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Connection Restrictions

Real world does not allow connecting anything to anything. So inventory MUST enforce as many restrictions as possible. Connection restrictions may be expressed in several complimentary ways:

The connection may be established only when all five kinds of restrictions are met.


Connection Type restricts a physical type of connection. I.e. meaningless to connect RJ-45 jack to C14 electrical socket. The connection may be established only with the same or compatible types.

Connection type examples:

Type may be considered as mechanical form-factor, something like the form, size, and patterns of pins and holes.

Connection type compatibility may be complex. See Connection Type Restrictions discussion for explanation.


Connections of same Connection Type may be symmetrical, or genderless; or be of two mutual fitting sides (male and female). NOC supports 3 genders:

  • s - genderless, or side connection.
  • m - male connection.
  • f - female connection.

Genders may be mated according the table:


Or mnemonically: side-to-side, male-to-female, female-to-male. Unlike real life, NOC doesn't support advanced combinations of relations.

Males and females are equal in rights and the division is very arbitrary.

Possible genders on connections may be additionally restricted by Connection Types. See Genders Restriction Discussion for additional explanation.


Connection direction determines the hierarchy of the connected object. NOC supports three directions:

  • i - Inwards: The connected object will be put inside the current one.
  • o - Outwards: The current object will be put inside the connected one.
  • s - Side: Objects will be connected but neither object will be put inside the peer one.

i connections are usually slots for various extension modules, line cards, PSU e.t.c. They allow the gaining of additional features by putting something inside.

o connections are usually extension modules themselves. They should be put into something to became valuable.

s connections are neither previous cases. They are used to connect the object with the outer world. Various cables, patch cords, power cables are good examples of s connections.

s connections utilize genders, while the gender of i and o connections is only conventional. i connections are usually females, while o are male ones.

Directions can be connected by following way:


Or mnemonically: side-to-side, inwards-to-outwards, outwards-to-inwards. Following chart explains inwards-to-outwards kind of relation:

I/O Direction

Unlike the genders, directions are rarely misused.


While types, genders, and directions are merely physical properties, which can easily be observed with the naked eye, protocols define agreements on electrical, optical, and other kinds of signals. Connection is the physical media, while protocols are the logical use of it.

Consider example: RJ-45 port (Connection type Electrical | RJ45, gender female, direction side) is only the hole in the box. It may serve as an ethernet port: maybe 10Mbit/s, or 100Mbit/s, or gigabit one. It may provide or consume power over PoE. It may be a console port, utilizing RS-232 serial protocol. It may support 2 or 4-wire RS-485 serial protocol. It may be dumb passive cross-panel entry, leading floors away. You still may plug RJ-45 jack anyway, but will be any use of that?

So the protocols define possible usage of connection. Refer to the Inventory Protocols for the full list of protocols, provided by NOC. Protocols may be symmetric, when both peers utilizing the same configuration, like autoconfigured ethernet ports. Protocols may be asymmetric, like PoE consumer and PoE provider, RS-232 DTU and DCU.

Asymmetric protocols are denoted by > and < prefix, like '>RS-232' and '> leads inside the protocol, meaning that it will be consumed. i.e. '>POE' means that the device may consume power over PoE over the given connection. < leads outside the protocol, meaning that it will be provided. i.e. '<POE' means that the device can provide power over PoE over the given connection. The protocol without > and < can be provided and consumed as well.

Protocols are gender-agnostic. i.e. RS-232 DCU may use DB-9 male or female sockets as well.

The connection may support several protocols, i.e. ethernet may be coupled with PoE, and so on.

i and o directions enforce strict protocol match. i connection may provide at least one protocol which peer's o connection may consume or vise versa. s connections may provide protocols, or be protocol-agnostic with empty protocols list. Protocol-agnostic connections dependency will be described later.

Protocol compatibility matrix:


Mnemonic rules: Pure providers shall not be mated with pure providers, pure consumers shall not be mated with pure consumers.

Protocol-agnostic connections are the proxies or the media. They cannot deal with the protocol itself, but they can transport protocol to a connection, which can handle it. The best example of protocol-agnostic connections is the cable. It has two ends, and it can transport signal to the other end. Transport capabilities and restrictions are discussed in the Crossing section.

Protocol-agnostic connections are traced to the other ends and cannot be connected only in one of two cases:

  • Provided or consumed protocol can be traced to compatible endpoint (s port with compatible protocol).
  • Provided or consumed protocol cannot be traced to the endpoint with any other protocol. (dark fibre principe).


The crossing is the additional set of rules which can be applied to protocol-agnostic s connections within the same object to define the possible protocol flow. Usually, crossing represents static multiplexing which can be defined o model or object level. Static multiplexing means the signal with given protocol may pass trannsparently from input to one or more output slots.

Crossing is defined as table of items, each connects particular input with particular output. Additonal restrictions, named discriminators, are possible.

inputInput connection name
input_discriminatorOptional input discriminator
outputOutput connection name
output_discriminatorOptional output discriminator, for describe output mappings
gain_dbSignal gain, in dB


Unlike other restrictions, which defines the object's communications with the outer world (extravertive nature), crossing defines an object's internals (introvertive nature).

The common rules of the signal passing are:

flowchart TD
    c_input{`input` matched?}
    c_input_discriminator{Has input_discriminator?}
    c_input_match{Input discriminator matched?}
    skip([Skip Rule])
    passed([Signal Passed to output])
    start --> c_input
    c_input -- Yes --> c_input_discriminator
    c_input -- No --> skip
    c_input_discriminator -- Yes --> c_input_match
    c_input_discriminator -- No --> passed
    c_input_match -- Yes --> passed
    c_input_match -- No --> skip

Signal is replicated to all matched outputs. Additionaly, signal gain/loss may be applied.


DAC/Twinax cable

graph LR
    s1 --> s2
    s2 --> s1

Unidirectional Splitter

1:4 splitter with equal distribution

InputOutputGain (dB)
graph LR
in -- -6dB --> out1
in -- -6dB --> out2
in -- -6dB --> out3
in -- -6dB --> out4

Bidirectional Splitter

1:4 splitter with equal distribution in dowstream, allowing to pass signal upstream with 3 dB attenuation.

InputOutputGain (dB)
graph LR
in -- -6dB --> out1
in -- -6dB --> out2
in -- -6dB --> out3
in -- -6dB --> out4
out1 -- -3dB --> in
out2 -- -3dB --> in
out3 -- -3dB --> in
out4 -- -3dB --> in

95%/5% splitter

Common TV system splitter, passing 95% of the signal to transit and redirecting 5% to output.

graph LR
in -- -0.2dB --> transit
in -- -139.8dB --> output