Catalyst 2950 Desktop Switch Software Configuration Guide, 12.1(11)YJ
Configuring LRE
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Configuring LRE

Table Of Contents

Configuring LRE

Ports on the 2950 LRE

LRE Links and LRE Profiles

LRE Profiles

LRE Sequences

CPE Ethernet Links

Configuring LRE Ports

Environmental Guidelines for LRE Links

Guidelines for Using LRE Profiles

CPE Ethernet Link Guidelines

Considerations for Connected Cisco 575 LRE CPEs

Considerations for Connected Cisco 585 LRE CPEs

Assigning a Global Profile to All LRE Ports

Assigning a Profile to a Specific LRE Port

Assigning a Global Sequence to All LRE Ports

Assigning a Sequence to a Specific LRE Port

Using Rate Selection to Automatically Assign Profiles

Precedence

Profile Locking

Link Qualification and SNR Margins

LRE Link Persistence

LRE Link Monitor

Upgrading LRE Switch Firmware

Configuring for an LRE Upgrade

Performing an LRE Upgrade

Global Configuration of LRE Upgrades

Controller Configuration of LRE Upgrades

LRE Upgrade Behavior Details

LRE Upgrade Example


Configuring LRE


This chapter describes how to configure the Long-Reach Ethernet (LRE) features on your switch. This chapter consists of these sections:

Ports on the 2950 LRE

LRE Links and LRE Profiles

Configuring LRE Ports

Upgrading LRE Switch Firmware


Note For complete syntax and usage information for the commands used in this chapter, refer to the switch command reference for this release and the online Cisco IOS Interface Command Reference for Release 12.1.


Ports on the 2950 LRE

The Catalyst 2950 LRE switches use Long-Reach Ethernet (LRE) technology to transfer data, voice, and video traffic over categorized and noncategorized unshielded twisted-pair cable (Category 1, 2, and 3 structured and unstructured cable such as existing telephone lines).

Connecting a switch LRE port to a remote Ethernet device (such as a PC) requires two types of connections:

LRE link—This is the connection between the switch LRE port and the RJ-11 wall port on an LRE customer premises equipment (CPE) device such as the Cisco 575 LRE CPE or Cisco 585 LRE CPE. This connection can be through categorized or noncategorized unshielded twisted-pair cable and can extend to distances of up to 4921 feet (1500 m).

CPE Ethernet link—This is the connection between the CPE Ethernet port and an Ethernet device, such as a PC. This connection is through standard Category 5 cabling and can extend to distances of up to 328 feet (100 m).

The actual line speed in either direction between a switch LRE port and remote Ethernet device depends on the LRE link speed and the CPE Ethernet link speed. For example, if a PC Ethernet port is configured to 100 Mbps and the LRE port is configured with an upstream link speed of 5.69 Mbps, the actual upload rate provided to the PC user is 5.69 Mbps, not 100 Mbps.

For LRE troubleshooting information, see the "Troubleshooting LRE Port Configuration" section. Additional LRE details are in the switch command reference.

LRE Links and LRE Profiles

The LRE link settings define the connection between the switch LRE port and the CPE RJ-11 wall port. The LRE link provides symmetric and asymmetric bandwidth for data, voice, and video traffic. Symmetric transmission is when the downstream and upstream bandwidths are the same. Asymmetric transmission is when the downstream and the upstream bandwidths differ. Downstream transmission refers to the traffic going from the LRE switch to the CPE device. Upstream transmission refers to the traffic going from the CPE device to the LRE switch.

The switch controls upstream and downstream rates on the LRE link by using configurations called profiles. Depending on the profile, the upstream and downstream bands on an LRE link can range from approximately 1 Megabit per second (Mbps) to 18.750 Mbps.

This section discusses these topics:

LRE Profiles

LRE Sequences

CPE Ethernet Links

LRE Profiles

You can assign profiles on a per-port or switch-wide basis. When the LRE switch establishes a link with the CPE device, the switch downloads its profile settings to the CPE device so that the switch and CPE device operate with the same configuration.

The LRE switches are shipped with system-defined profiles. You can configure a profile on either a global or per-port basis. By default, all LRE ports on the switch are enabled with the LRE-10 profile. This default profile allows the upstream and downstream transmission rate on the LRE link to be 12.5 Mbps.

Table 10-1 contains the full list of LRE profiles, as well as their downstream and upstream rates (in Mbps and their theoretical upstream and downstream signal-to-noise (SNR) rates (in decibels).


Note Consult the regulations for connecting to the PSTN in your area.



Note Use the rates and distances in Table 10-1 as guidelines only. Factors such as the type of cable that you use, how it is bundled, and the interference and noise on the LRE link can affect the actual LRE link performance. Contact Cisco Systems for information about limitations and optimization of LRE link performance. The downstream and upstream rates in the table are slightly less than the gross data rates displayed by the show controllers lre profile names privileged EXEC command.


