Usage Guidelines

This command is used in the MAC domain. When this command is used on a particular interface, the UDC feature for all the cable modems on that interface is enabled.

Usage Guidelines

Use this command to automatically upgrade the Downstream PHY firmware on the Cisco cBR-8 router.

Usage Guidelines

This command is applicable only for S-CDMA channels. You should configure S-CDMA to apply the active-code setting.

Usage Guidelines

This command limits the maximum number of CMs for a given upstream port by looking at the minimum guaranteed upstream bandwidth allocated to each CM. Cable modems providing residential services and commercial services can be given different weights according to their traffic needs. This command affects only whether CMs can register with the CMTS—it does not affect CMs that have already come online.

The CMTS uses the minimum guaranteed upstream bandwidth field from the CM’s DOCSIS configuration file to calculate whether the CM can come online or not. If the CM’s minimum guaranteed upstream bandwidth would exceed the total upstream bandwidth multiplied by the overbooking percentage specified by this command, the CM cannot come online on that upstream. The CM will attempt to find another upstream, and if it cannot register on any upstreams, it will attempt to lock on to a new downstream.

Note	A CM with a guaranteed upstream bandwidth does not consume that bandwidth unless it has active traffic. By guaranteeing a CM a minimum upstream bandwidth, individual customers are assured of never being totally shut out from network access in a very high-traffic situation.

The following table shows the approximate bandwidth for each upstream channel, depending on channel width, symbol rate, and modulation type, when admission control is used at 100 percent. When setting admission control to other values, scale the bandwidth values in the following table accordingly, so as to plan for the maximum number of CMs effectively allowed per upstream port.

For example, with a 3.2 MHz channel width and QPSK modulation, the total bandwidth is approximately 5 Mbps. This is the maximum allowable bandwidth that can be allocated to CMs at the default admission rate of 100%. If each CM is allocated a minimum upstream bandwidth of 128 kbps, this means a maximum of 40 CMs will be allowed to come online.

To verify whether or not upstream admission control is configured and activated, use the show interface command for a cable upstream to display its configuration information. If upstream admission control is configured and enabled, the output contains an entry stating “CIR admission control enforced.” If upstream admission control is disabled, no admission control entry is displayed in the output.

Note	Setting the admission control limit to below the current total reserved bandwidth for the channel does not immediately force any CMs offline, but may prevent CMs from reconnecting if they drop offline at a later time. Increasing the admission control limit allows more CMs to connect.

When an upstream becomes overbooked, use the test cable ucc command to move a cable modem that is currently online from one upstream port to another. For example, the following example shows that the cable modem with the IP address of 10.128.1.128 is being moved from port C3/0/U0 to C3/0/U1:

Router# show cable modem 10.128.1.128
 
Interface   Prim Online     Timing Rec    QoS CPE IP address      MAC address
            Sid  State      Offset Power
Cable3/0/U0 101  online     1919    5.25  7   0   10.128.1.128    0030.1976.7067
Router# test cable ucc c3/0 101 1
Router# show cable modem 10.128.1.128
 
Interface   Prim Online     Timing Rec    QoS CPE IP address      MAC address
            Sid  State      Offset Power
Cable3/0/U1 101  online     1920    5.25  7   0   10.128.1.128    0030.1976.7067

Usage Guidelines

This command allows the user to define the maximum reserved bandwidth per bonding group. The default maximum reserved bandwidth value is 80 percent. However the user can choose to configure a higher (up to 96 percent) or lower reserved bandwidth so that there is bandwidth allocated for zero committed information rate (CIR) best effort traffic.

Usage Guidelines

This command sets the attribute mask of upstream channel.

Usage Guidelines

This command is used to balances service flows across upstream channels in a MAC domain. This command is used only for UB-online cable modems.

Usage Guidelines

To verify whether or not ECN MULPIv3.0-N-14.1145-1 feature is activated, enter the show running-config command and look for the cable upstream bcast-init-ranging tcc-enc excl-timing information. By default, it is disabled.

Usage Guidelines

You can configure up to 32 static upstream bonding groups for each Media Access Control (MAC) domain. However, you can configure only 16 upstream channels for each MAC domain. If you delete an upstream bonding group using the no form of the command, the Cisco CMTS router enforces the bonded upstream service flows associated with the deleted upstream bonding group to readmit.

Under the upstream bonding configuration submode, you can specify the following for an upstream bonding group:

• Upstream channels
• Bandwidth reservation
• Provisioned attribute masks

Note	While adding upstream channels under the upstream bonding group, ensure that the upstream channel is pre-configure using the following command: downstream integrated-cable slot/ subslot/ port rf-channel rf-channels [upstream grouplist]

Router(config-if)#cable upstream bonding-group 106
Router(config-upstream-bonding)#upstream 0
Router(config-upstream-bonding)#upstream 6
Upstream 6 is not yet defined in MD Cable9/0/0.

