US 2004/0057385 A1Published application

Methods for discovering network address and port translators

AssigneeNortel Networks Limited

InventorMichael E. Roshko

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Abstract

Network Address and Port Translators (NATs) have the potential to interrupt the end-to-end nature of Internet applications, thereby threatening end-to-end security and other end-to-end functions. Thus it is important to be able to discover the existence of NATs and their type. Accordingly there is provided a method of discovering the existence and type of NAT that involves instigating a test call between media endpoints on a Media Gateway (MG) and a Media Gateway Controller (MGC). The MGC is able to deduce the existence of a NAT by examining the media packets sent to its endpoint. If a NAT is determined to be present the MGC instructs the endpoint on the MG to send media packets to another endpoint on the MGC. By comparing the IP addresses and ports of the media packets received at the endpoints of the MGC, the MGC is able to deduce whether the type of NAT is Cone or Symmetric.

Claims28

Dependent claims

A method of determining the presence of a Network Address and Port Translator between a Telephony Service Provider Network and a network comprising a Media Gateway, said Telephony Service Provider Network comprising a Media Gateway Controller, said method comprising:

instigating a test call between a first endpoint on the Media Gateway Controller acting as a calling party, and an endpoint on the Media Gateway acting as a called party;
receiving a reply comprising the local Session Description Protocol of the endpoint of the Media Gateway at the Media Gateway Controller;
receiving an empty/noise media packet from the Media Gateway at the first endpoint of the Media Gateway Controller;
and
comparing the source IP address and port of the empty/noise media packet received at the first endpoint of the Media Gateway Controller with the IP address and port contained in the received local Session Description Protocol of the endpoint of the Media Gateway,
wherein if the IP addresses are different or the ports are different then a Network Address and Port Translator is determined to be present, otherwise, if the IP addresses are the same and the ports are the same then a Network Address and Port Translator is determined not to be present.

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Dependencies are inferred from the claim text.