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NE40E V800R010C00 Feature Description - NAT and IPv6 Transition 01

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The Port Control Protocol (PCP) establishes PCP connections between customer premises equipment (CPE) and Carrier Grade NAT (CGN) devices to implement point-to-point (P2P) applications between terminal users accessing different CGN devices. PCP is used in two-level Network Address Translation (NAT444) and Dual-Stack Lite (DS-Lite) scenarios. In a PCP application, a CGN device functions as a PCP server, and a CPE functions as a PCP client. The CGN devices assign public IP addresses and port numbers to the users on the CPEs. A P2P server uses the public IP addresses and port numbers to establish P2P connections between terminal users so that the users connected to the CGN devices can access P2P services, such as teleconferences, online games, and P2P data transmission.


During the IPv4-to-IPv6 transition, carriers use transition techniques, such as NAT444 and DS-Lite, to translate between public and private address realms and save IPv4 addresses. If symmetric NAT (5-tuple mode) is used, two terminal users on different internal networks (in private address realms) are difficult to communicate, which fails to meet the basic P2P application requirement for node communication. A CGN device connected to a terminal user rejects any session request initiated by the terminal user connected to the other CGN device, hindering the P2P communication between the terminal users on different private networks.

Therefore, the CGN device must support the PCP protocol. The CGN device establishes a PCP connection to a CPE and assigns public network resources to private network terminals accessing the CPE to implement P2P applications between P2P terminal users.


PCP offers the following benefits.

  • PCP can be smoothly implemented without changes in the existing IPv4-to-IPv6 transition infrastructure or service deployment.

  • PCP helps improve P2P application user experience and consequently user loyalty.

Updated: 2018-07-04

Document ID: EDOC1100027155

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