Table 10-1 LRE Profiles  

Profile Name
LRE Link Downstream Rate (Mbps)
LRE Link Upstream Rate (Mbps)
Theoretical Min SNR Downstream
Theoretical Min SNR Upstream

LRE-15

16.667

18.750

31

25

LRE-10 (default)

12.500

12.500

25

19

LRE-5

6.250

6.250

16

13

LRE-998-15-4

16.667

4.688

31

25

LRE-997-10-4

12.500

4.688

31

25

LRE-15LL

16.667

18.750

31

25

LRE-10LL

12.500

12.500

25

19

LRE-5LL

6.250

6.250

16

13

LRE-10-5

12.500

6.250

25

13

LRE-10-3

12.500

3.125

25

19

LRE-10-1

12.500

1.563

25

13

LRE-8

9.375

9.375

25

25

LRE-7

8.333

8.333

19

19

LRE-15-5

16.667

6.250

31

13

LRE-15-3

16.667

3.125

31

19

LRE-15-1

16.667

1.563

31

13

LRE-4

4.167

4.167

13

13

LRE-3

3.125

3.125

13

13

LRE-2

2.083

2.083

13

13

LRE-4-1

4.167

1.563

19

13

LRE-4-1LL

4.167

1.563

19

13


Your data rates will always be less than the gross data rate listed in table. A small percentage of the link rate is used by 2950 LRE switch for supervisory functions with the CPE device connected remotely.

In general, profiles are named for the data rate that you expect to achieve and not the gross data rate as given in the table. All system-defined profiles have the prefix LRE, followed by the downstream user data rate and then the upstream user data rate. If the profile is symmetric, only one data rate is given. The two profiles defined to comply with public frequency usage plans 998 and 997 (LRE-998-15-4 and LRE-997-10-4) are exceptions to this. These two uniquely named profiles work in any private deployment.

If you are not using sequences and you have not assigned a profile to an LRE port, the port has a default value of LRE-10. Port profiles have priority over global profiles. If you assign a global profile to the switch, the switch uses the global profile except on any LRE ports on which a specific profile was assigned.

When you assign a different profile to a switch LRE port, the port immediately resets and uses the newly assigned profile.

Use the LL profiles (LRE-5LL, LRE-10LL, and LRE-15LL) with care. These profiles have the low-latency (LL) feature enabled and the interleaver feature disabled. The LL feature does not delay data transmission, but it makes data more susceptible to interruptions on the LRE link.

All other profiles, port and global, have the interleaver feature enabled and the LL feature disabled. The interleaver feature provides maximum protection against small interruptions on the LRE link but delays data transmission.

The symmetric profiles (LRE-5, LRE-10, LRE-15, LRE-8, LRE-7, LRE-4, LRE-3, and LRE-2) provide full-duplex throughput on the link between the LRE switch and CPE device. Under ideal conditions, this can mean up to 30 Mbps of bandwidth on the LRE link if you are using the LRE-15 profile.

LRE Sequences

The LRE switches are shipped with predefined sequences. Sequences are sets of profiles and are used in conjunction with the rate selection feature. The rate selection feature enables the switch to automatically select profiles. You can also define your own sets of sequences using IOS commands or CMS. See the "Using Rate Selection to Automatically Assign Profiles" section for further information.

Table 10-2 outlines the predefined sequences for rate selection contained in Cisco IOS. When executing rate selection, the switch uses a sequences to choose an appropriate profile for a given LRE interface.

Table 10-2 LRE Rate Selection Sequences  

LRE-SEQ-
COMPLETE-REACH
LRE-SEQ-
DOWNSTREAM
LRE-SEQ-SYM
LRE-SEQ-SYM-
LONGREACH
LRE-SEQ-
SYMLL
LRE-SEQ-
UPSTREAM
LRE-SEQ-
VIDEO-
TRANSMIT1
LRE-SEQ-
VIDEO-
TRANSMIT2

LRE-15

LRE-15

LRE-15

LRE-5

LRE-15LL

LRE-15

LRE-15

LRE-15

LRE-10

LRE-15-5

LRE-10

LRE-4

LRE-10LL

LRE-10

LRE-15-5

LRE-15-5

LRE-15-5

LRE-15-3

LRE-8

LRE-3

LRE-5LL

LRE-8

LRE-15-3

LRE-10

LRE-10-5

LRE-15-1

LRE-7

LRE-2

 

LRE-7

LRE-15-1

LRE-10-5

LRE-8

LRE-10

LRE-5

LRE-4-1

 

LRE-15-5

LRE-10

LRE-15-3

LRE-7

LRE-10-5

LRE-4

   

LRE-10-5

LRE-10-5

LRE-10-3

LRE-15-3

LRE-10-3

LRE-3

   

LRE-5

LRE-10-3

LRE-15-1

LRE-10-3

LRE-10-1

LRE-2

   

LRE-4

LRE-10-1

LRE-10-1

LRE-5

LRE-8

     

LRE-15-3

   

LRE-15-1

LRE-7

     

LRE-10-3

   

LRE-10-1

LRE-5

     

LRE-3

   

LRE-4

LRE-4

     

LRE-2

   

LRE-3

LRE-4-1

     

LRE-4-1

   

LRE-2

LRE-3

           

LRE-4-1

LRE-2

           

Beginning with the first profile in a sequence, the switch attempts to apply each profile within that sequence to the LRE interface. The switch continues these attempts until it converges (convergence time refers to the time required for the switch to settle on an appropriate profile for the LRE interface). The link is DOWN until a link is established by one of the profiles in the sequence, after which, it is UP.

