Patent Publication Number: US-2006004906-A1

Title: Method, system and computer program product for transmitting a media stream between client terminals

Description:
TECHNICAL FIELD OF THE INVENTION  
      The present invention relates to a method of transmitting a media stream of data from a sending client terminal to a receiving client terminal which is protected by a protective means. More in detail, a method is disclosed for avoiding transmission of data to be restrained by a firewall or by an arrangement for network address translation.  
     BACKGROUND OF THE INVENTION  
      So-called firewalls, shields or other types of protective security arrangements are installed in, or connected to most computer systems and communication networks of today. Unfortunately, such security arrangements may be necessary in order to keep undesired malicious attacks or insidiously hidden computer viruses away from a secure and therefore still uncontaminated branch of a network. An attack intended to cause destruction to a network or a computer virus that manages to pass by the security gates that protect a computer system may cause serious damage. The damage applies to an internal computer network or a residential computer system as well as to various electronic equipment related to it. As an alternative to a firewall, the user of a client terminal in a network may have a so-called network address translator, NAT, between his part of the network and the external network. The arrangement provides an additional obstacle for external users who wants information about the hidden IP-addresses behind the NAT arrangement and provides the user with a sufficient number of IP-addresses within his internal network.  
      A firewall and/or a network address translator are often arranged in a way that they allow traffic to enter into a protected zone only on condition that corresponding traffic has been transmitted out of that protected zone. For a situation when the communication channel has not been utilised for a period of time, the state of a firewall or network address translator changes from a data transmissible modes i.e. from an open mode, to a locked mode.  
      One flay of keeping the state open to data transmission is to instruct the particular firewall to open, or to maintain its open state while sending other data, but this solution is closely dependent on the specific type of firewall and the manufacturer of this firewall. Therefore, the prior art solution to the problem is too specific to be useful generally, and it is difficult to generalise the solution for applicability in a broader sense due to the amount of specifications necessary in order to achieve the desired general applicability.  
      Another way according to prior art technology is to instruct the administrator of a certain firewall arrangement to keep certain ports of the firewall open to transmission. Although this is one of the methods frequently used today, the method is uncertain and thus does not meet the rigorous security requirements placed upon state of the alt computer systems and corporate security policies that are utilised by companies and public authorities.  
     SUMMARY OF THE INVENTION  
      It is therefore an object of the present invention to alleviate the previously mentioned shortcomings of prior art associated with group communication services. This is accomplished by a method and corresponding system for transmitting a media stream of data from a sending client terminal to a receiving client terminal, the terminals being arranged in a protected computer environment including at least one protective means in association with a data forwarding means, which protective means is intended to protect the receiving client terminal from data transmitted from unauthorised sending clients, the method comprising the steps of: 
          transmitting authorisation data from the receiving client terminal to sending client terminal via the protective means for instructing the means to allow return of a media stream from the sending client terminal to the receiving client terminal during a predetermined period of time, characterised by:     the receiving client terminal is adapted to independently transmit authorisation data via the protective means at shorter intervals than said predetermined period of time for maintaining the allow return mode of the protective means.        

      Firewalls are typically configured so as to decide which gates to be open and which to be closed. As an example, the firewall may be configured so as to allow traffic to return from a certain external client terminal only provided that data has been sent to this particular client terminal in advance from inside of the protected zone. This is called an “allow return” state.  
      By means of the present invention, termination of the transmissible state of the protective means in favour of an impermeable state is avoided. The termination is carried out in order to enhance security, but also cuts off meaningful data streaming into a network of computers. The present invention lets in useful data while still maintaining the required network security since firewalls do not have to be open for an incoming data stream more than necessary, in particular when considering the large number of different firewalls available on the market, each with different characteristics. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The features, objects, and further advantages of this invention will become apparent by reading this description in conjunction with the accompanying drawings, in which like reference numerals refer to like elements and in which:  
       FIG. 1  illustrates a schematic overview of the means required for transmitting a media stream of data according to the present invention.  
       FIG. 2  is a signalling chart depicting the sequential method steps for transmitting a media stream of data according to the present invention. 
    
