Table Of Contents
This chapter describes the Cisco CVA122/CVA122E Cable Voice Adapter and its interaction with the Cable Modem Termination System (CMTS)—the cable system headend equipment that provides Internet (TCP/IP) connectivity for subscribers over the cable broadband infrastructure. The chapter provides physical and functional overviews of the Cisco CVA122/CVA122E Cable Voice Adapter.
Cisco CVA122/CVA122E Cable Voice Adapter Description
This section provides an overview of the Cisco CVA122/CVA122E Cable Voice Adapter, its hardware, and its basic operation:
The Cisco CVA122 Cable Voice Adapter and Cisco CVA122E Cable Voice Adapter function at the most basic level as a cable modem—a modulator/demodulator that provides high-speed network access on the cable television system to residential subscribers. The two models are based on
•The Cisco CVA122 Cable Voice Adapter is based on the Data-Over-Cable Service Interface Specifications (DOCSIS), a standard developed with service providers to ensure that any DOCSIS-certified cable modem can interoperate with any bidirectional, DOCSIS-qualified CMTS. The DOCSIS standard supports the North American National Television Systems Committee (NTSC) channel plan, with 6 MHz channel widths, a downstream range of 88 to 860MHz, and an upstream range of 5 to 42 MHz.
•The Cisco CVA122E Cable Voice Adapter is based on the European Data-Over-Cable Service Interface Specifications (EuroDOCSIS), which is almost identical to the DOCSIS standard, except that it supports the European Phase Alternating Line (PAL) and Systeme Electronique Couleur Avec Memoire (SECAM) channel plans, with 8 MHz channel widths, a downstream range of 88 to 860MHz, and an upstream range of 5 to 65 MHz.
Note Unless otherwise indicated, all information in this manual applies to both the Cisco CVA122 and Cisco CVA122E Cable Voice Adapters.
Tips Information about DOCSIS and EuroDOCSIS requirements and current specifications are available at the CableLabs web site at http://www.cablelabs.com.
The Cisco CVA122/CVA122E 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 CVA122/CVA122E Cable Voice Adapter through either the Ethernet or USB interface.
The cable voice adapter then acts as an IP bridge, providing Internet access by forwarding traffic between the PC and the CMTS. Subscribers can use the Cisco CVA122/CVA122E 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 CVA122/CVA122E Cable Voice Adapter can connect to two PCs by attaching a PC to each interface (Ethernet and USB). In addition, the cable voice adapter's Ethernet interface can connect to an Ethernet hub, and additional computers can then be connected to the hub.
Note To be complaint with the USB specification, the Cisco CVA122/CVA122E Cable Voice Adapter does not support networking multiple PCs using a USB bridging hub.
In addition to providing DOCSIS connectivity, the Cisco CVA122/CVA122E Cable Voice Adapter 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).
The Cisco CVA122/CVA122E Cable Voice Adapter can optionally be configured as an IP router, using static routes and the RIPv2 routing protocol. When operating in routing mode, the cable voice adapter can treat its cable, Ethernet, and USB interfaces as separately routable interfaces.
Bridging and routing operations are summarized in the following sections.
When acting as a DOCSIS-compliant cable modem, the Cisco CVA122/CVA122E Cable Voice Adapter provides IP bridging for one or more PCs and other customer premises equipment (CPE). In this 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.
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 CVA122/CVA122E Cable Voice Adapter.
You can connect a PC directly to the Ethernet port, the USB port, or both ports; if supported by the service provider, you can also connect an Ethernet hub directly to the Ethernet port and then connect multiple PCs to the hub. In bridging mode, the Cisco CVA122/CVA122E 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 cable voice adapter. 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 allowed only one PC per cable voice adapter, subscribers could connect only one PC to the cable voice adapter, even if the MAX CPE parameter were set to the maximum possible value of 254.
Note For better network performance, Cisco recommends a maximum limit of 16 CPE devices; this recommended maximum might be less depending on the services the subscriber has purchased.