Note

The changes made to the configuration, using the attributes command in the upstream bonding configuration submode, on the working line card are synchronized with the configuration on the protect line card only after exiting the configuration mode. Use the end command to exit to Privileged EXEC mode, before using the show running configuration command.

Router(config-if)#cable upstream bonding-group 106
Router(config-upstream-bonding)#upstream 0
Router(config-upstream-bonding)#upstream 6
Router(config-upstream-bonding)#upstream 7
.
.
.
Router(config-if)#cable upstream bonding-group 110
Router(config-upstream-bonding)#upstream 12
Router(config-upstream-bonding)#upstream 13
Router(config-upstream-bonding)#upstream 14

Usage Guidelines

The cable upstream chan-class-id command is associated with the CM Steering on the Cisco CMTS Routers feature.

An upstream channel descriptor (UCD) message includes type, length, value (TLV) 18 and 19 for an upstream logical channel based on the channel class ID and ranging hold-off priority configuration. If a channel class ID is not configured, the UCD does not include TLV18 and 19 irrespective of the ranging hold-off priority configuration.

Usage Guidelines

The last-choice-width parameter is supported only by the Cisco uBR-MC16S, Cisco uBR-MC16U/X, Cisco uBR-MC28U/X, and Cisco uBR-MC5X20S/U cable interface line cards. When one of these particular cards is installed, the system attempts to increase the channel width from the smallest channel width value to the largest channel width value.

When you specify both channel width values, the smaller value is taken as the last-choice-width parameter and the larger value is taken as the first-choice-width parameter. In the event of noise in the channel, the symbol rate automatically steps down to a value that is lower than the first-choice-width and greater or equal to the last-choice-width to maintain a stable channel.

Note

The UBR-MC20X20V cable interface line card has three variants, UBR-MC20X20V-0D, UBR-MC20X20V-5D, and UBR-MC20X20V-20D. The UBR-MC20X20V-0D line card supports 20 upstreams and zero (no) downstreams. The UBR-MC20X20V-5D line card supports 20 upstreams and five downstreams, and the UBR-MC20X20V-20D line card supports 20 upstreams and 20 downstreams.

Note

In Cisco IOS Release 12.2(15)BC1 and later releases, changing the channel width could force a frequency hop, if the current frequency does not fit within the new channel width parameters, or if the system needs to reset the fixed frequency or shared frequency group parameters to match the new channel width.

Caution

In DOCSIS 1.X networks, do not change the channel width more than one step at a time on an interface that has cable modems that are currently online. The DOCSIS 1.X specifications require that cable modems remain online when the channel width is changed in single step increments (such as 800,000 to 1,600,000 Hz), but cable modems can go offline when you change the channel width in larger amounts (such as changing it from 800,000 to 3,200,000 Hz). To check if the DOCSIS 2.0 cable modems support changing the channel width by two steps, test each brand of modem before attempting it on a live network. Also, after changing the channel width, do not change the channel width again until all cable modems have performed their ranging adjustments for the new width (which could take up to a minute, depending on the number of cable modems).

Note	To specify only one channel width for the Cisco uBR-MC16U/X, Cisco uBR-MC28U/X, or Cisco uBR-MC5X20S/U/H card, specify the same value for both the first-choice-width and last-choice-width parameters. For example:cable upstream 0 channel-width 800000 800000

When using this command to change channel-widths for an upstream interface on the Cisco uBR-MC5X20S cable interface line card, some DOCSIS 1.1 CMs can go offline if you do not change the minislot size to the corresponding value. See the following examples for the correct channel-width and minislot pairings:

Router(config-if)# cable upstream 0 channel-width 3200000
Router(config-if)# cable upstream 0 minislot 4
Router(config-if)# cable upstream 0 channel-width 1600000
Router(config-if)# cable upstream 0 minislot 8
Router(config-if)# cable upstream 0 channel-width 800000
Router(config-if)# cable upstream 0 minislot 16
Router(config-if)# cable upstream 0 channel-width 400000
Router(config-if)# cable upstream 0 minislot 32
Router(config-if)# cable upstream 0 channel-width 200000
Router(config-if)# cable upstream 0 minislot 64
 

Note

This limitation does not affect DOCSIS 1.1-compliant CMs. Also, in Cisco IOS Release 12.2(15)CX, Cisco IOS Release 12.2(15)BC2, and later releases, there is no need to manually change the minislot size on the Cisco uBR-MC16U/X, Cisco uBR-MC28C, and Cisco uBR-MC28U/X cards. These cards automatically change the minislot size when the channel width is changed, to produce 32 symbols per minislot.

Note	Starting with Cisco IOS 12.2(33)SCG2, when the channel-width value in the cable upstream channel-width command is specified as 6.4 MHz in the TDMA or mixed TDMA/A-TDMA mode, the DOCSIS mode automatically changes to A-TDMA-only (DOCSIS 2.0) mode.

