This configuration is optional. Each service flow (SF) carries traffic based on certain defined parameters. One of them is the minimum reserved traffic rate.

The minimum reserved traffic rate specifies the minimum traffic rate, in bits/sec, reserved for a service flow. The value of minimum reserved traffic rate is calculated from the byte following the MAC header check sequence (HCS) to the end of the cyclic redundancy check (CRC), including every protocol data unit (PDU) in a concatenated MAC frame. If this parameter is omitted, then it defaults to a value of 0 bits/sec (that is, no bandwidth is reserved for the flow by default).

The Cisco CMTS schedules forwarding traffic of all service flows such that each flow receives at least its minimum reserved traffic rate when transmitting packets with the assumed minimum reserved rate packet size. If the service flow requests less bandwidth than its minimum reserved traffic rate, the Cisco CMTS reallocates the excess reserved bandwidth for other purposes. All best effort service flows with or without their minimum reserved traffic rate configured, share the excess bandwidth.

Upstream admission control tallies up the total amount of guaranteed minimum upstream throughput reserved by CMs on an upstream interface. When the total exceeds an allowable level, no more CMs requiring a guaranteed minimum upstream rate are allowed online on that upstream port.

The Cisco CMTS upstream admission control is turned off by default and must be activated. To set the upstream admission control as a percentage of the upstream channel capacity, use the following command in cable interface configuration mode. The admission control is set as a percentage of the specified upstream channel capacity. The acceptable range is from 10 to 1000 percent.

Router(config-if)# cable upstream usport admission-control percentage

For example:

Router(config-if)# cable upstream 0 admission-control ?
    Max Reservation Limit As Percentage of Raw Channel Capacity

Note	If percentage is left blank or set to 100%, the Cisco CMTS will only allow the total of the actual available upstream bandwidth to be guaranteed. If percentage is set to its maximum of 1000, then up to 10 times of the actual interface bandwidth may be “guaranteed”.

Differential encoding on the upstream is a digital encoding technique whereby a binary value is denoted by a signal change rather than a particular signal level. To enable differential encoding on upstream traffic to a specified cable interface, use the following command in cable interface configuration mode. Upstream differential encoding is enabled by default.

Router(config-if)# cable upstream usport differential-encoding

The Cisco uBR7200 series CMTS uses forward error correction (FEC) to attempt to correct any upstream data that might have been corrupted. When FEC is activated, all CMs on the network also activate FEC.

Note	Although upstream FEC is an option, it is recommended that you use upstream FEC. FEC is activated by default and should not be disabled.

To activate the upstream forward error correction and to enable FEC, use the following command in cable interface configuration mode.

Router(config-if)# cable upstream usport fec

Each upstream port must be activated to enable upstream data transmission from the CMs on the HFC network to the Cisco uBR7200 series CMTS.

Note	The upstream cable interface does not operate until you either set a fixed upstream frequency or create and configure a spectrum group. For more information, see the Setting the Upstream Frequency.

To activate the upstream ports, perform the following steps:

To enable upstream power adjustment for a specified cable interface, use one of the following commands in cable interface configuration mode.

Router(config-if)# cable upstream  power-adjust continuepwr-level
 

Router(config-if)# cable upstream usport power-adjust noiseperc-pwr-adj

Router(config-if)# cable upstream 0 power-adjust thresholdvalue

Router(config-if)# end
Router#

To return the automatic upstream power-adjustment ranging value to the default of 4 dB, enter the following command in cable interface configuration mode:

Router(config-if)# no cable upstream n power-adjust continue

To return the automatic upstream power-adjustment noise value to the default of 30 percent, enter the following command in cable interface configuration mode:

Router(config-if)# no cable upstream n power-adjust noise

To return the upstream power-adjustment threshold value to the default of 1 dB, enter the following command in cable interface configuration mode:

Router(config-if)# no cable upstream n power-adjust threshold

The scrambler on the upstream RF carrier enables CMs on the HFC network to use built-in scrambler circuitry for upstream data transmissions. The scrambler circuitry improves reliability of the upstream receiver on the cable interface line card.

Caution

The upstream scrambler is activated by default and should not be disabled under normal circumstances. Disabling it can result in corrupted packets. Disable it only for prototype modems that do not support the upstream scrambler.

To activate the upstream scrambler, use the following command in cable interface configuration mode. The upstream scrambler is enabled by default.

