CA2198632A1 - Communications system and gateway for multimedia communication - Google Patents

Abstract

A reflective means (RF) in a communications system (KS1) with a broadband transmission network (KK) and connecting means (AM1, AM2) for linking subscriber stations (T1, T2) to the broadband transmission network (KK),where the reflective means (RF) reflect predetermined signals from a subscriber station (T1, T2) so that they can be passed on to another subscriber station (T1, T2), and to allow other predetermined signals to pass, e.g. for distribution services.

Description

2l98632 COl\IMUNICATIONS ~;Y5il~;~ AND GATEWAY
FOR MULTIMEDL~ COMMUNICATION

Field of the Invention The present invention concerns a co,~ unications system having a conllJIullications system coll.ylisillg a broadband tr~ncmicsion network and connecling means for colmecting subscriber stations to the broadband tr~ncmicsion 5nctwolk. The invention also concel"s a gateway for such a communications system which interfaces the co.~....l..-ic~ions system with another collllllullications system.

Desul i~)lion of the Prior Art Such a co...... l.,-ic~lions system is known from W. Kaiser "Interactive Brcadb~n-l Co.. ~ lions", Springer Publishers, Berlin, et al. 1982, pages 66 -70. In the known co.. ..~ ications system several subscribers are connecled to a central station by means of a broadband tr~ncmi~sion network, which in this n-~e is a coaxial nclwolk. The central station offers services which can be requested by the subscribers and are distributed to the subscribers. The subscribers are com~ecled to the coaxial nclwolk via com~eclion boxes and gateway nodes. This known co~-.. l-i~ations system provides seveMl channels through which the central station tr~n.cmitc the information to the subscribers. The lespeclive subscriber can select the desired channel. Individual return channelsfrom the subsclil,cr to the central station are available for an interactive dialog bcl~,en a subscriber and the central station. Direct co.. l-ic~tion belween the subscribers is not possible.

A conll"ullications system in which subscribers are connected to a broadb~nd tr~ncmi~sion network via conl-.oc~ means is also known from the prepublished patent application DE 43 29 173 Al. The subscribers of this known colnlllunications system are able to co,l,ll-ul~icate with each other. To that end a subscriber coll~ecting unit assigned to the respective subscriber contains a means for tuning to a predetermined channel via which the respective subscriber leceives information from another subscriber. The tuning to a channel takes place by means of a previously received signal whereby the respective subscriber s CO~ g unit is h~lllled of the predetermined channel.

Su~lunal~ of the Invention The task of the present invention is a low-cost facilitation of cc,~ ions belweell subscriber stations via a broadband l,a.. ~ ion network.
This task is fulfilled by a col.. uicPtions system having a broadband tr~n~mi~sion wolk and co~-Pcling means for connPcting subscriber stations to the broadband lli1.-.~...i.~sion n~lwol~, chala.;l~ ed in that the co...~ ui~ ;ons system includes a reflective means which reflects predel~lln;ll~d signals colllillg from at least one of the subsclil~l stations and coupled into the bro~b~n~ sion l~lwol~ via the associated comleclillg means.

The task of the invention is also fulfilled by a yaleway for such a COI.~ ;ons system which interfaces the co.. -irations system with ano~
co.~ ions system, characleli~ed in that the gat~;way colllplises the reflective lS means.

If the co~ tions system of the invention has a g~tew-ay to another col~------l-ir~ions system it is advantageous if the reflective means is :~tt~ d to this galeway.

Another advantage of the c~lllll-unicalions system of the invention is the amplification of the signals reflected by the reflective means through an amplifier.

Descli~tion of the Drawings The invention is described in the following by means of configuration examples in figures 1 to 7, where:

Figure 1 is a first configuration example of the co"~ u"ications system of the invention Figures 2a and 2b are two examples of frequency responses of a reflection filter, Figure 3 is a second configuration example of the coll.lllullications system of the invention with several reflection filters, Figure 4 is an example of the frequency lc~onses of the various reflection filters in figure 3, Figure 5 is a third configuration example of the co.. ~ ications system of the invention with an amplifier, Figure 6 is an example of the frequency responses of the reflection filter and of the filter precP~ing the amplifier in figure 5, and Figure 7 is a configuration example of a circulator with an amplifier colln~ct~Pd thereto.

