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This feature module describes the Cisco CVA120 Series Cable Voice Adapters, its major benefits, and how to configure it. This document includes the following major sections:
The Cisco CVA120 Series Cable Voice Adapters is a residential voice-enabled cable modem that provides high-speed data and voice services to home offices and homes over an Internet Protocol (IP). The Cisco CVA120 Series Cable Voice Adapters can deliver data at speeds exceeding analog dial up or Integrated Services Digital Network (ISDN) lines. The supported telephony features allow the Multiple Service Operator (MSO) to provide primary line voice service and secondary line service, using a single coaxial cable connection.
The Cisco CVA120 Series Cable Voice Adapters functions at its most basic level as a cable modem—a modulator/demodulator that provides high-speed network access on the cable television system to residential and small office/home office (SOHO) subscribers.
The Cisco CVA120 Series Cable Voice Adapters can optionally provide Voice over IP (VoIP) services, allowing subscribers to make telephone, modem, and fax calls over TCP/IP networks such as the Internet. These calls can be made to other VoIP devices, or to telephone, modem, or fax devices on the regular telephone network (the Public Telephone Switched Network, commonly known as PTSN). Custom class features such as 3-way calling, caller id, call return, and distinctive ringing are supported.
The Cisco CVA120 Series Cable Voice Adapters is equipped with both an Ethernet port and USB port. An optional uninterruptible power supply (UPS) can also provide power to the unit when the main AC-input power supply fails. The cable voice adapter is also designed to configure easily after installation by automatically registering itself on the network.
The Cisco CVA120 Series Cable Voice Adapter is available in two models, depending on the cable networking standard that is being used:
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Note Information about DOCSIS and EuroDOCSIS requirements and current specifications are available at the CableLabs web site at http://www.cablelabs.com. |
Both models of the Cisco CVA120 Series Cable Voice Adapter feature one F-connector interface to the cable system, one RJ-45 (10BASE-T Ethernet) hub port, one USB device port, and two RJ-11 analog voice ports. The USB interface enables the cable voice adapter to connect to a PC with a USB interface, without having the user to open the unit and install an Ethernet network interface card (NIC). If supported by the PC and service provider, PCs can be connected to the cable voice adapter using both the Ethernet and USB interfaces.
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Note Unless otherwise indicated, the terms Cisco CVA120 Series Cable Voice Adapter and cable voice adapter refer to both the Cisco CVA122 Cable Voice Adapter and Cisco CVA122E Cable Voice Adapter. |
The Cisco CVA120 Series Cable Voice Adapter uses its cable interface to connect to the CMTS over the Hybrid/Fiber Coax (HFC) cable system. A personal computer (PC) connects to the Cisco CVA120 Series Cable Voice Adapter through either the Ethernet or USB interface. The Cisco CVA120 Series Cable Voice Adapter then provides Internet access by forwarding traffic between the PC and the CMTS. Subscribers can use the Cisco CVA120 Series Cable Voice Adapter to create high-speed, permanent access to the Internet, without the need for telco-based services such as leased lines.
If supported by the service provider, the Cisco CVA120 Series Cable Voice Adapter can connect to multiple PCs by attaching a PC to each interface (Ethernet and USB). In addition, the Cisco CVA120 Series Cable Voice Adapter's Ethernet interface can connect to an Ethernet hub, and multiple computers can then be connected to the hub.
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Note You can connect the Cisco CVA120 Series Cable Voice Adapter to only one PC using the USB port because the cable voice adapter acts as a USB peripheral device. The cable voice adapter can also connect to a USB hub, which connects multiple peripherals to one PC, but the USB hub cannot connect multiple PCs to the cable voice adapter. |
The Cisco CVA120 Series Cable Voice Adapter provides IP bridging for one or more PCs and other customer premises equipment (CPE) when acting as a DOCSIS/EuroDOCSIS-compliant cable modem. In bridging mode, traffic from the cable voice adapter's Ethernet and USB interfaces is transparently forwarded on to the cable interface for transmission to the CMTS. Similarly, the cable voice adapter receives traffic on the cable interface and forwards it to the PCs attached to the Ethernet and USB interfaces.
