This section discusses the upgrade strategies for all components in the Cisco Unified Communications Release 5.0 deployment scenarios. Details of individual components upgrades are not described unless additional information or clarification is required.
The following upgrade strategies are available with the Cisco Unified Communications Release 5.0:
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Single Stage Upgrade using Existing Hardware (Flash-cut)—All components in the network start at the 4.1 release set and all components can be upgraded to Cisco Unified Communications within a single maintenance window.
•Single Stage Upgrade using New Hardware (either Flash-cut or Shrink-and-Grow)—A parallel Cisco Unified Communications network should be built using new hardware and pre-staged with configuration to support the existing production network.
All users can then be moved from the existing production network to the new network in one of two ways:
–In a single maintenance window using a Flash-Cut upgrade process
- or -
–In several maintenance windows using a Shrink-and-Grow upgrade process (where a single maintenance window is used to implement the new release versions on the new hardware, but multiple windows are used to migrate the users)
The above upgrade strategies involving the Single Stage upgrade approach are appropriate for small sites (less than 300 seats) with a smaller number of components in the network.
•Multi-Staged System Upgrade using Existing Hardware (Hybrid System)—The components in individual sites can be upgraded from the 4.1 release set software to the Cisco Unified Communications release set in stages during separate maintenance windows.
At the completion of each intermediate stage, the network exists as a "hybrid system" with a mix of the following:
–Some components are operating on the 4.1 release set
–Other upgraded components are operating on Cisco Unified Communications release set
Note "Hybrid system" refers only to inter-product versions, not to intra-product versions. For instance, all Cisco CallManager servers in the same cluster, or all servers that are part of the same ICM system, will remain at the same software release version.
The Multi-Staged System upgrade approach is recommended for medium-to-large sites (ranging from 301-1499 seats for medium and 1500-4999 seats for large) with a greater number of components in the network.
•Multi-Site Migration (via Hybrid Network with Release Set inter-working)—Components are upgraded from the 4.1 release set to Cisco Unified Communications on a site-by-site basis during separate maintenance windows.
At the completion of each maintenance window, a "hybrid network" exists with a mix of the following:
–Sites whose components are operating on the 4.1 release set
–Sites whose components are operating on the Cisco Unified Communications release set
–Sites whose components are a "hybrid system" as described inMulti-Staged System Upgrade Using Existing Hardware (Hybrid System)
This model assumes that sites may be upgraded independently. However, with the Multi-Site Migration strategy, you must account for distributed applications with shared components among sites. For example, if you have deployed a distributed ICM system, a Cisco Emergency Responder supporting multiple Cisco CallManager clusters, or a Cisco CallManager cluster using Clustering-over-WAN (CoW), then these sites must be upgraded concurrently.
Users can be moved in stages from the existing production network to the new network operating on Cisco Unified Communications release software.
The Multi-Site Migration strategy is recommended for large multi-site environments (more than 5000 seats) with a large number of components in the network.
Single-Stage Upgrade Using Existing Hardware
All components in the network start at the 4.1 release set and all components are upgraded to Cisco Unified Communications release software within a single maintenance window (MW). Since all components are upgraded within a single maintenance window, interoperability is not required between the 4.1 release set and Cisco Unified Communications release set.
The Single Stage upgrade on existing hardware approach is typically not recommended for large customer sites/networks, since it has to be performed within a single maintenance window.
Figure 2 shows the single maintenance window that is involved in the Single Stage upgrade on existing hardware approach:
Figure 2 Single Stage Upgrade Using Existing Hardware
Single-Stage Upgrade Using New Hardware
A parallel Cisco Unified Communications network should be built using new hardware and pre-staged with configuration to support the existing production network. All users can be then moved from the existing production network to the new network operating with Cisco Unified Communications release software either in a single maintenance window (using Flash-Cut) or in several maintenance windows (using Shrink-and-Grow).