PacketCable Limitations

The 200,000 Hz channel width cannot be used on:

• Upstreams that support PacketCable voice calls
• Upstreams that use Unsolicited Grant Service (UGS) or UGS with Activity Detection (UGS-AD) service flows.

Using this small channel width with voice and other UGS/UGS-AD service flows results in rejected calls because of “DSA MULTIPLE ERRORS”.

Usage Guidelines

This command limits the maximum number of codes-per-minislot for a given upstream port. You should configure S-CDMA to apply the active-code setting.

Usage Guidelines

Concatenation is part of DOCSIS 1.0 extension support. Concatenation provides for improved bandwidth efficiency but must be supported at both the headend CMTS and the CM.

DOCSIS concatenation combines multiple upstream packets into one packet to reduce packet overhead and overall latency and increase transmission efficiency. Using concatenation, a DOCSIS CM needs to make only one bandwidth request for a concatenated packet, compared to making bandwidth requests for each individual packet. This technique is especially effective for bursty real-time traffic such as voice calls.

Concatenation support improves upstream per CM data throughput. The Cisco CMTS radio frequency (RF) line card driver can receive only one MAC frame in a data burst. Thus the CM must make explicit bandwidth requests for every packet it sends upstream. This limits the maximum upstream data throughput received by the CM due to the inherent request-to-grant round-trip latency of the hybrid fiber-coaxial (HFC) cable system incurred by every packet. To increase this per-CM upstream throughput, the Cisco CMTS driver has been enhanced to receive a concatenated burst of multiple MAC frames from the same CM.

Note	Concatenation is not supported on the Cisco uBR-MC11 FPGA and Cisco uBR-MC16B cable interface line cards.

Usage Guidelines

The cable upstream connector command maps a MAC domain upstream port to a particular physical RF port on the cable line card front panel. For all cable line cards except the Cisco uBR-MC3GX60V, the default mapping assigns one upstream port to one physical port. The default mapping of Cisco uBR-MC3GX60V cable line card assigns four upstream ports to one physical port. The physical ports are mapped sequentially in the order in which they appear on the front panel.

The no version of this command removes the upstream port mapping and shuts down the upstream port. The port must be remapped to another physical port before it can come online again.

Tip	Use the cable upstream max-ports command to set the maximum number of upstream ports per MAC domain before using the cable upstream connector command.

Each MAC domain can have up to 8 upstream ports. Each upstream port can be mapped to a physical port.

Usage Guidelines

Use this command to configure the upstream controller profile.

When configuring a new i-CMTS controller profile, keyword I-CMTS is needed. If user input RPHY or do not input any keyword, the system will consider it as a RPHY controller profile.

Usage Guidelines

The DOCSIS-specified method of contention resolution for CMs used to send data or requests on the upstream channel is a truncated binary exponential backoff with the initial backoff window and the maximum backoff window controlled by the CMTS. The Cisco CMTS router specifies backoff window values for both data and initial ranging, and sends these values downstream as part of the Bandwidth Allocation Map (MAP) MAC message.

The values specified in this command are exponential power-of-two values. For example, a value of 4 indicates a window between 0 and 15; a value of 10 indicates a window between 0 and 1023.

To manually specify the data-backoff values, use the following formula as a guideline for the start and end binary exponents:

0.33 = (2**stop- 2**start)/n

where n is the number of CMs on the upstream. Choose start and stop values that come closest to the value of 0.33 (which is the optimal probability to transmit on a contention-based system).

Usage Guidelines

Use the cable upstream description command to assign arbitrary labels to the upstreams on the cable interfaces. These labels can contain any information that identifies the upstream and that could aid in network management or troubleshooting.

Tip	Use the show interface cable upstream command to display the labels that are assigned to a particular upstream.

Usage Guidelines

To verify whether or not upstream differential encoding is activated, enter the show running-config command and look for the cable interface configuration information. If upstream differential encoding is enabled, a differential encoding entry is displayed in the output of the show running-config command. If upstream differential encoding is disabled, no differential encoding entry is displayed in the output.

If you are having trouble, make sure that the cable connections are not loose or disconnected; the cable interface line card is firmly seated in its chassis slot; the captive installation screws are tight; you have entered the correct slot and port numbers; and you selected a valid frequency for your router.

Usage Guidelines

The DOCSIS 2.0 specification builds on the existing TDMA to support advanced modulation profiles that increase potential upstream bandwidth. The A-TDMA profiles support higher QAM rates of up to 64-QAM and wider channel widths of up to 6.4 MHz (5.12 Msymbols).

Note	The advanced hardware-based spectrum management features for the Cisco uBR-MC16S/U/X, Cisco uBR-MC28U/X, and Cisco uBR-MC5X20S/U cards are supported only in the DOCSIS 1.0/1.1 TDMA-only mode. They cannot be used in the mixed or A-TDMA-only modes.

