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The Cisco Catalyst 4224 Access Gateway Switch (Catalyst 4224) is an integrated switch/router that provides Voice-over-IP (VoIP) gateway and IP telephony services to a small branch office. This section provides an overview of the Catalyst 4224.
This section contains the following topics:
For a synopsis of basic VoIP concepts, see the following section in this manual:
"Synopsis of Basic VoIP Concepts"
For Voice-over-IP (VoIP) configuration examples, see the following section in this manual:
The Catalyst 4224 supports the following features:
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Note These cards can be shared with the Cisco 1600 series, Cisco 1700 series, Cisco 2600 series, and Cisco 3600 series platforms. |
The Catalyst 4224 supports Cisco IOS software feature sets from the Cisco IOS Release 12.1.4T. The following Cisco IOS images are available:
The Catalyst 4224 can be deployed as part of a centralized call processing network with a Cisco CallManager and Survivable Remote Site Telephony (SRST) software that provides Ethernet switching, IP routing, VoIP gateway, and IP telephony services for a small branch office.
Centralized call processing allows network administrators to deploy and manage IP telephony applications at the corporate headquarters or the corporate data center. Deploying and managing key systems or PBXs in branch offices is no longer necessary. Centralized call processing provides remote branch office users with access to IP telephony applications at centralized locations over the IP WAN.
Centralized call processing has the following benefits:
Figure 1-1 shows the Catalyst 4224 at a remote site with a centrally deployed Cisco CallManager at corporate headquarters.
In the diagram, a Cisco CallManager cluster at a central site uses Simple Client Control Protocol (SCCP) to control IP phones at two branch offices. In the branch VoIP network, a Catalyst 4224 acts as an H.323 gateway, interconnecting the analog devices, the PSTN, and IP WAN. This system uses ISDN Basic Rate Interface (BRI) as a lifeline to the PSTN.
If the WAN link (or the Cisco CallManager cluster) becomes unavailable, Survivable Remote Site Telephony (SRST) allows the Catalyst 4224 to keep the IP phones on the branch networks running. Under these circumstances, the Catalyst 4224 functions as an H.323 gateway, thereby ensuring uninterrupted connectivity to the PSTN.
The term IP telephony identifies a networking solution that integrates a switched LAN, the Cisco CallManager, and IP phones.
The Catalyst 4224 is designed to work as part of a centralized Cisco CallManager network that supports up to 24 remote users. As part of an IP telephony solution, the Catalyst 4224 provides:
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Note The Catalyst 4224 has digital signal processors (DSPs) installed on the motherboard but does not support a DSP farm. Transcoding and conferencing services are supplied to the branch office by a central Cisco CallManager. |
Using the auxiliary VLAN feature, you can segment phones into separate logical networks even though the data and voice infrastructure are physically the same. The auxiliary VLAN feature places the phones into their own VLANs without the need for end-user intervention. You can plug the phone into the switch, and the switch provides the phone with the necessary VLAN information.
Key Ethernet switch features include:
As enterprises extend IP telephony from central sites to remote offices, it is important to provide backup redundancy at the remote branch office. The Survivable Remote Site Telephony (SRST) software feature on the Catalyst 4224 automatically detects a failure in the network and uses Cisco Simple Network Automated Provisioning (SNAP) to provide call-processing backup for the IP phones in the remote office.
The Catalyst 4224 provides call processing for the duration of the failure and ensures that the phones remain operational. Upon restoration of the WAN and connectivity to the network, the system automatically shifts call-processing functions to the primary Cisco CallManager cluster. Configuration for this capability is done only once in the Cisco CallManager at the central site.
Voice Over IP (VoIP) receives voice traffic at one location, converts it to TCP/IP packets for the benefits of toll-bypass, and transports the packets across the WAN to their destination.
To facilitate the migration to VoIP, the Catalyst 4224 includes an integrated high-density eight-port FXS module. These FXS ports can connect analog phones, modems, and fax machines to the Catalyst 4224.
