FAQ Logical Topology.pdf

Topology

1 Introduction

A topology is a (pictorial) description of the

structure and hierarchy of a network, including

the devices and communication paths.

The Logical Topology describes the configura-

tion of an installation from the point of view of

the communication flow. The Physical

Topology gives a, mostly simplified,

description of the physical layout of the

communication media and the physical

location of the KNX Devices.

Lines. This structure is reflected in the Indivi-

dual Address of KNX devices.

There is only one single Backbone Line .

Main Lines are hierarchically subordinate to

the Backbone Line. Up to 15 Main Lines may

be defined in an installation. Main Lines may

be numbered from 1 to 15. The Backbone Line

has Main Line number 0. No Main Line may

have Main Line number 0.

Main Lines may be connected to Backbone

Lines by means of an optional Backbone

Coupler . There may at maximum be one

Backbone Coupler in a Main Line. The Back-

bone Coupler belongs to the Main Line, not to

the Backbone Line. A Backbone Coupler

always has Device number 0 and Line number

2 Logical Topology, medium

independent

The logical topology of a KNX installation is

structured in a Backbone Line, Main Lines and

Backbone Line

Legend

BbC Backbone Coupler

Main Line

BbC

Figure 1 - Backbone Line & Main Lines

Lines are hierarchically subordinate to the

Main Lines. Up to 15 Lines may be defined per

Main Line in an installation. Lines may be

numbered from 1 to 15. A Main Line must

always have Line Number 0. No Line may

have Line Number 0. Line Numbers are written

preceded by the number of the Main Line the

Line is connected to.

Lines may be connected to Main Lines by

means of a Line Coupler . There may at

maximum be one Line Coupler in a Line. The

Line Coupler belongs to the Line, not to the

Main Line. The Line Coupler always has the

Device number 0. No other device may have

the device number 0.

Examples :

“4.9” may be the notation for the Line 9

connected to Main Line 4.

Main Line M

Legend

Line Coupler

Line

M.1

M.2

M.3

M.1

Figure 2 - Main Line & Lines

An Area consists of the whole of a Main Line

with subordinate Lines and all connected

devices. A KNX installation may therefore

count up to 15 Areas. The Area number is the

number of the Main Line it contains. The

Backbone Line with the devices attached to it

is not seen as an Area.

A Subnetwork is any part of this topology with

the same Main Line number and the same

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Topology

Line number. The Backbone Line, any Main

Line and any Line are Subnetworks.

The KNX End Devices may be connected

anywhere in this topology. Up to 255 KNX End

Devices can be addressed in any Subnetwork.

KNX End Devices may be numbered from 1 to

255. No KNX End Device may have Device

number 0.

Legend

}

Legend

BbC Backbone Coupler

Backbone Line

{

Line Coupler

Main Line

End Device

BbC

Line

Figure 3 - Backbone Line, Main Lines and Lines

Bit 15

Bit 0

2.1 Hierarchical Structure

The Logical Topology defines a hierarchical

organisation of the KNX Network: messages

may only pass from one Subnetwork to

another following a path in the Logical

Topology.

MMMM L L L L D D D D D D D D

Main Line

number

Line

number

Device number

This Individual Address is written as M.L.D

2.2 Individual Address

Every KNX Device (Backbone Coupler, Line

Coupler, KNX End Device, ...) must have an

Individual Address. This Individual Address is

unique throughout the complete topology. The

Individual Address of any device is composed

as follows:

Reserved Individual Addresses :

Device number “0” is reserved for Backbone

Couplers and Line Couplers.

NOTE A S A B ACKBONE C OUPLER IS INSTALLED IN A

M AIN LINE , ALSO ITS L INE NUMBER IS “0”.

Legend

}

Legend

BbC Backbone Coupler

Backbone Line

{

Line Coupler

Main Line

End Device

Line

BbC

1.0.0

1.0.1

1.0.2

2.0.0

2.0.1

2.0.2

3.0.0

3.0.1

3.0.2

15.0.0

15.0.1

15.0.2

1.0.255

2.0.255

3.0.255

15.0.255

1.1.0

1.2.0

1.2.1

1.2.2

1.3.0

1.3.1

1.3.2

1.15.0

15.1.0

15.1.1

15.1.2

15.2.0

15.3.0

15.15.0

1.1.1

1.1.2

1.15.1

1.15.2

15.2.1

15.2.2

15.3.1

15.3.2

15.15.1

15.15.2

1.1

1.2

1.3

1.15

15.1

15.2

15.3

15.15

1.1.255

1.2.255

1.3.255

1.15.255

15.1.255

15.2.255

15.3.255

15.15.255

Figure 4: Logical Topology reflected in the Individual Address es

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Topology

Examples :

“4.9.12” may be the Individual Address for any KNX End Device.

