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| United States Patent | 5136716 |
| Link to this page | http://www.wikipatents.com/5136716.html |
| Inventor(s) | Harvey; George A. (Maynard, MA);
Koning; Gerard (Brookline, NH);
Hawe; William (Pepperell, MA);
Lauck; Anthony (Wellesley, MA);
Oran; David (Bloomington, IN);
Harper; John (Basingstoke, GB2);
Miles; Kevin (Reading, GB2) |
| Abstract | A distributed digital data processing system includes a plurality of nodes
which communicate over a network. A node maintains one or more objects,
each of which may be a file, that is, an addressable unit in the system,
such as a program, database, text file, or the like, or a directory which
may contain one or more files or other directories. One node maintains a
naming service which associates each object in the system with one or more
protocol towers. Each protocol tower identifies the object name and a
series of entries each identifying a name for each of the protocol layers,
along with the communications parameters and address information, to be
used in communicating with the object. When a node requires access to an
object maintained by another node, it first retrieves from the naming
service the protocol towers for the object. The node also maintains a
tower identifying the names of each of the protocols over which it can
communicate. The node then compares the protocol names in the retrieved
protocol towers with the protocol names over which it can communicate. If
the protocol names in a retrieved tower match the protocol names in the
node's tower, the node uses the communications parameters and address
information in future communications with the object. If the node is
unable to identify a retrieved protocol tower which matches its supported
tower or towers, it is unable to communicate with the object. |
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Title Information  |
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Drawing from US Patent 5136716 |
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Session control in network for digital data processing system which
supports multiple transfer protocols |
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| Publication Date |
August 4, 1992 |
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| Filing Date |
March 8, 1990 |
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| Parent Case |
This is a continuation of copending application Ser. No. 094,306, filed on
Sep. 4, 1987, now abandoned. |
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Title Information |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to the field of digital data processing
systems and more specifically to networks for use in connection with
distributed systems.
2. Description of the Prior Art
A digital data processing system, or computer, typically includes a
processor, associated memory and input/output units enabling a user to
load programs and data into the computer and obtain processed data
therefrom. In the past, computers were expensive, and so to be cost
effective had to support a number of users. More recently, however, the
cost of computers, particularly the processors and memories, has decreased
substantially, and so it is relatively cost effective to provide a
computer to one or at most only a few users.
A benefit of providing only a single computer for a large number of users
was that the users could easily share information. Thus, for example, if
all persons working in a bookkeeping or accounting department use a single
common computer, they may maintain common accounting and bookkeeping
databases up to date, and when necessary accounting reports may be
generated from those databases. However, if they use separate computers,
the data is stored in separate databases, on each computer, and so
generating accounting reports would be more difficult.
As a result, networks were developed to provide a distributed computer
system, that is, a system which permits diverse computers to communicate
and transfer data among them. In addition, the networks allow the sharing
of expensive input/output devices, such as printers and mass storage
devices, and input/output devices which may be rarely used, such as links
to the public telecommunications network. In a network, each computer is a
node which communicates with other nodes over one or several wires. In
addition, nodes may be provided which store and manage databases or other
data files on mass storage devices, or which manage printers or links to
the public telecommunications network.
A problem arises with networks, however, since each computer manufacturer
essentially has a different protocol for allowing nodes to communicate
over the networks. For example, computers from International Business
Machines, Inc., communicate using a System Network Architecture ("SNA")
protocol standard, computers from Digital Equipment Corporation
communicate using a Digital Network Architecture ("DNA") protocol
standard, and Univac computers communicate using a DCA protocol standard.
In an effort to establish protocol standards to allow computers and other
nodes from diverse manufacturers to communicate, the International
Standards Organization (ISO) has established an Open Systems Integration
(OSI) protocol standard.
One similarity among all of the protocols is that each is divided into a
plurality of layers, with each layer providing services to the
communication. For example, the OSI protocol includes seven layers. Low
layers control the generation and reception of electrical signals over the
communications medium to allow the communication of individual bits, the
sequencing of the bits into blocks, and the determination of the node
which is to respond to the signals. Intermediate layers control the
sequencing of blocks of received bits into messages of data in case the
blocks are received out of order, and the division of data messages into
blocks for transmission over the network if the network cannot transmit an
entire message in a block. In addition, another intermediate layer
controls the transfer of data to and from the proper programs which may be
running on the node. Upper layers control the transfer of data to and from
the programs running on the node and the addition of error detection and
correction information and its decoding to ensure proper receipt of the
data. While the protocols are all divided into layers, the services
provided by each of the layers are diverse, as is the mechanism for
communicating among the layers.
