Public network architecture

End-to-end network architecture

Control messages coordinate access and sessions. Subscriber traffic and voice media follow packet paths outside the control plane. Dashed connections indicate planned or in-progress work.

Control and signalling User data and media Protected transport Planned or in progress

Current connected LTE sites use Lodestar's London control and user-plane functions. UK interconnection is in progress and a West Midlands user plane is planned.

Read the master diagram as text

Current LTE radio access travels through protected backhaul. S1-MME carries signalling to the MME, while S1-U carries subscriber data to the gateway user plane. The London 4G EPC reaches Internet and IMS service networks over SGi. Within IMS, SIP signalling, RTP voice media and RTCP reporting are distinct application flows. Lodestar Voice consumer access is coming soon and will use a customer-provided Internet connection. A generic UK interconnection is being arranged. In the intended regional model, West Midlands S1-U would terminate at a regional SGW-U. London SGW-C and PGW-C would control the regional SGW-U and PGW-U over Sxa and Sxb using PFCP, while regional PGW-U would provide the SGi service paths.

Architecture status at the September 2026 review
Architecture area	Reviewed status	What the status establishes	What remains
LTE radio attachment	Current	Three LTE nodes had S1 connectivity and corresponding installed protected transport associations in the 14 September evidence review	Connection does not prove continuous coverage, customer capacity or successful service on every handset
London 4G EPC	Current and configured	MME, subscriber and policy functions, separated gateway control and user-plane functions, and the shown EPC reference points are present in the reviewed architecture	Current state does not guarantee every dependency or session is healthy continuously
IMS platform	Current and configured	Registration, serving control, policy, charging, messaging application and anchored media roles are present in the reviewed architecture	This does not establish completed external carrier acceptance or external SMS handoff
Lodestar Voice access	Active build	The fixed over-the-top SIP access path and its relationship to IMS are defined	Consumer access is not yet available to order
Proposed UK interconnection	In progress	The intended SIP and media handoff is represented as a service edge	No completed or activated external carrier route is claimed
West Midlands user plane	Planned	The CUPS design keeps London control while placing SGW-U and PGW-U forwarding closer to West Midlands RAN	Regional hosting, transport, selection, routing and service acceptance remain to be completed
Nuneaton and Bedworth rollout	Exploratory	The area is being considered within the regional architecture	No town-wide coverage or committed launch date is claimed
Direct mobile-core emergency carriage	In development	The separate service requirement is recognised in the architecture status	Current reported tests concern handset limited-service selection onto another network, not carriage through Lodestar's core

Radio access and protected backhaul

The radio access network does not send every packet to the same core function. S1-MME carries access and mobility signalling to the MME. S1-U carries the subscriber bearer directly to the serving gateway user plane.

The logical path separates S1-MME signalling from S1-U subscriber traffic across protected transport.

Read the radio and backhaul diagram as text

Current LTE eNodeBs connect through a protected backhaul boundary. S1-MME uses S1AP signalling between the radio and MME. S1-U carries GTP-U subscriber traffic between the radio and SGW-U. The MME controls sessions and mobility, but it is not in the user-data path.

S1-MME signalling

The handset first establishes radio control with the eNodeB over LTE-Uu. Non-Access Stratum mobility and session messages are then carried inside S1AP procedures over SCTP on S1-MME toward the MME. This control path coordinates attachment, authentication, security state, mobility and EPS bearer creation. Subscriber Internet or media packets are not forwarded through the MME.

S1-U bearer transport

Once an EPS bearer has been established, subscriber packets leave the radio on S1-U using GTP-U over IP and terminate at SGW-U. The bearer continues through the EPC user plane to PGW-U over S5-U, then leaves over SGi for the selected service network. Tunnel endpoint identifiers bind each hop to the correct bearer context, but live identifiers and addresses are not published.

Protected site transport

The reviewed eNodeB transport terminates at a core-side security gateway using IKEv2 and IPsec. S1AP over SCTP and GTP-U remain separate logical flows through that protected transport, then terminate at MME and SGW-U respectively. Peer addresses, traffic selectors, negotiated cryptography, ports and management routes remain within restricted operations documentation.

Managed LTE TDD profile

A managed radio profile reviewed for this architecture uses LTE Band 40 in TDD mode with a configured 20 MHz carrier. This records an aggregate configuration, not an RF measurement, coverage result, capacity claim or site-specific licensing assessment.

Public radio and backhaul profile
Layer	Reviewed architecture	Traffic relationship	Operational meaning
Radio access	LTE E-UTRAN with eNodeB functions serving compatible user equipment	LTE-Uu carries both radio control and user-plane radio bearers	A connected radio node provides service only within its usable local radio footprint
Managed spectrum profile	LTE Band 40, time-division duplex, configured for a 20 MHz carrier	Uplink and downlink use scheduled time resources within the same paired-free carrier	The profile records configuration, not measured coverage, capacity or an individual licence schedule
Access signalling	S1-MME between eNodeB and MME	S1AP over SCTP carries access, mobility and EPS session procedures	The eNodeB initiates the logical S1 association; signalling is bidirectional after establishment
Subscriber bearer	S1-U between eNodeB and SGW-U	GTP-U carries encapsulated subscriber IP packets independently of the MME path	Loss of S1-U can stop packet forwarding even while control signalling remains observable
Backhaul boundary	Connected sites reach the London core through IKEv2/IPsec protected transport	Control and user-plane interfaces remain logically distinct across the transport	IPsec terminates at the core-side security gateway before EPC service processing
Connectivity evidence	Three LTE nodes had S1 connectivity and corresponding installed protected associations in the 14 September 2026 review	Connection state demonstrates core attachment, not an RF survey	It does not establish continuous town-wide coverage, handset compatibility or customer capacity

Network zones and traffic separation

LTE radio, protected transport, EPC control, subscriber forwarding, IMS and operations are separate network roles. Signalling, packet data and voice media terminate at different functions rather than following one common path.

