IBM 8260 manual Passive Port Technology, Active Port Technology

wideband/wideband configuration when the port is in trunk mode. This is done to ensure that when the ring is reconfigured outside the module, a signal with a lot of accumulated jitter does not hit a wideband/narrowband configuration until it has gone through a JADC to remove the excessive jitter.

So, the following is a summary of the differences between the active and passive modules.

∙A passive module has no active re-timing from port to port. The data is passed sequentially through the ports using relays to bypasses unused ports.

∙The signal is re-timed and re-amplified for each port on the active modules. This allows longer lobes and a higher number of stations per ring segment.

∙On the active modules, the DPLL on each port converts the analog signal from the external station to digital for transmission to the backplane. This means that the signal on the active modules are in digital form, making it economically possible to offer per-port switching on the active modules by using a switch fabric on the module that can switch the signals from each port to any one of the 10 backplane rings on the ShuntBus.

Note: Currently, the Dual Fiber Repeater module and the 18-port per-port switching modules allow you to perform per-port switching.

8.5Passive Port Technology

In the passive module implementation, the data is switched from port to port with no active re-timing or regenerative element between ports. This is done by a relay on each port. Data from attached workstations is passed from one port to the next without any re-timing and regeneration. Note that if a port is disabled or not used, the relay on that port will be wrapped to prevent the station on that port from entering the ring. This will result in the signal flowing to the active ports on each module.

On a passive module, as the signal moves from one port to another, jitter accumulated. Therefore, to pass the signal from the passive module to the backplane, we must remove the accumulated jitter and also convert the signal from analog to digital. In the opposite direction, we must convert the signal from digital to analog, before passing the signal from the backplane to the passive module.

8.6 Active Port Technology

In the active module implementation, each port contains a Dual Phase Lock Loop (DPLL) function. DPLL performs the following functions:

1.It removes the jitter received on each port before passing it to the next port on the module.

The advantage of this function is that with the active modules, the maximum number of stations supported on a 4 and 16 Mbps ring is always 250 stations regardless of the type of cabling used. Also, you are allowed to mix UTP and STP cabling on the same module and/or the same ring segment of the 8260. For example, you can mix up to 250 stations connected to the 8260 active modules using STP and various types of UTP (category 3, 4 and 5) to form a single ring operating at 4 or 16 Mbps.

142 8260 Multiprotocol Intelligent Switching Hub