Specifications

5-7
Cisco ONS 15454 Installation and Operations Guide, R3.2
March 2002
Chapter 5 SONET Topologies
Bidirectional Line Switched Rings
5.2.3 K3 Byte Remapping
The ONS 15454 uses the K3 overhead byte for BLSR automatic protection switching (APS) to allow an
ONS 15454 BLSR to have more than 16 nodes. If a BLSR is routed through third-party equipment that
cannot transparently transport the K3 byte, you can remap it to either the Z2, E2, or F1 bytes on OC48AS
cards. (K3 byte remapping is not available on other OC-N cards.) If you remap the K3 byte, you must
remap it to the same byte on each BLSR trunk card that connects to the third-party equipment. All other
BLSR trunk cards should remain mapped to the K3.
For example, in Figure 5-7, a BLSR span between Node 2 and Node 4 passes through third-party
equipment. Because this equipment cannot transparently transport the K3 byte, the OC48AS card at
Node 2/Slot 12 and the OC48AS card at Node 4/Slot 5 are provisioned to use an alternate byte. Other
BLSR trunk cards are not changed.
Figure 5-7 A BLSR with a remapped K3 byte
Do not perform K3 byte remapping unless it is required to complete a BLSR that uses third-party
equipment. For K3 byte remapping procedures, see the “Remap the K3 Byte” procedure on page 5-14.
5.2.4 BLSR Bandwidth
BLSR nodes can terminate traffic that is fed from either side of the ring. Therefore, BLSRs are suited
for distributed node-to-node traffic applications such as interoffice networks and access networks.
BLSRs allow bandwidth to be reused around the ring and can carry more traffic than a network with
traffic flowing through one central hub. BLSRs can also carry more traffic than a UPSR operating at the
same OC-N rate. Table 5-2 shows the bidirectional bandwidth capacities of two-fiber BLSRs. The
71088
Node 1
West East
West East
West East
West East
Third party
optical equipment
Slot 5
Slot 12
Node 3
Slot 5
Slot 12
Node 2
Slot 5
Slot 12
Node 4
Slot 5
Slot 12
Remapped
K3