TCP/IP: (Transmission Control Protocol/Internet Protocol)Network communication protocol is the most basic Internet protocol and the basis of international Internet . It`s composed by network layer IP protocol and transport layer TCP protocol. TCP/IP defines how electronic devices connect to the Internet, and the data transmission standard. LAN: (Local Area Network,LAN)It refers to a computer group composed by multiple computers in a certain area. It`s generally within a thousands of meters. LAN can achieve document management, software application sharing, printer sharing, work group scheduling, e-mail and fax communication...these functions. WAN: (Wide Area Network,WAN)It usually crosses the big physics range, the coverage range from a few tens of kilometers to thousands of kilometers. It can connect multiple cities or countries, or across several continents and provide long-distance communication to form the international remote internet. VPN: (Virtual Private Network,VPN)It can be understood as a virtual internal exclusive communication line in an enterprise. It can use the special encrypted communication protocol to establish an exclusive communication line for multiple enterprises in different places which have connected to Internet. UNICAST: It`s a point- to- point connection between the client and server. “Point -to –point” means each client receives the remote stream from server. The server will send unicast stream only when the client requested. MULTICAST: To realize point-to multipoint connection between the sender and each receiver. If a sender transmits the same data to multiple receivers simultaneously, it just need copy one same data packet. It improves datatransfer efficiency and reduces the backbone network jam possibility. SIP: (Session Initiation Protocol)It`s multimedia communication protocol and established by the IETF (Internet Engineering Task Force). It is a text-based application layer control protocol, it`s used for creating, modifying and releasing one or multiple participants conversation. H.264: It`s the 10th part of MPEG-4, that is the highly compressed digital video codec standard suggested by JVT（JVT, Joint Video Team）which is composed by ITU-T video coding experts group(VCEG) and ISO / IEC moving pictures experts group (MPEG) ONVIF: It`s a global video open interface standard, it`s an international open standard network interface development forum of network video products which is established by AXIS united BOSCH and SONY. It is committed to use public and openness principle. The ONVIF specification will ensure the intercommunity between different video products suppliers. Full Duplex: It`s a communication transmission term. Communication allows data transmit in two directions simultaneously, it is equivalent to two simplex communication mode combination. Full duplex refers to the data transmission in two directions simultaneously (A→B and B→A) . Refers to A→B, and B→A simultaneously, it is instantaneous synchronous. Half Duplex: It refers to one action only within a period of time. Early walkie-talkie and HUB devices are half duplex based. PTT: PTT is transmit button, press the PTT to talking and loosen the PTT to receiving. Frequency Response: It is also called response curve, it`s the curve which describes gain variation with the changing of frequency. Any sound device or carrier (a device to record sound signal) all has its frequency response curve. The ideal frequency response curve should be flat, it does not produce distortion after the sound signal passed. Audio sampling: Convert the sound wave convert into a series of binary data and reappear the original voice, the A/D converter use tens thousands of times per second rate for audio sampling, every sampling recorded the original analog sound waves status in the moment, that is sample. Sampling numbers per second is sampling frequency or rate, the unit is HZ (Hertz). Alarm input/Alarm output: It is also On off input/output, that is contactor, there have 2 states between the contactors, it`s connect or disconnect.There are 2 kinds of switching signal: Active & passive, active switching signal will drive voltage when two contactors are connected. Power Over Ethernet: It it based on Ethernet Cat.5 wiring to transmit the data signal to IP terminals(eg:IP phone, IP camera...etc), and it also can offer the DC power to device at the same time. IP66/IP65/IP54: IP protection degree, the 1st number means the dustproof capability, No.6 means no dust inside; the 2nd number means the waterproof capability,No.6 means no harmful effect for spraying the water to the shell everywhere, No.5 degree is weaken than No.5 degree, and No.4 degree is weaken than No.5.