In the network depicted in Figure 7-3, the desired operation is to permit all users to call each other within the cluster and also to permit a subset of the users to make PSTN calls. The text following Figure 7-3 explains how to achieve this.
Chapter 7 Multisite WAN with Centralized Call Processing
Dial Plan Considerations
Figure 7-3 IP WAN with Three Branches
In the case of Figure 7-3, the partitions detailed in Table 7-2 would be configured to allow users to have access to either all intracluster locations or all intracluster locations and a local gateway.
IP WAN PSTN ISDN backup V V IP IP IP IP IP IP V IP IP IP 40811 Aggregation Branch offices Cluster
Table 7-2 Required Partitions for Intracuster and Local Gateway Access
Partition Name Designated Devices Assigned to Partition
Cluster-X Users All IP phones within the cluster Cluster-X Hub PSTN Access PSTN gateway(s) at hub location Cluster-X Branch 1 PSTN Access PSTN gateway at Branch 1 Cluster-X Branch 2 PSTN Access PSTN gateway at Branch 2
The calling party search spaces in Table 7-3 would then need to be defined. These calling search spaces would allow users to be assigned the ability to dial either numbers within the cluster only or all numbers within the cluster as well as PSTN calls through the local gateway.
This example presents one of the simplest configurations for multisite WAN local call processing. The dial plan would consist essentially of a single pattern for PSTN calls, typically a 9. Gateway selection would depend entirely upon the partition and calling search space of the calling device, as detailed above. Additional considerations, which would require a more ambitious dial plan, are listed in the “Calling Search Space” section on page 5-15.
Cisco CallManager Cluster Considerations
The following design parameters apply for Cisco CallManager clusters in a centralized call processing environment using Cisco CallManager Release 3.0(5):
Table 7-3 Calling Search Space and Partition Assignments
Calling Search Space Partitions Assigned To
Cluster-X Internal Only Cluster-X Users Devices that can make only internal calls
Cluster-X Hub Unrestricted Cluster-X Users
Cluster-X Hub PSTN Access
Internal calls and PSTN calls through hub location gateways Cluster-X Branch 1 Unrestricted Cluster-X Users
Cluster-X Branch 1 PSTN Access
Internal calls and PSTN calls through Branch 1 gateway Cluster-X Branch 2 Unrestricted Cluster-X Users
Cluster-X Branch 2 PSTN Access
Internal calls and PSTN calls through Branch 2 gateway Cluster-X Branch 3 Unrestricted Cluster-X Users
Cluster-X Branch 3 PSTN Access
Internal calls and PSTN calls through Branch 3 gateway
Chapter 7 Multisite WAN with Centralized Call Processing
Cisco CallManager Cluster Considerations
With WAN Cisco CallManager clusters, all active devices are required to register with a single Cisco CallManager. This allows the Cisco CallManager to maintain call state for all calls and thereby ensure that the specified bandwidth to a location is not exceeded.
Figure 7-4 shows devices registered to a single Cisco CallManager.
Figure 7-4 Registration to a Single Cisco CallManager in a Cluster
Where more than 2500 remote devices are required, multiple WAN clusters can be configured and interconnected using H.323. For a more detailed discussion, see Chapter 3, “Cisco CallManager Clusters.”
In this model, a single Cisco CallManager redundancy group should be
configured, and it should be the default Cisco CallManager redundancy group. All devices would then be assigned to this group to ensure that they all are registered to the same Cisco CallManager.
Centralized call processing cluster X Primary Secondary Cluster X Location 1 Cluster X Location 2 IP IP IP IP 40814
DSP Resource Provisioning for Transcoding and
Conferencing
Centralized call processing is typically done in environments where the provisioning of dedicated call processing at each site is not cost effective or is administratively unacceptable. The benefits of such a configuration are its central administration and low cost when spread across many sites. Digital signal processor (DSP) resources are required for transcoding and conferencing of calls. These resources are dedicated to each individual Cisco CallManager and must be located at the aggregation site.
Figure 7-5 shows the allocation of DSP resources.
Figure 7-5 DSP Resource Allocation
The number of allocated resources is based upon the requirements for transcoding to voice mail and transcoding to G.711 for other applications such as
conferencing. These numbers are calculated based upon the ratio of users to voice mail ports and the volume of conference calls placed. In cases where the placement of resources per Cisco CallManager is deemed cost prohibitive, the
Primary Secondary Cluster X Location 1 Cluster X Location 2 Conf Trans Trans Conf IP IP IP IP Centralized call processing cluster X 40815
Chapter 7 Multisite WAN with Centralized Call Processing
DSP Resource Provisioning for Transcoding and Conferencing
Figure 7-6 Call Flow for a Centrally Transcoded Call to Voice Mail
Conferencing poses another example of an application that uses G.711 only. Consequently, if the party wanting to make a conference call can traverse the WAN using only a low-bit-rate codec, the call must be transcoded to G.711 before the conference is initiated. See Figure 7-7.
Figure 7-7 Call Flow for a Centrally Transcoded Call with Conferencing
In the scenario shown in Figure 7-7, the call from the branch traverses the WAN using G.729a but must be transcoded to G.711 before being added to the conference resource.
IP WAN
Compressed call leg G.711 call leg Router/gateway Router/gateway Trans IP IP IP IP 40816 IP WAN
Compressed call leg G.711 call leg Router/gateway Router/gateway IP IP 40817 Conf IP IP IP Trans
Voice Messaging Considerations
Voice mail, like call processing, is usually not cost effective at the branch locations. Centrally locating voice mail simplifies voice mail administration as well as the provisioning of IP phones.
Whether interconnecting to a legacy system or an IP-based voice mail system, you must plan adequate capacity for concurrent voice mail sessions and provision associated transcoding resources if a low-bit-rate codec is required over the wide-area network. See Figure 7-8.
Figure 7-8 Centralized Call Processing Voice Mail Cluster Placement
Centralized Call Processing Cluster X Primary Secondary Cluster X Location 1 Cluster X Location 2 Conf MTP MTP Conf Application server(s) IP IP IP IP 40818
C H A P T E R
8
Quality of Service
This chapter addresses the Quality of Service (QoS) requirements for implementations of IP telephone solutions over an enterprise network. By applying the prerequisite tools, you can achieve excellent quality voice, video, and data transmissions over an IP infrastructure, irrespective of media and even at low data rates. For more detailed information on designing Quality of Service networks for AVVID deployments, please see the Cisco AVVID QoS Design
Guide at
http://www.cisco.com/univercd/cc/td/doc/product/voice/ip_tele/index.htm This chapter includes the following major sections: