Communications system with load sharing communications interface

A number of narrow band networks are interconnected via a broad band network having a signalling protocol different from that or those of the narrow band networks. Calls between terminals associated with first and second narrow band networks are set up by the selection by a call server of a phantom trunk between the networks. This phantom trunk is used to relay the addresses of the two terminals to be connected. By recognizing that two connection requests have been received at opposite ends of the same phantom trunk, a processor in the second network determines that a connection between the terminals via the broad band network is required. Selection of the phantom trunk and sending of address messages is effected via a selected one of a number of identical connection brokers coupled to the call server. The workload of the call server is shared among the connection brokers coupled thereto.

This invention relates to arrangements and methods for establishing narrow 
band connections over a broad band network. 
BACKGROUND OF THE INVENTION 
Digital telecommunication systems are currently evolving from the so-called 
first generation of narrow band networks, which are primarily directed to 
the handling of voice and data traffic, to a new generation of broad band 
networks which can carry a full range of multimedia services. Within a 
typical narrow band network, traffic and control information are carried 
in 64 kbit/s bearer channels using time division multiplexing (TDM). 
Routing to establish communications channels between end users is 
determined by the network nodes each of which is provided with a set of 
routing tables so as to set up an optimum route for each communication. 
The new broad band networks however are asynchronous in nature and carry 
traffic in the form of packets of cells each of which incorporates a 
header containing information whereby the packet is routed by the 
asynchronous switching fabric. Thus, if narrow band network traffic is to 
be carried over a broad band network, there is a problem of interfacing 
the narrow band circuit switched environment with the broad band packet 
environment. Further, there are differences in signalling protocols 
between the two types of network, and there is thus a need for a mechanism 
for carrying the narrow band signalling traffic over the broad band 
network such that the narrow band signalling remains fully functional. 
It will be appreciated that there is currently a large investment in narrow 
band network systems and there is thus a requirement for interworking 
between the two types of network such that narrow band traffic can be 
transported over a broad band network so as to provide end to end 
connectivity between narrow band network terminals. To achieve this 
interworking, it is necessary to adapt the narrow band traffic for 
transmission over the broad band network and to ensure that the narrow 
band signalling messages are accommodated. 
Our co-pending application Ser. No. 08-907521 entitled "System and method 
for establishing a communication connection" describes an arrangement and 
method in which a connection broker acts as a single point of contact for 
the provision of connection services to a call server in a 
telecommunications network and orchestrates interconnection of first and 
second narrow band networks. Every request relating to a connection 
involving any link on the node is constrained to pass through this single 
entity. This arrangement provides an effective method of interconnecting 
the narrow band networks. However, we have found that, under conditions of 
heavy traffic demand, the performance and scale of the node can be limited 
by the ability of the connection broker to handle all the interactions 
with the call server. In particular the speed with which a connection may 
be established and the number of connection requests that may be handled 
simultaneously are both limited to what can be achieved by a single, 
monolithic connection broker. Furthermore, as the connection broker 
represents a single critical item failure of which completely prevents the 
node from performing its function of establishing communication 
connections, it is desirable to provide a standby device that can be 
switched in to service in the event of a failure. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved system and method 
for transporting narrow band traffic over a broad band network. 
According to one aspect of the invention there is provided a method of 
establishing a narrow band communication channel across a broad band 
network, from a first terminal associated with a first narrow band network 
node to a second terminal associated with a second narrow band network 
node, the broad band network having a signalling protocol dissimilar to 
that or those provided in the respective narrow band nodes, each said 
narrow band node incorporating a call server having a plurality of 
substantially identical connection brokers coupled thereto, the method 
comprising: 
at the first narrow band node and on a first communication circuit, 
receiving an incoming call request from the first terminal, the incoming 
call request containing an address of the first terminal and a destination 
address associated with the second terminal; 
selecting via a said connection broker at the first node a phantom trunk 
different from the first communication circuit, the phantom trunk having a 
circuit identity and being arranged to support a narrow band communication 
between the first and second nodes; 
in a first message, sending the destination address and the circuit 
identity of the phantom trunk from the first node to the second node; 
in a second message, sending the circuit identity and the address of the 
first terminal to the second node; 
identifying via a said connection broker at the second node the presence of 
the circuit identity in both the first and the second message whereby to 
establish that the requested communication connection is between the first 
and second terminals; and 
establishing the communication connection between the first and second 
terminals through the broad band network. 