Functional network zones
Zone	Traffic or responsibility	Connected functions	Separation
LTE radio access	LTE-Uu radio access, S1AP signalling and GTP-U subscriber traffic	UEs, eNodeB functions and protected RAN transport	Radio access terminates before EPC control and user-plane roles.
Protected RAN transport	Separate S1-MME and S1-U paths from connected radio sites	MME for signalling and SGW-U for subscriber packets	The user bearer does not pass through the MME.
EPC control and subscriber services	Mobility, authentication, policy and gateway control	MME, HSS, PCRF, SGW-C and PGW-C	Control functions make session and policy decisions without forwarding subscriber payloads.
EPC user plane	GTP-U bearer forwarding and SGi service access	SGW-U and PGW-U	Packet forwarding remains separate from MME, HSS and PCRF processing.
IMS service network	SIP registration and service control, Diameter policy and charging, RTP voice media and RTCP reporting	CSCF roles, HSS, PCRF, service applications and media relay	SIP signalling, RTP media and RTCP control remain distinct application flows.
Network operations	Configuration, provisioning, telemetry and service persistence	Restricted management and observability functions	Operations are outside subscriber service paths. The public dashboard receives selected health information only.

Protocol layers across the service path
Path	Protocol relationship	Information carried	Where it terminates
LTE-Uu control	RRC over the LTE radio protocol stack; NAS messages are transported between the device and MME	Radio connection control, mobility, authentication and EPS session requests	RRC terminates at the eNodeB; NAS terminates at the MME
LTE-Uu user plane	Subscriber IP packets carried through the LTE PDCP, RLC, MAC and physical layers	Internet, IMS signalling, messaging and voice media packets assigned to an EPS radio bearer	Radio bearer terminates at the device and eNodeB
S1-MME	S1AP over SCTP and IP	Access, mobility and bearer-control procedures, including transported NAS messages	eNodeB and MME
S1-U	GTP-U over UDP and IP	Encapsulated subscriber packets, separated from the S1-MME signalling path	eNodeB and SGW-U
S11 and S5-C	GTPv2-C over UDP and IP	Gateway session control, bearer identifiers, tunnel information and bearer parameters	MME, SGW-C and PGW-C as shown in the EPC diagram
Sxa and Sxb	PFCP over UDP and IP	Rules that create, modify and remove user-plane forwarding state	Gateway control and corresponding user-plane roles
S5-U	GTP-U over UDP and IP	Subscriber bearer packets between the serving and packet gateway user planes	SGW-U and PGW-U
SGi	IP service access	Subscriber traffic after the EPC tunnelled path, directed to the selected Internet or IMS service network	PGW-U and the relevant service network
S6a, Cx, Gx, Rx and Ro	Diameter applications; live transport and endpoint values are not published	Subscriber, authentication, IMS selection, policy and charging information according to the reference point	HSS, PCRF and charging roles shown in the function registers
SIP and SDP	SIP session signalling with SDP bodies where media is negotiated	IMS registration, session establishment, service routing, messaging and session release	Endpoints, CSCF roles and invoked service applications
RTP and RTCP	Separate real-time media and media-control flows over IP	Encoded voice packets and the associated reception, timing and participant reports	Media endpoints and the anchored media relay

Trust boundaries

Protected RAN transport terminates before traffic enters the core service fabric. Core control, user-plane forwarding, IMS and management each have a separate function and traffic scope. The public status path carries selected health information and has no management role. “Protected” describes the controlled transport boundary; it is not a third-party security certification.

Security boundary

The engineering model ends at logical functions and standard interfaces. Addressing, internal hostnames, routes, firewall policy, transport parameters, credentials, subscriber identifiers, radio identifiers, exact sites and software versions remain in restricted operations documentation.

4G EPC control and user-plane separation

Lodestar's deployed mobile core is a 4G EPC. Its gateway control and user-plane functions are separated, which also provides the technical basis for the planned regional data-plane design.

HSS and PCRF are separate logical roles. S6a and Cx reach HSS, while Gx and Rx reach PCRF. The deployed mobile core is a 4G EPC, not a 5G standalone core.

Read the 4G core diagram as text

S1-MME connects the RAN to MME. MME connects to HSS using S6a and to SGW-C using S11. SGW-C connects to PGW-C using S5-C. SGW-C controls SGW-U through Sxa and PFCP, while PGW-C controls PGW-U through Sxb and PFCP. The user bearer travels from the RAN to SGW-U using S1-U, then to PGW-U using S5-U. PGW-U sends service traffic toward Internet and IMS networks over SGi. PGW control reaches PCRF over Gx. IMS access policy reaches PCRF over Rx.

