Cisco ONS 15454 SDH Reference Manual, Release 4.0
Chapter 9, Circuits and Tunnels
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Circuits and Tunnels

Table Of Contents

Circuits and Tunnels

9.1 Overview

9.1.1 VC High-Order Path Circuits

9.1.2 VC Low-Order Path Tunnels for Port Grouping

9.2 Viewing Circuit Properties

9.2.1 Circuit Status

9.2.2 Circuit States

9.2.3 Circuit Protection Types

9.2.4 Viewing Circuit Information on the Edit Circuit Window

9.3 Cross-Connect Card Capacities

9.4 DCC Tunnels

9.5 Multiple Drops for Unidirectional Circuits

9.6 Creating Monitor Circuits

9.7 SNCP Circuits

9.8 MS-SPRing Protection Channel Circuits

9.9 J1 Path Trace

9.10 Path Signal Label, C2 Byte

9.11 Automatic Circuit Routing

9.11.1 Bandwidth Allocation and Routing

9.11.2 Secondary Sources and Drops

9.12 Manual Circuit Routing

9.13 Constraint-Based Circuit Routing


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 15454 high-order and low-order circuits and low-order and DCC tunnels. To provision circuits and tunnels, refer to the Cisco ONS 15454 SDH Procedure Guide. Chapter topics include:

Overview

Viewing Circuit Properties

Cross-Connect Card Capacities

DCC Tunnels

Multiple Drops for Unidirectional Circuits

Creating Monitor Circuits

SNCP Circuits

MS-SPRing Protection Channel Circuits

J1 Path Trace

Automatic Circuit Routing

Manual Circuit Routing

Constraint-Based Circuit Routing

9.1 Overview

You can create VC high-order path circuits and VC low-order path tunnels across and within ONS 15454 SDH nodes and assign different attributes to circuits. For example, you can:

Create one-way, two-way, or broadcast circuits.

Assign user-defined names to circuits.

Assign different circuit sizes. The E3 and DS3i cards must use VC low-order path tunnels. E1 cards, optical cards, and Ethernet cards use VC high-order path circuits. Available sizes are VC4, VC4-2c, VC4-3c, VC4-4c, VC4-8c, VC4-16c, and VC4-64c for optical cards and some Ethernet cards depending on the card type. Of the Ethernet cards, only the G-1000 can use VC4-3c and VC4-8c.

Automatically or manually route VC high-order path circuits.

Automatically route VC low-order path tunnels.

Automatically create multiple circuits.

Provide full protection to the circuit path.

Provide only protected sources and destinations for circuits.

Define a secondary circuit source or destination that allows you to interoperate an ONS 15454 SDH subnetwork connection protection (SNCP) ring with third-party equipment SNCPs.

Create PCA circuits. You can provision circuits to carry traffic on MS-SPRing protection channels when conditions are fault-free. Traffic routed on MS-SPRing protection channels, called extra traffic, has lower priority than the traffic on the working channels and has no means for protection.

During ring or span switches, protection channel circuits are pre-empted and squelched. For example, in a 2-fiber STM-16 MS-SPRing, VC4s 9-16 can carry extra traffic when no ring switches are active, but protection channel circuits on these VC4s are pre-empted when a ring switch occurs. When the conditions that caused the ring switch are corrected and the ring switch removed, protection channel circuits are restored (assuming the MS-SPRing is provisioned as revertive).

Provisioning traffic on MS-SPRing protection channels is performed during circuit provisioning. The protection channel checkbox displays whenever Fully Protected Path is deselected on the circuit creation wizard. See the Cisco ONS 15454 SDH Procedure Guide for more information. When provisioning protection channel circuits, two considerations are important to keep in mind:

If MS-SPRings are provisioned as non-revertive, protection channel circuits will not be restored following a ring or span switch until the MS-SPRing is manually switched.

Protection channel circuits will be routed on working channels when you upgrade an MS-SPRing, either from a a 2-fiber to a 4-fiber, or from one optical speed to a higher one. For example, if you upgrade a 2-fiber STM-16 MS-SPRing to an STM-64, VC4s 9-16 on the STM-16 MS-SPRing become working channels on the STM-64 MS-SPRing.

