline lengths in a range of 305­476 km. The quasi-optical system equipped
on the antennas allows simultaneous observations at 22, 43, 86, and 129 GHz. The first fringes
of KVN were obtained at 22 GHz on 2010 June 8. Test observations at 22 and 43 GHz on
2010 September 30 and 2011 April 4 confirmed that the full cycle of VLBI observations works
according to specification: scheduling, antenna control system, data recording, correlation, post-
correlation data processing, astrometry, geodesy, and imaging analysis. We found decorrelation
due to instability in the hardware at times up to 600 s is negligible. The atmosphere fluctuations
at KVN baseline are partly coherent, which allows us to extend integration time under good
winter weather conditions up to 600 s without significant loss of coherence. The postfit residuals
at KVN baselines do not exhibit systematic patterns, and the weighted root mean square (wrms)
of residuals is 14.8 ps. KVN is ready for imaging compact radio sources both in snapshot and full-
track modes with residual noise in calibrated phases less than 2 degrees at 22 and 43 GHz and with
dynamic ranges of 300 for snapshot mode and 1000 for full-track mode. With simultaneous
multi-frequency observations, KVN can be used to make parsec-scale spectral-index maps of
compact radio sources.