# Unified CM Session Management Edition

Canonical: https://warmtransfer.net/knowledge/cucm-session-management-edition

Last verified: 2026-09-25

Cisco describes Session Management Edition (SME) as Unified CM operating in a specific deployment mode[^10]. In current documentation, WarmTransfer's reading of the sources is that SME is a deployment role of Unified CM software rather than a separate product line with its own release train[^36].

## Architecture and topology

In a pure SME deployment, calls traverse only trunk interfaces, and the SME hosts no line interfaces[^34]. An SME cluster uses the same topology as a regular Unified CM cluster, with a publisher node holding the master configuration repository[^33]. Cisco recommends a 1:1 redundancy ratio for call processing subscribers in an SME cluster[^35].

In a base configuration, the SME acts as a routing aggregation point for leaf clusters and provides centralized PSTN access for all connected leaf clusters[^39][^5]. The 8.5 SME guide similarly identifies aggregating PSTN access onto 1 or more centralized IP PSTN trunks as an SME benefit[^22]. In more advanced configurations, the SME can host centralized voice messaging, mobility, and conferencing services[^2], and commonly used applications such as conferencing or videoconferencing can connect directly to the SME cluster[^4]. During migrations from legacy PBXs to Unified CM, SME can aggregate multiple PBXs[^30].

The Collaboration 14 Preferred Architecture recommends deploying SME with 4 or more Unified CM clusters to centralize dial plan and trunking and avoid a full-mesh SIP trunk topology[^17]. Without SME, the Preferred Architecture interconnects Unified CM clusters with a full mesh of SIP trunks so calls do not traverse intermediate clusters[^18]. The Collaboration 14 enterprise CVD call control chapter states that it does not cover Unified CM SME[^8].

In Webex Calling Dedicated Instance, a customer is eligible for an SME deployment when it has 3 clusters deployed in the Dedicated Instance cloud[^12]. An SME for a Dedicated Instance customer must go through a Cisco Business Unit approval process[^11]. In Dedicated Instance, a single SME cluster can span regions to serve a multi-region customer and route calls between regions[^13]. WarmTransfer's reading of the sources is that the on-premises Preferred Architecture threshold of 4 or more clusters and the Dedicated Instance eligibility rule of 3 clusters are different criteria for different offerings, not conflicting statements about 1 product[^50].

Cisco measures SME performance in calls per second across each pair of protocols, and the figure varies by hardware platform and software version[^7].

## Dial plan and Intercluster Lookup Service

The Collaboration 14 Preferred Architecture design overview recommends Global Dial Plan Replication (GDPR) to replicate dial plan information between clusters[^29]. GDPR uses Intercluster Lookup Service (ILS) as its transport, so a multi-cluster deployment requires ILS between all Unified CM clusters[^20]. GDPR can advertise 1 +E.164 number, 1 enterprise significant number, and up to 5 alphanumeric URIs for each directory number[^19]. In Unified CM 15, an ILS network supports up to 10 hub clusters with 20 spoke clusters per hub, reaching up to 200 clusters in total[^21].

## Trunk configuration and call handling

Unified CM 15 lists Session Management Edition among the destinations a SIP trunk can connect to, alongside gateways, proxies, applications, and remote clusters[^45]. A SIP trunk accepts up to 16 destination addresses in Unified CM 15[^44].

The 8.6 SME guide states that SIP is the protocol of choice for intercluster trunks because Unified CM SIP trunks offer more features than H.323 intercluster trunks[^43]. The guide recommends enabling Run on all Active Unified CM Nodes on all route lists[^37]. When Run on all Active Unified CM Nodes is enabled on a SIP trunk, the outbound trunk call leaves from the same node that received the inbound call[^38]. When several trunks run on all nodes toward the same destination, each trunk needs a unique incoming and destination port number to be identified[^52].