9.1.1 VC High-Order Path Circuits

The E1 card, STM-N cards, and Ethernet cards all use high-order path circuits. You can create unidirectional or bidirectional, revertive or non-revertive, high-order path circuits. Cisco Transport Controller (CTC) can route circuits automatically or you can use CTC to manually route circuits.

You can provision circuits at any of the following points:

Before cards are installed. The ONS 15454 SDH allows you to provision slots and circuits before installing the traffic cards. (To provision an empty slot, right-click it and select a card from the shortcut menu.) However, circuits cannot carry traffic until you install the cards and place their ports in service. For card installation procedures and ring-related procedures, see the Cisco ONS 15454 SDH Procedure Guide.

After cards are installed, but before their ports are in service (enabled). You must place the ports in service before circuits will carry traffic.

After cards are installed and their ports are in service. Circuits will carry traffic as soon as the signal is received.


Note Circuits assigned to a state other than OOS using an E1, E3, and DS3i card for the source and destination ports can change to IS even though a signal is not present on the ports. Some cross connects transition to IS, while others are OOS_AINS. A circuit state called partial may appear during a manual transition for some abnormal reason, such as a CTC crash, communication error, or one of the connections could not be changed.


9.1.2 VC Low-Order Path Tunnels for Port Grouping

VC low-order path tunnels can be created for the E3 and DS3i cards. VC low-order path tunnels (VC_LO_PATH_TUNNEL) are automatically set to bidirectional with port grouping enabled. Three ports form a port group. For example, in one E3 or one DS3i card, four port groups are available: Ports 1 to 3 = PG1, Ports 4 to 6 = PG2, Ports 7 to 9 = PG3, and Ports 10 to 12 = PG4.


Note CTC shows VC3-level port groups, but the XC10G creates only VC4-level port groups. VC4 tunnels must be used to transport VC3 signal rates.


Tunnels are routed automatically. The following rules apply to port-grouped circuits:

A port group goes through a VC_LO_PATH_TUNNEL circuit, with a set size of VC4.

The circuit must be bidirectional and cannot use multiple drops.

The circuit number must be set to one.

The Auto-ranged field must be set to Yes.

The Use secondary destination field must be set to No.

The Route Automatically field must be set to Yes.

Monitor circuits cannot be created on a VC3 circuit in a port group.

Circuits assigned to a state other than OOS using an E1, E3, and DS3i card for the source and destination ports can change to IS even though a signal is not present on the ports. Some cross connects transition to IS, while others are OOS_AINS. A circuit state called partial may appear during a manual transition for some abnormal reason, such as a CTC crash, communication error, or one of the connections could not be changed.

You can provision circuits at any of the following points:

Before cards are installed. The ONS 15454 SDH allows you to provision slots and circuits before installing the traffic cards. (To provision an empty slot, right-click it and select a card from the shortcut menu.) For card installation procedures and ring-related procedures, see the Cisco ONS 15454 SDH Procedure Guide.

After cards are installed, but before ports are in service (enabled). You must place the ports in service before circuits will carry traffic.

After cards are installed and their ports are in service. Circuits will carry traffic when the signal is received.

9.2 Viewing Circuit Properties

The ONS 15454 Circuits window (Figure 9-1) 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: HOH (high-order circuit), LOH (low-order circuit), VCT (VC low-order tunnel), or VCA (VC low-order aggregation point).

Size—Circuit size. Low-order circuits are VC12 and VC3. High-order circuit sizes are VC4, VC4-3c, VC4-4c, VC4-8c, VC4-16c, VC4-64c.

Protection—The type of circuit protection. See the "Circuit Protection Types" section.

Direction—The circuit direction, either two-way or one-way.