Router(config-if)# cable upstream usport scrambler

To enable upstream timing adjustment for a specified cable interface, use one of the following commands in cable interface configuration mode.

Router(config-if)# cable upstream usport time-adjust continue seconds

Router(config-if)# cable upstream usport time-adjust threshold  seconds

Router(config-if)# end
Router#

To return the upstream time-adjustment ranging value to the default of 2 seconds, enter the following command in cable interface configuration mode:

Router(config-if)# no cable upstream usport time-adjust continue

To return the upstream time adjustment threshold value to the default of 1 second, enter the following command in cable interface configuration mode:

Router(config-if)# no cable upstream usport time-adjust threshold

You can configure rate limiting and traffic shaping on a DOCSIS upstream channel. This delays the scheduling of the upstream packet, which in turn causes the packet to be buffered on the cable CPE device. This allows the user’s TCP/IP stack to pace the application traffic appropriately and approach throughput commensurate with the subscriber’s defined QoS levels.

To configure this, use the following command in cable interface configuration mode.

Router(config-if)# [no] cable upstream <n1> rate-limit [token-bucket]

Using Cisco IOS Release 12.0(5)T1 or higher, the software supports:

• Generic calendar queuing routines
• New token bucket policing function
• Grant shaping application of the calendar queues
• Upstream rate shaping option to the token-bucket keyword
• A default state change from 1 second burst policing to token-bucket with shaping

Tip	Upstream grant shaping is per CM (SID). Shaping can be enabled or disabled for the token-bucket algorithm.

Note

Before the introduction of this feature, the CMTS would drop bandwidth requests from a CM it detected as exceeding its configured peak upstream rate. Such request dropping affects the throughput performance of IP-based protocols such as FTP, TCP, and SMTP. With this feature, the CMTS can shape (buffer) the grants for a CM that is exceeding its upstream rate, rather than dropping the bandwidth requests.

Router# show interface cable 3/0 sid 1 counters 

Sid   Inpackets  Inoctets   Outpackets Outoctets  Ratelimit  Ratelimit 
                                                  BWReqDrop  DSPktDrop
1     67859      99158800   67570      98734862   2579       0          

The DOCSIS-specified method of contention resolution for CMs wanting to transmit data or requests on the upstream channel is a truncated binary exponential backoff value, with the initial backoff window and the maximum backoff window controlled by the CMTS. The Cisco uBR7200 series CMTS 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 are configurable on the Cisco uBR7200 series software and are 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. You can set fixed start and end values for data backoff on the upstream ports, or you can set the upstream ports for automatic data backoff. You have the same options for ranging backoff. For both backoff windows, the default start value is 0; the default end value is 4. Valid values are from 0 to 15.

Note	It is not recommended that you adjust default values, but that you enable the automatic dynamic backoff algorithm.

To set data or ranging backoff values for an upstream port, use one or more of the following commands in cable interface configuration mode.

Use the commands below to enter the upstream channel width in hertz (Hz). For NTSC operations, valid values are 200000 Hz (160 kilo symbols per second [ksps]), 400,000 Hz (320 ksps), 800,000 Hz (640 ksps), 1,600,000 Hz (1280 ksps), and 3,200,000 Hz (2560 ksps). The default is 1,600,000 Hz.

If no acceptable channels of the specified width are found, the spectrum management card automatically begins to scan the upstream spectrum for the next largest available channel width; for example, if the spectrum management card is unable to find a usable 1.6 MHz upstream channel, it automatically begins searching for usable 800 kHz channels.

Caution

Higher symbol rates are more susceptible to RF noise and interference. If you use a symbol rate or modulation format beyond the capabilities of your HFC network, you might experience packet loss or loss of cable interface connectivity.

Note

For QAM-16 channel widths of 400 kHz (320 ksps) or greater, Cisco recommends that you use QAM-16 modulation for long and short data, and that you use QPSK for request, initial, and station communications. For QAM-16 channel widths of 200 kHz (160 ksps), all communication must be able to use QAM-16. That is, 160 ksps with QAM-16 requires an exceptional signal-to-noise ratio (SNR) in your upstream channels. When you use QAM-16 for request, initial, and station maintenance messages with channel widths greater than 400 kHz, the QAM-16 preamble and message data take longer to transmit than the QPSK format.