According to another aspect of the invention there is provided a 
telecommunications system comprising a broad band network and a plurality 
of narrow band network each having a respective node interfaced with said 
broad band network whereby the narrow band networks are interconnected via 
the broad band network, the broad band network having a signalling 
protocol dissimilar to that or those provided in the respective narrow 
band networks, the telecommunications system being arranged to establish a 
communication connection between a calling communication device in a first 
said narrow band network and a receiving communication device in a second 
said narrow band network; wherein each said narrow band node incorporates 
a call server having a plurality of substantially identical connection 
brokers coupled thereto and selection means for means for selecting a said 
connection broker to orchestrate a said interconnection; 
wherein each said call server is responsive to a request message containing 
the address of the calling communication device and a destination address 
associated with the receiving communication device so as to identify a 
circuit identity associated with a first communication circuit used to 
send the call request to the call server; 
wherein each said connection broker is, on selection by the call server, 
arranged to select a phantom trunk different from the first communication 
circuit, the phantom trunk having a circuit identity and being arranged to 
support a narrow band communication between the first and second narrow 
band networks, the connection broker having means for sending, in a first 
message, the destination address and the circuit identity from the first 
narrow band network to the second narrow band network and for sending, in 
a second message, the circuit identity and the address of the calling 
communication device to the second narrow band network; and 
wherein each receiving narrow band node has means for identifying the 
presence of the circuit identity in both the first and second message to 
establish that the communication connection is between the calling 
communication device and the receiving communication device whereby to 
establish the communication through the broad band network. 
According to a further aspect of the invention there is provided a narrow 
band telecommunications network node adapted to interface with a broad 
band network whereby to communicate with one or more similar narrow band 
nodes via communications channels established over the broad band network, 
said narrow band node comprising a call server having a plurality of 
substantially identical connection brokers coupled thereto and selection 
means for means for selecting a said connection broker to orchestrate a 
said interconnection with a similar node; 
wherein said call server is responsive to a request message containing the 
address of the calling communication device and a destination address 
associated with the receiving communication device so as to identify a 
circuit identity associated with a first communication circuit used to 
send the call request to the call server; wherein each said connection 
broker is, on selection by the call server, arranged to select a phantom 
trunk different from the first communication circuit, the phantom trunk 
having a circuit identity and being arranged to support a narrow band 
communication between the node and the similar node, the connection broker 
having means for sending, in a first message, the destination address and 
the circuit identity from the first narrow band network to the second 
narrow band network and for sending, in a second message, the circuit 
identity and the address of the calling communication device to the 
similar node whereby to establish the communication through the broad band 
network. 
In our arrangement, we provide, multiple identical clones of the connection 
broker in each node, the connection broker clones being distributed on 
separate processing elements and simultaneously active. Each connection 
broker is able to process call server requests relating to connections 
involving any link on any network adaptor in the node. Each connection 
broker operates on its own processing element independently of the other 
connection brokers and communicates with the call server via its own 
dedicated NCI signalling channel which is not shared with any other clone 
or function. The call server has equal access to all connection broker 
clones and is free to direct connection requests to any one clone of its 
choosing. It is also possible for a single connection to be set-up, 
modified, and released via different connection broker clones. Each 
connection broker clone is provisioned with its own identical copy of the 
terminal number database, but holds no dynamic status information about 
links on the node. No data is exchanged between the connection broker 
clones of any one node. 
By this selective use of a number of connection brokers at each narrow band 
node, the volume of fabric control transactions may be evenly shared over 
the total connection broker processing capacity provided by the sum of all 
the processing elements available, regardless of the distribution of 
activity over network adaptors. Full access by the call server to 
manipulate connections involving all links on all network adaptors is 
maintained in the event of failure of one or more connection broker 
processing elements. Further, the functionality of the call server may be 
readily distributed thus avoiding any risk of a bottleneck in the 
communications between a connection broker and that call server thus 
allowing the construction of very large nodes handling high volumes of 
connection activity.

Referring first to FIG. 1 which is introduced for explanatory purposes, 
this illustrates a schematic view of a narrow band communications system 
node 10. 
A number of subscriber terminals 12, such as landline telephones or modems, 
are coupled, typically, to a plurality of line interfaces 14 (although 
only one need be supplied for an operational system). The line interfaces 
14 are each connected to a switching fabric 16 that is arranged to route 
an input of the switching fabric 16 to an appropriate output thereof, as 
will readily be appreciated. The line interfaces 14 are also coupled, 
usually on an individual basis, to a call server 18 arranged to administer 
and control, for example, the set-up and rear-down of calls across the 
narrow band network 10. The call server 18 is further coupled to the 
switching fabric 6. A trunk signalling interface 20, that acts to decode 
and interpret signalling schemes used within the narrow band network 10, 
is coupled between the call server 18 and the switching fabric 16. Output 
from the switching fabric 16 are coupled to a plurality of trunk 
interfaces 22 (although only one need be supplied for an operational 
system). The trunk interfaces 22 are further coupled to secondary 
exchanges 26, such as PBXs or BSSs, within the narrow band network 10. 
As will be appreciated, the term "subscriber terminal" is used merely to 
describe a particular endpoint connection for a line or trunk interface. 
User information (traffic) 28-30 enters the narrow band infrastructure via 
line interfaces 14 or trunk interfaces 22. Control information from 
individual subscribers enters via the line interfaces 14, whereas control 
information, i.e. inter-node signalling from connected trunked networks 
(e.g. the secondary exchanges 26) can enter either via the same trunks as 
the traffic 30 or through the use of dedicated channel resources (not 
shown). The call server 18 processes incoming call requests and selects an 
appropriate outgoing trunk or line, as will readily be appreciated. More 
particularly, the call server 18 (through the switching fabric 16) 
controls the connection of specific lines to specific trunks across 
through the use of fabric control messages 32 that specify the making and 
breaking of connections between subscriber terminals 12. 
