Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-02
2003-10-21
Olms, Douglas (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S338000, C370S389000, C370S388000
Reexamination Certificate
active
06636499
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of data communications networks. More particularly, the present invention relates to an apparatus and method for automatic network device cluster discovery.
2. Background
A network is a communication system that links two or more computers and peripheral devices, and allows users to access resources on other computers and exchange messages with other users. A network allows users to share resources on their own systems with other network users and to access information on centrally located systems or systems that are located at remote offices. It may provide connections to the Internet or to the networks of other organizations. The network typically includes a cable that attaches to network interface cards (“NICs”) in each of the devices within the network. Users may interact with network-enabled software applications to make a network request, such as to get a file or print on a network printer. The application may also communicate with the network software, which may then interact with the network hardware to transmit information to other devices attached to the network.
A local area network (“LAN”) is a network that is located in a relatively small physical area, such as a building, in which computers and other network devices are linked, usually via a wiring-based cabling scheme. A LAN typically includes a shared medium to which workstations attach and through which they communicate. LANs often use broadcasting methods for data communication, whereby any device on the LAN can transmit a message that all other devices on the LAN then “listen” to. However, only the device or devices to which the message is addressed actually receive the message. Data is typically packaged into frames for transmission on the LAN.
Currently, the most common LAN media is Ethernet, which traditionally has a maximum bandwidth of 10 Mbps. Traditional Ethernet is a half-duplex technology, in which each Ethernet network device checks the network to determine whether data is being transmitted before it transmits, and defers transmission if the network is in use. In spite of transmission deferral, two or more Ethernet network devices can transmit at the same time, which results in a collision. When a collision occurs, the network devices enter a back-off phase and retransmit later.
As more network devices are added to a LAN, they must wait more often before they can begin transmitting, and collisions are more likely to occur because more network devices are trying to transmit. Today, throughput on traditional Ethernet LANs suffers even more due to increased use of network-intensive programs, such as client-server applications, which cause hosts to transmit more often and for longer periods of time.
FIG. 1
is a block diagram illustrating a network connection between a user
10
and a server
20
.
FIG. 1
is an example which may be consistent with any type of network, including a LAN, a wide area network (“WAN”), or a combination of networks, such as the Internet.
When a user
10
connects to a particular destination, such as a requested web page on a server
20
, the connection from the user
10
to the server
20
is typically routed through several routers
12
A-
12
D. Routers are internetworking devices. They are typically used to connect similar and heterogeneous network segments into Internetworks. For example, two LANs may be connected across a dial-up line, across the Integrated Services Digital Network (“ISDN”), or across a leased line via routers. Routers may also be found throughout the Internet. End users may connect to a local Internet Service Provider (“ISP”) (not shown).
As the data traffic on a LAN increases, users are affected by longer response times and slower data transfers, because all users attached to the same LAN segment compete for a share of the available bandwidth of the LAN segment (e.g., 10 Mbps in the case of traditional Ethernet). Moreover, LANs commonly experience a steady increase in traffic even if the number of users remains constant, due to increased network usage of software applications using the LAN. Eventually, performance drops below an acceptable level and it becomes necessary to separate the LAN into smaller, more lightly loaded segments.
LANs are becoming increasingly congested and overburdened. In addition to an ever-growing population of network users, several factors have combined to stress the capabilities of traditional LANs, including faster computers, faster operating systems, and more network-intensive software applications.
There are two traditional approaches to relieving LAN congestion. The first is to simply install a faster networking technology, such as FDDI, ATM, or Fast Ethernet. However, these approaches are expensive to implement. The other traditional approach is to use bridges and routers to reduce data traffic between networks. This solution is also relatively expensive both in money and configuration time, and is only effective when inter-segment traffic is minimal. When inter-segment traffic is high, some bridges and routers can become a bottleneck due to their limited processing power. They also require extensive setup and manual configuration in order to maintain their performance. In addition, despite large buffers, packet loss is always a possibility.
Switching is a technology that alleviates congestion in Ethernet, Token Ring, and Fiber Distributed Data Interface (FDDI) and other similar LANs by reducing traffic and increasing bandwidth. LAN switches are designed to work with existing media infrastructures so that they can be installed with minimal disruption of existing networks.
A Media Access Control (“MAC”) address is the unique hexadecimal serial number assigned to each Ethernet network device to identify it on the network. With Ethernet devices, this address is permanently set at the time of manufacture. Each network device has a unique MAC address, so that it will be able to receive only the frames that were sent to it. If MAC addresses were not unique, there would be no way to distinguish between two stations. Devices on a network monitor network traffic and search for their own MAC address in each frame to determine whether they should decode it or not. Special circumstances exist for broadcasting to every device on the network.
Ethernet uses variable-length frames of data to transmit information from a source to one or more destinations. Every Ethernet frame has two fields defined as the source and destination addresses, which indicate the MAC addresses of the network devices where a frame originated and where it is ultimately destined, respectively.
FIG. 2-A
illustrates the structure of an Ethernet frame, as defined by the IEEE. As shown in
FIG. 2-A
, the Ethernet frame
22
includes a Preamble
24
, a Start of Frame Delimiter
26
, a Destination Address
28
, a Source Address
30
, a Length of data field
32
(sometimes used as a Protocol Type field), a variable-length Data field
34
, a Pad
36
, and a Checksum
38
. The Preamble
24
is a seven-byte field, with each byte containing the bit pattern 10101010 to allow for clock synchronization between sending and receiving stations (not shown). The Start of Frame Delimiter
26
is a one-byte field containing the bit pattern 10101011 to denote the start of the frame itself. The Destination Address
28
and the Source Address
30
are typically six-byte fields which specify the unique MAC addresses of the receiving and sending stations. Special addresses allow for multicasting to a group of stations and for broadcasting to all stations on the network. The Length of Data field
32
specifies the number of bytes present in the Data field
34
, from a minimum of 0 to a maximum of 1500. The Pad field
36
is used to fill out the length of the entire frame
22
to a minimum of 64 bytes when the Data field
34
contains a small number of bytes. Finally, the Checksum field
38
is a 32-bit hash code of the Data field
34
, which can used by the receiving station to detect data tr
Cisco Technology Inc.
Olms Douglas
Ritchie David B.
Thelen Reid & Priest LLP
Wilson Robert W.
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