Public Switched Telephone Network (PSTN)

Communication networking Networking modes Connection oriented Connectionless Switching modes Circuit switching Packet switching

Connection oriented Pros Cons Switching Modes Guaranteed service Efficient bandwidth utilization Cons Delay in connection setup Switching Circuit switching – PSTN, SDH/SONET, DWDM Packet switching – X.25, Frame Relay, ATM Modes Depending on estimated traffic- PVC Depending on demand- SVC

Connection oriented

Connectionless

Data Communications

Evolution of Data Networking Architecture Time Architecture 1970s Standalone mainframes Early 1980s Networked mainframes Standalone workstations Early to late 1980s Local area networking Mid-1980s to mid-1990s LAN internetworking Mid-1990s Internet commercialization Mid- to late 1990s Application-driven networks Late 1990s Remote-access workers Early 2000s Home area networking Mid-2000s Personal area network and the Internet

Data Traffic Communications Applications Web surfing and emails Transaction processing File transfer Interactive computing and information retrieval

Data Flow Aspects of data flow DTE – DCE – Transmission Channel – Physical Interface Modems and modulation Data transmission types Simplex Half duplex Full duplex Coding scheme Data transmission modes Asynchronous Synchronous Error control

DTE, DCE, Tx. DTE DCE Tx and Rx info Error control Establishes, maintains and terminates the session between DTE and the Channel Channel coding PBX, Modem

Modems and modulation Conversion of digital to analog for Tx medium

Modulation schemes Single-carrier Multicarrier Sub-band divided single carrier

Scheme Description Single carrier 2B1Q 4 levels of amplitude for 2 bits/Hz. ISDN, HDSL 64-QAM Modulates both amplitude and phase. 6 bits/Hz 256-QAM ?? Bits/Hz 16-QAM ?? bits/Hz QPSK Phase modulation. Over the air transmission, broadcast and satellite channels CAP Carrier amplitude phase modulation. Combination of amplitude and phase modulation Multicarrier OFDM Orthogonal frequency division multiplexing. For wireless broadcast and broadband solutions. 802.11a, 802.11g, 802.16 DMT Discrete multitone. Variable spectral efficiency for each sub-bands. DSL

OSI Reference Layer