Design Guidelines for Multisite WAN with Centralized Call-Processing
Deployment
Follow these guidelines back implementing the multisite WAN archetypal with centralized
call processing:
■ Minimize adjournment amid Cisco UCM and alien locations to abate articulation cutthrough
delays (also accepted as clipping). The ITU-T G.114 advocacy specifies
a 150 ms best one way.
■ Use HSRP for arrangement resiliency.
■ Use the locations apparatus in Cisco UCM to accommodate alarm acceptance ascendancy into
and out of alien branches.
■ The cardinal of IP phones and band appearances accurate in SRST access at each
remote armpit depends on the annex router platform, the bulk of anamnesis installed,
and the Cisco IOS release. SRST on a Cisco IOS aperture supports up to 720 phones,
whereas Unified CME active in SRST access supports 240 phones. Generally speaking,
however, the best of whether to accept a centralized alarm processing or distributed
call processing access for a accustomed armpit depends on a cardinal of factors,
such as
■ IP WAN bandwidth or adjournment limitations
■ Criticality of the articulation network
■ Feature set needs
■ Scalability
■ Ease of management
■ Cost
42 Authorized Self-Study Guide: Cisco Articulation over IP (CVOICE)
Note If a broadcast call-processing archetypal is accounted added acceptable for a customer’s
business needs, the choices accommodate installing a UCM array at anniversary armpit or active Unified
CME at the alien sites.
■ At the alien sites, use the afterward appearance to ensure alarm processing survivability
in the accident of a WAN failure:
■ For SCCP phones, use SRST on a Cisco IOS aperture or Unified CME active in
SRST mode.
■ For SIP phones, use SIP SRST.
■ For MGCP phones, use MGCP Aperture Fallback.
SRST or Unified CME in SRST mode, SIP SRST, and MGCP Aperture Fallback can reside
with anniversary added on the aforementioned Cisco IOS gateway.
For specific allocation recommendations, accredit to the Cisco Unified Communications SRND
based on Cisco UCM 6.x at the afterward link:
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_implementation_
design_guide_book09186a008085eb0d.html
Multisite WAN with Broadcast Call-Processing Deployment
The archetypal for a multisite WAN deployment with broadcast alarm processing, as illustrated
in Figure 1-27, consists of assorted absolute sites, anniversary with its own call-processing
agent array affiliated to an IP WAN that carries articulation cartage amid the distributed
sites.
An IP WAN interconnects all the broadcast alarm processing sites. Typically, the PSTN
serves as a advancement affiliation amid the sites in case the IP WAN affiliation fails or
does not accept anymore accessible bandwidth. A armpit affiliated alone through the PSTN is a
standalone armpit and is not covered by the broadcast alarm processing model.
WAN connectivity options accommodate the following:
■ Leased lines
■ Frame Relay
■ ATM
■ ATM and Frame Relay SIW
■ MPLS VPN
■ IPsec V3PN
Multisite broadcast alarm processing allows anniversary armpit to be absolutely self-contained. In
the accident of an IP WAN abortion or bereft bandwidth, a armpit does not lose callprocessing
service or functionality. Cisco UCM artlessly sends all calls amid the sites
across the PSTN.
Chapter 1: Introducing Articulation over IP Networks 43
Multisite WAN with Broadcast Alarm Processing
Design Characteristics of Multisite WAN with Broadcast Call-Processing
Deployment
The multisite archetypal with broadcast alarm processing has the afterward design
characteristics:
■ Best of 30,000 SCCP or SIP IP phones or SCCP video endpoints per cluster.
■ Best of 1100 MGCP gateways or H.323 accessories (gateways, MCUs, trunks, and
clients) per UCM cluster.
■ PSTN for all alien calls.
■ DSP assets for conferencing, transcoding, and MTP.
■ Articulation mail, unified messaging, and Cisco Unified Presence components.
■ Capability to accommodate with bequest PBX and voice-mail systems.
■ H.323 clients, MCUs, and H.323/H.320 gateways that crave a attendant to place
calls charge annals with a Cisco IOS Attendant (Cisco IOS Absolution 12.3(8)T or later).
UCM again uses an H.323 block to accommodate with the attendant and accommodate call
routing and bandwidth administration casework for the H.323 accessories registered to it.
Multiple Cisco IOS Gatekeepers ability be acclimated to accommodate redundancy. Cisco IOS
Gatekeepers ability additionally be acclimated to accommodate alarm acquisition and bandwidth management
between the broadcast UCM clusters. In best situations, Cisco recommends that
each UCM array accept its own set of endpoint gatekeepers and that a abstracted set
of gatekeepers be acclimated to administer intercluster calls. It is accessible in some circumstances
to use the aforementioned set of gatekeepers for both functions, depending on the size
of the arrangement and complication of the punch plan.
■ MCU assets are appropriate in anniversary array for multipoint video conferencing.
Depending on conferencing requirements, these assets ability be either SCCP or
H.323, or both, and ability all be amid at the bounded sites or broadcast to the
remote sites of anniversary array if bounded conferencing assets are required.
■ H.323/H.320 video gateways are bare to acquaint with H.320 videoconferencing
devices on the accessible ISDN network. These gateways ability all be amid at
the bounded sites or broadcast to the alien sites of anniversary array if bounded ISDN
access is required.
■ High-bandwidth audio (for example, G.711, G.722, or Cisco Wideband Audio)
between accessories in the aforementioned site, but low-bandwidth audio (for example, G.729 or
G.728) amid accessories in altered sites.
■ High-bandwidth video (for example, 384 kbps or greater) amid accessories in the
same site, but low-bandwidth video (for example, 128 kbps) amid accessories at different
sites. The Cisco Unified Video Advantage Wideband Codec, operating at
7 Mbps, is recommended alone for calls amid accessories at the aforementioned site. Note that
the Cisco VT Camera Wideband Video Codec is not accurate over intercluster
trunks.
■ Minimum of 768 kbps or greater WAN articulation speeds. Video is not recommended on
WAN access that accomplish at speeds lower than 768 kbps.
■ Alarm acceptance ascendancy is provided by UCM locations for calls amid sites controlled
by the aforementioned UCM array and by the Cisco IOS Attendant for calls between
UCM clusters (that is, intercluster trunks). AAR is additionally accurate for both intracluster
and intercluster video calls.