Cisco ONS 15327 Reference Manual, Release 4.1
Chapter 6, Circuits and Tunnels
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Circuits and Tunnels

Table Of Contents

Circuits and Tunnels

6.1  Circuit Properties

6.1.1  Circuit Status

6.1.2  Circuit States

6.1.3  Circuit Protection Types

6.1.4  Edit Circuits Window

6.2  Manage VT1.5 Bandwidth

6.3  VT Tunnels and Aggregation Points

6.4  DCC Tunnels

6.5  BLSR Protection Channel Circuits

6.6  Path Trace

Circuits and Tunnels

Note The terms "Unidirectional Path Switched Ring" and "UPSR" may appear in Cisco literature. These terms do not refer to using Cisco ONS 15xxx products in a unidirectional path switched ring configuration. Rather, these terms, as well as "Path Protected Mesh Network" and "PPMN," refer generally to Cisco's path protection feature, which may be used in any topological network configuration. Cisco does not recommend using its path protection feature in any particular topological network configuration.

This chapter explains Cisco ONS 15327 STS and virtual tributary (VT) circuits and VT and data communications channel (DCC) tunnels. To provision circuits and tunnels, refer to the Cisco ONS 15327 Procedure Guide.

Chapter topics include:

Circuit Properties

Manage VT1.5 Bandwidth

DCC Tunnels

BLSR Protection Channel Circuits

Path Trace

6.1  Circuit Properties

On the ONS 15327 you can create unidirectional and bidirectional circuits. For path protection circuits, you can create revertive or non-revertive circuits. Circuits are routed automatically or you can manually route them. With the auto range feature, you do not need to build multiple circuits of the same type individually; the Cisco Transport Controller (CTC) can create additional sequential circuits if you specify the number of circuits you need and build the first circuit.

You can provision circuits either before or after cards are installed if the ONS 15327 slots are provisioned for the card that carries the circuit. However, circuits do not carry traffic until the cards are installed and the ports and circuit status is in service (IS); out-of-service, auto in-service (OOS-AINS); or out-of-service, maintenance (OOS-MT).

The ONS 15327 Circuits window, which appears in network, node, and card view, is where you can view information about circuits, including:

Name—Name of the circuit. The circuit name can be manually assigned or automatically generated.

Type—Circuit types are: STS (STS circuit), VT (VT circuit), VTT (VT tunnel), or VAP (VT aggregation point).

Size—Circuit size. VT circuits are 1.5. STS circuit sizes are 1, 3c, 6c, 9c, 12c, 24c, or 48c.

Protection—Type of circuit protection.

Direction—Circuit direction, either two-way or one-way.

Status—Circuit status. See the "Circuit Status" section.

Source—Circuit source in the format: node/slot/port "port name"/STS/VT. (Port name appears in quotes.) Node and slot always appear; port "port name"/STS/VT might appear, depending on the source card, circuit type, and whether a name is assigned to the port. If the circuit size is a concatenated size (3c, 6c, 12c, etc.) STSs used in the circuit are indicated by an ellipsis, for example, "S7..9," (STSs 7, 8, and 9) or S10..12 (STSs 10, 11, and 12).

Destination—Circuit destination in same format (node/slot/port "port name"/STS/VT) as the circuit source.

# of VLANS—Number of VLANS used by an Ethernet circuit.

# of Spans—Number of inter-node links that constitute the circuit. Right-clicking the column displays a shortcut menu from which you can choose to show or hide circuit span detail.

State—Circuit state. See the "Circuit Status" section.

6.1.1  Circuit Status

The circuit statuses that appear in the Circuit window Status column are generated by CTC based on conditions along the circuit path. Table 6-1 shows the statuses that can appear in the Status column.

Table 6-1 ONS 15327 Circuit Status 



CTC is creating a circuit.


CTC created a circuit. All components are in place and a complete path exists from circuit source to destination.


CTC is deleting a circuit.


A CTC-created circuit is missing a cross-connect or network span; a complete path from source to destination(s) does not exist.

In CTC, circuits are represented using cross-connects and network spans. If a network span is missing from a circuit, the circuit status is INCOMPLETE. However, an INCOMPLETE status does not necessarily mean a circuit traffic failure has occurred, because traffic might flow on a protect path.

Network spans are in one of two states: up or down. On CTC circuit and network maps, up spans appear as green lines, and down spans appear as gray lines. If a failure occurs on a network span during a CTC session, the span remains on the network map but its color changes to gray to indicate that the span is down. If you restart your CTC session while the failure is active, the new CTC session cannot discover the span and its span line do not appear on the network map.

