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Port Control Protocol (PCP) is a computer networking protocol that allows hosts on IPv4 or IPv6 networks to control how the incoming IPv4 or IPv6 packets are translated and forwarded by an upstream router which performs Network Address Translation (NAT) or packet filtering. By allowing hosts to create explicit port forwarding rules, handling of the network traffic can be easily configured to make hosts placed behind NATs or firewalls reachable from the rest of the Internet (so they can also act as network servers), which is a requirement for many applications. Additionally, explicit port forwarding rules available through PCP allow hosts to reduce the amount of generated traffic by eliminating workarounds in form of outgoing NAT keepalive messages, which are required for maintaining connections to servers and for various NAT traversal techniques such as TCP hole punching. At the same time, less generated traffic reduces the power consumption, directly improving the battery runtime for mobile devices.〔 PCP was standardized in 2013 as a successor to the NAT Port Mapping Protocol (NAT-PMP), with which it shares similar protocol concepts and packet formats. == Overview == Many applications and network equipment deployments require their network locations to be reachable from outside their local networks, following the originally envisioned model of IP end-to-end connectivity across the Internet, so they can operate as network servers and accept connections from remote clients. An example of such equipment is an IP camera, which includes a network server that provides remote surveillance over IP networks. Usually, network equipment deployments place the devices behind routers or firewalls that perform NAT (to enable sharing of an IPv4 address, for example) or packet filtering (for improved network security and protection), ending up with breaking the end-to-end connectivity and rendering the equipment and applications inaccessible from the rest of the Internet.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Port Control Protocol」の詳細全文を読む スポンサード リンク
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