Note	Starting with Cisco IOS Release 12.2(33)SCG and later, the default upstream DOCSIS mode is ATDMA only.

The DOCSIS 2.0 specification allows an upstream to be configured in one of the following three modes:

• A-TDMA only mode—Upstreams only support cable modems that register using A-TDMA modulation profiles. The CMTS does not allow DOCSIS 1.0 and DOCSIS 1.1 cable modems to register and come online on these upstreams. The Cisco uBR-MC5X20S /U , Cisco uBR-MC16U/X, and Cisco uBR-MC28U/X cards also support 6,400,000 Hz (5,120,000 symbols/sec) when operating in DOCSIS 2.0 (A-TDMA-only) mode.

Changing the DOCSIS mode to A-TDMA only mode automatically changes the symbol rate to 5.12 megasymbols per second and the channel width to 6.4 MHz. It also automatically disables the dynamic upstream modulation.

Note

Starting with Cisco IOS 12.2(33)SCG2, when the channel-width value in the cable upstream channel-width command is specified as 6.4 MHz in the TDMA or mixed TDMA/A-TDMA mode, the DOCSIS mode automatically changes to A-TDMA-only (DOCSIS 2.0) mode. Changing DOCSIS mode to A-TDMA only mode will not automatically change the symbol rate to 5.12 megasymbols per second and the channel width to 6.4 MHz. The symbol rate and channel width before the DOCSIS mode change are maintained after the change.

In addition, the following are required to support the DOCSIS 2.0 A-TDMA features:

• • Cable modems must be DOCSIS 2.0 compliant.
  • The DOCSIS configuration file for the cable modem must either omit the DOCSIS 2.0 Enable field (TLV 39), or it must set TLV 39 to 1 (enable). If you set TLV 39 to 0 (disable), a DOCSIS 2.0 CM uses the TDMA mode.
  • The upstream must be configured for either A-TDMA-only or mixed TDMA/A-TDMA mode.
• TDMA-only mode—Upstreams only support cable modems that register using TDMA modulation profiles. DOCSIS 2.0 cable modems can register on these upstreams only by using a DOCSIS 1.0/DOCSIS 1.1 modulation profile (which typically would happen only when a DOCSIS 2.0 cable modem cannot find an A-TDMA channel in its DOCSIS domain).

Changing the DOCSIS mode to TDMA-only mode automatically changes the symbol rate to 1.28 megasymbols per second and the channel width to 3.2 MHz. It also automatically disables the dynamic upstream modulation.

• Mixed mode—Upstreams support both DOCSIS 1.0/DOCSIS 1.1 cable modems using TDMA modulation profiles and DOCSIS 2.0 cable modems using A-TDMA modulation profiles. (The maximum channel width in mixed mode is 3.2 MHz.)

Changing the DOCSIS mode to mixed mode also automatically changes the symbol rate to 1.28 megasymbols per second and the channel width to 3.2 MHz. Dynamic upstream modulation is also automatically disabled.

Note	Mixed mode upstreams do not support the 6.4 MHz channel width.

The DOCSIS 3.0 specification allows an upstream to be configured in one of the following modes:

• SCDMA-d3 mode—Upstreams only support cable modems that register using DOCSIS 3.0 S-CDMA modulation profiles.
• SCDMA mode—Upstreams only support cable modems that register using DOCSIS 2.0 S-CDMA modulation profiles.

Note	The DOCSIS 3.0 option scdma-d3 (4SR) is available only when the CMTS is configured to operate in the global modulation profile format and is not available in the default mode. This option is available only for the Cisco UBR-MC20X20V cable interface line card, and not for other legacy line cards.

Refer to the cable upstream channel-width command for valid values of supported channel widths and DOCSIS modes for cable interfaces.

Note	Changing the DOCSIS Mode for an Upstream Port Forces the Cable Modems on That Upstream to Go Offline and Reregister

When you switch the DOCSIS mode of an upstream between the TDMA-only and mixed TDMA/A-TDMA modes, cable modems that are currently online on that upstream are taken offline and are forced to reregister. This helps the CMTS to determine the capabilities of the cable modems on the new channels.

If you change an upstream port to A-TDMA only mode, DOCSIS 1.x cable modems will not be able to come online on that upstream. If you change an upstream to TDMA only mode, DOCSIS 2.0-compliant cable modems are expected to attempt to come online on another upstream that is configured for A-TDMA or mixed mode. If no such upstreams are configured, or if the cable modem is configured to use only that particular upstream, it comes online in the DOCSIS 1.x mode.

Note

DOCSIS 2.0-compliant cable modems that are already online on a TDMA-only upstream do not automatically reregister on another upstream that has been configured for mixed-mode operations. The cable modem must either be reset or the CMTS must send an Upstream Channel Change (UCC) message to instruct the cable modem to move to the new channel.