While most calls in narrow band systems are two-way, it is helpful to 
introduce, at this time, the nomenclature associated with one-way 
connections, namely the connection (TA, TB) refers to the one-way 
connection from terminal TA to terminal TB while (TB, TA) refers to a 
complementary (or independent supported) connection in the reverse 
direction. 
Turning now to FIG. 2, there is shown a block diagram, in accordance with a 
preferred embodiment of the present invention, of the interconnections of 
subscriber terminals between narrow band and broadband networks. In this 
figure, a broadband network generally indicated as 41 is used to transport 
the user and/or control information. To facilitate an understanding of the 
architectural differences between the prior art and the preferred 
embodiment of the present invention, common infrastructure is labelled 
with identical reference numerals. 
At a first narrow band network node 40, a number of subscriber terminals, 
such as landline telephones or modems (not shown for the sake of clarity), 
are coupled, typically, to a plurality of line interfaces 14-15 (although 
only one need be supplied for an operational system) of a narrow band 
system. The line interfaces 14-15 are connected to a switching fabric 16 
that is arranged to route an input of the switching fabric 16 to an 
appropriate output thereof. The line interfaces 14-15 are also coupled 
(usually on an individual basis) to a call server 18 arranged to 
administer and control, for example, the set-up and tear-down of calls 
across the narrow band network. The call server is coupled to a memory 19 
that is arranged to store, amongst other things, circuit indicators codes 
(CICs) associated with both real trunks and phantom trunks. More 
particularly, the memory can record a "busy" or "vacant" status against 
each of these real or phantom trunks. The call server 18 is further 
coupled to a plurality of substantially identical connection brokers 44, 
which in turn are coupled to the switching fabric 18 via bus 45. The 
connection brokers 44 can be considered as clones each of which operates 
in an identical manner to handle narrow band connections across the 
broadband network. The use of the connection brokers 44 represents a 
significant departure in the system architecture of the preferred 
embodiment of the present invention from that of prior art FIG. 1. A trunk 
signalling interface 20, arranged to act to decode and interpret 
signalling schemes used within the narrow band network, is coupled between 
the call server 18 and the switching fabric 16. Outputs from the switching 
fabric 16 are coupled to a plurality of trunk interfaces 22-24, (although 
only one need be supplied for an operational system. The plurality of 
trunk interfaces are again coupled to secondary exchanges(not shown for 
the sake of clarity), such as PBXs or BSSs, within the narrow band 
network. 
The switching fabric 16 is further coupled to a first trunk network adaptor 
46 that allows interconnection and inter-operability of the narrow band 
network with a broadband network 48 implemented, for example, as 
asynchronous transmission mode (ATM) operation. More particularly, 
interconnection of the trunk network adaptor 46 is through a broadband 
network edge switch 50, that is coupled to and hence controlled by the 
connection broker clones 44 by control lines 51. The combined function of 
the trunk network adaptor 46 and the broadband network edge switch 50 will 
be described subsequently. Other narrow band networks 52-54 are coupled, 
in a similar fashion, to the broadband network 48 via respective trunk 
network adaptors 58-60 and broadband network edge switches 60-62. As will 
be appreciated, other narrow band networks 52-54 will be realised through 
infrastructure architectures similar to that described immediately above. 
The broadband network 48 is further coupled to a second node 64, typically 
a different network, which is also responsive to the connection broker 
clones 44 via connection 65. The second node 64 is also arranged to be in 
communication with the trunk signalling interface 20 via communications 
bus 67. Additionally, as will be understood, the broadband network may 
support point-to-point broadband communications, such as video telephony 
between subscriber terminals (not shown). 
As will be appreciated, the terms node and exchange are interchangeable and 
are used to describe stand-alone networks, e.g. distinct narrow band 
networks operated by different operators. 
According to the preferred embodiment of the present invention, narrow band 
signalling within the communication system, generally, is controlled by 
the call server 18, while broadband signalling, i.e. signalling that may 
be sent between different narrow band networks 52-54 via the intermediate 
broadband network 48, is controlled by the connection broker clones 44. 
Consequently, the call server 18 is not itself concerned with broadband 
signalling interconnection and operation. 
According to the present invention, therefore, the narrow band line 
interfaces 14-15, trunk interfaces 22-24 and switching fabric 16 are 
supplemented by a broadband network 48 and trunk (i.e. narrow 
band/broadband) network adaptors 46, 56-58 that act to provide gateway 
functionality. Specifically, the trunk network adaptors 46, 56-58 perform 
traffic (user information) inter-networking functions and signalling 
(control information) encapsulation, with the signalling ultimately 
relayed back to a call server 18. 
A principal feature of a preferred embodiment of the present invention is 
the new function performed by the connection broker clones 44, which 
function is used to provide a uniform connection abstraction 66 for the 
call server 18, independent of whether the connection crosses (and is 
retained entirely within) the narrow band network or the broadband 
network, or in the case where the connection crosses both the narrow band 
and broadband networks. This necessitates use of a uniform terminal name 
space identity (i.e. a standardised address format) for all terminals 
across the entire communication system, i.e. both narrow band and 
broadband systems. 
