Overview
Although CDRouter is not a DOCSIS protocol tester, it is perfectly suited for testing and verifying the higher layer network functionality of DOCSIS-based cable gateway devices. The basic CDRouter test setup for cable gateways is very similar to the test setup for DSL-based gateways. Like the DSL test setup, CDRouter does not have the ability to terminate a cable gateway's RF WAN connection directly. As a result, a CMTS must be included in a basic cable gateway test setup, as opposed to a DSLAM for DSL gateways. In either setup the function of the CMTS or DSLAM is essentially the same - to terminate the gateway device under test's WAN connection (DOCSIS or DSL, respectively) and transparently bridge all traffic to the public internet.
There are a few key considerations when choosing a suitable CMTS for use in this test setup. The first is that the cable gateway should be capable of connecting to and maintaining a stable and robust physical layer connection with whatever CMTS is used. Although the exact configuration of the DOCSIS physical layer is irrelevant, if the physical connection between the cable gateway and the CMTS is unreliable, test results obtained with CDRouter may be inconsistent or subpar.
Another important consideration is that the CMTS should support bridging. In a bridge environment all traffic (not including DOCSIS registration related traffic) from the cable gateway is forwarded to the CMTS's WAN interface. This allows CDRouter to communicate directly with the cable gateway via the CMTS WAN interface. A further consideration is that the test network should be isolated. The DUT should be the only device connected to the CMTS while tests are running. Isolation of the test network minimizes the possibility of CDRouter receiving unwanted packets from other devices which may alter test results.
Test Setup
The basic CDRouter test setup for a cable gateway is shown below.
As mentioned previously, most CMTS platforms will work for this type of setup. In cases where a CMTS must be purchased specifically for CDRouter testing, we recommend the Jade TINY CMTS from Daphne. The Jade TINY is compact, easy to use, and relatively inexpensive. It also supports bridging and is completely self-contained - it integrates all services required for DOCSIS registration (DHCP, FTP, TFTP, etc.) without the need for external servers. The Jade TINY is an ideal platform for use in this application.
The Jade TINY has two RF ports - one upstream (receive) and one downstream (transmit). As a result, a few additional components are required in order to connect a typical cable gateway to the Jade TINY. Specifically, a diplex filter, coaxial cables, and a variety of flat attenuators will be needed. The following readily available components are recommended:
The diplex filter is a three port device that combines the high frequency downstream signal and low frequency upstream signal. The cable gateway and CMTS should be connected to the diplex filter as shown below.
CMTS Configuration
The Jade TINY CMTS can be easily configured via the web-based management interface. We recommend configuring the Jade TINY for bridging which offers the least complex and most flexible test setup for CDRouter testing of cable gateways.
A brief description of the primary areas within the Jade TINY that must be configured prior to use with CDRouter is provided below. Example values are also provided where appropriate.
Subnets
There are a few different subnets and associated DHCP pools which must be defined within the TINY's DHCP configuration (Services > DHCP Conf).
- The private subnet used by the cable modem (CM) portion of the cable gateway. Typically the Jade TINY and the CM belong to the same private IP network, which allows the CM to communicate with the CMTS during registration while still being isolated from the public internet. The private network used for the CM can be further partitioned into "Provisioned" and "Unprovisioned" segments. A "Provisioned" CM is one in which the MAC address of the CM is associated with a particular Customer and Contract within the Jade TINY database. An "Unprovisioned" CM is one that is not associated with a Customer and Contract. The Jade TINY DHCP server is capable of supporting separate pools for provisioned and unprovisioned CM. For example, the pool for provisioned CM could be 172.18.1.2 through 172.18.1.52, whereas the unprovisioned pool could be 172.18.1.53 through 172.18.1.60.
- The public subnet used by the CPE or router portion of the cable gateway. The Jade TINY's DHCP server can also be configured to assign public, routable, addresses within this subnet to all cable gateways. However, for CDRouter usage this public DHCP pool is not required and if not defined, packets from the cable gateway will be forwarded directly to the Jade TINY's Ethernet interface. In this scenario the Jade TINY is essentially a bridge which has the benefit of allowing any WAN mode to be used and tested on the cable gateway. If the Jade TINY's internal DHCP server is used to assign IP addresses to the cable gateway, the only possible configuration for CDRouter testing is static mode (
testvar wanMode static). In this setup the address assigned to a particular cable gateway by the Jade TINY DHCP server is treated as a static IP within CDRouter
Network Settings
The Jade TINY's basic network settings can be configured in the CMTS Config > Network menu. The Jade TINY's Ethernet IP address lies within the designated CM private subnet (for example 172.18.1.1). The default gateway is the address of the default router for the public internet. If the Jade TINY's internal DHCP server is used to assign public addresses to the cable gateway, the default gateway address (55.66.77.254 for example) must match the value of the testvar wanIspIp in any CDRouter configuration files.
Addition of Cable Modem to CMTS Database
The cable modem portion of the cable gateway that is being tested must be added to the Jade TINY database within the Cable Modems > ADD menu. Note that all cable modems are specified by MAC address.
Customer Creation
Optionally a unique customer can also be created within the Customers > ADD menu. Recall that a cable modem that is not associated with a Customer and Contract will be designated as "unprovisioned" but will still be allowed to connect provided its MAC address is in the database. When creating a new customer be sure to specify the cable modem and contract in order for the cable gateway to be considered "provisioned".
In most cases the default DOCSIS 1.0 and 1.1 contracts should both work fine, although new contracts can easily be created within the Customers > Contract menu.
CDRouter Configuration
If the CMTS has been properly set up for bridging it should be completely transparent to CDRouter. As a result, any of the WAN connection modes supported by the cable gateway (DHCP, PPPoE, etc) can be terminated and tested by CDRouter.
A basic configuration for testing a cable gateway device using PPPoE as the WAN connection mode is provided below. Note that these testvars should be modified as needed to match the configuration of the cable gateway.
testvar lanInterface eth1
testvar lanType ethernet
testvar lanIp 192.168.1.1
testvar wanInterface eth2
testvar wanIspIp 192.168.200.1
testvar wanIspAssignIp 192.168.200.2
testvar wanNatIp 192.168.200.2
testvar wanIspNextIp 192.168.200.254
testvar wanMode PPPoE
testvar pppoeConnectOnDemand no
testvar pppoeUser qacafe
testvar pppoePassword qacafe123
Questions or comments about this article?
Please contact QA Cafe Support: support@qacafe.com
www.qacafe.com
© 2008 QA Cafe
