Still on Today's reading: Single-Site and Multi-Site Deployment Models

The Single-Site Model consists of:

-call-processing agent cluster located at a single site or campus with no telephony services provided over an IP WAN.
-all CUCMs, Apps, Data-stream Protocol (DSP) are in the same location.

-multiple clusters inside a LAN or MAN can be implemented and connected through inter-cluster trunks if more IP phones needed here.

DESIGN CHARACTERISTICS:

-Single CUCM cluster
-Max 30,000 Signaling Connection Control Part [SCCP] or Serial Interface Proc (SIP) IP phones or SCCP video endpoints per cluster.
-max 1,100 H.323 devices per CUCM cluster
-PSTN for all calls outside the site.
-DSP resources for conferencing, transcoding and Media termination Point [MTP]
-voice mail, unified messaging, Cisco Unified Presence, audio and video comps.
-capability to integrate with legacy PBX and voice-mail systems

-H.323 clients, multipoint control units, H.323/H.320 gateways: if gatekeeper is required these must register with a Cisco IOS gateway release 12.3(8)T or later. CUCM then uses an H.323 trunk to integrate with the gatekeeper and provide call routing and bandwidth management services for the H.323 devices registered to it.

-Multipoint control unit resources: req for multipoint video-conferencing. May be either SCCP or H.323 or both.

-H.323/H.320 video gateways:needed to comm with H.323 video conferencing devices on the ISDN network.

-High-bandwidth audio:

-High-bandwidth video

Benefits:

-ease of deployment
-a common infrastructure for a converged solution
-simplified dial plan
-no required transcoding resources(single high-bandwidth codec in use)

-significant cost benefits
-allows CUC to take adv of many IP-based apps on the enterprise.
-allows each site to be self-contained - no dependency for service or loss of call-processing in the event of IP WAN failure or insufficient bandwidth.


GUIDELINES AND BEST PRACTICE TO FOLLOW WHEN IMPLEMENTING SINGLE_SITE MODEL:

-provide a highly available, fault-tolerant infrastructure
-know the calling patterns for your enterprise
-use G.711 codec for all endpoints - this eliminates the consumption of DSP resources for transcoding
-use SIP, SRST and MGCP gateways for PSTN - this simplifies the dial plan config.
-implement the recommended network infrastructure.


MULTISITE CENTRALIZED DEPLOYMENT MODEL

Consists of {

-a single call-processing agent cluster that provides services for many remote sites and uses the IP WAN to transport CUC traffic between the sites.

The IP WAN also carries call-control signaling between the central site and remote sites

WAN CONNECTIVITY OPTIONS:

-leased lines
-Frame Relay
-ATM
-ATM and Frame Relay service internetworking (SIW)
-Multiprotocol label switching (MPLS) VPN
-Voice and video Enabled VPN (V3PN) IPSec protocol

Routers at WAN edges req QoS mechs (priority queuing and traffic shaping) to protect voice traffic from dta traffic across the WAN where bandwidth is typically scarce.

Call Admission Control (CAC) is also needed to avoid oversubscribing the WAN links with voice traffic and deteriorating quality of established calls.

When the IP WAN is down, a variety of Cisco gateways can provide the remote sites with PSTN access.

DESIGN FEATURES:

-single CUCM cluster
-max 30,000 SCCP or SIP IP phones or SIP video endpoints per cluster.
-max 1000 locations per CUCM cluster
-max 1,100 H.323 devices or 1,100 MGCP gateways per CUCM cluster.

-PSTN for all external calls.
-DSP resources for conferencing, transcoding and Media termination Point [MTP]
-voice mail, unified messaging, Cisco Unified Presence, audio and video comps.
-capability to integrate with legacy PBX and voice-mail systems

-H.323 clients, multipoint control units, H.323/H.320 gateways: if gatekeeper is required these must register with a Cisco IOS gateway release 12.3(8)T or later. CUCM then uses an H.323 trunk to integrate with the gatekeeper and provide call routing and bandwidth management services for the H.323 devices registered to it.

-Multipoint control unit resources: req for multipoint video-conferencing. May be either SCCP or H.323 or both.

-H.323/H.320 video gateways:needed to comm with H.323 video conferencing devices on the ISDN network.

-High-bandwidth audio:

-High-bandwidth video

-Min of 768kbps or higher WAN link speeds - video not recomm for WAN links with speed lower than 768kbps.

-CUCM locations and automated alternate routing (AAR) - CUCM provides CAC.

-must have SRST versions 4.0 and higher as they support video

-CUCM Express versions 4.0 and higher - maybe used in place of SRST routing.\

-Cisco Unity Server - CUCM Express maybe be integrated with the Unity Server in the branch office or remote site.

GUIDELINES AND BEST PRACTICE TO FOLLOW WHEN IMPLEMENTING MULTISITE WAN MODEL WITH CENTRALIZED CALL PROCESSING:

-Minimize delay between CUCM and remote locations to reduce voice cut-through delays (clippings). 150 ms maximum one-way is Cisco's recomm.

-Use the locations mech in CUCM to provide CAC into and out of remote branches.

-Number of branch IP phones and line appearances that are supported in the SRST mode at each remote site depends on the branch router platform, the amount of installed mem and IOS releases.

SRST on a Cisco IOS gateway supports up to 720 phones, whereas the CUCM Express in SRST mode supports 240 phones.

The choice of whether to adopt a centralized call-processing model or a distributed call-processing model depends on:

-IP WAN bandwidth or delay limitations

-criticality of the voice network

-Feature set needs

-Scalability

-Ease of management

-Cost

In the event a dist call-proc mod is chosen, the choices include installing the CUCM cluster at each site or running CUCM Express at remote sites.

-another design guideline is to use these features for call processing survivability in the event of WAN failure at remote sites:

a. for SCCP phones use CUCM in a Cisco IOS gateway or CUCM Express in SRST mode.

b. for SIP phones, use SIP SRST

c. for MGCP phones, use MGCP gateway fallback

They can all reside with each other on a Cisco IOS gateway.

-Hot Standby Router Protocol (HSRP) may also be used to provide backups for gateways and gatekeepers in a VoIP environment.

**CAC is used to avoid oversubscribing the WAN links with voice traffic and deteriorating the quality of established calls.