Full duplex flow control for Ethernet networks

Details Full duplex flow control for Ethernet networks Full duplex flow control for Ethernet networks

2000-07-14

2003-11-11

Kizou, Hassan (Department: 2662)

Multiplex communications

Data flow congestion prevention or control

Control of data admission to the network

C370S282000, C709S232000

Reissue Patent

active

RE038309

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to networks in general including Ethernet networks, and more specifically to implementing an Ethernet network having full duplex flow control.
BACKGROUND OF THE INVENTION
A network is a communications facility that permits a number of workstations, computers or other equipment (hereinafter collectively “computer(s)”) to communicate with each other. Portions of a network involve hardware and software, for example, the computers or stations (which individually may comprise one or more central processing units, random access and persistent memory), the interface components, the cable or fiber optics used to connect them, as well as software that governs the access to and flow of information over the network. In networks in which data flow is 100 Mbits/sec. (“Mbps”) or higher, the transmission medium is often fiber optics. In networks in which a slower data rate is acceptable, e.g., 10 Mbps, the transmission medium may be coaxial cable or, as is often the case for an Ethernet network, twisted wires.
In a network, network architecture defines protocols, message formats and other standards to which the computers and other equipment, and software must adhere. Most network architectures have adopted a model comprising functional layers in which a given layer is responsible for performing a specific set of functions, and for providing a specific set of services. Thus, the services provided by each layer and the interlayer interfaces can define a network architecture. Protocols define the services covered across a layer interface and the rules followed in the processing performed as a part of that service. organizations have proposed models and standards that have been accepted within the networking community. The International Standards Organization (“ISO”), for example, has proposed a seven layer reference model for computer networking that is called the open systems interconnect (“OSI”) architecture. Another set of standards has been promulgated by the Institute of Electrical and Electronics Engineers (“IEEE”) set of proposed local area network (“LAN”) standards known as IEEE Project
802
. This model conforms to the seven-layer OSI model, but directly solely to the lowest two OSI layers, namely the physical layer and the data link layer.
FIG. 1
depicts a network according to the IEEE Project
802
modification to the ISO seven layer model, in which two computers
10
,
10
′ are can communicate data to each other over a physical link medium
20
, e.g., cable. Of course, in practice, a network may have many hundreds of computers rather than two.
The bottommost layer
30
in both the ISO and Project
802
model is a physical layer that is concerned with connections between two machines (e.g., computers
10
,
10
′) to allow transmission of bit streams over a physical transmission medium (e.g., cable
20
). Thus, physical layer
30
is concerned with types of cabling, cable plugs, connectors, and the like.
As will be described shortly, the present invention is directed to Ethernet networks adhering to the carrier sense multiple access with collision detection (“CSMA/CD”) standard. In the 802 model for CSMA/CD, a reconciliation interface
40
defined by a Media Independent Interface (“MII”) standard exists for the reconciliation sublayer
40
interface between physical layer
30
and a media access control (“MAC”) sublayer
50
B. The existing MII signal set provides independent four bit-wide paths for transmission and reception of data, and includes specific “hooks” for link level data flow control. (As used herein, flow control refers to inhibiting access to a network, or one or more links within the network.)
Interestingly, before adoption of MII, the MAC standard defined a single carrier sense signal (“CRS”) from the physical layer to the MAC that the MAC used to describe the state of the transmit and receive medium. This one CRS signal was used by the MAC transmit process to implement deferral of data transmission, and was by the MAC receive process to frame received data. With introduction of MII, this one CRS signal was decoupled into a CRS signal that again went to the MAC transmit process to implement deferral of data transmission, and into a receive data valid (“RX_DV”) signal that went to the MAC receive process. Thus, with MII, CRS is used solely by the MAC transmit process.
Under MII, data and delimiters are synchronous to the corresponding clock, and two asynchronous media status signals are provided, namely carrier sense (“CRS”), and collision (“COL”). MII provides a two wire serial management interface for control and status gathering, namely management data clock (“MDC”), and management data input/output (“MDIO”). In the OSI seven-layer model, the layer above the physical layer is a data link layer that is responsible for error-free transmission of data frames between network nodes. A data link control protocol describes operation and interfaces of this layer, which must also shield higher layers in the model from concerns about the physical transmission medium.
But in the 802 model shown in
FIG. 1
, the data link layer is subdivided into MAC layer
50
B and an overlying logical link control (“LLC”) layer
50
A. The media access control sublayer is concerned with access control methods to determine how to control the use of the physical transmission medium. The LLC sublayer
50
A is responsible for medium-independent data link functions and allows the network layer
60
above to access LAN services independently of how the network is implemented. According to the
802
architecture, LLC sublayer
50
A provides services to network
60
in the same fashion as would a conventional data link protocol in a wide area network.
The MAC sublayer
50
B provides services to the overlying LLC sublayer
50
A, and manages sharing of the transmission medium among the different stations on the network. A media access management function receives a frame from the data encapsulation function after the necessary control information has been added. Thereafter, media access management is responsible for ensuring physical transmission of the data. The data frame in an Ethernet full-duplex environment has a maximum size of 1,518 bytes.
Several 802 standards exist for MAC sublayer
50
B, but only the carrier sense multiple access with collision detection (“CSMA/CD”) standard is relevant to the present invention, more specifically the 802.3 standard. The existing 802.3 MAC standard presently contains several mechanisms for performing flow control in a half-duplex environment, including a Deference process, and WatchForCollission and BackOff procedures. CSMA/CD defines data encapsulation/decapsulation and media access management functions performed by MAC sublayer
50
B itself, the data encoding/decoding function being performed by underlying physical layer
30
.
Physical transmission of the data may be ensured using carrier sensing to defer transmission until the network is clear. In brief, a transmitting station (e.g., computer or user
10
) listens or monitors the transmission medium (e.g., cable
20
) before transmitting to determine whether another station (e.g., computer or user
10
′) is currently transmitting a message, e.g., to learn whether the medium is free. Using the services of the physical layer
30
, the media access management determines whether the transmission medium (or carrier) is presently being used. If the medium is not being used, media access management passes the data frame to physical layer
30
for transmission. Even after transmission of the frame has begun media access management continues to monitor the carrier. If the carrier is busy, media access management continues monitoring until no other stations are transmitting. Media access management then waits a specified random time to allow the network to clear and thereafter begins transmission.
But other station(s) having messages to send may all listen simultaneously, discern that the transmission medium appears quiet, and begin to transmit messages

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