rminals. The F-BCMCSCH carries packets containing content generated by a content server, carries downlink signaling messages generated by the Broadcast Protocol Suite, and can also carry payload from other routes. It uses OFDM symbol parameters to carry out its functions. It does have Forward Link, but does not have a Reverse Link. Forward Link messages are sent for transmission directly on it or are tunneled through the Inter-Route Tunneling Protocol of a unicast route. The Reverse Link messages are tunneled through the Inter-Route Tunneling Protocol of a unicast route as well. 6.6 625k-MC (625kiloHertz-spaced MultiCarrier) Mode The 802.20 standard also defines the physical layer, medium access control, and the signaling layer for 625k-MC, which is an enhancement of ATIS5-0700004.2005. ATIS-0700004.2005 is a High Capacity - Spatial Division Multiple Access (HC-SDMA) radio interface standard. The 625k-MC PHY/MAC/RLC/DLC Protocol Reference model is as shown in Figure 6.11 which is based on TDD scheme. 625k-MC mode's RF/PHY/MAC/RLC/DLC specifications are based on the L0/L1/L2/L3 spec- ifications defined in ATIS-0700004.2005. The 625k-MC mode, which is uniquely designed around multiple antennas with spatial processing and SDMA, enables the transfer of IP traffic, including broadband IP data, over a layered reference model. The physical and data link layers (MAC and LLC) support higher data rates and throughputs by enabling multiple 625kHz carrier aggregation, hence the name 625k-MC mode. Adaptive modulation and channel coding, along with uplink and downlink power control, are incorporated to provide reliable transmission across a wide range of link conditions. Modulation, coding, and power control are complemented by a 5 The Alliance for Telecommunications Industry Solutions (ATIS) based in Washington, D.C. is a standards organi- zation that develops technical and operational standards for the telecommunication industry. Next Generation Mobile Communications Ecosystem fast automatic repeat-reQuest (ARQ) mechanism to