If you change an upstream port to the mixed TDMA/A-TDMA mode, and some cable modems remain offline, or appear to come online but cannot pass traffic, upgrade the modem software to a DOCSIS-compliant software version.

Note	The cable physical plant must support the higher upstream bandwidths and symbol rates to be able to use the A-TDMA or mixed mode modulation profiles.

Usage Guidelines

Configuring D-PON for a MAC domain enables D-PON for all MAC domains on that line card. However, only a single MAC domain can be used within a D-PON fiber node. This is to ensure proper scheduling of the upstream and to prevent multiple Optical Network Terminals (ONTs) from transmitting upstream data at the same time.

Note	On cBR Series Converged Broadband Routers, when the cable upstream dpon command is configured for a specific MAC domain or interface, it is localized to that MAC domain or interface alone.

You should configure the cable upstream ranging-init-technique 2 command to prevent the use of additional broadcast initial ranging opportunities for the non-DPON reference upstream channels.

When you shutdown an upstream channel, the D-PON associated with that MAC domain will stop working. To enable D-PON again, you must manually shut down and enable the MAC domain using the shutdown and no shutdown command.

Usage Guidelines

The DOCSIS 1.1 and 2.0 specifications allow a CMTS to specify a pre-equalization coefficient in the DOCSIS ranging response (RNG-RSP) MAC management messages it forwards to the cable modems (CM)s. When this is enabled, a CM can engage in transmit-side equalization (pre-equalization) to mitigate the effects of certain impairments in the cable plant, such as in-channel tilt, and group delay.

These impairments are more significant with higher order modulation formats such as 64-QAM or 16-QAM, and near the first octave break-point of the diplex filters (34 MHz to 38 MHz). This break-point exists predominantly as a time-domain group delay issue, and becomes severe for longer amplifier cascades.

Each amplifier causes the DOCSIS upstream signal to traverse two diplex filters. All diplex filter frequency splits (5-42 MHz, 5-65 MHz, or 5-88 MHz) share this characteristic, which is not visible in a frequency response measurement or sweep test.

For more information about the use of pre-equalization, see the DOCSIS 2.0 RFI specification section 6.2.15, Transmit Pre-Equalizer, and section 8.3.6 Ranging Response (RNG-RSP) MAC Management Messages.

DOCSIS 1.1 specifies the Type 4 type length value (TLV), and an 8-tap equalizer. DOCSIS 2.0 adds the Type 9 TLV, and increases the equalizer to support 24 taps to compensate for more complex impairments.

The cable upstream equalization-coefficient command configures the CMTS to send Type 4 TLV or Type 9 TLVs in the DOCSIS RNG-RSP MAC management messages to the CMs.

The no form of the command disables the CMTS from sending Type 4 TLV or Type 9 TLVs in the DOCSIS RNG-RSP MAC management messages to the CMs.

After the CMTS stops sending pre-equalization TLVs to the CM, the CM must retain these values until the modem’s cable interface resets, or a modification is made to the upstream channel descriptor (UCD), which would make the stored equalization coefficients invalid.

You can reset the cable modem’s interface by:

• Power cycling the cable modem
• Resetting the cable modem from the CMTS using the clear cable modem command

Router# clear cable modem aaaa.bbbb.cccc reset

You can reset the equalizer coefficient of all CMs on an upstream by:

• Changing the upstream center frequency. A 16-kHz or 32-kHz change is sufficient and unlikely to take many CMs offline.
• Briefly changing the periodic ranging messages in the modulation profile between 16-QAM and Quadrature Phase Shift Keying (QPSK), or 64-QAM and 16-QAM.

A CMTS operating in a pure DOCSIS 2.0 upstream mode sends equalizer data supporting 24 taps to all modems during initial ranging.

The cable up 0 docsis-mode atdma command configures a DOCSIS 2.0-only upstream mode on the CMTS.

A CMTS operating in a DOCSIS 1.1 or mixed TDMA-ATDMA upstream mode sends equalizer data supporting 8 taps to all modems during initial ranging. The CMTS cannot send data supporting 24 taps until it is notified by the CM, that it is DOCSIS 2.0 compliant in the Registration Request (REG-REQ) message, immediately preceding the online state.

This can be configured on the CMTS using the cable up 0 docsis-mode tdma-atdma command.

When a CM receives a Type 4 TLV in the RNG-RSP MAC management message from the CMTS, it must combine the previously stored values with the new values from the CMTS. Under certain HFC plant conditions, a dynamic impairment occurs that require the CM to adjust its main equalizer tap. The DOCSIS standard specifies a convolution function that is sometimes unable to adjust for dynamic impairments. The result, is a CM whose signal-to-noise ratio (SNR) value as received by the CMTS, is quite low compared to other CMs on the same upstream.

