00 · Header

T6 · Migrations

Coexistence and interop

Phased Unified CM to Webex Calling, and multi-tenant calling beside Dedicated Instance. This room is the dial plan that keeps both sides talking while users still live on both. Retrieved 2026-10-14.

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01 · Executive summary

Both sides stay routable

• A phased move splits users across Unified CM and Webex Calling. Each batch needs dial-plan updates on both platforms and on the Local Gateway. [cite:1]
• Put Webex Calling +E.164 patterns in their own partition. The inbound calling search space on the Local Gateway trunk must not include that partition, or the design loops. [cite:2]
• A Local Gateway does not split a shared feature. Call queues and the users who depend on them move in the same batch. [cite:3]
• Dedicated Instance interop trunks are certificate-based and created by Cisco. The base-configuration article says not to modify or delete them. A main number and a PSTN connection are required on the interop location. [cite:4] [cite:5]
• Calls that originate from premises users cannot use cloud PSTN. Cloud PSTN is for Webex Calling users. [cite:6]

02 · Architecture map

Two call controls, one trunk that must not loop

flowchart LR
  UCM[Unified CM] --> LGW[Local Gateway]
  LGW --> WxC[Webex Calling]
  WxC --> DI[Dedicated Instance]

03 · Core concepts

Keep the batch, the partition, and the PSTN in their lanes

What each platform owns during coexistence

04 · Ecosystem & sister technologies

Glossary, map, sisters, edges

Glossary

Phased migration

Users move in groups. Until the last group moves, some users are on Unified CM and some are on Webex Calling. Each group requires dial-plan updates on Unified CM, Webex Calling, and the Local Gateway. [cite:1]

Single-step migration

nw9po3o: the user moves from Jabber to the Webex App at the same time the calling service moves from Unified CM to Webex Calling. [cite:1]

Dual-step migration

Step 1 moves the soft client to the Webex App and leaves calling on Unified CM. Step 2 moves calling. nw9po3o recommends this for larger customers who want those changes separated. [cite:1]

Webex Calling partition

A Unified CM partition that holds +E.164 route patterns for destinations that now live on Webex Calling. The Local Gateway trunk’s inbound calling search space must not contain it. [cite:2]

Fixed extension length

nqojzwt: every extension in a Webex Calling deployment has the same length. Internal extension length in Control Hub can be any value between two and ten. [cite:2]

Abbreviated inter-site dialing

Extension dialing between locations works only when the dialed extension is unique. Overlaps need a steering digit and a site code. [cite:2]

Steering digit

The first digit of the routing prefix for abbreviated enterprise inter-location dialing. nqojzwt says to avoid overlap with the first digit of any location and with location outbound dial digits. [cite:2]

Local Gateway

q0pgpb: one or more Local Gateways are required if the organization keeps hybrid dual call control, so Webex Calling and Unified CM endpoints can call each other and so on-premises PSTN can be used. [cite:3]

Shared feature

A feature whose members must stay together. q0pgpb names call queues. Hunt groups are in the same dependency list in that section. [cite:3]

Calls to On-Premises Extensions

A per-location Control Hub setting. Unknown extensions of calling-number length 2–10 digits route to a PBX on an existing trunk or route group. [cite:6]

Cloud PSTN boundary

n0xb944: Cloud PSTN, Cisco PSTN or Cloud Connected PSTN, provides PSTN access for Webex Calling users. Calls originating from premises users cannot access cloud PSTN. [cite:6]

Route group

One to ten trunks. Trunks at the same priority share calls at random. If the higher-priority trunks are unavailable, the call uses a lower priority. [cite:6]

WXC-DI trunk

2vpf1: one SIP trunk to each Dedicated Instance data center in a region, for basic interop. Default trunks created by Cisco. The article says they should not be modified or deleted. [cite:4]

Interop location

2vpf1: a location is mandatory to activate the interop SIP trunk. A PSTN connection and a main number are required. Without the main number, users cannot make or receive calls through the route group for that location. Premise-based PSTN is allowed when you are not using CCPP. [cite:4]

Certificate interop

ofrt6u: the preconfigured SIP connectivity between Dedicated Instance and multi-tenant is certificate-based and rides the Cisco Webex backbone. Those trunks have to be activated before calls work. [cite:7]

