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Configuring DOCSIS Mini-PIM Interfaces

Data over Cable Service Interface Specifications (DOCSIS) define the communications and operation support interface requirements for a data-over-cable system. The topics below discuss the overview of DOCSIS Mini-PIM interface, its configuration details, and software features supported on DOCSIS Mini-PIM interfaces.

DOCSIS Mini-PIM Interface Overview

Data over Cable Service Interface Specifications (DOCSIS) define the communications and operation support interface requirements for a data-over-cable system. Cable operators use DOCSIS to provide Internet access over their existing cable infrastructure for both residential and business customers. DOCSIS 3.0 is the latest interface standard, allowing channel bonding to deliver speeds higher than 100 Mbps throughput in either direction, far surpassing other WAN technologies such as T1/E1, ADSL2+, ISDN, and DS3.

DOCSIS network architecture includes a cable modem with a DOCSIS Mini-Physical Interface Module (Mini-PIM) located at customer premises and a cable modem termination system (CMTS) located at the head-end or data center locations. Standards-based DOCSIS 3.0 Mini-PIM is interoperable with CMTS equipment. The DOCSIS Mini-PIM provides backward compatibility with CMTS equipment based on the following standards:

  • DOCSIS 2.0

  • DOCSIS 1.1

  • DOCSIS 1.0

The cable modem interface of Mini-PIM is managed and monitored by CMTS through SNMP. This DOCSIS 3.0 Mini-PIM can be deployed in any multiple service operator (MSO) networks. The primary application is for distributed enterprise offices to connect to a CMTS network through the DOCSIS 3.0 (backward compatible to 2.0, 1.1, and 1.0) interface. The DOCSIS Mini-PIM uses PIM infrastructure developed for third-party PIMs.

The Mini-PIM can also be used with encapsulations other than GRE, PPPoE, and IP-in-IP.

Note:

The following interface trace options are supported:

  • all—Enable all interface trace flags

  • event—Trace interface events

  • ipc—Trace interface IPC messages

  • media—Trace interface media changes

CMTS manages and monitors the cable modem interface of then Mini-PIM through SNMP. This DOCSIS 3.0 Mini-PIM can be deployed in any multiple MSO network. Figure 1 shows a typical use for this Mini-PIM in an MSO network.

Figure 1: Typical DOCSIS End-to-End Connectivity Diagram Network architecture diagram illustrating connectivity in a distributed enterprise network with SRX devices, LAN security, MPLS tunnels, and primary and backup routes.

Software Features Supported on DOCSIS Mini-PIMs

Table 1 lists the software features supported on DOCSIS Mini-PIMs.

Table 1: Software Features Supported on DOCSIS Mini-PIMs

Software Feature

Description

DHCP and DHCPv6 clients

The DHCP and DHCPv6 clients are used to get the IP address from the CMTS using the DHCP protocol. DHCP is supported on IPv4 and IPv6. One of the main components of the configuration file is the static public IP address, which CMTS assigns to the cable modem. The management IP address is configured on the Mini-PIM’s hybrid fiber coaxial (HFC) interface, which performs the following tasks:

  • Allows CMTS to execute remote monitoring and management of the Mini-PIM’s cable interface.

  • Downloads the configuration file from CMTS and uses it for configuring the cable interface.

QoS support

The device is configured through the existing QoS CLI. Because the configuration on the Routing Engine and Mini-PIM is done together, the QoS configuration has to be consistent between the Routing Engine and the cable modem interface. The QoS mechanisms on the Routing Engine are decoupled from the QoS mechanisms on the Mini-PIM.

The configuration file downloaded from CMTS contains parameters for primary and secondary flows. These parameters are programmed in the DOCSIS Mini-PIM. The Mini-PIM sends these parameters to the Routing Engine through the PIM infrastructure. The secondary flows are prioritized over primary flows in the DOCSIS Mini-PIM.

SNMP support

CMTS issues the SNMP requests that go to the cable modem. The DOCSIS MIB on the Routing Engine displays the Ethernet interface of the cable modem. The following features are supported on the DOCSIS Mini-PIM:

  • NAT support

  • Dying gasp support

  • Back pressure information

MAC address

The MAC address of the DOCSIS Mini-PIM is statically set at the factory and cannot be changed. The MAC address is retrieved from the Mini-PIM and assigned to the cable modem interface in Junos OS.

Transparent bridging

The DOCSIS Mini-PIM performs transparent bridging by sending the packets received on the Ethernet interface to the HFC interface and vice versa, without any modifications to the packet. All the other services such as webserver, DHCP server, and DNS server are disabled on the DOCSIS Mini-PIM during transparent bridging.

Example: Configuring the DOCSIS Mini-PIM Interfaces

This example shows how to configure DOCSIS Mini-PIM network interfaces.

Requirements

Before you begin:

Overview

In this example, you configure the DOCSIS Mini-PIM interface as cm-2/0/0. You specify the physical properties by setting the interface trace options and the flag option. You then set the logical interface to unit 0 and specify the family protocol type as inet. Finally, you configure the DHCP client.

Configuration

Procedure

CLI Quick Configuration

To quickly configure this example, copy the following command, paste it into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the command into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Step-by-Step Procedure

To configure the DOCSIS Mini-PIM network interfaces:

  1. Configure the interface.

  2. Set the interface trace options.

  3. Specify the flag option.

  4. Set the logical interface.

  5. Specify the family protocol type.

  6. Configure the DHCP client.

Results

From configuration mode, confirm your configuration by entering the show interfaces cm-2/0/0 command. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

If you are done configuring the device, enter commit from configuration mode.

Verification

Confirm that the configuration is working properly.

Verifying the DOCSIS Interface Properties

Purpose

Verify that the DOCSIS interface properties are configured properly.

Action

From operational mode, enter the show interfaces cm-2/0/0 command.

The output shows a summary of DOCSIS interface properties. Verify the following information:

  • The physical interface is Enabled. If the interface is shown as Disabled, do either of the following:

    • In the CLI configuration editor, delete the disable statement at the [edit interfaces interface-name] level of the configuration hierarchy.

    • In the J-Web configuration editor, clear the Disable check box on the Interfaces>interface-name page.

  • The physical link is Up. A link state of Down indicates a problem with the interface module, interface port, or physical connection (link-layer errors).

  • The Last Flapped time is an expected value. The Last Flapped time indicates the last time the physical interface became unavailable and then available again. Unexpected flapping indicates likely link-layer errors.

  • The traffic statistics reflect the expected input and output rates. Verify that the number of inbound and outbound bytes and packets matches the expected throughput for the physical interface. To clear the statistics and see only new changes, use the clear interfaces statistics interface-name command.