Context switching for on-the-fly processing of fragmented frames

• US 7,089,486 B1
• Filed: 08/16/2002
• Issued: 08/08/2006
• Est. Priority Date: 08/16/2002
• Status: Active Grant

• Current Assignee: Juniper Networks Incorporated
• Original Assignee: Juniper Networks Incorporated
• Inventors: Novak, Steven, Marleux, Benoit
• Primary Examiner(s): Baker, Stephen M.
• Application Number:
  US10/219,819
• Time in Patent Office: 1,453 Days
• Field of Search: 714/807, 714/811, 370/474
• US Class Current: 714/807
• CPC Class Codes: H04L 12/2801 Broadband local area networks

Abstract

A frame analyzer component and a memory management unit process frames received over cable television lines. The frame analyzer component may receive frames that were transmitted over the cable television lines and that were processed by a digital signal processor. The frame analyzer component checks incoming frames or frame fragments for consistency and errors. Results from the frame analyzer component relative to frame fragments may be stored in a context memory. When a later fragment of the frame arrives, the previous context of the frame can be restored and used to continue processing the frame. The memory management unit stores the frames and frame fragments in separate memory management tables.

Claims

1. A method for processing data items comprising:

determining whether a received data item is a complete data item or a portion of a complete data item;

accessing, when the received data item is determined to be a portion of the complete data item, state information relating to processing of the received data item, the state information being stored in a memory that is indexed based on source identification information that defines a sending device of the received data item, the source identification information including a service ID (SID) that uniquely defines a cable modem; and

analyzing the received data item based on the state information to determine whether the data item contains errors.

2. The method of claim 1, wherein the data items are received based on a time division multiple access (TDMA) scheme.

3. The method of claim 1, further comprising:

discarding data items that are determined to contain errors.

4. The method of claim 1, wherein each data item is a complete data frame or a frame fragment.

5. The method of claim 4, wherein the analysis includes at least one of checking for frame header consistency and performing cyclic redundancy checks.

6. The method of claim 1, further comprising:

forwarding data items that are determined to not contain errors to a memory management unit configured to store data items in a memory.

7. The method of claim 6, wherein one of the data items is stored in a separate first-in-first-out (FIFO) buffer in the memory.

8. A system comprising:

a digital signal processing component configured to receive analog data and convert the analog data to digital data items, at least one of the data items being output by the digital signal processing component as fragments of a complete data item;

an analyzer component configured to receive the data items from the digital signal processing component and perform validation processing on the data items as the data items are received from the digital signal processing component, the analyzer component, when processing those of the data items that are received as fragments, retrieving previously stored information that describes a state of the analyzer component when the analyzer component finished processing a previous fragment of the data item and resuming processing of the data item at the described state;

a memory management unit coupled to the analyzer component and configured to receive the data items and the fragments from the analyzer component and to store the data items in buffers, the memory management unit further including

a first table in which references to non-fragmented data items are stored, and

a second table in which references to the fragments are stored as entries that are indexed based on sources of the fragments.

9. The system of claim 8, wherein, when all of the fragments corresponding to a data item are entered in the second table at a particular table entry, the memory management unit transfers contents of the particular table entry to an entry in the first table.

10. The system of claim 8, wherein the memory management unit further includes:

a first pointer that points to an entry in the first table that corresponds to a location at which new data items are stored; and

a second pointer that points to an entry in the first table that corresponds to a location from which the data items are removed from the first table.

11. The system of claim 8, wherein the data items are data frames.

12. The system of claim 8, wherein the validation processing includes at least one of checking for frame header consistency and performing cyclic redundancy checks.

13. The system of claim 8, wherein the digital signal processing component receives the analog data over cable television lines.

14. A method for processing data items received over a communication line, the method comprising:

storing a received one of the data items in a memory buffer;

determining if the received one of the data items is a complete data frame or a fragment of a data frame;

updating an entry in a first table to reference the memory buffer when the data item is a complete data frame;

updating an entry in a second table to reference the memory buffer when the data item is a fragment of the data frame; and

transferring, when a last fragment of the data frame has been stored in the memory buffer, the entry in the second table to the first table.

15. The method of claim 14, wherein the communication line is a cable television line.

16. The method of claim 14, wherein the memory buffer is a first-in-first-out (FIFO) memory buffer.

17. The method of claim 14, further comprising:

determining if the received one of the data items is the complete data frame or the fragment of a data frame based on information in a header of the received one of the data items.

18. The method of claim 14, wherein updating the entry in the second table is based on a transmission source of the data item.

19. The method of claim 14, wherein the entry updated in the first table is an entry pointed to by a first pointer.

20. The method of claim 19, wherein the first pointer is incremented after the entry in the first table is updated.

21. The method of claim 19, further comprising:

reading data items in the memory buffer based on a position of a second pointer associated with the first table.

22. A memory management device comprising:

a first table configured to store a plurality of entries that reference first buffers in a memory, the entries in the first table corresponding to complete data frames stored in the first buffers; and

a second table configured to store a plurality of entries that reference second buffers in the memory, the entries in the second table corresponding to fragments of data frames stored in the second buffers, the second table entries being addressable based on a transmitting source of the fragments of the data frames.

23. The device of claim 22, further comprising:

a first pointer referencing one of the plurality of entries in the first table at which received data items are to be added to the first table; and

a second pointer referencing one of the plurality of entries in the first table at which received data items are to be removed from the first table.

24. The device of claim 23, wherein, when a plurality of data frame fragments that together form a complete data frame have been written to one of the second buffers, the corresponding entry in the second table is transferred to the entry in the first table referenced by the first pointer.

25. The device of claim 23, wherein the first pointer is incremented after one of the plurality of entries in the first table is updated.

26. The device of claim 23, wherein the first and second buffers are first-in-first-out (FIFO) buffers.