1 Voice and Video Networks Reserved Capacity –Circuit capacity is reserved during duration of each call –At each switch –On each trunk line Circuit Reserved Capacity Reserved Capacity

2 Voice and Video Networks Reserved Capacity –Another name for this type of circuit is circuit switching –Circuit Switching Characteristics a connection is established before 2 stations begin transmitting bandwidth (range of frequencies) is dedicated to the connection until the connection is terminated

3 Voice and Video Networks Reserved Circuit Capacity Guarantees Throughput –Never get less than reserved capacity –Nothing like congestion on the Internet Reserved Circuit Capacity is Expensive –Pay for it whether you use it or not –Good for voice, because conversations are fairly constant –Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for a long time until next download

4 Packet-Switched Data Networks Packet Switching –Circuit switching is expensive due to reserved capacity –Packet switching breaks transmissions into messages –Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently –Messages are called packets (sometimes, frames or other names) Message Packets

5 Packet-Switched Data Networks Packet Switching –packets can travel any path to a destination –packets contain destination address and sequencing information (puts packets back in proper order) –example class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route how can this be done? Message Packets

6 Packet-Switched Data Networks Packet Switching –example class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route use a car, bus or walk (different network technologies) go towards Ft. Campbell and then down 101st or out college street? Which door of mall will you enter?

7 Circuit-Switched Data Networks Circuit Switching –example class (message) send you to Ruby Tuesday’s in Mall reserved 3 busses that will arrive at end of class –make the reservation ahead of time (establish a circuit) –pay for 36 seats (12 per bus) - if only 2/3 of the class is here, I have wasted capacity

8 Packet Switched Data Networks Multiplexing –Packets from many conversations are mixed (multiplexed) over each trunk line –Only pay for the capacity used –Dramatic trunk line cost savings –The reason for packet switching Multiplexing on Trunk Line

9 Brief History of the Internet USSR launches Sputnik, USA forms Advanced Research Projects Agency (ARPA) DoD supports ARPAnet as a research into networks (4 nodes - UCLA, Stanford, UCSB, Univ. of Utah) First international nodes in England and Norway TCP/IP established as Internet Protocol

10 Internet History Continued NSF Net established 5 connected supercomputer sites NSF Net upgraded to T1(1.54Mbps) with international connections Backbone upgraded to T3 (45 Mbps) WWW introduced by CERN Original NSF retired and replaced with NSP Tier 1, 2, 3, 4

11 The Internet ISPs and NSPs –Began in the United States –Is being copied and adopted by other countries –However, not universal