Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via frequency channels
Reexamination Certificate
1999-06-04
2002-09-17
Chin, Wellington (Department: 2735)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via frequency channels
C370S352000
Reexamination Certificate
active
06452946
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to master and slave communications systems, and more particularly to a technique for exchanging data between a master system and multiple slave systems.
BACKGROUND OF THE INVENTION
Master and slave communications systems exist in many forms.
FIG. 1
is a depiction of an exemplary master and slave communications system
10
that has a main controller
12
acting as the master system and various peripherals
16
,
18
, and
20
acting as the slave systems. The peripherals are remote to the main controller, but are connected to the main controller via a remote node
14
. The node
14
is located at the same site
21
as the peripherals, and functions to minimize the number of connections that are required between the main controller and the peripherals. The connection
22
between the main controller and the remote node can be through a direct cable connection or the connection can be made through a network such as an intranet or the Internet. An application for the master and slave communications system as shown in
FIG. 1
is a campus communications system having a main PBX that handles many of the communications functions of the campus and having remote nodes that support the operation of devices such as telephones, fax machines, printers and computers.
FIG. 2
is an expanded view of a remote node
24
that is connected to a main PBX
26
as described with reference to FIG.
1
. The remote node includes three line shelves
28
,
30
, and
32
, with each line shelf having the capacity to support sixteen line cards
34
,
36
,
38
, and
40
. The line cards in
FIG. 2
represent the peripherals
16
,
18
, and
20
in FIG.
1
. The line cards typically have the ability to support up to twenty-four terminal devices (i.e., telephone, fax, printer, computer, etc.). In the system of
FIG. 2
, the main PBX is the master system and the line cards are the slave systems.
At the data link layer, or layer
2
, of the open systems interconnection (OSI) model, the main PBX
26
and the line cards
34
-
36
communicate with each other using protocols such as binary synchronous control (BSC), synchronous data link control (SDLC), or high-level data link control (HDLC). The data link layer protocols are intended to ensure error-free and reliable point-to-point transmissions of data. When errors do occur in the transmission of data, the data link layer protocols initiate the retransmission and/or correction of the errors.
In systems such as the one shown in
FIG. 2
, the main PBX
26
is continuously exchanging frames of data with the line cards
34
-
40
(peripherals). The exchange of data may include determining the status of the line cards or exchanging data such as real-time voice conversations, e-mail messages, voice mail messages, FAX data, printer data, etc. For example, the main PBX may signal the line cards to determine if the line cards can receive data or if the line cards need to send data to the main PBX. In another example, the main PBX may transfer printer data to a line card that will be used by an attached printer to generate a document. Referring specifically to line shelf one
28
, frames of data are continuously being sent back and forth between the main PBX and the sixteen line cards. The frames are exchanged in a sequential manner, and before the main PBX can exchange frames with the next line card, the main PBX must wait to receive a response from the current line card.
FIG. 3
is an example of an exchange of frames that takes place according to HDLC protocol between the main PBX
26
and the sixteen line cards
34
-
40
shown in
FIG. 2. A
polling frame (POLL)
46
is first transmitted from the main PBX to line card one, and in response a receive ready (RR), or acknowledgment, frame
48
is transmitted from line card one to the main PBX. Next, a polling frame
50
is transmitted from the main PBX to line card two
36
and an information frame (I-Fr)
52
is transmitted back to the main PBX in response. The main PBX responds to the information frame with a receive ready frame
54
to complete the transmission. Next, the main PBX transmits an information frame
56
to line card three and a receive ready frame
58
is transmitted back to the main PBX in response. Shown as an example, if a polling frame
60
receives no response because a line card is removed or malfunctioning, a time-out
62
may be triggered after a time-out period (e.g., 2 ms) has expired. The sequential exchange of frames continues through all sixteen line cards to complete one exchange cycle. Possible transaction times are shown on the time-line at the left side of the figure. In the example shown, one signaling cycle through a sixteen-card line shelf takes approximately ten milliseconds, as denoted by the right-side time-line.
Because frames of data must be exchanged sequentially and bidirectionally between the main PBX
26
and the line cards
34
-
40
, a minimum of thirty-two transmissions are performed between the main PBX and the remote node
24
in one exchange cycle. The total time required to complete one exchange cycle is at least thirty-two times the time required to transmit one frame from the main PBX to the remote node. The sequential nature of the signaling between the main PBX and the line cards makes the system extremely sensitive to transmission delays that occur between the main PBX and the line cards. When the distance between the main PBX and the line cards is relatively great, the likelihood of transmission delay increases. In delay-sensitive communications systems, such as communications systems carrying real-time voice and/or video data, the main PBX and line cards are required to be relatively close to each other in order to maintain the quality of the transmitted data. However, in many situations it is advantageous to locate remote nodes far from the main PBX such that delay problems become quite likely.
As a result of the need to locate remote nodes at a relatively long distance away from the main PBX, there is still a need for a communications system that can exchange time-critical data between a master system and multiple slave systems in a timely manner, even though the master and slave systems are separated by a communications link that may exhibit significant delay.
SUMMARY OF THE INVENTION
A method and a system for improving the exchange of data between a master system and multiple slave systems involve bundling multiple abbreviated messages into a single frame and transmitting the single frame across a long delay communications link. The abbreviated messages do not comply with a given transmission protocol, but the single frame does. At the receiving end, the abbreviated messages are extracted from the single frame to build multiple protocol-compliant frames that are sequentially transmitted across relatively short delay communications links to the individual slave systems. By bundling multiple abbreviated messages into a single frame, the number of frame transmissions required across the long delay communications link is significantly reduced.
In a preferred embodiment, the master and slave communications system includes a main PBX and a remote node that communicate at the data link layer of the OSI model according to the high-level data link control (HDLC) protocol. The main PBX includes a main HDLC controller, while the remote node includes a remote HDLC controller and sixteen line cards on each of three line shelves. The main PBX is preferably connected to the public switched telephone network (PSTN), although this is not critical to the invention.
The main HDLC controller is a subsystem that generates combined-message frames which are transmitted according to HDLC protocol to the remote node. A combined-message frame is formed by combining, or bundling, address-specific messages together into an information field of the combined-message frame. The address-specific messages are generated by the main HDLC controller and, in a preferred embodiment, represent an abbreviated version of the data that is necessary t
Chin Wellington
Pham Brenda
Siemens Information and Communications Network, Inc.
LandOfFree
Apparatus and method for improving performance in master and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for improving performance in master and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for improving performance in master and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2883952