Systems and methods for transmission of data in a communication system

1. A method of transmitting data from a node located in a public network to one of a plurality of devices located in a private network said public network being connected to said private network by a restrictive gateway which allows connections between the public and private networks to be established in only one direction the restrictive gateway preventing communication from being initiated by the node to the one of said plurality of devices such that the node waits until a further device in the private network establishes a communication with the node before the node is able to transmit data to the one of said plurality of devices, said method comprising:

determining that further device located in the private network has an existing connection with the node via the restrictive gateway comprising:

receiving a first identifier from the one of said plurality of devices, where the first identifier is received from the one of said plurality of devices during a previous connection between the one of said plurality of devices and the node;

receiving a second identifier from the further device;

comparing the first identifier with the second identifier; and

determining that the further device is located in the private network if the first identifier and the second identifier are associated with the same network;

transmitting from the node to the further device located in the private network a message addressed to the one of said plurality of devices via the connection between the node and the further device; and

forwarding the message from the further device to the one of said plurality of devices via a connection established within the private network.

2. A method as claimed in claim 1 wherein the message comprises a request for the one of said plurality of devices to establish a connection with the node or another node located in the public network.

3. A method as claimed in claim 2 further comprising establishing a connection from the one of said plurality of devices with either the first node or the other node the public network in response to receiving the request.

4. A method as claimed in claim 1 wherein the message comprises data intended for the one of said plurality of devices.

5. A method as claimed in claim 1 further comprising determining if the further device is able to establish a connection within the private network with the one of said plurality of devices.

6. A method as claimed in claim 1 further comprising allocating a session at the node for each of said plurality of devices.

7. A method as claimed in claim 6 wherein the session for each of said plurality of devices is used by each of said plurality of devices to communicate in the public network.

8. A method as claimed in claim 6 further comprising controlling the predetermined intervals in dependence on the number of sessions allocated to the devices in the private network.

9. A method as claimed in claim 1 wherein each of said plurality of devices establish a connection with the node at predetermined intervals.

10. A method as claimed in claim 1 wherein the public network is the internet.

11. A node located in a public network arranged to transmit data to one of a plurality of devices located in a private network, said public network being connected to said private network by a restrictive gateway which allows connections between the public and private networks to be established in only one direction, the restrictive gateway preventing communication from being initiated by the node to the one of said plurality of devices such that the node waits until a further device in the private network establishes a communication with the node before the node is able to transmit data to the one of said plurality of devices, said node being configured to:

determine that a further device located in the private network has an existing connection with the node via the restrictive gateway;

receive a first identifier from the one of said plurality of devices, where the first identifier is received from the one of said plurality of devices during a previous connection between the one of said plurality of devices and the node;

receive a second identifier from the further device;

compare the first identifier with the second identifier; and

determine that the further device is located in the private network if the first identifier and the second identifier are associated with the same network; and

transmit to the further device located in the private network a message addressed to the one of said plurality of devices via the connection with the further device wherein said message is forwarded from the further device to the one of said plurality of devices via a connection established within the private network.

12. A communication system comprising a node located in a public network and a plurality of devices located in a private network, said public network being connected to said private network by a restrictive gateway which allows connections between the public and private to be established in only one direction, wherein the node is arranged to transmit data to one of the plurality of devices, the restrictive gateway preventing communication from being initiated by the node to the one of said plurality of devices such that the node waits until a further device in the private network establishes a communication with the node before the node is able to transmit data to the one of said plurality of devices, wherein said node being configured to:

determine that a further device located in the private network has an existing connection with the node via the restrictive gateway;

receive a first identifier from the one of said plurality of devices, where the first identifier is received from the one of said plurality of devices during a previous connection between the one of said plurality of devices and the node;

receive a second identifier from the further device;

compare the first identifier with the second identifier; and

determine that the further device is located in the private network if the first identifier and the second identifier are associated with the same network; and

transmit to the further device a message addressed to the one of said plurality of devices via the connection with the further device; wherein the further device comprises means for forwarding the message to the one of said plurality of devices via a connection established within the private network.