Packet Over SONET/SDH

Packet Over SONET/SDH (POS) maps IP datagrams into the SONET frame payload using Point-to-Point Protocol (PPP). SONET is a physical layer protocol. IP is a connectionless network layer protocol.

This implementation of SONET is intended to support line rates of OC-3c, OC-12c and OC-48c, and uses concatenation to form larger SONET frames. The following terminology is used throughout this chapter:

A SONET path is the logical connection between the two points on a connection where the SONET frame is assembled (on the sending side) and disassembled (on the receiving side). The remote end of a SONET path is referred to as the path-far-end.

A SONET line is the transmission medium between the two points. The remote end of a SONET line is referred to as the line-far-end.

A SONET section is any portion of a SONET connection such as a segment of optical fiber between two repeaters, the repeaters themselves, or a multiplexer.

Related Information

Administrators should be familiar with SONET and IP operation and theory before configuring the Avici router to run SONET. The following texts are recommended as further reading:

• SONET A Guide to Synchronous Optical Networks, Goralski, Walter J.,1997, McGraw-Hill, ISBN 0-07-0245563-0
  
  
• Understanding SONET/SDH Standards and Applications, Chow, Ming-Chwan, 1995 Andan Publisher, ISBN 0-9650448-2-3
  
  

POS Default Settings

This implementation of Packet Over SONET/SDH includes a variety of widely used default settings. You can accept many of these defaults and therefore skip some steps of configuring POS. The defaults are as follows:

Table 6-1. Packet Over SONET Default Settings 

Command	Default Setting	Description of Default Setting
clock source	line	Selects the clock recovered from the incoming data stream as the clock source for data transmission on this interface.
sonet flag c2	22 (PPP)	Sets the overhead byte that identifies the type of payload carried on this interface to 22 - indicating support for Point to Point Protocol.
sonet framing	SONET	Configures the interface for SONET framing.
sonet path-trace	host-name/Interface-type/bay/slot/port/Line-rate	The following string is inserted as a path trace message for each interface: host-name/Interface-type/bay/slot/port/ Line-rate
sonet scramble-atm	Enabled	Scrambling on a SONET interface makes data appear more random.
sonet threshold line	1 (all thresholds)	Sets the threshold values for events occurring in the line layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS). An Avici SNMP trap is sent when this threshold is exceeded.
sonet threshold line-far-end	1 (all thresholds)	Sets the threshold values for events occurring in the line layer at the remote end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS). An Avici SNMP trap is sent when this threshold is exceeded.
sonet threshold path	1 (all thresholds)	Sets the threshold values for events occurring in the path layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS). An Avici SNMP trap is sent when this threshold is exceeded.
sonet threshold path-far-end	1 (all thresholds)	Sets the threshold values for events occurring in the path layer at the remote end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS). An Avici SNMP trap is sent when this threshold is exceeded.
sonet threshold section	1 (all thresholds)	Sets the threshold values for events occurring in the section layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Severely Errored Framing Seconds (SEFS). An Avici SNMP trap is sent when this threshold is exceeded.

Overview of POS Configuration

PROCEDURE: Use the following procedure to configure POS on a Avici router:

Step 1 Enable the POS interface.

Step 2 Optionally, modify the default settings:

• Change the clock source for the interface to internal.
  
  
• Enable scrambling on the interface.
  
  
• Change the SONET threshold settings.
  
  
• Modify the default path-trace message.
  
  

  Step 3 Perform a SONET path trace to test the connection.

  Step 4 Configure a SONET loopback interface to analyze any problems in the connection.

  Step 5 Display SONET settings, thresholds, and performance.

These steps are described in detail in the following sections.

Enabling the POS Interface

Your startup configuration file should already include a no shutdown command for each interface. This command activates the interface. If an interface is not activated during system startup, use the no shutdown command to activate the interface.