The Single Stage upgrade on new hardware approach is not recommended for large customer sites/networks for the following reasons:
•The upgrade cannot be performed within a single maintenance window.
•The expense of a complete new parallel network is significant.
Figure 3 shows the maintenance windows that are involved in the Single Stage upgrade on new hardware approach:
Figure 3 Single Stage Upgrade Using New Hardware
Multi-Staged System Upgrade Using Existing Hardware (Hybrid System)
Individual components and/or sites can be upgraded in stages, from the 4.1 release set software to Cisco Unified Communications release software, during separate maintenance windows. At the completion of each intermediate stage, the site exists as a "hybrid system" with a mix of the following:
•Some components operating on the 4.1 release set
•Other upgraded components operating on the Cisco Unified Communications release software
The Multi-Staged System upgrade on existing hardware is the recommended approach for medium-to-large networks. In this case, individual components within a single site and/or individual sites in a multi-site environment are progressively upgraded over the span of several days or weekends.
This type of staging is required because:
•Sufficient time may not be available (maintenance window) to take the system out of service for the complete upgrade of all the components involved.
•You must test existing functionality following the upgrade.
•You must test new functionality following the upgrade.
You can view a staged upgrade as a series of maintenance windows separated by inter-maintenance window intervals. During each maintenance window, one or more components of the system or a subset of the components is upgraded.
Customers typically have a maintenance window during which service disruptions are likely to have minimal impact and affect only a limited number of users, for example, during the night or during a weekend.
Before the staged upgrade is completed, the whole network exists in a partially upgraded state where some components have been upgraded to Cisco Unified Communications release software and the remaining components are operating with the 4.1 release set software.
Backward compatibility of the components is critical during the staged upgrade, so that Cisco Unified Communications components are able to interoperate with the 4.1 release set components. If any component is not backward compatible, this can potentially result in prolonged periods of service outage spanning several maintenance windows (possibly several weeks).
Therefore, during multi-stage upgrades, it is mandatory to have interoperability between the 4.1 release set software and Cisco Unified Communications software versions. For more information on software and backward compatibility considerations, see System Upgrade Dependencies at
http://www.cisco.com/univercd/cc/td/doc/systems/unified/unified1/sum/ch2_prep.htm#wp1191159 
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Figure 4 shows the maintenance windows that are involved in the Multi-Staged System upgrade on existing hardware approach:
Figure 4 Multi-Staged System Upgrade Using Existing Hardware (Hybrid System)
Multi-Site Migration
Components are upgraded from the 4.1 release set to Cisco Unified Communications release set on a site-by-site basis during separate maintenance windows.
At the completion of each maintenance window, a "hybrid network" will exist across multiple sites. Within each site, either a Single Stage or Multi-Stage System Upgrade strategy can be used to upgrade that particular site's components from the 4.1 release set to the Cisco Unified Communications release set.
Interworking can be expected among sites on "pure" 4.1 release set versions and sites on "pure" Cisco Unified Communications release set versions as shown in Figure 5. However, interworking will not be possible between these "pure" sites and "hybrid system" sites.
Note If you have a component that is common to multiple sites, such as a shared Cisco Emergency Responder or ICM system, this may impact the interoperability itself, the order in which sites may be upgraded, and/or which sites must be upgraded concurrently.
Users can be moved in stages from the existing production network to the new network operating with Cisco Unified Communications release software. The number of users on the existing 4.1 release network will shrink while the number on the Cisco Unified Communications network will grow correspondingly.
This migration process can span several weeks and, sometime months, if necessary. During this upgrade approach, it is essential that the two networks, existing and new, should be able to communicate with each other.
Figure 5 shows the maintenance windows that are involved in the Multi-Site Migration approach:
Figure 5 Multi-Site Migration
Table 3 provides a summary of the preceding upgrade strategies:
When your upgrade plan is in place and you are ready to upgrade, go to Performing a System Upgrade on the Optimize tab.