Extensible Markup Language (XML) services:
Cisco Unified CallManager provides access to directories. IP
phones can be used to perform lookups in the available
directories. Also, IP phones can use XML-based applications
that are accessible and configured as IP phone services.
Programming interface to external applications:
Through a programming interface, external applications can be
integrated with the Cisco Unified CallManager IP telephony
solution. Examples of such applications are Cisco IP
Communicator, Cisco IP Interactive Voice Response (IVR), Cisco
Personal Assistant, and Cisco Unified CallManager Attendant
Console. Cisco IP Communicator gets special mention. As seen in
Figure [1], this product is a virtual phone, represented by an
interactive screen on a PC. A variety of third-party products
use Cisco Unified CallManager programming interfaces.
Figure shows a company using Cisco Unified CallManager.
The company has two sites: the headquarters and a branch. A
Cisco Unified CallManager cluster is located in the
headquarters. Each site has a voice gateway for PSTN access. In
the example, a user in the branch office wants to place a call
to a user located at headquarters. The call follows these
steps: Step 1 When the branch user dials the telephone
number, the IP phone sends signaling messages to a member of
the Cisco Unified CallManager cluster. Step 2 The Cisco
Unified CallManager server processes the call by looking up the
called number in the Cisco Unified CallManager’s call routing
table. Step 3 When the Cisco Unified CallManager server
determines the IP address of the destination telephone, the
Cisco Unified CallManager sends a signaling message to the
destination telephone. The destination telephone starts
ringing, and the user who is being called can accept the call.
Step 4 After the call is accepted, the
telephones start sending and receiving RTP packets that carry
audio signals.
Content 2.5 Implementing VoIP in
an Enterprise Network 2.5.5 Enterprise IP
Telephony Deployment Models Enterprises have these choices
for deploying Cisco Unified CallManager as listed on Figure
: - Single site: An enterprise can deploy the IP
telephony solution at a single site only. In this deployment,
there is a local Cisco Unified CallManager cluster that serves
local telephones only.
- Multisite with centralized
call processing: The enterprise can deploy the IP telephony
solution at multiple sites with centralized call processing.
With centralized call processing deployment, there is a single
Cisco Unified CallManager cluster that is located at one of the
sites. The Cisco Unified CallManager cluster serves local and
remote IP phones.
- Multisite with distributed call
processing: The enterprise can deploy the IP telephony
solution at multiple sites with distributed call processing.
With distributed call processing deployment, there is a Cisco
Unified CallManager cluster at each site. Each Cisco Unified
CallManager cluster serves local IP phones.
- Clustering over WAN: An enterprise can deploy the IP
telephony solution at multiple sites. In this deployment, Cisco
Unified CallManager servers are located at more than one site.
However, all of the Cisco Unified CallManager servers belong to
a single cluster. The members of the cluster are separated by
an IP WAN. IP phones usually use the local servers as their
call agents.
Caution
The
clustering-over-WAN deployment model requires the round-trip
delay between any pair of servers to be less than 40 ms. Hybrid
deployments are also possible. For example, Cisco Unified
CallManager clusters can reside at multiple sites, but there
can also be sites in the enterprise that do not have a Cisco
Unified CallManager cluster and are served by a cluster at a
remote site. Figures to show examples of possible deployments
of the Cisco Unified CallManager. - Single Site:
In Figure , IP telephony is deployed at a single building with
a local Cisco Unified CallManager cluster and application
servers.
- Local voice gateways offer PSTN access and
provide DSP resources.
- The IP WAN is not used for
voice; the PSTN is used for all external calls.
- Multisite with Centralized Call Processing:
Figure shows a company with two sites that is using a
centralized call-processing model.
- There is one Cisco
Unified CallManager cluster, and all Cisco Unified CallManager
servers are located at the headquarters site.
- Application servers are also centralized, but each site has
local DSP resources.
- Because there are local DSPs at
each site, conference calls using the DSP resources do not have
to cross the IP WAN if all participants of the conference are
at the same site.
- The IP WAN carries data and voice.
All signaling messages from branch IP phones have to cross the
IP WAN. Media streams cross the IP WAN only for intersite
calls.
- Each site has local PSTN access.
- CAC
is used to limit the number of VoIP calls between the two
sites. If CAC denies calls, the Automated Alternate Routing
(AAR) feature of the Cisco Unified CallManager reroutes the
calls through the PSTN.
- If the IP WAN goes down, the
branch router uses Cisco SRST to maintain IP telephony
operation for calls within the branch. All other calls are
routed through the PSTN.
- Multisite with
Distributed Call Processing: Figure shows the distributed
call processing deployment at two sites.
- Each site has
its own Cisco Unified CallManager cluster with local
servers.
- Local application servers and DSP resources
are available at each site.
- The IP WAN carries data
and voice. Only intersite calls use the IP WAN.
- Both
the signaling messages and media streams of intrasite calls
remain local to each site because of the presence of a call
agent in each site.
- Both sites have local PSTN
access.
- CAC is used to limit the number of VoIP calls
between the two sites. If CAC denies a call, the call is
rerouted through the PSTN using AAR.
- If the IP WAN
goes down, the local Cisco Unified CallManager clusters reroute
intersite calls over the PSTN via the cluster’s local
gateways.
- Clustering over WAN:
Figure shows clustering over an IP WAN.
- Each site has
local Cisco Unified CallManager servers, but the servers all
belong to a single cluster. Application servers and DSP
resources are locally available at each site.
- IP
phones at the Los Angeles office use local Cisco Unified
CallManager servers as the primary call agents, while the
servers in San Diego are used as backup call agents. IP phones
in San Diego are configured in a similar way to the phones in
Los Angeles using the local Cisco Unified CallManager servers
as the primary call agents and the servers in Los Angeles as
backup.
- The IP WAN carries data and voice. Only
intersite calls use the IP WAN. Both the signaling messages and
media streams of intrasite calls remain local to each site
because of the presence of a call agent at each site. Both
sites have local PSTN access. CAC is used to limit the number
of VoIP calls that can occur between the two sites. If calls
are denied by CAC, the calls are rerouted through the PSTN by
AAR. If the IP WAN goes down, the local Cisco Unified
CallManager clusters reroute intersite calls over the PSTN
using the local gateways.
- All intracluster
communication between Cisco Unified CallManager servers (for
example, database synchronization or exchange of account data)
goes over the IP WAN. The company must guarantee a required
round-trip time of less than 40 ms for the intracluster traffic
between the two sites.
Content
2.5 Implementing VoIP in an Enterprise Network
2.5.6 Cisco IOS Configurations for VoIP Cisco
IOS routers can be used as VoIP gateways. For a basic VoIP
configuration, two gateways are needed. Both need a connection