SUMMARY OF THE INVENTION
The invention provides a new and improved distributed computer system which
permits nodes to communicate over a network using a plurality of diverse
communication protocols.
In brief summary, the new system includes a plurality of nodes which
communicate over a network. A node maintains one or more objects, each of
which may be a file, that is, an addressable unit in the system, such as a
program, database, text file, or the like, or a directory which may
contain one or more files or other directories, or any other addressable
resource in the system. One node maintains a naming service which
associates each object in the system with one or more protocol towers.
Each protocol tower identifies the object name and a series of entries
each identifying a protocol name for each of the protocol layers, along
with the communications parameters and address information, to be used in
communicating with the object. When a node requires access to an object
maintained by another node, it first retrieves from the naming service the
protocol towers for the object. The node also maintains a tower
identifying the names of each of the protocols over which it can
communicate. The node then compares the protocol names in the retrieved
protocol towers with the protocol names over which it can communicate. If
the protocol names in a retrieved tower match the protocol names in the
node's tower, the node uses the communications parameters and address
information in future communications with the object. If the node is
unable to identify a retrieved protocol tower which matches its supported
tower or towers, it is unable to communicate with the object.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention is pointed out with particularity in the appended claims.
The above and further advantages of this invention may be better
understood by referring to the following description taken in conjunction
with the accompanying drawings, in which:
FIG. 1 is a general block diagram of a distributed digital data processing
system constructed in accordance with the invention;
FIG. 2 is another block diagram useful in understanding the invention; and
FIGS. 3A and 3B are diagrams of data structures which are useful in
understanding the operation of the system depicted in FIGS. 1 and 2.
DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT
FIG. 1 is a general block diagram of a distributed digital data processing
system constructed in accordance with the invention. With reference to
FIG. 1, the system includes a plurality of nodes, including server nodes
10A through 10N (generally identified by reference numeral 10) and a
plurality of client nodes 11A through 11N (generally identified by
reference numeral 11) interconnected by a communications link 12. The
server nodes 10 provide a number of services to client nodes 11. The
client nodes 11 are used by users to perform or initiate data processing.
Examples of services provided by server nodes 11 include printing and
telecommunications services, data processing, mass storage backup of data
which is processed by the client nodes 11 or by a server node 10, and
common database control for client nodes 11, allowing a plurality of
client nodes to access a common database. It will be appreciated that not
all server nodes provide all of such services to the client nodes 10; in
some cases, one or only a few server nodes 10 may provide a particular
service to the client nodes 11. In addition, some of the server nodes 10
may provide multiple services to the client nodes 11.
At least one server node 10 in the system provides a naming service 13. In
brief, a naming service provides from a single location, namely the server
node containing the naming service, the location of any object in server
nodes 10 and client node 11 and which may be accessed by a client node 11.
An object is typically an file, for example, a program or a data file,
which is identified by a name, or a directory, which may contain a file or
other directory, which is also identified by a name, or any other
addressable resource in the system. A client node 11 which requires access
to an object, provides the naming service 13 with the name of the object,
and the naming service identifies the client node 11 or server node 10
which controls the object and through which the object can be accessed.
Each client node 11 also includes a multiple-layer message section 14
including a session control layer 15, a set of upper layers 16 and a set
of lower layers 17. Each of the layers in message section 14 is used to
enable the transmission and reception of messages over communications link
12. The lower layers 17 facilitate the generation and reception of
electrical signals over the communications medium to allow the
communication of individual bits, the sequencing of the bits into blocks,
the determination of the node which is to respond to the signals and the
sequencing of blocks of received bits into messages of data in case the
blocks are received out of order, and the division of data messages into
blocks for transmission over the network if the network cannot transmit an
entire message in a block. The upper layers 16 control the transfer of
data to and from the programs running on the node and the addition of
error detection and correction information and its decoding to ensure
proper receipt of the data. The session control 15 controls the transfer
of data to and from the proper programs which may be running on the node.
FIG. 2 depicts details of the session control 15 on a client 11. With
reference to FIG. 2, the session control includes an upper interface
module 20 which provides a uniform interface to the upper layers 16, and
more specifically to programs which run on client 11, and a lower
interface module 21 which provides an interface to the lower layers 17 in
the message section 14. A connection control module 22 processes
transmission requests which are received at upper interface module 20
passes them to the lower layers 17. If a virtual circuit does not exist
for transferring messages, the connection control module 22 enables the
lower layers 17 to establish a virtual circuit in a conventional manner.