Detailed Desc~ ion of the ~cfellcd Embo-limPnt The confi~uldlion examples use the same ,ere.~ l~ce symbols for equal or equally o~laling ele,^n~nt~.

Figure 1 illuSIlal~S the configuration example of a first co--------i-ications system KS1 with a broadband lli.n~ sion network KK, to which a first subscriber station T1 is linked via a first connPclil~g means AM1, and a second subscriber station T2 is linked via a second cc ~ Pcl;i-g means AM2. The broadband l~ sion ~ WOIk KK of the present configuration eA~ ple is a coaxial llclwolk and the comlec~ g means AM1 and AM2 are conventional anlel~l~a sockets. The subscriber stations T1 and T2 are common te...~ for sending or lcCcivhlg speech, pictures and data. The first co.. ~nic.. l;ons system KS1 is linked to a second co~ ic~ions system KS2 via a galcway UE. This gateway UE contains a gateway node UP which in the invention is preceded by a reflective means in the form of a reflection filter RF. In the present configuration examples the second cunnllullicdtions system KS2 is located outside of the building. The gateway node UP l~l~selll~ a known transition belween the first and the second col~"~lunications system. The second colllmllllic~lions system KS2 uses optical glass fibers for the ll~n~ sion of the bro~q-~lb~n-l signals. For that reason an optical/electrical signal coll~ sion takes place in the gale~dy UE.

Such an allall~elnelll of the first and the second collllllunicdlions systems KS1 and KS2 is used for example for the tr~ncmi~sion of analog video signals as described in the essay "FITL CATV: A tl~ncl~ sion system with optical amplifiers for analog TV signals" by W. Schmid et al., Electrical Co.. ~ ions, third quarter 1993, pages 248 to 259. For example, the subsclil~r stations T1 and T2 can receive cable television signals from a not illustrated central station within the second co.. ~.. -ir~ions system KS2. Other distribution and call-up services can also be provided via the described co.. ~ cations ~ ~lllS KS1 and KS2, such as for example video-on-dcl.. ~ and also by telephone. Each subsclib~r station T1 and T2 has a ~ignqlling means (set-top box) for int~.aclively ltili~ing and controlling the offered s~ ices. The ll;.~.~i...i.~sion of the signals for ~lrOllllill~ the distribution and call-up se-vices or the hl~.aclive ~ignqli7~q-tion is done within a pred~,t~ ed frequency range. This frequency range is for example 5 - 30 MHz for the hll~la~;live si~n~li7~tion and 47 - 860 MHz for the ll~ ,;on of the signals for the di~llibulion and call-up sel vices from the central station to the subscriber stations.
The frequency range which is not needed for the distribution and call-up services, e.g. above 860 MHz, can be used for a co.. ~ ir~tion belweell the subsclil~l stations inside the b~ lin~, i.e. within the first co.. ~ irdlions system KS1. To that end the reflection filter RF of the invention is co~ ed to the coaxial l~lwol~ KK in the first co.. -~-iralions system KS1. It is advantageous to install the reflection filter RF to the gate~.ay node UP. However it is also possible for the reflection filter to be col-l-rcted in a different area of the co~ nir~tionssystem KS1. This will be explained further by means of the figure 3. The reflection filter RF is configured to have a predetermined frequency range whichallows signals from the first co.. ~ ions system KS1 to cross over to the second co.. ,-icalions system KS2, and vice versa.

This frequency range can be used for the distribution and call-up services and for the i~ aclive sign~li7~tion from the subscriber stations T1 and T2 to devices inside of the second co....... u,-ic~ions system KS2. FLulllel,llore thereflection filter RF has a pledel~ llnilled frequency range in which it reflectssignals from the first co---.--~ ic~lions system KS1, i.e. signals from the subscriber stations T1 and/or T2. Due to the fact that the conventional a~llelu~a sockets used as col-l-Pct~ means couple out exclusively from one direction of the coaxial cable, and can only couple into one direction without heavily d~n"illg the l~s~;live signal level, by al.anging the reflection filter RF it is possible to pl~vide in a simple .. l~mer a co.. ,.. ..-ic~l;on b~ n the subscriber stations T1 and T2 within the frequency range in which the reflection filter RF reflects.

