Communication network interface with screeners for incoming messages

• US 5,400,331 A
• Filed: 04/28/1993
• Issued: 03/21/1995
• Est. Priority Date: 04/28/1993
• Status: Expired due to Term

• Current Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Original Assignee: Allen-Bradley Company (Rockwell Automation, Inc.)
• Inventors: Chami, Hassan A., Pieronek, Donald S., Engdahl, Jonathan R., Lucak, Mark A., Gee, David J.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Kizou, Hassan
• Application Number:
  US08/054,944
• Time in Patent Office: 692 Days
• Field of Search: 370/60, 370/60.1, 370/61, 370/85.1-85.8, 370/85.13-85.15, 370/92-93, 370/94.1-94.3, 370/110.1, 340/825.07, 340/825.3, 340/825.52, 340/825.53
• US Class Current: 370/401
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

Each message carried by a communication network has a packet that contains data, a tag, and a generation count wherein duplicate packets sent in different messages have identical generation counts. A station includes a modem that connects to the communication network in order to receive messages. A fixed screener circuit has a first memory that stores a set of tag values and a fixed screener determines when a packet tag matches a tag value in the first memory. The station also has an interface through which tag values are received from an external device, such as a host computer. A general purpose screener includes a second memory with a plurality of storage locations in which to store tag values from the interface and a generation count associated with each tag value. A first comparator in the general purpose screener determines when a tag contained in a packet matches a tag value in the second memory, and a second comparator determines when a generation count in the packet matches the generation count in the second memory that is associated with the matching tag value. A control circuit produces a signal when the first comparator indicates a tag match and the second comparator indicates that the generation counts do not match. The station ignores the packet in the absence of the signal.

Claims

1. A media access controller for a communication network that carries a message having at least one packet wherein each packet contains data and a tag indicating the data'"'"'s nature, said media access controller comprising:

a circuit for connection to the communication network in order to receive messages;

a fixed screener coupled to said circuit and including a first memory that stores a first set of tag values for packets which carry station management data and commands, said fixed screener determines when the tag contained in said at least one packet of a message received from the network matches a member of the first set of tag values and produces a first signal when a match is found;

an interface for receiving tag values from an external device;

a general purpose screener coupled to said circuit and said interface and having a second memory that stores a second set of tag values which were received by said interface, a comparator which determines when the tag contained in said at least one packet of a message received from the network matches a member of the second set of tag values and produces a second signal when a match is found and a control circuit for writing a tag value received by said interface into the second memory;

a third memory coupled to said circuit for storing the data contained in said at least one packet received from the network; and

a router controller that receives the first and second signals and responds by erasing the data from said at least one packet stored in said third memory when neither the first signal nor the second signal indicates that a tag match was found.

2. The media access controller as recited in claim 1 further comprising a supplemental screener interface connected to said circuit for sending the tag contained in said at least one packet to a supplemental screener and for receiving a third signal from the supplemental screener;

and wherein said router controller responds to an absence of the first signal, second signal and third signal by erasing the data from said at least one packet from the third memory.

3. The media access controller as recited in claim 1 wherein said circuit includes a modem.

4. The media access controller as recited in claim 1 wherein the control circuit of said general purpose screener can alter the second set of tag values by writing a tag value contained in a packet received from the network into the second memory.

5. The media access controller as recited in claim 1 further comprising a data interface which enables transfer of the data from said at least one packet stored in said third memory to an external device.

6. The media access controller as recited in claim 1 wherein the second memory also stores a tag index with each tag value which indicates how the data in an associated packet should be processed;

and further comprises means for transferring a tag index from the second memory into said third memory upon the comparator producing the second signal.

7. The media access controller as recited in claim 1 wherein said third memory comprises a plurality of first-in, first-out memories;

and wherein the second memory also stores a routing identifier associated with each tag value, wherein the routing identifier indicates which of the plurality of first-in, first-out memories is to store the data from said at least one packet when the associated tag value matches the tag from said at least one packet.

8. A media access controller for a communication network that carries a message having at least one packet wherein each packet contains data, a tag indicating the data'"'"'s nature and a control bit which indicates whether the tag is a fixed tag or a generic tag;

said media access controller comprising;

a circuit for connection to the communication network in order to receive messages, the circuit being identified on the communications network by a unique station address;

a fixed screener coupled to said circuit and being enabled when the control bit contained in said at least one packet of a message received from the network indicates that the tag in said at least one packet is a fixed tag, wherein when the fixed screener is enabled, the fixed screener is operable to determine whether a predetermined portion of the tag in said at least one packet contains a network address which corresponds to said unique station address, and produces a first signal when a match is found between said network address and said unique station address;

a general purpose screener coupled to said circuit, and having a first memory that stores a set of tag values, a comparator being enabled when the control bit contained in said at least one packet of a message received from the network indicates that the tag in said at least one packet is a generic tag, wherein when the comparator is enabled, the comparator is operable to determine whether the tag in said at least one packet matches a member of the set of tag values and produces a second signal when a match is found between the tag in said at least one packet and a member of the set of tag values;

a second memory coupled to said circuit for storing the data contained in said at least one packet received from the network; and

a router controller that receives the first and second signals and responds by erasing the data from said at least one packet stored in said second memory when neither the first signal nor the second signal indicates that a tag match was found.