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Note In bridging mode, the PCs must be assigned IP addresses in the same subnet as the CMTS. Typically, a Dynamic Host Configuration Protocol (DHCP) server at the headend automatically assigns the IP addresses to each PC that is authorized to connect to the Cisco CVA120 Series Cable Voice Adapter. |
You can connect a PC directly to the Ethernet port or to the USB port. You can connect a PC to both the Ethernet and USB ports, if this configuration is supported by the service provider.
In bridging mode, if only one PC is connected to both the Ethernet and USB interface ports, the cable voice adapter learns which port is in operation first, puts that MAC address in the bridge table, and forwards traffic from that port to the cable interface. If CPE devices are connected to both the Ethernet and USB ports, both ports are active. In this case the first CPE device that generates an Address Resolution Protocol (ARP) request that maps its IP address to a MAC address is put into the bridge table first and that CPE device will have its traffic forwarded first.
Also, if supported by the service provider, you can connect an Ethernet hub directly to the Ethernet port and then connect multiple PCs to the hub. In bridging mode, the Cisco CVA120 Series Cable Voice Adapter supports a maximum 254 PCs, depending on the maximum number allowed by the CMTS.
By default, one PC is supported for each Cisco CVA120 Series Cable Voice Adapter. This PC can be connected to either the Ethernet port or the USB port. If two PCs are connected to each port, then only the first PC that is discovered is allowed to access the network. The service provider can change this limit by changing the MAX CPE parameter in the DOCSIS configuration file. However, the CMTS at the headend can also enforce its own limit on CPE devices, and the CMTS limit overrides the MAX CPE parameter. So if the headend allows only one PC per cable voice adapter, subscribers can connect only one PC to the cable voice adapter, even if the MAX CPE parameter is set to the maximum value of 254.
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Note For better network performance, Cisco recommends a maximum limit of 16 CPE devices; this recommended maximum might be less depending on the services that the subscriber has purchased. |
See Figure 1 for a typical configuration.
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Note All Cisco IOS releases that support the Cisco CVA120 Series Cable Voice Adapter support basic DOCSIS/EuroDOCSIS connectivity that provides both high-speed Internet data access and VoIP connectivity. |
The Cisco CVA120 Series Cable Voice Adapter ships from the factory with a Cisco IOS software image stored in nonvolatile Flash memory that supports DOCSIS/EuroDOCSIS-compliant IP bridging data operations.
The Cisco CVA120 Series Cable Voice Adapter supports Voice over IP (VoIP), which transmits voice, modem, and fax calls over a TCP/IP network such as the Internet. Depending on the services purchased from the cable service provider, subscribers can place and receive calls without using the local exchange carrier.
The cable voice adapter contains two voice ports, which support two simultaneous voice, modem, and fax calls. You can connect a single-line analog telephone, fax, or modem device to each voice port, or you can connect a dual-line telephone device to the first voice port.
You can also connect multiple telephones, modems, and fax devices to each of the voice ports. However, the multiple telephones act as extensions to each voice line, so that only one call at a time can be made per voice port.
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Note The Cisco CVA120 Series Cable Voice Adapter supports only analog Foreign Exchange Station (FXS) telephone, modem, and fax devices. You cannot connect Foreign Exchange Office (FXO) devices, such as a PBX, to the cable voice adapter voice ports. |
Voice signals are packetized and transported in compliance with the following protocols:
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Note The Cisco CVA120 Series Cable Voice Adapter supports both H.323 and SGCP/MGCP call controls, but only one method can be active at a time. |
Figure 2 illustrates a broadband cable system that supports VoIP transmission.
The CMTS at the headend routes IP telephony calls from the point of origination to the destination, transmitting them along with other traffic (both voice and data). To route voice calls across the local IP network to a destination on the Internet or the Public Switched Telephone Network (PSTN), the Cisco CVA120 Series Cable Voice Adapter and CMTS deploy IP telephony as a local-loop bypass service.
One of the following call routing methods is then used, depending on the protocol being used:
The gateway at the destination typically interconnects the IP network to the Public Switched Telephone Network (PSTN) so that calls can be made to any phone, not just those that are part of the IP telephony network.
Voice calls are digitized, encoded, compressed, and packetized in an originating gateway; and then, decompressed, decoded, and reassembled in the destination gateway. A server maintains subscriber profiles and policy information. See the Cisco service provider voice documentation set if you have Cisco gatekeeper, gateway, or other applicable products.
