Residential Access

Residential  access is connecting home  end  systems ( typically a PC but increasingly a home network) into the network. One form  of residential  access  is the  dial up modern  over an ordinary  analog telephone line into  a residential ISP ( Internet Service Provider). The  home modern converts  the digital output of the PC into  analog  format for transmission over the analog phone  line. This analog phone line  is made of twisted  pair  copper wire and is the same telephone line sued to  make  ordinary phone calls. At the  other end  of the analog phone line a modern  in the internet serves  provider(ISP) convert the  analog signal  back into  digital form  for input to the ISP router. Thus  the  access network is simply  a pair of  modems  analog  with a point to point  dial up phone  line.

Today  modern  speeds allow dial up access at rates upto 56kbps. However  due to the  poor  quality of the twisted pair time  line between  many  homes  and ISP many users get an  effective rate significantly less than 56 5bps. Moreover while  a residential user uses a dial up  modern to surf the web  the user cannot receive and make ordinary  phone  calls over  the phone  line. Fortunately new  broadband access technologies are providing  residential users higher bit  rates and they  are also  providing a means for users to access  the internet and talk on the phone  at the same time. There are two common  types of  broadband residential  access.

1.Digital subscriber line (DSL)

2.Hybrid Fiber Coaxial Cable(HFC)

DSL access is typically  by a telephone  company. Sometimes in partnership with  an independent ISP. Similar to dial  up modems. DSL is a new  modem technology  again  running over existing twisted pair telephone lines. But  by restricting the distance between  rates  are typically asymmetrical into directions with a higher rate from ISP router to home  than form  the home  to ISP router.DSL can provide bit rates  more than  10 Mbps from ISP to home  and more  than 1 Mbps form home  to ISP.

DSL divides  the communication link  between  the home  and the ISP into three non  overlapping  frequency  bands.

3. A high  speed downstream channel in th e50KJs to | MHz band

4.A medium  speed  upstream channel in the 4 KHz to 50 KHz band

5. An ordinary  two  way  telephone  channel  in the 0 to  4 KHz band

While DSL and dial  modems use ordinary phone lines. HFC access networks are  extensions of the  current  cable network used for  broadcasting cable television. In a traditional cable systems a cable  head end  broadcasts through a distribution network of  coaxial cable and amplifiers  to residence. As illustrated in figure 2.4 fiber optics connect the cable  head end to neighbourhood level junctions from which  traditional coaxial cable  is then  used to reach individual houses and apartments. Each  neighbourhood  junction  typically  supports 500 to 5000 homes.

DSL HFC requires  special modems called cable modems typically  the cable modern is an external device and connects to the home Pc through  a 10 Base T Ethernet port. As with DSL the downstream channel is typically allocated more transmission rate than  the upstream channel.

                                                            figure A Hybrid Fiber Coaxial Access Network

One important  characteristics of GFC is that it is a  shared broadcast  medium. In particular  every  packet  sent by  the head end travels downstream to every link  to every home and  every packet sent by a travels through  the upstream channel  to the head end.

One of the attractive features of DSL and HFC  is that  user will by  stay connected to the ISP while  simultaneously making  and  receiving ordinary telephone  calls.