For a narrow band to narrow band connection in a single narrow band network 
(e.g. owned by a particular operator), each connection broker clone 44 
passes the connection messages to the switching fabric 16 of the narrow 
band network then establishes the connection in accordance with known 
techniques, and does not utilise the broadband network 48. For a broadband 
to broadband connection, each connection broker clone 44 instructs the 
broadband network and/or trunk network adaptors 46, 56-58 to make or break 
a call connection, and therefore mimics standard broadband operation. 
For a narrow band to broadband connection, however, both actions must be 
performed contemporaneously. Specifically, each connection broker clone 44 
both instructs the switching fabric 16, through the call server 18 in the 
narrow band network, to hold open a routing path for a call and negotiates 
with a trunk network adaptor 46 of the broadband network for the 
allocation of a suitable channel resource. Once both paths have been 
determined, the respective connection broker clones 44 send dedicated 
messages to the switching fabric 16 and the trunk network adaptor 46 to 
establish the connection. This achieves the connection abstraction as seen 
by the call server. 
In an operational communication system, compatibility between operators is 
desirable, if not essential. As such, establishing an interconnection 
(usually termed a "gateway"), between different "mixed nodes" is a 
significant issue. In this context, the term "mixed nodes" is used to 
describe different networks, operated by different operators, that each 
typically have switchable narrow band/broadband capabilities and defined 
service capabilities. However, intermediate broadband networks may not be 
able to support these services (or any service of similar nature) not be 
to interpret narrow band control channel signalling required to set up a 
define narrow band services, i.e. there are different signalling protocols 
between the different adjacent exchanges. Therefore, a preferred 
embodiment of the present invention provides a mechanism for establishing 
interconnection of narrow band networks through an intermediate broadband 
network to assimilate the narrow band control channel signalling regimes 
and format. In this case, the interconnection of the narrow band networks 
(through the intermediate broadband network 48) requires the functional 
coordination of separate call servers and connection brokers located in 
the respective networks. 
Turning now to FIG. 3, an abstract architecture for a connection broker 
clone 44 of a preferred embodiment of the present invention is shown. 
Although a hardware implementation is dependent upon (and hence determined 
by) by specific requirements, a typical implementation extends the 
capabilities of an existing, prior art narrow band telephone exchange. By 
way of example and explanation only, the connection broker clone 44 of 
FIG. 3 contains resolution intelligence 68 that typically realised as a 
processor. The function of the resolution intelligence 68 will be 
described subsequently. A terminal number data base 69 that maps the 
uniform terminal numbers onto network-specific location addresses is 
coupled to the resolution intelligence 68. A time division multiplexed 
(TDM) switch fabric adaptor 70 (in the case of a TDM narrow band system) 
provides protocol conversion between the resolution intelligence 68 (via a 
client orientated interface port 71) and a TDM switching fabric interface 
72 (analogous to the switching fabric 16 of FIG. 2). Typically, a 
dedicated connection protocol 72 is utilised between the resolution 
intelligence 68 and the TDM switching fabric adaptor 70, although this 
need not be the case. A broadband network adaptor 73 is also coupled 
through the client interface port 71 to the resolution intelligence 68, 
with communication between the resolution intelligence 68 and broadband 
network adaptor 73 typically based on the dedicated connection protocol 
72. The broadband network adaptor is analogous to the trunk network 
adaptor 46 of FIG. 2. Other adaptors 74 for ancillary networks or services 
may also be coupled to the resolution intelligence 68 via the client 
interface 71. The broadband network adaptor 73 and the other adaptors 74 
will accordingly be respectively coupled to the broadband network edge 
switch 50 via control lines 51 or appropriate communication resources 75. 
The resolution intelligence is also coupled to a server interface port 76 
that provides an interconnection facility, via lines 66, to call server 
18. The server interface port is also coupled through a secondary port 77 
(termed a "peer connection broker server interface") arranged to 
interconnect the resolution intelligence 68 of the connection broker 44 to 
another connection broker as shown in FIG. 4. Note that, for clarity, only 
one connection broker clone and only one network adaptor are shown in each 
node in FIG. 4. Similarly, the client interface port 71 (FIG. 3) is also 
coupled to a ternary port 78 termed a "peer connection broker client 
interface") arranged to couple the resolution intelligence 68 of the 
connection broker 44 to a subscriber terminal principally connected to 
another connection broker (as shown in FIG. 4). 
Prior art telephone exchanges typically have a distributed processing 
architecture with multiple fault-tolerant processors and an interprocessor 
communications facility, while the switching fabric may be supported by a 
special purpose processor, as will be understood. 
In the preferred embodiment of the present invention, each connection 
broker clone 44 supports a set of real-time processes within a single 
fault tolerant processor, i.e. within the resolution intelligence 68. The 
inter-processor communications facility (supported by the dedicated 
connection protocols 72) of the connection broker clone 44 is used to 
communicate with the switching fabric 16 and the call server 18. As has 
previously been described, each connection broker clone may use the 
interprocessor communications facility to access the broadband interfaces 
on the trunk network adaptors. However, as communication networks evolve 
to be more broadband orientated, the call server 18 and the associated 
connection broker clones 44 may reside on processors with only broadband 
interfaces that are connected directly to the broadband network 48. The 
narrow band connection fabric would then be provided with a broadband 
control interface. 
