Network emulator for private communication terminal equipment

A private communication system and an allocated, private communication terminal equipment that is not directly connectable, i.e. that is "external", has a respective terminal equipment emulation unit allocated to it. This terminal equipment emulation unit pair are connectable to one another at least via a public dialed communication network, where the connection of at least one message path and of an additional signaling path is controlled via the public dialed communication network and the switching of the paths suited to the terminal equipment emulation unit pair is checked. With the assistance of the terminal equipment emulation unit pair, isolated or external communication terminal equipment can be connected without diminishing the scope of performance features of private communication networks. Misconnections and false signalings are avoided by checking the connection suited to the terminal equipment emulation unit pair with the assistance of a specific check procedure.

BACKGROUND OF THE INVENTION 
The invention is directed to a communication arrangement with a private 
communication system to which private communication terminal equipment 
that are not directly connectable are allocated. 
Private communication networks are formed by private communication systems 
that are partly or fully integrated with one another. The integrating of 
the private communication systems is partially achieved via private 
property and partially via public communication networks. In particular, 
the public analog and the integrated services digital telephone 
communication network--referred to in the field as the ISDN network--as 
well as digital data networks--for example, the packet network or a 
synchronous through-connection network--particularly represent public 
communication networks. The private communication systems can be 
differently designed in view of their configuration size; however, a 
uniform signaling is provided in the private communication network. Since 
the signaling in private communication networks comprises substantially 
more signaling versions compared to the signaling in the public 
communication networks (particularly caused by the additional performance 
feature control), consequently additional signaling information are to be 
communicated, and additional signaling paths or signaling channels 
conducted via the public communication networks are required. EP0 642 282 
A1 discloses that the additional signaling path between communication 
systems is to be realized with the assistance of an additional means over 
an analog telephone communication network, over a separate channel of a 
data communication network, or by an overlay connection over a telephone 
connection. 
In private communication networks, further, isolated or a few communication 
terminal equipment units, i.e. communication terminal equipment units that 
cannot be connected to a communication system via private property are 
connected to a private communication system. The advantageous, additional 
performance features of a private communication network, however, should 
thereby be preserved. Up to now, exclusively used transmission lines, i.e. 
hard-wired connections in public communication networks, have been 
provided for the connection of such "isolated" communication terminal 
equipment to a communication system. Such exclusive lines are available 
without limitation for a transmission of information and are 
intrusion-proof since every connection on an exclusively used line is 
unambiguously reached only by the private communication network own 
communication system. The exclusivity of the transmission lines, however, 
represents a substantial financial expense for the connection of an 
"isolated" communication terminal equipment unit. It is also known to 
bring such "isolated" communication terminal equipment to a private 
communication system via dialed connections of a public communication 
network. This, however, means a substantial limitation of the performance 
features useable by the communication terminal equipment and, due to 
signaling errors or bad controls in the public communication networks, an 
unambiguous allocation of private communication system to private 
communication terminal equipment is also no longer possible. 
SUMMARY OF THE INVENTION 
An object of the invention is to connect "isolated or external" 
communication terminal equipment to a private communication system in 
cost-beneficial fashion, whereby the advantageous performance features of 
a private communication network should be preserved. 
According to the invention, a communication arrangement is provided with a 
private communication system to which private communication terminal 
equipment that cannot be directly connected are allocated. The private 
communication system and the allocated private communication terminal 
equipment are respectively connected to a terminal equipment emulation 
unit. The terminal equipment emulation unit allocated to the communication 
terminal equipment and to the communication system form a terminal 
equipment emulation unit pair which are respectively connected to at least 
one public dialed communication network via at least one terminal. Means 
for automatic call setup via the public dialed communication network are 
provided in the terminal equipment emulation unit pair. Said means 
controls the connection of at least one message path and of an additional 
signaling path via the public dialed communication network, and checks 
switching of the at least one message path and the additional signaling 
path suited to the terminal equipment emulation unit. 
The critical aspect of the communication arrangement of the invention is 
that the private communication system and the allocated private 
communication terminal equipment is respectively connected to a terminal 
equipment emulation unit and the terminal equipment emulation unit 
allocated to the communication terminal equipment and the terminal 
equipment emulation unit allocated to the communication system form a 
terminal equipment emulation unit pair and are respectively connected to 
at least one public dialed communication network via at least one 
terminal. Means for automatic call setup via the public dialed 
communication network are provided in the terminal equipment emulation 
unit pair, whereby the setup of at least one message path and of an 
additional signaling path via the public dialed communication network (KN) 
is controlled by said means and the switching of the paths suited to the 
terminal equipment emulation unit pair (PNEP) is checked. "Isolated or, 
respectively, external" communication terminal equipment can be connected 
with the assistance of the terminal equipment emulation unit pair of the 
invention without diminishing the performance features of private 
communication networks. A further advantage of the communication 
arrangement of the invention may be seen therein that the terminal 
equipment emulation unit can control a direct access into the connected, 
public dialed communication network for the respectively allocated 
communication terminal equipment, whereby a reduction of the scope of 
performance features is to be taken into account. Misconnections and false 
signalings are avoided by checking the connection suited to the terminal 
equipment emulation unit pair with the assistance of a specific check 
procedure. 
