As a part of ongoing research activities at ELLemtel. an experimental system using a Universal. Communication Switch, UCX, has been constructed. The UCX is a hybrid switch with hardware-implemented switching functions for both position ("circuit") and LabeL ("packet") muLtiplexed data. Thus, it can efficientLy switch both circuit and packet trafic. The system interfaces the outside world via devices which couLd connect circuit as weLL as packet oriented terminals or networks. Such a switch wouLd be a usefuL element in a future universal telecommunication network, capable of handLing both circuit and packet information. ALSO, the technique of hybrid switching allows a gracefuL evoLution towards this future network.
BACKGROUNDTraffic in the pubLic teLecommunication networks has become more and more heterogeneous. For instance, in addition to ordinary telephone voice caLLs, we have services Like teletex, videotex and other types of data traffic which are of an inherentLy packet oriented nature. With the introduction of the Integrated Services Digital. Network, ISDN, these newer types of traffic wiLL be of increasing importance. An ISDN user, whether residentiaL and connected with the basic 28 + D access, or business and connected via a PBX with the primary rate access to the network, wiLL generate a mix of circuit and packet oriented traffic. The standard way of deaLing with this is to have a circuit switch in the access node, using circuit switching of the user B and D channels to separate circuit connections from packet connections. The circuit connections are then switched onto a circuit network, whereas packet connections, after beeing handLed by network protocol terminators, might be switched onto a separate packet network. In practice, there might be a rather Large number of different apptication specific networks the ISDN user is connected to via the access node. ALL these different networks have to be operated and maintained separateLy, they generaLLy cannot to any Large extent share the same resources in terms of transmission facilities and operations/maintenance personneL etc. Furthermore, since it is LikeLy that we with time wiLL see a change in the overall. traffic distribution towards more packet oriented applications of various types, the traditionaL approach with severaL different appLication specific networks might become very expensive as the appLications continue to diversify. In order to aLLeviate this 'situation, what is needed is a generaL or universal. network, based on transmisson and switching principLes capabLe of efficientLy handling aLL types of appLications. whether circuit or packet oriented. At the same time, this new network should be easy to introduce into todays existing network structure with its Large share of circuit type traffic. It should not be necessary to first make huge investments into completeLy new network structures, radicaLLy different from existing ones, and then move the traffic from the oLd networks to the new one, thus basicalLy scrapping the oLd equipment. It shouL...
