another CM would receive.
Content 2.3 Deploying Cable System Technology 2.3.5 Provisioning a Cable Modem Data and TV signals travel down the cable on different channels. Downstream data travels to a user on a 6-MHz channel. On the cable, the data looks just like a single TV channel and takes up the same amount of space. When the user sends data back up the cable, only 2 MHz are used. The reason the downstream and upstream channel sizes are different is because it is assumed that most users download more than they upload. Putting both upstream and downstream data on the cable system requires two types of equipment: Between these two components, all the computer networking, security, and management of Internet access over cable television is implemented. There are several steps used to provision a CM. The CMTS at the headend must have operational provisioning servers, such as DHCP and TFTP servers. DOCSIS defines the initialization and registration steps. CMs are designed and coded to follow specific steps : Step 1 Downstream setup: The CM powers up and then scans and locks the downstream path for the appropriate RF data channel (frequency) that will be used for the physical and data link layers to be established. Step 2 Upstream setup: The CM listens to the management messages received through the downstream path. The messages include information on how, where, and when to communicate in the upstream path and are used to establish the upstream physical and data link layers. Step 3 Layers 1 and 2 establishment: The CM communicates with CMTS to establish physical and data link layers. Step 4 Obtaining an IP address: After establishing Layer 1 and Layer 2 connectivity with the CMTS, the CM requests IP configuration parameter information (IP address, default gateway, and TFTP server) from the DHCP server. Step 5 Getting the DOCSIS configuration: The CM requests a DOCSIS configuration file from the TFTP server. A DOCSIS configuration file is an ASCII file created by special DOCSIS editors and includes settings, such as downstream channel identification, class of service (CoS) settings, baseline privacy settings, general operational settings, network management information, and vendor-specific settings. Step 6 Register QoS with CMTS: The CM registers, negotiates, and ensures QoS settings with the CMTS. Step 7 IP network initialization: When the CM initialization and registration is complete, the PC-based network initialization takes place. That is, the PC requests its own IP configuration parameters from the DHCP server. If multiple PC connections behind the CM are required, a router can be used. A common scenario is for the router to obtain a public IP address from the DHCP server of the cable provider. The home router also performs Network Address Translation (NAT), Port Address Translation (PAT) and serves as a DHCP server for the PCs connected behind the router.
Content 2.4 Describing DSL Technology 2.4.1 What is DSL Several years ago, research by Bell Labs identified that a typical voice conversation over a local loop only required the use of bandwidth of 300 Hz to 3 kHz. For many years, the telephone networks did not use the bandwidth beyond 3 kHz. Advances in technology allowed DSL to use the additional bandwidth above 3 kHz up to 1 MHz to deliver high-speed data services over ordinary copper lines. As an example, asymmetric DSL (ADSL) uses a frequency range from approximately 20 kHz to 1 MHz. Fortunately, only relatively small changes to existing telephone company infrastructure are required to deliver high-bandwidth data rates to subscribers. Figure shows a representation of bandwidth space allocation on a copper wire for ADSL. The green area represents the space used by POTS, while the other colored spaces represent the space used by the upstream and downstream DSL signals.DSL is not a complete end-to-end solution but rather a physical layer transmission technology similar to dial, cable, or wireless technologies. Service providers deploy DSL connections in the last step of a local telephone network, the local loop. The connection is set up between a pair of modems on either end of a copper wire that extends between the customer premises equipment (CPE) and the DSL access multiplexer (DSLAM). A DSLAM is the device located at the central office (CO) of the provider and concentrates connections from multiple DSL subscribers.Figure shows the key equipment that you need to provide a DSL connection to a SOHO. The two key components are the DSL transceiver and the DSLAM.The DSL transceiver connects the teleworker’s computer to the DSL line. Usually the transceiver is a DSL modem connected to the teleworkers computer using a USB or Ethernet cable. Newer DSL transceivers can be built into small routers with 10/100 switch ports suitable for home office use.The DSLAM is at the central office and combines individual DSL connections from users into one high capacity link to the Internet. The advantage that DSL has over cable technology is that DSL is not a shared medium. Each user has a separate direct connection to the DSLAM. Adding users does not impede performance unless the DSLAM Internet connection on the other side becomes saturated.
Content 2.4 Describing DSL Technology 2.4.2 How Does DSL Work? DSL transmission is either downstream or upstream based on the direction of the transmission. Downstream transmission is from a CO toward a subscriber, and upstream transmission is from a subscriber toward a CO. DSL types fall into two major categories, taking into account downstream and upstream speeds: The term xDSL covers a number of DSL variations, such as Asymmetric DSL (ADSL), high-data-rate DSL (HDSL), Rate Adaptive DSL (RADSL), symmetric DSL (SDSL), ISDN DSL (IDSL), and very-high-data-rate DSL (VDSL).DSL types that do not use the voice frequency band allow DSL lines to carry both data and voice signals simultaneously (for example, ADSL and VDSL types), while other DSL types occupying the complete frequency range can carry data only (for example, SDSL and IDSL types). Data service provided by a DSL connection is always on. The data rate that DSL service can provide depends on the distance between the subscriber and the CO. The shorter the distance: the higher the bandwidth available. If a subscriber is close enough to a CO offering DSL service, the subscriber might be able to receive data at rates of up to 6.1 Mbps out of a theoretical maximum of 8.448 Mbps.
Content 2.4 Describing DSL Technology 2.4.3 DSL Variants The following properties differentiate DSL variants: Figure shows some examples of DSL variants. DSL types include ADSL, RADSL, VDSL, IDSL, SDSL, HDSL, and Symmetrical High-Data-Rate