For trunk design between clusters, the 8.6 guide recommends:
- Leaf clusters build route lists of multiple prioritized SIP trunks (1 per group of SME nodes in each data center), with Run on all Nodes enabled and a unique incoming port on each trunk[^25].
- SME clusters configure standard Unified CM Groups for each SIP trunk, defining destination IP addresses and ports for every call processing node in the leaf cluster[^49].
- SIP OPTIONS ping is used on all SIP trunks so Unified CM tracks trunk state dynamically instead of per call and on timeout[^28].

On call offer types, the 8.6 guide notes that Unified CM SIP trunks use Delayed Offer by default and recommends Delayed Offer for outbound trunk calls[^9]. Where Early Offer is required, the guide recommends the "Early Offer support for voice and video calls (insert MTP if needed)" option because it needs fewer MTP resources[^14]. The guide also notes that IP PSTN service providers typically require SIP Early Offer on trunks and that most support voice calls only[^23]. Unified CM SIP trunks support topology-aware RSVP call admission control using SIP Preconditions, as well as locations-based call admission control that does not know the WAN topology[^51].

Cisco marks the SME Deployment Guide Release 8.x as out of date and states that most of its content moved into the Unified CM Trunks and Deployment Models chapters of the Collaboration SRND[^1].

## Licensing and migration

In Unified CM 15, Session Management Edition can register to Cisco Smart Software Manager (CSSM) or to a Smart Software Manager satellite using the same process as Unified CM[^48]. SME can register to the same Smart Account virtual account as Unified CM or to a separate virtual account[^56]. When registered with Specific License Reservation (SLR), an SME requires a minimum set of licenses reserved in CSSM at the time the SLR authorization code is generated[^47].

Cisco announced end of sale for perpetual SME licensing on 2021-05-19, setting the last day to order as 2021-11-17[^31]. End of software maintenance occurred on 2022-11-17, end of service contract renewal on 2024-02-13, and the last date of support was 2024-11-30[^32]. The perpetual SME end-of-sale notice covered product IDs including SME-SESSION, LIC-SME-SESSION, SME-RTU, SME-VERS-12.5, and LIC-SME-SESS-UPG[^3]. Cisco directs customers with perpetual SME licensing to migrate to Session Management Edition under Collaboration Flex Plan 3.0 (A-FLEX-3)[^26]. WarmTransfer's reading of the sources is that the session-based SME licensing described in the 8.x guide and 8.0 data sheet reflects the retired perpetual model, whereas current SME is licensed through Smart Licensing and Flex 3.0[^42].

## See also

- See also [Unified CM call admission control](https://warmtransfer.net/knowledge/cucm-call-admission-control).
- See also [SIP OPTIONS pings and trunk keepalives](https://warmtransfer.net/knowledge/sip-options-keepalive).
- See also [Unified CM dial plan partitions and calling search spaces](https://warmtransfer.net/knowledge/cucm-dial-plan).
- See also [Unified CM SIP trunks and security profiles](https://warmtransfer.net/knowledge/cucm-sip-trunks).
- See also [Unified CM and Webex Calling coexistence during a migration](https://warmtransfer.net/knowledge/cucm-webex-calling-coexistence).

## Applicability

Applies to: Cisco Unified Communications Manager Session Management Edition, Cisco Unified Communications Manager, and Cisco Webex Calling Dedicated Instance. Deployments: on-premises and dedicated instance. Sources checked 2026-09-25. The 8.5 SME guide addresses aggregating PSTN access[^22]. The 8.6 SME guide covers SIP trunk design[^43]. Cisco designates the SME Deployment Guide Release 8.x as out of date[^1]. In Unified CM 15, SIP trunks accept up to 16 destinations[^44]. For Webex Calling Dedicated Instance, an SME deployment requires 3 clusters in the Dedicated Instance cloud[^12]. Cisco announced end of sale for perpetual SME licensing on 2021-05-19[^31].

## What remains uncertain

Current SRND Unified CM Trunks and Deployment Models SME sections are not covered by the sources below. SME as an aggregation point for Webex Calling or Teams coexistence is not covered by the sources below. SME nodes clustered over the WAN and the maximum RTT between them are not covered by the sources below. The SME role in ILS hub design and GDPR route strings is not covered by the sources below. Current Early Offer and Best Effort Early Offer guidance for SME trunks is not covered by the sources below. Flex 3.0 SME ordering SKUs and metering units are not covered by the sources below. Current SME calls per second by protocol pair and VM size are not covered by the sources below. The contents of the SME SLR minimum license set are not covered by the sources below.