The Catalyst 4224 supports a wide range of voice interface cards with the most popular signaling protocols. Supported protocols and interface types include T1-PRI, E1-PRI, T1-CAS, E1-CAS R2, ISDN BRI, and FXO.
Table 1-1 describes the voice interface cards supported by the Catalyst 4224.
Table 1-1 Voice Interface Cards
| Module | Description |
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Two-port FXO voice/fax interface card (North American version) |
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Two-port BRI S/T terminal equipment voice/fax interface card (also supports data) |
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Additional VoIP gateway benefits include:
The Catalyst 4224 supports the following WAN features:
The Catalyst 4224 supports the following IP routing features:
Table 1-2 describes the data interface cards supported by the Catalyst 4224.
The Catalyst 4224 provides the performance and intelligent services of Cisco IOS software for branch office applications. The Catalyst 4224 can identify user applications—such as voice or multicast video—and classify traffic with the appropriate priority levels. Quality of service (QoS) policies are enforced using Layer 2 and 3 information such as 802.1p and IP precedence. The Catalyst 4224 queues use weighted random early detection (WRED), weighted round-robin (WRR), and type-of-service/class-of-service (ToS/CoS) mapping to ensure that QoS is maintained as packets traverse the network.
To ease the deployment of QoS, the Catalyst 4224 supports Cisco QoS Policy Manager (QPM). QPM is a complete policy management tool that enables provisioning of end-to-end differentiated services across network infrastructures with converged voice, video, and data applications. The combination of QPM and CiscoWorks Service Management Solution enables network administrators to adjust service levels in accordance with defined QoS policies. The end result is network-wide intelligent and consistent QoS that enables performance protection for voice applications while reducing costs for growing networks.
The Catalyst 4224 provides the same security to voice and video networks that is available for data networks. The Catalyst 4224 supports the optional Cisco IOS Software Firewall Feature Set, IP Security (IPsec) with data encryption standard (DES), and Triple DES (3DES). Hardware encryption using the onboard encryption accelerator provides higher performance than software-based encryption, and frees processor capacity for other services.
The Catalyst 4224 supports the following encryption features:
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Note DES and 3DES software is controlled by U.S. export regulations on encryption products. For additional details visit the following URL: |
http://www.cisco.com/wwl/export/crypto/
This section contains the following topics:
The Catalyst 4224 consists of the following physical subsystems:
From a logical view, the Catalyst 4224 looks like a router that connects an Ethernet switch and a TDM switch in one system.
Figure 1-2 shows a logical view of the Catalyst 4224.
The Catalyst 4224 has six digital signal processors (DSPs) installed on the motherboard. The DSPs convert voice signals into data packets and data packets into voice signals. The DSPs on the Catalyst 4224 do not perform transcoding and hardware conferencing. These services are performed at the central site by Cisco CallManager. The DSPs only support VoIP. They do not support Voice over Frame Relay (VoFR) and Voice over ATM (VoATM). The DSPs are not field upgradeable.
The DSPs compress and decompress packets based on codecs. The Catalyst 4224 supports the following codecs:
The number of DSP channels that you can use depends upon the VIC configuration. The following rules apply when you allocate DSP channels for T-1/E-1 VWICs:
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Note You can disable the eight-Port FXS Module using the command line interface (CLI), and thereby free up eight DSP channels for additional digital voice channels. |
The following rules apply when you allocate DSP channels for BRI, FXS, and FXO VICs:
The following sample configuration shows DSP allocations:
In the sample configuration, port 3/0 is an analog VIC that uses two of the four channels in DSP 1. Slot 4 contains the eight-port FXS Module. This module takes up two DSPs. DSP four, five, and six are being used for the 12 voice channels on a MFT VWIC.
DSP resources are used for signaling and voice bearer channels. The signaling channel is used for detecting off-hook/on-hook transitions.
