Multiplex communications – Network configuration determination
Reexamination Certificate
1998-06-12
2002-11-26
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Network configuration determination
C370S351000
Reexamination Certificate
active
06487177
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is related to a method and system to be utilized in data communications. In particular, the present invention is related to a method and system to be utilized in data communications involving at least one data communications network. Yet still more particularly, the present invention is related to a method and system, to be utilized in data communications involving at least one data communications network wherein bridging and/or routing occurs.
2. Description of the Related Art
Data communications is the transfer of data from one or more sources to one or more sinks that is accomplished (a) via one or more data links between the one or more sources and one or more sinks and (b) according to a protocol. Weik,
Communications Standard Dictionary
203 (3rd ed. 1996). A data link is the means of connecting facilities or equipment at one location to facilities or equipment at another location for the purpose of transmitting and receiving data. Weik,
Communications Standard Dictionary
206 (3rd ed. 1996). A protocol, in communications, computer, data processing, and control systems, is a set of formal conventions that govern the format and control the interactions between two communicating functional elements in order to achieve efficient and understandable communications. Weik,
Communications Standard Dictionary
770 (3rd ed. 1996).
A data communications network is the interconnection of three or more communicating entities (i.e., data sources and/or sinks) over one or more data links. Weik,
Communications Standard Dictionary
618 (3rd ed. 1996).
Data communications networks connect and allow communications between multiple data sources and sinks over one or more data links. The concept of a data link includes the media connecting one or more data sources to one or more data sinks, as well as the data communications equipment utilizing the media. The data communications networks utilize protocols to control the interactions between data sources and sinks communicating over the one or more data links. Thus, it follows that such protocols must take into account the data communications requirements of data sources and sinks desiring communication over the one or more data links, and the nature of the underlying,one or more data links themselves, in order to ensure that the requirements of such data sources and sinks are met.
Of necessity, data communication protocols must take into account both the technology of the underlying data links and the data source and sink communications requirements. The underlying data links, data source, and data sink communications requirements give rise to a high degree of complexity.
It has been found that the complexity can be reduced to a manageable level by modularizing the concepts of data communication, as reflected in data communication network protocols. One such well-known modular approach is the International Standards Organization's Open Systems Interconnections (OSI) 7 layer (or level) model.
Those skilled in the art will recognize that data communication protocols exist which do not follow the OSI model exactly. However, insofar as the OSI model is a conceptual model dealing with the problem of network communications, non-OSI models still provide the same of the OSI model, although the terminology utilized in such protocols may be different from OSI terminology. Notwithstanding the foregoing, the OSI model still provides the most straightforward conceptual approach to the problems involved in network communication, and thus the OSI 7 layer model will be utilized, below, to discuss communications problems which exist in the art. Furthermore, while the OSI model does have seven layers, the first, second, and third levels will be most relevant to the detailed description to follow.
OSI Level 1 is the physical level, and deals with the true electrical signals and electrical circuits that are utilized to carry information. OSI Level 2 is known as the data link layer (or service layer interface/media access control layer when reference is made to a LAN context) and is a conceptual level whereby access to the physical level (OSI Level 1) is actually controlled and coordinated. A good example of OSI Level 2 is LAN protocol, which coordinates and controls access to the physical layer (OSI Level 1), or media over which actual transmission occurs, by use of data frames (packages of binary data) to which are appended headers containing a source address and a destination address. In LAN terminology, these addresses are referred to as media access control (MAC) addresses.
OSI Level 2 deals with access and control of actual media over which data is transmitted. Physical constraints often put an upper limit on the number of stations that can be physically connected (at OSI Level 1). OSI Level 2 defines ways that multiple discontinuous OSI Level 1, or physical, segments can be stitched together to achieve what appears to be one large coherent (or contiguous) network. The OSI Level 2 achieves this by managing “bridges” between physical segments. In Ethernet LAN, these bridges are termed transparent bridges, and in token-ring LAN these bridges are termed source-route bridges.
Conceptually one step removed from OSI Level 2 is OSI Level 3, the network layer. Network designers prefer to work with one large network, with a defined number of homogeneous network addresses. Consequently, OSI Level 3 has been developed. OSI Level 3 allows network designers to treat what may, in fact, be a tremendously large number of non-contiguous network segments strung together by OSI Level 2 entities as one large homogenous network. That is, OSI Level 3 allows network designers to refer to one network level protocol defined set of addresses. OSI Level 3 entities then pass such defined network addresses down to OSI Level 2 entities, which actually figure out where such network addresses are to be located on a true physical network.
OSI Level 2 entities typically achieve this by “mapping” the OSI Level 3 network addresses onto OSI Level 2 service layer addresses. Thus, when an OSI Level 3 entity passes a network layer address to an OSI Level 2 entity, the OSI Level 2 entity typically uses a look-up table to convert the OSI Level 3 address into its OSI Level 2 equivalent.
Due to the fact that what appears, from an OSI Level 3 standpoint, to be one large contiguous network, can in fact be many smaller non-contiguous networks stitched together by OSI Level 2 entities, it sometimes happens that an OSI Level 3 address is passed down to an OSI Level 2 entity which does not recognize the OSI Level 3 address. That is, there is no known mapping from the OSI Level 3 address to the OSI Level 2 address.
When this occurs, the typical response of the OSI Level 2 entity is to engage in “broadcast (i.e., network exploration is done in order to determine an OSI Level 2 address supporting the OSI Level 3 address in question) Broadcast merely means that the OSI Level 2 entity transmits to every other OSI Level 2 entities with whom it can communicate, and essentially asks if any of those stations support the OSI Level 3 address which is unknown to the OSI Level 2 broadcasting entity. Any such OSI Level 2 entity supporting the OSI Level 3 address can then answer back, and support of the OSI Level 3 address can thereby be established.
When a broadcast occurs, it in effect forces every OSI Level 2 entity, and every OSI Level 3 entity attached to the OSI Level 2 entities, who can “hear” the OSI Level 2 entity to interrupt what they are doing and determine whether or not they support the OSI Level 3 address in question. For those stations which do not support the address, such interruptions are needless.
In addition, every time that a broadcast message encounters a bridge, the broadcast is retransmitted onto the physical segments which are bridged. Such retransmission loads the network and again interrupts the OSI Level 2 entities connected to the bridged physical segments.
Even given the power of OSI Level 3 to create a large vi
Bracewell & Patterson L.L.P.
Nortel Networks Limited
Yao Kwang Bin
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