EPC function register
Function	Interfaces	Plane	Responsibility
MME	S1-MME, S11 and S6a	Control	Terminates LTE access signalling, manages mobility and coordinates EPS session control.
HSS	S6a and Cx	Subscriber control	Provides subscriber and authentication information to the EPC and IMS serving-function lookup to IMS.
PCRF	Gx and Rx	Policy control	Supplies policy decisions for packet-data bearers and IMS session requirements.
SGW-C	S11, S5-C and Sxa	Gateway control	Maintains serving-gateway control state and programs the SGW-U forwarding role through PFCP.
SGW-U	S1-U, S5-U and Sxa	User plane	Forwards the subscriber bearer between the LTE radio access network and PGW-U.
PGW-C	S5-C, Gx and Sxb	Gateway control	Coordinates packet-data network sessions, policy control and PGW-U forwarding state.
PGW-U	S5-U, Sxb and SGi	User plane	Forwards subscriber packets to the selected Internet or IMS service network.

LTE attachment and default bearer establishment

The handset establishes radio control with the eNodeB, then sends mobility and packet-data requests as NAS messages carried by S1AP over S1-MME. The MME uses S6a toward HSS for the subscriber and authentication information needed by the attachment procedure. It coordinates security and session state, but it never becomes part of the subscriber packet path.

The MME requests serving-gateway session control over S11. SGW-C continues packet-gateway control over S5-C to PGW-C. The packet-gateway control role selects the requested packet-data service and can obtain policy decisions from PCRF over Gx. The request and response procedures also carry bearer identifiers, tunnel endpoint information and QoS parameters between the control functions.

SGW-C and PGW-C install the corresponding forwarding state in SGW-U and PGW-U over Sxa and Sxb using PFCP. The eNodeB receives the radio and S1-U bearer information needed to complete the path. These control exchanges create the route for packets, but do not carry the packets themselves.

Bearer forwarding in both directions

For uplink traffic, the eNodeB encapsulates subscriber packets in GTP-U on S1-U. SGW-U forwards the bearer to PGW-U over S5-U, and PGW-U sends the resulting IP traffic to the selected Internet or IMS service network over SGi. Downlink traffic follows the reverse forwarding state back through PGW-U, SGW-U and the serving eNodeB. MME, HSS, PCRF, SGW-C and PGW-C can change or release that state, but they do not forward the payload.

An EPS bearer identity distinguishes bearer state for a device. GTP-U tunnel endpoint identifiers distinguish the forwarding context on each tunnelled hop. Traffic Flow Templates can associate packet flows with particular bearers. The public page describes those relationships without exposing live identities, addresses, tunnel values or subscriber records.

Policy, QoS and IMS traffic

The default bearer provides packet-data connectivity for its service. Where an application requires separate treatment, the EPC can establish or modify a dedicated bearer under policy control. P-CSCF can describe an authorised IMS session to PCRF over Rx, while PCRF supplies packet-data policy toward the packet-gateway control role over Gx. The resulting rules can be enforced in the user plane through the gateway control functions.

This page does not claim a specific live QCI, ARP, bandwidth, Traffic Flow Template or admission-control policy. Those values depend on service configuration and bearer state. SIP signalling, RTP voice packets and RTCP reporting remain distinct application flows even when they are carried inside EPS user-plane bearers.

Logical LTE attachment and default-bearer procedure
Procedure	Control exchange	State established or consulted	Subscriber payload
Radio connection	The device establishes RRC signalling with the serving eNodeB over LTE-Uu	Radio signalling context between the device and eNodeB	Not yet forwarded through the EPC bearer path
Attach and packet-data request	NAS mobility and session requests are carried by S1AP over S1-MME to the MME	Initial device, access and requested packet-data context at the MME	NAS remains control signalling, not subscriber IP traffic
Subscriber authentication	MME consults HSS over S6a and coordinates the LTE security procedure	Authenticated mobility context and permitted subscriber service information	No payload is sent through HSS
Serving-gateway control	MME asks SGW-C to create session state over S11	Serving-gateway control context and bearer identifiers	No payload is sent through SGW-C
Packet-gateway and policy control	SGW-C reaches PGW-C over S5-C; PGW-C can consult PCRF over Gx for packet-data policy	Packet-data network session, policy decisions and parameters for forwarding	No payload is sent through PGW-C or PCRF
User-plane programming	SGW-C and PGW-C install forwarding rules in SGW-U and PGW-U using PFCP on Sxa and Sxb	Per-session forwarding state and the tunnel relationships for each user-plane hop	The rules prepare the path; PFCP does not carry the subscriber packets
Access-bearer completion	MME and eNodeB complete the S1 and radio bearer control procedure	Radio bearer and S1-U tunnel context associated with the EPS bearer	Packet forwarding can begin after the required state is in place
Uplink forwarding	No MME hop is used for payload forwarding	Established TEIDs and bearer rules select the path	Device to eNodeB, then S1-U to SGW-U, S5-U to PGW-U and SGi to the service network
Downlink forwarding	Control functions can later modify or release the bearer, but remain outside its packet path	Reverse tunnel and bearer state identify the serving eNodeB and device bearer	Service network to PGW-U, S5-U to SGW-U, S1-U to eNodeB and LTE radio to the device

Packet-data service roles
Service role	Bearer destination	Policy relationship	Traffic carried
Internet packet data	Internet service network through PGW-U and SGi	Gx between packet-gateway control and PCRF	General IP traffic for the subscriber data service.
IMS voice and messaging	IMS service network through PGW-U and SGi	Gx for bearer policy and Rx between P-CSCF and PCRF	SIP registration and service signalling, RTP voice media and associated RTCP control.