In addition, if a virtual circuit does exist, the connection control
module 22 enables the lower layers 17 to perform a transfer using the
virtual circuit.
In connection with receipt of messages from the lower layers 17, the
connection control 22 routes the messages to the upper layers 16 so as to
ensure delivery to the proper users or applications programs. If a message
requests a program which is not running, the connection control 22 enables
the client node 11 to begin processing the program.
When the connection control 22 receives a request, including an object
name, from the upper interface 20 to initiate a transfer for which no
virtual circuit exists, the connection control 22 first passes the request
to an address selection module 23 to obtain an address for use in the
message to be transmitted over the communications link 12 to identify the
intended recipient. The address selection module 23 maintains a cache (not
shown) of object names and addresses and if the object name is in the
cache, the address selection module may pass the address directly to the
connection control module 22.
Alternatively, if the object name is not in the cache, the address
selection module 23 passes the object name to an address resolution module
24. The address resolution module then passes the object name to a naming
service clerk module, which uses a clerk interface 26 to obtain from a
server node 10 all protocol towers relating to the object name.
With reference to FIG. 3A, a protocol tower 30 is a data structure having a
plurality of entries, each with at least two fields. The first entry is an
object name entry, which begins with an object name field 31. Each of the
other entries is a protocol name entry which contains as a first field a
protocol name field 32(0) through 32(N) (generally identified by reference
numeral 32). In each of the protocol name entries is a parameter and
address information field 33(0) through 33(N) (generally identified by
reference numeral 33) each containing parameter and address information.
The object name entry may also contain a parameter and address field 34
which contains parameter and address information.
Each object which is maintained in the system depicted in FIG. 1 and which
can be obtained by a client node 11 from other nodes 10 and 11 has one or
more associated protocol towers 30. Each protocol tower 30 identifies, in
the sequential protocol name fields 32, the names of the protocols through
which the object may be accessed. In addition, in the protocol tower, in
the parameter and address information fields 33, identifies the parameters
which are used in transferring through each of the layers and the address
information which is used in messages transmitted over communications link
12 to enable the object to be accessed.
With reference again to FIG. 2, the naming service clerk module 25, on
request from the address resolution module 24, obtains, from the naming
service 13 and through clerk interface 26, all of the protocol towers
associated with an object name, and transfers them to the address
resolution module 24. The address resolution module 24 also maintains a
set of protocol identification tables. One such protocol identification
table 35 is depicted in FIG. 3B. With reference to FIG. 3B, a protocol
identification table 35 includes a plurality of entries 36(0) through
36(N) (generally identified by reference numeral 36) which sequentially
contain the names of the sequential protocol layers which the client node
11 can support.
Upon receiving the protocol towers 30 associated with the object identified
in the request from the upper interface module 20 from the naming service
clerk module 25, the address resolution module 24 then iteratively
compares the contents of the entries 36 to the entries 32 to determine if
the sequence of names in the entries in the protocol identification table
35 correspond to the sequence of names in a protocol tower. If there is a
match, the address resolution module 24 passes the protocol tower 30 which
provided the match to the address selection module 23, which caches the
protocol tower 30. The address selection module 23 also passes the
protocol tower to the connection control module 22, which uses the
parameter and address information from the parameter and address fields 33
in each of the entries in enabling the lower layers 17 (FIG. 1) to engage
in transferring messages over communications link 12.
If, on the other hand, the address resolution module 24 determines that
there is no protocol tower whose sequence of protocol names 32 corresponds
to the sequence of protocol names in a protocol table 35, the address
resolution module notifies the address selection module 23, which in turn
notifies the connection control module 22. The connection control module
22, in turn, notifies the user or applications program which made the
request that it is unable to satisfy the request. The user or applications
program may then take selected error recovery operations.
It will be appreciated that the invention provides a simplified mechanism
for determination of protocols to be used in transferring messages over a
communications link 12 in a network. The user at a client node 11 only has
to know the name of an object, such as a directory or file, to which
access is required, but not the protocol identification or parameters
which are required to access the object.
The foregoing description has been limited to a specific embodiment of this
invention. It will be apparent, however, that variations and modifications
may be made to the invention, with the attainment of some or all of the
advantages of the invention. Therefore, it is the object of the appended
claims to cover all such variations and modifications as come within the
true spirit and scope of the invention.
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Description |
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