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Administrative Things

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Presentation on theme: "Administrative Things"— Presentation transcript:

1 Administrative Things
Textbook in the bookstore ? Lecture notes on the web ?? Any questions and suggestions so far ??? … Lecture-3

2 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

3 A Review of Last Lecture
network edge: applications and hosts connection-oriented and connectionless services Internet protocols: ??? and ??? network core: routers, network of networks data switching: circuit switching and packet switching comparison of the two switching approaches virtual circuit networks and datagram networks access networks, physical media Dail-up, DSL, Cable modem, LAN, wireless LAN, 3G, Satellite Twisted pair copper, Coaxial cable, fiber optics, ratio Lecture-3

4 Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs e.g., UUNet, BBN/Genuity, Sprint, AT&T national/international coverage 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 Lecture-3

5 Internet structure: network of networks
“Tier-2” ISPs: smaller (often 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 Lecture-3

6 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 Lecture-3

7 A packet passes through many networks
local ISP Tier 3 ISP local ISP local ISP local ISP Tier-2 ISP Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP local ISP local ISP local ISP local ISP Lecture-3

8 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

9 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 Lecture-3

10 Four sources of packet delay
1. nodal processing: check bit errors determine output link 2. queueing time waiting at output link for transmission depends on congestion level of router A B propagation transmission nodal processing queueing Lecture-3

11 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 Lecture-3

12 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 Lecture-3

13 Caravan analogy (more)
toll booth toll booth 100 km 100 km ten-car caravan 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? 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! Lecture-3

14 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 Lecture-3

15 Queueing delay (revisited)
R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate 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! Lecture-3

16 “Real” Internet delays and routes
What do “real” Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes Lecture-3

17 “Real” Internet delays and routes
traceroute: fester.engr.uconn.edu to Three delay measurements from Fester.engr.uconn.edu to traceroute to ( ), 30 hops max, 40 byte packets ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 4 uconn-edge.net.uconn.edu ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 10 pos4-1.pr1.lga1.us.mfnx.net ( ) ms ms ms 11 so cr1.lga1.us.mfnx.net ( ) ms ms ms 12 so cr1.iad1.us.mfnx.net ( ) ms ms ms 13 so cr1.dca2.us.mfnx.net ( ) ms ms ms 14 so mpr3.sjc2.us.mfnx.net ( ) ms ms ms 15 so cr1.sjc3.us.mfnx.net ( ) ms ms ms 16 pos0-0.er2a.sjc3.us.mfnx.net ( ) ms ms ms 17 alt1-1.java.sun.com ( ) ms ms ms Lecture-3

18 Packet loss queue (aka buffer) preceding link in buffer 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 Lecture-3

19 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

20 Protocol “Layers” Question: Networks are complex! many “pieces”: hosts
routers links of various media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Lecture-3

21 Organization of air travel
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing a series of steps Lecture-3

22 Organization of air travel: a different view
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing Layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below Lecture-3

23 Layered air travel: services
Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination Lecture-3

24 Distributed implementation of layer functionality
ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Departing airport arriving airport intermediate air traffic sites airplane routing airplane routing airplane routing Lecture-3

25 Why layering? Dealing with complex systems:
explicit structure allows identification, relationship of complex system’s pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer’s service transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system layering considered harmful? Lecture-3

26 Internet protocol stack
application: supporting network applications FTP, SMTP, STTP transport: host-host data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Lecture-3

27 Layering: logical communication
Each layer: distributed “entities” implement layer functions at each node entities perform actions, exchange messages with peers application transport network link physical Lecture-3

28 Layering: logical communication
data E.g.: transport take data from app add addressing, reliability check info to form “datagram” send datagram to peer wait for peer to ack receipt analogy: post office application transport network link physical transport ack data data transport Lecture-3

29 Layering: physical communication
data application transport network link physical network link physical application transport network link physical data application transport network link physical application transport network link physical Lecture-3

30 Protocol layering and data
Each layer takes data from above adds header information to create new data unit passes new data unit to layer below source destination application transport network link physical application transport network link physical M H t n l message M H t n l segment datagram frame Lecture-3

31 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core 1.4 Network access and physical media 1.5 ISPs and Internet backbones 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History Lecture-3

32 Homeworks Reading assignments Written assignments
Chapter 1: a good overview of computer networks Written assignments Part of 1st written assignment Chapter 1: Problem #5, 10, 16 (a, b, c) More (& due date) will be posted on the web Try traceroute program again and do some delay analysis choose whatever destination you like Lecture-3

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