Note: Descriptions are shown in the official language in which they were submitted.
1 309764
MI~HOD OF OPEi~ATlNG A PACKEI SW~CHING NETWORK
This invention relates to a method of operating a packet switching
network, and is particularly concerned with such operation that allows a
computer to control a terminal cluster via the packet switching network.
Within data communications, two major standards dominate. One is
CCITT x.2s, the international standard for data communication by way of a publicdata packet network. The other is Systems Network Architecture (SNA), IBM's
protocol, which has become a defacto standard, at least in North America, by
virtue of widespread use.
1 0 Supporting communications between SNA computers and SNA
terminals on a packet switching network has passed through several phases, each
of which has compromised either the SNA functions, the packet switching
functions or i~oth. Early implementations required each terminal cluster
controller, and hence all of the terminals connected thereto, to be connected to a
single computer. Thus, the switching capability of the packet network was not
used beyond merely establishing the virtual circuit to a predetermined computer.A later implementation allowed terminals to establish communications with any
one of a number of computers available from the packet network; however, as
these terminals no longer belonged to any one computer important SNA
2 0 management services were not supported.
An object of this invention is to provide an improved method of
operating a packet switching network.
In accordance with the present invention there is provided a method of
operating a packet switching network comprising at least a first network access
module having a plurality of terminals coupled thereto via a terminal cluster
controller and at least two second network access modules each having a respective
computer coupled thereto via a terminal cluster controller and at least two second
network access modules each having a respective computer coupled thereto, the
method comprising the steps of: storing in the first network access module
3 o information relating to a configuration of the terminal cluster controller and said
plurality of terminals; establishing a first switched virtual circuit connectionb0tween the first network access module and one of the second network access
modules having a first computer coupled thereto, wherein the first network access
module provides a representation of said configuration of the terminal cluster
controller and said plurality of terminals from the stored information to the first
B ~
1 30q164
comput~r via this first switched virtual circuit connection for control of the
terminal cluster controller and said plurality of terminals by said first
computer; establishing a second switched virtual circuit connection between the
first network access module and one of the second network access modules having a
5 second computer coupled thereto, wherein the first network access module
provides a representation of a single one of said plurality of terminals coupledthereto via the terminal cluster controller to the second computer via this second
switched virtual circuit connection; and translating addresses in the first network
access module for communications via the second switched virtual circuit
1 0 connection between the second computer and said single one of said plurality of
terminals.
The present invention provides a method of controlling remote
terminal clusters through the packet network. This method allows support of the
SNA network management functions while terminals within these clusters are able
15 to establish communication links with any compatible computer, including the
SNA controlling computer available from the packet network. The invention
allows the establishment of the terminal communication sessions independent of
the computer controlling the terminal cluster.
This invention will be further understood from the following
2 0 description with reference to the accompanying drawing, in which: the figure illustrates, as a block diagram, a data communications system.
To facilitate the following system description a brief discussion of the
System Network Architecture (SNA) network components follows. SNA provides
several types of network components or nodes which are arranged in a
2 5 hlerarchlcal manner to provide a hardware basis for data communications. Forthe system under discussion, three node types are of interest. At the highest level
is the type 5 node, the processor or computer, that controls SNA network
resources, supports application and transaction programs, provides SNA neiwork
access to SNA network operators, and supports end user services. The next lower
3 0 level is the type 4 node, the communications controller, that routes and controls
the flow of data through the SNA network. At the lowest level is the type 2.0
peripheral node and the type 2.1 peripheral node, also known as a terminal
cluster controller, that provides end-user access and services. The type 2.0
peripheral node supports session types 1, 2, and 3 for SNA. Type 2.1 terminal
3S supports session type 6.2.
B
1 30q764
In the simplest form, the SNA network consists of a computer
connected to a communications controller which is connected to a terminal cluster
controller having several connected terminals. End users. who use the terminals,communicate with the computer by way of the two intermediate nodes, namely the
terminal cluster controller and the communications controller.
Packet switching networks are typically implemented on two types of
devices which may be separate or integrated. These are packet switching nodes
and packet network access interface modules. For this description the makeup of
the packet network does not matter as each access module acts as an end point of1 0 the virtual circuit through the packet network.
When interconnecting SNA nodes by way of a packet switching
network, the link between the communications controller (type 4 node) and the
terminal cluster controller (type 2.0 peripheral node) is established as a
switched virtual circuit. This switched virtual circuit takes the place of a
1 5 dedicated link such as a leased telecommunications line.
As stated earlier, the use of a packet network to replace dedicated
links has required compromising some of the strengths of the two separate
systems. Clearly the ability of terminals to both independently establish sessions
with various computers and to be managed as provided by SNA is desirable.
