Public IP transport network

Details Public IP transport network Public IP transport network

1997-03-11

2003-11-18

Rao, Seema S. (Department: 2666)

Multiplex communications

Pathfinding or routing

Combined circuit switching and packet switching

C370S401000

Reexamination Certificate

active

06650631

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to the integration of multiple types of local area networks (LANs) into a wide area network (WAN) using a set of protocols generally known as TCP/IP where TCP stands for Transmission Control Protocol, and IP is Internet Protocol. The invention provides multiple types of interconnection using PSTN (Public Switched Telephone Network) facilities to provide cost effective IP internetwork data transport. The system will provide an equal access model pursuant to the MFJ (Modified Final Judgment) and currently applicable statutes for accessing inter-LATA Internet carriers. The following background material introduces various computer network concepts and definitions and those familiar with computer networks and TCP/IP may wish to skip to following subsections.
COMPUTER NETWORK BACKGROUND
A computer network is simply a collection of autonomous computers connected together to permit sharing of hardware and software resources, and to increase overall reliability. The qualifying term “local area” is usually applied to computer networks in which the computers are located in a single building or in nearby buildings, such as on a college campus or at a single corporate site. When the computers are further apart, the terms “wide area network” or “long haul network” are used, but the distinction is one of degree and the definitions sometimes overlap.
A bridge is a device that is connected to at least two LANs and serves to pass message frames or packets between LANs, such that a source station on one LAN can transmit data to a destination station on another LAN, without concern for the location of the destination. Bridges are useful and necessary network components, principally because the total number of stations on a single LAN is limited. Bridges can be implemented to operate at a selected layer of protocol of the network. A detailed knowledge of network architecture is not needed for an understanding of this invention, but a brief description follows by way of further background.
At the heart of any computer network is a communication protocol. A protocol is a set of conventions or rules that govern the transfer of data between computer devices. The simplest protocols define only a hardware configuration, while more complex protocols define timing, data formats, error detection and correction techniques and software structures.
Computer networks almost universally employ multiple layers of protocols. A low-level physical layer protocol assures the transmission and reception of a data stream between two devices. Data packets are constructed in a data link layer. Over the physical layer, a network and transport layer protocol governs transmission of data through the network, thereby ensuring end-to end reliable data delivery.
The most common physical networking protocol or topology for small networks is Ethernet, developed by Xerox. When a node possesses a packet to be transmitted through the network, the node monitors the backbone and transmits when the backbone becomes clear. There is no central backbone master device to grant requests to gain access to the backbone. While this type of multipoint topology facilitates rapid transmission of data when the backbone is lightly utilized, packet collisions may occur when the backbone is heavily utilized. In such circumstances, there is a greater chance that multiple nodes will detect that the backbone is clear and transmit their packets coincidentally. If packets are impaired in a collision, the packets are retransmitted until transmission is successful.
Another conventional physical protocol or topology is Token Ring, developed by IBM. This topology employs a “token” that is passed unidirectionally from node to node around an annular backbone. The node possessing the token is granted exclusive access to the backbone for a single packet transfer. While this topology reduces data collisions, the latency incurred while each node waits for the token translates into a slower data transmission rate than Ethernet when the network is lightly utilized.
As computer networks have developed, various approaches have been used in the choice of communication medium, network topology, message format, protocols for channel access, and so forth. Some of these approaches have emerged as de facto standards, but there is still no single standard for network communication. However, a model for network architectures has been proposed and widely accepted. It is known as the International Standards Organization (ISO) Open Systems Interconnection (OSI) reference model. The OSI reference model is not itself a network architecture. Rather it specifies a hierarchy of protocol layers and defines the function of each layer in the network. Each layer in one computer of the network carries on a conversation with the corresponding layer in another computer with which communication is taking place, in accordance with a protocol defining the rules of this communication. In reality, information is transferred down from layer to layer in one computer, then through the channel medium and back up the successive layers of the other computer. However, for purposes of design of the various layers and understanding their functions, it is easier to consider each of the layers as communicating with its counterpart at the same level, in a “horizontal” direction.
The lowest layer defined by the OSI model is called the physical layer, and is concerned with transmitting raw data bits over the communication channel. Design of the physical layer involves issues of electrical, mechanical or optical engineering, depending on the medium used for the communication channel. The layer next to the physical layer is called the data link layer. The main task of the data link layer is to transform the physical layer, which interfaces directly with the channel medium, into a communication link that appears error-free to the next layer above, known as the network layer. The data link layer performs such functions as structuring data into packets or frames, and attaching control information to the packets or frames, such as checksums for error detection, and packet numbers.
Although the data link layer is primarily independent of the nature of the physical transmission medium, certain aspects of the data link layer function are more dependent on the transmission medium. For this reason, the data link layer in some network architectures is divided into two sublayers: a logical link control sublayer, which performs all medium-independent functions of the data link layer, and a media access control (MAC) sublayer. This sublayer determines which station should get access to the communication channel when there are conflicting requests for access. The functions of the MAC layer are more likely to be dependent on the nature of the transmission medium.
Bridges may be designed to operate in the MAC sublayer. Further details may be found in “MAC Bridges,” P802.1D/D6, September 1988, a draft publication of IEEE Project 802 on Local and Metropolitan Area Network Standards, or in later drafts of this document.
The basic function of a bridge is to listen “promiscuously,” i.e. to all message traffic on all LANs to which it is connected, and to forward each message it hears onto LANs other than the one from which the message was heard. Bridges also maintain a database of station locations, derived from the content of the messages being forwarded. Bridges are connected to LANs by paths known as “links.” After a bridge has been in operation for some time, it can associate practically every station with a particular link connecting the bridge to a LAN, and can then forward messages in a more efficient manner, transmitting only over the appropriate link. The bridge can also recognize a message that does not need to be forwarded, because the source and destination stations are both reached through the same link. Except for its function of “learning” station locations, or at least station directions, the bridge operates basically as a message repeater.
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