Contiguous numbers

ny65x1bb recommends keeping contiguous phone numbers on the same call control when you split users between multi-tenant and Dedicated Instance. [cite:5]

Mind map

mindmap
  root((Coexistence))
    Partition
    Local Gateway
    Dedicated Instance
    Batches

Sister-technology matrix

Integration map

Cross-platform bridges

Future-integration hooks

• Canon plan: T6-R08 is the acceptance test after a batch. This room stops at the routing that makes that test possible.
• nqojzwt points overlapping extensions at Preferred Architecture for Cisco Collaboration 15 on-premises for the enterprise numbering plan. Read that guide before you invent a site-code length. [cite:2]
• ofrt6u: customers who already built registration-based interop trunks must relink the route list and dial plan to the certificate-based route group. The article’s example says a route pattern that pointed at xWxC_ _RL should point at xWxC_MT_ _RG. [cite:7]
• A fifth PSTN market count, and any claim that premises users can burst onto Cisco Calling Plan, stays out of this room. n0xb944 already draws that line.

Ecosystem troubleshooting

05 · Flow

One range moves

06 · Config

Paths

1. Read nw9po3o and choose single-step or dual-step before you touch a phone. Dual-step keeps calling on Unified CM while the soft client moves. [cite:1]
2. On Unified CM, add the Webex Calling partition and the +E.164 route patterns for ranges that have already moved. Add the partition to the calling search spaces that need it. [cite:2]
3. On the SIP trunk from the Local Gateway, confirm the inbound calling search space cannot see that partition. [cite:2]
4. In Control Hub calling service settings, set internal extension length (2–10), and set routing-prefix length and steering digit only if you need an enterprise numbering plan. [cite:2]
5. For each mixed location, enable Calls to On-Premises Extensions toward the trunk or route group that still reaches the PBX. [cite:6]
6. Build route groups with at least one trunk and at most ten. Same priority load-balances at random. A lower priority is the failure path. [cite:6]
7. If Dedicated Instance is in the estate, leave WXC-DI trunks and route groups in place, set the interop location’s PSTN connection and main number, and activate the certificate trunk. Point custom dial plans at that route group. [cite:4] [cite:7]
8. Move one site or one dependency batch. q0pgpb says test a subset of that group, including any call queue or hunt group that moved with them, before the next batch. The test script is T6-R08. [cite:3]

07 · Limits

Numbers these articles state

08 · Troubleshooting

Failures

09 · Self-question ladder

Twelve rungs

10 · Lab

Paper lab

• Goal: on paper, move one DID range and keep the return path from looping.
• Prereq: no production cluster. Use the ranges printed in nqojzwt as the example, not a customer’s live numbers.
• Step 1. Write the Webex Calling partition and one +E.164 route pattern for +1 221 555 2XXX.
• Step 2. List two calling search spaces that gain that partition, and write “denied” on the Local Gateway trunk inbound CSS. Expected: the loop sentence is satisfied.
• Step 3. Give two sites the same four-digit extension. Expected: inter-site dialing needs a steering digit. Pick a steering digit that no extension range starts with.
• Step 4. Put three agents of one call queue on the batch list. Expected: all three move together.
• Evidence: the partition name, the CSS that is excluded, the steering digit, and the batch.
• Break it: add the Webex Calling partition to the Local Gateway inbound CSS. Recovery: remove it and say which sentence you broke.
• Reflection: which calls are still premises-originated and therefore cannot use cloud PSTN.

No production trunk passwords belong in the notes.

11 · Quiz

Twelve questions

12 · Audio

Slots for Studio

13 · Interview

Oral answers

30 seconds. Phased coexistence means some users are still on Unified CM. [cite:1] I give moved ranges a Webex Calling partition, and I keep that partition out of the Local Gateway trunk’s inbound CSS so the call does not loop. [cite:2]

2 minutes. Extension length is global, from two to ten digits. Inter-site extension dialing needs unique extensions or a steering digit and site code. [cite:2] Shared features such as call queues move with every dependent user. [cite:3] Premises-originated calls stay on premises PSTN. [cite:6] Route groups hold up to ten trunks and fail from equal priority down to a lower priority. [cite:6]

30 seconds, Dedicated Instance. Interop trunks are certificate-based, one per data center, and 2vpf1 says not to edit or delete them. The location needs a PSTN connection and a main number. [cite:4] [cite:7]

2 minutes, batches. I pick single-step or dual-step first. Dual-step moves the Webex App before calling. [cite:1] I migrate a site or a dependency set together, then test that subset before the next group. Directory sync stays on the pilot group. [cite:3]

What you will not say. You will not claim a Microsoft Teams or Amazon Connect parity matrix. You will not put premises users on Cisco Calling Plan.