Typically, voice calls made using the Public Switched Telephone Network (PSTN) require 64 Kbps of bandwidth when transmitted across digital systems. With IP telephony, however, telephone calls can be delivered at rates as low as 8000 bps in a packet format using different compression algorithms. Depending on the Cisco IOS software image being used, the Cisco CVA120 Series Cable Voice Adapter supports the following algorithms:
To achieve acceptable voice quality and reduce network bandwidth usage, several voice processing techniques are used. Digital Signal Processors (DSPs) provide the stream-to-packet and packet-to-stream conversion, and voice processing capabilities. Typical voice processing services include echo cancellation, voice compression, Voice Activity Detection (VAD) or silence compression, and Dual Tone Multi-Frequency (DTMF) tone detection and generation.
Data traffic typically is sent only on a "best effort" basis, and if a packet is lost or delayed, it can be easily retransmitted without significantly affecting the connection. Such delays and losses are unacceptable, however, for real-time traffic such as voice calls.
For this reason, the CMTS and cable voice adapter router assign separate service identifiers (SIDs) for the voice and data traffic flows. Each SID has a separate class of service (CoS) that determines how its traffic flow is handled, allowing voice traffic to have a higher priority than the data traffic.
The CMTS and router can use different traffic shaping mechanisms to ensure that the higher priority voice traffic always has the bandwidth it needs. This allows voice calls (and other real-time traffic) to share the same channel as data traffic, without the quality of the voice calls being degraded by bursty data transmissions.
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Note Separate CoS flows are available only when the cable voice adapter is connected to a CMTS that
supports multiple classes of service. In addition, the cable voice adapter's configuration file must
enable multiple classes of service. The DOCSIS 1.0 specification does not support multiple CoS flows, so when the cable voice adapter interoperates with a DOCSIS 1.0 CMTS, voice and data traffic are both transmitted on a "best effort" basis. This can cause poorer voice quality and lower data throughput when calls are being made from the router's telephone ports. |
The Cisco CVA120 Series Cable Voice Adapter supports the following service classes:
This service class is assigned to the primary SID for the cable voice adapter. In addition to being used for data traffic, the cable voice adapter uses this SID for all MAC message exchanges with the CMTS, and for SNMP management traffic.
All traffic using this SID is transmitted on a "best effort" basis, but data traffic within this class can be prioritized into eight different priority levels. Although all data traffic still has lower priority than the voice traffic, this allows certain data traffic (such as MAC messages) to be given higher priority than other data traffic. The CMTS system administrator defines the traffic priority levels and must include the traffic priority fields in the configuration file downloaded to the cable voice adapter.
The CMTS system administrator typically configures these secondary classes of service so that they have higher quality of service (QoS) classes for use by higher priority voice traffic. These classes should also have a minimum upstream data rate specified for the channel to guarantee a specific amount of bandwidth for the corresponding traffic flows. When static SIDs are used, that bandwidth is always reserved for voice calls; however, when dynamic multi-SID assignment is used, that bandwidth is reserved only when the voice calls are active.
In architectures using the VoIP H.323v2 protocol stack, the session application manages two call legs for each call: a telephony leg managed by the voice telephony service provider, and the VoIP leg managed by the cable system operator—the VoIP service provider. Use of the H.323v2 protocol typically requires a dial plan and mapper at the headend or other server location to map IP addresses to telephone numbers.
When both legs of the call have been set up, the session application creates a conference between them. The opposite leg's transmit routine for voice packets is given to each provider. The CMTS router passes data to the gateway and gatekeeper. The H.323v2 protocol stack provides signaling using H.225 and feature negotiation using H.245.
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Note For more information on using H.323v2, see the document H.323 Version 2 Support , available on CCO and the Documentation CD-ROM. |
To make and receive H.323 calls, the Cisco CVA120 Series Cable Voice Adapter must be configured for the following:
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Note To support voice configurations using Cisco gatekeeper products with RAS, Cisco IOS Release 12.0(5)T or higher images with gatekeeper support are required. The headend must have IP multicast enabled. The cable interface must be designated as the default for RAS to discover the gatekeeper. The gatekeeper then resolves all dialed destinations sent to the RAS protocol. |
The Cisco CVA120 Series Cable Voice Adapter supports the Simple Gateway Control Protocol (SGCP) and Media Gateway Control Protocol (MGCP). Both MGCP and SGCP are signaling protocols that interact with a remote call agent (CA) to provide call setup and teardown for VoIP calls.