“4.9.0”

is the Individual Address of the Line Coupler that couples Line 4.9 to Main Line 4.

“7.0.0”

is the Individual Address of the Backbone Coupler coupling Main Line 7 to the

Backbone Line.

3 Media in the Logical Topology

The Subnetwork is the smallest part of the

Logical Topology that shall be implemented

with one single Physical Layer type. It is not

allowed to split up a Subnetwork into different

Physical Layer types.

In open media, it may be im possible to phy-

sically separate:

a) Subnetworks

In this case, the Backbone Couplers and

Line Couplers are optional. Lines may

then be connected to Main Lines without

a Line Coupler and Main Lines may be

connected to the Backbone Line without a

Backbone Coupler.

A Domain is is that part of the Logical

Topology over which the data signals of one

Physical Layer type propagate, possibly with

resending with identical characteristics but

without changing the message contents and

with respect of the Logical Topology.

The smallest possible Domain therefore is a

Subnetwork. A larger Domain may enclose

one or more united Subnetworks.

b) Domains

If in 2 Domains identical transmission

characteristics are used, messages pass

undetected from one Domain to another.

To allow separating Subnetworks and

Domains and thus respect the Logical

Topology, the Link Layers of open media limit

their communication by using a Domain

Address . This Domain Address separates

between Domains in one KNX Network and

between different KNX Networks. The Domain

Address is an unstructured 16-bit number.

Every Domain has an own unique Domain

Address within an installation.

Domain Address 0000h is reserved for cross-

media broadcast communication.

Closed Media are these Physical Layer Types

on which the message signals propagate

along the medium in a controllable way.

EXAMPLE T WISTED P AIR

Open Media are these Physical Layer Types

on which the message signals do not follow a

wirelike physical medium

EXAMPLE P OWERLINE , R ADIO F REQUENCY

Legend

}

BbC Backbone Coupler

Backbone Line

{

Line Coupler

Main Line

End Device

Line

BbC

Domain Address

0x2431

Domain Address

0x1F2A

Domain Address

0x1011

Domain Address

0x242C

Figure 5 - Examples of Domains and Domain Addresses

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Topology

3.1 Message Routing

To allow in principle for connection oriented

communication between any two devices in a

KNX installation, possibly connected to dif-

ferent media with none or more, possibly

different media in-between, the Individual

Address must be unique throughout all used

media.

If neighbouring Subnetworks are connected to

each other via a Line- or Backbone-Coupler

- this is mandatory a Media Coupler in case of

coupling different media - this coupler shall

filter the messages in both directions.This

routing is a functionality of the Network Layer

in the Coupler.

The filtering is based on the destination ad-

dress field and for open media additionally on

the Domain Address-field in the message.

4 Notes

• Lines may also be connected directly to the

Backbone Line. This is however not

recommended.

4.1 Twisted Pair

• For KNX Twisted Pair media, Electrical

Segments are defined. An Electrical

Segment is a part of a Subnetwork that is

electrically uninterrupted. If in an Electrical

Segment the Twisted Pair is short-circuited,

no communication is possible in that

Electrical Segment.

NOTE F OR P OWERLINE , IF WE TAKE THE SAME

DEFINITION OF E LECTRICAL S EGMENT AS “P ART OF THE

P HYSICAL M EDIUM THAT IS ELECTRICALLY

UNINTERRUPTED ”, AN E LECTRICAL S EGMENT MAY AS

WELL ENCOMPASS MORE THAN ONE LINE .

The following cases are possible:

1. Destination Address = Group Address

The routing is in this case based on a routing

table containing information which group

addressed messages shall be passed.

2. Destination Address = Individual Address

The routing is in this case based on a

comparison between the coupler's own

Individual Address and the destination

address.

• The Electrical Segment is part of the

Physical Topology of the KNX Network, not

of the Logical Topology. In KNX TP1, up to

4 Electrical Segments may be connected

using 3 Repeaters.

NOTE R EPEATERS CAN EXTEND THE RANGE OF A

S UBNETWORK IN KNX TP1-64. I N KNX TP1-256 THEY

ARE NOT NECESSARY .

• A Subnetwork may exist of at least one, to

up to four electrical segments. Every

electrical segment may be powered by one

or two Power Supply Units.

3. Destination Address = Broadcast

• Closed media: messages are always

passed in both directions

• Open media: messages are passed or

not based on the Domain Address

a) Domain Address ≠ 0x0000

The Media Coupler does not pass

the message to the other medium.

b) Domain Address = 0x0000

The Media Coupler passes the

message to the other medium.

Disclaimer

This document is provided by the Konnex Association “as is”. It has no normative value and shall not be used for

any product development. This document has not been subject to the approval process within Konnex

Association. No guarantee is given that this document is complete and up-to-date.

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