See Figure 1-1 for a typical configuration.
Figure 1-1 Cisco CVA122/CVA122E in a Bridging Configuration
Note All Cisco IOS releases that support the Cisco CVA122/CVA122E Cable Voice Adapter support basic DOCSIS connectivity that provides both high-speed Internet data access and VoIP connectivity.
The cable voice adapter ships from the factory with a Cisco IOS software image stored in nonvolatile Flash memory that supports DOCSIS-compliant bridging data operations. Based on the feature licenses your company purchased, other Cisco IOS images can be downloaded from Cisco Connection Online (CCO). These images might provide additional functionality, depending on the software release.
When configured as a router, the Cisco CVA122/CVA122E Cable Voice Adapter can directly connect one PC to each of its Ethernet and USB ports at the rear of the router. The Ethernet port can also be connected to a standard 10BaseT Ethernet hub, which then connects additional computers or Ethernet devices at the site to a local area network (LAN).
In routing mode, the Cisco CVA122/CVA122E Cable Voice Adapter is typically configured to use the IP address of the headend router as its default IP gateway. Routing mode does not have a maximum limitation on the number of CPE devices, as is the case in bridging mode; however, the CMTS can still limit the number of CPE devices by limiting the number of IP addresses that any particular cable modem can provide services for. If this is the case, the cable voice adapter can use NAT/PAT translations to use one IP address for multiple CPE devices.
Upgrading the Software Image
When Cisco IOS images are updated to new releases, the service provider can download them as needed to Cisco CVA122/CVA122E Cable Voice Adapters installed in the field (based on the software licenses purchased). See the release notes for the cable voice adapter for a complete list of features and Cisco IOS images that are currently supported.
Service providers can use the 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 cable voice adapter before it begins operation.
The DOCSIS configuration file can also contain the name of the software image that the cable voice adapter should be running. If necessary, the CMTS can 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 CVA122/CVA122E 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 image.
The section "Initial Power-On and Provisioning" explains this process. See the Cisco CVA122 Cable Voice Adapter Features guide for a description on how to download a software image and configuration file to a Cisco CVA122/CVA122E Cable Voice Adapter installed in the field.
Upgrading the ROM Monitor Software
The Cisco CVA122/CVA122E Cable Voice Adapter supports both a primary and secondary ROM Monitor (ROMMON). The primary ROMMON is permanently installed, while the 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 passes control to the secondary ROMMON, which first performs a 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, or if the new ROMMON software becomes corrupted, the primary ROMMON is still available to boot the Cisco CVA122/CVA122E Cable Voice Adapter and load the Cisco IOS software image. The upgrade of the secondary ROMMON can then be attempted again.
Initial Power-On and Provisioning
The cable voice adapter ships from the Cisco factory ready to work in a DOCSIS-compliant bridging data-only mode. However, before the cable voice adapter can transmit traffic, the CMTS at the headend must properly provision the unit as follows:
•The appropriate service must be purchased from the cable system. If certain features, such as VoIP support, are desired, a license for the appropriate Cisco IOS software image must also be purchased.
•When the cable voice adapter is first brought online, the CMTS at the headend downloads a DOCSIS configuration file to the cable voice adapter. This file—which is a binary file that must be in the format required by the DOCSIS specification—configures the cable voice adapter for the appropriate level of services and sets other parameters as needed.
•At this point the cable voice adapter is completely configured for basic DOCSIS operations, but if necessary, the DOCSIS configuration file can also specify that the cable voice adapter should download another Cisco IOS image from the CMTS.
•To customize the cable voice adapter's configuration further, the DOCSIS configuration file can also specify a Cisco IOS configuration file that the CMTS should download to the cable voice adapter. This second configuration file is an ASCII text file that contains the Cisco IOS commands needed to configure the cable voice adapter for advanced features, such as VoIP.