IMS registration, signalling and media

IMS uses SIP for registration and session control, Diameter for subscriber, policy and charging relationships, RTP for voice media and RTCP for associated control reporting. Lodestar Voice fixed access remains in development; its signalling and media routes are planned.

During registration, I-CSCF supports selection of S-CSCF. Originating service signalling follows P-CSCF to S-CSCF. Voice service logic has a separate logical media-control relationship to the relay; RTP voice media and RTCP use the anchored media path.

Read the IMS diagram as text

Mobile IMS signalling first reaches P-CSCF. Registration continues to I-CSCF and S-CSCF, with Cx queries terminating at HSS. Originating service SIP goes from P-CSCF to S-CSCF. P-CSCF uses Rx toward PCRF. S-CSCF can invoke messaging, voice application and online charging functions. Voice service logic can request media anchoring through a separate logical control relationship. The fixed access route is planned for Lodestar Voice, which is not yet available to order. RTP voice media and RTCP are anchored separately from SIP signalling and media control.

IMS function register
Function	Interfaces	Responsibility
P-CSCF	SIP and Rx	First IMS signalling contact for the access device and the application-function side of IMS policy control.
I-CSCF	SIP and Cx	Home-network IMS entry and serving-function selection during initial registration.
S-CSCF	SIP, Cx, ISC and Ro	Maintains serving registration state, routes sessions and invokes service and charging functions.
HSS	Cx	Provides IMS subscriber and serving-function information.
PCRF	Rx	Receives IMS session information from P-CSCF for policy decisions; Gx links that policy role to the packet gateway.
Messaging application	ISC and SIP MESSAGE	Handles the IMS messaging service reached from S-CSCF.
Voice application	ISC, SIP and logical media control	Applies voice session and service logic invoked by S-CSCF and requests media anchoring without carrying the media itself.
Online charging	Ro and Diameter credit control	Receives online credit-control requests from the serving IMS function.
Media relay	Logical media control, RTP and RTCP	Receives media-control requests and anchors RTP voice media and its associated RTCP separately from SIP call control.

Registration

After the device has IP connectivity to the IMS service network and has obtained a P-CSCF contact, it sends an initial SIP REGISTER to P-CSCF. P-CSCF forwards the registration toward the home-network I-CSCF. I-CSCF queries HSS over Cx to find an assigned S-CSCF or the capabilities needed to select one, then routes the REGISTER to that serving function.

S-CSCF uses Cx to obtain the IMS subscriber information needed for the service relationship. A normal registration can return an authentication challenge through the same SIP path. The device then sends an authenticated REGISTER and receives a successful response when the checks complete. Registration is refreshed before it expires; failure or expiry removes the serving state. This is the logical procedure rather than a publication of live identities, realms, timers or authentication material.

Originating session signalling

After registration, an originating SIP INVITE travels from the device to P-CSCF and then to its serving S-CSCF. The INVITE and its Session Description Protocol body describe the requested session and proposed media capabilities. I-CSCF is involved in registration and serving-function selection, but it is not inserted into every originating request path.

S-CSCF applies the subscriber's service routing and can invoke voice or messaging applications over ISC before selecting the next SIP destination. Calls that require the proposed UK interconnection will not use that route until the arrangement has been completed and accepted. Provisional and final SIP responses return along the signalling path, followed by ACK when the session is established.

Policy and charging

P-CSCF supplies authorised IMS session information to PCRF over Rx. PCRF relates the service requirements to packet-data policy through Gx, allowing the EPC to establish or modify bearer treatment where configured. S-CSCF can use Ro toward the online charging role. Diameter carries these subscriber, policy and charging exchanges; it does not carry SIP messages or voice media.

Session media and release

SIP carries registration, routing, call setup, application invocation and session teardown. Once session negotiation succeeds, voice packets use the separate RTP path through the media relay. RTCP carries associated reception, timing and participant reports. RTCP describes conditions observed by the media endpoints but does not itself provide radio admission control or packet-data quality of service.

A SIP BYE and its response end the application session. Any dedicated bearer or policy state created for the session can then be removed or changed by the EPC, while a default packet-data bearer may remain available for other traffic. The public diagram deliberately omits live codecs, media addresses, port ranges, policy values and interconnection routing.

IMS messaging

For supported IMS messaging, S-CSCF invokes the messaging service over ISC. SIP MESSAGE carries the application message separately from RTP and RTCP voice media. The current application role does not establish a completed external SMS handoff. Subscriber identities, message routing data, storage details and delivery records remain within the restricted service environment and are not part of this public architecture.