Figures 2a and 2b lesl)e- Iiv~:ly illustrate an example of an i(le5~li7ed curve of the reflection fflter RF. It depicts the reflection of filter RF within the r~ uell;y. In figure 2a the reflection filter RF is a low-pass filter. The reflection filter RF allows signals to pass below the limiting frequency fO and reflects signals from the first co.. ~.. i~ .,~ions system KS1 above the frequency fO. Figure 2b illu~llates the alt. ,llalive configuration of the reflection filter RF as a band-pass filter which reflects signals from the first co~ C~lions system KSl within the frequency range fX to fY. The configuration of the reflection filter RF depends on the l~ ;.yeclive application within the first collullunicalions system KS1, and the eclive a110wable r.~uel~-;y range in which reflection of the signals is not ~ ille-l.

The following desclibes an example whelein the first co.. ,-icdlions system KS1 according to figure 1 uses a reflection filter with a curve according to figure 2a, i.e. a low-pass filter. The known distribution and call-up services are .,.illed in the down~lle~l~ direction below the limiting frequency fO of the reflection filter RF. The sign~li7~tion of the subscriber stations Tl and T2 to control the call-up services also takes place below the frequency fO. Speech andpicture co"~"l~ irst;oll bclween the first subscriber station T1 and the second subscriber station T2 takes place in a frequency above fO. To that end the e-;live lli-n~ g and leceivillg parts of both subscriber stations T1 and T2 are tuned to this frequency.

A signal is now l,~l- .,.i~led from the first subscriber station T1 to the second subscriber station T2. This signal is emitted by the l,~3...~."ill~r of the first subscriber station T1 and is coupled into the coaxial cable llclwolk KK by the first ~"1~nlu socket AMl. Rec~lse of the con,le-;lion of the anl~lllla socket AM1, thet.~n.~ d signal of the first subscriber station T1 is coupled into the coaxial cable ll~two~ KK in the direction of the second co""----,-i~ ions system KS2.
Stray signals oc;ullillg during the coupling of the signal coming from the firstsubscriber station T1 in the direction of the second a,ltemla socket AM2 can be ignored bec~.lse of the strong directional effect of the first a..l~;"na socket AMl.
The signal which is coupled into the coaxial cable ll~lwo~k KK is reflected by the reflection filter RF to the first co~ ic~ions system, and is tr~n.cmined via thecoaxial cable KK to the second a"t~ mla socket AM2, where the signal is coupled out and passed on to the second s~sclil~r station T2. The second subscriber station T2 ,~cei~es and ~,ocesses the signal coming from first subscriber station T1. The tr~ncmicsion of a signal from the second subscriber station T2 to the first subscriber station T1 via the coaxial cable KK by means of reflection from the reflection filter RF takes place in a co"csponding ,llaml~r.

It is also possible to establish different IlAl,~",i~ion frequencies for the two subscriber stations T1 and T2. The r~ceiver in the Icspcclive lcceiving station T1 or T2 must then be tuned to the les~eclive ll;.n.~lllill;l~g frequency of the other subscriber station. This can be made possible for example by a signal emitted previously by the ll~n.~"~ g subsclibe. station to the rcceivillg subscriber station, informing it of the respective tr~n.cmi~sion frequency of the receiving subscriber station.