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

Source—The circuit source in the format: node/slot/port "port name"/virtual container/tributary unit group/tributary unit group/virtual container. (Port name will appear in quotes.) Node and slot will always display; port "port name", virtual container and tributary units might display, depending on the source card, circuit type, and whether a name is assigned to the port. If the circuit size is a concatenated size (4-2c 4-4c, 4-8c, etc.) VCs used in the circuit will be indicated by an ellipsis, for example, "VC7..9," (VCs 7, 8, and 9) or VC10..12 (VC 10, 11, and 12).

Destination—The circuit destination in same format (node/slot/port "port name"/vc/tug) as the circuit source.

# of VLANS—The number of VLANS used by an Ethernet circuit.

# of Spans—The 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—The circuit state. See the "Circuit States" section.

Figure 9-1 ONS 15454 Circuit Window in Network View

9.2.1 Circuit Status

The circuit statuses that display in the Circuit window Status column are generated by CTC based on conditions along the circuit path. Table 9-1 shows the statuses that can appear in the Status column.

Table 9-1 ONS 15454 Circuit Status 

Status
Definition/Activity

CREATING

CTC is creating a circuit.

ACTIVE

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

DELETING

CTC is deleting a circuit.

INCOMPLETE

A CTC-created circuit is missing a cross-connect or network span; a complete path from source to destination(s) does not exist, or an Alarm Interface Panel (AIP) change occurred on one of the circuit nodes and the circuit is in need of repair. (AIPs store the node MAC address.)

In the 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, for traffic may flow on a protect path.

Network spans are in one of two states: up or down. On CTC circuit and network maps, up spans are displayed as green lines, and down spans are displayed as gray lines. If a failure occurs on a network span during a CTC session, the span remains in on the network map but its color changes to grey to indicate 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 will not display on the network map.

Consequently, circuits routed on a network span that goes down will display as ACTIVE during the current CTC session, but they will display as INCOMPLETE to users who log in after the span failure.


9.2.2 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 9-2. 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, although alarms are suppressed.


You can assign a state to circuits at two points:

During circuit creation you 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 9-2 ONS 15454 Circuit States 

State
Definition

IS

In service; able to carry traffic.

OOS

Out of service; unable to carry traffic.

OOS-AINS

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. Low-order circuits generally switch to IS when source and destination ports are IS, OOS_AINS, or OOS_MT regardless whether a physical signal is present. High-order circuits switch to IS when a signal is received.

OOS-MT

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.


PARTIAL is appended to a circuit state whenever all circuit cross-connects are not in the same state. Table 9-3 shows the partial circuit states that can display.

Table 9-3 Partial ONS 15454 Circuit States

State
Definition

OOS_PARTIAL

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

OOS_AINS_PARTIAL

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

OOS_MT_PARTIAL

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. 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 15454 SDH 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 15454 SDH 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. Two common examples of state changes you will see when provisioning circuits using CTC are as follows:

When provisioning low-order circuits and tunnels as OOS-AINS, the circuit state transitions to IS shortly after the circuits are created with the circuit source and destination ports are IS, OOS_AINS, or OOS_MT. The source and destination ports on the low-order 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 low-order source port and destination port states change to IS.

When provisioning high-order 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, high-order source and destination ports change to IS.

9.2.3 Circuit Protection Types

The Protection column on the Circuit window shows the card (line) and SDH topology (path) protection used for the entire circuit path. Table 9-4 shows the protection type indicators that you will see in this column.

Table 9-4 Circuit Protection Types

Protection Type
Description

None

Circuit protection is not applicable

2F MS-SPR

Circuit is protected by a two-fiber MS-SPRing

4F MS-SPR

Circuit is protected by a four-fiber MS-SPRing

MS-SPR

Circuit is protected by both a two-fiber and a four-fiber MS-SPRing

SNCP

Circuit is protected by an SNCP

1+1

Circuit is protected by a 1+1 protection group

protected

Circuit is protected by diverse SDH topologies, for example, an MS-SPRing and an SNCP, or an SNCP and 1+1

2F-PCA

Circuit is routed on a protection channel access path on a two-fiber MS-SPRing; PCA circuits are unprotected

4F-PCA

Circuit is routed on a protection channel access path on a four-fiber MS-SPRing; PCA circuits are unprotected

