Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1998-04-23
2002-04-23
Jung, Min (Department: 2731)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S401000
Reexamination Certificate
active
06377571
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to data communications, and more particularly to techniques for improving the flexibility and useability of point-to-point communication protocols, such as the Point-to-Point Protocol (PPP).
2. Related Art
Historically, computer networks and the public switched telephone network (PSTN) developed independently, and are in many ways dissimilar. Computer networks carried only data and the PSTN carried voice. Computer networks broadcast information on shared physical circuits in packets with source and destination identifiers while the PSTN dedicates physical circuits from source to destination for each call session. Computer networks broadcast data on digital circuits, while the PSTN carries voice over both analog local subscriber lines and digital long distance circuits.
The PSTN is now assuming many of the characteristics associated with computer networks. The PSTN is increasingly being used to connect individual computers and local area computer networks (LANs) to other computer networks to form wide area networks (WAN) such as the Internet. This requires that the PSTN handle both circuit-switched and packet-switched communications. Initially this is being accomplished by adding equipment to the PSTN which allows packet-switched technology to be overlaid on the existing circuit-switched backbone of the PSTN.
Protocols such as the Point-to-Point Protocol (PPP), is used for transporting multi-protocol datagrams over point-to-point links such as those setup by a traditional dial-up PSTN connection. One version of the PPP is described in Request For Comments RFC 1661, published in July 1994 by the Point-to-Point Protocol Working Group of the Internet Engineering Task Force IETF. A typical scenario involves a home user calling an Internet Service Provider (ISP) to make a home PC a temporary Internet host. The PC first calls the ISP's router via a modem. After the router's modem has answered the phone and established a physical connection the PC sends the router a series of packets in the payload field of one or more PPP frames. Once an IP address is assigned to the PC by the ISP the PC can now act as an Internet host and can send and receive IP packets.
Network access servers have been developed to interface digital packet-switched networks of computers, e.g. LANs, with analog local subscriber lines of the PSTN. These network access servers come in a number of forms. Integrated network access servers combine a packet processor and line server in the same housing, while split network access servers separate line servers and packet processors with at least one intermediate digital network.
Integrated network access servers interface a LAN with remote clients via one or more analog subscriber lines. Integrated network access servers combine in a single box, a line server and a packet processor. The integrated network access server typically exists as a node on a LAN. The line server connects to analog telephone lines, and the packet processor connects to a packet-switched network. The line server and packet processor connect to each other through internal connections within the integrated module. The line server includes modems each of which connects to analog subscriber telephone lines and handles data communications across the subscriber lines with remote clients. Transmission of data across these analog subscriber lines requires a modem to convert the digital signals generated by computers into analog tones for transmission over telephone network analog facilities. The packet processor connects to a packet-switched network, e.g. the LAN. The packet processor makes decisions about whether a call can be accepted from a telephone line and how to forward the constituent data packets to local clients on the LAN.
Some integrated network access servers allow local clients on the LAN to dial-out to the remote client over a long distance connection. The dial-out process is initiated by a local client with processes which allow it to communicate through the communication server. The communication server includes a bank of modems. The client dials a number, the number is passed across the LAN to the packet processor and then to the line server. The line server allocates one among a number of the modems to make the call over the analog subscriber line to the remote client. Network Products Corporation (NPC) 1440 West Colorado Blvd., Pasadena, Calif. 91105-1414 provides such capability. The advantage to this product is that it lets clients on a LAN share modem resources of a local line server. The disadvantage to this product is that it is predicated on an architecture in which a LAN is connected over analog subscriber lines to a WAN. Increasingly LANs are connected directly to a WAN via a digital network such as the Integrated Services Digital Network (ISDN).
ISDN can be viewed as an evolutionary progression and a conversion of analog telephone systems into an eventual all-digital network with both voice and data to be carried end-to-end in digital form. The ISDN network architecture is based on standards set by the International Telecommunications Union (ITU) with standards in the United States largely driven by American National Standards Institute (ANSI). ISDN provides relatively high speed digital transmission service on an “as needed” basis, and is different from LAN transmission media in that it is a circuit-switched transmission media which provides a point-to-point transmission service on an intermittent basis. ISDN enables LANs to be interconnected with each other to form a WAN.
Split network access servers may interface a LAN with remote clients via an intermediate digital network plus one or more analog subscriber lines. Split network access servers include separate line servers and packet processors connected to one another across a PPP channel on a WAN such as the Internet. This arrangement allows a virtual private network to be created between a remote line server and a local packet processor. A typical scenario involves a remote client dialin. The remote client dials the remote line server over a local analog subscriber line. The remote line server passes the communication in a PPP packet to the local packet processor. The local packet processor passes the communication to the appropriate client connected to the packet processor via the LAN. The advantage to split network access servers is that they allow inexpensive call setup from remote clients dialing in through remote line server to local clients on a LAN. The calls are inexpensive because they may be routed over the Internet as packets, rather than over a dedicated long distance voice circuit. The disadvantage to split network access servers is that they do not support dial-out from local clients on the LAN to remote clients.
Methods for improving the utilization of the PPP connections are being developed. These methods known as tunneling protocols, allow a single channel to multiplex multiple sessions from several users each with a plurality of packets. The specifics of a tunneling protocol are set forth in the point-to-point tunneling protocol (PPTP) June 1997 draft-ietf-pppext-pptp-01.txt, prepared by the Internet Engineering Task Force (IETF), which is incorporated by reference as if fully set forth herein. This document specifies a protocol which allows the PPP to be tunneled through an IP network. PPTP specifies a call-control management protocol which allows the line server to control access for dial-in circuit-switched calls originating from a PSTN or ISDN.
What is needed are techniques which overcome the disadvantages of split and integrated network access servers.
SUMMARY
The present invention provides local clients with the capability to dial-out through a packet processor to a remote line server to access a remote client.
Accordingly, the present invention can be characterized as a call-setup method implemented on a system which includes a local client coupled to a remote client through respectively, a packet processor, a first networ
3Com Corporation
Jung Min
McDonnell Buehnen Hulbert & Berghoff
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