Note The Cisco CVA122/CVA122E Cable Voice Adapter downloads the DOCSIS configuration file each time it is powered on, but it downloads the Cisco IOS image and Cisco IOS configuration file only when needed. A new configuration file or image can be downloaded whenever necessary, such as when the cable service offers new services or subscribers upgrade their services.
To ensure that subscribers obtain the exact services they have ordered, the Cisco CVA122/CVA122E Cable Voice Adapter arrives from the Cisco factory with a unique identifier (UID) that consists of a serial number and MAC address. These factory-assigned values are on a label at the bottom of the cable voice adapter; for convenience, these values are also in a barcode label that can be easily scanned for easy entry into the service provider's provisioning and billing system.
Using the MAC address of the cable voice adapter as the key, the CMTS downloads the DOCSIS configuration file and Cisco IOS image that will provide the services that this particular subscriber has purchased. Service technicians at the headend typically create a number of standard configuration files to match the range of services offered by the provider; these configuration files can be created manually or with tools provided by Cisco Systems for this purpose.
The following sections describe the initial power-on and provisioning sequence in more detail, as well as the requirements that must be met by both the cable voice adapter and the CMTS before provisioning can succeed.
Initial Power-On Sequence
When connected and first powered on, the Cisco CVA122/CVA122E Cable Voice Adapter performs the following DOCSIS-mandated procedure for automatic installation and configuration:
1. The cable voice adapter boots the Read Only Memory (ROM) from the ROMMON partition of its Flash memory.
2. The cable voice adapter performs a self-test, initializes processor hardware, and boots the main operating system software—the Cisco IOS release image stored in Flash memory.
3. The cable voice adapter acquires a temporary downstream channel by matching the clock sync signal that is regularly sent out by the CMTS in the downstream frequency range.
4. The cable voice adapter then waits for an Upstream Channel Descriptor (UCD) message from the CMTS and configures itself for the upstream frequency specified in that message.
5. The cable voice adapter waits for the next upstream bandwidth allocation map message (MAP). These messages are regularly sent from the CMTS to find the next available shared request timeslot. The cable voice adapter then uses this timeslot to send a ranging request message to the CMTS, communicating the cable voice adapter's user ID (UID, which includes its unique MAC address), using a temporary service identifier (SID) of 0 (zero) to indicate it has not yet been allocated an upstream channel.
6. In reply to the cable voice adapter's ranging request, the CMTS sends a ranging response containing a temporary SID to be used for the initial cable voice adapter configuration and bandwidth allocation. As needed, the cable voice adapter adjusts its transmit power levels using the power increment value given by the CMTS in its ranging response message.
Note At this point, the cable voice adapter has established connectivity with the CMTS but is not yet online. The next steps allocate permanent upstream and downstream frequencies, as well the configuration required for IP network connectivity.
7. After the next MAP message broadcast, the cable voice adapter uses a shared request timeslot to invoke the Dynamic Host Configuration Protocol (DHCP) to establish IP connectivity with the TCP/IP network at the headend.
8. The DHCP server—typically a dedicated server at the headend, but it could also be a CMTS such as a Cisco uBR7200 series universal broadband cable voice adapter—sends a response containing the cable voice adapter's IP address, as well as the IP addresses for the default gateway and time of day (ToD) server. It also sends the IP address for the authorized Trivial File Transfer Protocol (TFTP) server from which the cable voice adapter should download its DOCSIS configuration file. Depending on the particular network configuration, other information could be provided, such as the IP addresses for a syslog server or security server.
9. The cable voice adapter configures itself for the specified IP address and gets the current date and time from the specified ToD server.
10. Using the TFTP protocol, the cable voice adapter downloads the specified DOCSIS configuration file and configures itself for the appropriate parameters. The DOCSIS configuration file defines the cable voice adapter's operating mode such as the provisioned downstream and upstream service assignments, assigned frequencies, data rates, modulation schemes, Class of Service (CoS), type of services to support, and other parameters. Cisco provides tools to help automate the creation of configuration files.