Figure 3 illusl,~tes a second configuration example of the co~ icalions system of the invention with several reflection filters located in dirrel~nl areas of the coaxial cable network KK. Figure 3 depicts the first co.. i-ic~tions system KSl with the coaxial cable network KK, to which the first subscriber station T1 is linked via the first ~ e~ socket AMl, the second subscriber station T2 is linkedvia the second ~ socket AM2, a third subscriber station T3 is linked via a third ~ socket AM3, and a fourth subscriber station T4 is linked via a fourth ~.~t~ .. ~ socket AM4. As depicted by the first configuration example in figure 1, the first co~ -ic~tions system KSl changes over to the second co---~ a~tions system KS2 via the gal~w~y node UP. A first reflection filter RFl is located in this gat~ y node UP. A second reflection filter RF2 is located belweell the first ~ t~ socket AMl and the second ~ r~ socket AM2, and a third reflection filter RF3 is located belwæll the second anl~ d socket AM2 and the third a,~ a socket AM3. By establishing the fl~luel~cy ranges in which the reflection filters RP1, RF2 and RF3 reflect signals, the subscriber stations Tl, ..., T4 can be combined into groups among which co.. ~ alion is possible.

Figure 4 illu~llatt;s an example of the fl~ ~luel~;y ~e~Ol ses of reflection filters RFl, RF2 and RF3 in figure 3. In the three coordination sy~l~"~s the reflection of the dirr~le"l reflection filters is depicted above the frequency. As in the first configuration example in figure 1, the first reflection filter RFl is a low-pass filter. The reflection filter RFl allows signals below a frequency fl to pass, and reflects the signals above the frequency fl. The second reflection filter RF2 is a band-pass filter which reflects signals in a frequency range f2 to f3. The third reflection filter RF3 is also a band-pass filter which reflects signals in a frequency range f4 to f5. In the present example fl < f4 < f2 < f5 < f3. In this configuration example, the subscriber stations ll~l)sn~il on dirr~ ~;"l frequencies.
This means that the receivers of the subscriber stations which participate in the 219863~

co.. ~ Ation must be tuned to these dirrelellt frequenciés. The first subscriber station Tl tr~n.Ymitc on a frequency fT1, where fl < fT1 < f4. The second subscriber station T2 ~ Y~ Y on a frequency fr2, where f4 < fT2 < f2. The third subscriber station T3 tr~nYmitY on a frequency fT3, where f2 < fT3 < f5.
The fourth subscriber station T4 ll~ .--ilY on a frequency fT4, where fS < fT4 <f3.

The first subsclil~r station Tl in the present configuration example Y a signal on the frequency frl. This signal is coupled into the coaxial cable llelwolk KK by the first ~ q socket AMl, and is reflected by the f~st reflection filter RFl. The reflected signal is allowed to pass by the second reflection filter RF2; it is coupled out of the coaxial cable nelwolk by the second al~ llla socket AM2 and passed on to the second subsc,il~r station T2. In addition, the reflected signal is also allowed to pass by the third reflection filter RF3 and is coupled out of the coaxial cable nelwoll~ KK by the third allt. mla socket AM3 for l,assill~, on to the third subsclil~l station T3, and also by thefourth ~ socket AM4 for passillg on to the fourth s~sclil~r station T4. A
signal ~ ~ by the subscriber station T1 on frequency fTl is tllclefole èceived by all the subscriber stations. The second subscriber station T2 tr~nYmits a signal on rl~luell~ fr2, which is coupled into the coaxial cable network KK bythe second alllel~lla socket AM2. This signal is allowed to pass by the second reflection filter RF2, it is howe~,l reflected by the first reflection filter RFl. The third reflection filter RF3 also blocks this signal, which is ll;~n~ ed by the second subscriber station T2, so that the signal is exclusively disllibul~d by the second subscriber station T2 to the first subscflbel station Tl. A signal tr~n~mittPd by the third subscriber station T3 on frequency f3 is coupled into the coaxial cable n~,lwolk KK by the third alllemla socket AM3, and is reflected by the third reflection filter R~3. This reflected signal is then coupled out of the coaxial cable l~lwolk KK by the fourth ~ nl~A socket AM4 and passed on to the fourth subscriber station T4. A signal IlAIl~llliU~rl by the fourth subscriber station T4 on frequency fT4 is coupled into the coaxial cable nclwolh KK by the fourth alllemla socket AM4; it is allowed to pass by the third reflection filter RF3 and is reflected by the second reflection filter RF2. This reflected signal is then coupled out of the coaxial cable nclwolk KK by the second antenna socket AM2 and passed on to the second subscriber station T2. The signal from the fourth subscriber station T4, which is reflected by the second reflection filter RF2, is allowed to pass by the third reflection filter RF3 and is ~.1bsc4uently coupled out of the coaxial cable llclwol~ KK by the third ~ socket AM3 and passed on to the third subscriber station T3.