Further advantageous developments of the terminal equipment emulation unit 
are provided. The advantageous developments refer to different types of 
communication terminal equipment--analog or digital--, to different public 
communication networks--public analog or digital telephone network or 
public data network--, as well as to different realizations of the 
additional signaling path for the communication of the additional 
signalings, and to different check procedures. 
The communication arrangement of the invention is explained in greater 
detail below with reference to four block circuit diagrams.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a private communication system KS to which a terminal 
equipment emulation unit KPNE-KS is connected via an analog interface a/b. 
An analog communication terminal equipment unit KE-A comprising an analog 
interface a/b is usually directly connected to this analog interface a/b 
via a subscriber line (not shown). In the communication arrangement of the 
invention, the analog interface a/b of the communication terminal 
equipment unit KE-A is connected to a further terminal equipment emulation 
unit KPNE-KE. Together, the terminal equipment emulation unit KPNE-KE, 
KPNE-KS at the side of the communication system and communication terminal 
equipment form a terminal equipment emulation unit pair PENP. 
Both terminal equipment emulation units KPNE-KE, KS are respectively 
connected to the public, analog telephone communication network 
FE--bounded by broken lines--via an analog interface a/b--likewise 
indicated by dot-dashed lines. 
Two different call requests are possible from the analog communication 
terminal equipment KE-A. This is, first, a call request to the allocated 
private communication system KS and, second, a call request into the 
public, analog telephone communication network FE without collaboration of 
the allocated communication system KS. A call request into the public, 
analog telephone communication network FE for the connection of an analog 
communication terminal equipment KE-A to its communication system KS can 
be inadmissible and, consequently, is optionally predictable. 
It is assumed for the exemplary embodiment that, given a call 
initialization, a connection in the private communication network PKN 
(i.e. to the allocated private communication system KS or vice versa) is 
requested. The call request initiated by a loop closure in the 
communication terminal equipment KE is acquired in the terminal equipment 
emulation unit KPNE-KE with the assistance of a signaling unit SU and a 
call setup procedure, i.e. a dial procedure via the public telephone 
communication network FE to the terminal equipment emulation units KPNE-KS 
at the side of the communication system is automatically initiated with 
the assistance of the signaling units SU-FE and of the call controller VST 
provided in the terminal equipment emulation units KPNE. The call setup is 
implemented with a call number communicated in a multi-frequency method 
(MFV). After a check procedure to be explained later, the terminal 
equipment emulation unit KPNE-KE at the terminal equipment side 
communicates the ring back of the private communication network to the 
analog communication terminal equipment KE. In a telephone communication 
terminal equipment KE, the voice circuit thereof is then directly 
connected to the private communication system KS. During the further 
course of the call, the communication terminal equipment KE-A can control 
additional performance features not provided in the public, analog 
telephone communication network FE with additional keys--indicated by a 
key T shown in the communication terminal equipment KE. The additional 
information are thus communicated with the assistance of the 
multi-frequency method. 
Given a call request directly into the public telephone communication 
network FE, an additional, switching-oriented key VT is provided in the 
communication terminal equipment KE-A. Upon actuation thereof, the 
terminal equipment emulation unit KPNE-KE of the communication terminal 
equipment side is informed that a dialed connection directly into the 
public, analog telephone communication network FE is requested. This means 
that the signaling communicated from the communication terminal equipment 
KE is directly forwarded to the public, analog telephone communication 
network FE. The capacitor C provided in the terminal equipment emulation 
unit KPNE serves for the current-associated separation and the switch VSC 
serves for the decoupling of the message and signaling path. 
During the course of the check procedure, the terminal equipment emulation 
unit KPNE-KE of the communication terminal equipment side communicates 
numerical information for example, a running number of the connection) 
about the set-up connection and a defined connection identifier) 
identifies the private subscriber line) to the terminal equipment 
emulation unit KPNE-KS of the communication side encoded with MFV 
characters. When the communicated information coincide with the 
anticipated information, a ring back is communicated to the terminal 
equipment emulation unit KPNE-KE of the communication terminal equipment 
side. This is interpreted as an acknowledgment, whereupon the connection 
is through-connected to the communication terminal equipment KE-A and the 
running number is incremented by a predetermined value. 
