How remote meter reading works: SNMP, the Printer MIB and collection agents

Why remote readings replaced the phone call

Click billing depends on a meter reading per machine per period. Collecting those by phone, email or on the engineer’s next visit is slow, gets missed and invites estimates and disputes. Reading the meters over the network removes most of that work and gives you a reading on the same date for every machine.

Remote collection also brings data you never had from a phone call: toner levels, paper jams, error codes and how long a device was stopped. That is what makes automatic toner shipping and proactive service possible. All of it starts with one protocol.

SNMP in brief

The Simple Network Management Protocol lets a manager ask a device for values. Almost every networked office printer and MFP includes an SNMP agent, usually enabled by default. Requests go to the device on UDP port 161. (Traps, which devices send unprompted, use UDP port 162, but meter reading normally polls rather than waiting for traps.)

Each value has an object identifier, or OID: a dotted path through a tree of definitions, such as 1.3.6.1.2.1.43.10.2.1.4. The definitions are published in MIB files (Management Information Base). The collector sends a get request for an OID, or walks a branch of the tree, and the device replies.

The three versions you will meet

The community string is effectively a shared password. Most devices ship with a read community of public. SNMPv3 replaces it with users, and offers three security levels: no authentication, authentication only, and authentication with privacy (encryption), usually called authPriv. Which hashing and encryption algorithms are available depends on the device’s firmware.

The standard Printer MIB (RFC 3805)

The Printer MIB was first published as RFC 1759 in 1995 and revised as Printer MIB v2 in RFC 3805 in 2004. It sits under 1.3.6.1.2.1.43 and is supported, at least in part, by almost every network printer. For meter reading and supplies, three parts matter.

• Marker life count (prtMarkerLifeCount): the number of units a marking engine has produced over its life. The unit is given by a companion object, usually impressions, and can differ between devices.
• Supplies table: each toner, drum, waste box and other supply with its maximum capacity and current level. Levels may be exact, or special values meaning “unknown” or “some remaining” when the device cannot measure precisely.
• Alert table: current conditions such as jams, covers open and supplies low or empty, with a code and a description.

Device status and detected error state come from the separate Host Resources MIB (RFC 2790), which most printers also support. Together these let a collector read a total page count, toner levels and current problems from almost any networked device, whatever the brand.

What the standard counter does not tell you

A copier contract bills mono and colour separately, often counts large-format pages differently, and may treat copies, prints and scans differently. The standard life count is one total per marking engine. A colour MFP normally has one marking engine, so the standard MIB gives you one number that mixes mono and colour pages.

There are other traps. Some devices count impressions (one side of a sheet) and some count sheets; a duplex page is two impressions but one sheet. Some include internal test and report pages. Two machines of the same model on different firmware can behave differently. If you bill from the standard total, you will eventually bill the wrong thing.

Manufacturer private MIBs

Each manufacturer has its own branch of the OID tree under 1.3.6.1.4.1, identified by an enterprise number assigned by IANA. In that branch they expose the counters the machine itself uses for billing: total, black, full colour, single or two colour, large size, copy, print, fax and scan, and others depending on the model. These are the figures the engineer sees on the counter page.

Private MIBs are where the real work lies. Object names and layouts differ between manufacturers and sometimes between model generations from the same manufacturer. Some are well documented; others are not. A collector that reads billing counters reliably across a mixed fleet has profiles for each maker’s layout and falls back to the standard Printer MIB when a device is not recognised.

Practical rule: when you first connect a machine, print its counter page and compare it with the remote reading, counter by counter. If they match, you can bill from it. If they do not, find out why before the first invoice.

Software agents and device-based collection

Something on or near the customer’s network has to send the SNMP requests. There are two broad approaches, and many dealers use both.

A software agent is the practical choice for a mixed fleet and for print audits, because it sees every network printer at the site, including the desktop devices that are not on contract. Device-based services are useful where a site will not allow software on its PCs, or for manufacturer-specific diagnostics.

Networks, VLANs and firewalls

SNMP polling stays inside the customer’s network: the agent talks to printers on UDP 161 locally. What leaves the site is the agent’s report, which should go out over HTTPS on port 443, the same as web browsing. A well-designed collector needs no inbound ports, no port forwarding and no VPN.

• If printers are on a different VLAN from the agent’s host, routing and any access lists between them must allow UDP 161 from the host to the printers.
• If the site uses a web proxy, the agent must be able to use it for its outbound connection.
• Discovery scans across address ranges can trigger intrusion detection. Agree the ranges with the customer’s IT, or add printers by IP address.
• Printers connected by USB cannot be read over SNMP. They need a network connection to be monitored.

Security checklist for the customer’s IT

Office IT teams are right to ask questions about anything installed on their network. These answers cover most of them.

• Use read-only access. Meter reading never needs SNMP write access, so disable the write community or give it a long random value.
• Change the default read community from public where the site allows, and configure the agent to match.
• Use SNMPv3 with authentication and privacy on networks that require encrypted management traffic.
• Where the device supports it, restrict SNMP access to the agent host’s IP address.
• Confirm that the collector reads counters, supply levels and status only. SNMP does not carry document content.
• Ask where the collected data is stored and put a data processing agreement in place for it.

Making remote readings billable

A remote reading is only useful for billing if it lands on the right machine and is plausible. Match devices to your records by serial number, not by IP address, because addresses change. Treat a reading lower than the previous one, or far above the machine’s normal use, as a question rather than a fact: it may be a board replacement, a swapped machine or a bad read.

In SubClik, a printer that reports the same serial number as a machine on record is linked to it, and readings are saved every day as meter readings for contract click billing. Readings that look wrong are held for the office to accept, correct or reject. Our guide to meter billing mistakes covers what to do with them, and the agent itself is available from the download page.