1. Field of the Invention
The present invention relates generally to communications over packet networks. More particularly, the present invention relates to establishing modem communication over a packet network, such as the Internet, utilizing the Internet Protocol (“IP”).
2. Related Art
In recent years, packet-based networks, such as the Internet, have begun to replace the traditional analog telephone networks for transportation of voice and data. For example, with the emergence of voice over IP (“VoIP”), telephone conversations may now be captured, packetized and transported over the Internet. In a conventional VoIP system, telephone conversations or analog voice may be transported over the local loop or the public switched telephone network (“PSTN”) to the central office (“CO”). From the CO, the analog voice is transported to a gateway device at the edge of the packet-based network. The gateway device converts the analog voice or speech to packetized data using a codec (coder/decoder), according to one of various existing protocols, such as G.729, G.711, G.723.1, etc. Next, the packetized data is transmitted over the Internet using the Internet Protocol for reception by a remote gateway device and conversion back to analog voice.
Today, many have diverted their focus to using the existing packet-based network and gateway devices, which have been designed to support the transportation of analog voice or speech over IP, to further support modem communication over IP, or as it is referred to in the industry, Modem over Internet Protocol (“MoIP”). FIG. 1 illustrates a block diagram of a conventional communication model for MoIP based on a packet-based network, such as the Internet. As shown, communication model 100 includes first client communication device 110 in communication with first gateway communication device 120 over PSTN providing transmit and receive channels 112 and 114. Communication model 100 further includes second client communication device 150 in communication with second gateway communication device 140 over PSTN providing transmit and receive channels 144 and 142. Communication model 100 enables communications between first gateway communication device 120 and second gateway communication device 140 via packet network 130 utilizing the Internet Protocol. The Internet Protocol implements the network layer (layer 3) of a network protocol, which contains a network address and is used to route a message to a different network or subnetwork. The Internet Protocol further accepts packets from the layer 4 transport protocol, such as Transmission Control Protocol (“TCP”) or User Data Protocol (“UDP”), and adds its own header and delivers the data to the layer 2 data link protocol. TCP provides transport functions, which ensures that the total amount of bytes sent is received correctly at the other end. UDP, which is part of the TCP/IP suite, is an alternate transport that does not guarantee delivery and it is widely used for real-time voice and video transmissions where erroneous packets are not retransmitted.
For purposes of MoIP, communication devices 110, 120, 140 and 150 are capable of performing modem functions. The term modem stands for modulator-demodulator (i.e. digital-to-analog/analog-to-digital converter). Modem is a device that is capable of adapting a terminal or computer to an analog telephone line by converting digital pulses to audio frequencies and vice versa. Modems may support a variety of data modulation standards, such as ITU (International Telecommunications Union) standards: V.92, V.90, V.34, V.32bis, V.32, V.22bis, V.22, V.21 or Bell 103, specifications of which are hereby incorporated by reference. Communication devices 110, 120, 140 and 150 may also be cable modems, DSL modems or ISDN terminal adapters, which are all digital and technically not modems, but referred to as modems in the industry. Typically, modems have built-in error correction, such as MNP2-4 and/or LAPM and data compression, such as MNP5, V.42bis or V.44. Modems are also capable of supporting various voice and facsimile standards.
Conventionally, the communication process for MoIP begins when first client modem ((“M1”) or first client communication device 110) calls first gateway modem ((“G1”) or first gateway communication device 120). As a result, G1 calls second gateway modem ((“G2”) or second gateway communication device 140), and G2 in turn calls second client modem ((“M2”) or second client communication device 150). In order to support VoIP in their default mode of operation, typically, G1 and G2 communicate in voice mode and are configured to use a compressed voice protocol, such as the ITU standard G.723.1. However, when M2 answers the incoming call from G2, M2 generates an answer tone, e.g. 2100 Hz, that causes G1 and G2 to switch to an uncompressed voice protocol, such as an ITU standard G.711, which provides toll quality audio at 64 Kbps using either A-Law or mu-Law pulse code modulation methods. This uncompressed digital format is used in order to allow easy connections to legacy telephone networks. By switching to G.711, the tones generated by M2 may propagate through G1 and G2 with less distortion in order to reach M1 at the other side. One existing method provides for maintaining G1 and G2 in G.711, such that M1 and M2 are able to handshake over packet network 130 and transfer data using G.711 packets using the Internet Protocol. However, such solution suffers from many problems, such as packet loss, jitter and delay, which cannot be tolerated by high-speed modems.
In a preferred alternative approach, known as modem relay, modem connections may be terminated locally, such that M1 and G1 handshake and make a connection locally and, similarly, M2 and G2 handshake and make a connection locally. However, due to the existence of various data modem and facsimile modem protocols, there is an intense need in the art for a universal solution to be used by gateway devices G1 and G2, such that they can distinguish between various modem protocols and communicate information relating thereto between G1 and G2 during the modem relay establishment process.