System-on-chip　(SoC)　designs　provide　integrated　solutions　to　challenging　design　problems　in　the　telecommunications,　multimedia,　and　consumer　electronics　domains.　However,　the　communication　subsystem　gradually　becomes　a　bottleneck　of　SoC　as　the　technology　of　semiconductor　has　a　great　progress　and　complexity　of　system　increased.　Network-on-chip　(NoC)　can　meet　the　distinctive　challenges　of　providing　a　communication　subsystem　for　SoC.　This　paper　prompts　NoC　can　be　defined　as　a　layered　communication　subsystem　of　complex　SoC,　sketches　a　simple　network-on-chip　example　and　analyses　the　characteristics　of　NoC,　layered　communication　protocol　and　some　key　research　problems.　©2010　IEEE.