IMS registration, originating session and media procedure
Exchange	Logical route	Purpose	Relationship to the packet bearer
IMS connectivity	Device through LTE radio, S1-U, S5-U and PGW-U to the IMS service network over SGi	Provides IP reachability to the IMS signalling contact	This is EPS user-plane traffic even though the application payload is SIP signalling
Initial registration	Device to P-CSCF, then toward I-CSCF using SIP REGISTER	Begins home-network registration and serving-function discovery	SIP packets are carried inside the established packet-data bearer
Serving-function lookup	I-CSCF to HSS over Cx	Finds the assigned S-CSCF or the capabilities required to select one	Diameter control exchange outside the RTP media path
Authentication and registration state	Challenge and authenticated REGISTER traverse P-CSCF and the selected S-CSCF; S-CSCF uses Cx toward HSS	Authenticates the registration and establishes serving state and subscriber service information	No voice media is created by the registration exchange
Originating request	Device to P-CSCF and serving S-CSCF using SIP INVITE with SDP	Requests a session and proposes the media capabilities and endpoints	Application signalling continues inside the packet-data bearer
Service invocation	S-CSCF to the applicable voice or messaging service over ISC	Applies subscriber service routing and application logic	SIP service control remains separate from RTP and RTCP
Policy relationship	P-CSCF to PCRF over Rx, related to EPC policy control over Gx	Relates authorised IMS session requirements to packet-data policy where configured	May result in bearer creation or modification; it does not carry the media itself
External call route	SIP toward the proposed UK interconnection	Would provide an external signalling handoff after the arrangement is completed and accepted	Marked in progress; no live interconnection is claimed
Voice media	RTP between media endpoints through the anchored media relay, with associated RTCP flows	Carries encoded audio and media-session reporting after negotiation	Separate application flows carried in the EPC user plane, not through CSCF or MME functions
Session release	SIP BYE and response traverse the serving signalling path	Ends the application session and allows related policy or dedicated-bearer state to be removed	The default packet-data bearer can remain available for other IP traffic

Mobile and fixed voice paths

Mobile users reach the current IMS platform through LTE and the mobile core. Lodestar Voice is a separate, coming-soon over-the-top SIP service that will use an Internet connection arranged by the customer.

SIP carries application signalling, RTP carries voice media and RTCP reports on the media session. On mobile access, all three are carried inside EPS user-plane bearers rather than S1-MME. UK interconnection remains in progress.

Read the service path diagram as text

A mobile user reaches IMS through LTE radio access and Lodestar's EPC. SIP, RTP and RTCP are distinct application flows, but all are carried inside EPS user-plane bearers over S1-U, S5-U and SGi; none uses S1-MME. The coming-soon Lodestar Voice path would bring fixed SIP, RTP and RTCP through the customer's own Internet connection. UK interconnection remains in progress, so its signalling and media paths are planned rather than current.

Voice access comparison
Property	Lodestar Mobile IMS	Lodestar Voice fixed access
Access network	Lodestar LTE radio access and 4G EPC	Customer-provided Internet connection
Core entry	Packet-data bearer reaches the IMS service network through PGW-U and SGi	Fixed SIP access edge is in development
Session signalling	SIP registration and call control through the IMS serving functions	SIP registration and call control are planned through the fixed access edge
Media and media control	RTP carries voice media and RTCP reports on that media session, separately from SIP signalling	RTP and RTCP will use the customer's Internet connection and a planned media path
Current state	Mobile IMS platform current, with handset compatibility limited to supported devices	Consumer access in development and not available to order
External dependency	Radio access, protected backhaul, EPC and IMS must all be available	Customer broadband, router and electricity must be available as well as Lodestar's service

Lodestar Voice fixed access

Lodestar Voice is a standalone over-the-top SIP service. A fixed endpoint will reach Lodestar's IMS service through an Internet connection supplied and managed by the customer. This is a different access path from Lodestar Mobile, even where both services use common IMS functions.

Lodestar does not supply or control the customer's broadband connection, router or electricity. The service does not include backup power, backup Internet or a separate emergency-calling route. If the customer connection, local equipment, electricity or Lodestar service is unavailable, calling may stop.

Voice power and emergency limitations

London and West Midlands data-plane architecture

Current connected sites use the London EPC. In the intended regional model, Southern RAN continues through the London user plane while the West Midlands RAN can attach to a closer, future regional user plane.

Solid connections are the current London service path. Dashed connections are the planned West Midlands model.

Read the regional diagram as text

Current connected radio sites use the London EPC and London user plane. S1-MME reaches the London MME, S1-U reaches the London SGW-U, London gateway control reaches the user plane over Sxa and Sxb using PFCP, and PGW-U reaches Internet or IMS service networks over SGi. The intended model keeps Southern RAN on that path. For West Midlands RAN, S1-MME would remain in London while a planned S1-U path reaches regional SGW-U and PGW-U roles. Those roles would remain under London gateway control, break Internet traffic out regionally, and reach London IMS through a protected service path.

Current and planned regional paths
Function or path	Current London architecture	Planned West Midlands architecture
MME and subscriber functions	Provided from London	Remain shared from London
Gateway control	SGW-C and PGW-C in the London control plane	Remain shared from London
Gateway user plane	SGW-U and PGW-U in London	Regional SGW-U and PGW-U functions planned
RAN control	S1-MME reaches the London MME	S1-MME continues to the London MME
Subscriber bearer	S1-U reaches the London SGW-U	S1-U is intended to reach the regional SGW-U
User-plane programming	London gateway control programs the London user plane over Sxa and Sxb using PFCP	London gateway control is intended to program the regional user plane over protected transport
Internet service path	PGW-U uses the London SGi path	A regional SGi path and IP breakout are planned
IMS service path	PGW-U reaches the London IMS service network	Regional PGW-U is intended to use a protected service path to the London IMS network

Regional forwarding under shared control

The intended regional design keeps S1-MME attached to the London MME, so mobility, authentication and EPS session control remain with the existing subscriber functions. London SGW-C and PGW-C also remain authoritative for gateway sessions. They would establish and update PFCP sessions over protected transport to regional SGW-U and PGW-U functions.

