6-20
Cisco ONS 15454 Installation and Operations Guide
November 2001
Chapter6 Circuits and Tunnels
Cross-Connect Card Capacities
Figure6-14 A six-node ring with two VT1.5 tunnels
When planning VT1.5 circuits, weigh the benefits of using tunnels with the need to maximize STS
capacity. For example, a VT1.5 tunnel between Node 1 and Node 4 passing ( tr anspa rent ly) thr ough
Nodes 2 and Node 3 is advantageous if a full STS is used for Node 1 – Node 4 VT1.5 traffic (that is, the
number of VT1.5 circuits between these nodes is close to 28). A VT tunnel is required if:
•Node 2 or Node 3 have XC cards, or
•All VT1.5-mappable STSs at Node 2 and Node 3 are in use.
However, if the Node 1 – Node 4 tunnel will carry few VT1.5 circuits, creating a regular VT1.5 circuit
between Nodes 1, 2, 3, and 4 might maximize STS capacity.
When you create a VT1.5 circuit, CTC determines whether a tunnel already exists betw een sour ce and
drop nodes. If a tunnel exists, CTC checks the tunnel capacity. If the capacity is sufficient, CTC routes
the circuit on the existing tunnel. If a tunnel does no t e xis t, or if an exi sti ng tunne l d oes n ot ha ve
Table6-5 VT1.5-Mapped STS Use in Figure 6-6
Node VT Tunnel (BLSR) VT Tunnel (UPSR, 1+1) No VT Tunnel (BLSR) No VT Tunnel (UPSR) No VT Tunnel (1+1)
14 6 4 6 6
20 0 4 3 8
32 3 4 3 6
42 3 2 3 3
50 0 0 2 0
60 0 0 2 0
61851
VT1.5 source
Node 1
Node 4
VT1.5
drop
Node 2
Node 3
VT Tunnel
Node 6 28 VT1.5
circuits
28 VT1.5
circuits
Node 5
VT1.5
drop
BLSR