Network cost information element

To communicate the cost of the Wi-Fi network to clients, Microsoft has defined a vendor extension to the 802.11 protocol. This extension is the Network Cost IE.

Note
The 802.11 protocol allows vendor-defined information elements (IEs), and requires clients that do not understand a particular IE to ignore it and continue processing the remaining IEs. This minimizes the compatibility risk of adding a new IE to products that interact with existing clients of other operating system types.

The following table shows the Network Cost IE format:

Field name Size (octets) Value Description

Attribute ID

1

0xDD

Type (vendor extension)

Length

1

0x08

Length of the following fields

Organizationally Unique Identifier (OUI)

3

0x00, 0x50, 0xF2

Vendor (Microsoft)

OUI Type

1

0X11

OUI type (network cost)

Cost attribute (Required)

4

Variable

DWORD, little endian byte order

The following figure shows the format of the cost attribute field:

format cost attribute field

The following table shows the possible cost level bits (exactly one is required):

Value Name Description

0x01

Unrestricted

No incremental cost applies for transferring data on this connection.

0x02

Fixed

Data transfer is metered and counts against a data limit. No difference in cost applies within this limit.

0x04

Variable

Incremental cost applies for all usage on this link.

The following tables shows the possible cost flag bits:

Value Name Description

0x01 00 00

Over Data Limit

Usage has exceeded the data limit and different network costs or conditions apply.

0x02 00 00

Congested

The network operator is experiencing or expecting heavy load and requests reduced activity where possible.

0x04 00 00

Roaming

The connection is roaming outside the provider’s home network or affiliates.

0x08 00 00

Approaching Data Limit

Usage is near the data limit; different network costs or conditions may apply soon.

The following table shows some sample cost attribute values:

Value Name Description

Default WLAN

0x00 00 00 01

Unrestricted connection; standard WLAN backed by fixed broadband.

Portable Hotspot Default

0x00 00 00 02

Metered network; limit unknown or not yet reached; matches Windows default for mobile broadband connections.

Over Limit / Throttled

0x00 01 00 01

User has exceeded data limit; speed is reduced, but no further usage limitation applies.

Over Limit / Charges

0x00 01 00 04

User has exceeded data limit; additional usage incurs incremental charges.

Portable Hotspot / Roaming

0x00 04 00 04

Connection is roaming; incremental charges apply due to network state.

Add network cost support to your device

  1. Add the IE to your device’s WLAN beacon and probe response, which is fixed to the Portable Hotspot Default value shown in the table with the sample cost attribute values. Verify that a Windows 8, Windows 8.1, or Windows 10 computer that connects to this network automatically selects the Reduce network usage option for this network.

  2. When roaming, replace the default value with the Portable Hotspot / Roaming value that is listed in the table with the sample cost attribute values.

  3. Optionally, work with your partner carriers to determine cases where other values may be appropriate, such as the following:

    • Unrestricted while on certain bearers (LTE, HSPA+, etc.),

    • Defined channel to detect over-limit states.

    • Operator-defined behavior when past data limit.

  4. Optionally, if your device can use Wi-Fi as a second-hop network, check for this IE on the network to which you connect and relay its value (or its absence) to your own SSID. If none is present, use the Default WLAN value that is listed in the table with the sample cost attribute values.

Related topics

Communication channels

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