It is an advantage to use tunable filters as reflection filters in the first co,~ ralions system KSl, e.g. LC low-pass filters with varactor diodes as the variable capaci~-~cc. The frequency ranges in which the lespeclivc reflection filter reflects signals can then be adjusted by the subscriber stations Tl, ..., T4.
For c~ le by means of a key stroke in a subscriber station, a central control means (not illustrated) inside the first col~,....nications system KSl can be i,~.med with which other subscriber stations a co---.--~l-ir~ion should be enabled.
The central control means then tunes the reflection filter in a way so that the desired co--..--~ iration can be carried out.

Figure 5 ill~ t~s a third configuration example of the co.. ~ ;calions system of the invention with an amplifier for amplifying the signa1s reflected by the reflection filter. Most of the first co~ ic~tions system KSl in figure 5 coll~s~onds to the first co...~ r~tions system KSl in figure l. In the present third configuration example, in addition to the first co.. ~-ir"lions system KSl of figure l, a further col~n~lil~g means AMV for linking an amplifier V to amplify the signals reflected by the reflective means RF, is located ~lw~en the reflection filter RF at the gat~ay node UP and the first anlelma socket AMl for linking thefirst subscriber station Tl to the coaxial cable l~lwo.~ KK.
The amplifier V is able to reduce the d~l~ing of the entire tr~n~mi.~sion path ell the subscriber stations Tl and T2.

The further conl-~cl;,-g means AMV in the present configuration example is a bidi~ ional means for coupling signals in both directions in and out of thecoaxial cable n~lwo.k KK. A further filter VF is located bclwcen the further col-l~l;.~g means AMV and the amplifier V. This further filter VF is needed to S filter out the signals for the distribution and call-up services and the h~ aclive ~ignqli7qtion of subscriber stations T1 and T2, and only allows those signals topass which are amplified by amplifier V for the co.. l~ica~ion bclweell the subscriber stations T1 and T2 within the co---~ ni~ ons system KS1. Therefore the further filter VF is preferably a complelllel~ filter to the reflection filter RF.

Figure 6 illustrates an example of the fi~-luen;y l~onses of reflection filter RF and the filter VF which plecedes amplifier V in figure 5. Both coordination s~lt;ms in-licate the reflection of the 1~ ~e~;liv~; filter above the frequency. The reflection filter RF has a low-pass chal~cl~l and allows all frequencies below the li.-~ p r~ uell~;y fO to pass, and reflects all r,~luel~cies above this li...il;~ frequency fO. The further filter VF has a high-pass character and reflects all signals which are below the limiting frequency fO. The signals above the limiting frequency fO are allowed to pass by the further filter VF.

The in- and out-coupling by the further conl-.~clil~g means AMV of the signals to be amplified takes place via the very same cable. For that reason a bidile~ liollal tr~n~mi~.sion takes place in the cable bclween the amplifier V and the further conl-~cl;l~ means AMV. To enable the use of conventional amplifiers with a Scpdl~lc input and output for amplifying the reflected signals, it is advantageous to switch a circulator Z bcl~n the further filter VF and the amplifier V. Such a circulator Z is known for example from Meinke/Gnn~ h, Pocket Book of High-Frequency Technology, 4th. Edition, Chapter I 35. The circulator has three or more connections which may either be input or output. A
signal can only flow in one direction within the circulator. In the present configuration example the circulator has three connections 1, 2 and 3. Connection 1 is linked to the further filter VF, connection 2 to the input VE of amplifier V, and co~ c~;lion 3 to the output VA of amplifier V. The signal which is reflectedby the reflection filter RF and is coupled out of the coaxial cable ll~lwo~l~ KK by the further CO~ fcl;i-g means AMV, is received by the col~neclion 1 of circulator Z, which passes it on in the direction of connection 2. The signal leaves the circulator Z from the connection 2 and is supplied through input VE to the amplifier V, where it is a nplified. The amplified signal is passed via output VA
of the amplifier V to the com~eclion 3 of circulator Z, which in turn directs it to its connection 1. The amplified signal is allowed to pass by the further filter VF
and is ~se luently coupled into the coaxial cable l.etwolk KK by the further co~---Pc~ means AMV.

