Multiplex communications – Diagnostic testing – Of a repeater
Reexamination Certificate
1999-01-27
2001-02-06
Olms, Douglas W. (Department: 2732)
Multiplex communications
Diagnostic testing
Of a repeater
C370S315000, C370S401000, C370S445000, C375S211000
Reexamination Certificate
active
06185190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to integrated circuit technology and to integrated circuit use in data communications technology. More particularly, the present invention relates to data communications technology utilizing packet-type signaling systems. Applications of the present invention will be particularly suited to data communications protocols such as 100BASE-T4 Ethernet.
2. The Prior Art
Many modern data communications systems utilize data packet technology. Packet-based systems present particular challenges for designers of methods which can detect and correct for erroneous conditions. In packet-based data communications, data signals or symbols are collected into groups rather than being transmitted continuously. These groups are commonly known as packets or frames. Data transmitted and received in a packet-based system will be sent and received as a series of packets rather than as a continuous signal. This obviates the need to establish a direct and continuous connection between the transmitter and receiver, allowing greater flexibility in network design.
In order to preserve data addressing and integrity, as well as to allow data communications receivers to implement functions such as alignment and recovery, it is common practice in the art to encapsulate data being sent in a packet form: for a given group of data, signals or symbols designating the start of a packet are added before the data signals or symbols; signals or symbols designating the end of a packet are added after the data signals or symbols. Therefore, a packet will typically include data signals or symbols “surrounded” by non-data signals or symbols. Packets, then, will be comprised of both data components or elements and non-data components or elements.
The pre-data packet components or elements (comprised of non-data signals or symbols) are typically used (among other functions) to designate the presence of the following data, and are commonly known as “preambles”. Those of ordinary skill in the art will recognize that the term “preamble” used in this context is intended to be inclusive; as such, it includes other common terms for pre-data packet components or elements, such as: start-of-stream delimiter (SSD), start-of-frame delimiter (SFD), and start-of-stream (SOS), for example. End of packet delimiters are commonly referred to as EPDs or EOPs (end-of-packet). The inventive concepts herein, as will be understood by those of ordinary skill in the art, are equally effective and applicable to preambles (pre-data packet components or elements) of any length or type.
Accordingly, the packet-type geometry may be designated:
<PREAMBLE><DATA><EPD>
It is well-known to those of ordinary skill in the art that both the preamble and the EPD may be used to carry important non-data information about the packet, such as timing, length, and error status, among others. Thus, a key function of receiving devices is the reception and use of these non-data packet elements.
It is also well-known to those of ordinary skill in the art that communication protocols define the form and use of preambles and EPDs; this allows a wide variety of communications equipment to communicate effectively. One of the major protocols used in the current development of Fast Ethernet technology is designated 100BASE-T4 Ethernet (or T4), defined by a Supplement to IEEE Standard 802.3u-1995, hereby incorporated herein by reference as if set forth fully herein. The T4 protocol calls for the transmission of data at an effective rate of 100 Mbits/sec. In order to maintain reliability of transmission over the conventional twisted pair medium, the 100BASE-T4 protocol requires that the transmission and reception be implemented over three pairs of twisted pair wires; this reduces the data transmission rate to one-third of 100 Mbits/sec, or approximately 33 MHz. The transmission rate is still further reduced by encoding the data according to the 8B6T protocol shown in FIG.
1
. The 8B6T coding scheme maps data octets (8 bits, or 1 byte) of binary (1,0) data into ternary symbols (+,0,−). Each byte of data is mapped to a pattern of six ternary symbols, called a 6T code group. The 6T code groups are fanned out to the three independent serial transmission channels. The ternary symbol transmission rate, then, is six-eighths ({fraction (6/8)}) of the channel data rate (about 33 Mb/s), or precisely 25 MHz. As will be apparent to those of ordinary skill in the art, the reduction in symbolic rate greatly improves potential data communications reliability over the multiple twisted pair medium.
FIG. 2
depicts a diagram of a type 100BASE-T4 physical layer device (PHY) relationship to the ISO Open Systems Interconnection (OSI) Reference Model and the IEEE 802.3 CSMA/CD LAN Model as described by Supplement to IEEE Standard 802.3u-1995 referred to above. In the diagram, the “MEDIUM” refers to the physical medium over which data is transmitted, in this case, four twisted pairs of wires. The “MDI” is a Medium Dependent Interface—an interface between the specific medium used (MEDIUM) and the Physical Layer Device (PHY). The PHY may include a Physical Medium Attachment (PMA), a Physical Coding Sublayer (PCS) and a Media Independent Interface (MII) along with an optional auto-negotiation (AUTONEG) function.
Physical level communication between PHY entities in a T4 network takes place over four twisted pairs.
FIG. 3
shows a typical T4 connection between a first Node “A” or PHY entity and a second Node “B” or PHY entity of a T4 network wired in the optional repeater configuration with twisted pair crossovers as shown. Referring to
FIG. 3
, the four twisted pairs include two pairs used for bidirectional communications and designated at Node “A” as BI_D
3
and BI_D
4
as well as a pair used exclusively for A to B communication (TX_D
1
) and a pair used exclusively for B to A communication (RX_D
2
).
The Physical Coding Sublayer (PCS) serves the function of coupling an MII to a PMA as shown in FIG.
2
. The PCS Transmit function accepts data nibbles (4-bit data segments) from the MII. The PCS Transmit function encodes these nibbles using an 8B6T coding scheme and passes the resulting ternary symbols to the PMA. In the reverse direction, the PMA conveys received ternary symbols to the PCS Receive function. The PCS Receive function decodes them into octets, and then passes the octets one nibble at a time up to the MII. The PCS also contains a PCS Carrier Sense function, a PCS Error Sense function, a PCS Collision Presence function, and a management interface.
FIG. 4
shows in block diagram form the division of responsibilities between the PCS, PMA and MDI layers. The MDI is shown at the right of FIG.
4
and the MII is shown at the left of FIG.
4
.
Ethernet transceivers designed to the 100BASE-T4 standard will necessarily include means for 8B6T encoding/decoding and recovery of the clock-data channels. The data will be encoded, fanned into the three transmission channels (3 of the 4 twisted pairs), and transmitted across the twisted pairs. At the receiving end, the data will be recovered from the three received channels, decoded, and sent into the receiving device.
In packet-based data communications systems, signals do not travel in continuous streams. Rather, data travels in small groups (of from about 64 to about 1500 bytes in the 100BASE-T4 Ethernet system), called packets or frames. Packets, then, are the basic unit of such data communications systems; all encoding, decoding and alignment functions are based on the packet geometry.
In order to delineate and signal the arrival and departure of packets, one or more preamble fields and closing fields are typically appended to each packet. The preamble and closing fields have known characteristics which can signal the receiving devices. As is known to those of ordinary skill in the art, it is through the reception of these signals that the decoding and alignment functions can be effectively implemented.
The T4 protocol defines the packe
Dreyer Stephen F.
Jin Robert X.
Peng Kathy L.
West Eric T.
Hom Shick
LSI Logic Corporation
Olms Douglas W.
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