PCA

Circuit is routed on a protection channel access path on both two-fiber and 4-fiber MS-SPRings; PCA circuits are unprotected

unprot (black)

Circuit is not protected

unprot (red)

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

unknown

Circuit protection types display in the Protection column only when all circuit components are known, that is, when the circuit status is ACTIVE (if the circuit is in some other status, protection type is displayed as "unknown")


9.2.4 Viewing Circuit Information on the Edit Circuit Window

The detailed circuit map displayed on the Edit Circuit window allows you to view information about ONS 15454 SDH circuits. Routing information that is displayed includes:

Circuit direction (unidirectional/bidirectional)

The nodes, VC4s, TUG3, TUG2s, and VC12s through which circuit passes including slots and port numbers

The circuit source and destination points

OSPF Area IDs

Link protection (SNCP, unprotected, MS-SPRing, 1+1) and bandwidth (STM-N)

For MS-SPRings, the detailed map shows the number of MS-SPRing fibers and the MS-SPRing Ring ID. For SNCPs, 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

Loopbacks

Path trace states

Path selectors states

For example, in an SNCP, the working path 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 9-5.

Table 9-5 Port State Color Indicators

Port Color
State

Green

IS

Grey

OOS

Purple

OOS_AINS

Light blue

OOS_MT


Letters within the squares on each node indicate switches and other conditions. For example,

F = Force switch

M = Manual switch

L = Lockout switch

Moving the mouse cursor over nodes, ports, and spans will display such information as the number of alarms on a node (organized by severity), a port's state of service (that is, in-service, out-of-service), and the protection topology. You can 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 an SNCP span to change the state of the path selectors in the SNCP circuit.

9.3 Cross-Connect Card Capacities

The XC10G is required to operate the ONS 15454 SDH. XC10Gs support high-order cross-connections (VC4 and above). The XC10G does not support any low-order circuits such as VC-11, VC-12, and VC3. The XC10G card works with the TCC2 card to maintain connections and set up cross-connects within the node. You can create circuits using CTC. The XC10G card cross connects standard VC4, VC4-4c, VC4-16c, and VC4-64c signal rates and non-standard VC4-2c, VC4-3c, and VC4-8c signal rates, providing a maximum of 384 x 384 VC4 cross-connections. Any VC4 on any port can be connected to any other port, meaning that the VC cross-connection capacity is non-blocking. The XC10G card manages up to 192 bidirectional VC4 cross-connects.

VC4 tunnels must be used with the E3 and DS3i cards to transport VC3 signal rates. Three ports form a port group. For example, in one E3 or one DS3i card, there are four port groups: Ports 1 to 3 = PG1, Ports 4 to 6 = PG2, Ports 7 to 9 = PG3, and Ports 10 to 12 = PG4.


Note In SDH Software R3.4 and earlier, the XC10G does not support VC3 circuits for the E3 and DS3i cards. You must create a VC tunnel. See the Cisco ONS 15454 SDH Procedure Guide for more information.



Note "Common Control Cards," contains detailed specifications of the XC10G card.


9.4 DCC Tunnels

SDH provides four data communications channels (DCCs) for network element operations, administration, maintenance, and provisioning: one on the SDH regenerator section layer and three on the SDH multiplex section layer. The ONS 15454 SDH uses regenerator section DCC for inter-15454 data communications. It does not use the multiplex section DCCs; therefore, the multiplex section DCCs are available to tunnel DCCs from third-party equipment across ONS 15454 SDH networks. If D4 through D12 are used as data DCCs, they cannot be used for DCC tunneling.

A DCC tunnel end-point is defined by slot, port, and DCC, where DCC can be either the regenerator section DCC, Tunnel 1, Tunnel 2, or Tunnel 3. You can link a regenerator section DCC to a multiplex section DCC (Tunnel 1, Tunnel 2, or Tunnel 3) and a multiplex section DCC to a regenerator section DCC. You can also link multiplex section DCCs to multiplex section DCCs and link regenerator section DCCs to regenerator section DCCs. To create a DCC tunnel, you connect the tunnel end points from one ONS 15454 SDH optical port to another.