## Sources

[^1]: Cisco marks the SME Deployment Guide Release 8.x as out of date and says most of its content moved into the Unified CM Trunks and Deployment Models chapters of the Collaboration SRND. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide Release 8.x](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_x/SME_Deployment_Guide.html), Caution notice at top of guide. Checked 2026-09-25.
[^2]: In more advanced configurations, the SME can also host centralized voice messaging, mobility and conferencing services. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, advanced configuration paragraph. Checked 2026-09-25.
[^3]: The perpetual SME end-of-sale notice covers product IDs including SME-SESSION, LIC-SME-SESSION, SME-RTU, SME-VERS-12.5 and LIC-SME-SESS-UPG. Source: [End-of-Sale and End-of-Life Announcement for the Cisco Perpetual Licensing for Session Management Edition (SME)](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-callmanager/eos-eol-notice-c51-2471470.html), Table 2, product part numbers. Checked 2026-09-25.
[^4]: The 8.5 SME guide says commonly used applications such as conferencing or videoconferencing can connect directly to the SME cluster. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide 8.5(1) - Overview](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_5_1/overview.html), Overview chapter, benefits. Checked 2026-09-25.
[^5]: In a base configuration, the SME also provides centralized PSTN access for all the leaf clusters connected to it. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, base configuration paragraph. Checked 2026-09-25.
[^6]: A SIP trunk that uses a standard Unified CM Group runs its SIP daemon on up to three nodes in the cluster. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SIP trunk node distribution. Checked 2026-09-25.
[^7]: Cisco measures SME performance in calls per second across each pair of protocols, and the figure varies by hardware platform and software version. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, performance paragraph. Checked 2026-09-25.
[^8]: The Collaboration 14 enterprise CVD call control chapter states that it does not cover Unified CM SME. Source: [Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Call Control](https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Collaboration/enterprise/14/collbcvd/control.html), Multi-Cluster Considerations. Checked 2026-09-25.
[^9]: The 8.6 SME guide says Unified CM SIP trunks use Delayed Offer by default and recommends Delayed Offer for outbound trunk calls. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SIP Delayed Offer and Early Offer. Checked 2026-09-25.
[^10]: Cisco describes Session Management Edition as Unified CM operating in a specific deployment mode. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, opening paragraph. Checked 2026-09-25.
[^11]: An SME for a Dedicated Instance customer must go through a Cisco Business Unit approval process. Source: [Introduction to Dedicated Instance](https://help.webex.com/en-us/article/dk3o5r/Introduction-to-Dedicated-Instance), Cisco Session Manager Edition (SME) section. Checked 2026-09-25.
[^12]: In Webex Calling Dedicated Instance, a customer is eligible for an SME deployment when it has three clusters deployed in the Dedicated Instance cloud. Source: [Introduction to Dedicated Instance](https://help.webex.com/en-us/article/dk3o5r/Introduction-to-Dedicated-Instance), Cisco Session Manager Edition (SME) section. Checked 2026-09-25.
[^13]: In Dedicated Instance, a single SME cluster can span regions to serve a multi-region customer and route calls between regions. Source: [Introduction to Dedicated Instance](https://help.webex.com/en-us/article/dk3o5r/Introduction-to-Dedicated-Instance), Cisco Session Manager Edition (SME) section. Checked 2026-09-25.
[^14]: Where Early Offer is required, the 8.6 SME guide recommends the 'Early Offer support for voice and video calls (insert MTP if needed)' option because it needs fewer MTP resources. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SIP Delayed Offer and Early Offer. Checked 2026-09-25.
[^15]: The Flex Plan 3.0 data sheet lists SME as an on-premises offering available under the Enterprise Agreement and Named User buying models. Source: [Cisco Collaboration Flex Plan 3.0 and Webex Suite Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/cisco-collaboration-flex-plan/collaboration-flex-plan3-data-sheet.html), Calling products, features, benefits, and deployment models, Table 5. Checked 2026-09-25.
