1. Overview-Part2

2. Physical Media Twisted Pair (TP) two insulated copper wires
Category 3 UTP: traditional phone wires, 10 Mbps Ethernet
Category 5 UTP: 100Mbps Ethernet
Bit: propagates between transmitter/receiver pairs
physical media: what lies between transmitter & receiver
guided media:
signals propagate in solid media: copper, fiber, coax
unguided media:
signals propagate freely, e.g., radio

3. Physical Media: coax, fiber
Coaxial cable:
higher bit rates than twisted pair
baseband:
single channel on cable
legacy Ethernet
broadband:
multiple channels on cable
Cable TV systems
Fiber optics:
glass fiber carrying light pulses, each pulse a bit
high bit rate:
Terabits/sec with wavelength division multiplexing (WDM)
low signal attenuation; immune to electromagnetic interference

4. Physical media: radio Radio link types: terrestrial
local area (802.11b)
wide-area (WAP, i-mode, 3G)
satellite
Geostationary: 250 msec end-end delay
Low-altitude: many satellites needed
signal carried in electromagnetic spectrum
no physical “wire”
propagation environment effects:
reflection
obstruction by objects
interference

5. Internet structure: network of networks
roughly hierarchical
at the top: “tier-1” ISPs (Internet backbones)
international coverage
directly connected to other tier-1 ISPs
e.g., UUNet, BBN/Genuity, Sprint, AT&T
NAP
Tier-1 providers also interconnect at public network access points (NAPs)
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
Tier 1 ISP
Tier 1 ISP

6. Internet structure: network of networks
“Tier-2” ISPs: smaller (often national/regional) ISPs
Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier-2 ISPs also peer privately with each other, interconnect at NAP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet.
Tier-2 ISP is customer of
tier-1 provider
Tier 1 ISP
NAP
Tier 1 ISP
Tier 1 ISP

7. Internet structure: network of networks
“Tier-3” ISPs and local ISPs
last hop (“access”) network (closest to end systems)
local
ISP
Tier 3
Local and tier- 3 ISPs are customers of
higher tier ISPs
connecting them to rest of Internet
Tier-2 ISP
Tier 1 ISP
NAP
Tier 1 ISP
Tier 1 ISP

8. How do loss and delay occur?
packets queue in router buffers, wait for turn
packet being transmitted (delay) A
free (available) buffers: arriving packets
dropped (loss) if no free buffers
packets queueing (delay) B

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

10. Delay in packet-switched networks
3. Transmission delay:
R=link bandwidth (bps)
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 (~2x108 m/sec)
propagation delay = d/s
Note: s and R are very different quantities! A B
propagation
transmission
nodal
processing
queueing

11. Caravan analogy
toll
booth
toll
booth
100 km
100 km
ten-car
caravan
Cars “propagate” at 100 km/hr
Toll booth takes 12 sec to service a car (transmission time)
car~bit; caravan ~ packet
Q: How long until caravan is lined up before 2nd toll booth?
Time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec
Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr
A: 62 minutes

12. Caravan analogy (more)
toll
booth
toll
booth
100 km
100 km
ten-car
caravan
Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth.
1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router!
See Ethernet applet at AWL Web site
Cars now “propagate” at km/hr
Toll booth now takes 1 min to service a car
Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth?

13. Nodal delay dproc = processing delay dqueue = queuing delay
typically a few microsecs or less
dqueue = queuing delay
depends on congestion
dtrans = transmission delay
= L/R, significant for low-speed links
dprop = propagation delay
a few microsecs to hundreds of msecs

14. Queueing delay (revisited)
R=link bandwidth (bps)
L=packet length (bits)
a=average packet arrival rate (packets/sec)
traffic intensity = La/R
La/R ~ 0: average queueing delay small
La/R -> 1: delays become large
La/R > 1: more “work” arriving than can be serviced, average delay infinite!

15. Packet loss queue (aka buffer) preceding a link has finite capacity
when packet arrives to full queue, packet is dropped (aka lost)
lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

16. 1961-1972: Early packet-switching principles
Internet History
: Early packet-switching principles
1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1967: ARPAnet conceived by Advanced Research Projects Agency (ARPA)
1969: first ARPAnet node operational
1972:
ARPAnet demonstrated publicly
NCP (Network Control Protocol): first host-to-host protocol
first program
ARPAnet has 15 nodes
Roberts

17. 1972-1980: Internetworking, new and proprietary nets
Internet History
: Internetworking, new and proprietary nets
1970: ALOHAnet microwave network in Hawaii
1973: Metcalfe’s PhD thesis proposed Ethernet
Proprietary architectures: DECnet, SNA, XNA
1974: Cerf and Kahn - architecture for interconnecting networks
1979: ARPAnet has 200 nodes

18. 1980-1990: new protocols, a proliferation of networks
Internet History
: new protocols, a proliferation of networks
1983: deployment of TCP/IP
1982: SMTP protocol defined
1983: DNS defined for name-to-IP-address translation
1985: FTP protocol defined
1988: TCP congestion control
new national networks: CSNET, BITnet, NSFnet
100,000 hosts connected to confederation of networks

19. 1990, 2000’s: commercialization, the Web, new apps
Internet History
1990, 2000’s: commercialization, the Web, new apps
Early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web
HTML, HTTP: Berners-Lee
late 1990’s: commercialization of the Web
Late 1990’s – 2000’s:
more killer apps: instant messaging, peer2peer file sharing
est. 50 million host, 100 million+ users
backbone links running at Gbps