Showing results for 
Search instead for 
Did you mean: 

Cable Modem Termination Systems (CMTS): Architecture, Configuration, and Troubleshooting

Community Manager
Community Manager

Read the bioWith Eric Bautista

Welcome to the Cisco Support Community Ask the Expert conversation. This is an opportunity to get an overview of the Cisco Cable Modem Termination System (CMTS) platforms and the uBR product family.

Eric Bautista is a customer support engineer at the Cisco Technical Assistance Center (TAC.) He is responsible for supporting the Cisco uBR CMTS platforms. He has 3.5 years of experience in cable technology. Previous to his current role, Bautista supported Cisco WAN and optical technologies, including QoS and SONET/SDH.

Remember to use the rating system to let Eric know if you have received an adequate response.

Eric might not be able to answer each question due to the volume expected during this event.

Remember that you can continue the conversation on the Service Provider sub-community discussion forum shortly after the event. This event lasts through September 21, 2012. Visit this forum often to view responses to your questions and the questions of other community members.

Webcast Related links:

21 Replies 21

Community Manager
Community Manager

Hello Eric,

Great presentation this morning during the live webcast. Here is one question that you were going to follow up  with

   Vaseem Kazia asked this:

Can you please comment on IPv6 HW Acceleration Support on Cisco 7225 and Cisco 7246?

Thanks a lot,

Cisco Support Community Moderator

Neither the uBR7225VXR, nor the uBR 7246VXR Platforms support hardware acceleration of IPv6 data packets.  I am not aware of any plans to add this support.

Currently, hardware (PXF) acceleration of IPv6 data packets is only supported on the uBR10k platform with the following requirements:

  • PRE-4
  • 12.2(33)SCE or later IOS release

Community Manager
Community Manager

   Mohammed Hussain asked the following:

Is there any specific IOS for CMTS UBRs? or we use the same as Cisco Routers/Switches?

Thanks for the reply

Cisco CMTS platforms have their own IOS releases.  You will need to specify both platform and processor when selecting the appropriate image.

At the time of this post, the following releases are available.

  • 12.2(33)SCG
  • 12.2(33)SCF3
  • 12.2(33)SCE6
  • 12.2(33)SCD8
  • 12.2(33)SCC7
  • 12.2(33)SCB11

You can view the available images on the Download Software page on CCO.

Community Manager
Community Manager

Dapo Ajayi asked the following:

  What are the SPA (shared port adapter) and SIP modules? Where do they fit on the CMTS (linecard or the NPE, or separate slots)? And why would one use them, in terms of benefits?

Only the uBR10k CMTS platform supports the SIP and SPA modules. 

The SIP needs to be installed in Slots 1, 2, 3, or 4 of the Cisco uBR10k router (referred to as WAN slots).

The SPA's would then be installed into the SIP.

The various SPA's available are:

  • Cisco Wideband SPA - For Wideband / M-CMTS solutions.
  • 1-Port 10-Gigabit Ethernet Shared Port Adapter - For network connectivity
  • 5-Port Gigabit Ethernet Shared Port Adapter - For network connectivity

Here is an excerpt from the Cisco uBR10012 Universal Broadband Router SIP and SPA Software Configuration Guide:

SPA Interface Processors (SIP)

  • A SIP is a carrier card that inserts into a router slot like a line card. It provides no network connectivity on its own.
  • A SIP contains one or more bays (subslots), which are used to house one or more SPAs. The SPA provides interface ports for network connectivity.
  • During normal operation the SIP should reside in the router fully populated either with functional SPAs in all bays, or with a blank filler plate (SPA-BLANK=) inserted in all empty bays.
  • SIPs support online insertion and removal (OIR) with SPAs inserted in their bays. SPAs also support OIR and can be inserted or removed independently from the SIP.

Shared Port Adapters (SPA)

  • A SPA is a modular type of port adapter that inserts into a bay of a compatible SIP carrier card to provide network connectivity and increased interface port density. A SIP can hold one or more SPAs, depending on the SIP type.
  • SPAs are available in various types. The Cisco Wideband SPA is a single-wide, half-height SPA. Figure 2-1 shows how bays are numbered on the Cisco Wideband SIP.

Community Manager
Community Manager

Jordan Morgan asked:

  Is it best to use cable map-advance dynamic  or static?

Community Manager
Community Manager

Un-answered questoins from the live event:

  • Can I put DC and AC in teh same chassis working togheter?
  • Do you have to configure the frequency on the CMTS or the up-converter?

The Cisco uBR10012 router does not support mixing AC and DC PEMs. Both PEMs must be either AC PEMs or DC PEMs.


The UBR-MC28U and UBR-MC16U linceards (for uBR7200 platforms), have internal upconverters.  Thus, the frequencies would be configured on the CMTS itself.

The UBR-MC28X and UBR-MC16X linceards (fort uBR7200 platforms) do not have internal upconverters. Thus an external upconverter would be needed and it's on that device where you would configure the desired frequencies.


The UBR10-5X20U-D and UBR-MC20X20V linecards (for the uBR10k platform), also have internal upconverters.  Thus, the frequencies would be configured on the CMTS as well.

Community Manager
Community Manager

Other questions:

  • With NPE1 or 2, is the I-O controller card necessary anymore? Or, is there any configuration where this card needs to be considered?
  • What solutions are available for monitoring SNR on the CMTS as well as Customer eMTAS?
  • How many bundles can you configure on a uBR 200? Is there a limitation?

Both the uBR7200-NPE-G1 and uBR7200-NPE-G2 processors have built-in IO functionality (including

(Flash memory and auxiliary and console ports) so an I/O controller card is no longer necessary.

An I/O controller, however, can still be used if a customer considers it necessary.


SNR readings can be taken on the CMTS itself or via SNMP.  These would reflect values for Cable Modems and/or eMTA's.


The total number of Bundles supported per CMTS is 40 (with the numeric range from 1 to 255).

Community Manager
Community Manager

Thanks for all the answers provided. Here is another question that was asked in the live event:

When stacked ports are on the MC20x20 line card, is it to fulfill more bandwidth? Or, does it work a two-way interface or interface as a bridged port?

The Cisco UBR-MC20X20V line cards have five  downstream (DS) ports and twenty upstream (US) ports. The line card  supports five cable interfaces, and the 20 DS and 20 US channels are  dynamically associated with any of these five MAC domains. The card has  twenty US spigots and five DS spigots. Each of the US spigots support  either two-frequency stacked US channels across ten ports or a single US  channel across twenty ports. Each of the DS spigots support  four-frequency stacked channels across five ports.

Please see Figure 1 here:

Also reference the "cable upstream logical-port connector physical-port" configuration command.