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IEEE Std 802.16-2001

LOCAL AND METROPOLITAN AREA NETWORKS—PART 16:

6.2.3.4.2.1 Interaction with fragmentation

Simultaneous fragmentation and packing allows efficient use of the airlink, but requires guidelines to be followed so it is clear which MAC SDU is currently in a state of fragmentation. To accomplish this, when a Packing subheader is present, the fragmentation information for individual MAC SDUs or MAC SDU fragments is contained in the corresponding Packing subheader. If no Packing subheader is present, the fragmentation information for individual MAC SDU fragments is contained in the corresponding Fragmentation subheader. This is shown in Figure 30.

 

 

 

 

 

 

 

r MAC SDUs

 

 

 

 

 

 

 

 

 

PSH FC=10,FSN=x+r-1 Length=d+2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MACHeader LEN= y =Type00001Xb

PSH FC=01,FSN=x Length=a+2

 

PSH FC=00,FSN=x+1 Length=b+2

 

 

PSH FC=00,FSN=x+2 Length=c+2

Unfrag-

 

 

 

 

 

 

 

 

 

1

 

 

Last fragment

 

Unfragmented

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

of MAC SDU

 

MAC SDU

 

mented

 

 

 

 

 

 

 

 

 

 

 

 

 

length=a

 

length=b

 

MAC SDU

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

length=c

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

First fragment of MAC SDU length=d

HeaderMAC y=LEN 00010Xb=Type

FSH

FSN=FC=11,x+r +1eLength=

2

 

 

 

 

 

 

 

 

Continuing fragment of MAC SDU length=e

MAC Header

y=LEN 00010Xb=Type

FSH

3

 

 

 

s -

FC=11, FSN=x+r+1

r +1 MAC PDUs

f+1

Continuing

 

 

 

 

 

 

 

 

Length=

fragment of

 

 

 

 

 

 

 

 

 

MAC SDU

 

 

 

 

 

 

 

 

 

length=f

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HeaderMAC y=LEN 00010Xb=Type

FSH

FSN=FC=11,x+s +1gLength=

4

 

 

 

 

 

 

 

 

Continuing fragment of MAC SDU length=g

 

 

 

 

 

 

 

t MAC SDUs

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MACHeader LEN= y =Type00001Xb

PSH FSN=FC=01,x+s+1 Length=h+2

 

PSH FSN=FC=00,x+s+2 Length=i+2

 

 

PSH FSN=FC=00,x+s+3 Length=j+2

Unfrag-

 

 

 

 

 

 

 

 

 

PSH FC=00,FSN=x+s+t Length=k+2

5

 

 

Last fragment

 

Unfragmented

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

of MAC SDU

 

MAC SDU

 

mented

 

 

 

 

 

 

 

 

 

 

 

 

 

length=h

 

length=i

 

MAC SDU

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

length=j

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Unfragmented

MAC SDU length=k

Note: If Type=0x03, a GM subheader (not shown in figure) is also present immediately following the Generic MAC header.

Figure 30—Packing with fragmentation

Note that while it is legal to have continuation fragments packed with other fragments, the circumstances for creating continuation fragments would preclude this from happening.

6.2.3.5 CRC calculation

A service flow may require that it be carried on a connection in MAC PDUs with CRCs added (11.4.8.12). In this case, a CRC, as defined in IEEE 802.3, shall be included in each MAC PDU with HT=0; i.e., request MAC PDUs are unprotected. The CRC shall cover the Generic MAC Header and the Payload of the MAC PDU. The CRC shall be calculated after encryption; i.e. the CRC protects the Generic Header and the ciphered Payload.

82

Copyright © 2002 IEEE. All rights reserved.

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