For additional information on rate selection, see the "Using Rate Selection to Automatically Assign Profiles" section.

CPE Ethernet Links

The CPE Ethernet link settings define the connection between the CPE Ethernet port and a remote Ethernet device, such as a PC.


Note From CMS and the CLI, you can configure and monitor the Ethernet link on a Cisco 575 LRE CPE and Cisco 585 LRE CPE. For information about the switch LEDs, see the Catalyst 2950 Series Hardware Installation Guide.


Keep these considerations in mind when you have CPE devices connected to the LRE ports:

Use the shutdown interface configuration command to disable the LRE interface transmitter on any LRE ports that are not connected to a CPE device. This prevents access to the LRE port and prevents the power emitted from the port from affecting other ports.

You cannot configure the flow-control setting on the LRE ports. The flow-control setting on the CPE Ethernet port is automatically disabled in half-duplex mode and is automatically enabled in full-duplex mode.

You can connect Cisco 575 LRE CPEs and Cisco 585 LRE CPEs to the same LRE switch.

You can hot-swap the CPE devices without powering down the switch or disrupting the other switch ports.

Use the show controllers ethernet-controller privileged EXEC command to display the internal switch statistics, the statistics collected by the LRE switch interface, and the statistics collected by the CPE LRE interface. For information about this command, refer to the switch command reference.

Configuring LRE Ports

These sections describe configuration guidelines and how to assign a profile to all or to individual LRE ports. These sections contain more information about LRE links, ports, and profiles:

Environmental Guidelines for LRE Links

Guidelines for Using LRE Profiles

CPE Ethernet Link Guidelines

Assigning a Global Profile to All LRE Ports

Assigning a Profile to a Specific LRE Port

Using Rate Selection to Automatically Assign Profiles

LRE Link Persistence

LRE Link Monitor

Environmental Guidelines for LRE Links

The guidelines for your LRE environment are based on these factors:

Maximum distance between the LRE switch and CPE devices—LRE runs on Category 1, 2, and 3 structured and unstructured cable. The maximum distance supported on the LRE link is from 3500 to 5000 feet, depending on the profile. The higher the rate, the shorter the distance. In buildings where LRE traffic runs over bundled telco cabling, the maximum distance is approximately 30 percent lower.

Each terminated bridge tap in a room can further reduce LRE link distances by 300 feet. The quality of the cable, the size of the cable bundles, and cross talk within the bundle also can affect overall reach.

Site type—If your site has either a PBX providing telephone service throughout or has direct connections to the PSTN, you must identify the requirements of your local public telephone service provider.

If your site is a single building (or is a connected set of buildings), consult a qualified electrician to ensure that the wiring conforms to the appropriate regulations for indoor circuits.

If your site has separate buildings, you must determine how the buildings are cabled to each other. Where the wiring between the LRE switch and CPE device leaves the building (or the armored conduits certified for inside wiring standards), it must be protected against lightning and shorts to high-voltage power. This protection might be provided by fuses or overvoltage protectors that comply with local regulations for outside wiring protection. Consult an expert in local telecommunications regulations for the details of this protection.

Age and type of wiring—You can estimate the type of wiring you have based on your site's age and type.

Newer installations less than 15 years old often use Category 3 cable in bundles of 25 pairs. There is no significant difference between 25-pair bundles and larger bundles.

Older installations (hotel, school, hospital, commercial—North America) 15 to 30 years old often use 24 AWG wiring with between 1 and 12 twists per foot (similar to Category 1) in bundles of 25 or more.

Older installations (residential—North America) 15 to 30 years old often use 26 AWG wiring with between 1 and 12 twists per foot (possibly type-2) in bundles of 100 or more.

Older installations (Europe) 15 to 30 years old often use 0.4 mm (similar to 26 AWG) wiring with between 1 and 12 twists per foot in bundles of 100 or more.

Older installations (Asia) 15 to 30 years old often use 0.4 mm (similar to 26 AWG) wiring with between 1 and 12 twists per foot in bundles of 100 or more.

Older installations over 30 years old often use heavy gauge wire (22 or 20 AWG) with no significant twist. In many cases, the cabling is set into the fabric of the building. The cables might be tightly or loosely bundled. For this estimate, assume that they are tightly bundled in groups of 25 or more.

Cross talk (noise) and interference—LRE operates with any number of wires in a cable binder carrying the LRE signal. Anywhere from one wire pair to every wire pair in the cable can carry LRE signals at the same time. LRE operates in full cable binders and adjusts power levels on each LRE link to maximize the performance of all connections.

