Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2000-11-30
2004-07-13
Ho, Duc (Department: 2665)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S355000, C370S401000, C370S469000, C375S222000
Reexamination Certificate
active
06763018
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
This is a telecommunications invention that relates generally to the field of remote access to packet switched networks over point to point links. More particularly, the invention relates to a network access server and method for performing distributed processing of the Point-to-Point Protocol (PPP) and distributed packet forwarding of Internet Protocol (IP) packets using a tunneling protocol, such as the Layer 2 Tunneling Protocol (L2TP). The invention is particularly suitable for use in a high density remote access server, such as a remote access server simultaneously connecting a large number of remotely located users to a packet switched network, e.g., the Internet.
B. Description of Related Art
The methods and techniques disclosed herein can be performed by an element of communications equipment referred to herein as a “network access server”, also known as a “remote access server.” A network access server is a device that is capable of receiving a plurality of simultaneous incoming calls from remote users via a circuit switched network, such as the Public Switched Telephone Network (PSTN), and routing them to a packet switched computer network, such as a corporate backbone network, or Internet, for transmission to a host computer system or other device connected to the computer network. The network access server is also capable of handling multiple simultaneous calls from the computer network and directing them onto the PSTN for transmission to the remote user.
The patent to Dale M. Walsh et al., U.S. Pat. No. 5,528,595, which is fully incorporated by reference herein, describes a network access server. The network access server of the Walsh et al. patent has been commercialized widely by 3Com Corporation (previously U.S. Robotics Corp.) under the trade designation Total Control™ Enterprise Network Hub. Network access servers similar in functionality, architecture and design are available from other companies, including Ascend Communication, Lucent Technologies, and others. The invention is suitable for implementation in network access servers from the above companies, and other similar devices.
Typically, the individual remotely located users dial in to the remote access server over a public switched telephone network, cable modem network, ADSL connection, wireless network connection, or other type of communications link. Part of the connection process is the establishment of a Point-to-Point Protocol connection between the remote user's modem and the remote access server.
Industry and international standards bodies have established sets of functional requirements, conventions or rules that govern the transmission of data over circuit switched and packet switched computer networks. These functional requirements or rules are known in the art as “protocols.” The implementation of protocols is necessary in order to bring order, and standardization, to the communications field and allow equipment of diverse manufacturers to interoperate. Some protocols are considered low level transmission media related protocols, such as modulation schemes implemented in a modem, for example V.34, V.90, etc. Other protocols are considered higher level, as they relate to functions performed at higher levels in the OSI model, and are concerned with such features as error control, transmission control protocols and network level routing and encapsulation of data.
The requirements of these latter protocols are typically prepared as an International Engineering Task Force “Request For Comment” (RFC) document, circulated among the industry and eventually adopted by the standards bodies. Sometimes, they are introduced prior to formal approval by a standards body and adopted by players in the industry, becoming de facto standards. The present invention is concerned with the distributed processing of these higher-level network control protocols, and in particular the Point-to-Point Protocol (PPP). The PPP is well known in the art and described in RFC 1661, the contents of which are incorporated by reference herein.
Briefly, the PPP describes an encapsulation mechanism for transporting muliprotocol packets across layer 2 point-to-point links. Typically, a user obtains a OSI-model layer 2 (i.e., data link layer) connection to a network access server using a number of techniques (dialing up over the PSTN, over an ISDN line, over an ADSL connection, etc.) and then runs PPP over that connection. In such a connection, the layer 2 termination point and the PPP session endpoint reside on the same physical device, namely the network access server on one side and the remote user's modem on the other side.
The patent to Daniel L. Schoo, et al., U.S. Pat. No. 6,009,101, the contents of which are incorporated by reference herein, describes a method by which the processing of the PPP is distributed among multiple computing platforms in the network access server, in order to increase the efficiency and throughput of the network access server. A first portion of the processing is performed in the modem digital signal processor (DSP) of the network access server, and the remainder of the processing is performed in the gateway computing platform, e.g., DSP or general purpose computing platform in the routing card in the network access server.
Tunneling protocols, by which frames of data are routed from one node to another on a network, are also known in the art. One of these tunneling protocols that can be used with the invention is the Layer 2 Tunneling Protocol or L2TP, which is described in RFC 2661, the contents of which are incorporated by reference herein. Persons skilled in the art are familiar with the contents of RFC 2661. The L2TP protocol describes a mechanism for tunneling PPP packets across an intervening network in a way that is transparent to both end users and applications. The L2TP extends the PPP model by allowing the layer 2 and PPP endpoints to reside on different devices interconnected by a packet switched network. With L2TP, a user has a layer 2 connection to an access concentrator (e.g., modem bank, or an ADSL Digital Subscriber Line Access Multiplexer or DSLAM), and the concentrator then tunnels the individual PPP frames to a remotely located remote access server over an IP network. This allows the actual processing of the PPP frames to be divorced from the termination of the layer 2 circuit.
One benefit of L2TP is that the separation between the processing of PPP frames and termination of the layer 2 circuit can avoid long distance telephone charges. The layer 2 connection may be a local call to a local switched circuit concentrator, which then extends the logical PPP session over a shared infrastructure such as a frame relay circuit or the Internet to the PPP terminating unit, which can be located anywhere. From the user's perspective, there is no perceptible difference in having the layer 2 circuit terminate and PPP processing occur in a network access server directly, or the PPP frames processed in a remotely located remote access server using L2TP.
The distributed PPP processing techniques of the Schoo patent, and the off-loading of PPP processing entirely as described in L2TP are, in and of themselves, insufficient mechanisms for handling the processing requirements of next-generation, ultra-high capacity network access servers. The market is demanding that such devices meet performance, throughput, and high availability requirements that are orders of magnitude above what was typically provided for only a few years ago. This phenomenon is a result of the explosive growth in the Internet, and the need for Internet Service Providers to install remote access servers that can keep up with the demand for Internet access. These next-generation network access servers are being designed to handle thousands, and even tens of thousands of PPP sessions simultaneously in a single chassis.
The present invention provides a method and network access server architecture in which high speed Internet Protocol data forwarding is separa
Harper Matthew H.
Kung Ching
Puthiyandyil Sanil Kumar
Radhakrishnan Shaji
Ramankutty Rajesh
3COM Corporation
Ho Duc
McDonnell Boehnen & Hulbert & Berghoff LLP
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