West Midlands S1-U would terminate on the regional SGW-U. S5-U would carry the bearer onward to the regional PGW-U, which could provide a shorter SGi path for Internet traffic. IMS traffic would still reach the London IMS service network through a protected service path. The regional site would therefore shorten packet forwarding without becoming an independent subscriber, policy or IMS core.

The shared control relationship also defines the failure boundary. Loss of the regional user plane or its transport would affect bearers using that plane. Loss of London control or subscriber functions could affect new attachment, session changes and recovery even when regional forwarding equipment remains reachable. The design does not claim independent regional core resilience.

Nuneaton and Bedworth development

A wider Nuneaton and Bedworth deployment remains exploratory. It will not be described as live until site selection, power, backhaul, spectrum licensing, radio commissioning, regional user-plane commissioning, routing, monitoring and service acceptance have been completed for the relevant locations.

The regional design is intended to reduce the distance travelled by subscriber traffic without duplicating every core function. Mobility, subscriber, policy, gateway control and IMS roles remain shared from London, while the latency-sensitive packet-forwarding roles can be placed closer to the radio access network.

Operations and network monitoring

Management access, radio lifecycle, service monitoring and persistence remain behind restricted operational boundaries. Only intentionally selected service-health information is exposed to the public dashboard.

Restricted management reaches radio lifecycle, core, IMS and separated persistence functions. Metrics and probes feed alert evaluation before deliberately selected information reaches the public status service.

Read the operations diagram as text

Enrolled operators reach a restricted management edge. Separate internal paths support radio ACS and lifecycle work, core and IMS service operations, and subscriber, mobility, policy, IMS and charging persistence. Metrics and probes feed alert evaluation. Only selected status information is then published to the public dashboard.

Radio provisioning and lifecycle

The radio-management path separates operator entry from device-facing management functions. The logical ACS role handles managed-device sessions, configuration retrieval and application, inventory and operational state. Firmware distribution and maintenance workflow sit alongside that role so a software image or configuration change can be controlled without exposing a management endpoint through the public site.

Radio telemetry can show reachability, reported configuration and component state. It does not by itself prove that a handset can attach, that RF coverage is usable or that subscriber packets are crossing the complete service path. Those conditions require service-path and radio observations as well as management reachability.

Core, IMS and service-path observability

EPC and IMS functions expose selected internal health observations to restricted exporters and probes. Metrics collection records component state, resource and protocol observations suitable for operations. Alert evaluation applies operational conditions to those observations and presents them to internal dashboards or responders.

The public dashboard is downstream of that internal process. It receives only deliberately selected service state and incident information. It does not receive subscriber records, raw radio-management data, configuration, credentials or an administrative route back into the network.

Persistence boundaries

Persistent state is separated by responsibility: HSS-related subscriber and authentication information, MME mobility and EPS session context, radio-management and device state, packet-data policy, IMS registration and service state, and charging information. The diagram groups these as persistence because it is a public functional view, but it does not imply one shared database or one common security boundary.

Backup, replication, recovery procedures, database technology, storage locations and administrative access remain restricted operational information. A successful health probe also does not prove that persistence is current, recoverable or consistent across every dependent service.

Operations responsibility
Operational role	Information handled	Relationship to public access
Operator entry	Enrolled administrative access and the authorisation state needed to reach management services	Restricted management boundary; it is separate from public and subscriber service access
Radio provisioning	Managed radio inventory, configuration retrieval and application, lifecycle workflow and maintenance state	Restricted operations only; radio-management functions are not exposed through the public website or dashboard
Radio telemetry	Reachability, reported operational state and selected radio or transport health observations	Used for operations and alerting; a healthy management session does not by itself prove usable RF service
EPC operations	Service state and dependencies for MME, subscriber roles, gateway control and gateway user-plane functions	Restricted operations only; packet-data service interfaces are not management interfaces
IMS operations	Registration, signalling, application and media-relay service health without publishing subscriber transactions	Restricted operations only; selected aggregate service state may feed observability
Subscriber persistence	Authentication and subscription information required by HSS and the related EPC or IMS functions	Remains within the subscriber-control role and is not published through status systems
Policy and charging persistence	Policy, service and charging state needed by PCRF, gateway control and IMS applications	Separated from the public status path and from user-plane packet forwarding
Metrics and health probes	Selected counters, reachability checks, component state and service-path observations	Collected inside the operations boundary; raw management data is not a public feed
Alert evaluation	Operational conditions derived from metrics and health events	Used by operators and can inform a deliberately limited service-status publication
Public dashboard	Selected service availability and incident information	Public information surface only; it cannot configure, provision or administer the network