The forwarding performance for interVLAN routing on the Catalyst 4224 is 35 Kpps for 64-byte packets. Fast Switching is the default switching path. The Catalyst 4224 supports Cisco Express Forwarding (CEF).
The Catalyst 4224 can function as a Layer 2 switch connected to a Layer 3 router. When a packet enters the Layer 2 engine directly from a switch port, it is placed into one of four queues in the dynamic, 32-Mbyte shared memory buffer. The queue assignment is based on the dot1p value in the packet. Any voice bearer packets that come in from the IP phones on the voice VLAN are automatically placed in the highest priority (Queue 3) based on the 802.1p value generated by the IP phone. The queues are then serviced on a WRR basis. The control traffic, which uses a CoS/ToS of 3, is placed in Queue 2.
Table 1-3 summarizes the queues, CoS values, and weights for Layer 2 QoS on the Catalyst 4224.
Table 1-3 Queues, CoS values, and Weights for Layer 2 QoS
| Queue Number | CoS Value | Weight |
|---|---|---|
The weights specify the number of packets that are serviced in the queue before moving on to the next queue. Voice Real-Time Transport Protocol (RTP) bearer traffic marked with a CoS /ToS of 5 and Voice Control plane traffic marked with a CoS/ToS of 3 are placed into the highest priority Queues. If the queue has no packets to be serviced, it will be skipped. WRED is not supported on the Fast Ethernet ports.
The WRR default values cannot be changed. There are currently no CLI commands to determine QoS information for WRR weights and queue mappings. You cannot configure port-based QoS on the Layer 2 switch ports.
To be consistent with Cisco IP Telephony QoS design recommendations, you should configure separate voice and data VLANs. The following sample configuration shows how to configure separate voice and data VLANs.
Packets arriving on the specified voice VLAN will automatically have the 802.1p priority values read on ingress. Unlike the Catalyst 3500, trunking mode does not have to be used to distinguish between a voice and a data VLAN on a single port.
If the voice and data VLAN must be the same (a single subnet), using the dot1p extension will enable the Catalyst 4224 to recognize the dot 1p CoS value from the IP phone and place the packet in a queue based on the 802.1p value. The following sample configuration shows how to configure a single voice and data VLAN with dot1p.
Similar to other voice-enabled Catalyst platforms, the Catalyst 4224 learns that an IP phone is attached to the port via the CDP message exchange.
You can configure QoS on the Layer 3 CPU from the CLI, which is very similar to the interface on the Cisco 1750, Cisco 2600 series, and Cisco 3600 series routers.
The Catalyst 4224 supports WAN QoS queuing and scheduling. Table 1-4 shows Catalyst 4224 WAN QoS queuing and scheduling features.
The Service Policy command is disabled for Frame Relay.
In summary, the Catalyst 4224 supports the following Cisco IOS Layer 3 WAN QoS features:
This section provides platform specific guidelines for configuring the Catalyst 4224.
This section contains the following topics:
For Voice over IP (VoIP) configuration examples, see the following section in this manual:
The Catalyst 4224 boots up as a Layer 2 switch. The following sample configuration shows a default port configuration.
Unlike the Catalyst 3500, you do not need to preconfigure VLANs with a VLAN database command. To be consistent with Cisco IP Telephony QoS design guidelines, you should configure a separate VLAN for voice and data. The following example shows a recommended configuration.
This sample configuration instructs the IP phone to generate a packet with an 802.1q VLAN ID of 160 and an 802.1p value of 5 (default for voice bearer traffic).
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Note Portfast is supported only on nontrunk ports. |
If you have only a single subnet available, use the same subnet for voice and data. The following sample configuration shows a port configuration for a single subnet.
This sample configuration instructs the IP phone to generate an 802.1 Q frame with a null VLAN ID value and an 802.1p value (default is CoS of 5 for bearer traffic). The voice VLAN and data VLAN are both 160 in this example.