Therefore, circuits routed on a failed network span appear as ACTIVE during the current CTC session, but they appear as INCOMPLETE to users who log in after the span failure.


A TL1-created circuit or a TL1-like CTC-created circuit is complete and has upgradable cross-connects. A complete path from source to destination(s) exists. The circuit can be upgraded.


A TL1-created circuit or a TL1-like CTC-created circuit with upgradable cross-connects is missing a cross-connect or circuit span (network link), and a complete path from source to destination(s) does not exist. The circuit cannot be upgraded until missing components are in place.


A TL1-created circuit or a TL1-like CTC-created circuit is complete but has at least one non-upgradable cross-connect. UPSR_HEAD, UPSR_EN, UPSR_DC, and UPSR_DROP connections are not upgradable, so all unidirectional path protection circuits created with TL1 are not upgradable.


A TL1-created circuit or a TL1-like CTC-created circuit with one or more non-upgradable cross-connects is missing a cross-connect or circuit span (network link); a complete path from source to destination(s) does not exist.

6.1.2  Circuit States

State is a user-assigned designation that indicates whether the circuit should be in service or out of service. The states that you can assign to circuits are shown in Table 6-2. To carry traffic, circuits must have a status of active and a state of in service (IS), out of service auto in service (OOS_AINS), or out of service maintenance (OOS_MT). The circuit source port and destination port must also be IS, OOS_AINS, or OOS_MT.

Note OOS_AINS and OOS_MT allow a signal to be carried, but alarms are suppressed.

You can assign a state to circuits at two points:

During circuit creation you can assign a state to the circuit on the Create Circuit wizard.

After circuit creation, you can change a circuit state on the Edit Circuit window.

Table 6-2 Circuit States 



In service; able to carry traffic.


A loopback is initiated on a port that supports an IS circuit. Facility or terminal loopbacks affect circuit traffic. For more information about loopbacks, refer to the "General Troubleshooting" chapter in the Cisco ONS 15327 Troubleshooting Guide.


Out of service; unable to carry traffic.


Out of service, auto in service; alarm reporting is suppressed, but traffic is carried and loopbacks are allowed. Raised fault conditions, whether their alarms are reported or not, can be retrieved on the CTC Conditions tab or by using the TL1 RTRV-COND command. VT circuits change to IS when a signal is received; traffic is carried, but alarms are suppressed and loopbacks are allowed.


Out of service, maintenance; alarm reporting is suppressed, but traffic is carried and loopbacks are allowed. Raised fault conditions, whether their alarms are reported or not, can be retrieved on the CTC Conditions tab or by using the TL1 RTRV-COND command.

PARTIAL is appended to a circuit state whenever all circuit cross-connects are not in the same state. Table 6-3 shows the partial circuit states that can appear.

Table 6-3 Partial Circuit States



At least one connection is OOS and at least one other is in some other state.


At least one connection is OOS_AINS and at least one other is in IS state.


At least one connection is OOS_MT and at least one other is in some other state except OOS.

PARTIAL states can occur during automatic or manual transitions. Some cross-connects transition to IS, while others are OOS_AINS. PARTIAL can appear during a manual transition caused by an abnormal event such as a CTC crash, communication error, or one of the cross-connects could not be changed. Refer to the Cisco ONS 15327 Troubleshooting Guide for troubleshooting procedures.

Circuits do not use the soak timer for transitional states, but ports do. When provisioned as OOS-AINS, the ONS 15327 monitors a circuit's cross-connects for an error-free signal. It changes the state of the circuit from OOS-AINS to IS or to AINS-partial as each cross-connect assigned to the circuit path is completed. This allows you to provision a circuit using TL1, verify its path continuity, and prepare the port to go into service when it receives an error-free signal for the time specified in the port soak timer. Two common examples of state changes you see when provisioning DS-1 and DS-3 circuits using CTC are as follows:

When provisioning VT1.5 circuits and VT tunnels as OOS-AINS, the circuit state transitions to IS shortly after the circuits are created when the circuit source and destination ports are IS, OOS_AINS, or OOS_MT. The source and destination ports on the VT1.5 circuits remain in OOS-AINS state until an alarm-free signal is received for the duration of the soak timer. When the soak timer expires, the VT1.5 source port and destination port states change to IS.