14 · Citations

Ledger

Retrieved 2026-10-14. Mirrors cites/T6-R07.md.

1. Plan to migrate from Unified CM to Webex Calling — help.webex — article nw9po3o — help.webex.com article nw9po3o — retrieved 2026-10-14. Single-step and dual-step. Users split across platforms during transition. Dial-plan updates on Unified CM, Webex Calling, and Local Gateways for each group.
2. Design to migrate from Unified CM to Webex Calling — help.webex — article nqojzwt — help.webex.com article nqojzwt — retrieved 2026-10-14. Dedicated Webex Calling partition. Inbound CSS on the Local Gateway trunk must not include it. Extension length is global, two to ten. Abbreviated inter-site dialing only when the extension is unique. Steering digit. Example range +1 221 555 2XXX, site code 121, pattern 8121.2XXX. Two DIDs (main and voicemail portal). Best match while the directory number remains on Unified CM. Basic emergency needs a customer-owned +E.164. Singapore is a media point of presence. Calling-party transformation. Three PSTN options and hybrid trunking. The retrieved markdown did not print a header date. re-check
3. Implement the migration from Unified CM to Webex Calling — help.webex — article q0pgpb — help.webex.com article q0pgpb — retrieved 2026-10-14. Local Gateways for hybrid dual call control. Shared services cannot be split across that connection: BLF, hunt or queue, shared line, pickup, park, intercom, executive/admin. Migration Insights grouping. Unknown-extension routing and its maximum length. Reuse a trunk, route group, or dial plan when sufficient. Migrate dependent users together. US and Canada location address for PIDF-LO. Scoped directory sync. Test a subset after each batch. Header date was not in the retrieval. re-check
4. Dedicated Instance for Webex Calling - base configuration — help.webex — article 2vpf1 — help.webex.com article 2vpf1 — retrieved 2026-10-14. WXC-DI location, one SIP trunk per Dedicated Instance data center, route group. Do not modify or delete the default trunks. PSTN connection and main number required.
5. Dedicated Instance – customer deployment models — help.webex — article ny65x1bb — help.webex.com article ny65x1bb — retrieved 2026-10-14. Contiguous numbers on one call control. Calling features are not fully harmonized. Keep pickup, hunt group, and manager/secretary users on one platform.
6. Configure trunks, route groups, and dial plans for Webex Calling — help.webex — article n0xb944 — help.webex.com article n0xb944 — retrieved 2026-10-14. Route group of 1 to 10 trunks. Same priority is random. Calls to On-Premises Extensions, 2–10 digits, per location. Premises-originated calls cannot access cloud PSTN.
7. Activate inter-op SIP trunk to Webex Calling multi-tenant — help.webex — article ofrt6u — help.webex.com article ofrt6u — retrieved 2026-10-14. Certificate-based interop over the Webex backbone. Activate the trunks. Point dial plans at the certificate route group. Example xWxC_ _RL to xWxC_MT_ _RG.

15 · Re-engineer later

Open

• Open questions: the live Control Hub label for the interop location’s main-number field, beyond the column names in 2vpf1.
• Facts still TODO-verify: 1. Peer PBX parity for extension length and group features. These articles do not publish that matrix.
• Assets missing: a redacted dial-plan sketch, audio, screenshots of the partition and the trunk CSS.
• Ideas for v1.0: a worked NYC/RTP numbering table copied only from the numbers nqojzwt already prints.
• Next review: re-check nw9po3o, nqojzwt, q0pgpb, 2vpf1, ny65x1bb, n0xb944, and ofrt6u on the next pass. Header dates were not printed in the extracts used on 2026-10-14, so this room does not invent them.