1. A method, in a network optimizer of a proxy server, of supporting a delta compression technique for reducing network resource transmission size between a near end network optimizer of a client device and a far end network optimizer, wherein the far end network optimizer is coupled with an origin server hosting network resources, the method comprising: receiving from the client device a first request for a network resource, the first request including a first version identifier that identifies a first version of the network resource stored in the near end network optimizer of the client device; responsive to determining that the network optimizer of the proxy server has access to the first version of the network resource as identified with the first version identifier, transmitting a second request to the far end network optimizer, the second request including a second version identifier of the network resource identifying a second version of the network resource stored in the network optimizer of the proxy server; receiving a first response from the far end network optimizer, the first response including a first differences file that specifies a first set of one or more differences between the second version of the network resource with a most current version of the network resource received at the far end network optimizer from the origin server, wherein the first response does not include the entire network resource; and transmitting to the client device a second response including a second differences file that identifies a second set of one or more differences between the most current version of the network resource and the first version of the network resource identified in the first request, wherein the second response does not include the entire network resource and causes the near end network optimizer of the client device to generate an updated version of the network resource.