Each ONS 15454 SDH can support up to 32 DCC tunnel connections. Table 9-6 shows the DCC tunnels that you can create.

Table 9-6 DCC Tunnels

DCC
SDH
Layer
SDH
Bytes
STM-1
(All Ports)
STM-4, STM-16, STM-64

SDCC

Regenerator Section

D1 - D3

Yes

Yes

Tunnel 1

Multiplex Section

D4 - D6

No

Yes

Tunnel 2

Multiplex Section

D7 - D9

No

Yes

Tunnel 3

Multiplex Section

D10 - D12

No

Yes


Figure 9-2 shows a DCC tunnel example. Third-party equipment is connected to STM-1 cards at Node 1/Slot 3/Port 1 and Node 3/Slot 3/Port 1. Each ONS 15454 SDH node is connected by STM-16 trunk cards. In the example, three tunnel connections are created, one at Node 1 (STM-1 to STM-16), one at Node 2 (STM-16 to STM-16), and one at Node 3 (STM-16 to STM-1).


Note A DCC will not function on a mixed network of ONS 15454 SDH nodes and ONS 15454 SDH nodes. DCC tunneling is required for ONS 15454 SDH nodes transporting data through ONS 15454 SDH nodes.


Figure 9-2 DCC Tunnel

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

Each ONS 15454 SDH can have a maximum of 32 DCC tunnel connections.

Each ONS 15454 SDH can have a maximum of 10 regenerator section DCC terminations.

A regenerator section DCC that is terminated cannot be used as a DCC tunnel end-point.

A regenerator section DCC that is used as a DCC tunnel end-point cannot be terminated.

All DCC tunnel connections are bidirectional.


Note A multiplex section DCC cannot be used for tunneling if a data DCC is assigned.


9.5 Multiple Drops for Unidirectional Circuits

Unidirectional circuits can have multiple drops for use in broadcast circuit schemes. In broadcast scenarios, one source transmits traffic to multiple destinations, but traffic is not returned back to the source.

When you create a unidirectional circuit, the card that does not have its backplane receive (Rx) input terminated with a valid input signal generates a loss of service (LOS) alarm. To mask the alarm, create an alarm profile suppressing the LOS alarm and apply it to the port that does not have its Rx input terminated.

9.6 Creating Monitor Circuits

You can set up secondary circuits to monitor traffic on primary bidirectional circuits. Monitor circuits can be created on E1 or STM-N cards. Figure 9-3 shows an example of a monitor circuit. At Node 1, a VC4 is dropped from Port 1 of an STM-1 card. To monitor the VC4 traffic, test equipment is plugged into Port 2 of the STM-1 card and a monitor circuit to Port 2 is provisioned in CTC. Circuit monitors are one-way. The monitor circuit in Figure 9-3 is used to monitor VC4 traffic received by Port 1 of the STM-1 card.


Note Monitor circuits cannot be used with EtherSwitch circuits.


Figure 9-3 VC4 Monitor Circuit Received at an STM-1 Port

9.7 SNCP Circuits

Use the Edit Circuits window to change SNCP selectors and switch protection paths (Figure 9-4). In this window, you can:

View the SNCP circuit's working and protection paths

Edit the reversion time

Edit the Signal Fail/Signal Degrade thresholds

Change PDI-P settings

Perform maintenance switches on the circuit selector

View switch counts for the selectors

Figure 9-4 Editing SNCP Selectors

9.8 MS-SPRing Protection Channel Circuits

You can provision circuits to carry traffic on MS-SPRing protection channels when conditions are fault-free. Traffic routed on MS-SPRing protection channels, called extra traffic, has lower priority than the traffic on the working channels and has no means for protection. During ring or span switches, protection channel circuits are preempted and squelched. For example, in a 2-fiber STM-16 MS-SPRing, STMs 9-16 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 MS-SPRing is provisioned as revertive.