Caution The DOCSIS configuration file must be in the exact format given by the DOCSIS specification. An incorrect DOCSIS configuration file can cause the Cisco CVA122/CVA122E Cable Voice Adapter to constantly cycle offline. Such errors include: wrong downstream frequency; wrong UCD; wrong downstream Channel ID; invalid CoS; incorrect BPI privacy configurations or shared secret strings.
11. The cable voice adapter sends another registration request to the CMTS containing the CoS parameters given in the DOCSIS configuration file.
12. The CMTS verifies that the cable voice adapter is using the appropriate CoS profile and converts the temporary SID into a data SID with a service class index that points to the applicable CoS profile.
Note Depending on the software image being run and the capabilities of the CMTS, the DOCSIS configuration file can also specify multiple CoS profiles. Each CoS profile is assigned its own SID, either dynamically or statically, depending on the capabilities of the CMTS and software image being used.
13. The cable voice adapter completes its secondary ranging and is then online, passing data between the cable network and the PCs and other CPE devices connected to the cable voice adapter.
Note At this point the cable voice adapter is online and operational in the basic DOCSIS bridging mode ("plug and play" mode). The next step is done only if the DOCSIS configuration file specifies that the cable voice adapter must also download a Cisco IOS configuration file and new Cisco IOS image.
14. If the DOCSIS configuration file specifies that the cable voice adapter must download another Cisco IOS image and a Cisco IOS configuration file, the cable voice adapter uses TFTP to download the image and configuration files into its local memory. It then installs the new Cisco IOS image and runs the configuration file.
15. If Baseline Privacy Interface (BPI) encryption is configured and enabled on both the cable voice adapter and CMTS, the cable voice adapter and CMTS negotiate the appropriate encryption/decryption parameters. After encryption is enabled, all information sent over the cable interface is encrypted to prevent interception or modification by an unauthorized party.
Figure 1-2 illustrates the traffic flow during this process.
Figure 1-2 Cisco CVA122/CVA122E Cable Voice Adapter Provisioning Overview
Note For more detail on the provisioning process, see the DOCSIS Radio Frequency Interface (RFI) specification (SP-RFII01-990731 or later revision).
After the Cisco CVA122/CVA122E Cable Voice Adapter goes online, it sends traffic between the attached PCs and other CPE devices and the network (Internet, Intranet, VoIP). Because the cable voice adapter is operating in DOCSIS bridging mode, the service provider typically provides the IP addresses to the PCs and other CPE devices. The number of IP addresses each subscriber can obtain depends on the services purchased from the provider.
The following requirements must be met before a cable voice adapter can be provisioned:
•All required CMTS routing and network interface equipment must be installed, configured, and operational. This includes all headend routers, servers (DHCP, TFTP, and TOD), network management systems, and/or other configuration or billing systems required for your network.
•Based on the quality and capacity of your cable plant, your system administrator or network planner must have defined your network's IP address allocation plan; spectrum management plan outlining the recommended operating parameters to optimize performance; channel plan identifying the channels available to assign to specific Cisco CVA122/CVA122E Cable Voice Adapters; and dial plan to match the supported VoIP protocol.
•A CMTS customer service representative must have recorded all needed subscriber information, initiated a work order, and arranged an installation date with the subscriber. For subscriber sites that support multiple telephones or fax devices on a telephone line, all wiring associated with the telephone line extension must be in place. Inside wiring must be in compliance with the country of operation to prevent degradation of service.
•The CMTS system administrator or appropriate personnel must have specified the policy parameters for the Cisco CVA122/CVA122E Cable Voice Adapter and all computers and other CPE devices to be supported at the subscriber site. See Cisco's Network Registrar (CNR) product documentation for more information.
•The CMTS system administrator or appropriate personnel must have defined and pushed DHCP and DOCSIS configuration files to the appropriate servers so that each cable voice adapter, when initialized, can transmit a DHCP request, receive its IP address, obtain its TFTP and TOD server addresses, and download its DOCSIS configuration file. Cisco IOS images and Cisco IOS configuration files must also be prepared for subscribers who are purchasing services that require new software images and advanced configurations.
