What is the Speed of the Internet? Internet Computing KUT Youn-Hee Han

Computer Network2 Media Types for Internet Internet data flows across: Copper wire Fiber Wireless (radio) Physics tells us that these all represent electromagnetic propagation Einstein Says… The speed of light, hence the speed of electromagnetic propagation is a constant  C = 300 x 10 6 m/s = 3.0 x 10 8 m/s Hence the speed of the Internet is:  300 x 10 6 m/s = 3.0 x 10 8 m/s  well… not exactly

Computer Network3 Propagation Speed “C” is the speed of propagation in “free space” It is well known that… Copper: 2.3 x 10 8 m/s Fiber: 2.0 x 10 8 m/s Radio: 3.0 x 10 8 m/s “Speed” of the Internet is… between 2.0 x 10 8 and 3.0 x 10 8 m/s Let’s assume Internet propagation speed S… S = 2.0 x 10 8 m/s

Computer Network4 How Long Will It Take To Download? Let’s download the following image file from a location Assume the distance D is 5288 km If it were just one bit! D / S = 5288 * 1000 / 2.0 x 10 8 = 26.4 x sec Size: 62,728 bytes D / S = 62,728 x 8 x 26.4 x = 13,248 s = 3.7 hours! Is this correct? 62,728 bytes

Computer Network5 How Long Will It Take To Download? One bit at a time!

Computer Network6 How Long Will It Take To Download? Keeping the Pipe Full!

Computer Network7 Four sources of packet delay Processing Delay (= D proc )  Time to examine the packet’s header and determine where to direct the packet Queuing Delay (= D queue )  Time to exist in queue  In Input queue, it depends on the number of earlier-arriving packets that are queued  In Output queue, it depends on the number of waiting for transmission across the link Transmission Delay (= D trans )  Time to push all of the packet’s bits into the link (= Packet Length / Transmission Rate)  E.g., Packet Length: 1,500 Bits, Transmission Rate : 100 Mbps, Transmission Delay = ? Propagation Delay (= D prop )  Time to propagate from the beginning of the link to the end of the link (= Distance / Propagation Speed)  E.g., Distance: 1Km, Propagation Speed: 3*10^8 m/sec, Propagation Delay = ? Queuing (Input queue) Processing Queuing (Output queue) Transmission Propagation

Computer Network8 1. nodal processing: check bit errors determine output link 2. queueing time waiting at output link for transmission depends on congestion level of router Four sources of packet delay A B propagation transmission nodal processing queueing

Computer Network9 3. Transmission delay: R=link bandwidth (bps) =Transmission Rate L=packet length (bits) time to send bits into link = L/R 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x10 8 m/sec) propagation delay = d/s Note: s and R are very different quantities! Four sources of packet delay A B propagation transmission nodal processing queueing

Computer Network10 Total Delay d proc = processing delay typically a few microsecs or less d queue = queuing delay depends on congestion d trans = transmission delay = L/R, significant for low-speed links d prop = propagation delay a few microsecs to hundreds of msecs

Computer Network11 Delay and Loss in Packet-Switched Network Queuing Delay and Packet Loss Queuing delay depends on  Packet arrival rates, Link transmission rate, Traffic pattern (periodic or in bursts), etc. Traffic Intensity (=TI) in input queue  To estimate the extent of the queuing delay  L: the average packet length (bits)  a: the average packet arrival rate at the queue (packets/sec)  R: Processing rate (in bits/sec) If TI > 1, Packet Loss (Drop) happens at the queue Design your system so that TI is no greater than 1 Golden Rule 1 Average queuing delay Traffic Intensity

Computer Network12 Packet Size Issue Revisited ` Huge-packet Switching Network Small-packet Switching Network Time (in seconds) Time (in msec.) Link Transmission Rate – 1.5 Mbps Large-packet Length - 7,500,000 bits Small-packet Length – 1,500 bits (Total Number of Packets – 5,000 packets) Queuing & Processing & Propagation Delays are zero Assumption Packetizing One hop delivery delay - 5 seconds = 7,500,000 bits / 1.5 Mbps Total delivery delay - ? One hop delivery delay - 1 msec. = 1,500 bits / 1.5 Mbps Total delivery delay - ? Router Source HostDestination Host Router Source HostDestination Host pipelining: each link works in parallel