The greatest impact on LRE performance is from the frequency response of the cable at the higher frequencies. LRE signals are more susceptible to interference at higher frequencies. The LRE upstream signal operates at the high end of the frequency spectrum. Cables have higher attenuation at higher frequencies and also interfere with other pairs in the bundle at higher frequencies. This interference or cross talk can significantly impact the signal quality.

Guidelines for Using LRE Profiles

When assigning a profile to a switch LRE port, keep these considerations in mind:

Phone lines typically operate at a frequency of up to 3.4 kHz. On the LRE link, the downstream transmission runs in a low-frequency band from approximately 1 to 3.5 MHz. The upstream transmission runs in a high-frequency band from approximately 4 to 8 MHz. Higher frequencies are more susceptible to interference. Consequently, upstream signals are susceptible to cross-talk and disruption on the link.

To maintain the quality of the LRE connection, use the asymmetric port profiles. These profiles use a low upstream rate but provide a high downstream rate.


Note All POTS telephones not directly connected to the CPE device require microfilters with a 300-ohm termination. Microfilters improve voice call quality when voice and data equipment are using the same telephone line. They also prevent nonfiltered telephone rings and nonfiltered telephone transitions (such as on-hook to off-hook) from interrupting the LRE connection.


When the link between the LRE switch and the CPE device must co-exist in the same cable bundle as an asymmetric digital subscriber line (ADSL), we recommend that you use either the ANSI profile (LRE-998-15-4) or the ETSI profile (LRE-997-10-4). For details on which profile to use elsewhere, consult the regulations for connecting to the PSTN in your area.

LRE signaling can coexist with ADSL signaling in one cable bundle. However, LRE signaling is not compatible with T1 signals in the same cable bundle.

Use the show controllers lre status link privileged EXEC command to display the LRE link statistics and profile information on the LRE ports. For information about these commands, refer to the switch command reference.

CPE Ethernet Link Guidelines

Follow these guidelines when configuring CPE Ethernet links:

Considerations for Connected Cisco 575 LRE CPEs

Considerations for Connected Cisco 585 LRE CPEs

Considerations for Connected Cisco 575 LRE CPEs

You can configure the Cisco 575 LRE CPE Ethernet port to operate at 10 or 100 Mbps and at half- or full-duplex mode, depending on the capability of the remote Ethernet device. Autonegotiation for port speed and duplex mode is supported.

The default speed for the CPE Ethernet port is auto. The default duplex mode is half duplex with back pressure.


Note When the default speed is set to 10 or 100 Mbps with half duplex, the values set are the same. If the remote values are 10 Mbps with full duplex, the Cisco 575 LRE CPE Ethernet port is profile independent. All LRE profiles are set to be 10 Mbps with half duplex except for LRE-10 (the default), which is set to 10 Mpbs with full duplex. For a setting of 100 Mbps with full duplex, the value is set to 100 Mbps with half duplex.


The speeds on the LRE links and CPE Ethernet links do not need to match. However, to prevent the possible loss of data when the LRE link is slower than the CPE Ethernet link, make sure that the CPE Ethernet port is set to half-duplex mode. Use duplex autonegotiation only if the remote device supports 802.1X full-duplex flow control. The PC user should notice no significant difference in performance between 100-Mbps half duplex and 100-Mbps full duplex. Use the cpe duplex and cpe speed interface configuration commands, respectively, to change the duplex and speed settings on the Cisco 575 LRE CPE Ethernet port.

Considerations for Connected Cisco 585 LRE CPEs

You can configure the Cisco 585 LRE CPE Ethernet port speed and duplexing from the command line, depending on the capability of the remote Ethernet device. Autonegotiation for CPE port speed and duplex mode is supported.

The default speed for the CPE Ethernet ports is auto. The default duplex mode is half duplex at 100 Mbps with back pressure.

You can enable or disable the CPE Ethernet ports on a per-port basis.

The loopback interface configuration command is not supported on the LRE ports. External loopback on the LRE ports is also not supported. Connecting a CPE Ethernet port to another Ethernet port on the same CPE device can create a loop. If this happens, the switch stops sending to the CPE device and blocks Ethernet traffic coming from the CPE device.

Assigning a Global Profile to All LRE Ports

Global profiles are set on a switch-wide basis.

Port sequences, global sequences, and port profiles have priority over global profiles (see the "Precedence" section for a full discussion of rate selection precedence). If you assign a global profile to the switch, it cannot over-ride any previously or subsequently set sequence port profile. (For further information on sequence and profile precendence, see Guidelines for Using LRE Profiles.)

Changes to the global profile settings are immediately put in effect, and the global mode automatically becomes the active mode.

Beginning in privileged EXEC mode, follow these steps to assign a global profile to the LRE ports:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

lre profile profile_name

Enter the global profile name. Select from the list in Table 10-1.

Step 3 

end

Return to privileged EXEC mode.

Step 4 

show controllers lre profile details

Verify the change.

Use the show controllers lre privileged EXEC commands to display the LRE link statistics and profile information on the LRE ports. For information about these commands, refer to the switch command reference.