Note The CMTS uses the cable voice adapter's unique MAC address for the cable interface to ensure that the cable voice adapter downloads only the file(s) appropriate for the levels of service that have been purchased.
•If DHCP is also being used to provision the IP addresses used by the CPE devices at the subscriber's site, the DHCP server must be able to respond to those requests as well.
•The CMTS system administrator must ensure appropriate databases are updated to activate and support the new subscriber account in the provisioning, billing, and/or network management systems in place for your network after each cable voice adapter is registered with the CMTS.
•The following files should be prepared and available on the TFTP server:
–DOCSIS configuration file—This is required for every installation. The DOCSIS configuration file specifies the DOCSIS-mandated parameters, such as upstream and downstream frequencies, as well as optional features, such as whether to download a new software image or a Cisco IOS configuration file.
–Cisco IOS image—If upgrading to a Cisco IOS image different from the factory default, that image must be specified in the DOCSIS configuration file and available on a TFTP server that is accessible through the cable interface.
–Cisco IOS configuration file—This text file contains the Cisco IOS command-line interface (CLI) commands that configure the cable voice adapter for any special configurations and optional features. It must be made available on a TFTP server that is accessible through the cable interface.
This section provides an overview of how data is transmitted to and from the Cisco CVA122/CVA122E Cable Voice Adapter across the cable system's HFC network. Figure 1-3 illustrates a typical broadband data cable system, showing the network path between the Cisco CVA122/CVA122E Cable Voice Adapter and the CMTS headend equipment (Cisco uBR7200 series universal broadband router or other DOCSIS-compliant CMTS).
Figure 1-3 Cisco Broadband Data Cable System
The Cisco CVA122/CVA122E Cable Voice Adapter provides the connection between the PC and the cable system, modulating the data transmitted to and from the PC so that it can be carried over the coaxial cable installed by the service provider. To avoid interfering with the cable video signals that are also transmitted over this same coaxial cable, the DOCSIS specification allows only certain frequencies to be used for data transmissions. Separate frequencies are used for the data sent from the CMTS to the cable modem (the downstream direction) and for the data sent from the cable modem to the CMTS (the upstream direction).
The CMTS divides the cable plant into downstream channels and upstream segments or clusters of nodes. Each Cisco CVA122/CVA122E Cable Voice Adapter on the network is configured to receive data on a particular downstream channel. A downstream channel contains one or more upstream segments; partitioning the upstream plant into smaller segments significantly reduces the number of potential ingress sources and failure points.
Because 90% of the data transmitted on the Internet is, on average, sent from the network to the user, the cable system allocates the majority of bandwidth for downstream data (data sent from the CMTS to the cable voice adapter). Downstream transmissions use a 6 MHz data channel in the 88 to 860 MHz range, providing an approximate maximum bandwidth of 27 or 26 Mbps. This bandwidth is shared among all subscribers who have been assigned to this particular downstream channel.
The CMTS receives the downstream data from its Internet or other WAN connections. It addresses the data to the appropriate Cisco CVA122/CVA122E Cable Voice Adapter and modulates it for transmission on the cable network. When the data arrives at the subscriber's site, the cable voice adapter modulates it for transmission over the Ethernet or USB connection to the appropriate CPE device.
The data transmitted in the upstream direction (from the user to the network) is typically much less than that on the downstream direction, so a smaller bandwidth is allocated to it. The upstream transmissions share a 200 kHz-wide to 3.2 MHz-wide channel in the 5 to 42 MHz range, providing a bandwidth of up to 10 Mbps.
Depending on the quality of the physical plant and the CMTS used at the headend, users on a single downstream can be allocated across several upstreams to ensure a responsive network. Service providers can allocate different upstream bandwidths depending on the services purchased by a subscriber. For example, a subscriber purchasing basic home service might be allocated a 128 kbps upstream, while businesses purchasing premium services might be allocated a 384 kbps upstream.