In a mixed modulation profile, where station maintenance is of a lower order modulation format than the data grants, it is possible for the modem to enter a steady state where the SNR estimate is:

• Below the required estimate for data grants to be processed by the CMTS
• Above the requirement for station maintenance

This results in a modem that responds to DOCSIS Layer 2 pings, but not to Layer 3 traffic. The following commands can be used to check status:

• ping docsis {cm-mac address | cm ip address }—succeeds
• ping ip {cm IP address | CPE IP address }—fails

A cable modem whose SNR estimate is in this condition may enter the expired(pt) state when baseline privacy interface plus (BPI+) is enabled. A modulation profile where station maintenance and data grants are of the same order modulation, prevents this condition.

The CMTS may be configured to enable cable upstream pre-equalization on a per upstream port basis, and may be configured to disable the sending of upstream equalization-coefficients on a per modem MAC address or Organizational Unique Identifier (OUI) basis, using the related global exclude commands.

Some DOCSIS 2.0 compliant CMs / embedded media terminal adapters (EMTA)s have been known to report as DOCSIS 1.1 compliant to the CMTS, unless connected to a DOCSIS 2.0 format upstream. These CMs are treated by the CMTS as DOCSIS 1.1, and only send 8-tap equalizer coefficients. A firmware or SNMP set may be used on these cable modems to enable the proper reporting of DOCSIS 2.0 compliance under a DOCSIS 1.1-style upstream (for example, 3.2 MHz, 16-QAM, TDMA format).

Some older DOCSIS cable modem firmware versions will incorrectly process the transition from 8 to 24 taps when in a mixed TDMA-ATDMA mode, and will experience degrading or low SNR MER as displayed with show cable modem phy command . Upgrade the CM firmware, and temporarily move these modems to a pure DOCSIS 1.1 or 2.0 channel or disable pre-equalization for these devices with the exclude command.

Usage Guidelines

The pre-equalizer direct load mechanism is enabled by default. However, to use this direct load mechanism, you must enable the pre-equalization coefficient on an upstream port using the cable upstream equalization-coefficient command.

The cable upstream equalization-error-recovery command enables the CMTS to send Type-Length-Value (TLV) Type 9 in the DOCSIS RNG-RSP MAC management messages. This mechanism helps CMs come online when TLV Type 4 convolved method causes CMs to go offline.

Note	The TLV Type 9, called pre-equalizer direct load, supports only the DOCSIS 2.0 or 3.0-certified modems. When a CM receives TLV Type 9, the CM replaces its data with the new data provided in the DOCSIS RNG-RSP MAC management messages.

Usage Guidelines

The cable upstream ext-power command is used to configure the following feature:

• Upstream Channel Bonding

Usage Guidelines

The Cisco CMTS uses FEC to attempt to correct any upstream data that might have been corrupted. To use this feature, you need to activate FEC on the upstream RF carrier. When FEC is activated, the Cisco CMTS commands all CMs on the network to activate FEC.

Usage Guidelines

This command enables and disables DOCSIS layer 2 fragmentation, which reduces run-time jitter experienced by constant bit rate (CBR) slots on the corresponding upstream. Disabling fragmentation increases the run-time jitter, but also reduces the fragmentation reassembly overhead for fragmented MAC frames. For ports running CBR traffic, fragmentation should be enabled (the default).

Note	Do not confuse DOCSIS Layer 2 fragmentation with IP Layer 3 fragmentation.

Usage Guidelines

DOCSIS 1.1 allows the CMTS to fragment DOCSIS frames to improve performance, especially in networks that combine real-time traffic, such as voice, with data traffic. The cable upstream fragment-force command allows you to specify the size of frames that should be fragmented, as well as the number of fragments that should be created when fragmenting.

Tip	This command takes effect only when fragmentation has been enabled on the upstream using the cable upstream fragmentation command (which is the default configuration). Whether fragment is enabled or not, is decided by the cable upstream fragmentation command.

In the default configuration, the Cisco CMTS fragments DOCSIS frames that are 2,000 bytes or larger in size, and it fragments these frames into equally-sized fragments. Starting from Cisco IOS Release 12.2(21a)BC, 12.2(33)SCB, and later releases, the larger frames are fragmented by the threshold. Instead of dividing frames into equal number of fragments as before, the concatenated frames are cut into many fragments, as defined in the threshold size, with the last one being the shortest. For example, the previous form of the cable upstream fragment-force command fragments a concatenated frame of 9000 into 5 frames of 1800. The new form of the cable upstream fragment-force command fragments a concatenated frame of 9000 into frames of 2000, 2000, 2000, 2000, and 1000.

Do not use a fragment size greater than 1,600 bytes on the Cisco uBR10-MC5X20S cable interface line card running Cisco IOS Release 12.3(23)BC1. Do not use a fragment size greater than 2,000 bytes on the Cisco uBR10-MC5X20U cable interface line card, and do not use a fragment size greater than 3,500 bytes on all other cable interface line cards, unless otherwise instructed by a Cisco TAC engineer.

