Zhone’s SLMS devices use two types of bridges — symmetric bridges which have the same bridging behavior and asymmetric bridge which have different bridging behavior.
The bridge interfaces for symmetric bridges provide the same bridging behavior (bridge interfaces for TLS are the one example of a symmetric bridge interface) and bridge interfaces for asymmetric bridges provide different bridging behavior.
Uplink and downlink bridge configurations are the most common asymmetric bridges but intralink bridges are also asymmetric bridges. The different behavior for these four bridge types are useful in creating network bridges.
Symmetric bridges use TLS and wire bridge interfaces:
TLS bridge interfaces have the same behavior regardless of which ports are being bridged.
TLS bridge interfaces only work in conjunction with other TLS bridge interfaces. The bridge path is automatically created with default static bridge parameters.
Wire bridge interfaces, which are a reserved TLS bridge, have the same behavior regardless of the ports being bridged.
A wire bridge is only connected to another wire bridge in a two bridge interface configuration and reserves a VLAN ID for two ports for the entire system.
Note: When a VLAN ID is used for two wire bridges, that VLAN ID cannot be used anywhere else on the system.
Asymmetric bridges use three different bridge interface types:
Uplinks
Uplinks are normally used for upstream traffic toward the Internet core.
Uplink bridge interfaces only work in conjunction with asymmetric bridge interfaces.
Downlinks
Downlinks are normally used for downstream traffic toward the subscribers.
Downlink bridge interfaces only work in conjunction with asymmetric bridge interfaces.
Intralinks
Intralinks are normally used for subtending other SLMS devices.
Intralink bridge interfaces only work in conjunction with asymmetric bridge interfaces.
Asymmetric bridges are made up of one uplink and at least one downlink or intralink.
A single bridge asymmetric bridge may use all three asymmetric bridge interface types — uplink, downlink, and intralink — however, a single bridge may only have one uplink. The system may have multiple intralinks per bridge, but other SLMS devices may only have one intralink. There may be multiple downlinks.
Most commonly there is one uplink and multiple downlinks as you would have with a line concentrator which splits a high capacity upstream link into mulitple lower capacity downstream links. Intralink bridge interfaces are used for subtending other devices. Intralinks have different learning behavior than uplinks or downlinks.
When setting up Internet access for multiple subscribers you configure the system as a line concentrator. With the line concentrator model you create an asymmetric bridge with a high capacity link upstream configured to be the uplink, and have many downlinks configured for the subscribers.
For more information about bridging on Zhone devices see the manuals on Zhone website http://www.zhone.com/support/manuals/.
October 9, 2011