The Cisco CVA122/CVA122E Cable Voice Adapter receives the upstream data from the CPE devices to which it is connected. It modulates this data for transmission on the coaxial cable system to the CMTS. The CMTS then routes the data to the appropriate destination (local server, Internet, and so forth) through its WAN interfaces.
All DOCSIS cable modems use a request/grant mechanism to obtain bandwidth on the upstream. The CMTS grants the bandwidth according to the requestor's level of service, ensuring that the cable modem is not exceeding the maximum bandwidth for upstream transmissions that has been specified by the subscriber's service agreement.
Note End-to-end throughput varies based on the design and loading of network components, the mix of traffic, the processing speed and interface of the host server(s), the processing speed and network performance of the subscriber's computer, as well as other parameters. Because the network can be configured to support multiple levels of service with different performance requirements, the subscriber's service level agreement also affects throughput. DOCSIS also specifies fundamental performance limitations to ensure that the majority of subscribers experience good performance, rather than permitting a few users to consume the entire capacity.
The Cisco CVA122/CVA122E 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 telephone or FAX device to each voice port, or you can connect a dual-line telephone or FAX device to the first voice port.
Subscribers can connect standard analog telephones, modems, and FAX machines to the Cisco CVA122/CVA122E Cable Voice Adapter; IP telephones are not required. Depending on the voice network set up by the service provider, subscribers can place calls to numbers that are in the existing telco network; the called party does not have to be using VoIP telephone service.
Note The Cisco CVA122/CVA122E Cable Voice Adapter provides FXS (Foreign Exchange Station) services and supports analog phones, faxes, and modems. The Cisco CVA122/CVA122E Cable Voice Adapter's voice ports do not support devices requiring Foreign Exchange Office (FXO) services, such as PBX devices.
You can also connect multiple telephones, modems, and FAX devices to a single voice line. However, each multiple device acts as an extension to that voice line, so only one call at a time can be made per voice line. The Cisco CVA122/CVA122E Cable Voice Adapter supports multiple devices per voice line, however, the total REN value for all devices must not exceed the maximum number given in "Technical Specifications."
Note The REN value is a measure of the AC load that the device places on a voice line and is typically listed on each device. If too many devices are connected to the line, the telephones might not ring properly, and you might have difficultly completing telephone calls.
Telephones at each subscriber site must support touch-tone dialing; rotary dialing is not supported. Special telephone features such as call waiting, forwarding, and conferencing are supported only if using a Cisco IOS image that supports those particular features.
Note FAX devices—standard Group III and computer-based Group III machines up to 14,400 baud—are supported.
Caution In certain countries, the provisioning of voice telephony over the Internet or use of these products may be prohibited and/or subject to laws, regulations or licenses, including requirements applicable to the use of the products under telecommunications and other laws and regulations; customer must comply with all such applicable laws in the country where the customer intends to use the product.
The Cisco CVA122/CVA122E Cable Voice Adapter is a compact, easy-to-install device that contains:
•One F-connector interface to the cable system.
•One RJ-45 (10BaseT half-duplex Ethernet) interface to connect a PC directly to the cable voice adapter. If supported by the service provider, this port can connect an Ethernet hub, which then connects to multiple PCs.
•One USB device (type "B" connector) port to connect a PC directly to the cable voice adapter.
Note The Cisco CVA122/CVA122E Cable Voice Adapter does not support networking multiple PCs using a USB bridging hub.
•Two RJ-11 Foreign Exchange Station (FXS) ports to connect analog telephones, modems, and fax devices to the cable system and IP backbone.
Figure 1-4 Cisco CVA122/CVA122E Cable Voice Adapter Front View
Figure 1-5 Cisco CVA122/CVA122E Cable Voice Adapter Rear View
The following sections describe the cable voice adapter and its features in more detail:
See "Connector and Cable Specifications," for the pinouts and cabling information for each of these connectors.