Configuring interVLAN routing on the Catalyst 4224 is identical to configuring interVLAN routing on the Catalyst 6000 with an MSFC. Configuring an interface for WAN routing is consistent with other Cisco IOS platforms. The following sample shows a configuration for interVLAN routing.
The Catalyst 4224 supports standard IGP routing protocols such as RIP, Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (EIGRP), and open shortest path first (OSPF). It also supports multicast routing for PIM dense mode, sparse mode, and sparse-dense mode.
In a centralized Cisco CallManager deployment model, the DHCP server would probably be located across the WAN link. You should include an ip helper command on the voice VLAN interface that points to the DHCP server so that the IP phone can obtain the IP address and the TFTP server address. The following sample configuration shows a configuration for ip helper-address on the voice VLAN:
As an alternative, you could use the Cisco IOS DHCP server capabilities on the Catalyst 4224. The following sample configuration shows a configuration for the DHCP configuration options.
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Note DHCP option 150 is supported locally. This local support provides the IP address of the TFTP server, which has the IP phones' configuration. An ip helper-address would not be required in this case because the IP phone has its IP address and the TFTP server address. The configuration request to the TFTP server is a unicast packet. |
You configure voice ports on the Catalyst 4224 as you would in standard Cisco IOS software. The following sample configuration shows a configuration for the eight-port FXS Module:
You can use the range command. The following sample configuration shows how to configure the range command:
Switched Port Analyzer (SPAN), also known as port monitoring, is supported for up to two sessions. Spanning a VLAN is not supported. You can only span selected interfaces. The following sample configuration shows a configuration for setting a port monitor session with the range command:
This section contains the following topics:
Using the interface switchport access or switchport trunk VLAN commands automatically creates a voice VLAN and data VLAN. If you require an additional VLAN beyond the voice and data VLAN when connecting to another switch, you must add it manually using the VLAN database command from the EXEC prompt.
The following sample configuration shows how to define a VLAN manually:
The following sample configuration shows how to define a VLAN on a trunk port.
By default, the trunk interface accepts all VLANs created by the VLAN database. Therefore, you should use the switchport trunk allowed command to delete unwanted VLANs from the interface.
The Catalyst 4224 supports only dot1Q trunking. Dynamic Trunking Protocol (DTP) is not supported. A Catalyst switch that is trunked to the Catalyst 4224 must have the trunking mode set to either On or No negotiate and type dot1q.
The maximum of 16 channels are available for trunk voice ports. This can cause a problem when a PSTN or PBX uses an unavailable channel to send a call to the Catalyst 4224. To prevent this type of problem, follow this procedure:
Step 2 Allocate all 24 time slots for the PRI group. The following sample configuration shows a configuration for the range command.
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Note The DSP resources are not sufficient for the 24 time slots. Therefore you receive this message: insufficient DSP resources. Ignore this message. |
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Note You need to tell the switch or PBX to make the time slots out-of-service. If you do not allocate 24 time slots, a SERVICE message is not sent for the unallocated time slots. This is an important caveat. |
Step 3 Use the show voice dsp command to see how many channels are allocated with the available DSP resources. In a test case, 16 time slots could be allocated DSP resources.
Step 4 Busy-out the time slots for which DSP resources could not be allocated. The following sample configuration shows how to busy-out the time slots:
Step 5 Use the show isdn service command to ensure that the channel is out-of-service. The following sample configuration shows channels in service:
For incoming calls, only time slots 1-16 are used by the switch or PBX. North American CO ISDN switches should support SERVICE/SERVCE ACK messages for maintenance service of B-channels on the PRI span. For the CO switches that do not support this service, you must ask the provider to busy-out the channels.
When receiving or placing a call from an ISDN terminal (T1/E1 PRI), there is no Progress IE in the setup. (Progress IE = 0.) The Catalyst 4224 does not generate ringback when it receives an alert from Cisco CallManager. You can avoid this situation and force the Catalyst 4224 to generate a ringback using the progress indicator commands on the VoIP and POTS dial-peer statements. The following sample configuration shows how to generate a ringback.