Given public, analog telephone communication networks FE equipped with 
digital switching equipment, the telephone number of the respectively 
calling communication terminal equipment can be communicated to the 
respectively called communication terminal equipment. A check of the 
correct connection can be implemented on the basis of these telephone 
numbers. The check procedure can advantageously additionally sequence, 
since the through-connected connection path, i.e. the message path, is 
thereby additionally checked. 
FIG. 2 likewise shows a private, analog communication terminal equipment 
unit KE-A that is allocated to a private communication system KS, whereby 
the connection is not conducted via the public, analog telephone 
communication network FE but via the integrated services digital telephone 
communication network ISDN. For this purpose, terminal equipment emulation 
unit KPNE are provided that are respectively connected to the 
communication terminal equipment KE-A or to the communication system KS 
via an analog signaling unit SU-KE. This analog signaling unit SU-KE is 
connected to a codec unit COD via two connecting switches VSC. A 
connection controller VST connecting the connection switches VSC to the 
analog signaling unit SU-KE and to a line termination unit LT converts the 
signaling information si communicated from the communication terminal 
equipment KE-A into ISDN-conforming signaling information si, or controls 
the automatic call setup of the respectively allocated terminal equipment 
emulation unit KPNE. The line termination unit LT is also connected to the 
codec unit COD. The connection to the ISDN network ISDN is implemented by 
an SO interface SO--indicated with dot-dashed lines--realized in the line 
termination unit LT. The SO interface SO comprises two message channels 
B1, 2 each having 64 kbit/s and a signaling channel D having 16 kbit/s. 
Given a call request, a call setup, a dialing procedure to the respectively 
allocated terminal equipment emulation unit KPNE is automatically 
initiated and a check is implemented on the basis of the telephone numbers 
communicated from the ISDN communication network ISDN as well as the check 
procedure explained in FIG. 1. The additional signaling information si to 
be communicated before and during a call setup for the realization of 
additional performance features provided in private communication networks 
PKN are communicated via an additional signaling path DZ, i.e. via the 
second message channel B2 provided in the ISDN network ISDN or via the 
packet service or packet channel of the signaling channel--D-channel--of 
the ISDN basic access SO. The signaling information si provided for this 
purpose are correspondingly formed in the call controller VST and are 
communicated to the line termination unit LT. The message and signaling 
channels B1, 2, D are multiplexed to form an aggregate bit stream in this 
line termination unit LT and are matched to the physical conditions of the 
SO interface SO. 
FIG. 3 shows a digital, private communication terminal equipment KE-D that 
is allocated to a private communication system KS. Both the communication 
terminal equipment KE-D as well as the communication system KS 
respectively comprise a digital interface DS--indicated by dot-dashed 
lines. The digital interface DS comprises one digital or two digital 
message channels B+(B) and a digital signaling channel D. Digital 
interfaces DS having two message channels B+(B) and one signaling channel 
B, for example, represent SO-interfaces of the integrated services digital 
telephone communication network ISDN. Digital interfaces DS having one 
message channel B and one signaling channel D are particularly utilized in 
private communication networks KPN. 
The digital interface DS is realized in an access unit LT-D both in the 
terminal equipment emulation unit KNPE-E, KNPE-KS of the communication 
system side as well as of the communication terminal equipment side. In 
this, the signaling channel D is separated and conducted to a call 
controller VST. The at least one message channel B is conducted via an 
exchange switch VSC to a further line termination unit LT that comprises 
an ISDN basic access, i.e. an SO-interface SO. The ISDN signaling channel 
DI incoming from the call controller VST is multiplexed in the line 
termination unit LT to form an ISDN-suited data stream and is matched to 
the physical conditions of the SO-interface SO. The message channels B 
directed from the line termination unit LT to the digital line termination 
unit LT-D are directly switched and are additionally conducted onto the 
call controller VST. The SO-interface SO of the terminal equipment 
emulation unit KPNE are connected to terminals of the public, integrated 
services digital telephone communication network ISDN. 
Given a connection request of the communication terminal equipment or 
communication system side initiated by call information communication in 
the signaling channel D, the communicated dial characters are 
intermediately stored and a connection is set up via the ISDN network ISDN 
to the terminal equipment emulation unit KPNE-KS of the communication 
system side. The connection telephone number of the terminal equipment 
emulation unit KPNE-KE of the communication terminal equipment side 
communicated from the ISDN network ISDN is thus checked for coincidence 
with the anticipated connection telephone number. Subsequently, the check 
procedure which has already been described is now implemented with digital 
information signals . . . ! to check the correlation of the useful and 
signaling channel. After the end of the check procedure, the ring back of 
the private communication network KNP is conducted to the digital 
communication terminal equipment KE, whereupon the intermediately stored 
dialing characters are communicated via the ISDN network to the 
communication system. 