When provisioning STS circuits as OOS-AINS, the circuit and source and destination ports are OOS-AINS. As soon as an alarm-free signal is received the circuit state changes to IS and the source and destination ports remain OOS-AINS for the duration of the soak timer. After the port soak timer expires, STS source and destination ports change to IS.

6.1.3  Circuit Protection Types

The Protection column on the Circuit window shows the card (line) and SONET topology (path) protection used for the entire circuit path. Table 6-4 shows the protection type indicators that you see in this column.

Table 6-4 Circuit Protection Types

Protection Type

The circuit has no protection.


The circuit is protected by a two-fiber bidirectional line switched ring (BLSR).

Path Protection

The circuit is protected by a path protection.


The circuit is protected by a 1+1 protection group.


The circuit is protected by diverse SONET topologies, for example, a BLSR and a path protection, or a path protection and 1+1.


The circuit is routed on a protection channel access path on a two-fiber BLSR. PCA circuits are unprotected.


The circuit is routed on a protection channel access path on two-fiber BLSRs. PCA circuits are unprotected.

Unprot (black)

The circuit is not protected.

Unprot (red)

A circuit created as a fully-protected circuit is no longer protected due to a system change, such as a traffic switch.


Circuit protection types appear in the Protection column only when all circuit components are known, that is, when the circuit status is ACTIVE or UPGRADABLE. If the circuit is in some other status, protection type appears as "unknown."

6.1.4  Edit Circuits Window

Use the Edit Circuits window to view general circuit information, create monitor circuits, change path protection selectors and path protection paths, and change a circuit state. For path protection circuits, you can also:

View the path protection circuit's working and protection paths

Edit the reversion time

Edit the Signal Fail/Signal Degrade thresholds

Change payload defect indication path (PDI-P) settings

Perform maintenance switches on the circuit selector

View switch counts for the selectors

From the Edit Circuits window you can display a detailed circuit map by checking Show Detailed Map. The detailed map allows you to view information about ONS 15327 circuits graphically. Routing information that appears includes:

Circuit direction (unidirectional/bidirectional)

The nodes, STSs, and VTs through which circuit passes including slots and port numbers

The circuit source and destination points


Link protection (path protection, unprotected, BLSR, 1+1) and bandwidth (OC-N)

For BLSRs, the detailed map shows the number of BLSR fibers and the BLSR Ring ID. For path protection configurations, the map shows the active and standby paths from circuit source to destination, and it also shows the working and protect paths.

Alarms and states can also be viewed on the circuit map, including:

Alarm states of nodes on the circuit route

Number of alarms on each node organized by severity

Port service states on the circuit route

Alarm state/color of most severe alarm on port


Path trace states

Path selectors states

By default, the working path on the detailed circuit map is indicated by a green, bidirectional arrow, and the protect path is indicated by a purple, bidirectional arrow. Source and destination ports are shown as circles with an S and D. Port states are indicated by colors, shown in Table 6-5.

Table 6-5 Port State Color Indicators

Port Color







Light blue


Notation within the squares on each node indicate switches and other conditions. Move the mouse cursor over nodes, ports, and spans to see tooltips with information including the number of alarms on a node (organized by severity), a port's state of service (for example, in-service, out-of-service), and the protection topology.

Right-click a node, port, or span on the detailed circuit map to initiate certain circuit actions:

Right-click a unidirectional circuit destination node to add a drop to the circuit.

Right-click a port containing a path trace capable card to initiate the path trace.

Right-click a path protection span to change the state of the path selectors in the path protection circuit.

6.2  Manage VT1.5 Bandwidth

The ONS 15327 XTC card performs port-to-port, time-division multiplexing (TDM). Because VT1.5 multiplexing is STS-based, understanding how VT1.5 circuits use the XTC VT matrix resources is necessary to avoid unexpected depletion of the VT matrix capacity. The key VT matrix principles are as follows:

The VT matrix has 24 logical STS ports. All VT1.5 multiplexing is achieved through these logical STS ports.

Each VT matrix STS port has capacity for 28 VT1.5s. Therefore, the VT matrix has a capacity for 672 VT1.5 terminations.

Because each logical STS termination on the VT matrix can carry 28 VT1.5s, the VT matrix capacity is 672 VT 1.5s (24 times 28).

