RADIUS Accounting for ISPs: Track Data Usage & Automate Billing

Understanding RADIUS Accounting

RADIUS accounting works alongside authentication to log session data. Every time a subscriber connects, the NAS (your MikroTik router) sends accounting packets to the RADIUS server: Accounting-Start when the session begins, Interim-Updates at regular intervals, and Accounting-Stop when the session ends.

Each accounting record includes: username, session duration, bytes uploaded, bytes downloaded, NAS IP, assigned IP address, and termination cause. This data is essential for usage-based billing, FUP enforcement, and network analytics.

Configuring Accounting on MikroTik

Enable RADIUS accounting for PPPoE and Hotspot services:

# Enable PPP RADIUS accounting
/ppp aaa
set use-radius=yes accounting=yes interim-update=5m

# Enable Hotspot RADIUS accounting
/ip hotspot profile
set default radius-accounting=yes radius-interim-update=5m

# Verify RADIUS configuration
/radius print detail

The interim-update=5m setting is crucial — it sends usage data every 5 minutes. Without it, you only get usage totals when the session ends, which could be days later for always-on PPPoE connections.

Reading Accounting Data

RADIUS accounting data is stored in the radacct table in your FreeRADIUS database. Here are useful queries:

# Top 20 data consumers today
mysql -e "SELECT username,
  ROUND(SUM(acctinputoctets)/1073741824, 2) AS upload_gb,
  ROUND(SUM(acctoutputoctets)/1073741824, 2) AS download_gb,
  ROUND(SUM(acctinputoctets + acctoutputoctets)/1073741824, 2) AS total_gb
FROM radacct
WHERE acctstarttime >= CURDATE()
GROUP BY username
ORDER BY total_gb DESC
LIMIT 20;" radius

# Monthly usage per subscriber
mysql -e "SELECT username,
  ROUND(SUM(acctinputoctets + acctoutputoctets)/1073741824, 2) AS total_gb
FROM radacct
WHERE acctstarttime >= DATE_FORMAT(NOW(), '%Y-%m-01')
GROUP BY username
ORDER BY total_gb DESC;" radius

Implementing Fair Usage Policy (FUP)

FUP throttles subscribers who exceed a data cap to a lower speed tier. This ensures fair bandwidth distribution across all subscribers. The typical workflow:

• Define FUP thresholds — e.g., 300 GB/month for 10 Mbps plan, after which speed drops to 2 Mbps
• Monitor usage — track cumulative usage from RADIUS accounting data
• Trigger throttle— when threshold is reached, change the subscriber's RADIUS rate-limit attribute
• Apply via CoA — send Change of Authorization to MikroTik to apply the reduced speed immediately
• Reset monthly — restore original speed at the beginning of each billing cycle

Data Cap Alerts and Notifications

Proactive communication keeps subscribers happy. Send alerts at usage milestones:

How ISPbills Automates Usage Billing

ISPbills reads RADIUS accounting data and automates the entire usage billing workflow:

• Real-time usage tracking — per-subscriber usage graphs updated every 5 minutes from interim accounting
• FUP automation — define FUP rules per package and ISPbills handles throttling and restoration automatically
• Data cap alerts — configurable SMS/email notifications at 75%, 90%, and 100% thresholds
• Usage-based billing — charge subscribers per GB of usage with automatic invoice generation
• Top-up system — subscribers can purchase additional data packages through the customer portal
• Usage reports — monthly usage reports per subscriber, per package, and network-wide