The communication of the signaling information relating to the private 
communication network KPN can occur via three differently realized 
signaling paths, i.e. signaling channels DZ: 
a) Given communication terminal equipment KE with only one message channel 
B, the additional signaling channel DZ can be realized in the second 
message channel B2. For this purpose, the call controller VST forms the 
corresponding signaling information and sends them or receives them. 
b) The additional signaling channel DZ is realized in the packet service of 
the signaling channel D of the ISDN basic access, i.e. of the SO-interface 
SO of the ISDN network ISDN. In this realization, the additional signaling 
channel DZ is switched to the unit LT by the call controller VST. 
c) The additional signaling channel DZ is realized via a further signaling 
access unit SAE via a public data communication network IDN--indicated by 
a broken line and the possible interfaces X.25, X.21 in FIG. 1. 
d) The additional signaling channel DZ is additionally multiplexed in one 
of the two message channels B with the assistance of a multiplex unit MUX 
indicated by broken lines. A compression of one of the two message 
channels B1, B2--for example, from 64 kbit/s into 56 kbit/s--is required 
for this purpose. The additional signaling information are then 
communication in the additional signaling channel DZ, for example with 8 
kbit/s. 
The realization versions B through D are provided given communication 
terminal equipment KE-D with two message channels B1, B2. 
FIG. 4 likewise shows a communication terminal equipment KE-D and a 
communication system KS with a digital interface DS having one or two 
message channels B1, B2 and one signaling channel D. These two data 
interfaces DS are respectively connected to a terminal equipment emulation 
unit KPNE-KS, KPNE-KE of the communication system side and of the 
communication terminal equipment side and are conducted therein onto a 
digital line termination unit LT-D. In the latter, the signaling channel D 
is separated and conducted to a call controller VST. The at least one 
message channel B1, B2 is connected at least onto one codec unit COD-the 
second unit is indicated with broken lines. The at least one message 
channel B1, B2 directed to the communication system KS is conducted to a 
signaling unit SA-FE via an exchange switch VSC. The message channel B1, 
B2 directed to the communication terminal equipment KE-D is switched 
between the signaling unit SA-FE and the CODEC unit CODEC with the 
assistance of an exchange switch VSC and is conducted onto the call 
controller VST, to which end a further input of the exchange switch VSC is 
connected to the call controller VST, whereby the exchange switch VSC is 
switched by the call controller VST--indicated with dot-dashed lines. 
Given a call request of the communication terminal equipment side or 
communication system side communicated by a signaling information in the 
signaling channel D, two connections are set up via the public, analog 
telephone communication network FE, or one connection is set up via the 
public telephone network FE and one connection is set up via the public 
data network IDN to the allocated terminal equipment emulation unit KPNE 
depending on the number of message channels B1 or B2. Given public 
telephone communication networks FE with digital switching equipment, as 
well as in the public digital data network IDN, the correct call setup is 
checked on the basis of the communicating telephone numbers of the calling 
communication terminal equipment KE-D. The check procedure--as described 
in FIGS. 1-3--is sequenced after the call setup. Subsequently, the 
intermediately stored, "private" dialing numbers are communicated to the 
communication system KS via the connection over the public data network 
IDN. Further signaling controls are likewise transmitted via the 
connection in the public data network IDN during the connection. 
Alternatively (not shown), a further connection, i.e. a further signaling 
path DZ, is possible via the public, analog telephone communication 
network FE for the communication of the signaling information. With a 
modem unit (not shown), the signaling information are thus matched to the 
transmission form prescribed in the public telephone communication network 
FE. For this purpose, the terminal equipment emulation unit KPNE are to be 
respectively equipped with a further signaling unit SA-FE--shown with 
broken lines--, whereby the signaling unit SAE for connection to the 
public data network IDN is omitted. Given an "in-band" communication of 
the signaling information, compression and decompression units KOMP as 
well as multiplexers MUX (not shown) are required, their functions being 
described in FIG. 3. In this version of the realization, the basic access 
unit SAE is likewise eliminated. 
Although various minor changes and modifications might be proposed by those 
skilled in the art, it will be understood that my wish is to include 
within the claims of the patent warranted hereon all such changes and 
modifications as reasonably come within my contribution to the art.