Referring to the figure, there is illustrated a simplified data
communications network having computers 10 and 20, a terminal cluster
controller 30, and a packet switching data network 40. The packet network 40
includes access modules 42, 44, and 46. The computers 10 and 20 are connected
to the access modules 42 and 44 respectively via communications controllers 15
2 5 and 25 respectively using X.25 communication links 52 and 54 respectively. The
terminal cluster controller 30 is connected to the access module 46 via an SDLC
link 56. Switched virtual circuits 60 and 62 complete communication links
between the access module 46 and each of the access modules 42 and 44. The
terminal cluster controller 30 has terminals 32 and 34 connected to it.
B
1 309764
In operation, on activation of a service provided in access module 46
for supporting SNA terminal clusters, a switched virtual circuit, e.g. 60, is
established between the terminal clus~er controller 30 and a predetermined
computer, e.g. 10, which is to own and control the terminal cluster controller 30
5 Once established, the virtual circuit remains until the service is deactivated. The
virtual circuit provides computer 10 with a representation of the real cluster
controller 30 and its terminals 32 and 34. Network management information can
be sent to or requested from the terminals 32 and 34, without each of them having
an individual virtual circuit connection to computer 10.
1 0 The terminals 32 and 34 may access any SNA computer connected to
the packet network 40, for example as represented by the computers 10 and 20,
for running application programs. To do so, a terminal, for example the terminal32, calls the computer 20, causing the establishment of the virtual circuit 62.
The virtual circuit 62 presents to the computer 20 a representation of a virtual1 5 terminal cluster, the representation showing a terminal cluster having a single
terminal attached. By having a virtual circuit 60 from the terminal cluster
controller 30 to the network management computer 10 while terminals attached
to the terminal cluster controller 30 establish and release virtual circuits to
application computers, for example virtual circuit 62 connecting the terminal 322 0 to the application computer 20, SNA network management functions are preserved
while taking advantage of the packet switching network to route calls from
terminals to application computers. In this case, the representation of the
terminal cluster controller seen by the computer 10 differs from that seen by the
computer 20, as discussed above.
Establishing the virtual circuit 60 supports communications between
the computer 10 selected as the network management computer and the terminal
cluster controller 30, which allows the terminal cluster controller and the
terminals coupled thereto to be monitored and controlled by the computer 10. Theconditions allowing the virtual circuit 60 to be established will now be described
in further detail.
If several terminal cluster controllers (only one is shown in
the figure for simplicity) are connected to the access module 46, each
B
1 309764
could have a different computer designated as the network management
computer. Thus there can be several network management computers in
the network, but each terminal cluster controller is assigned to only
one of them.
Because the virtual circuit 60 presents a representation of
the real terminal cluster to the network management computer 10, the
access module 46 must store termina1 cluster configuration data and
address translation information to allow network management
information from the network management computer to be routed
I0 correctly to terminals 32 and 34. The representation of the cluster
presented by the access module 46 to the network management computer
10 is one of the terminals 32 and 34 attached to the terminal cluster
controller 30 being inhibited from accepting new communications
sessions. This condition prevents the network management computer 10
from trying to establish a communications session with a terminal
which is already involved in a communications session with another
computer, e.g. 20. However, the apparent inhibited status of the
terminals does not interfere with the ability of the network
management computer I0 to exchange network management information with
the terminals 32 and 34, regardless of any concurrent communications
sessions in which the terminals are engaged.
Similarly, because virtual circuit 62 presents a
representation of a terminal cluster controller having one terminal
coupled thereto, address translation information must be stored to
allow communications between the application computer 20 and the
terminal, in this case terminal 32.
The virtual circuit 60 is established when the service in the
access module 46 is activated. The mechanism used is an automatic
direct call. The access module 46 stores the information required to
implement an automatic direct call from each terminal cluster
controller 30 connected to the access module 46 to each designated
network management computer 10. The computer designated as the
network management computer 10 must have the terminal cluster
controller 30 included in its network configuration table prior to
initial activation of the service in the access module 46.
In addition to exchanging network management information, the
network management computer 10 may be allowed to control the terminal
1 309764
cluster controller 30 using its own commands and tests. This is done
by storing in the access module 46 a data field which indicates,
whether or not the network management computer 10 is allowed control
over the terminal cluster controller 30.
Although the drawing shows only two computers and one
terminal cluster controller coupled to the packet network 40,
obviously many more may be so coupled in a practical system.
Numerous modifications, variations, and adaptations may be
made to the particular embodiments of the invention described above
without departing from the scope of the invention, which is defined in
the claims.
