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CASE STUDY 3 OF 4 · STX CLOUD COMMUNICATIONS TRANSFORMATION

Trading floor voice, moved to the cloud

Transforming STX from legacy PSTN infrastructure into a secure cloud communications platform.

CLIENT LONDON STOCK EXCHANGE GROUPROLE HEAD OF DESIGN AT MVINEPLATFORMS BROWSER, ANDROIDSTATUS DELIVERED TO PRODUCTION

PROJECT OUTCOMES

DEPLOYEDDeployed across the STX network, numbering preserved throughout migration
TESTEDPassed penetration and ethical security testing in a regulated environment

Strategic Context

STX is LSEG's core voice network, connecting trading firms across the UK and Ireland. It ran over fixed-line PSTN infrastructure terminating into trading turrets and PBX systems.

With BT retiring PSTN, LSEG initiated a full migration to cloud delivery. That meant moving a regulated, latency-sensitive, compliance-recorded network onto the internet, in phases, while trading continued. STX numbering had to be preserved, legacy Featurenet had to keep working throughout, and the new system had to deliver fixed-line equivalent security over internet channels.

The harder design problem sat above all of that. A browser client had to feel as trustworthy as a handset bolted to a desk. Connection state, encryption status, recording visibility and session continuity all had to be readable at a glance, by someone who picked up a call mid-trade and was not going to read a release note first.

BT Featurenet Legacy voice network DPNSS to SIP Protocol bridge Trading turrets Fixed-line endpoints Legacy, retired in stages STX cloud infrastructure Session handling, routing, recording Numbering continuity Existing STX numbers preserved Cloud platform, built new Browser client Android client Optional SIP into trading systems Admin and recording Front end, designed Customer-side integration
Legacy network retired in stages, onto new cloud infrastructure, with the designed front ends. Scroll sideways to see it all.

My Role

I led UI/UX across the browser and Android applications, focusing on secure interaction modelling and behavioural consistency.

Responsibilities included:

  • Defining cross-platform interaction patterns
  • Designing call state transitions and trust signalling
  • Structuring directory search and number resolution flows
  • Designing administrative and recording tooling
  • Aligning interaction decisions with telecom infrastructure constraints
  • Accounting for accessibility within a high-security environment

LSEG gave us basic brand guidelines and no UI direction, so the interface decisions were mine. A fast, cost-effective build was part of the brief.

Identity provisioning and onboarding were managed by LSEG. My focus was the live communication and oversight layer.

Call State & Trust Signalling

Call state precision was central to regulatory confidence.

I defined explicit differentiation between incoming, connecting, active, on-hold, recording and disconnected states. Recording status remained persistently visible during live sessions. Secure session indicators were embedded directly within the call interface so users could confirm encryption and network identity at all times.

Browser client: a recent calls list on the left and an active call on the right showing the contact, call timer, Recording in progress and Connected status, with mic and hang up buttons.
Browser call view: recording and connection state always visible.

Cross-platform Behaviour

Browser and Android imposed different layout constraints. Interaction logic remained consistent.

I standardised:

  • Call initiation sequence
  • State hierarchy
  • Control positioning logic
  • Directory structure and search prioritisation

Someone moving between the browser client and their phone found calls, states and controls in the same places.

Three Android screens: recent calls with an expanded call history, an active call with recording and connection status, and a company information page.
Android: recent calls, live call and company info, same model as the browser client.

Administrative & Recording Control

Compliance required structured oversight.

I designed administrative interfaces supporting extension visibility, session history and recording access workflows. Recording tooling was structurally separated from live communication controls to reinforce compliance boundaries.

Company administration page for a sample company, showing trunk setup, main office details and a table of users with edit, email and delete actions.
Company administration: trunk setup, office details and users.

Constraints & Trade-offs

  • Interoperability with legacy Featurenet during phased migration
  • Telecom infrastructure and SIP limitations
  • Strict penetration testing and security standards
  • Browser compatibility without plugins
  • A fast, cost-effective build
  • Regulated financial environment

Features were rolled out in phases to match the infrastructure migration.

Impact

OPERATIONAL
  • Enabled migration from PSTN to cloud-based communications
  • Maintained interoperability during transition
  • Preserved STX numbering continuity
SECURITY
  • Delivered encrypted sessions with fixed-line equivalent security
  • Passed penetration and ethical security testing
COMMERCIAL
  • Mvine programme, £1M multi-year. I led the UI and UX.
  • Deployed across the STX network