A system architecture and associated mechanism by which a preferred 
embodiment of the present invention connects subscriber terminals across 
an intermediate broadband network is shown in FIG. 4. In order for a data 
call, for example, to be supported between terminal TA (e.g. a land line 
telephone identified by reference numeral 12) on a first node 40 and 
terminal TB (e.g. a modem within a computer, identified by reference 
numeral 85) on second node 52, the preferred embodiment of the present 
invention utilises the existence of a common signalling relation between 
both narrow band nodes. It is the establishment of a common narrow band 
signalling link (or resource) 79 and protocol that is essential to the 
system of the present invention; the broadband network need only have the 
capability of relaying traffic between the narrow band networks. The 
broadband network consequently appears as a transparent channel resource 
since no modification of the narrow band traffic is required. 
The first node 40 and the second node 52 both contain trunk network 
adaptors 46, 56, connection broker clones 44 and 80, and call servers 18 
and 81 which are coupled permanently together over the common narrow band 
signalling link 79 that provides a plurality of virtual (or "phantom") 
traffic trunks. The call servers 18 and 81 are therefore potentially 
connected to other call servers (not shown) of different narrow band 
networks (not shown) by additional signalling resources 82-83. The call 
servers 18 and 81 are respectively coupled to connection broker clones 44 
and 80, which in turn are coupled to respective trunk network adaptors 46 
and 56. The trunk network adaptors 46 and 56 are coupled together through 
a broadband network 48, while the connection broker clones 44 and 80 are 
interconnected by a virtual link 84. Terminal TA 12 is coupled to trunk 
network adaptor 46, while terminal TB 85 is coupled to trunk network 
adaptor 56. 
In a preferred embodiment of the present invention, the signalling link 79 
is realised a permanent connection between the two call servers 18 and 81, 
although this connection may be dynamically assigned or provided by a 
radio frequency link. Indeed, in a scenario where the first node 40 and 
second node 52 pre-exist as narrow band gateway nodes between network A 
and network B, real narrow band E1 trunks already exist between these two 
exchanges and, as such, signalling can be carried in a time-slot of those 
E1 trunks, i.e. conventionally in time-slot sixteen. Alternatively, in a 
North American-based system, the two different exchanges could be 
connected to a common STP network. Once the broadband network 48 is in 
place, however, supplementary signalling bandwidth can be supported by 
establishing links through the broadband network. Nonetheless, these 
multiple paths represent a single logical "signalling relation" by which 
SS7 user parts (i.e. the call servers) are able to communicate and 
interact. 
The virtual link 84 established between the two connection broker clones 44 
and 80 offers a permanent "ability to communicate". In a preferred 
embodiment, the virtual link 84 therefore takes the form of an ATM virtual 
channel connection. However, it is also possible for an SS7 network to be 
used as the bearer for this communication, e.g. in relation to a TCAP 
application. The communication links between the connection broker clones 
44 and 80 and both the network adaptors 46, 56 and the switching fabrics 
are also permanent, while connections that carry traffic between the 
network adaptors 46, 56 and the interconnected subscriber terminals TA 12, 
85 are made and broken for the duration of a specific call or for 
particular portions of those calls. 
The system of the preferred embodiment of the present invention operates by 
virtue of the provisions of at least two (and probably tens to thousands 
of) assignable signalling channel resources or "phantom trunks" between 
the respective switching fabrics, principally residing between the 
respective calls servers 18 and 81 and respective connection broker clones 
44 and 80. The nodes then utilise narrow band signalling to simulate the 
presence of virtual (or "phantom") terminals at either node. The preferred 
embodiment of the present invention considers that these phantom trunks 
are dedicated to a single node and, as such, only allow the formation of a 
call in one direction from the first node 40 to the second node 52 or vice 
versa. Thus, a phantom route between the two nodes consists of two 
undesirable effects which could otherwise occur if the same phantom trunk 
was seized by each node trunk are prevented. Beneficially, the phantom 
trunks do not tie up real communication resources that exist between the 
respective narrow band networks. 
Referring now to FIG. 5, this illustrates the configuration of connection 
broker clones within a narrow band node. As shown, each connection broker 
44 is associated with a respective processing element 144, a terminal 
number database 145 and a network adaptor 56. A mesh interconnect is 
provided between the connection brokers and the network adaptors such that 
each connection broker can use any network adaptor to establish a 
connection. Selection of a connection broker to handle a connection is 
effected in a number of ways. Typically, the call server selects 
connection brokers on either a random basis or a sequential basis so as to 
spread the work load among the connection brokers. Alternatively a `round 
robin` system of selection may be employed. On receiving a connection 
request, the selected connection broker clone performs the following 
functions. 
1. It accesses its local copy of the terminal number database 145 to 
identify the network adaptor or adaptors involved in the connection. 
2. It passes appropriate commands to those network adaptors instructing 
them to perform the actions required to handle the connection request. 