Provisioning traffic on MS-SPRing protection channels is performed during circuit provisioning. The protection channel check box appears whenever Fully Protected Path is deselected on the circuit creation wizard. Refer to the Cisco ONS 15454 Procedure Guide for more information. When provisioning protection channel circuits, two considerations are important to keep in mind:

If MS-SPRings are provisioned as non-revertive, protection channel circuits will not be restored automatically after a ring or span switch. You must switch the MS-SPRing manually.

Protection channel circuits will be routed on working channels when you upgrade a MS-SPRing from a 2-fiber to a 4-fiber or from one optical speed to a higher optical speed. For example, if you upgrade a 2-fiber STM-16 MS-SPRing to an STM-64, STMs 9-16 on the STM-16 MS-SPRing become working channels on the STM-64 MS-SPRing.

9.9 J1 Path Trace

The 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 9-7 shows the ONS 15454 SDH cards that support path trace. Cards not listed in the table do not support the J1 byte.

Table 9-7 ONS 15454 SDH Cards Capable of Path Trace

J1 Function
Cards

Transmit and receive

E3

DS3i

G1000-4

Receive only

OC3 IR 4/STM1 SH 1310

OC12/STM4-4

OC48 IR/STM16 SH AS 1310, OC48 LR/STM16 LH AS 1550

OC192 LR/STM64 LH 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.

9.10 Path Signal Label, C2 Byte

One of the overhead bytes in the SDH frame is the C2 Byte. The SDH standard defines the C2 byte as the path signal label. The purpose of this byte is to communicate the payload type being encapsulated by the high-order path overhead (HO-POH). The C2 byte functions similarly to EtherType and Logical Link Control (LLC)/Subnetwork Access Protocol (SNAP) header fields on an Ethernet network; it allows a single interface to transport multiple payload types simultaneously. C2 byte hex values are provided in Table 9-8.

Table 9-8 STM Path Signal Label Assignments for Signals 

Hex Code
Content of the STM SPE

0x00

Unequipped

0x01

Equipped — non specific payload

0x02

TUG structure

0x03

Locked TU-n

0x04

Asynchronous mapping of 34,368 kbit/s or 44,736 kbit/s into the container-3 (C-3)

0x12

Asynchronous mapping of 139,264 kbit/s into the container-4 (C-4)

0x13

Mapping for ATM

0x14

Mapping for DQDB

0x15

Asynchronous mapping for FDDI

0xFE

0.181 Test signal (TSS1 to TSS3) mapping SDH network (see ITU-T G.707)

0xFF

VC-AIS


If a circuit is provisioned using a terminating card, the terminating card provides the C2 byte. A low-order path circuit is terminated at the X10G or XCVXL and the cross-connect card generates the C2 byte (0x02) downstream to the VC terminating cards. The cross-connect generates the C2 value (0x02) to the terminating card. If an optical circuit is created with no terminating cards, the test equipment must supply the path overhead in terminating mode. If the test equipment is in "path through mode," the C2 values usually change rapidly between 0x00 and 0xFF. Adding a terminating card to an optical circuit usually fixes a circuit having C2 byte problems.

9.11 Automatic Circuit Routing

If you select automatic routing during circuit creation, CTC routes the circuit by dividing the entire circuit route into segments based on protection domains. For unprotected segments of circuits provisioned as fully protected, CTC finds an alternate route to protect the segment, creating a virtual SNCP. Each segment of a circuit path is a separate protection domain. Each protection domain is protected in a specific protection scheme including card protection (1+1, 1:1, etc.) or SDH topology (SNCP, MS-SPRing, etc.).

The following list provides principles and characteristics of automatic circuit routing:

Circuit routing tries to use the shortest path within the user-specified or network-specified constraints. Low-order tunnels are preferable for low-order circuits because low-order tunnels are considered shortcuts when CTC calculates a circuit path in path-protected mesh networks.

If you do not choose Fully Path Protected during circuit creation, circuits can still contain protected segments. Because circuit routing always selects the shortest path, one or more links and/or segments can have some protection. CTC does not look at link protection while computing a path for unprotected circuits.

Circuit routing will not use links that are down. If you want all links to be considered for routing, do not create circuits when a link is down.