Care must be taken when using the circulator that its opeialing frequency range is larger than the amplification bandwidth of the amplifier. Otherwise it is possible for a feedbaclr of the amplified signal to occur via the direct link belwecn comleclion 3 and comleclion 2 of circulator Z. The amplification al,angcllle could then begin to oscillate.

The use of the reflection filters for co~ on within the CO~ l;OnS system KS1, particularly the reflection filters which can be tuned by the subsclit~r stations, results in new possibilities for the use of protocols (e.g.
CSMA, Token Ring, etc.) for tr~n~mi~sion of the signals, becallse the l,~ll~....... i~cion characle.ii,lics of the broadb~ntl tran.~mi.~sion llctwoll~ can be controlled.

Using a packet t~ ion via the broadb~n(3 hi.l~ sion llc~wolk allows an identific~tion to be placed in the header, which il~dic~es to a filterwllctLer it should let the following packets to pass or to reflect them.

The use of the present invention is not at all limited to its use in a co... l-ic~ions system with a coaxial cable ne~wolk as the tran~mi~sion medium.
The invention can also be used in an optical network for example. In that case 219~632 dielectric filters or Fabry-Poirot filters are available for example as the reflection means.

Claims (10)

What is claimed is:

1. A communications system (KS1) comprising - a broadband transmission network (KK) and - connecting means (AM1, ..., AM4) for connecting subscriber stations (T1, ..., T4) to the broadband transmission network (KK), characterized in that the communications system (KS1) includes a reflective means (RF) which reflects predetermined signals coming from at least one of the subscriber stations (T1, ..., T4) and coupled into the broadband transmission network (KK) via the associated connecting means (AM1, ..., AM4).

2. A communications system as claimed in claim 1, characterized in that it comprises a gateway node (UP) to another communications system (KS2), and that the reflective means (RF) is provided at said gateway node (UP).

3. A communications system as claimed in claim 1, characterized in that it includes a plurality of reflective means (RF1, ..., RF3), and that said plurality of reflective means (RF1, ..., RF3) are provided at different points of the communications systems (KS1).

4. A communications system as claimed in claim 1, characterized in that the reflective means (RF) is a first filter having a frequency range in which it reflects signals and which is tunable from at least one of the subscriber stations (T1, ..., T4).

5. A communications system as claimed in claim 1, characterized in that it comprises an amplifier (V) for amplifying the signals reflected from thereflective means (RP).

6. A communications system as claimed in claim 5, characterized in that between the reflective means (RF) and the amplifier (V) a circulator (Z) isprovided, via which the reflected signals are fed to the amplifier (V).

7. A communications system as claimed in claim 5, characterized in that a second filter (VF) is connected ahead of the amplifier (V).

8. A communications system as claimed in claim 7, characterized in that the second filter (VF) is complimentary to the reflective means (RF), so that the reflected signals are passed and the signals not reflected are blocked.

9. A communications system as claimed in claim 1, characterized in that the broadband transmission network (KK) is a coaxial network, and that the connecting means (AM1, ..., AM4) are antenna sockets.

10. A gateway (ÜE) for a communications system (KS1) having a broadband transmission network (KK) and connecting means (AM1, ..., AM4) for connecting subscriber stations (T1, ..., T4) to the broadband transmission network (KK), wherein the communications system (KS1) includes a reflective means (RF) which reflects predetermined signals coming from at least one of the subscriber stations (T1, ..., T4) and coupled into the broadband transmission network (KK) via the associated connecting means (AM1, ..., AM4); wherein the gateway interfaces the communications system (KS1) with another communications system (KS2), characterized in that the gateway (ÜE) comprises the reflective means (RF) of the communications system.