3. It receives from the network adaptors their responses to those commands, 
and formulates from these responses an overall response which it then 
communicates to the call Server via the associated NCI signalling channel. 
Within a node, the connection broker clones 44 operate substantially 
independently of one another. Each utilises its own respective processing 
element 144 so that all connection broker clones within a node operate 
simultaneously in parallel. There is no communication between connection 
broker clones within a node, and no status information is retained 
concerning a connection request once the response has been returned to the 
call server. 
Failure of a connection broker clone 44, or of the processing element 144 
on which it runs, results in loss of communication on the associated NCI 
signalling channel. The call server is responsible for responding to this 
condition by refraining from directing any connection requests over the 
NCI signalling channel concerned until communication with that connection 
broker clone is re-established. While one or more connection broker cones 
is/are unavailable, all connection requests are divided, by the call 
server, between those connection broker clones which are still fully 
functional. This may slightly reduce the performance of the node in terms 
of the volume of connection requests it can process in a given time, but 
will not restrict the range of links or network adaptors that can be 
involved in connections. 
Failure of a connection broker clone, the processing element on which it 
runs, or the communications link carrying the NCI Signalling Channel 
between it and the call server during the processing of a connection 
request, could also leave the call server unsure if the request has been 
actioned or not. This can be resolved by the call server repeating the 
request via a different connection broker clone on expiry of a time-out in 
the event that the originally selected connection broker clone's response 
is not received. Each Network adaptor 56 retains the definitive view of 
the current status of all connections involving its links, and receiving 
an instruction to set a link into a state which it already occupies is not 
regarded as indicating a fault. 
To increase the connection request capacity and performance of a Node it is 
only necessary to introduce additional, identical, connection broker 
clones on additional processing elements, each with their own 
corresponding NCI signalling channel. No modification to existing 
connection broker clones is required. Increasing the number of connection 
broker clones reduces the time needed to handle each connection request, 
increases the number of connection requests that may be processed 
simultaneously, and reduces the impact on the node's performance of any 
failure of a connection broker clone or of an associated processing 
element. 
In relation to the structure, content and function of call set-up messages 
between difference exchanges (i.e. different nodes), this can best be 
understood with reference to FIG. 4, the flow diagram of FIG. 6 and the 
subsequent tabulated summary of message functions. 
An incoming call (or "initial address message", IAM) from terminal TA is 
received 200 at the first node 40, whose call server 18 receives the 
incoming message and determines that the call must be routed to the second 
node 52. The incoming call will at least contain a CIC relating to the 
trunk assigned between TA and the call server 18 together with a telephone 
number of the called party, namely TB in this example. The telephone 
number does not otherwise provide any indication of a port address to be 
used by TB in any subsequent communication and therefore principally acts 
to provide a routing instruction for use by the call servers. As such, the 
telephone number merely represents an address location of TB, although it 
may need to be subsequently transposed in order to arrive at a valid 
cross-node address. 
In response to receipt of the incoming call and to save real communication 
resources (i.e. real communication links that can supports 64 kbps speech, 
for example), the first call server 18 selects a free phantom terminal PTx 
and then uses this phantom terminal to establish 202 a phantom trunk 
between itself and a second call server 81 located in second node 52. 
Indeed, the call server 18 selects an available, node-unique ("disjoint") 
address field indicative of the free phantom terminal PTx from its 
associated memory 19. The free phantom terminal PTx, in fact identifies a 
terminating address of the phantom trunk. 
Typically, a phantom terminal identity is comprised from point codes 
associated with the two call servers 18, 81 and the CIC of the phantom 
trunk. In this instance, ordering of the point codes of the two call 
servers will identify a relative direction for the communication. 
The first call server 18 then utilises the phantom trunk to relay 204 a 
modified call message (to the second call server 81 of the second node 52) 
comprised from a CIC associated with the phantom trunk together with the 
valid telephone number of TB. The second call server 81 is therefore able 
to utilise the telephone number of TB to "wake-up" or alert TB to the fact 
that there is something in the communication system that will be of 
interest to TB, albeit that TB is yet to receive any meaningful 
information. Unfortunately, at this time, the CIC pertaining to the 
connection between TA and the first call server 18 has been "lost" to the 
second node 52 since it is neither communicated nor encoded with the 
modified call message. In other words, the call server 18 of the first 
node 40 notifies the call server 81 of the second node 52 about the 
incoming call 100 by sending 104 a modified incoming call message on a 
phantom trunk, and thus passes on the dialled digits (i.e. the address of 
the called party) received from TA. 
Furthermore, in response to the incoming call 100, the allocated connection 
broker clone 44 of the first node 40 is arranged to establish 206 a 
phantom cross-office path between PTx and TA, with information pertaining 
to this cross-office path typically stored in the terminal number data 
base 69 by the resolution intelligence 68. In other words, terminal TA is 
coupled to phantom terminal PTx. Also, the preferred embodiment of the 
present invention is arranged such that the first connection broker clone 
44 is triggered into action by the communication of the modified call 
message (to the second call server 81). Specifically, substantially 
contemporaneously with the sending of the modified call message, the first 
connection broker clone 44 of the first node 40 notes that the phantom 
terminal PTx is one end of an outgoing phantom trunk to the second node 
52. The first connection broker clone therefore passes 208 a connection 
request 106 to a second connection broker clone 80 at the second node 52 
via virtual link 84, which connection request contains the CIC of the 
phantom trunk and the identity of TA (possibly derived from the original 
CIC assigned to the trunk between TA and the first call server 18). In the 
preferred embodiment, though, the actual address of the call-originating 
unit, i.e. TA, is sent. 