    
     DETAILED DESCRIPTION  
      The following description is of the best mode presently contemplated for practising the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims.  
      With reference to  FIG. 1 , a schematic overview illustrates the means required for transmitting a media stream of data according to the present invention. A sending client terminal  10  is connected to a router  40 , preferably via a global interconnecting computer network, such as the Internet. The router  40  may be any kind of data forwarding network means, such as a switch or a bridge between various units and client terminals in a communication network. The receiving client terminal  20  receives the transmitted media stream of data after the stream having passed a protective means  30  arranged in-between the router  40  and the receiving client terminal  20 . The protective means  30  may be any kind of firewall-related hardware equipment or a software-based virus shield. One example of a protective means is a network address translator, NAT. The reason for arranging a network address translator may be that the user is not provided with a sufficient number of IP-addresses. By utilising a network address translator for instance between the user&#39;s residential network and the external network, this shortage of addresses is managed.  
      In accordance with one embodiment, the function of a network address translator is the following: a client terminal A is to establish communication with another client terminal B. Client terminal A is protected by a firewall and/or a network address translator  30 . Client terminal B pays attention to signals that are input on its gate number “x”. When executing the signalling, client terminal A is about to transmit a signal from gate number “y” to client B&#39;s gate number “x”. However, the firewall and/or network address translator arrangement  30  restrains this packet and retransmits it from a gate number “z” of the protective means  30  to gate number “y” of the client terminal A. Now, there has been established a state in the firewall and/or NAT  30  with a mapping of a gate on the external side from gate “z” of the protective means  30  to gate “y” of client terminal A, i.e. client terminal B now transmits data to gate “z” and the firewall and/or NAT translates this to port “y” of client terminal A. In order to maintain the allow return mode, client terminal A must continuously transmit information to client terminal B through the firewall and/or network address translation arrangement  30 .  
      With reference to  FIG. 2 , a signalling chart is depicting the sequential method steps for transmitting a media stream of data from the sending client terminal  10  to the receiving client terminal  20  in accordance with the invention. The sequence begins (S 100 ) with setting (S 110 ) the transmission state of the protective means  30  by to an “allow return” mode by sending authorising instructions to the protective means  30  from the receiving client terminal  20 . The allow return mode is often already set by default on protective means by the manufacturer. There are also firewalls which only can operate according to the allow return rule. Next step is to set (S 120 ) the intervals of sending authorisation data to a period of time which is less than the predetermined period of time for return data is allowed. Authorisation data is sent (S 130 ) from the receiving client terminal  20  to the protective means  30  in accordance with the above intervals. This means the time for which the media stream of data originating from the sending client terminal  10  is allowed to pass the protective means  30  in order to reach the receiving client terminal  20 . This step is followed by transmission (S 140 ) the media stream of data from the sending client terminal  10  to the receiving client terminal  20 , the media stream passing through the permeable protective means  30  of the receiving client terminal  20 , which protective means is not yet closed for the incoming media stream due to the allow return mode. Subsequently, it is determined (S 150 ) by means of the sending client terminal  10  whether the predetermined period of time between each transmission of authorisation data has lapsed. In case the time has lapsed, the sequence returns back to transmitting (S 130 ) authorisation data and otherwise continues towards a user inquiry. This user inquiry (S 150 ) relates to whether the user of the method according to the invention wants to quit and thereby end (S 160 ) the session of information exchange or not. If not, the sequence returns back to the previous step of determining whether the predetermined period of time has lapsed (S 140 ).  
      In accordance with the present invention, software is developed in parallel with the method of transmitting a media stream of data. The software resides in a memory associated with the means for transmitting according to  FIG. 1 . The software is designed for instructing the hardware to carry out the sequential method steps previously described in this application with particular reference to  FIG. 2 .