The front panel on the Cisco CVA122/CVA122E Cable Voice Adapter contains 4 LEDs to provide information about the cable voice adapter's status and network connections. Figure 1-6 illustrates each LED and Table 1-1 lists its meaning.
Figure 1-6 Cisco CVA122/CVA122E Cable Voice Adapter Front Panel LEDs
Note If the cable voice adapter fails one of its self-tests, the LEDs also contain information about the type of failure. See Table 4-1 for more details.
As shown in Figure 1-5, the Cisco CVA122/CVA122E Cable Voice Adapter contains a coaxial cable F-connector, one Ethernet 10Base T (RJ-45) connector, and one USB device (device, type "B") connector. The cable F-connector must always be connected to the cable system for proper operation. The Ethernet and USB connectors can be connected in one of the following configurations:
•A PC can be connected to either the Ethernet or USB connector.
•If supported by the service provider, two PCs can be connected, one to the Ethernet connector and the second to the USB connector.
•If supported by the service provider, an Ethernet hub can be connected to the Ethernet connector, and multiple PCs can be connected to the hub.
Note The USB specification does not support networking multiple PCs using a USB bridging hub.
The Cisco CVA122/CVA122E Cable Voice Adapter supports up to 254 PCs (and other CPE devices) in bridging mode. No maximum limit exists in routing mode. However, the CMTS can impose its own limitation on the maximum number of PCs and CPE devices.
Note For network performance reasons Cisco recommends a maximum limit of 16 CPE devices. The service provider may also set a different limit by changing the MAX CPE parameter in the DOCSIS configuration file—the default MAX CPE value is one CPE device.
The Cisco CVA122/CVA122E Cable Voice Adapter contains two analog (FXS) voice ports at the rear of the unit. These ports can be connected directly to analog telephones, modems, or FAX devices in the following ways:
•A single-line telephone, modem, or FAX device can be connected to each voice port, using a two-wire connection.
•A two-line analog telephone, modem, or FAX device can be connected to the first voice port (labeled "V1+V2"), using a four-wire cable. When a two-line telephone is plugged into this port, the second line acts as if it were plugged into the V2 port. If a two-line telephone is used, a device plugged into the V2 port acts as an extension to the second line of the two-line telephone.
•Adapters can be used to connect multiple analog devices to a single voice port. When multiple telephones connected to a voice port, they function as extensions.
The Cisco CVA122/CVA122E Cable Voice Adapter supports up to two simultaneous voice connections, one on each voice port. Only one voice call—telephone, modem, or FAX —per VoIP line is active at a time. The actual number of voice ports and voice devices supported depends on the services purchased from the service provider.
Caution Do not connect the voice ports to telephone wires that exit the building under any circumstances—this is a safety hazard. The Cisco CVA122/CVA122E Cable Voice Adapter is not designed to connect to the Public Telephone Switched Network (PTSN).
Multiple analog telephone devices can be connected to each of the VoIP telephone lines, provided the total Ringer Equivalence Number (REN) for all telephones does not exceed the limits given in "Technical Specifications."
Note A REN value is assigned to each terminal device to denote the percentage of the total load to be connected to the telephone loop used by the device, to prevent overloading. When the REN value is exceeded, the telephones might not ring properly or at all.
The Cisco CVA122/CVA122E Cable Voice Adapter uses an external AC-input power supply. See Table A-1 in "Technical Specifications," for the AC-input power supply power specifications, including input voltage and operating frequency ranges.
The Cisco CVA122/CVA122E Cable Voice Adapter does not contain a power switch. After the cable system technician installs, connects, powers on, and initializes the unit, it is intended to remain connected to the broadband network when operating normally.
The same power supply supports both U.S. and international operation. Different power cords are required, however, depending on the country of operation.
Caution Use only a Cisco-provided power supply and a cord appropriate to the country of operation. Using any other vendor's power supply and cord can cause loss of data or permanent damage.