The second node 52 reacts to the modified incoming call message (received 
on the phantom trunk) by mapping 210 the received circuit indicator code 
(CIC) of the phantom trunk onto an associated second phantom terminal Pty. 
Again, the second phantom terminal Pty has been selected by the second 
call server 81 of the second node 52 from its associated memory 82, with 
the memory up-dated to record that Pty represents a terminating point of 
the phantom trunk. Selection of the phantom terminal Pty is on a unique 
basis. 
The second node 52, in response to the second call server 81 receiving the 
modified incoming call message, already appreciates that the destination 
of the incoming call ultimately lies with terminal TB. Therefore, at an 
appropriate time, the second call server 81 requests 212 a connection from 
TB to the second phantom terminal Pty (in the form of a second phantom 
cross-office path request between the phantom trunk and the called 
subscriber TB), and offers the incoming call request to TB using 
conventional signalling. 
Furthermore, the resolution intelligence of the second connection broker 
80, in response to receiving (in any order) both requests resolves out 214 
the two phantom terminals PTx and Pty, converting the two requests 
"Connect TA to PTx" and "Connect TB to Pty" into the single real 
connection request "Connect TA to TB". Specifically, the second connection 
broker clone 80 is able to deduce the fact that there is a common CIC for 
the phantom trunk, and so the requirement for a direct connection between 
TA and TB is identified by virtue of this commonality. The second 
connection broker clone 80 then makes an actual trunk connection 216 
between TA and TB via the second trunk network adapter 56. At about the 
same time, the second connection broker clone 80 (of the second node 52) 
instructs 218 the first connection broker clone 44 (of the first node 40) 
that the path to TB is in place. 
Acceptance by the terminal TB of the call, and confirmation of the 
connection by the second connection broker clone 80 is notified from the 
second call server 81 to the first call server 18, and the first 
connection broker clone 44 also notifies 116 its associated call server 18 
that the path to TB is in place. At this point 220, the first call server 
18 may start billing the call. 
The phantom trunk remains intact for the whole duration of the call, with 
tear down of the broadband connection operating in a complementary sense 
to the call set-up procedure described in detail above. The skilled 
addressee will appreciate that to clear-down a broadband call, the call 
servers may clear a call using standard procedures for a narrowband (or 
SS-7) communication, as will readily be appreciated. Particularly, as part 
of this procedure, both call servers will issue request to their 
respective connection brokers. Thereafter, the connection broker clone at 
the outgoing end of the phantom trunk will pass its release request onto 
the other connection broker clone by sending the CIC of the phantom trunk. 
The terminating connection broker clone will issue a clear-down of the 
broadband connection on receipt of whichever of the two messages it 
receives first. It is noted that the phantom trunk is not re-usable until 
both call severs have been told (by their respective connection broker 
clones) that the broadband connection has cleared. 
The functions performed by the principal message signalling are summarised 
in the table immediately below: 
______________________________________ 
Message Function Content 
______________________________________ 
100-102 Incoming Call 
Identifies address of 
destination terminal and initial 
CIC to TA. 
104 IAM On selected phantom trunk, 
first connection broker clone 44 
send modified incoming call 
message containing 
destination code (CIC) for 
phantom trunk/phantom 
terminal PTx. 
106 Connection Second node maps phantom 
Request trunk CIC onto associated 
phantom terminal Pty. Second 
call server receives real 
terminal number for TB and 
connection attributes, such as 
bit-rate, coding, etc. 
108 Connection First connection broker clone 
Request send phantom trunk CIC, real 
terminal number for TA and 
connection attributes to second 
connection broker clone. 
110 Broadband For proxy signalling, use a 
Connection proxy signalling link for BA 56. 
Request Include a destination 
broadband network address 
(NSAP) for TA and the VPI/VCI 
for TB, together with 
connection attributes. 
112 Ringing? Message from the second call 
server indicating incoming call 
to TB. May contain OLI, etc. 
114 ANSwer CIC 
116 answer TA may get this in-band 
______________________________________ 
It will be understood that the above description of a preferred embodiment 
is given by way of example only and that various modifications may be made 
by those skilled in the art without departing from the spirit and scope of 
the invention. 
As will be understood, an exemplary address format for each phantom 
terminal is typically arranged to be a special case of the format used for 
real (i.e. physical rather than imaginary) terminals. As such, a preferred 
embodiment of the present invention uses an ASN.1 Object Identifier to 
identify phantom trunks. Alternatively, a partitioned E.164 address or a 
superset of E.164 may be utilised, while for a simple SS7-based 
implementation the tuple (OPC, DPC, CIC) can uniquely identify a trunk 
(whether real or phantom). However, as will be appreciated, another scheme 
is needed for non-SS7 terminals, such as telephones. For example, the CI 
field could be extended to 32 bits (rather than the normal 16 bits) and 
DPC can then be equated to OPC to identify a "line" type of terminal while 
the CIC can be used to identify the line on the exchange. Generally, 
however, the only requirement for establishing a phantom trunk is for the 
connection broker clone to appropriately tag and record (in the terminal 
number data base 69) such a phantom trunk as either incoming or outgoing. 
