Overhead Circuit Types
The following table shows the overhead circuit types that might appear in the Type column of the Overhead Circuits tab.
 
Type
Description
User Data - F1
Creates a UDC circuit on the F1 overhead byte. A UDC circuit allows you to create a dedicated data channel between ONS nodes.
User Data - D4-D12
Creates a UDC circuit on the MS-DCC (D4 to D12) overhead bytes.
Local Orderwire
Creates a local orderwire overhead circuit. Local orderwire circuits require an AIC or AIC-I card at the source and destination nodes. You cannot create local orderwire circuits if regenerators are used between ONS nodes.
Express Orderwire
Creates an express orderwire overhead circuit. Express orderwire circuits require an AIC-I card at the source and destination nodes.
DCC Tunnel - D1-D3
Creates a DCC tunnel on the SDH RS-DCC (D1 to D3) overhead bytes.
DCC Tunnel - D4-D12
Creates a DCC tunnel on the SDH MS-DCC (D4 to D12) overhead bytes.
IP Tunnel - D1-D3
Creates an IP tunnel on the D1 to D3 RS-DCC overhead bytes. The IP tunnel takes RS-DCC traffic from non-ONS equipment, encapsulates the traffic into the TCP/IP UDP and sends it across the ONS network to the other ONS node.

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