Multiplex communications – Channel assignment techniques – Using time slots
Reexamination Certificate
1998-05-20
2001-05-29
Kizou, Hassan (Department: 2662)
Multiplex communications
Channel assignment techniques
Using time slots
C370S438000, C370S445000, C370S501000
Reexamination Certificate
active
06240101
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to computer networks, and more particularly to cascading of repeaters in a network.
BACKGROUND OF THE INVENTION
Drastic price reductions of personal computers (PC's) have allowed large and small organizations to give computers to more office workers. An expansion of business often requires that more computers be installed and connected to existing computers and servers. Distribution of tasks among office workers often requires that these computers be linked together on a network.
Local-area networks (LAN's) connect computers in an office complex together. These LAN's are often connected to other LAN's or the Internet. As more computers are installed, the number of connections or ports on the LAN needs to increase. Additional networking equipment must be installed to make the additional ports available.
Repeaters are commonly used to increase the number of ports on a LAN. A repeater typically has four, eight, or sixteen ports. Any transmission to any of the ports is repeated to all the other ports on the repeater. Thus all the ports see transmissions from any of the repeater ports.
As more computers are purchased and installed, additional ports are needed to connect the new computers to the network. Eventually, all of the ports on the repeater are used, so additional repeaters must be installed.
FIG. 1
illustrates cascading of repeaters to increase the number of available ports on a LAN. Repeaters
111
,
112
each have four connections or ports. Stations
22
,
24
,
26
on repeater
111
, and stations
32
,
34
,
36
on repeater
112
, are client computers such as PC's, or server machines.
The fourth port on repeater
111
is connected to the first port of repeater
112
by a cable. Any transmission from stations
22
,
24
,
26
are repeated both to the other stations on repeater
111
, and through the cable to repeater
112
. Repeater
112
then repeats the transmission to its stations
32
,
34
,
36
. The reverse is also true: a transmission from station
36
is repeated by repeater
12
to stations
32
,
34
, but is also repeated to stations
22
24
,
26
by repeater
111
. Thus any transmission from any of the six stations is repeated to the other five stations by the two cascaded repeaters
111
,
112
.
As additional PC's are installed, a third repeater could be cascaded by moving station
36
to the third repeater, and connecting the fourth port of repeater
112
to one of the ports of the third repeater. Thus additional repeaters can be cascaded to existing repeaters to expand the network. Such cascading is sometimes referred to as chaining or daisy-chaining.
There are physical limits to the number of repeaters that can be cascaded together. Delays within the repeaters and from the cables limit the number of repeaters that can be cascaded together. In the 10 Mbps network, this limit is four repeaters, but in the 100 Mbps network, the limit is just two repeaters. Cascading repeaters is somewhat inefficient since one or two ports on each repeater are used for cascading rather than for connecting computers (stations). In the example of
FIG. 1
, only six of the eight ports are used for connecting computer stations.
More efficient networks can be constructed by stacking rather than cascading repeaters.
FIG. 2
shows stacking and cascading of repeaters. A proprietary backplane bus is used to connect repeaters
210
,
212
together using a stacking connector. Stacking bus
18
contains the data and control signals required for the operation of repeaters
10
,
12
as one logical repeater unit. Stacked repeaters
210
,
212
are grouped together as one repeater unit for determining the maximum cascaded-repeater limit.
Since a separate stacking connector couples repeaters
210
,
212
to stacking bus
18
, all of the four ports are available for connecting to computer stations. Repeater
210
connects to four stations
22
,
24
,
26
,
28
, while repeater
212
connects to three stations
34
,
36
,
38
. The fourth port of repeater
212
is used to cascade to repeater
214
using the technique of FIG.
1
. Repeater
214
connects to three more stations
31
,
33
,
35
.
Repeaters
210
,
212
are stacked together while repeaters
212
,
214
are cascaded. Repeater
214
could be cascaded with two more repeaters since repeater
210
is stacked rather than cascaded. Stacked repeaters are grouped together as one repeater unit when determining the limit of repeaters that can be cascaded together. Thus stacking allows for more ports than simple cascading.
FIG. 3
highlights that stacking can occur internally and externally. Repeaters
310
,
312
have stacking connections to internal stacking bus
20
, while repeaters
314
,
316
have stacking connections to internal stacking bus
21
. Buffers
19
,
19
′ buffer signals from internal stacking busses
20
,
21
to external stacking bus
18
. Thus busses
20
,
21
,
18
connect repeaters
310
,
312
,
314
,
316
together, allowing sixteen computer stations to be connected to the four repeaters.
Repeaters
310
,
312
are each separate integrated circuit (IC) chips on repeater board or card
15
, while repeaters
314
,
316
are IC chips on card
17
. External bus
18
is a backplane bus that connects separate repeater cards together on a chassis. Thus 8-port repeater cards can be constructed from four-port repeater chips. Of course, other sizes are possible.
Collisions, Jamming, One-Port-Left
Collisions are error conditions that occur when two or more computer stations simultaneously transmit. When a repeater detects that two of its ports are simultaneously receiving data, it activates a collision signal and transmits a jamming sequence to all ports to prevent another station from beginning transmission. The jamming sequence collides with the data transmitted by the stations. The stations sense a collision by the simultaneous transmit and receive sequences and abort transmission.
Once all stations have stopped transmitting, the repeaters stop sending the jamming sequence. The colliding stations each wait a predetermined amount of time (the backoff period) and then retransmit. The retransmission time is randomly determined for each station.
For a chain of cascaded repeaters, any collision first occurs at a specific point in the chain. The repeater that first detects the collision is the first to generate the jamming sequence. Eventually all repeaters in the chain generate the jamming sequence. Each repeater continues to generate the jamming sequence until exactly one port is inputting data. The repeater that enters the one-port-left state stops jamming the remaining port that is inputting data, but continues to jam the other local ports. When input activity on the remaining port ceases, the repeater stops jamming the other ports.
All repeaters in the chain sequentially enter the one-port-left state once the station causing the collision backs off. The repeaters then exit the one-port-left state in the reverse order.
Detecting One-Port-Left for Stacked Repeaters
When repeaters are stacked together, they must act as one unit. The one-port-left state must be determined for all the stacked repeaters together as if they were all one repeater. The stacking bus contains signals to quickly detect the one-port-left state for the stacked repeaters. The delay to detect one-port-left must be minimized.
FIG. 4
shows an analog solution to detect the one-port-left state of a group of stacked repeaters. The stacking bus includes activity line
18
′ that is pulled low by resistor
42
. When either repeater
410
,
412
receives data or a jam signal on one or more of its ports, it pulls activity line
18
′ high. The voltage on activity line
18
′ is determined by the amount of current through resistor
42
. When only one of repeaters
410
,
412
drives activity line
18
′, then its voltage is I*R where I is the current driven from each repeater to activity line
18
′. When both repeaters
410
,
412
drive activity line
18
&p
Co Ramon S.
Hsu Daniel
Auvinen Stuart T.
Kingston Technology Co.
Kizou Hassan
Logsdon Joseph
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