Using the call agent, SGCP and MGCP communicate with the voice gateways, dynamically resolving and routing calls. This creates a distributed system that enhances performance, reliability, and scalability while still appearing as a single VoIP gateway to external clients.
The remote call agent also provides the signaling and feature negotiation that would otherwise be provided by the Cisco CVA120 Series Cable Voice Adapter when using the H.323v2 protocol. Similarly, the call agent also provides the mapping of IP addresses to telephone numbers, eliminating the dial plan mapper and static configurations that are required on the router when using the H.323v2 protocol.
The SGCP and MGCP protocols implement the gateway functionality using both trunk and residential gateways. The Cisco CVA120 Series Cable Voice Adapter functions in this mode as a residential gateway with two endpoints.
SGCP and MGCP can preserve Signaling System 7 (SS7) style call control information, and preserve additional network information such as routing information and authentication, authorization, and accounting (AAA) security information. SGCP and MGCP allow voice calls to originate and terminate on the Internet, and allow one end to terminate on the Internet and the other to terminate on a telephone on the PSTN.
The Cisco CVA120 Series Cable Voice Adapter can be configured for IP routing mode. To operate in routing mode, the Cisco CVA120 Series Cable Voice Adapter supports:
The DHCP proxy support feature is useful in the following situations:
When configured for DHCP proxy support, during startup the Cisco CVA120 Series Cable Voice Adapter sends a proxy DHCP request to the DHCP server using the Ethernet interface's MAC address. The DHCP server replies with a second IP address that the router assigns to either the Ethernet interface or to the NAT pool, depending on which option was specified.
This feature was introduced in Cisco IOS Release 12.1(1)T.
When configured for routing mode, the Cisco CVA120 Series Cable Voice Adapter defaults to using the Routing Information Protocol Version 2 (RIPv2). In routing mode, the Cisco CVA120 Series Cable Voice Adapter automatically configures itself to use the headend's IP address as its IP default gateway. This allows the Cisco CVA120 Series Cable Voice Adapter to send packets not intended for the Ethernet interface to the headend.
RIPv2 routing is useful for small internetworks because it optimizes Network Interface Center (NIC)-assigned IP addresses by defining Variable-Length Subnet Masks (VLSMs) for network addresses, and it allows Classless Interdomain Routing (CIDR) addressing schema.
This feature was introduced in Cisco IOS Release 12.0(4)XI1.
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Note The Cisco CVA120 Series Cable Voice Adapter supports only static routes and the RIPv2 routing protocol. |
When Cisco IOS images are updated to new releases, the service provider can download them as needed to Cisco CVA120 Series Cable Voice Adapters installed in the field (based on the software licenses purchased). See the Cisco CVA120 Series Cable Voice Adapter Release Notes for a complete list of features and Cisco IOS images that are currently supported.
Service providers can use the Cisco CVA120 Series Cable Voice Adapter's Media Access Controller (MAC) address to uniquely identify each particular unit in the field. The CMTS uses this value to download the proper DOCSIS configuration file to the Cisco CVA120 Series Cable Voice Adapter before beginning operation.
The DOCSIS configuration file can also contain the name of the software image that the Cisco CVA120 Series Cable Voice Adapter should be running. If necessary, the CMTS can also download the proper software image to the cable voice adapter and force it to reboot using the new image.
The download of the DOCSIS configuration file usually takes only a few seconds and is done every time the Cisco CVA120 Series Cable Voice Adapter reboots. The download of the software image can take several minutes to complete, during which time network connectivity is not available. However, the software image must be downloaded only once, until the subscriber needs to be updated with a new or updated image.
A Cisco IOS software image is preloaded on the Cisco CVA120 Series Cable Voice Adapter before it is shipped from the factory. However, when updated software images are available, a new Cisco IOS software image can be downloaded to a cable voice adapter installed in the field.
