Multiplex communications – Channel assignment techniques – Arbitration for access to a channel
Reexamination Certificate
2000-01-18
2003-10-28
Cangialosi, Salvatore (Department: 2661)
Multiplex communications
Channel assignment techniques
Arbitration for access to a channel
C370S389000, C710S240000
Reexamination Certificate
active
06639918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to bus management. In particular, the present invention relates to the behavior of border nodes within a high performance serial bus system.
2. The Prior Art
BACKGROUND
Modern electronic equipment has greatly enhanced the quality of our lives. However, as the use of such equipment has increased, so has the need to connect equipment purchased from different manufacturers. For example, while a computer and a digital camera may each be useful when used alone, the ability to connect the digital camera to the computer and exchange information between the two makes the combination even more useful. Therefore, a need was apparent for a serial bus standard that would allow for the connection and communication between such devices.
The IEEE 1394-1995 standard was developed to satisfy this need. This standard revolutionized the consumer electronics industry by providing a serial bus management system that featured high speeds and the ability to “hot” connect equipment to the bus; that is, the ability to connect equipment without first turning off the existing connected equipment. Since its adoption, the IEEE 1394-1995 standard has begun to see acceptance in the marketplace with many major electronics and computer manufacturers providing IEEE 1394-1995 connections on equipment that they sell.
However, as technologies improved, the need to update the IEEE 1394-1995 standard became apparent. Two new standards are being proposed at the time of the filing of this application, herein referred to as the proposed IEEE 1394a, or P1394a standard, and the proposed IEEE 1394b, or P1394b standard. Improvements such as higher speeds and longer connection paths will be provided.
In the discussion that follows, it will be necessary to distinguish between the various standards that are being proposed as of the date of this application. Additionally, it will be necessary to distinguish hardware and packet transmissions that are compatible with the P1394b standard and not earlier standards.
Thus, the term “Legacy” will be used herein to refer to the IEEE 1394-1995 standard and all supplements thereof prior to the P1394b standard. Thus, for example, a Legacy node refers to a node compatible with the IEEE 1394-1995 standard and all supplements thereof up to, but not including, the P1394b standard.
Additionally, packets of data will be referred to herein depending on the context the packets are in. For example, a packet of data that is compatible with the P1394b standard and is travelling through a PHY compatible with the P1394b standard will be referred to as Beta format packets. Packets of data that are compatible with the Legacy standard but are travelling through a PHY compatible with the P1394b standard will be referred to as Legacy format packets. Finally, packets of data that are compatible with the Legacy format and are travelling across a data strobe link will be referred to as Alpha format packets.
Furthermore, in the discussion that follows PHYs that are compatible with the P1394b standard may be referred to in various ways, depending upon the context the PHY is operating in and the capability of the PHY. For example, a PHY that has circuitry compatible with the P1394b standard but not any previous standards will be referred to as a B only PHY. Also, a PHY that is compatible with the P1394b standard and is directly attached with only devices compatible with the P1394b standard will be referred to as B PHYs. Finally, a PHY that is communicating with both Legacy devices and devices compatible with the P1394b standard will be referred to as a border device, border PHY, or border node.
Finally, a communications systems that has only B PHYs attached will be referred to as a B bus.
Data Transmission in Legacy Systems
One area that has been improved in the P1394b standard is in the way that data transmission takes place on the bus.
FIG. 1
is a prior art example of a Alpha format data packet
100
according to Legacy specifications. In the Legacy specifications, a data packet will begin with the transmission of a Data Prefix (“DP”) identifier, shown as DP
102
in FIG.
1
. Importantly, in the Legacy specification, a DP must have a duration of no less than 140 nanoseconds (ns), though a DP may be of any greater length.
Typically, a DP is followed by the transmission of clocked data, known as the payload, shown as clocked data
104
in FIG.
1
. On a Legacy bus, the payload will be clocked at a rate of 100 Megabits per second (Mb/s), 200 Mb/s, or 400 Mb/s. These data rates are known as S
100
, S
200
, and S
400
, respectively.
Finally, the payload is followed by a Data End (“DE”), shown as DE
106
in FIG.
1
. In the Legacy specifications, a DE must be at least 240 ns in length.
As is appreciated by one of ordinary skill in the art, the Legacy specifications thus define a timer-based system, where data transmission begins and ends according to a fixed timer.
Compatibility Issues in Legacy Systems
As mentioned above, there are three clocked data rates present in Legacy systems, S
100
, S
200
, and S
400
. Initially, when the IEEE 1394-1995 standard was introduced, devices could only communicate at the S
100
rate. Later, devices were introduced that comnnunicated at the S
200
and S
400
rates.
One problem that occurred in the prior art was how to insure compatibility between the various devices on the market that were communicating at these different rates.
FIG. 2
illustrates such a compatibility problem.
FIG. 2
has three nodes, nodes #
0
, #
1
, and #
2
. Node #
2
, the root node in this example, wishes to communicate with node #
1
. As is indicated in
FIG. 2
, nodes #
1
and #
2
are capable of communicating at the S
400
data rate, while node #
0
is only capable of communication at the lower S
100
rate.
FIG. 3
illustrates the prior art solution of speed filtering on a Legacy bus.
FIG. 3
shows root node #
2
transmitting S
400
data in packet P
1
to node #
1
. In the prior art, to prevent node #
0
from receiving the S
400
data that it cannot understand, it is “shielded” from such data by having root node #
2
transmit a null packet P
2
to it.
In the
FIG. 3
Packet Detail illustration, packets P
1
and P
2
are shown together on a common time axis. Packet P
1
comprises a DP
300
, S
400
data
302
, and a DE
304
. Null packet P
2
comprises a DP
306
, and a DE
308
. As is appreciated by one of ordinary skill in the art, the null packet accomplishes its shielding by extending the DP for the amount of time required to send S
400
data
302
. As is known by those of ordinary skill in the art, on a Legacy bus all nodes must remain synchronized in their interpretation of idle time. Thus, the null packet effectively ‘busies’ node #
0
while root node #
2
transmits S
400
data to node #
1
and thus shields node #
0
from speeds it cannot understand.
Data Transmission in P1394b
FIG. 4
is a representation of the prior art data packet structure according to the P1394b standard. As is known by those of ordinary skill in the art, P1394b utilizes a packet structure that is scaled to speed unlike the fixed timer system utilized in Legacy standards. Specifically, the packet structure in P1394b is based upon symbols, rather than the fixed intervals found in the Legacy standards.
In
FIG. 4
, a typical prior art packet
400
of P1394b data is shown. As is known by those of ordinary skill in the art, a data packet begins in P1394b with the transmission of at least two packet starting symbols. In this example, a Speed Code symbol Sb
1
and a Data Prefix symbol DP
1
are shown as the packet starting symbols. Then, PI394b data bytes B
1
through Bn are transmitted. Bytes B
1
through Bn may be referred to herein as the payload. Finally, the transmission of data is terminated by transmitting DE symbols DE
1
and DE
2
.
Compatibility Problems Between P1394b and Legacy Nodes and Clouds
FIG. 5
shows a data communications system comprising both P1394b and Legacy
Hauck Jerrold V.
Whitby-Strevens Colin
Apple Computer Inc.
Cangialosi Salvatore
Sierra Patent Group Ltd.
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