Turning again to the general architecture of FIG. 2, a particular 
embodiment of the present invention utilises an ATM network and the 
International Telecommunications Union, Telecommunications Section (ITU-T) 
signalling system No. 7 to implement the broadband network and narrowband 
control signalling, respectively. 
Particularly, a narrowband node utilises the ISDN User Part (ISUP) of ITU-T 
Signalling System No 7 to communicate with other exchanges (e.g. 
narrowband network 52) to support multi-node operation. The exchange 
terminates some narrowband lines directly and terminates narrowband trunks 
via trunk network adapter 46 connected to an Asynchronous Transfer Mode 
(ATM) network 48. 
The trunk network adapter 46 translates bearer channels to an ATM scheme, 
with a one-to-one relationship existing between each bearer channel and an 
ATM virtual channel (VC). Typically, the broadband network edge switches 
50, 60-62 and hence the trunk network adapters 46, 56-58 are connected to 
the ATM network 48 using ATM Forum User to Network Interface (UNI) version 
4.0 interfaces for the traffic bearer channels and the control lines 51, 
while the connection brokers establish Q.2931 connections 51 to trunk 
network adapters 46, 56-58 using the proxy signalling option of UNI 4.0. 
Narrowband signalling to other exchanges can use either existing narrowband 
connections or can be routed via network adapters (e.g. 46, 58) and the 
broadband network using either circuit emulation or frame forwarding. The 
concept is applicable to both fully and quasiassociated signalling 
schemes. Connections to another mixed mode node are implemented in a 
similar fashion. 
Each trunk network adapter is arranged to have a unique ATM address (NSAP) 
such that a specific terminal is identified by the Network Service Access 
Point (NSAP) address of its network adapter, together with the ATM VPINCI 
that it transmits and receives on, i.e. the Virtual Path Identifier (VPI) 
and Virtual Channel Identifier (VCI). 
As will now be understood, the connection broker clone 44 passes 
narrowband-to-narrowband requests to the narrowband switching fabric 16, 
whilst broadband-to-broadband connections (within the same node) are 
established using proxy signalling to set-up the connection directly. For 
narrowband-to-broadband connections, two requests are needed; one to the 
narrowband switching fabric 16 and one to the broadband network edge 
switches 50, 60-62. However, for a broadband-to-phantom terminal 
connection, the first connection broker clone passes the connection 
request to the second connection broker clone (reference numeral 70 of 
FIG. 3) at the other end of the phantom route. The connection is then made 
by using a proxy signalling scheme emanating from the second connection 
broker 70. It should be noted that the present invention envisages that 
the phantom terminals are implemented as broadband terminals, and so 
narrowband-to-phantom terminal connection is handled as a combination of a 
narrowband-to-broadband connection and a broadband-to-phantom terminal 
connection. 
It will also be appreciated that the service inter-working function 
provided by the present invention is also applicable to networks that have 
intermediately coupled broadband networks. In this instance, the 
interconnection between call servers can provide gateway functions, such 
as billing and screening, while the connection broker clones permit 
end-to-end connections between the narrowband terminals. Similarly, 
signalling inter-working functions not otherwise available to respective 
narrowband networks can be provided by connecting call servers together 
via the phantom trunks. 
In summary, the second connection broker clone recognises two connection 
requests have been received to the opposite ends of the same phantom 
trunk, and in response thereto establishes a direct route through the 
broadband network between the first subscriber terminal 12 and the second 
subscriber terminal 68. 
The present invention therefore advantageously provides a mechanism for the 
interconnection of mixed nodes through an intermediate broadband network 
which is otherwise unable to interpret and therefore unable to support the 
control channel signalling protocols separately utilised within the 
narrowband networks. Such operation could be supported, for example, by a 
modified trunk network adapter (of a broadband network) equipped with 
narrowband signalling software, but generally occurs between different 
infrastructure exchanges. Consequently, by employing the mechanism of the 
preferred embodiment to establish a common control channel, the modified 
trunk network adapter can support a narrowband traffic resource to 
participate in narrowband services without requiring the intervention of a 
signalling interworking function. 
Beneficially, the combination of phantom trunks and the connection broker 
clone architecture results in a system implementation that requires no 
modifications to present narrowband signalling schemes and which supports 
all narrowband services. Additionally, only minimal changes are required 
to existing narrowband call servers. Indeed, the present invention 
provides a system that is scaleable to arbitrarily complex networks and 
which can operate over any underlying connection fabric including TDM, ATM 
or Frame Relay. 
It will be understood that the above description of a preferred embodiment 
is given by way of example only and that various modifications may be made 
by those skilled in the art without departing from the spirit and scope of 
the invention.