Docsity
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Docsity AI
Docsity AI
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search for your university

Find the specific documents for your university's exams

Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

Exception Codes in 802.11 MAC Layer Receiver, Study Guides, Projects, Research of Computer Science

University of South Carolina (USC) - ColumbiaComputer Science

Exception codes that can be generated from within the various blocks of the 802.11 mac layer receiver and its sub-blocks. The codes are represented in binary and indicate different types of errors, such as crc errors, protocol version errors, address format errors, and sequence number errors. The document also explains the implications of each error and how the design should respond.

Typology: Study Guides, Projects, Research

Pre 2010

Uploaded on 09/17/2009

koofers-user-s53-3
koofers-user-s53-3 🇺🇸

9 documents

1 / 3

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
CSCE 491 – 802.11 Design Project – Fall 2002 Page 1
CSCE 491 Project Specification – Part 3
Fall 2002
Dr. James P. Davis
[email protected]
Exception Codes
The following list of exception codes, shown in the table, are likely to be
generated from within the various blocks of the 802.11 MAC Layer Receiver
block and its sub-blocks. The bus ‘ErrCode’ encodes the exception code in a 4-
bit value (shown in binary), where the MSB is on the left, LSB is on the right.
# Code Exception Description
1 0000 No Exception This should be the default value for this bus, and is the
value that the Receiver block would make available to the
MAC Control block (not part of this project) on completion
of processing of the current received frame.
2 0001 CRC Error Generated by the FCS_Decoder block, this exception
indicates that an error in the CRC calculation was
detected. It is sufficient to note the error, not where the
error actually occurred.
3 0010 Protocol Version Error Generated by FCH_Decoder block, indicates that a value
for the protocol version in the Frame Control word is a
value other than the base supported (namely, ‘00’).
4 0011 Frame Type/Subtype
Mismatch
Generated by FCH_Decoder, indicates that the value for
the subtype doesn’t match that of the specified type
encountered in the control word. Could indicate a CRC
error (which would be found later in processing) or
possible intrusion attempt using frame spoofing.
5 0100 Frame Address Sync
Error
Generated in Addr_Decoder block, covers the case
where the RA is equal to the TA. This is an erroneous
case, signifying that the station is sending frames to itself.
Might indicate spoofing. Only occurs for RTS and Data
frames involving 2 addresses.
6 0101 Fragmentation Sync
Error
Generated in the Seq_Control_Decoder block, where we
have a Data frame fragment, and the Fragment No. is
defined in proper sequence, but is less than ‘1111’;
however, we have the MoreFrags bit reported by the
FCH_decoder block set to zero.
7 0110 Erroneous Fragment
Error
Generated by the Seq_Control_Decoder block, where the
previous frame had a fragment number (‘b0000 – b1111’)
with MoreFrags bit set, but the current frame has its
MoreFrags bit set but no Fragment No. following the
sequence (either zeros or fragment number other than
that expected).
pf3

Partial preview of the text

Download Exception Codes in 802.11 MAC Layer Receiver and more Study Guides, Projects, Research Computer Science in PDF only on Docsity!

CSCE 491 Project Specification – Part 3

Fall 2002

Dr. James P. Davis

[email protected]

Exception Codes

The following list of exception codes, shown in the table, are likely to be

generated from within the various blocks of the 802.11 MAC Layer Receiver

block and its sub-blocks. The bus ‘ErrCode’ encodes the exception code in a 4-

bit value (shown in binary), where the MSB is on the left, LSB is on the right.

# Code Exception Description 1 0000 No Exception This should be the default value for this bus, and is the value that the Receiver block would make available to the MAC Control block (not part of this project) on completion of processing of the current received frame. 2 0001 CRC Error Generated by the FCS_Decoder block, this exception indicates that an error in the CRC calculation was detected. It is sufficient to note the error, not where the error actually occurred. 3 0010 Protocol Version Error Generated by FCH_Decoder block, indicates that a value for the protocol version in the Frame Control word is a value other than the base supported (namely, ‘00’). 4 0011 Frame Type/Subtype Mismatch

Generated by FCH_Decoder, indicates that the value for the subtype doesn’t match that of the specified type encountered in the control word. Could indicate a CRC error (which would be found later in processing) or possible intrusion attempt using frame spoofing. 5 0100 Frame Address Sync Error

Generated in Addr_Decoder block, covers the case where the RA is equal to the TA. This is an erroneous case, signifying that the station is sending frames to itself. Might indicate spoofing. Only occurs for RTS and Data frames involving 2 addresses. 6 0101 Fragmentation Sync Error

Generated in the Seq_Control_Decoder block, where we have a Data frame fragment, and the Fragment No. is defined in proper sequence, but is less than ‘1111’; however, we have the MoreFrags bit reported by the FCH_decoder block set to zero. 7 0110 Erroneous Fragment Error

Generated by the Seq_Control_Decoder block, where the previous frame had a fragment number (‘b0000 – b1111’) with MoreFrags bit set, but the current frame has its MoreFrags bit set but no Fragment No. following the sequence (either zeros or fragment number other than that expected).

# Code Exception Description 8 0111 Duplicate Sequence Number Error

Generated in the Seq_Control_Decoder block, where the Sequence No. is zero, or some non-zero value, for more than one non-fragmented frame in sequence. This implies that the Sequence No. has the same value as that of the previous received frame (must be from the same sender), there is no fragmentation indicated (i.e., the MoreFrags bit is not set) and the Retry bit is also not set. 9 1000 Sequence Sync Error Generated in the Seq_Control_Decoder block, where the current frame’s Sequence No. is some value other than that of the previous frame’s, plus one, or if zero (following the wrap of Sequence No. values from 2**12 minus 1, wrapping to zero as the next value in frame sequence). This would be for a given frame sequence from a specific sender address. 10 1001 Address Format Error Generated by the Addr_Decoder block. The addresses received for TA or RA do not have their MSB 2 bits as zero, as provided by the specification, for the various frame subtypes we are using. 11 1010 Byte Count Error For each frame of a given type and subtype, we come up short of the total number of words that should be shifted into the Receiver block. Each of these has a pre-defined number of words, so we should maintain a word count to insure that all blocks should be getting their appropriate data. This might manifest itself by the Sequencer getting out of sync with the shifter, in that some of the decoder blocks never get enabled, because there isn’t any more data from the PHY Layer to shift and pass on to them. The frame is too short. This could be detected in several places in the design, but perhaps the best place is in the shifter (hence, the word counter that we haven’t used up to this point). 12 1011 Retry Sync Error Detected in the Seq_Control_Decoder block, based on the posting of the RetryFlag by the FCH_decoder block. If the Sequence No. is the next one in the sequence 13 1100 Duplicate Frame Error Detected in the Seq_Control_Decoder block, based on checking the Sequence No., or Frag No. (if we are fragmenting), and it is the same as the previous frame received from the given sender (and we are the targeted receiver), and the RetryBit detected by FCH_Decoder is not set to ‘1’ indicating this is NOT a retry frame. It could be a reflection of the frame, arriving at a later time than the original frame’s image. Presuming we received the original correctly, the Receiver would have already signaled the Transmitter to send an appropriate ACK response. Note this is valid only for Data frames. 14 1101 Retry Frame Encountered

Detected in the Seq_Control_Decoder block, based on checking the Sequence No., or Frag No. (if we are fragmenting), and it is the same as the previous frame received from the given sender (and we are the targeted receiver), and the RetryBit detected by FCH_Decoder is set to ‘1’ indicating this IS a retry frame. In this case, we have already seen a good version of this frame, but a delay in response failed to arrive back to the sender.