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Note alert enable 8 is a hidden command option, which you cannot find by using the ? at the CLI. |
The following sample configuration shows what happens when you try to find this command option:
This ringback situation applies only to PRI. It does not apply to BRI.
Prior to support for H.323 Version 2, you needed to enable the MTP Required checkbox. This checkbox is located in the Catalyst 4224 H.323 Gateway Configuration page in Cisco CallManager to define an H.323 gateway. All Cisco IOS H.323 gateways with Cisco IOS 12.07 or later now support H.323 Version 2. You should not ordinarily enable this checkbox box when defining the Catalyst 4224 as an H.323 Gateway. The only time you should check the box is if transcoding is used at the central site. Transcoding would be necessary in situations where the Catalyst 4224 uses G.729 for IP WAN calls and a voice mail system at the central site supports G.711 only.
If you enable MTP Required on the Catalyst 4224 H.323 Gateway, analog POTS calls to an IP phone locally connected will traverse the IP WAN. The call between the analog FXS POTS and the IP Phone is anchored at the central site transcoding device. This is normal behavior for a Cisco IOS H.323 gateway when MTP Required is enabled. This leads to performance that is not optimal. Therefore, unless transcoding is required, Media Termination Point (MTP) should not be enabled on the H.323 Gateway definition for Catalyst 4224. Another option would be to use G.711 across the IP WAN.
The following sample configurations show how the VoIP endpoints can be verified.
With the MTP Required checkbox enabled:
With the MTP Required checkbox not enabled:
When the MTP Required checkbox is enabled, a call between a local IP phone and an FXS analog POTS connected to the Catalyst 4224 is anchored at the transcoder at the Central site, and local calls use WAN bandwidth. When the MTP Required checkbox is not enabled, the local FXS-to-IP phone call is directly connected between the Catalyst 4224 H.323 gateway and the IP phone.
You must always use the following command to configure the IP address of the gateway. This command ensures that the IP address included in the H.323 packet is deterministic—it consistently indicates the same address for the source. If the end point is non-deterministic, the call is anchored at the serial interface port and silence or one-way audio occurs. The following sample configuration shows the H323-gateway voip bind srcaddr command:
You must place the h323 bind interface command on the interface with the IP address that Cisco CallManager uses to define the H.323 gateway.
You should configure ports as switched access ports. However, there may be implementations where your requirements dictate configuring ports as trunks and you want to standardize this configuration across all 24 ports. This is not the recommended configuration. Because of DHCP request timeouts on Windows 95/NT, portfast may be a desirable feature. However, portfast is not supported on ports in trunking mode. To reduce the forwarding delay time of a port, use the global configuration commands for the specific VLAN and reduce the forwarding timers to the minimum value of four seconds. See the following sample configuration:
These commands configure VLAN ports to forward data in eight seconds.
If you connect Catalyst 4224 to another switch, make sure that the timers are the same value. Otherwise Spanning Tree issues may arise. Also note that only 802.1Q trunking is supported on the Catalyst 4224.
Frame relay does not support LLQ/CBWFQ. The service policy output command is currently disabled. Therefore, only ip rtp priority is supported as a voice priority queuing scheme. FRF.12 is supported on frame relay links.
The recommended configuration for FRF.12 and ip rtp priority is shown in the following procedure. The parameter values are for illustrative purposes only. Your values may differ.
Step 2 Apply the map class to a frame relay sub interface. The following sample configuration shows how to apply the map class:
Step 3 Apply frame relay shaping at the main interface. The following sample configuration shows how to apply shaping:
The maximum number of VLANs multiplied by the number of multicast groups must be less than or equal to 242. For example, the number for 10 VLANs and 20 groups would be 200, which is within the 242 limit.
The maximum number of multicast groups is related to the maximum number of VLANs. The product of the number of multicast groups and the number of VLANs cannot exceed 242. Multicast support includes the following items:
Posted: Sat Apr 5 04:00:25 PST 2003
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