1. Odd Mesh Header Date: 2008-03-17 Authors: March 2008
Month Year
doc.: IEEE yy/xxxxr0
March 2008
Odd Mesh Header
Date:
Authors:
Javier Cardona et al.
John Doe, Some Company

2. Month Year
doc.: IEEE yy/xxxxr0
March 2008
Abstract
Odd mesh header affects alignment of upper layer headers. Why not make it even?
Javier Cardona et al.
John Doe, Some Company

3. An 802.11 frame in the standard...
Month Year
doc.: IEEE yy/xxxxr0
March 2008
An frame in the standard...
Javier Cardona et al.
John Doe, Some Company

4. A typical 802.11 frame in memory...
Month Year
doc.: IEEE yy/xxxxr0
March 2008
A typical frame in memory...
Possible sizes (bytes):
2-byte aligned: 26, 30
4-byte aligned: 24, 28, 32, 36
Javier Cardona et al.
John Doe, Some Company

5. Odd Mesh Header... Mesh Header Sizes (bytes): 5, 11, 17 or 23
Month Year
doc.: IEEE yy/xxxxr0
March 2008
Odd Mesh Header...
Mesh Header Sizes (bytes):
5, 11, 17 or 23
Javier Cardona et al.
John Doe, Some Company

6. Why is alignment important?
Month Year
doc.: IEEE yy/xxxxr0
March 2008
Why is alignment important?
For efficiency, upper layer expect packets correctly aligned. 4-byte is common.
DMA access, cache lines, MMU, all benefit when data is aligned to certain byte-boundaries.
Some wireless cards do already add padding bytes to the header to make it 4-byte aligned. And some can only add 2*n sized padding.
Javier Cardona et al.
John Doe, Some Company

7. Month Year
doc.: IEEE yy/xxxxr0
March 2008
Straw Poll
Would you be interested in a proposal to make the Mesh Header length...
1) 4*n ) 2*n 3) Leave as is
mesh flags: mesh seq:4
mesh TTL: 1
mesh seq: 4
address: 6 [ae > 0]
address: 6 [ae > 1]
address: 6 [ae > 2]
reserved: 2 [ae == 0 or ae == 2]
Javier Cardona et al.
John Doe, Some Company