Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
1998-02-27
2001-03-06
Chin, Wellington (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
C370S230000, C370S448000
Reexamination Certificate
active
06198722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for optimizing flow control of message traffic on a local area network (LAN). More particularly the present invention relates to a flow control method and apparatus that can be added to existing networks without disruptively interfering with existing network protocols or operations.
2. Description of the Related Art
A local area network, or LAN, is a system that provides interconnection and a communication protocol between a number of independent computing stations within a proximate area, such as a single building or a campus of adjacent buildings. An overview of local area network concepts and technology is set forth in William Stallings' book entitled
Local Networks
, Third Edition, MacMillan Publishing Company, 1990, and is hereby incorporated herein by reference.
Networks are typically constructed from network condensers such as routers, switches, bridges, repeater units, and hubs. End users that connect to the network, e.g., a desktop computer, provide a network node. Nodes are typically workstations, servers, printers, etc., and condensers concentrate the nodes into a common network. Routers and switches/bridges, intelligently or blindly, direct network traffic. At the most basic level, network condensers are devices that interconnect network nodes attached to a structured wiring plant. Network condensers are most often employed to concentrate, amplify, and restructure incoming signals; they allow the different nodes to communicate with one another by repeating signals they receive to some or all of the nodes attached to them, which is the basic function common to all the network repeater units mentioned above.
For simplicity, the term repeater unit will usually be used throughout the remainder of this specification to refer to network condensers performing the basic function of retransmitting a data packet received from a node though with the understanding that some types of network condensers perform more complex processing of network node transmissions.
Data is communicated over the network in units that are usually referred to as “frames” or “packets.” In addition to data to be transmitted, each packet includes protocol control information such as the address of the packet source (transmit station) and the address of the packet destination (receive station).
As indicated above, there are several accepted terms that describe different kinds of network condensers in terms of their processing of network node transmissions. For example, routers, switches, bridges, repeater units and hubs are all physical units that are used to interconnect nodes on a LAN or to interconnect LANs themselves. A repeater is the simplest type of interconnect device since a repeater merely replicates incoming packets on its remaining ports. Switches or bridges buffer data packets that they receive and look at the address field of each data packet to make a routing decision, sending packets only out of selected ports. Routers look at both the address and the protocol header of each packet to determine the routing for each packet. All of these condenser devices typically include several ports, sometimes numbering in the hundreds. The ports provide the physical means to build a network; specifically, the ports are most often used to provide network connection points for the nodes. However, as indicated above, a port can also be used to connect one network condenser to another.
The interconnection pattern or layout of a network is called a topology. One such well known topology has a star configuration. In a star topology network, each node has a dedicated communication medium connected to a port on the repeater unit, e.g. each node has its own cable connection to the repeater unit. A packet transmitted by the node propagates through the medium and is received by the repeater unit which recovers the data contained in the packet and retransmits it to the destination station to which it is addressed. Similarly, the repeater unit transmits packets which propagate through the medium and are received an attached node or another repeater unit.
LANs utilize one of two types of data transmission techniques: either baseband or broadband. Baseband transmission uses signaling which can encompass the entire frequency range of the transmission medium and can be implemented with all media types but is typically implemented with twisted pair, coaxial, or fiber optic cable. Broadband transmission uses signaling where the signal is encoded within a limited frequency range. The signal used to modulate a broadband signal to a specific frequency range is referred to as a “carrier.” By restricting the frequency range, broadband systems can multiplex many independent communication channels onto a single medium.
In a baseband LAN, digital data is converted to signals typically using Nonreturn-to-zero (NRZ) encoding. The signals are transmitted onto the medium encoded as voltage pulses typically using the well known Manchester encoding method. Transmission is bi-directional; that is, a signal inserted at any point on the medium propagates in both directions to the ends of the medium where it is absorbed. Baseband systems can extend only a limited distance, usually about a 1.0 KM maximum for copper based media without regeneration, due to attenuation of the signal. Fiber optic baseband systems are cable of distances of approximately 40 KM.
Because of the wide variety of physical, electrical, optical and procedural characteristics available to designers of equipment for local area networks, it has become widely acknowledged that certain standards must be observed. For example, the International Organization for Standardization (ISO) has developed a voluntary Open Systems Interconnection (OSI) model which defines a general computer networking system architecture. In principle, an “open” system may be designed in a unique manner but still be able to communicate with other open systems, provided that the implementation conforms to a minimal set of OSI standards. The OSI model is general and applies to both wide area networks and LANs.
The problem of complexity in computer network communication is best handled by using a layered architecture approach, in which all networking functions are partitioned into several groups, called layers, in such a way that upper layers use services provided (or functions performed) by lower layers. The OSI model implements the layered architecture concept and defines a number of layers, the particular functions performed by each layer, and interlayer interfaces. The partitioning of all networking functions into layers is guided by two contradictory constraints. When more layers are used, each becomes smaller and simpler. On the other hand, the use of many layers creates many interlayer interfaces, and the processing overhead necessary to handle additional interfaces eventually offsets the benefits gained by layer simplification.
The OSI model partitions networking functions into seven layers, as shown in FIG.
1
. These layers include the Physical (or medium) layer
1
, the Data-link layer
2
, the Network layer
3
, the Transport layer
4
, the Session layer
5
, the Presentation layer
6
, and the Application layer
7
. As noted above, the OSI model also defines the interlayer interfaces. A message to be sent from a program running on a first computer to a program running on a second computer must be passed from the application layer
7
of the first computer all the way down to the physical layer
1
of the first computer, across the network medium, and up from the physical layer
1
of the second computer, all the way up to the application layer
7
of the second computer. Thus, under the OSI model networked computers must implement the seven layer “protocol stack” in order to allow applications to communicate.
Once the OSI model was adopted, more refined standards defining each of the OSI layers could be developed. For example, if a standard is established for the data-link
Chin Wellington
Limbach & Limbach LLP
National Semiconductor Corp.
Pham Brenda H.
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