In the following example, the no shutdown command activates interface pos 1/1/1 and the show interface pos command displays the new setting:

router#configure Configuring from terminal, memory, or network [terminal]? terminal Enter configuration commands, one per line. End with CNTL/Z. router(config)#interface pos 1/1/1 router(config-if)#no shutdown router(config-if)#end router#show interface pos 1/1/1

POS 1/1/1 is up, line protocol is down Internet address is 5.10.1.2 255.255.0.0 MTU 4470 bytes, BW 622 Mbit/Sec Encapsulation PPP, CRC-32 Loopback: None, Keepalive: Disabled, Scramble: Enabled LCP: Closed, IPCP: Closed, OSICP: Closed Received: 0 bytes 0 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors, 0 unknown protocols Transmitted: 0 bytes 0 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors Medium Type SONET, Line Coding: NRZ, Line Type: ShortSingleMode Sonet Loopback: None, Sonet Clock Source: Line Tx Path Trace: "<NULL>" Rx Path Trace: "<NULL>"

The interface is now up and ready to be configured for routing.

Modifying the POS Default Settings

Notice in the output from the show interface pos command that the interface comes up with many values preset to defaults. See "POS Default Settings."

You can operate your POS interface using these defaults or you can modify the defaults. The steps to modify the defaults are described in the following sections.

Modifying Clock Source

An interface can clock transmitted data from either its own internal clock (internal) or from a clock recovered from the incoming data stream (line).

NOTE Be aware that the default for industry-standard routers is to obtain their clock from line. If both ends of the fiber are configured to recover the clock from line, the connection will not work, characterized by SONET failing to come up.

The default value for the clock source is line.

PROCEDURE: Use the following steps for modifying clock source:

Step 1 Use the shutdown command to disable the interface.

Step 2 Use the clock source internal command to change the clock source for data transmitted on this interface to the internal clock.

In the following example:

• The shutdown command disables interface POS 1/1/1.
  
  
• The clock source command selects the internal clock as the clock for data transmission.
  
  
• The show running-config command displays the new setting:
  
  

router(config)#interface pos 1/1/1 router(config-if)#shutdown router(config-if)#clock source internal router(config-if)#no shutdown router(config-if)#end router#show running-config . . .

module 1/1 4xoc3c no shutdown ! interface pos 1/1/1 clock source internal ip address 3.3.3.2 255.255.255.0 mtu 4400 ppp negotiation-timeout 30 no shutdown . . .

Modifying SONET Flags

SONET flags provide information about the transport overhead of a packet. Only the c2 flag is supported. The c2 byte indicates the type of payload supported on the interface.

The default for the c2 flag is 22 (hexidecimal = 0x16) indicating support for PPP links.

NOTE The only value supported for the c2 flag is 22.

Example: In the following example, the sonet flag c2 command sets the c2 flag to 222 on POS interface 1/1/1 and the show running configuration command displays the new setting

router(config)#interface pos 1/1/1 router(config-if)#sonet flag c2 222 router(config-if)#end router#show running-config . . .

interface pos 1/1/1 sonet flag c2 222 description Chicago-Lab4 Row7 mtu 4400 crc 16 . . .

Modifying SONET Scrambling

Scrambling makes data appear more random and therefore prevents the bit patterns from becoming all 1s or 0s. If scrambling is enabled, both ends of the link must be configured to support scrambling. If only one end of the link is configured to enable scrambling, no connection is established.

The default for SONET scrambling is enabled.

Use the no sonet scramble-atm command to disable scrambling.

