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The Automatic Protection Switching (APS) feature provides link redundancy and allows switchover of Packet over SONET (POS) circuits in the event of circuit failure and is often required when you connect Synchronous Optical Networking (SONET) equipment to telecommunications equipment. In the single router (SR) APS feature both protect and working interfaces must be on same router.
APS is a mechanism of using a protect POS interface in the SONET network as the backup for a working POS interface. When the working interface fails, the protect interface quickly assumes its traffic load. Based on the configuration, the two circuits can be terminated in the same router. The protection mechanism has a 1+1 architecture with bidirectional connection. Bridging refers to the transmission of user data to both working interface and protect interface. In nonbridging scenario the user data is sent to working interface only.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for 1+1 SR-APS Without Bridging" section.
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•Prerequisites for 1+1 SR-APS Without Bridging
•Restrictions for 1+1 SR-APS Without Bridging
•Information About 1+1 SR-APS Without Bridging
•How to Configure 1+1 SR-APS Without Bridging
•Configuration Examples for 1+1 SR-APS Without Bridging
•Feature Information for 1+1 SR-APS Without Bridging
Configure the working interface first, along with the IP address of the interface. This configuration helps to prevent the protect interface from becoming the active circuit during APS configuration. If the protect interface becomes active in case if it has been configured first by mistake, you can use shut or no shut command to make the working interface active.
•Both the protect and working interfaces should be configured identically. No warning message will be displayed if the configurations are different between the interfaces.
•Behavior of the APS pair (protect and working interfaces) will be indeterministic if the configurations of protect and working interfaces are not identical.
•APS switch over within 50 milliseconds is not supported during online insertion and removal (OIR) or during crash of the shared port adapter (SPA) or carrier card (CC).
•APS switching simultaneously with Route Processor (RP) or forwarding plane (FP) high availability (HA) need not be within 50 milliseconds.
You need to understand the following concept in order to configure 1+1 SR-APS Without Bridging feature:
The APS feature provides link redundancy and allows switchover of POS circuits in the event of circuit failure and is often required when you connect SONET equipment to telecommunications equipment. In the SR-APS feature both protect and working interfaces must be on same router.
APS is a mechanism of using a protect POS interface in the SONET network as the backup for a working POS interface. When the working interface fails, the protect interface quickly assumes its traffic load. Based on the configuration, the two circuits can be terminated in the same router. The protection mechanism has a 1+1 architecture with bidirectional connection.
In the 1+1 architecture, there is one working interface (circuit) and one protect interface, and the same payload from the transmitting end is sent to both the receiving ends. The receiving end decides the interface that needs to be used. The line overhead (LOH) bytes (K1 and K2) in the SONET frame indicate both status and action. When one interface is down or the K1/K2 bytes have changed, APS brings up the protect interface using regular interface configuration messages.
Bridging refers to the transmission of user data to both the working interface and the protect interface. In nonbridging scenario the user data is sent to the working interface only. You must set the working interface to be the active interface. Cisco ASR 1000 Series Routers (ASR1000) supports only the nonbridging scenario.
In the nonbridging scenario the ASR1000 (with the APS enabled) transmits a signal to the remote end. The ASR1k transmits the signal (except K1/K2 bytes) only to the working interface and not to the protect interface. The K1/K2 bytes are transmitted only to the protect interface. However, ASR1000 can be connected to devices that support bridging APS, which means the devices transmit the same signal to both working and protect interfaces of ASR1000. But the ASR1000 will send the user data (except K1/K2 bytes) only to the working interface of that device. The K1/K2 bytes are transmitted to the protect interface.
SR-APS uses Protect Group Protocol (PGP) between working and protect interfaces. The protect interface APS configuration should include an IP address of a loopback interface on the same router to communicate with the working interface using PGP. Using the PGP, POS interfaces can be switched in case of a degradation or loss of channel signal, or manual intervention. In bidirectional mode, the receive and transmit channels are switched as a pair.
In bidirectional APS the local and the remote connections negotiate the ingress interface to be selected for the data path. The egress interface traffic is not transmitted to both working and protect interfaces.
This section contains the following procedures:
•Configuring APS Working and Protect Interfaces (required)
•Configuring Other APS Options (optional)
•Monitoring and Maintaining APS (optional)
•Configuring SONET Alarm Reporting (optional)
•Configuring LAIS as an APS Switchover Trigger (optional)
Perform this task to configure APS working and protect interfaces.
1. enable
2. configure terminal
3. interface pos slot/sub-slot/port
4. aps working circuit-number
5. aps protect circuit-number ip-address
6. end
7. show controllers pos
8. show interfaces pos
9. show aps
Perform this task to configure other APS options.
1. enable
2. configure terminal
3. interface pos slot/sub-slot/port
4. aps force circuit-number
5. aps group group-number
6. aps lockout circuit-number
7. aps manual circuit-number
8. aps revert minutes
9. end
Perform this task to monitor and maintain APS.
1. enable
2. configure terminal
3. show controllers pos
4. show interfaces pos
5. show aps
To configure the thresholds and the type of SONET alarms that are reported, use any of the following commands. The commands listed in this section are optional. To display the current Bit Error Rate (BER) threshold setting or to view the reporting of the SONET alarms, use the show controllers pos command.
