Voice over Internet Protocol (VoIP) is a technology that enable voice message transmission over data network (internet protocol). Codec is algorithm or special computer program to reduce number of bytes. The usage of appropriate codec at implementation VoIP is one thing determining in attainment of quality VoIP communications. This research implement and analys the usage of codec G711, G723 and G729 at protocol H323 for VoIP service. Examination by through simulation using ns-2. Codec G723 has smaller delay value and jitter value than codec G711 and G729. The result from simulation is codec G723 has smaller bit rate value, so more efficient for implementation at network that having not big bandwidth or network capacity. In communications process usage of codec G.723 will not encumber network - Kurniawan, Feri (Jurnal Ilmiah Ilmu Komputer, 2011)