In the following example, the no sonet scramble-atm command disables scrambling of the SONET payload on the interface, and the show interface pos command displays the new setting:

router(config)#int pos 1/1/1 router(config-if)#no sonet scramble-atm router(config-if)#end

POS 1/1/1 is up, line protocol is down Internet address is 5.10.1.2 255.255.0.0 MTU 4470 bytes, BW 622 Mbit/Sec Encapsulation PPP, CRC-16 Loopback: None, Keepalive: Disabled, Scramble: Disabled LCP: Closed, IPCP: Closed, OSICP: Closed Received: 0 bytes 0 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors, 0 unknown protocols Transmitted: 0 bytes 0 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors Medium Type SONET, Line Coding: NRZ, Line Type: ShortSingleMode Sonet Loopback: None, Sonet Clock Source: Internal Tx Path Trace: "<NULL>" Rx Path Trace: "<NULL>"

Modifying SONET Event Thresholds

Thresholds enable you to define the number of specific events that will trigger an SNMP trap. The default settings for the thresholds are as follows:

Table 6-2. SONET Event Thresholds 

SONET Layer	Valid Range	Default Setting	Description
line	For ES, SES and UAS: 1 - 900 For CV: 1 - 4294967295	1 (all thresholds)	Sets the threshold values for events occurring in the line layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS).
line-far-end	For ES, SES and UAS: 1 - 900 For CV: 1 - 4294967295	1 (all thresholds)	Sets the threshold values for events occurring in the line layer at the remote end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS).
path	For ES, SES and UAS: 1 - 900 For CV: 1 - 4294967295	1 (all thresholds)	Sets the threshold values for events occurring in the path layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS).
path-far-end	For ES, SES and UAS: 1 - 900 For CV: 1 - 4294967295	1 (all thresholds)	Sets the threshold values for events occurring in the path layer at the remote end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Unavailable Seconds (UAS).
section	For ES, SES and SEFS: 1 - 900 For CV: 1 - 4294967295	1 (all thresholds)	Sets the threshold values for events occurring in the section layer at the local end of a SONET connection. Thresholds include: Coding Violations (CV), Errored Seconds (ES), Severely Errored Seconds (SES), and Severely Errored Framing Seconds (SEFS).

NOTE The default thresholds are designed for smoothly operating SONET links where few errors occur. For error conditions such as when a fiber optic cable is unplugged from a SONET interface, large numbers of traps are generated.

Use the sonet threshold line command to modify the thresholds in the line layer at the local end of a connection.

Use the sonet threshold line-far-end command to modify the thresholds in the line layer at the remote end of a connection.

Use the sonet threshold path command to modify the thresholds in the path layer at the local end of a connection.

Use the sonet threshold path-far-end command to modify the thresholds in the path layer at the remote end of a connection.

Use the sonet threshold section command to modify the thresholds in the section layer of a connection.

In the following example, the thresholds for sending a SNMP trap from POS interface 1/1/1 are configured to send a trap when:

• The number of Severely Errored Framing Seconds (SEFS) encountered by a SONET/SDH section in a particular 15 minute interval rises above a threshold of 10.
  
  
• The number of Errored Seconds (ES) encountered by the local end of a SONET/SDH path in a particular 15 minute interval rises above a threshold of 20.
  
  
• The number of Unavailable Seconds (UAS) encountered by the remote end of a SONET/SDH line in a particular 15 minute interval rises above a threshold of 5.
  
  

  NOTE The sonet threshold commands define the circumstances under which an SNMP trap is generated. You must also use the snmp trap command to configure the interface to send SNMP traps. See snmp-server enable traps in the "SNMP Commands" chapter.

router(config)#interface pos 1/1/1 router(config-if)#sonet threshold section sefs 10 router(config-if)#sonet threshold path es 20 router(config-if)#sonet threshold line-far-end uas 5 router(config-if)#end

Modifying the Path-trace Message

By default, the following string is inserted as a path trace message for each interface:

host-name/Interface-type/bay/slot/port/Line-rate

For example, the first port of an OC-48c module installed in slot 10 of Bay 1 on a router with a host name of NY-35 has the following default path trace string:

NY-35/POS 1/10/1/48

Use the sonet path-trace message command to modify the path trace message on this interface.

NOTE In SDH mode, the path trace message is restricted to 13 characters.