[^16]: In the Flex Plan 3.0 Named User calling table, 'Session Manager' appears as an optional purchase for the Professional, Enhanced and Standard license types. Source: [Cisco Collaboration Flex Plan 3.0 and Webex Suite Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/cisco-collaboration-flex-plan/collaboration-flex-plan3-data-sheet.html), Named User Calling License Types, Table 7. Checked 2026-09-25.
[^17]: The Collaboration 14 Preferred Architecture recommends deploying SME with four or more Unified CM clusters, to centralize dial plan and trunking and avoid a full-mesh SIP trunk topology. Source: [Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Call Control](https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Collaboration/enterprise/14/collbcvd/control.html), Multi-Cluster Considerations. Checked 2026-09-25.
[^18]: Without SME, the Preferred Architecture interconnects Unified CM clusters with a full mesh of SIP trunks so calls do not traverse intermediate clusters. Source: [Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Call Control](https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Collaboration/enterprise/14/collbcvd/control.html), Multi-Cluster Considerations. Checked 2026-09-25.
[^19]: GDPR can advertise one +E.164 number, one enterprise significant number and up to five alphanumeric URIs for each directory number. Source: [Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Call Control](https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Collaboration/enterprise/14/collbcvd/control.html), Multi-Cluster Considerations. Checked 2026-09-25.
[^20]: GDPR uses ILS as its transport, so a multi-cluster deployment requires ILS between all Unified CM clusters. Source: [Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Call Control](https://www.cisco.com/c/en/us/td/docs/solutions/CVD/Collaboration/enterprise/14/collbcvd/control.html), Multi-Cluster Considerations. Checked 2026-09-25.
[^21]: In Unified CM 15, an ILS network supports up to 10 hub clusters with 20 spoke clusters per hub, up to 200 clusters in total. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Configure Intercluster Lookup Service](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_010100.html), Configure Intercluster Lookup Service, ILS Overview. Checked 2026-09-25.
[^22]: The 8.5 SME guide lists aggregating PSTN access onto one or more centralized IP PSTN trunks as an SME benefit. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide 8.5(1) - Overview](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_5_1/overview.html), Overview chapter, benefits. Checked 2026-09-25.
[^23]: The 8.6 SME guide notes that IP PSTN service providers typically require SIP Early Offer on trunks to them and that most support voice calls only. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, multi-cluster deployments 8.5 and later. Checked 2026-09-25.
[^24]: With SME, leaf systems keep a simplified dial plan and trunks that point to the SME cluster instead of separate dial plans toward every other system. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide 8.5(1) - Overview](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_5_1/overview.html), Overview chapter, benefits. Checked 2026-09-25.
[^25]: The 8.6 SME guide recommends that each leaf cluster build route lists of multiple prioritized SIP trunks, one per group of SME nodes in each data center, with Run on all Nodes enabled and a unique incoming port on each trunk. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, leaf cluster trunk recommendations. Checked 2026-09-25.
[^26]: Cisco directs perpetual SME customers to migrate to Session Management Edition under Collaboration Flex Plan 3.0 (A-FLEX-3). Source: [End-of-Sale and End-of-Life Announcement for the Cisco Perpetual Licensing for Session Management Edition (SME)](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-callmanager/eos-eol-notice-c51-2471470.html), Product Migration Options section. Checked 2026-09-25.
[^27]: The 8.6 SME guide says SIP normalization and transparency scripts can address SIP interoperability issues with third-party systems. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, third-party leaf systems. Checked 2026-09-25.
[^28]: SIP OPTIONS ping is recommended on all SIP trunks so Unified CM tracks trunk state dynamically instead of per call and on timeout. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SIP OPTIONS Ping. Checked 2026-09-25.
[^29]: The Collaboration 14 Preferred Architecture design overview recommends GDPR to replicate dial plan information between clusters. Source: [Preferred Architecture for Cisco Collaboration 14 On-Premises Deployments, Design Overview](https://www.cisco.com/c/en/us/td/docs/solutions/PA/overview/14x/clbpa14x.html), Multi-cluster deployment considerations. Checked 2026-09-25.