The DOCSIS configuration file can contain a filename for the software image that the Cisco CVA120 Series Cable Voice Adapter runs. If this filename does not match the software image that is currently installed on the cable voice adapter, the cable voice adapter must use the TFTP protocol to download the new image from the server specified in the DOCSIS configuration file.
After the new software image has been downloaded, the Cisco CVA120 Series Cable Voice Adapter resets itself and repeats the entire power-on and provisioning process. This includes downloading the DOCSIS configuration file again. However, because the software image is stored in nonvolatile Flash memory, the cable voice adapter does not have to download it again—the software download occurs only when the service provider specifies a new software image filename in the DOCSIS configuration file.
If the Cisco CVA120 Series Cable Voice Adapter cannot download the new image, it retries the download, as many as 16 attempts. If the cable voice adapter still cannot download the image, it falls back to its previous software image and attempts to go online with that image.
The service provider can also force the Cisco CVA120 Series Cable Voice Adapter to download new software by putting a new image filename in the DOCSIS configuration file and resetting the cable voice adapter. This should be done only after warning the customer that the modem will be offline for several minutes.
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Note Because it can take several minutes for this download to be accomplished and for the Cisco CVA120 Series Cable Voice Adapter to repeat its power-on sequence, the desired software image can also be installed on the router at the warehouse. In this case, the DOCSIS configuration files for each cable voice adapter should also be updated with the proper filename. |
The DOCSIS configuration file uses the type 43 Vendor-Specific Options field to specify that the Cisco CVA120 Series Cable Voice Adapter should download a Cisco IOS configuration file. See the "DOCSIS Configuration File" section for more information.
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Note Downloading a Cisco IOS configuration file is not usually required for plug-and-play bridging. Instead, it is normally used to configure the advanced feature sets. |
The Cisco CVA120 Series Cable Voice Adapter supports both a primary and secondary ROM Monitor (ROMMON). The primary ROMMON is permanently installed, but a secondary ROMMON is upgradable.
After power-on or a hard system reset, the primary ROMMON initially takes control. It then checks for the presence of a secondary ROMMON and if present, verifies that the secondary ROMMON has the correct checksum. If the secondary ROMMON passes these validation tests, the primary ROMMON then passes control to the secondary ROMMON, which then performs the power-on self-test and hardware initialization, and then loads and executes the Cisco IOS software image. Otherwise, the primary ROMMON remains in control and continues the boot process.
This approach allows the secondary ROMMON to be safely upgraded when new software is available. If the file transfer is interrupted, however, or if the new ROMMON software becomes corrupted, the primary ROMMON is still available to boot the cable voice adapter and load the Cisco IOS software image.
To upgrade the secondary ROMMON, use the copy tftp rommon: privileged EXEC command. See the following example:
If the download of the secondary ROMMON is successful, the cable voice adapter is automatically reloaded to transfer control to the new ROMMON.
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Caution If the download of the secondary ROMMON is interrupted by a power cycle, reset, or network interruption, the secondary ROMMON will become corrupted. You must then reset the cable voice adapter to allow the primary ROMMON to take control and reboot the system. After the system has rebooted with the primary ROMMON, you can repeat the download of the secondary ROMMON. |
The multiple service operator (MSO) can offer telephony service to their customers, increasing the MSO's monthly revenues. Customers can receive additional services that are competitively priced with existing services. Since the Cisco CVA120 Series Cable Voice Adapter's software is Cisco IOS-based, it has been proven reliable and feature rich.
Having both USB and Ethernet ports, an MSO can meet the needs of the consumers. A home office consumer can connect multiple PCs or devices to the Cisco CVA120 Series Cable Voice Adapter using the Ethernet plug, and, simultaneously, another family member can use the USB port for a second computer.
By offering an Uninterruptible Power Supply (UPS) backup battery, the MSO allows the end user to place calls and receive calls through the Cisco CVA120 Series Cable Voice Adapter even though the power might be out. In the event of a power outage, the customer has phone service for two hours of continuous talk time or eight hours of stand-by. Additionally, the battery signals to the MSO if it needs service, so that the MSO can contact the customer to replace it. The battery also has an LED to alert the end customer if it is running low.
After the Cisco CVA120 Series Cable Voice Adapter is installed, it automatically registers itself on the network and retrieves an IP address. The cable voice adapter is easy to install and installs quickly, thus saving the MSO money.
