Patent Application
20080080510
It is to be appreciated that while the present invention will be described below in the context of IP telephony applications, the invention is not so limited. That is, the present invention is more generally applicable to any SIP-based application with which it would be desirable to implement NAT.
Principles of the invention define the operation of a Network Address Translation (NAT) process (or Network Address Translator) targeted toward SIP-based applications. As mentioned above, SIP messages have embedded IP addresses of the sender in the “Via” and “Contact” header fields. When passing from the private domain to the public domain, local addresses need to be substituted with a global address (assigned by Internet Assigned Numbers Authority or IANA). To accomplish this, a NAT process needs to be capable of identifying outgoing SIP messages and substituting all relevant fields such that the SIP messages are routable over the Internet by one or more SIP servers. Such a process also should preferably be achieved while posing no special requirements on SIP phone specifications and in a manner that is simple and cost effective. As will be seen, principles of the invention achieve these and other advantages. First, we describe a non-SIP enabled NAT process in the context of
Thus,
Binding table 110 in
Unfortunately, as mentioned above, if the NAT approach shown in
Accordingly,
Thus,
Binding table 210 in
It is to be understood that the term “binding” generally refers to a correspondence or association generated or established between two or more elements. For example, each row in tabular data structure 210 is considered a binding wherein the column elements (local address and port, and global address and port) in a row are relationally associated with one another.
Advantageously, using the SIP-enabled NAT methodology of the invention, such randomly chosen port number will appear in the “Via” and “Contact” headers embedded in the bodies of IP packets and will substitute the original default port number (5060). The global IP address will substitute the address of the sender in the private domain. SIP-enabled NAT router 204 will then listen for responses to the request sent at the randomly chosen port number reserved to that particular dialog session.
Such binding will remain active for the entire SIP session and, at the expiration of the session, the binding will be destroyed (removed or deleted). Destruction of the binding serves as a security mechanism to prevent active ports from being advertised outside the dialog in which they are involved. Accordingly, as a result of the randomly selected port number, each dialog has a separate randomly chosen identifier, such that termination of one dialog will not affect another dialog.
For example, in one embodiment, the entries of binding table 210 are deleted in the following cases:
(1) when a BYE Request (i.e., a request method of SIP that terminates a call) is received, after having sent a 200 OK (i.e., a response code of SIP);
(2) when a BYE Request is sent, after having received a 481 or 408 Response (i.e., response codes of SIP), or after a client transaction timeout;
(3) when a CANCEL Request (i.e., a request method of SIP that cancels searches and “ringing”) is sent, after 200 and 487 Responses (i.e., response codes of SIP) are received; or
(4) when a CANCEL Request is received, if an ACK Request (a request method for SIP that confirms a final response for the INVITE Request) is received after having sent a 487 Response.
Advantageously, the above-described NAT process uses randomly selected port numbers to uniquely identify different SIP ongoing dialogs. Such randomly selected port number and the global IP address are the values that substitute the private port number and the private IP address in each SIP request sent by NAT router 204 over the Internet. The binding of local and global IP addresses based on SIP transactions, such as the presence of a NAT entry during a SIP session, is guaranteed independent of the transport protocol (e.g., UDP, TCP).
In step 312, SIP client 302 generates an INVITE Request with a local port equal to 5060 (i.e., default port address shown in column 216 of
In step 314, NAT router 304 generates a random port binding (e.g., for source computer 202-A in
In step 316, the one or more packets that constitute the INVITE Request are inspected by the NAT router, and the private IP address and port are respectively substituted with the global IP address and randomly selected port, as per the generated binding.
In step 318, the translated INVITE Request is then forwarded to the final destination, i.e., SIP-remote server 310.
Assuming a call was setup and occurred between SIP client 302 and SIP-remote server 310, the SIP client in step 320 sends a BYE Request message to terminate the call. The packets in the BYE message are subjected to the same translation in step 322 as the packets in step 316, i.e., they are translated using the same port number randomly selected for the binding generated in step 314. The translated BYE message is then forwarded to SIP-remote server 310 in step 324.
The remote server, in step 326, then sends a 200 OK response to NAT router 304. In step 328, the NAT router deletes the binding for that dialog and forwards the 200 OK response to the SIP client in step 330, thus ending the call.
It is to be appreciated that while the random port generation process of the invention is illustrated above for use in translating header fields (e.g., Via and Contact header fields) in a SIP message, the random port generation process can be applied to translation of other port numbers in the SIP message. For example, the process can be applied to the RTP port number in the SDP portion of a SIP message. It is to be understood that the SDP portion describes the session to be initiated. The IP address for the SDP portion of the SIP message will be the same as that for the signalling portion (i.e., header fields).
Turning now to
In this illustrative implementation, a processor 402 for implementing at least a portion of the methodologies of the invention is operatively coupled to a memory 404 and a network interface 406 via a bus 408, or an alternative connection arrangement.
It is to be appreciated that the term “processor” as used herein is intended to include any processing device, such as, for example, one that includes a central processing unit (CPU) and/or other processing circuitry (e.g., digital signal processor (DSP), microprocessor, etc.). Additionally, it is to be understood that the term “processor” may refer to more than one processing device, and that various elements associated with a processing device may be shared by other processing devices.
The term “memory” as used herein is intended to include memory and other computer-readable media associated with a processor or CPU, such as, for example, random access memory (RAM), read only memory (ROM), fixed storage media (e.g., hard drive), removable storage media (e.g., diskette), flash memory, etc.
Further, the phrase “network interface” as used herein is intended to include, for example, one or more devices capable of allowing the computing system 400 to communicate with other computing systems. Thus, the network interface may comprise a transceiver configured to communicate with a transceiver of another computer system via a suitable communication protocol.
Accordingly, one or more computer programs, or software components thereof, including instructions or code for performing the methodologies of the invention, as described herein, may be stored in one or more of the associated storage media (e.g., ROM, fixed or removable storage) and, when ready to be utilized, loaded in whole or in part (e.g., into RAM) and executed by the processor 402.
In any case, it is to be appreciated that the techniques of the invention, described herein and shown in the appended figures, may be implemented in various forms of hardware, software, or combinations thereof, e.g., one or more operatively programmed general purpose digital computers with associated memory, implementation-specific integrated circuit(s), functional circuitry, etc. Given the techniques of the invention provided herein, one of ordinary skill in the art will be able to contemplate other implementations of the techniques of the invention.
Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be made by one skilled in the art without departing from the scope or spirit of the invention.
