Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2001-07-11
2004-02-03
Jung, Min (Department: 2663)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S401000
Reexamination Certificate
active
06687245
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of telephony, and more particularly to Internet Protocol (IP) based telephony.
DESCRIPTION OF THE RELATED ART
Voice over Internet Protocol (VoIP) refers to the technology to make telephone calls and send faxes over IP-based data networks with a suitable quality of service (QoS) and superior cost/benefit. The main justifications for development of VoIP can be summarized as follows:
Cost reduction—VoIP technologies can provide substantial savings in long distance telephone costs, which is extremely important to most companies, particularly those with international markets.
Simplification—An integrated voice/data network allows more standardization and reduces total equipment needs.
Consolidation—The ability to eliminate points of failure, consolidate accounting systems and combine operations, providing for more efficient operations.
Advanced Applications—The long run benefits of VoIP include support for multimedia and multi-service applications, for which current telephone systems are not equipped.
Growth in the VoIP market is expected to be considerable over the near future. However, there remain many challenges facing developers of VoIP equipment, both in terms of voice quality, latency and packet loss as well as call control and system management. The primary challenges are: the severe restrictions on acquisition and use of registered IP version 4 addresses, the resulting need to use Network Address Translation (NAT) and related technologies, the limitations of existing firewall technologies, and the application layer requirements of VoIP protocols such as MEGACO, RTP, and RTCP.
The American Registry for Internet Numbers (ARIN) has placed severe restrictions on the allocation of routable, public IP addresses due to the popular growth on the Internet, and the rapid depletion of remaining available addresses. In order to conserve address space, ARIN strongly encourages end users to utilize NAT technology to conserve address space. The most common implementation of NAT is NAPT, or Network Address Port Translation. This allows a single public IP address to be used to support thousands of hosts using private (RFC 1918) addresses. The major problem with NAT is that it only modifies the source IP address and port information in the IP header, and not anywhere in the payload. A typical VoIP protocol uses the IP and port information of the host in the payload for caller identification and call routing. Thus, when a Media Gateway Controller (MGC) or Trunking Gateway (TG) receives communication from an end-node with conflicting information, considerable problems may result. Note that as used herein, the term “Trunking Gateway” refers to any device that simultaneously receives multiple analog inputs and encodes the signal into multiple corresponding IP data streams. A Trunking Gateway may also perform the reverse function of simultaneously taking multiple signals encoded into a multiple IP data streams and converting it to multiple corresponding analog signals.
The NAT process is also dynamic, and so a host will be associated with a specific port number only during the session in progress. The next session will almost assuredly be over a different port. This problem is exacerbated by the fact that two end nodes that need to communicate directly may be using the same private IP address.
Another issue relates to the firewall. Firewalls are typically designed to protect internal networks from external networks, and generally need to be aware of when sessions open and close so that the network does not remain vulnerable. Most protocols used on the Internet are TCP based, and thus the firewall can determine when sessions are opened and closed based on SYN and FIN messages. Unfortunately, most VoIP protocols are UDP based, and therefore do not utilize SYN and FIN messages that the firewall can detect. Complicating matters further, VoIP protocols often use pairs of ports for communication, initiated from both the inside and outside of the network. Firewalls tend to support single port communication only initiated from the inside. Additionally, triangulated communications between IP telephones present a particular problem, referred to as the “triangle problem”, described below.
The traditional solution to an upper-layer protocol that does not work with NAT is an Application Level Gateway (ALG). An ALG acts as a proxy by modifying the IP address and header information in the payload of the various protocols being used (MEGACO, RTP, RTCP) to match the information replaced by the standard NAT function. Additionally, the ALG typically “negotiates” with the NAT gateway to reserve any specific port or port ranges necessary to support the protocols. This has been done for a variety of protocols such as ICMP and FTP, and lately H.323 and SIP (two earlier VoIP standards), and solves the basic problem of public IP to private IP communication. What are not addressed are the more complex interactions such as triangulated routing shown in FIG.
1
. As
FIG. 1
shows, a Media Gateway Controller (MGC)
50
is coupled to Application Level Gateway
70
. The AGL
70
is coupled to two IP telephones
20
A and
20
B, respectively. The IP telephones
20
are also coupled to one another directly. If IP telephone
20
A contacts Media Gateway Controller
50
for Call Setup through ALG
70
, the MGC
50
contacts IP telephone
20
B (on the same network as IP telephone
20
A) through ALG
70
, and IP telephone
20
B attempts to contact IP telephone
20
A on the local network, the ALG
70
between IP telephones
20
A and
20
B must be sophisticated enough to only correct the private address information when appropriate.
The above problem may become very complex considering that the ALG
70
must maintain a local table of all internal hosts (IP telephones
20
), examine the call destination address information coming from the MGC
50
, and decide whether or not to modify it when routing it to the internal hosts
20
. The alternative would be to route all traffic through the ALG
70
regardless of whether the destination is in the internal network, perform the ALG function, then the NAT function twice, then the ALG function again, and then route it back out the same interface. This convoluted process would be required for every single packet, introducing substantial inefficiencies to the system.
Therefore, improved systems and methods for IP telephony are desired.
SUMMARY OF THE INVENTION
The present invention includes various embodiments of a system and method for performing IP telephony. In one embodiment, the system may include a network, at least one Media Gateway, such as an IP telephone or Trunking Gateway, a Service Gateway, operable to couple to the Media Gateway through the network, and a Media Gateway Controller, operable to couple to the Service Gateway and the at least one Media Gateway through the network.
In one embodiment, the Media Gateway may be an IP (Internet Protocol) telephone. The IP telephone may first be activated. In response, the Service Gateway may negotiate a client DHCP lease with the IP telephone. The Service Gateway may use an identifier, e.g., a vendor ID, of the IP telephone to determine a range of port numbers to assign to the IP telephone. In other words, the Service Gateway may receive the identifier from the IP telephone, and if the identifier is valid, assign the port range to the IP telephone. In one embodiment, the Service Gateway may receive a MAC ID of the IP telephone in addition to the vendor ID. The Service Gateway may determine if the MAC ID for the IP telephone is valid, and if the MAC ID is determined to be valid, then determine if the identifier is valid.
The range of port numbers may include one or more port numbers which are not reserved for use by other IP protocols. The client DHCP lease negotiations may include the IP telephone issuing a DHCP discover message to the Service Gateway, which may then issue a DHCP offer to the IP telephone if the identifier is determined to be valid. The DHCP offer may includ
Fangman Richard E.
Preston Jason D.
Hood Jeffrey C.
Jung Min
Meyertons Hood Kivlin Kowert & Goetzel P.C.
Voxpath Networks, Inc.
Williams Mark S.
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