[^30]: SME can aggregate multiple PBXs during a migration from legacy PBXs to Unified CM. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide 8.5(1) - Overview](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_5_1/overview.html), Overview chapter, benefits. Checked 2026-09-25.
[^31]: Cisco announced end of sale for perpetual SME licensing on 2021-05-19; the last day to order was 2021-11-17. Source: [End-of-Sale and End-of-Life Announcement for the Cisco Perpetual Licensing for Session Management Edition (SME)](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-callmanager/eos-eol-notice-c51-2471470.html), Table 1, End-of-Sale date row. Checked 2026-09-25.
[^32]: For perpetual SME licensing, end of software maintenance was 2022-11-17, end of service contract renewal 2024-02-13, and last date of support 2024-11-30. Source: [End-of-Sale and End-of-Life Announcement for the Cisco Perpetual Licensing for Session Management Edition (SME)](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-callmanager/eos-eol-notice-c51-2471470.html), Table 1, milestone rows. Checked 2026-09-25.
[^33]: An SME cluster uses the same topology as a regular Unified CM cluster, with a publisher node holding the master configuration repository. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, cluster topology paragraph. Checked 2026-09-25.
[^34]: In a pure SME deployment, calls traverse only trunk interfaces and the SME hosts no line interfaces. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, opening paragraph. Checked 2026-09-25.
[^35]: Cisco recommends a 1:1 redundancy ratio for call processing subscribers in an SME cluster. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, cluster topology paragraph. Checked 2026-09-25.
[^36]: In current documentation SME is a deployment role of Unified CM software rather than a separate product line with its own release train (inferred). Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, read with cisco-cucm-sysconfig-15-trunks SIP Trunk Overview. Checked 2026-09-25.
[^37]: The 8.6 SME guide recommends enabling Run on all Active Unified CM Nodes on all route lists. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, Run on all Active Unified CM Nodes. Checked 2026-09-25.
[^38]: With Run on all Active Unified CM Nodes enabled on a SIP trunk, the outbound trunk call leaves from the same node that received the inbound call. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, Run on all Active Unified CM Nodes. Checked 2026-09-25.
[^39]: In a base configuration, the SME is a routing aggregation point for a number of leaf clusters. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, base configuration paragraph. Checked 2026-09-25.
[^40]: The 8.5 SME guide presents SME as running the same Unified CM software, focused on aggregating leaf systems rather than serving endpoints. Source: [Cisco Unified Communications Manager Session Management Edition Deployment Guide 8.5(1) - Overview](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_5_1/overview.html), Overview chapter, opening section. Checked 2026-09-25.
[^41]: If the SME is a service aggregation point, sizing must also consider the share of calls to centralized voice messaging, the number of mobility users and conferencing load. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, service aggregation inputs. Checked 2026-09-25.
[^42]: The session-based SME licensing in the 8.x guide and 8.0 data sheet describes the retired perpetual model; current SME is licensed through Smart Licensing and Flex 3.0 (inferred). Source: [End-of-Sale and End-of-Life Announcement for the Cisco Perpetual Licensing for Session Management Edition (SME)](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-callmanager/eos-eol-notice-c51-2471470.html), Table 2 session PIDs and Product Migration Options, read with cisco-cucm-sysconfig-15-smart-licensing License Types. Checked 2026-09-25.
[^43]: The 8.6 SME guide calls SIP the protocol of choice for intercluster trunks because Unified CM SIP trunks offer more features than H.323 intercluster trunks. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SIP trunk overview. Checked 2026-09-25.
[^44]: In Unified CM 15, a SIP trunk accepts up to 16 destination addresses. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Trunks](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01000.html), Configure Trunks, SIP trunk destination settings. Checked 2026-09-25.