Circuit routing computes the shortest path when you add a new drop to an existing circuit. It tries to find the shortest path from the new drop to any nodes on the existing circuit.

If the network has a mixture of low-order-capable nodes and low-order-incapable nodes, CTC may automatically create a low-order tunnel. Otherwise, CTC asks you whether a low-order tunnel is needed.

9.11.1 Bandwidth Allocation and Routing

Within a given network, CTC will route circuits on the shortest possible path between source and destination based on the circuit attributes, such as protection and type. CTC will consider using a link for the circuit only if the link meets the following requirements:

The link has sufficient bandwidth to support the circuit

The link does not change the protection characteristics of the path

The link has the required time slots to enforce the same time slot restrictions for MS-SPRing

If CTC cannot find a link that meets these requirements, an error is displayed.

The same logic applies to low-order circuits on low-order tunnels. Circuit routing typically favors low-order tunnels because low-order tunnels are shortcuts between a given source and destination. If the low-order tunnel in the route is full (no more bandwidth), CTC asks whether you want to create an additional low-order tunnel.

9.11.2 Secondary Sources and Drops

CTC supports secondary sources and drops. Secondary sources and drops typically interconnect two "foreign" networks, as shown in Figure 9-5. Traffic is protected while it goes through a network of ONS 15454s.

Figure 9-5 Secondary Sources and Drops

Several rules apply to secondary sources and drops:

CTC does not allow a secondary destination for unidirectional circuits because you can always specify additional destinations (drops) after you create the circuit

Primary and secondary sources should be on the same node

Primary and secondary destinations should be on the same node

Secondary sources and destinations are permitted only for regular high-order or low-order connections (not for low-order tunnels and Multicard EtherSwitch circuits)

For point-to-point (straight) Ethernet circuits, only VC endpoints can be specified as multiple sources or drops

For bidirectional circuits, CTC creates an SNCP connection at the source node that allows traffic to be selected from one of the two sources on the ONS 15454 network. If you check the Fully Path Protected option during circuit creation, traffic is protected within the ONS 15454 network. At the destination, another SNCP connection is created to bridge traffic from the ONS 15454 network to the two destinations. A similar but opposite path exists for the reverse traffic flowing from the destinations to the sources.

For unidirectional circuits, an SNCP drop-and-continue connection is created at the source node.

9.12 Manual Circuit Routing

Routing circuits manually allows you to:

Choose a specific path, not necessarily the shortest path

Choose a specific VC4/TUG3/TUG2/VC12 on each link along the route

Create a shared packet ring for Multicard EtherSwitch circuits

Choose a protected path for Multicard EtherSwitch circuits, allowing virtual SNCP segments

CTC imposes the following rules on manual routes:

All circuits, except Multicard EtherSwitch circuits in a shared packet ring, should have links with a direction that flows from source to destination. This is true for Multicard EtherSwitch circuits that are not in a shared packet ring.

If you enabled fully path protected, choose a diverse protect (alternate) path for every unprotected segment (Figure 9-6).

Figure 9-6 Alternate Paths for Virtual SNCP Segments

For Multicard EtherSwitch circuits, the fully path protected option is ignored.

For a node that has an SNCP selector based on the links chosen, the input links to the SNCP selectors cannot be 1+1 or MS-SPRing protected (see Figure 9-7). The same rule applies at the SNCP bridge.

Figure 9-7 Mixing 1+1 or MS-SPRing Protected Links With an SNCP

Choose the links of Multicard EtherSwitch circuits in a shared packet ring to route from source to destination back to source (see Figure 9-8). Otherwise, a route (set of links) chosen with loops is invalid.

Figure 9-8 Ethernet Shared Packet Ring Routing

Multicard EtherSwitch circuits can have virtual SNCP segments if the source or destination is not in the SNCP domain. This restriction also applies after circuit creation; therefore, if you create a circuit with SNCP segments, Ethernet drops cannot exist anywhere on the SNCP segment (see Figure 9-9).

