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1.4 Stacking the hubs
Up to four hubs can be stacked to operate as one 10/100 dual-speed repeater with up to
32 dual-speed ports. One DS8-B hub per stack is needed to provide a switched intercon-
nection between the two separate 100Mbps and 10Mbps traffic domains in the stack. addi-
tional stacked units can be model DS8-A hubs.
The DS8-B models with the bridge module inside look the same as the DS8-A units (no
bridge inside). The “BR” LED on the front will light up when power is applied to indicate
that a bridge module is installed. (The “BR” LED will be off if the unit is a model DS8-A).
The DS8-B models cannot be stacked together, as their internal bridges would not be able
to function properly when more than one is present. Use DS8-B models un-stacked, or with
only 1 model DS8-B in a DS8 stack.
When stacking the units make sure to use only the shielded 9-inch long stacking cable pro-
vided with each DS8-A unit. The cable length is designed to provide proper operation of
up to four units in a stack, and longer cables or unshielded cables are not permitted as they
will not operate properly at 100Mbps speeds.
The 9-inch length is enough to provide for side-by-side stacking. This can be convenient
when locating the units in a rack, for example, as two DS8 hubs will fit side-by-side on a
tray in a standard 19” rack space.
When connecting DS8 hubs in a stack, use the stacking cable to connect the “Out” stack-
ing port from one unit to the “In” stacking port of the other. Push in the cable connectors
until they snap in firmly. Also, leave space in the left-rear area for the exhaust of the inter-
nal cooling fan in each unit.
1.5 Bridge module (model DS8-B)
The DS8-B hubs contain a factory-installed bridge module to interconnect the two traffic
domains, filtering and selectively forwarding packets to allow necessary packets to cross
between the domains. This enables all of the users and modules connected into either
domain, whether 100Mbps or 10Mbps to talk to each other and it keeps local traffic on one
domain from consuming any of the bandwidth of the other domain.
A
A
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Packet Source
Destination
Address
table
Filter/forward
source
address
address
maintenance
action
10Mb
Not in table
Not in table
Add source to table
Forward
10Mb
Not in table
In table
Add source to table
Filter
10Mb
In table
Not in table
None
Forward
10Mb
In table
In table
None
Filter
100Mb
Not in table
Not in table
Add source to table
Forward
100mb
Not in table
In table
Add source to table
Filter
100Mb
In table
Not in table
None
Forward
100Mb
In table
In table
None
Filter
2. Address learning (address table maintenance)
The DS8-B bridge module is a state machine design which has a total address table capac-
ity of 8K addresses. With a large address table, a dual-speed hub can serve the needs of a
medium to large network. The table shows what filter/forward action the DS8-B hub will
take in each packet-processing situation, and when a new node address will be added to
the internal address table. When a new node-address packet comes into a port for the first
time, then the new source address is “learned” at the same time that the packet is for-
warded. After learning, subsequent packets from the same node address are routinely
processed. The address table are flushed periodically to update the network status and to
purge any inactive station from the tables of both domains.
3. Throughput increase
By selectively forwarding packets from each domain to the other domain based on its
switching (bridging) logic, the DS8-B hub increases the available bandwidth for the users
on both sides of the network. As shown in the table it keeps the local traffic on each side
contained, preventing unnecessary packets and bad packets from travelling to the other
domain and using up bandwidth needlessly over there. This results in more available net-
work bandwidth on both sides and the throughput increase for all users on both domains.
4. Software transparency
The
RS
dual-speed hubs need no software set-up and are transparent to system and appli-
cation software, including network management software.
3.2 Auto-negotiation and speed-sensing
All eight RJ-45 ports independently support auto-negotiation for shared 10BASE-T and
100BASE-TX modes. When the ‘100’ LED is flashing it means that the corresponding port
is sending out auto-negotiating pulses out of that port. When a connection is made, the
other device should respond and both sides should agree to the speed being detected.
Depending upon the device connected, it will either operate at 10Mb or 100Mb speeds.
Silence means the port defaults to 10mbps.
When the ‘100’ LED is ON, the port has auto-negotiated for 100Mbps operation and is pro-
cessing packets at 100Mbps. When it is OFF, it is at 10Mbps. If a port is connected to a non-
negotiating device, it will default to 10Mbps speed. The dual-speed will operate in the
shared or half-duplex mode on all ports.
3.3 LED Description
PWR:
Illuminates GREEN to indicate ac power is applied to the unit
BR:
Bridge module LED
ON when a bridge module is present in the unit (model DS8-B)
OFF when no bridge module is present (model DS8-A)
A. Fan exhaust
A. Bridge module
Figure 1
Figure 2