Because the USB and Ethernet can be configured as independent switched interfaces, consumers can protect their data. Where one user can access confidential information on a web site, the other user is incapable of interfering with that data. One end user could be on a corporate web site, while the other end user is in a chat room without compromising any corporate confidential information.
The MSO, knowing that Cisco supports the evolving standards, is able to offer new services. As the customer premises equipment (CPE) devices are roughly 50% of the network upgrade costs, the CPE has a software roadmap that supports new features and call controls. The Cisco CVA120 Series Cable Voice Adapter's hardware is designed with additional memory capacity that is adequate to plan for new features and call controls.
The DOCSIS 1.0 specification states that a CMTS cannot age-out MAC addresses for CPE devices, so the first PC that is connected to the Cisco CVA120 Series Cable Voice Adapter is normally the only one that the CMTS recognizes as valid. If a subscriber replaces an existing PC or changes its network interface card (NIC) to one that has a different MAC address, the CMTS does not allow the PC to come online because this exceeds the maximum number of CPE devices specified by the MAX CPE parameter. A similar result would occur if a user decides to move a PC from one Cisco CVA120 Series Cable Voice Adapter to another.
Refer to the following Cisco documents for related information. The documents can be found online at Cisco Connection Online (CCO) or on the Documentation CD-ROM. You can also order printed copies of most current documents.
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Note The list that follows is not all-inclusive. New documents and revisions occur frequently. |
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Note Use the Cisco IOS Command Reference Master Indexes to obtain document pointers for specific software release feature sets and commands. |
Cisco CVA122 Cable Voice Adapter
Cisco CVA122E Cable Voice Adapter
The Cisco CVA120 Series Cable Voice Adapter supports the following Data-Over-Cable Service Interface Specifications (DOCSIS) standards:
Information about these specifications is available at the CableLabs web site at http://www.cablelabs.com.
The Cisco CVA120 Series Cable Voice Adapter supports the following MIBS:
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Note The Cable Device MIB is very similar to the RFI MIB in that both allow access to cable-related statistics. However, the Cable Device MIB provides statistics on the cable modem, and the RFI MIB provides statistics on the radio frequency transmissions over the cable television line. |
Table 1 shows the cable-specific MIBs that are supported on the Cisco CVA120 Series Cable Voice Adapter.
Table 1 Supported MIBs for the Cisco CVA120 Series Cable Voice Adapter
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For descriptions of supported MIBs and how to use MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.
The Cisco CVA120 Series Cable Voice Adapter supports the following Request for Comments (RFC) specifications:
For more information on each RFC, see the IETF web site at http://www.ietf.org/rfc.
Before going to a subscriber site to install the Cisco CVA120 Series Cable Voice Adapter, verify that the following have been done:
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Note Cisco recommends that a dedicated (new) CATV cable drop be run from the grounding block directly to the Cisco CVA120 Series Cable Voice Adapter. If such a drop is not available, careful qualification of existing cable is often necessary. Cable ground should be connected to the grounding system of the building or residence as close to the point of cable entry as practical and according to the local and national electrical regulations (for the United States, see the National Electrical Code Section 820-40 guidelines for proper grounding). |
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Note Installing a high pass filter between the Cisco CVA120 Series Cable Voice Adapter and the headend will prevent the cable voice adapter from connecting to the headend. |
Each service provider has its own recommendations and requirements for the CPE devices that are connected to the network. However, at the very minimum a PC should meet the requirements listed in Table 2.
Table 2 PC Minimum Requirements for the Cisco CVA120 Series Cable Voice Adapter
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1 The service provider might support other types of PCs and CPE devices for network connectivity. At the minimum, these CPE devices must meet the following requirements: 10Base T Ethernet connectivity, TCP/IP networking software, and the ability to obtain an IP address using the DHCP protocol. 2 Supplied with the Cisco CVA120 Series Cable Voice Adapter. |
Follow the operating and nonoperating environmental site requirements for operation of the Cisco CVA120 Series Cable Voice Adapter, as specified in the Cisco CVA122/CVA122E Cable Voice Adapter Hardware Installation Guide.
Follow the recommendations for power supply and power cord described in the Cisco CVA122 Cable Voice Adapter Hardware Installation Guide. Verify that the power source is within the values outlined in Appendix A of the Cisco CVA122/CVA122E Cable Voice Adapter Hardware Installation Guide.