Service effects of major failure domains
Unavailable component or path	Likely service effect	Important qualification
Radio site or site backhaul	Devices served only by that access path lose Lodestar radio service	A connected site does not by itself establish continuous coverage across a wider area
MME or S1-MME path	New attachment, mobility and EPS session signalling are affected	Behaviour of an already established bearer depends on retained state, timers and the specific fault
SGW-U, PGW-U or their bearer path	Subscriber packet forwarding through the affected user plane stops	Control signalling may still be visible even when subscriber data is not passing
HSS or PCRF relationship	New authentication, subscriber lookup or policy decisions are impaired	Existing sessions can behave differently according to cached state, policy and expiry timers
IMS service functions	IMS registration, calls or messages using the affected function are impaired	General Internet packet data follows a separate service path and is not automatically an IMS failure
Customer Internet, router or power for Lodestar Voice	The fixed SIP endpoint may be unable to register or place calls	Lodestar does not provide backup power, backup Internet or a separate emergency-calling path
Public dashboard	The public status view may be delayed or unavailable	A dashboard failure does not by itself prove that subscriber service has failed

Open the public network status dashboard

Emergency calling status

Lodestar's mobile core does not currently carry emergency calls. That capability is being developed.

In our tests on supported iPhone and Samsung VoLTE-capable phones, dialling an emergency number caused the handset to leave Lodestar and use another UK network through limited-service emergency access.

This was handset emergency network selection. It was not a commercial roaming arrangement or core-to-core handover. We did not retain enough technical detail to establish which radio technology or voice domain carried each call.

Success cannot be guaranteed for every handset, location, condition or available network. It depends on a compatible handset and accessible coverage from another network willing and able to accept the emergency call.

We did not retain the test dates, exact handset and software details, receiving networks or per-number results, and the tests were not coordinated with the other operators.

Do not place test calls to 999 or 112.

Network interface register

Standard LTE EPC and IMS reference points terminate at distinct logical functions. “Current” means a function or interface is present in the reviewed architecture or configuration; it does not mean every dependency is continuously healthy or that a related consumer service is available to order.

Public control and service interface register
Interface	Plane	Logical endpoints	Protocol	Purpose	Status
LTE-Uu	Radio access	User equipment and LTE eNodeB	LTE radio protocols	Radio access between a device and the LTE radio network	Current
S1-MME	Control	LTE radio and MME	S1AP over SCTP	Access, mobility and session signalling	Current
S1-U	User data	LTE radio and SGW-U	GTP-U over IP	Subscriber bearer transport into the EPC	Current
Protected RAN transport	Transport protection	eNodeB-side transport and core-side security gateway	IKEv2 and IPsec	Protects the logically separate S1-MME and S1-U paths between a connected site and the core boundary	Current
Regional S1-U	User data	West Midlands RAN and regional SGW-U	GTP-U over protected IP transport	Planned regional termination of subscriber bearers closer to West Midlands radio access	Planned
S11	Control	MME and SGW-C	GTPv2-C	Serving-gateway control and session management	Current
S5-C	Control	SGW-C and PGW-C	GTPv2-C	Gateway control between serving and packet gateway roles	Current
S5-U	User data	SGW-U and PGW-U	GTP-U over IP	Subscriber bearer between gateway user-plane roles	Current
Sxa	Control	SGW-C and SGW-U	PFCP	Control of the serving gateway user plane	Current
Sxb	Control	PGW-C and PGW-U	PFCP	Control of the packet gateway user plane	Current
Regional Sxa and Sxb	Control	London gateway control and regional SGW-U or PGW-U	PFCP over protected inter-site IP transport	Planned programming of regional user-plane forwarding while control remains in London	Planned
S6a	Subscriber control	MME and HSS	Diameter	Authentication and subscriber information	Current
Cx	IMS subscriber control	I-CSCF or S-CSCF and HSS	Diameter	IMS subscriber lookup and serving-function selection	Current
Gx	Policy control	Packet gateway control role and PCRF	Diameter	Policy and charging rules for packet data	Current
Rx	IMS policy control	P-CSCF application function and PCRF	Diameter	IMS session information for policy decisions	Current
Ro	Charging control	Serving IMS function and online charging	Diameter credit control	Online credit-control relationship	Current
SGi	User data	PGW-U and service networks	IP	Packet-data access to Internet or IMS service networks	Current
ISC	IMS service control	S-CSCF and IMS service applications	SIP over IP	Invocation of voice, messaging and related service logic	Current
IMS media control	Service control	Voice service logic and anchored media relay	Internal logical relationship; deployed control details are not published	Requests or updates media anchoring separately from SIP signalling and RTP or RTCP packets	Current
SIP	Signalling	Endpoints, CSCF roles and service applications	SIP over IP	Registration, call control, messaging and service invocation	Platform current; Voice access coming soon; external handoff in progress
RTP and RTCP	Media and media control	Endpoints, media relay and voice applications	RTP and RTCP over IP	RTP voice packets and associated RTCP reception and timing information	Platform current; Voice access coming soon; external handoff in progress
Lodestar Voice access	Fixed service access	Customer SIP endpoint and Lodestar Voice access edge	SIP, RTP and RTCP over customer-provided Internet	Reaches the IMS service without using Lodestar LTE radio access or EPC	Active build; coming soon
Proposed UK handoff	External service edge	IMS service edge and proposed UK interconnection	SIP plus RTP and RTCP	Intended external signalling and media handoff	In progress
Regional SGi	User data	Regional PGW-U and regional Internet or protected London IMS service paths	IP	Shorter planned Internet breakout while IMS service remains shared from London	Planned