When using DOCSIS concatenation, you might need to change the cable default-phy-burst command from its default size, so that multiple frames can be concatenated into a maximum-sized burst. If you set the cable default-phy-burst command to zero, the max burst then becomes the lowest of 255 mini-slots, the maximum concatenated burst setting in the DOCSIS configuration file, or the value of the long data grant burst that is specified in the upstream’s profile.

When you set the cable default-phy-burst command to zero, the CMTS fragments large requests into big chunks and the cable modems will not be able to register on specific groupings of upstream interfaces due to the large fragment size. We recommend the use of a fragment size of 2,000 bytes, if you want to set the cable default-phy-burst command to zero to provide upstream speed of above 5 Mbps.

Caution

Ensure that the number-of-fragments parameter is large enough to keep the size of each fragment of a maximum-sized burst less than the 1,600 bytes or 2,000 bytes or 3,500 bytes specified above. If fragments are too large, the cable modem might not be able to come online or pass traffic.

Note	The number-of-fragments option has been deprecated from Cisco IOS Release 12.2(21a)BC, 12.2(33)SCB, and later releases.

Note	Do not confuse DOCSIS Layer 2 fragmentation with IP Layer 3 fragmentation.

Usage Guidelines

The upstream channel frequency of your RF output must be set to comply with the expected input frequency of your cable interface line card. To configure an upstream channel frequency, you may:

• Configure a fixed frequency between the allowable ranges and enable the upstream port, or
• Create a global spectrum group, assign the interface to it, and enable the upstream port.

The allowable range for the upstream channel frequency depends on the cable interface line card and Cisco IOS software release being used. The following table provides the currently supported values.

Note	In Cisco IOS Release 12.2(15)BC2 and later releases, the allowable range of frequencies that you can select with the cable upstream frequency command is determined by the configuration of the upstream freq-range command.

Tip	If both a Cisco uBR-MC16E cable interface line card and a Cisco uBR-MC16C and/or a Cisco uBR-MC16S cable interface line card are present in the chassis, a spectrum group in the 42 MHz to 65 MHz range should not be assigned.

To configure the default upstream frequency (which is no fixed frequency), enter the cable upstream n > frequency command without specifying a center frequency.

Usage Guidelines

Enter this command to override the hardware spectrum manager’s decision to optimize hopping.

Note	Do not use this command unless you have a specific reason to disable optimum hopping configurations. For example, if you are experimenting with a Cisco uBR-MC16S or Cisco uBR-MC5X20S/U card, you can use this command to enforce blind hopping on individual upstream channels.

Usage Guidelines

This command specifies the priority of the corrective actions that should be taken when a frequency hop is necessary to correct excessive ingress noise on an upstream. For example, if the upstream on a Cisco uBR-MC16S card is set for the default settings (frequency , modulation , and channel-width ), the following occurs when the upstream noise exceeds the CNR threshold value for the current modulation profile:

1. The Cisco uBR-MC16S changes to a new frequency, if a clean frequency is available in its spectrum group.
2. If no clean frequency is available, the Cisco uBR-MC16S uses the Dynamic Upstream Modulation feature to switch the upstream to the secondary modulation profile.
3. If the noise levels still exceed the CNR threshold value for the secondary modulation profile, and if the upstream has been configured for a range of channel widths, the Cisco uBR-MC16S narrows the channel width of the upstream by half. If the noise levels are still excessive, the channel width is again cut in half, and this process continues until a clean upstream is found or the bandwidth is reduced to the minimum channel width that has been configured using the cable upstream channel-width command.

Allowable DOCSIS channel widths are 3.2 MHz, 1.6 MHz, 800 KHz, 400 KHz, and 200 KHz. If the channel width drops to 200 KHz, but the noise still exceeds the SNR threshold, the CMs go offline.

Note	The default specifies only a single channel width of 1.6 MHz. If this is not changed to specify a range of allowable channel widths (using the cable upstream channel-width command), the Cisco uBR-MC16S does not attempt to change the channel width.

To use the Dynamic Upstream Modulation feature, you must first create two modulation profiles (using the cable modulation-profile command) and assign them to the upstream (using the cable upstream modulation-profile command).

Usage Guidelines

Note	This command is available only on the Cisco uBR10-MC5X20H BPE, Cisco uBR-MC16U/X, and Cisco uBR-MC28U/X cable interface line cards. It cannot be used on other cable interface line cards.

Cable interface line cards, such as the Cisco uBR-MC28U/X cards, contain advanced hardware-based noise cancellation circuitry that digitally removes in-channel impairments such as ingress, common path distortion, and certain types of impulse noise. To configure how often these line cards should train their noise cancellation circuity, so as to adapt to changes in the noise types and levels, use the cable upstream ingress-noise-cancellation command.

