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Chapter 4Simulation and analytical modelling pThis framework not only includes statistics collection models and interfacing with othernetwork technologies (e.g. Ethernet, ATM, etc), but also the appropriate links betweenthe Headend (HE) equipment and cable modems for upstream and downstreamtransmissions. The latest version of the CSF (v.13) covers the basic functionality of theMAC and PHY layers of a DOCSIS v.1.0 compliant cable modem and Cable ModemTerminations System (CMTS). Some additional functions, such as prioritisation [102],committed information rate scheduler algorithm [120] and two schemes to reduce thenetwork's recovery time [105] and [106] were added at the University of Sheffield.The network architecture of the generic CSF model is presented in Figure 4.2. Itconsists of the Headend node, Statistics Collection block, Network cloud, and CableModems.a) Headend: The main purpose of this node is to receive messages from the upstreamchannel and to relay them to either the downstream channel or the Network cloud. Atraffic source module within the Headend node models incoming traffic from theNetwork side interface. Additionally, some other functions performed by this node(at the MAC layer) are CM initialisation, registration, scheduling of upstreamtransmission and routing of incoming frames to the Statistics Collection module.b) Cable Modem: This node connects both the upstream and downstreamunidirectional channels. With the use of the specific MAC protocol, it generatestraffic that is sent to the upstream channel. The CSF provides different types ofsource traffic, such as ON-OFF exponential distributed bursty traffic, 53-byteisochronous streams and World Wide Web (WWW) traffic flows.Upstream ChannelStatisticsCollectionInternet/NetworkcloudHeadendCableModemsDownstream ChannelFigure 4.2 – Generic CSF model.4-5