"A value which indicates the set of services that this entity primarily offers.

The value is a sum. This sum initially takes the value zero, Then, for each layer, L, in the range 1 through 7, that this node performs transactions for, 2 raised to (L - 1) is added to the sum. For example, a node which performs primarily routing functions would have a value of 4 (2^(3-1)). In contrast, a node which is a host offering application services would have a value of 72 (2^(4-1) + 2^(7-1)). Note that in the context of the Internet suite of protocols, values should be calculated accordingly:

layer  functionality
    1  physical (e.g., repeaters)
    2  datalink/subnetwork (e.g., bridges)
    3  internet (e.g., IP gateways)
    4  end-to-end  (e.g., IP hosts)
    7  applications (e.g., mail relays)

For systems including OSI protocols, layers 5 and 6 may also be counted."

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