# Does v1 allow the same data type to be exchanged over multiple ports?

**URL:** <https://forum.opencyphal.org/t/does-v1-allow-the-same-data-type-to-be-exchanged-over-multiple-ports/439>\
**Category:** Development & Maintenance\
**Created:** [April 12, 2019, 5:26am UTC](https://forum.opencyphal.org/t/does-v1-allow-the-same-data-type-to-be-exchanged-over-multiple-ports/439 "2019-04-12T05:26:09Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![scottdixon](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/scottdixon/32/39_2.png) [@scottdixon](https://forum.opencyphal.org/u/scottdixon)\
**Post date:** [April 12, 2019, 5:26am UTC](https://forum.opencyphal.org/t/does-v1-allow-the-same-data-type-to-be-exchanged-over-multiple-ports/439/1 "2019-04-12T05:26:09Z")

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I seem to remember, from back in Stockholm, that the SI types were designed to allow ports to exchange simple types. If we don’t allow a single type on multiple ports then you cannot use an SI type without first wrapping it in a structure type. I’m not saying either way is correct I’m just trying to find the thread of this decision and tug until I see where it was woven into the v1 specification.

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**Author:** ![pavel.kirienko](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/pavel.kirienko/32/9_2.png) [@pavel.kirienko](https://forum.opencyphal.org/u/pavel.kirienko)\
**Post date:** [April 12, 2019, 8:02am UTC](https://forum.opencyphal.org/t/does-v1-allow-the-same-data-type-to-be-exchanged-over-multiple-ports/439/2 "2019-04-12T08:02:04Z")

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It is specified in section 2.1.2.1:

> A data type can be used with an arbitrary number of different port identifiers assigned on a per-application basis, but not more than one fixed port identifier.

Not sure if the phrase “assigned on a per-application basis” is clear enough; suggestions are welcome.

EDIT: also it was discussed here: [Data type compatibility assurance](https://forum.opencyphal.org/t/data-type-compatibility-assurance/196)

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**Author:** ![pavel.kirienko](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/pavel.kirienko/32/9_2.png) [@pavel.kirienko](https://forum.opencyphal.org/u/pavel.kirienko)\
**Post date:** [April 12, 2019, 9:39am UTC](https://forum.opencyphal.org/t/does-v1-allow-the-same-data-type-to-be-exchanged-over-multiple-ports/439/3 "2019-04-12T09:39:57Z")

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I have amended the section 2.1.1.2 in my branch where I am collecting minor fixes as follows:

```auto
Port identifiers are assigned to various functions, processes, or data streams within the network
at the system definition time.
Generally, a port identifier can be selected arbitrarily by a system integrator
by changing relevant configuration parameters of connected nodes,
in which case such port identifiers are called \emph{non-fixed port identifiers}.
It is also possible to permanently associate any data type definition with a particular port identifier
at a data type definition time,
in which case such port identifiers are called \emph{fixed port identifiers};
their usage is governed by rules and regulations described in later sections.

A data type can be used with an arbitrary number of non-fixed different port identifiers,
but not more than one fixed port identifier.

```