[^45]: The Unified CM 15 trunk chapter lists a Session Management Edition among the destinations a SIP trunk can connect to, alongside gateways, proxies, applications and remote clusters. Source: [System Configuration Guide for Cisco Unified Communications Manager Release 15 and SUs - Configure Trunks](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01000.html), Configure Trunks, SIP Trunk Overview. Checked 2026-09-25.
[^46]: SME is sized with the SME sizing tool, whose inputs include the SIP trunks the cluster serves, users reaching SME over trunks, per-user intercluster and PSTN BHCA, PSTN trunks, average call holding time, and route and translation pattern counts. Source: [Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14](https://www.cisco.com/c/en/us/td/docs/solutions/PA/size/SRND_sizing14/sizing14.html), Using the SME Sizing Tool, input parameter list. Checked 2026-09-25.
[^47]: An SME registered with Specific License Reservation needs a minimum set of licenses reserved in CSSM when the SLR authorization code is generated. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Smart Software Licensing](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01.html), Smart Software Licensing, License Types. Checked 2026-09-25.
[^48]: In Unified CM 15, Session Management Edition can register to Cisco Smart Software Manager or to a Smart Software Manager satellite, using the same process as Unified CM. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Smart Software Licensing](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01.html), Smart Software Licensing, License Types. Checked 2026-09-25.
[^49]: On the SME cluster, the 8.6 guide recommends standard Unified CM Groups for each SIP trunk, with destination IP addresses and ports defined for every call processing node in the leaf cluster. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, SME cluster trunk recommendations. Checked 2026-09-25.
[^50]: The on-premises Preferred Architecture threshold (four or more clusters) and the Dedicated Instance eligibility rule (three clusters) are different criteria for different offerings, not conflicting statements about one product (inferred). Source: [Introduction to Dedicated Instance](https://help.webex.com/en-us/article/dk3o5r/Introduction-to-Dedicated-Instance), Cisco Session Manager Edition (SME) section, read against cisco-cvd-collab14-call-control Multi-Cluster Considerations. Checked 2026-09-25.
[^51]: Unified CM SIP trunks support topology-aware RSVP call admission control using SIP Preconditions, and locations-based call admission control that does not know the WAN topology. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, call admission control. Checked 2026-09-25.
[^52]: When several trunks run on all nodes toward the same destination, each trunk needs a unique incoming and destination port number so it can be identified. Source: [Cisco Unified Communications Manager Trunks (Session Management Edition deployment guide 8.6(1))](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/session_mgmt/deploy/8_6_1/trunks.html), Trunks chapter, Run on all Active Unified CM Nodes. Checked 2026-09-25.
[^53]: The SME 8.0 data sheet quoted up to 28 calls per second and 3,840 concurrent calls per server, and 224 calls per second and 30,000 concurrent calls per cluster, on MCS 7845-class servers. Source: [Cisco Unified Communications Manager Session Management Edition Version 8.0 Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-session-management-edition/data_sheet_c78-684404.html), Performance and scalability section. Checked 2026-09-25.
[^54]: The SME 8.0 data sheet licensed SME by session and defined a session as any SIP, H.323 or SCCP call that exits a trunk. Source: [Cisco Unified Communications Manager Session Management Edition Version 8.0 Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-session-management-edition/data_sheet_c78-684404.html), Licensing section. Checked 2026-09-25.
[^55]: The SME 8.0 data sheet names third-party PBXs from Avaya, Nortel, Siemens and Alcatel as leaf systems when they use SIP, H.323 or Q.SIG trunks. Source: [Cisco Unified Communications Manager Session Management Edition Version 8.0 Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-communications-manager-session-management-edition/data_sheet_c78-684404.html), Features and benefits section. Checked 2026-09-25.
[^56]: SME can register to the same Smart Account virtual account as Unified CM or to a separate virtual account. Source: [System Configuration Guide for Cisco Unified Communications Manager, Release 15 and SUs - Smart Software Licensing](https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/15/systemConfig/cucm_b_system-configuration-guide-15/cucm_b_system-configuration-guide-14_chapter_01.html), Smart Software Licensing, License Types. Checked 2026-09-25.