Follow the recommendations for radio interference, coaxial cable quality, and distance limitations described in the "Cabling" section of the Cisco CVA122/CVA122E Cable Voice Adapter Hardware Installation Guide.
This section describes the tasks that must be done to configure the Cisco CVA120 Series Cable Voice Adapter for normal operation as a DOCSIS-compliant cable modem. Because of DOCSIS regulations and because of the size of most cable modem networks, configuring the cable voice adapter is not normally done manually. Instead, the following configuration files are created and made available to the cable voice adapter on servers running at the headend, so that it can automatically configure itself at system power-on and reset. Each task in the list indicates if the task is optional or required.
The DOCSIS specification (SP-RFI-IO5-991105 or later revision) requires that a DOCSIS-compliant cable modem connect to a DHCP server at power-on or reset to establish temporary IP connectivity with the cable network. This enables the cable modem to download the additional configuration information needed to establish a permanent connection with the headend and cable network.
The DHCP server can be a CMTS with DHCP server capabilities (such as a Cisco uBR7200 series universal broadband router), or it can be a dedicated server located at the headend. The server can be configured manually for each cable modem, or the server can be part of an automated provisioning system such as Cisco Network Registrar (CNR).
The DHCP server provides the information shown in Table 3 to each cable modem.
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Note If the modem fails to obtain any of the information it is seeking, it displays an error messsage. All such messages are explained in the Cisco Cable CPE Error Messages book, viewable online at www.cisco.com/univercd/cc/td/doc/product/cable/cab_modm/ubcmerrs.pdf . |
Table 3 DHCP Server Parameters
After making a successful DHCP request, the cable modem contacts the ToD server to get the current date and time. The cable voice adapter also begins the TFTP download of the DOCSIS configuration file, which is described in the next section, "DOCSIS Configuration File."
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Note At this point in the registration process, the DHCP server provides an IP address only for the cable modem, not for the CPE devices it is connecting to the network. |
The DOCSIS specification requires that a DOCSIS-compliant cable modem downloads a DOCSIS configuration file during its power-on or reset sequence. This file must be in the format described in the SP-RFI-IO5-991105 specification (or later revision) and must contain the information shown in Table 4.
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Note The parameters shown in Table 4 are organized according to the categories used in the Cisco DOCSIS Cable Modem Configuration tool, which is available on CCO at http://www.cisco.com/support/toolkit/CableModem. |
Table 4 DOCSIS Configuration File Parameters
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| 1 The DOCSIS configuration file also contains fields for one-way cable modems that use telco-return, but these fields do not apply to the Cisco CVA120 Series Cable Voice Adapter, which is a two-way cable modem. |
The DOCSIS configuration file uses the type 43 Vendor-Specific Options field to specify that the cable voice adapter should download a Cisco IOS configuration file. The Cisco IOS configuration file is an ASCII text file that contains the CLI commands needed to configure the Cisco CVA120 Series Cable Voice Adapter for advanced features that are not specified in the DOCSIS configuration file.
Downloading a Cisco IOS configuration file is not normally required for plug-and-play DOCSIS IP bridging. However, downloading a configuration file is required to configure the cable voice adapter for Voice over IP (VoIP) operations.
Table 5 shows the values that are entered in the Vendor-Specific Information Field (VSIF) to download a Cisco IOS configuration file.
Table 5 Downloading a Cisco IOS Configuration File
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An optional way of configuring the Cisco CVA120 Series Cable Voice Adapter is to specify individual CLI commands as part of the VSIF field in the DOCSIS configuration file. Table 6 shows the values that are entered to specify a CLI command that should be executed after the cable voice adapter processes the DOCSIS configuration file and comes online.
Table 6 Specifying CLI Commands
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Tip The VSIF option to include CLI commands in the DOCSIS configuration file should be used to specify a very limited number of commands for specialized applications. To perform a more substantial configuration of the cable voice adapter, use VSIF option 128 to download a Cisco IOS configuration file. |
This section provides the following configuration examples:
The DOCSIS-compliant IP bridging mode configures the Cisco CVA120 Series Cable Voice Adapter for data-only connection to the cable network and Internet. This is the default configuration.