The XTC card can map up to 24 STSs for VT1.5 traffic. Because one STS can carry 28 VT1.5s, the XTC card can terminate up to 672 VT1.5s or 336 VT1.5 cross-connects. However, to terminate 336 VT1.5 cross-connects:

Each STS mapped for VT1.5 traffic must carry 28 VT1.5 circuits. If you assign each VT1.5 circuit to a different STS, the XTC card VT1.5 cross-connect capacity is reached after you create 12 VT1.5 circuits.

ONS 15327s must be in a BLSR. Source and drop nodes in path protection or 1+1 (linear) protection have capacity for only 224 VT1.5 cross-connects because an additional STS is used for the protect path.

6.3  VT Tunnels and Aggregation Points

To maximize XTC VT1.5 cross-connect resources, you can tunnel VT1.5 circuits through ONS 15327 nodes. VT1.5 tunnels do not use VT matrix capacity at ONS 15327 pass-through nodes, thereby freeing the XTC card cross-connect resources for other VT1.5 circuits.

VT aggregation points (VAPs) allow you to provision BLSR circuits from multiple VT1.5 sources to a single STS destination. Like circuits, a VAP has a source and a destination. The source is the STS grooming end, the node where the VT1.5 circuits are aggregated into a single STS. The VAP STS must be a port on an OC-N card. VT matrix resources are not used on the VAP source node, which is the key advantage of VAPs. The VAP destination is the node where the VT1.5 circuits originate. Circuits can originate on any ONS 15327 card.

6.4  DCC Tunnels

SONET provides four DCCs for network element operations, administration, maintenance, and provisioning: one on the SONET Section layer (DCC1) and three on the SONET Line layer (DCC2, DCC3, DCC4). The ONS 15327 uses the Section DCC for ONS 15327 management and provisioning.

You can use the three Line DCCs and the Section DCC (when not used for ONS 15327 DCC terminations) to tunnel third-party SONET equipment across ONS 15327 networks. A DCC tunnel end-point is defined by Slot, Port, and DCC, where DCC can be either the Section DCC or one of the Line DCCs. You can link a Section DCC to an Line DCC and a Line DCC to a Section DCC. You can also link Line DCCs to Line DCCs and link Section DCCs to Section DCCs. To create a DCC tunnel, you connect the tunnel endpoints from one ONS 15327 optical port to another.

Table 6-6 shows the DCC tunnels that you can create.

Table 6-6 DCC Tunnels

OC-3, OC-12, OC-48



D1 to D3




D4 to D6




D7 to D9




D10 to D12


When you create DCC tunnels, keep the following guidelines in mind:

Each ONS 15327 can have up to 32 DCC tunnel connections.

Each ONS 15327 can have up to 10 Section DCC terminations.

A section DCC that is terminated cannot be used as a DCC tunnel endpoint.

A section DCC that is used as a DCC tunnel endpoint cannot be terminated.

All DCC tunnel connections are bidirectional.

6.5  BLSR Protection Channel Circuits

You can provision circuits to carry traffic on BLSR protection channels when conditions are fault-free. Traffic routed on BLSR protection channels, called extra traffic, has lower priority than the traffic on the working channels and is unprotected. During ring or span switches, protection channel circuits are preempted and squelched. For example, in an OC-48 BLSR, STSs 25-48 can carry extra traffic when no ring switches are active, but protection channel circuits on these STSs are preempted when a ring switch occurs. When the conditions that caused the ring switch are remedied and the ring switch is removed, protection channel circuits are restored if the BLSR is provisioned as revertive.

Provisioning traffic on BLSR protection channels is performed during circuit provisioning. The protection channel check box appears whenever Fully Protected Path is unchecked on the circuit creation wizard. Refer to the Cisco ONS 15327 Procedure Guide for more information.

6.6  Path Trace

The SONET J1 Path Trace is a repeated, fixed-length string comprised of 64 consecutive J1 bytes. You can use the string to monitor interruptions or changes to circuit traffic. Table 6-7 shows the ONS 15327 cards that support path trace.

Table 6-7 ONS 15327 Cards Capable of Path Trace

J1 Function

Transmit and receive

XTC (DS-1)


Receive only

OC3 IR 4 1310

OC12 IR 1310

OC12 LR 1550

OC48 IR 1310

OC48 LR 1550

The J1 path trace transmits a repeated, fixed-length string. If the string received at a circuit drop port does not match the string the port expects to receive, an alarm is raised. Two path trace modes are available:

Automatic—The receiving port assumes that the first J1 string it receives is the baseline J1 string.

Manual—The receiving port uses a string that you manually enter as the baseline J1 string.