Overhead Circuit Types
The following table describes the types of overhead circuit that appear in the Type column of the Overhead Circuits tab.
 
Type
Description
User Data - F1
(ONS 15454 only) User data channel (UDC) provisioned on the F1 overhead byte. A UDC circuit allows you to create a dedicated data channel between ONS nodes.
User Data - D4-D12
(ONS 15454 only) User data channel provisioned on the line DCC channels (D4-D12).
Local Orderwire
(ONS 15454 only) Local orderwire circuit. Local orderwire circuits require an AIC-I card at the source and destination node. You cannot create local orderwire circuits if regenerators are used between ONS nodes.
Express Orderwire
(ONS 15454 only) Express orderwire circuit. Express orderwire circuits require a AIC-I card at the source and destination node.
DCC Tunnel - D1-D3
DCC tunnel provisioned on the section DCC channel (D1-D3) to transport traffic from third-party SONET equipment across ONS node networks.
DCC Tunnel - D4-D12
(ONS 15454 only) DCC tunnel provisioned on the line DCC channels (D4-D12).
IP Tunnel - D1-D3
IP tunnel on the section DCC (D1-D3). Creates an IP tunnel on the D1 to D3 overhead bytes. The IP tunnel takes SDCC traffic from non-ONS equipment, encapsulates the traffic into the TCP/IP UDP (user datagram protocol) and sends it across the ONS network to the other ONS node.

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