nt and use of connection identifiers in the two standards, as well as exclusion of some unused legacy protocols. The Internet Protocol CS (IPCS) and Generic Packet CS (GPCS) are two types of the service-specific CS that are supported by IEEE 802.16m, which are used to transport packet data over the air interface. When using GPCS, the classification is performed in protocol layers above the CS, and the relevant information for performing classification is transparently provided during connection set-up or change. The Asyn- chronous Transfer Mode CS (ATM CS) (see Section 5.1 of reference [1]) and Ethernet CS (see Section 5.2.4 of reference [1]) variants that were specified in the IEEE 802.16-2009 standard are no longer supported in IEEE 802.16m due to a lack of industry interest. Other air interface standards such as 3GPP LTE also use such logical interfaces between their Layer 2 service access points and the network layer protocols. The Packet Data Convergence Protocol (PDCP) in 3GPP LTE, among other functions listed above, performs ciphering and encryption of the MAC PDUs. This is an important difference between the MAC functions of IEEE 802.16 and 3GPP LTE. As shown in Figure 5-1, in IEEE 802.16m, the MAC PDUs are encrypted and integrity protected in a security The ATM CS is a logical interface that associates different ATM services with the MAC CPS SAP. The ATM CS accepts ATM cells from the ATM layer, performs classification, header compression (if provisioned), and delivers CS PDUs to the appropriate MAC SAP [1]. Mobile WiMAX. DOI: 10.1016/B978-0-12-374964-2.10005-0 Copyright © 2011 Elsevier Inc. All rights reserved. CHAPTER 5 The IEEE 802. 16m Convergence Sub-Layer Network Layer CS SAP Radio Resource Service Specific Control and Convergence Management Sublayer -MAC SAP MAC Sublayer Security Sublayer PHY SAP Physical Layer Control Plane Data Plane FIGURE 5-1 The location of the convergence sub-layer in the IEEE 802.16m protocol structure sub-layer, whereas in 3GPP LTE the MAC SDUs are already encrypted and int