Figure 9-9 Ethernet and SNCP

Low-order tunnels cannot be the endpoint of an SNCP segment. A SNCP segment endpoint is where the SNCP selector resides.

If you provision full path protection, CTC verifies that the route selection is protected at all segments. A route can have multiple protection domains with each domain protected by a different scheme.

Table 9-9 through Table 9-12 summarize the available node connections. Any other combination is invalid and will generate an error.

Table 9-9 Bidirectional VC/TUG/Regular Multicard EtherSwitch/Point-to-Point (Straight) Ethernet Circuits 

# of Inbound Links
# of Outbound Links
# of Sources
# of Drops
Connection Type

2

1

SNCP

2

1

SNCP

2

1

SNCP

1

2

SNCP

1

2

SNCP

1

2

SNCP

2

2

Double SNCP

2

2

Double SNCP

2

2

Double SNCP

1

1

Two Way

0 or 1

0 or 1

Ethernet Node Source

Ethernet

0 or 1

0 or 1

Ethernet Node Drop

Ethernet


Table 9-10 Unidirectional Circuit 

# of Inbound Links
# of Outbound Links
# of Sources
# of Drops
Connection Type

1

1

One way

1

2

SNCP Head End

2

1

SNCP Head End

2

1+

SNCP drop and continue


Table 9-11 Multicard Group Ethernet Shared Packet Ring Circuit

# of Inbound Links
# of Outbound Links
# of Sources
# of Drops
Connection Type
Intermediate nodes only

2

1

SNCP

1

2

SNCP

2

2

Double SNCP

1

1

-—

Two way

Source or destination nodes only

1

1

Ethernet


Table 9-12 Bidirectional Low-order Tunnels 

# of Inbound Links
# of Outbound Links
# of Sources
# of Drops
Connection Type
Intermediate nodes only

2

1

SNCP

1

2

SNCP

2

2

Double SNCP

1

1

Two way

Source nodes only

1

Low-order tunnel endpoint

Destination nodes only

1

Low-order tunnel endpoint


Although virtual SNCP segments are possible in low-order tunnels, low-order tunnels are still considered unprotected. If you need to protect low-order circuits use two independent low-order tunnels that are diversely routed or use a low-order tunnel that is routed over 1+1, MS-SPRing, or a mixture of 1+1 and MS-SPRing links.

9.13 Constraint-Based Circuit Routing

When you create circuits, you can choose Fully Protected Path to protect the circuit from source to destination. The protection mechanism used depends on the path CTC calculates for the circuit. If the network is composed entirely of MS-SPRing and/or 1+1 links, or the path between source and destination can be entirely protected using 1+1 and/or MS-SPRing links, no path-protected mesh network (Extended SNCP), or virtual SNCP, protection is used.

If Extended SNCP protection is needed to protect the path, set the level of node diversity for the Extended SNCP portions of the complete path on the Circuit Creation dialog box:

Required—Ensures that the primary and alternate paths of each Extended SNCP domain in the complete path have a diverse set of nodes

Desired—CTC looks for a node diverse path; if a node diverse path is not available, CTC finds a link diverse path for each Extended SNCP domain in the complete path

Don't Care—Creates only a link diverse path for each Extended SNCP domain

When you choose automatic circuit routing during circuit creation, you have the option to require and/or exclude nodes and links in the calculated route. You can use this option to:

Simplify manual routing, especially if the network is large and selecting every span is tedious. You can select a general route from source to destination and allow CTC to fill in the route details.

Balance network traffic; by default CTC chooses the shortest path, which can load traffic on certain links while other links have most of their bandwidth available. By selecting a required node and/or a link, you force the CTC to use (or not use) an element, resulting in more efficient use of network resources.

CTC considers required nodes and links to be an ordered set of elements. CTC treats the source nodes of every required link as required nodes. When CTC calculates the path, it makes sure the computed path traverses the required set of nodes and links and does not traverse excluded nodes and links.

The required nodes and links constraint is only used during the primary path computation and only for Extended SNCP domains/segments. The alternate path is computed normally; CTC uses excluded nodes/links when finding all primary and alternate paths on Extended SNCPs.