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IEEE Std 802.16-2001

LOCAL AND METROPOLITAN AREA NETWORKS—PART 16:

Uplink Burst #n

User

Bandwidth

PDU

Request PDU

 

 

CID = 0x2301

CID = 0x0399

Uplink Burst #n+1

Management

User

User

PDU

PDU

PDU

 

 

 

CID = 0x0EF1

CID = 0x5F3E

CID = 0x2555

Figure 26—MAC PDU concatenation showing example CIDs

6.2.3.3 Fragmentation

Fragmentation is the process by which a MAC SDU is divided into one or more MAC PDUs. This process is undertaken to allow efficient use of available bandwidth relative to the QoS requirements of a connection’s service flow.

Fragmentation may be initiated by a BS for a downlink connection. Fragmentation may be initiated by an SS for an uplink connection. A connection may be in only one fragmentation state at any given time.

The authority to fragment traffic on a connection is defined when the connection is created by the MAC SAP.

The fragments are set in accordance with Table 57.

Table 57—Fragmentation rules

Fragment

FC

FSN

 

 

 

First Fragment

10

Incremented modulo 8

 

 

 

Continuing Fragment

11

Incremented modulo 8

 

 

 

Last Fragment

01

Incremented modulo 8

 

 

 

Unfragmented

00

Incremented modulo 8

 

 

 

The sequence number allows the SS to recreate the original payload and to detect the loss of any intermediate packets. Upon loss, the SS shall discard all MAC PDUs on the connection until a new first fragment is detected or a nonfragmented MAC PDU is detected.

6.2.3.4 Packing

If packing is turned on for a connection, the MAC may pack multiple MAC SDUs into a single MAC PDU. Packing makes use of the connection attribute indicating whether the connection carries fixed-length or variable-length packets. The transmitting side has full discretion whether or not to pack a group of MAC SDUs in a single MAC PDU.

6.2.3.4.1 Packing fixed-length MAC SDUs

For connections that are indicated, by the fixed-length versus variable-length SDU indicator (11.4.8.15), to carry fixed-length MAC SDUs, the packing procedure described in this subclause may be used. In this case, the Request/Transmission Policy (11.4.8.12) shall be set to allow packing and prohibit fragmentation, and the SDU size (11.4.8.16) shall be included in DSA-REQ message when establishing the connection. The length field of the MAC header implicitly indicates the number of MAC SDUs packed into a single MAC

80

Copyright © 2002 IEEE. All rights reserved.

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