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NE40E V800R010C00 Feature Description - NAT and IPv6 Transition 01

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
PCP Connection Application During P2P Data Transmission

PCP Connection Application During P2P Data Transmission

PCP is used in a NAT444 or Dual-Stack Lite (DS-Lite) scenario to allow terminal users on different private networks connected to CGN devices to use P2P applications, such as teleconferences, online games, and P2P data transmission. Figure 5-2 demonstrates the PCP connection application during P2P data transmission.
Figure 5-2  PCP connection application during P2P data transmission
  1. Each PC establishes a Transmission Control Protocol (TCP) connection to the P2P server.
    NOTE:

    The following example demonstrates how PC1 establishes a TCP connection to the P2P server. The process on PC2 is similar to that on PC1.

    The PCs must support the Universal Plug and Play (UPnP) protocol and P2P software. Using UPnP-capable P2P software is recommended.

    1. The user on PC1 starts P2P software so that PC1 can automatically send a UPnP request packet to instruct CPE1 to open a User Datagram Protocol (UDP) listening port.
    2. Upon receipt, CPE1 performs the following operations:
      • Uses the UPnP proxy function to accept the UPnP request and triggers the PCP client function.
      • Uses the PCP client function to send CGN1 a PCP request for a public IP address and a public port number.
    3. CGN1 selects a public IP address from the public address pool and generates a NAT entry containing the mapping between the private and public addresses and between the private and public port numbers. CGN1 then sends a PCP response packet carrying the public IP address and port number allocated to PC1.
    4. CPE1 forwards the public IP address and port number to PC1. The public IP address and port number can be displayed on the P2P software interface.
    5. PC1 uses the public IP address and port number to establish a TCP connection to the P2P server.
  2. PC1 sends TCP packets carrying file information and user status information to the P2P server.
  3. The P2P server parses the TCP packets sent by PC1 and obtains and saves PC1's public IP address and port number.
  4. When PC1 sends a request to search for a file to the P2P server, the P2P server replies with all the file owners' information, including file owners' public IP addresses and port numbers. This example uses PC2 as a file owner.
  5. PC1 sends the P2P server a request to download the file saved on PC2.
  6. The P2P server forwards the download request to PC2.
  7. Upon receipt of the request, PC2 establishes a UDP connection to PC1 and sends packets to PC1 over the UDP connection.
  8. PC1 downloads the file from PC2. P2P transmission between PC1 and PC2 is complete.
    NOTE:

    Bidirectional P2P transmission can be implemented. The process of downloading a file to PC2 is similar to that to PC1.

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Updated: 2018-07-04

Document ID: EDOC1100027155

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