Assigning a Profile to a Specific LRE Port

You can set profiles on a per-port basis. You can assign the same profile or different profiles to the LRE ports on the switch. The default active profile on all LRE ports is LRE-10.

The switch resets the ports with the updated profile settings when changed.

Beginning in privileged EXEC mode, follow these steps to assign a profile to a specific LRE port:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface LRE-interface

Enter interface configuration mode, and enter the number of the LRE port to be configured.

Step 3 

profile profile_name

Enter the port profile name (select from the list in Table 10-1).

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show controllers lre profile details

Verify the change.

Use the show controllers lre privileged EXEC command to display the LRE link statistics and profile information on the LRE ports. For information about these commands, refer to the switch command reference.

Assigning a Global Sequence to All LRE Ports

Global sequences are set on a switch-wide basis. If you assign a global sequence to the switch, it over-rides any previously or subsequently set profiles. (For further information on sequence and profile precendence, see Guidelines for Using LRE Profiles.)

Changes to the global sequence settings are immediately put in effect, and the global mode automatically becomes the active mode.

Beginning in privileged EXEC mode, follow these steps to assign a global sequence to the LRE ports:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

lre rate selection sequence sequence_name

Enter the global sequence name. Select from the list in Table 10-2.

Step 3 

end

Return to privileged EXEC mode.

Step 4 

show controllers lre status sequence

Verify the change.

Use the show controllers lre status sequence details privileged EXEC commands to display the LRE link statistics and sequence information on the LRE ports. For information about these commands, refer to the switch command reference.

Assigning a Sequence to a Specific LRE Port

You can set sequences on a per-port basis. You can assign the same sequence or different sequences to the LRE ports on the switch. If you assign a sequence on a port basis, it overrides any previously or subsequently set profiles or global sequence.

The switch resets the ports with the updated sequence settings when changed.

Beginning in privileged EXEC mode, follow these steps to assign a sequence to a specific LRE port:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface LRE-interface

Enter interface configuration mode, and enter the number of the LRE port to be configured.

Step 3 

sequence sequence_name

Enter the port sequence name (select from the list in Table 10-2).

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show controllers lre status sequence

Verify the change.

Use the show controllers lre status sequence details privileged EXEC command to display the LRE link statistics and sequence information on the LRE ports. For information about these commands, refer to the switch command reference.

Using Rate Selection to Automatically Assign Profiles

An LRE network requires a profile to be configured for each LRE port that is connected to a CPE device (the default is LRE-10). You can use the rate selection feature to automatically choose a profile from a set of profiles that the switch port uses to establish an LRE link (a link between an LRE switch port and an attached CPE device).

Rate selection is enabled by default, but you must choose a sequence for rate selection to start (in other words, there is no default sequence defined). When rate selection is running, the switch chooses the profile for the LRE interface from a sequence, or predefined series of profiles, that are configured for that interface. The rate-selection algorithm begins with the first profile in the sequence and successively tries the next profiles (in descending order) until a link is established with the CPE device.

When enabled, the LRE switch executes rate selection in these scenarios:

When the switch is booted

When you enable the rate selection feature

When you connect a new CPE device to the switch

When a link is lost for 25 seconds before being restored

When a configured sequence is modified

In any of these cases, rate selection obtains the optimal profile for your line conditions.


Note When an LRE link is lost for fewer than 25 seconds, the switch does not execute rate selection to re-establish the link. The link is re-established at the profile used before link loss.


The switch chooses the appropriate profile for an LRE interface when it executes rate selection. If line conditions of the LRE interface change, rate selection must be executed again.

Precedence

The rate selection feature can be applied at both the port level and at the switch level. Profiles and sequences have a system-defined priority level that work with rate selection to determine the rate for a port or the entire switch. Port sequences have the highest priority; that is, they take precedence over any other profile or sequence. The priority levels, from highest to lowest, are as shown:

1. Port sequence: rate selection is enabled on the given port only with the given sequence.

2. Global sequence: rate selection is enabled for the entire switch with the given sequence.

3. Port profile: rate selection is enable for the given port only with the given profile.

4. Global profile: rate selection is enabled for the entire switch with the given profile.

See Table 10-1 for the list of profiles and Table 10-2 for the list of system-defined sequences. You can also use IOS commands or CMS to define your own sequences.


Note If rate selection is disabled for a port, then profiles are used.


Profile Locking

You can also use rate selection as an installation tool to lock in a particular profile. In this case, you execute rate selection only once at installation; afterwards, rate selection is never executed, even if one of the four listed events occur. You use the config command in privileged EXEC mode to lock the profile chosen by rate selection. (You can enter a special EXEC command to rerun rate selection on the interfaces that have locked the profiles, as needed.)

An advantage to profile locking is that the convergence time during bootup is faster if a profile is locked on an LRE port rather than having to go through a profile sequence.

Beginning in privileged EXEC mode, follow these steps to lock a profile in an LRE port that has rate selection enabled:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface LRE-interface

Enter interface configuration mode, and enter the number of the LRE port to be configured.

Step 3 

rate selection profile lock

Lock the profile.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show controllers lre profile details

Verify the change.