9. A media access controller for a station on a communication network that carries a message having a packet which contains data field, a tag field, and a generation count field in which the generation count field contains a generation count value, and in which duplicate packets have identical generation count values contained in their respective generation count fields, the media access controller comprising:

a network interface circuit for connection to the communication network in order to receive said message and the packet contained therein;

a general purpose screener coupled to said network interface circuit and including;

a) a first memory that has a plurality of storage locations with each storage location storing a tag value and a corresponding saved generation count value,

b) a first comparator which determines when the tag field contained in the packet received from the network matches the tag value in one of said plurality of storage locations in the first memory,

c) a second comparator which determines when the generation count value contained in the generation count field of the packet received from the network matches the saved generation count value in one of said plurality of storage locations in the first memory, and

d) a control circuit for activating a first signal when the first and second comparators indicate that the tag field of the packet matches the tag value in a selected one of said plurality of storage locations in the first memory while the generation count value in the generation count field of the packet does not match the saved generation count value in said selected one storage location;

a second memory coupled to said network interface circuit for storing the contents of the data field contained in the packet received from the network; and

a router controller that receives the first signal and responds by erasing the contents of the data field stored in said second memory if the first signal is not activated by the control circuit within an established period of time after the packet is received from the network.

10. The media access controller as recited in claim 9 further comprising a data interface for receiving tag values from an external device, and coupled to said general purpose screener;

and wherein said control circuit writes a tag value from said data interface into the first memory.

11. The media access controller as recited in claim 9 wherein when the first signal is activated by the control circuit, the general purpose screener operates the first memory to store the generation count value from the generation count field of the packet as the saved generation count value at said selected one storage location.

12. The media access controller as recited in claim 9 wherein said control circuit also activates the first signal when both an "accept always" indicia is present in the packet and said first comparator indicates that the tag field of the packet matches the tag value in one of said plurality of storage locations in the first memory.

13. A station for a communication network comprising:

a circuit which couples to the communication network in order to receive messages which include at least one packet wherein each packet contains data and a tag;

a fixed screener coupled to said circuit and including a first memory that stores a first set of tag values, said fixed screener determines when the tag contained in said at least one packet of a message received from the network matches a member of the first set of tag values and produces a first signal when a match is found;

an interface for receiving tag values from an external device;

a general purpose screener coupled to said circuit and said interface and having a second memory that stores a second set of tag values, a comparator which determines when the tag contained in said at least one packet of a message received from the network matches a member of the second set of tag values and produces a second signal when a match is found and a control circuit for writing said tag values received from said interface into the second memory;

a supplemental screener coupled to said circuit to receive the tag contained in said at least one packet of a message received from the network and producing a third signal when said tag received by the supplemental screener has a predefined value;

a third memory coupled to said circuit for storing the data contained in said at least one packet received from the network; and

a router controller connected to receive the first, second and third signals and responds by erasing said data stored in said third memory when none of the first, second and third signals is received within an established period of time after said at least one packet is received from the network.

14. A media access controller for a station connected to a communication network that carries a plurality of messages, each message having at least one packet which contains data field, a tag field, and a generation count field in which the generation count field contains a generation count value, and in which duplicate packets have identical generation count values contained in their respective generation count fields, the media access controller comprising:

a circuit for connection to the communication network in order to receive messages and said at least one packet contained therein, the messages including a tag programming message;

an interface for receiving tag values from an external device;

a general purpose screener coupled to said circuit and including;

a) a first memory that has a plurality of storage locations with each storage location storing a tag value and a corresponding saved generation count value,

b) a first comparator which determines when the tag field contained in said at least one packet received from the network matches a tag value in one of said plurality of storage locations in the first memory,

c) a second comparator which determines when the generation count value contained in the generation count field of said at least one packet received from the network matches the saved generation count value in one of said plurality of storage locations in the first memory, and

d) a control circuit for activating a control signal when the first and second comparators indicate that the tag field of said at least one packet matches the tag value in a selected one of said plurality of storage locations in the first memory while the generation count value in the generation count field of said at least one packet does not match the saved generation count value in said selected one storage location, said control circuit also for writing a new tag value into the first memory, which new tag value is received either from the interface or from said tag programming message handled by said circuit;

a second memory coupled to said circuit for storing the contents of the data field contained in said at least one packet received from the network; and

a router controller that receives the control signal and responds by erasing the contents of the data field stored in said second memory if the control signal is not activated by the control circuit within an established period of time after the packet is received from the network.