DM16E1 / DM4E1 Operation and Installation Manual - 204-4001-19
98
This configuration is done essentially by setting up the devices to point to point and cascading aggregate
cards. This means the TX of one device is connected to the RX of the next device and so on until the ring
is closed. By selecting which tributaries will be used and passing through the remaining ones, a low-cost
ring will result.
If backup is desired, a Bidirectional Ring should be used.
15.6. Bidirectional Ring Topology
First and foremost it is important to understand the difference between a Regular-Ring and Cross-Ring
since both can be run under bidirectional rings. Also note that the Main card can be wither associated to
the Aggregate 1 or to the Aggregate 2 slot. The same occurs with the backup card.
In Regular-Ring the main link is supplied by the Main card. As such, the Main card TX of one device is
connected to the Main card RX of the next device and so on until the ring is closed. This ring connects the
Main cards of all devices. The backup link is built similarly but on the opposite direction. This topology
does not allow monofiber interfaces because the TX of a given card is connected to one device and the
RX is connected to another one. This also implies that all cards in each link must be identical. When optic
aggregates are used it is possible to have ring sections with extended range cards.
Figure 29. Example of bidirectional ring with Regular-Ring topology
In Cross-Ring the main link is supplied by the Main card. As such, the Backup card TX fiber of one device
is connected to the Main card RX fiber of the next device and so on until the ring is closed, following the
sequence TX(Backup)->RX(Main). Conversely, the backup link is built connecting the Main card TX to the
Backup card RX of the next device until a ring is closed on the opposite direction to the main link, following
the sequence TX(Main)->RX(Backup). In the resulting architecture, one aggregate card is connected to
only one device. As such, the ring may be segmented into independent connections thus allowing the use
of 2-fiber cards, monofiber cards and electric interfaces (e.g. for radio links), all in the same ring. This ring
also allows aggregate cards to be replaced without losing the data link.
Figure 30. Example of bidirectional ring with Cross-Ring topology