Example: In the following example, the sonet path-trace command modifies the path trace for the interface, and the show interface pos command displays the new setting:

router(config)#interface pos 1/1/1 router(config-if)#sonet path-trace Path Trace from 10.5.1.3 router(config-if)#end router#show interface pos 1/1/1

. . . Tx Path Trace: "Path Trace from 10.5.1.3" Rx Path Trace: "<NULL>"

Sending a POS Path Trace

Path traces are used to detect and diagnose network problems. Use the sonet path-trace command to modify the default text string sent in a SONET frame where it can be detected by network analyzers.

In the following example, the sonet path-trace command injects the text string "Path trace from 10.5.1.123" into frames transmitted out the interface:

router(config)#interface pos 1/1/1 router(config-if)#sonet path-trace Path trace from 10.5.1.123 router(config-if)#end

Use the show interface pos command to display any path trace being transmitted or received on this interface:

router#show interface pos 1/1/1 . . . Tx Path Trace: "Path trace from 10.5.1.123" Rx Path Trace: "<NULL>"

Configuring a SONET Loopback Interface

Local loopbacks are used to test that a POS port is correctly functioning.

Use the loopback command with the line argument to set the interface to loop incoming packets out through the transmit fiber. This sends incoming traffic unchanged back to the sending router.

Use the loopback command with the internal argument to set the interface to loop outgoing packets back in through the receive fiber. This sends outgoing traffic unchanged back into the router.

Use the show interface pos command to display the new settings:

router(config)#interface pos 1/1/1 router(config-if)#loopback internal router(config-if)#end router#show interface pos 1/1/1

POS 1/1/1 is up, line protocol is up Internet address is 5.10.1.2 255.255.0.0 MTU 4470 bytes, BW 622 Mbit/Sec Encapsulation PPP, CRC-16 Loopback: Internal, Keepalive: Disabled, Scramble: Enabled LCP: Open, IPCP: Open, OSICP: Open Received: 645 bytes 13 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors, 0 unknown protocols Transmitted: 592 bytes 11 directed packets, 0 multicast packets, 0 broadcast packets 0 discards, 0 errors

Medium Type SONET, Line Coding: NRZ, Line Type: ShortSingleMode Sonet Loopback: None, Sonet Clock Source: Internal Tx Path Trace: "<NULL>" Rx Path Trace: "<NULL>"

Configuring Sonet Failure Delay

There is a delay between IPRiori detecting a Sonet defect (e.g. LOS, LOF, LAIS/MS-AIS, etc.) and the marking the link as having failed. The delay between detecting a Sonet defect and marking the link failure is configurable using the sonet failure-delay command. The delay value can be any value up to 60 seconds specified in seconds or milli-seconds.

Example: In the following example, the sonet failure-delay command configures the delay between detecting a Sonet defect and marking the link as failed for 2350 milli-seconds:

router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. router(config)#interface pos 1/1/1 router(config-if)#sonet failure-delay 2350ms router(config-if)#show interface pos 1/1/1 clock source internal sonet failure-delay 2350ms . . . ip router isis 1 no shutdown

Displaying POS Settings, Thresholds and Performance

IPriori includes a variety of commands to display information about SONET configuration and performance. The commands and the information they display are listed in the table below:

Table 6-3. Commands to Display POS Settings, Thresholds and Performance

Command Name	Description
show interface pos n/n/n	Displays a POS interface.
show sonet performance [current|previous] pos	Displays the SONET/SDH statistics for the current 15-minute interval and for previous 15-minute intervals. Displays statistics for all SONET interfaces or for a specified SONET interface.
show sonet thresholds pos n/n/n	Displays the SONET thresholds for a POS interface.
In the "Configuration and File Management Commands" chapter of the "IPriori Command-Line Interface Reference"
show running-config	Displays the currently operating configuration.

Copyright © 2005 Avici Systems Inc.
Avici® and TSR® is a registered trademark of Avici Systems Inc.
IPriori™, Composite Links™, SSR™, QSR, and NSR® are trademarks of Avici Systems Inc.

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