Mediation & CDR Processing
Last updated 12 Oct 2026
At a glance
Mediation is the pipeline between the network and rating. It collects raw usage records in each vendor's format, and turns them into one clean, deduplicated, subscriber-attributed usage event per billable activity. It decides what happened and to whom. It does not decide what that is worth, and it is not where real-time credit control happens.
The picture
Five raw records in, one usage event out. Mediation says what happened and to whom; rating decides what it is worth.
1 · Raw records
- P-CSCFpartial · call 7781
- S-CSCFpartial · call 7781
- IMS-ASpartial · call 7781
- S-CSCFpartial · call 7781 (resent)
- MSCtest number · 0 s
Each node writes its own vendor format
2 · Pipeline
1 Collect
from every node
2 Validate & filter
test record dropped
3 Normalise
one format, one unit
4 Correlate
3 partials → 1; resend removed
5 Enrich
MSISDN → account, destination zone
Failures go to an error queue, not the bin
3 · One usage event
- Account
- ACC-1001
- Service
- Voice (VoLTE)
- Duration
- 12 min
- Destination
- National mobile
- Price
- none yet
TMF635 describes usage records of this kind
4 · Route
- Rating
- Interconnect billing
- Revenue assurance
- Fraud management
Online charging does not wait for this pipeline: the network asks the OCS directly (Diameter Gy in 4G, the CHF over Nchf in 5G)
How it works
From network event to usage event
Voice switches, packet gateways, IMS nodes, SMS centres and 5G core functions record what each subscriber did. They write Call Detail Records (CDRs), Event Detail Records (EDRs) and IP Detail Records (IPDRs) in their own formats, often split across several nodes for one session. Mediation turns these into usage events rating can value, and routes copies to every other consumer.
The seven functions
| Function | What it does | What goes wrong without it |
|---|---|---|
| Collect | Pull or receive records from every network source | A node that is not collected is usage that is never billed |
| Filter | Drop non-billable records (test numbers, zero duration, internal traffic) | Customers charged for test or signalling traffic |
| Validate | Check mandatory fields, ranges and formats; send failures to an error queue | Bad records rejected downstream with no route to correction |
| Normalise | Convert vendor formats and units into one internal format | Rating needs a rule per network vendor and release |
| Correlate | Merge partial records for one session and remove duplicates | Double charges, or long sessions billed as fragments |
| Enrich | Add subscriber, account, service and reference data (destination, roaming partner) | Usage charged to the wrong account or tariffed as the wrong destination |
| Route | Deliver each record to the consumers that need it | Rating gets the usage but RA, fraud or interconnect billing do not |
As a staged pipeline
Collection
CollectorsFrom MSCs, packet gateways, IMS nodes, SBCs and others, by FTP, SFTP, FTAM or streaming interfaces.
Parsing & normalisation
ParserASN.1, CSV and proprietary binary formats parsed into one internal format; field names, dates, durations and units standardised.
Validation & filtering
ValidationZero-duration and test records filtered; records missing mandatory fields (calling number, timestamp) sent to an error queue.
Correlation
CorrelationPartial records for one session merged. A VoLTE call can produce records from the P-CSCF, S-CSCF and IMS application server; they become one event. Duplicates removed.
Enrichment
Enrichment / reference dataMSISDN to account mapping, service type, number-plan lookup for destination, roaming partner identification.
Delivery
Mediation → consumersTo rating in batch files, or by streaming where usage is rated near real time. Copies routed to interconnect billing, revenue assurance, fraud and analytics.
What mediation is not
How it fails
- Lost records: collection failure or file corruption. Usage never billed.
- Duplicates: correlation failure. The customer is charged twice.
- Late records: arriving after the bill run. Lost revenue or out-of-cycle adjustments.
- Enrichment errors: wrong subscriber mapping. Charges on the wrong account.
- Format changes after a network upgrade: new fields not parsed, records rejected.
Who owns what
| Entity | System of Record | System of Engagement | System of Reference | Notes |
|---|---|---|---|---|
| Raw usage records (CDR / EDR / IPDR) | Network elements | — | Mediation | Vendor-specific formats; often several partial records per session. |
| Normalised usage event | Mediation | — | Rating, Interconnect billing, Revenue Assurance, Fraud Management | TMF635 describes usage of this kind. Carries no price. |
| Rejected and suspended records | Mediation (error queue) | — | Revenue Assurance | Each one is unbilled usage until it is corrected and reprocessed. |
| Subscriber-to-account mapping used for enrichment | Billing account / Product Inventory | — | Mediation | Mediation holds a reference copy; a stale copy charges the wrong account. |
| Tariffs and zero-rating rules | Product Catalog | — | Rating | Mediation should not hold them. |
In practice
Mediation is usually a proprietary layer, sometimes a stand-alone product and sometimes part of a convergent charging suite. Its configuration is a large body of parsers, filters and correlation rules built up node by node and release by release.
Mediation is the most common point of revenue leakage in a telco, because every record passes through it and lost or late records are silent. The customer does not complain about a call that was never billed.
The trade-off
What it solves
Rating and every other consumer receive one clean, attributed usage event per activity, whatever the network vendor, node or release that produced it.
What it does not solve
- Real-time credit control, which runs between the network and the OCS.
- Wrong reference data. Enrichment against a stale account mapping charges the wrong customer.
- Records the network never wrote, or nodes nobody configured for collection.
What it adds
- Every network change needs a matching mediation change and test.
- Error queues need owners and a reprocessing process, or they become silent leakage.
- Logic placed in mediation filters is invisible to the catalog and to anyone reading prices.
Architecture decision
Where should a rule such as "do not charge traffic to this APN" live?
In the catalog, applied by rating
Choose when the rule is commercial (a zero-rated service, a promotion), so it must be visible in the product and auditable as a price.
In mediation filtering
Choose when the traffic is genuinely non-billable (signalling, test, internal) and would never appear on any customer's bill.
Breaks if commercial rules are implemented as mediation filters. The catalog then says one thing, customers are charged another, and nobody can trace why.
Takeaways
Key Takeaways
- Mediation turns vendor-specific network records into one clean usage event per billable activity
- Seven functions: collect, filter, validate, normalise, correlate, enrich and route
- Mediation says what happened and to whom; rating, driven by the catalog, decides what it is worth
- Mediation is not an OCS: real-time credit control runs between the network and the charging system
- Lost, late and duplicated records are silent, which makes mediation the most common point of leakage
Check yourself
After a core network upgrade, data revenue drops overnight but no customer complains. Where do you look first?Show answerHide
The mediation error queue. The new release probably changed the record format, the parser rejects the records, and the usage is never rated.
Some VoLTE calls appear three times on customer bills. Which mediation function failed?Show answerHide
Correlation. The partial records from the P-CSCF, S-CSCF and IMS application server were not merged into one event, so each was rated separately.
Marketing asks for a zero-rated music service. Mediation offers to filter out that traffic. What is the problem?Show answerHide
The price is then hidden in mediation. The catalog no longer describes what is charged, Revenue Assurance cannot see it, and changing or ending the offer means a mediation change. It belongs in the catalog and rating.