1. enable
2. configure terminal
3. interface pos slot/sub-slot/port
4. pos threshold {b1-tca | b2-tca | b3-tca | sd-ber | sf-ber} rate
5. pos report {b1-tca | b2-tca | b3-tca | lais | lrdi | pais | plop | prdi | rdool | sd-ber | sf-ber | slof | slos}
6. end
When you place the working interface into administrative shutdown state, the switchover happens with or without pos ais-shut. When pos ais-shut is enabled on the interface, the interface sends the line alarm indication signal (LAIS) alarm to the remote end of the administrative shutdown, and the LAIS alarm makes the switchover bit faster. The carrier-delay msec milliseconds command and ppp timeout retry seconds [milliseconds] command are also used to make the APS switchover happen faster.
The carrier-delay msec milliseconds command delays the link down event processing for POS interfaces. For example, if the carrier delay is set to 50 milliseconds (ms), the router will ignore all link down events that are cleared within 50 msec. If the link goes down there will be no APS switchover for 50 ms. The default carrier delay is 2 seconds and there will be no APS switchover for 2 seconds after the link goes down. Hence the carrier delay is set to 50 ms for faster switchover.
The ppp timeout retry seconds [milliseconds] command sets the PPP retry timeout to the specified time. For example, if the timeout retry is set to 200 ms, the router tries to establish PPP link in 200 ms after it detects the signal outage due to APS switchover. If the default retry timeout of 2 seconds is used, then the PPP link will be established 2 seconds after the APS switchover. Hence the PPP timeout retry is set to 50 ms for faster switchover.
1. enable
2. configure terminal
3. interface pos slot/sub-slot/port
4. pos ais-shut
5. carrier-delay msec milliseconds
6. ppp timeout retry seconds [milliseconds]
7. end
This section provides the following configuration example:
•Example: Configuring 1+1 SR-APS Without Bridging
The following example shows the configuration sequence for 1+1 SR-APS:
interface loopback 1
ip address 1.1.1.1 255.255.255.0
interface pos 2/0/0
aps group 1
aps working 1
pos ais-shut
end
interface pos 3/0/0
aps group 1
aps protect 1 1.1.1.1
pos ais-shut
end
The following example shows the sample output of APS configured on a router with a working interface:
Router# show aps
POS2/1/1 APS Group 0: protect channel 0 (Inactive)
Working channel 1 at 10.0.1.1 (Enabled)
bidirectional, revertive (60 seconds)
PGP timers (default): hello time=1; hold time=3
hello fail revert time=120
SONET framing; SONET APS signalling by default
Received K1K2: 0x00 0x05
No Request (Null)
Transmitted K1K2: 0x00 0x05
No Request (Null)
Remote APS configuration: (null)
POS2/1/0 APS Group 0: working channel 1 (Active)
Protect at 10.0.1.1
PGP timers (from protect): hello time=1; hold time=3
SONET framing
Remote APS configuration: (null)
The following example shows the display of POS controllers:
Router# show controller pos 2/1/0
POS2/1/0
SECTION
LOF = 0 LOS = 1 BIP(B1) = 0
LINE
AIS = 2 RDI = 2 FEBE = 14 BIP(B2) = 0
PATH
AIS = 2 RDI = 2 FEBE = 4 BIP(B3) = 6
PLM = 0 UNEQ = 0 TIM = 0 TIU = 0
LOP = 1 NEWPTR = 2 PSE = 0 NSE = 0
Active Defects: None
Active Alarms: None
Alarm reporting enabled for: SF SLOS SLOF B1-TCA B2-TCA PLOP B3-TCA
Framing: SONET
APS
working (active)
COAPS = 13 PSBF = 0
State: PSBF_state = False
Rx(K1/K2): 00/00 Tx(K1/K2): 00/00
Rx Synchronization Status S1 = 00
S1S0 = 00, C2 = CF
Remote aps status (none); Reflected local aps status (none)
CLOCK RECOVERY
RDOOL = 0
State: RDOOL_state = False
PATH TRACE BUFFER: STABLE
Remote hostname : SPA-APS2
Remote interface: POS2/2/0
Remote IP addr : 10.1.1.1
Remote Rx(K1/K2): 00/00 Tx(K1/K2): 00/00
BER thresholds: SF = 10e-3 SD = 10e-6
TCA thresholds: B1 = 10e-6 B2 = 10e-6 B3 = 10e-6
Clock source: internal
The following example shows the configuration information and statistics for a POS interface:
Router# show interface pos 2/1/0
POS2/1/0 is up, line protocol is up (APS working - active)
Hardware is SPA-4XOC12-POS
Internet address is 10.1.1.2/24
MTU 4470 bytes, BW 155000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, crc 16, loopback not set
Keepalive set (10 sec)
Scramble disabled
Last input 00:00:02, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 0 bits/sec, 0 packets/sec
30 second output rate 0 bits/sec, 0 packets/sec
102477 packets input, 2459448 bytes, 0 no buffer
Received 0 broadcasts (0 IP multicasts)
0 runts, 4 giants, 0 throttles 0 parity
4 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
102486 packets output, 2459934 bytes, 0 underruns
0 output errors, 0 applique, 2 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
10 carrier transitions
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To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
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Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.