When you enable ingress noise cancellation on an upstream, the Cisco CMTS periodically schedules a 256-symbol idle slot on the upstream channel. The interval option specified in the cable upstream ingress-noise-cancellation command determines how often this idle slot is generated.

The default for BPE cards is for the card to train its circuitry every 100 milliseconds. The smaller the triggering interval, the faster the card can adjust to changes in ingress noise, which makes the upstream more robust to noise problems, but at the cost of decreasing bandwidth on the upstream channel. To determine the bandwidth cost, in percentage of raw bandwidth, use the following formula:

(256/interval)/channel-symbol-rate 

where interval is the time period in milliseconds specified by the cable upstream ingress-noise-cancellation command, and channel-symbol-rate is the symbol rate in kilohertz. For example, if the upstream is using a 2.56 MHz channel rate and a noise cancellation interval of 10 milliseconds, the bandwidth cost is 1% of the total raw bandwidth:

(256/10)/2560 = 0.01 (1% of bandwidth) 

Broadband Processing Engine Support

The cable upstream ingress-noise-cancellation command is required on the Cisco uBR10-MC5X20H broadband processing engine (BPE) to enable ingress noise cancellation.

The Cisco uBR10-MCX520S/U BPEs have ingress noise cancellation capability enabled by default, so no configuration of ingress noise cancellation is available in the Cisco IOS software for these cards.

However, for configuration compatibility in support of high availability among Cisco uBR10-MC5X20S/U/H cards, the Cisco IOS software will accept configuration of the cable upstream ingress-noise-cancellation command for these BPEs without generating any warning or error when synchronizing the configuration.

Usage Guidelines

The cable upstream load-balance group command is used to configure the following feature:

Load Balancing and Dynamic Channel Change on the Cisco CMTS Routers

After you have used the cable load-balance group (global configuration) command to initially create and configure a load-balance group, use the cable upstream load-balance group command to assign this load-balance group to an upstream. This enables the cable interface to begin participating in load-balancing operations.

Tip	Use the cable load-balance group (interface configuration) command to assign this load-balance group to a downstream.

The following rules apply when creating and assigning load-balance groups:

• A downstream or upstream can belong to only one load-balance group.
• All downstreams and upstreams in a load-balance group must share physical radio frequency (RF) connectivity to the same group of cable modems. Downstreams can be in a separate load-balance group than upstreams, but all downstreams or all upstreams that have the same RF physical connectivity must be members of the same load-balance group. You cannot distribute downstreams or upstreams that share physical connectivity across multiple load-balance groups.
• Load balancing is done only on a per-chassis basis—all interfaces in a load-balance group must be in the same chassis.

Usage Guidelines

Use this command to specify whether DOCSIS 2.0 CMs should maintain their power spectral density when the Cisco CMTS changes their upstream modulation rate in an upstream channel descriptor (UCD) message. When you configure an upstream with the cable upstream maintain-psd command, the Cisco CMTS sets TLV 15 (Maintain Power Spectral Density) to ON in the UCD messages it sends to the CMs on that upstream.

When TLV 15 is on, and when the new UCD specifies a new upstream modulation rate for the CM, the CM must change its transmit power level to keep its power spectral density as close as possible to what it was before the modulation rate change. The CM must maintain this power spectral density until the CMTS sends a power adjustment command in a Ranging-Response (RNG-RSP) message.

The default configuration (no cable upstream maintain-psd ) configures TLV 15 to OFF, and CMs are not required to maintain their power spectral density after a modulation rate change. However, per the DOCSIS specifications, the CMs continue to maintain constant total input power on the upstream.

Note	This command affects only DOCSIS 2.0 CMs that are online an upstream that is configured for the DOCSIS 2.0 A-TDMA-only mode. This command has no effect on DOCSIS 1.0 and DOCSIS 1.1 CMs, which will continue to maintain constant total input power on the upstream, per the DOCSIS 1.x specifications.

Usage Guidelines

The threshold value specified for the power budget offset (max-channel-power-offset) must be less than the power threshold value (power-adjust continue) that determines the value of the Ranging Status field in the Ranging Response (RNG-RSP) messages that the Cisco CMTS router sends to the cable modem. You can specify the power threshold value using the cable upstream power-adjust command.

Usage Guidelines

This command is applicable only for S-CDMA channels. You should configure S-CDMA to apply the the maximum codes-per-subframe setting. The number of codes-per-subframe should not exceed the number of active codes.

Usage Guidelines

This command is applicable only for S-CDMA channels and the command limits the maximum number of interleave steps for a given upstream port. The max-interleave-step value should be less than the spreading-interval value specified using the cable upstream spreading-interval command.

Usage Guidelines

The cable upstream max-logical-chans command limits the number of logical channels per port on an upstream channel. The default value is 1.