Link Qualification and SNR Margins

When rate selection is running, the SNR is used as an indicator of link quality. The switch does not provide any internal mechanism to ensure link quality. There can be different requirements for link quality, depending on the required bit-error rate and the noise level of the environment. A noisier environment would require a higher SNR to be able to provide a stable link. A lower bit-error rate would require a higher SNR. Typically a 6-dB margin provides an error rate of 10-21 bits.

To provide link stability, you should add a margin to the required SNR. You can configure your margins to an amount that is appropriate for the noise level of your environment. Increasing the margin requirement can cause the system to choose a lower profile, which would in turn translate to a lower rate but with a higher reach.

The switch does not guarantee any margins after a link is activated; margins are only guaranteed only when the link is established. When a link is activated, if the SNR requirements do not match the configured margin level, the link is not established.

Downstream means the remote end of the link, and upstream the local end. The link has to satisfy both the local and remote margin requirements. If either one is not met, the link is advertised as down. This command has no significance if rate selection is disabled on the interface.

Table 10-3 lists the SNR requirements for downstream rates for different profiles.

Table 10-3 SNR Requirements for Downstream Rates

Profile
Gross Data Rate
QAM
Theoretical Minimum SNR
Low Noise SNR
Medium Noise SNR
High Noise SNR

LRE-4-1

4.17

16

19

21

23

26

LRE-7

8.333

16

19

21

23

26

LRE-8

9.375

64

25

27

29

32

LRE-5

6.25

8

16

19

21

24

LRE-10

12.5

64

25

27

29

32

LRE-15

16.667

256

31

33

35

39

LRE-10-5

12.5

64

25

27

29

32

LRE-10-3

12.5

64

25

27

29

32

LRE-10-1

12.5

64

25

27

29

32

LRE-15-5

16.667

256

31

33

35

39

LRE-15-3

16.667

256

31

33

35

39

LRE-15-1

16.667

256

31

33

35

39

LRE-998-15-4

16.667

256

31

33

35

39

LRE-997-10-4

12.5

256

31

33

35

39

LRE-2

2.08

4

13

15

17

20

LRE-3

3.13

4

13

15

17

20

LRE-4

4.17

4

13

15

17

20


Table 10-4 lists the SNR requirements for upstream rates for different profiles.

Table 10-4 SNR Requirements for Upstream Rates

Profile
Gross Data Rate
QAM
Theoretical Minimum SNR
Low Noise SNR
Medium Noise SNR
High Noise SNR

LRE-4-1

1.56

4

13

15

17

20

LRE-7

8.333

16

19

21

23

26

LRE-8

9.375

64

25

27

30

34

LRE-5

6.25

4

13

15

17

20

LRE-10

12.5

16

19

21

23

26

LRE-15

18.75

64

25

27

30

34

LRE-10-5

6.25

4

13

15

17

20

LRE-10-3

3.125

16

19

21

23

26

LRE-10-1

1.56

4

13

15

17

20

LRE-15-5

6.250

4

13

15

17

20

LRE-15-3

3.125

16

19

21

23

26

LRE-15-1

1.563

4

13

15

17

20

LRE-998-15-4

4.688

64

25

27

29

32

LRE-997-10-4

4.688

64

25

27

29

32

LRE-2

2.08

4

13

15

17

20

LRE-3

3.13

4

13

15

17

20

LRE-4

4.17

4

13

15

17

20


The margin range for link qualification is from 1 to 10 dB. The recommended value in a low-noise environment is 2 dB. The recommended value for medium noise environment is 4 dB. The recommended value in a high noise environment is 6 dB.

If a profile has a theoretical minimum of 25 dB and you configure a margin of 3 dB, when the link is established, the SNR should at the least be 28 dB to indicate a successful link. If a link is established and if the SNR value at link time is 27 dB, the link is advertised as down, and the next profile in the sequence is attempted. If you configure a margin of 0 (the default value), IOS does not check for the SNR value when the link is established.

Beginning in privileged EXEC mode, follow these steps to assign a margin to a specific LRE port:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface LRE-interface

Enter interface configuration mode, and enter the number of the LRE port to be configured.

Step 3 

margin [downstream value | upstream value]

Enter the downstream or upstream margin value (in dB)

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show controllers lre profile details

Verify the change.


Note The margin command is effective with any profile, but only in conjunction with rate selection and only when a link is being activated.


LRE Link Persistence

A brief LRE link down and up transition can cause the rest of the IOS modules to react immediately, for example, the Dynamic MAC addresses are removed from that ports table. You can use the link persistence feature to configure a delay duration on the Catalyst 2950 LRE of up to 20 seconds before link failure is reported.

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

interface LRE-interface

Enter interface configuration mode, and enter the number of the LRE port to be configured.

Step 3 

persistence time

Enter the length of time (in seconds) you wish to set for the persistence. (The default is 3 seconds)

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show controllers lre status persistence

Verify the change.

Refer to the lre persistence reference pages in the Catalyst 2950 Desktop Switch Command Reference for further details.