Glossary

UE: User equipment, such as a mobile handset.
LTE-Uu: The LTE radio interface between user equipment and an eNodeB.
RAN: Radio access network connecting user equipment to the mobile core.
E-UTRAN: The LTE radio access network built around eNodeB functions.
EPC: Evolved packet core, the packet core used by LTE.
MME: Mobility Management Entity for LTE access and session signalling.
HSS: Home Subscriber Server for subscriber and authentication information.
PCRF: Policy and Charging Rules Function.
SGW-C and SGW-U: Serving gateway control and user-plane functions.
PGW-C and PGW-U: Packet gateway control and user-plane functions.
CUPS: Control and user-plane separation, allowing gateway decisions and packet forwarding to run as distinct roles.
PFCP: Packet Forwarding Control Protocol used between gateway control and user-plane functions.
IMS: IP Multimedia Subsystem for voice, messaging and related session services.
P-CSCF: The first IMS signalling contact for a mobile user.
I-CSCF: The IMS function used to locate or select the serving function during registration.
S-CSCF: The serving IMS call-control and service-routing function.
APN: Access Point Name, used by the EPC to select a packet-data service role.
RRC: Radio Resource Control, used between a handset and eNodeB to establish and manage LTE radio signalling and bearers.
TDD: Time-division duplex, where uplink and downlink transmissions use different time resources within the same radio carrier.
PDCP: Packet Data Convergence Protocol, part of the LTE radio stack above RLC for control and user-plane packet handling.
RLC: Radio Link Control, providing LTE radio-link functions between PDCP and MAC.
MAC: Medium Access Control, coordinating scheduled access to the LTE radio resources.
NAS: Non-Access Stratum signalling between the user equipment and MME for LTE mobility and session procedures.
EMM and ESM: EPS Mobility Management and EPS Session Management procedures carried within NAS signalling.
S1AP: The application protocol used for LTE access and mobility signalling between eNodeB and MME.
EPS bearer: The logical packet-delivery path established for an LTE subscriber service.
TEID: Tunnel Endpoint Identifier, used to distinguish a GTP tunnel context on a bearer hop.
TFT: Traffic Flow Template, the packet filters used to associate traffic with an EPS bearer.
QCI: QoS Class Identifier, describing standard packet-forwarding treatment for an EPS bearer.
ARP: Allocation and Retention Priority, used when deciding whether a bearer can be established or retained.
PCEF: Policy and Charging Enforcement Function associated with the packet gateway role.
ISC: The IMS service-control relationship between S-CSCF and application services.
OAM: Operations, administration and maintenance functions used to run and observe the network.
ACS: Auto Configuration Server role used for managed-device provisioning and lifecycle operations.
IKEv2: Internet Key Exchange version 2, used to establish and maintain IPsec security associations.
IPsec: Network-layer protection used for the reviewed transport between connected radio sites and the core-side security gateway.
SCTP: The transport protocol used beneath S1AP signalling on S1-MME.
GTPv2-C: The gateway and session-control protocol used on EPC control interfaces such as S11 and S5-C.
GTP-U: The tunnelling protocol that carries subscriber bearer packets on interfaces such as S1-U and S5-U.
Diameter: The base protocol beneath subscriber, policy and charging interfaces such as S6a, Cx, Gx and Rx.
SIP: Session Initiation Protocol for registration and session signalling.
SDP: Session Description Protocol, carried with SIP to describe proposed media capabilities and session parameters.
RTP and RTCP: RTP carries real-time media. RTCP carries associated reception, timing and participant information.
SGi: The EPC user-plane connection to external service networks.

Technical references

ETSI and RFC definitions underpin the interface names below. Ofcom material supplies licensing and regulatory context. Inclusion does not mean third-party certification or regulatory approval.

ETSI TS 123 401LTE EPC architecture and reference points

ETSI TS 124 301EPS mobility and session management signalling

ETSI TS 123 203Policy, charging and bearer quality-of-service architecture

ETSI TS 123 214EPC control and user-plane separation

ETSI TS 123 228IMS architecture and session procedures

ETSI TS 123 122Mobile network selection and limited-service operation

ETSI TS 123 167IMS emergency-session architecture and access selection

ETSI TS 122 101Service requirements and handset emergency-number recognition

ETSI TS 124 229IMS SIP and SDP call-control procedures

ETSI TS 129 244PFCP and CUPS interfaces

ETSI TS 136 412S1 signalling transport

ETSI TS 136 413S1AP procedures and information elements

ETSI TS 136 101LTE user-equipment radio bands and supported channel bandwidths

ETSI TS 129 274GTPv2-C control interfaces and procedures

ETSI TS 129 281GTP-U user-plane transport

ETSI TS 124 341SMS over IMS access procedures

ETSI TS 129 212Policy and charging control interfaces

RFC 3261Session Initiation Protocol

RFC 3550RTP media transport and RTCP control

RFC 6733Diameter base protocol

RFC 7296Internet Key Exchange version 2

RFC 4301IPsec security architecture

Ofcom Shared Access licencesOfficial licensing and spectrum context

Ofcom General ConditionsEmergency access and communications obligations context

Lodestar network architecture