To set the upstream channel width, use the following commands in cable interface configuration mode:

The upstream channel frequency of your RF output must be set to comply with the expected input frequency of your Cisco cable interface line card. To configure upstream channel frequencies, perform one of the following tasks:

• Configure a fixed frequency from 5 to 42 MHz for NTSC operations, then enable the upstream port.
• Create a global spectrum group, assign the interface to it, and enable the upstream port.

Note	You can also select a default that does not set a specific fixed value.

Note	The upstream port is frequency agile. If you define spectrum groups, the frequency can change while the interface is up and carrying traffic.

A modulation profile consists of a table of physical layer characteristics for the different types of upstream bursts; for example, initial maintenance, long grant, request/data, request, short grant, and station maintenance.

Note

The upstream cable interface does not operate until you either set a fixed upstream frequency or create and configure a spectrum group. If you are setting a fixed upstream frequency, make sure that the frequency selected does not interfere with the frequencies used for any other upstream applications running on the cable plant.

To set a fixed upstream frequency, use the following commands in cable interface configuration mode.

The Cisco uBR7200 series CMTS controls the output power levels of CMs to meet the desired upstream input power level. The nominal input power level for the upstream RF carrier is specified in decibels per millivolt (dBmV). The default setting of 0 dBmV is the optimal setting for the upstream power level.

The valid range for the input power level depends on the data rate. At 1.6 MHz, the valid range is –10 to 25 dBmV. If your power levels operate at greater than the maximum valid level, use an inline attenuator to bring the power level to within the valid range.

Caution

If you increase the input power level, CMs on your HFC network increase their transmit power level. This increases the carrier-to-noise ratio (C/N) on the network, but also increases distortion products. Composite Second Order Beat (CSO) and Composite Triple Beat (CTB) values worsen by 2 dB for every 1 dB-increased C/N. The return path laser immediately enters a nonlinear mode called clipping, and all communication becomes unreliable. Many return lasers send short bursts above the clipping thresholds and fail on longer or successive bursts. You should not adjust your input power level by more than 5 dB in a 30-second interval. If you increase the power level by more than 5 dB within 30 seconds, cable interface service on your network is disrupted. If you decrease the power level by more than 5 dB within 30 seconds, cable interfaces on your network are forced offline.

Note	When you run the cable upstream 0 power-level command, Cisco recommends that the adjacent channel not have a large variation. The recommended maximum input power variance is 5 to 6 dBmV.

To set the upstream input power level in dBmV, use the following command in cable interface configuration mode. The default is 0 dBmV.

Router(config-if)# cable upstream usport power-level dbmv

To specify the minislot size (in ticks) for specific upstream cable interfaces, use the following command in cable interface configuration mode. Acceptable values are 2, 4, 8, 16, 32, 64, and 128. The default is 8.

Router(config-if)# cable upstream usport minislot-size  size

For additional information about channel width and minislot size, refer to the Cable Radio Frequency (RF) FAQs on Cisco.com.

Upstream traffic shaping, available on the DOCSIS upstream channel, delays the scheduling of the upstream packet, which in turn causes the packet to be buffered on the cable customer premises equipment (CPE) device. This allows the user’s TCP/IP stack to pace the application traffic appropriately and approach throughput commensurate with the subscriber’s defined quality of service (QoS) levels.

The bandwidth requests are buffered without incurring DOCSIS-related timeouts and retransmits. This enables the CMTS to enforce the peak upstream rate for each CM, without degrading overall TCP performance for the subscriber CPEs. Upstream grant shaping is per cable interface (per service ID (SID)).

Token-bucket policing with shaping is the per-upstream default rate-limiting setting at the CMTS. Shaping can be enabled or disabled for the token-bucket algorithm.

To enable upstream shaping for an upstream port on a Cisco cable interface line card, use one of the following commands in cable interface configuration mode.

This configuration in optional. A set of matching criteria is applied by the cable modems to packets to determine if a packet should be dropped. This set of matching criteria when applied to upstream traffic, is called the Upstream Drop Classifier (UDC).

The CMTS enables the UDC feature on the cable modems. The UDC configuration is done by the cable modem using a configuration file.

Effective with Cisco IOS Release 12.2(33)SCG5, the UDC feature can be enabled for all cable modems on any interface of a Cisco CMTS by using the cable udc-capability command in interface configuration mode.

This configuration is optional. To configure the upstream buffer control parameters for the CM queue using the service class name, use the cable service class command in global configuration mode.