LRE Link Monitor

You can use the link monitor feature to track undesirable or interesting conditions on a link and to take system-defined actions after certain thresholds are reached. The link monitor can track these conditions:

SNR, in decibels (db): The link must have a minimum SNR to function; a higher SNR value means a better noise margin on the link. Links are not establish if the SNR is insufficient. (See the "Link Qualification and SNR Margins" section for more information.)

Reed-Solomon (RS) errors: The RS Forward Error Correction circuit corrects small bursts of errors so that noise events do not cause Ethernet FCS errors. This is implemented in the octal chip as a 32-bit counter. The count resets on read.

Transmit (TX) Power, in dBm/Hz: This is fixed for the switch and adjusts automatically for the CPE device. The local transmit power is always constant and the same for a given profile. The remote transmit power varies according to distance from the switch to the CPE device, with a minimum transmit power of 91.9 dBm/Hz (corresponding to short distances) and a maximum transmit power of -55 dBm/Hz (corresponding to longer cable lengths or greater cable attenuation). The CPE device's power can reach its maximum at distances between 1500ft/450m and 3000ft/900m.

Software controlled Automatic Gain Control (SW AGC Gain), in dBm: This gives an indirect measure of the received power level. Higher values mean that the receive power is lower (and thus in need of more boost).

Link Fail Counts: The number of times the link failed. A link fail interrupts operation of the Ethernet link for a small number of milliseconds. During this interruption, some packets might be dropped (depending on traffic levels).

PMD Freeze Event Counter: Counts the occurrence of micro-interruption or saturation events. Micro-interruptions and ADC saturations are caused by impulse noise for a short duration. This is implemented in the octal chip as a 8-bit counter.

The link parameters need to be monitored both for the upstream and downstream directions.

You can use the information you get from the link monitor to log events, set traps, change to a lower rate profile, and disable the auto power back-off feature.

See the reference pages for the link monitor commands in the Catalyst 2950 Desktop Switch Command Reference for further details.

Upgrading LRE Switch Firmware

The 2950 Long-Reach Ethernet (LRE) switch can store and properly apply LRE binaries in case there are updates required to the firmware on the switches' local LRE controllers or connected customer premises equipment (CPE) devices.

Other desirable upgrade-related features include:

Allowing you to use an earlier version of the LRE software if required.

Simplifying the upgrade process as much as possible, especially in cases where you want the ability to upgrade multiple CPE devices by issuing a single command.


Note Whether upgrading a single CPE device or all CPE devices connected to an LRE switch, the expected duration of an LRE upgrade is 3 to 6 minutes (CPE devices connected to marginal links might take longer than this to upgrade).


You perform an upgrade with this command:

hw-module slot x upgrade lre [force][local lo n | remote lo x/y]

Automatic upgrading is not supported. You can upgrade in one of these ways:

Upgrade a single remote CPE device.

Upgrade a single local LRE controller (local LRE chipset).

Upgrade all CPE devices and local chipsets that require an upgrade (a system-wide upgrade, which is the default)

Configuring for an LRE Upgrade

In the absence of any LRE Upgrade configurations, the LRE upgrade attempts to upgrade all local LRE controllers and CPE devices to the most recent compatible versions of the LRE binaries required for each LRE target device. LRE upgrade configurations should rarely be required. The primary purpose of LRE upgrade configuration commands is to provide for downgrades of LRE binaries.

If you wish to override the switch's automatic selection of LRE binaries, you have these methods available:

Global LRE Upgrade Configuration Commands

LRE Controller configuration commands

You can use config global commands to specify the LRE binary or binaries for a specified target type. (A target type is the family [and optionally the model or model revision] of a device containing one or more upgradable hardware elements.) A target can be a local LRE controller on the switch or a remote CPE device.

You can perform global LRE upgrade configurations by issuing LRE upgrade controller configuration commands from the controller configuration submode. You can use the upgrade configuration command in the controller submode to override the system default selection of an LRE binary to be applied on a particular remote CPE device or local LRE controller. Controller configurations take precedence over global upgrade configurations.

The preserve keyword causes the LRE upgrade mechanism to not upgrade the local controller on which preserve is configured or any of the CPE devices connected to that controller. If you want to preserve (in other words, not upgrade) some of the CPE devices connected to a particular controller but allow upgrades to others, you can enter controller upgrade configuration commands for the links that you want to upgrade.

The no form of the upgrade command removes the command for applying a particular LRE binary. To resume default upgrade behavior for a given controller, configure the no upgrade commands on that controller


Note You also need to remove global configurations that might also affect the controller and devices connected to it.



Note When a config global command and a config controller command conflict, the config controller command has precedence.


Refer to the reference pages for the upgrade commands in the Catalyst 2950 Desktop Switch Command Reference for further details.

Performing an LRE Upgrade

You can upgrade either on a system-wide basis (in other words, upgrading the software on all connected CPE devices and local LRE chipsets) or on individual CPE device or LRE controllers. By default, a system-wide upgrade applies the most recent versions of LRE binaries that are most compatible with each upgradable hardware module. The system-wide upgrade method is the one that you use in almost all situations.

