The methods used for data communication over the PSTN

Normally the earlier PSTN is designed for carry voice, but after has been developed to carry data as well as voice.

There are many methods used for data communication over the PSTN. They are PSDN, ISDN, Dial up and  X DSL

       

PSDN (Public switched data Network) is runs over normal PSTN line. It is a Packet Switched data network that based on packet switching as opposed to circuit switching that used in PSTN. When we are connecting to the internet (WAN) we use normal PSTN twisted pair cabled. In this technology packets are routing according to the source and destination address.

 Integrated Services Digital Network (ISDN) turns the local loop into a TDM digital connection. It is purely digital network but runs on analog twister pair lines. Speed is one advantage ISDN has over telephone line connections. There are two ISDN implementations. They are,

 Basic Rate Interface (BRI)

 B channels – Bandwidth of 64kbps

D channels – Bandwidth of 16 kbps

          Designed as 2B + D

Primary rate Interface (PRI)

  B & D – Bandwidth of 64kbps

 The design varies according to the nation.

 Ex – North America & Japan 23B+D      

  

 

SDN Carries voice calls and data simultaneously on one line. It uses time division multiplexing (TDM) over two wire pairs. TDM Divides single channel into multiple channels.      

                         Dial-up connection also uses the PSTN for connect with WAN. It provides a low cost need based access. We can achieve bit rate up to 56kbps.In this method Modem is connected to a Telephone Line on the Customer End. Remote Access Server (RAS) is connected to Telephone Lines (33.6 Kbps connectivity) or E1/R2 Line (56 Kbps connectivity) on the Service Provider End. Then RAS provide dialing connectivity, authentication and metering. Disadvantage of this technology is achievable bandwidth depends on the line quality and the traffic of the network.

 

Digital Subscriber Line (DSL) technology is a broadband technology that uses existing twisted-pair telephone lines to transport high-bandwidth data to service subscribers. The term XDSL covers a number of similar yet competing forms of DSL technologies.DSL technology allows the local loop line to be used for normal telephone voice connection and an always-on connection for instant network connectivity. The two basic types of DSL technologies are asymmetric (ADSL) and symmetric (SDSL).  All forms of DSL service are categorized as ADSL or SDSL and there are several varieties of each type. Asymmetric service provides higher download or downstream bandwidth to the user than upload bandwidth. Symmetric service provides the same capacity in both directions.

Multiple DSL subscriber lines are multiplexed into a single, high capacity link by the use of a DSL Access Multiplexer (DSLAM) at the provider location. DSLAMs incorporate TDM technology to aggregate many subscriber lines into a less cumbersome single medium, generally T3/DS3 connection techniques to achieve data rates up to 8.192 Mbps.