When executing upgrades, you can elect to upgrade a single CPE device or local controller by using this command hw-module slot <x> upgrade lre [local lo n | remote lo x/y]. If no local or remote option is given, a system-wide upgrade is performed.

Global Configuration of LRE Upgrades

Beginning in privileged EXEC mode, follow these steps to perform a system-wide upgrade to configure the LRE binary to apply to a target device and upgradable hardware element combination:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

lre binary default target_device LRE_binary

Enter the device to which the LRE binary should be applied; and the LRE binary to be applied.

Step 3 

end

Return to privileged EXEC mode.

Step 4 

show lre upgrade version

Verify the change.


Note The lre upgrade default mode command essentially overrides the system default selection of an LRE binary for a specified family of CPE devices (target devices).


Controller Configuration of LRE Upgrades

Beginning in privileged EXEC mode, follow these steps to explicitly direct the LRE binaries to be applied to either the local controller or a specific VDSL link:

 
Command
Purpose

Step 1 

configure terminal

Enter global configuration mode.

Step 2 

controller lre chipset_number

Enter the particular LRE local chipset on the switch to be applied.

Step 3 

upgrade <[remote lo x/y] LRE_Binary | preserve>

Enter the LRE binary to be applied, or set preserve, which prevents the upgrade of any CPE devices connected to a controller or local chipset.

Step 4 

end

Return to privileged EXEC mode.

Step 5 

show lre upgrade version

Verify the change.

You can use the upgrade configuration command in the controller submode to override the system default selection of an LRE binary that will be applied on either end of a particular LRE link. Controller configurations take precedence over global upgrade configurations.

The preserve keyword causes the LRE upgrade mechanism to not upgrade the local controller on which preserve is configured or any of the CPE devices connected to that controller. If you want to preserve (in other words, not upgrade) some of the CPE devices connected to a particular controller but allow upgrades to others, you can enter controller upgrade configuration commands for the links you want to upgrade.

The no form of the command removes the command for applying a particular LRE binary. To resume default upgrade behavior for a given controller, do not configure the custom upgrade commands on that controller.

LRE Upgrade Behavior Details

You see on the console screen when you start an upgrade:

Switch>en
Switch#hw-module slot 0 upgrade lre
You are about to start an LRE upgrade on all LRE interfaces.
Users on LRE links being upgraded will experience a temporary disruption of Ethernet 
connectivity.
Start LRE upgrade ? [yes]:

If you answer yes or press the Enter key, the upgrade starts. If you answer no, you get the EXEC prompt.

You can expect this link behavior of the CPE device during an upgrade:

When the upgrade starts, the link is probably in the link-up state, the state of the link that is useful to you.

When the upgrade starts, the remote CPE device resets. Ethernet connectivity is temporarily lost.

The CPE device comes up, with the link slower (about 1 Mbps upstream and 4 Mbps downstream) but more reliable. The increased reliability is required for a successful LRE binary transfer. The LRE link stays at a slower speed for the duration of the upgrade. Ethernet connectivity is available.

When the upgrade is complete, the CPE device is again reset so that the upgraded LRE binaries are loaded and executed on the target CPE devices and local LRE chipsets. Ethernet connectivity is again disrupted until the CPE finishes resetting.

The link comes up when the CPE device comes back up, and then progresses to where it resumes full operation at its intended data rate.

LRE Upgrade Example

The following is an example of how an LRE upgrade can proceed:

Switch#hw-module slot 0 upgrade lre force remote lo 0/1
You are about to start an LRE upgrade on CPE Lo0/1.
Users on LRE links being upgraded will experience a temporary
disruption of Ethernet connectivity.

Start LRE upgrade ? [yes]:

Starting remote upgrade on CPE Lo0/1

Switch#
00:21:51: %LINEPROTO-5-UPDOWN: Line protocol on Interface
LongReachEthernet0/1, changed state to down

The CPE device is reset and the link is down. Ethernet connectivity is unavailable at this point.

00:22:37: %LINK-3-UPDOWN: Interface LongReachEthernet0/1, changed state to up
00:22:39: %LINEPROTO-5-UPDOWN: Line protocol on Interface
LongReachEthernet0/1, changed state to up

The CPE device finishes resetting. Ethernet connectivity is available but at low speeds. Upgrade data transfer begins.

00:23:55: %LINEPROTO-5-UPDOWN: Line protocol on Interface
LongReachEthernet0/1, changed state to down

Upgrade data transfer is complete. Reset the CPE device.

00:23:56: %LINK-3-UPDOWN: Interface LongReachEthernet0/1, changed state to up

The CPE device has finished resetting. The desired profile is applied.

00:23:58: %LRE_LINK-3-UPDOWN: Interface Lo0/1, changed state to UP
00:23:59: %LINK-3-UPDOWN: Interface LongReachEthernet0/1, changed state to up
00:24:02: %LINEPROTO-5-UPDOWN: Line protocol on Interface
LongReachEthernet0/1, changed state to up

Operation resumes in the profile link up state.

Switch#