1 Introduction and Overview of Network and Telecommunications (contd.)

2 Review: Video: Warriors of the Nethttps://www.youtube.com/watch?v=PBWhzz_Gn10

3 Some Key Points Data is transmitted as packets.Packets are handled by equipments at different layers. Each layer has its own protocol to follow. At each layer, information, or header, is added (or removed) based on the protocol before sending the packet to the lower (or higher) layer.

4 Why using “protocol layers”?

5 Organization of air travelticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Ticket Baggage Gate Takeoff/Landing Advantage of layering: information hiding and reuse Airplane routing airplane routing Layers: each layer implements a service by Perform certain actions within the layer Using the services of the layer directly below it

6 Protocols and Layers Protocols and layering is the main structure method used to divide up network functionality Each instance of a protocol talks virtually to its peer using the protocol Each instance of a protocol uses only the services of the lower layer

7 Internet protocol stackSet of protocols in use in called a protocol stack e.g., web server e.g., web browser e.g., HTTP

8 Internet protocol stackApplication: supporting network applications FTP, SMTP, HTTP Transport: process-process data transfer TCP, UDP Internet: routing of datagrams from source to destination IP Link: data transfer between neighboring network elements Ethernet, (WiFi), PPP Physical: bits “on the wire”

9 TCP vs. UDP: Two Communication ParadigmsStream Message Connection-oriented Connectionless 1-1 communication 1-1, 1-many, many-many Sequence of bytes Sequence of messages Arbitrary length transfer Limited to 64K bytes Widely used Multimedia applications Based on TCP (Guaranteed) Built on UDP (Not Guaranteed)

10 Message (Connectionless) Transport In the InternetUDP (message service) does not make any guarantees. A packet may be Lost Duplicated Delayed Delivered out-of-order

11 Why using message service?No connection establishment Get straight to the point No connection state A server can support more active clients simultaneously Fine application-level control over what data is sent, and when

12 Some Examples TCP today: >95% Internet trafficApplication TCP or UDP? TCP Remote terminal access Web File transfer Streaming multimedia UDP, TCP Internet telephony Name translation Typically UDP Remote file server TCP today: >95% Internet traffic ~75% on-demand and live streaming

13 Encapsulation Encapsulation is the mechanism used to effect protocol layering Lower layer wraps higher layer content, adding its own information (header) to make a new message for delivery Like sending a letter in an envelope; postal service doesn’t look inside

14 Hello World!HTTP message TCP HTTP message IP TCP HTTP message TCP HTTP message IP 802.11 Wire 802.11 IP TCP HTTP message IP TCP HTTP message TCP HTTP message HTTP message HTML Example

15 Another Illustration Think of these nesting dolls:

16 Why Using Packets? use the connection effectively and efficiently

17 Connections between ComputersOverhead Telephone and Telegraph Wires in Broadway, 1890 From Book of Old New York. Henry Collins Brown. 1913

18

19 Switch Model: Reducing the MessAnalogy Airport hubs

20 Tie-1 ISP: e.g., Sprint

21 Question Why you fly, you can check a map to determine what cities are on the route. However, there is no map of the internet, so how do you know what route a packet is taking?

22 An Analogy State College Philly NYC Boston Remote host: JackLocal host: Alice

23 Traceroute Widely used command-line tool to let hosts peek inside the network On all OSes (tracert on Windows) Provides delay measurement from source to router along end-end Internet path towards destination.

24 Traceroute Probe successive hops to find network pathsends 3 packets that will reach each router on path towards destination Each router returns packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes Remote host: Jack Local host: Alice

25 Traceroute Technically, a hop is defined as the action that occurs when a packet “jumps” from one router to the next. Remote host: Jack Local host: Alice 1 hop 2 hop 3 hop N-1 hop N hop

26 Traceroute Question 1 How many computers (incl. local host, remote host, and intermediate routers) does this route have?

27 Traceroute Question 2 How many hops does this route have?

28 Traceroute Question 3 Remote host: Jack Local host: Alice 1 hop 2 hop 3 hop N-1 hop N hop For a route with N hops, how many computer does it have?

29 Traceroute Question 4 Remote host: Jack Local host: Alice 1 hop 2 hop 3 hop N-1 hop N hop Local host sends 3 packets to each computer on the route (incl. routers and remote host). If the route has N hops, how many packets does local host send in total?

30 Traceroute Question 5 Remote host: Jack Local host: Alice 1 hop 2 hop 3 hop N-1 hop N hop For a route with N hops, how many packets are forwarded by the router that is closest to the local host?

31 Traceroute Example 1 C:\> tracert allspice.lcs.mit.edu1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) ms 280ms 260ms Cambridge1.bbnplanet.net ( ) ms 279ms 279ms Allspice.lcs.mit.edu ( ) 3 delay measurements

32 Traceroute Question 6 C:\> tracert allspice.lcs.mit.edu1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) ms 280ms 260ms Cambridge1.bbnplanet.net ( ) ms 279ms 279ms Allspice.lcs.mit.edu ( ) How many computers are there in this route? How many hops?

33 Traceroute Question 7 C:\> tracert allspice.lcs.mit.edu1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) ms 280ms 260ms Cambridge1.bbnplanet.net ( ) ms 279ms 279ms Allspice.lcs.mit.edu ( ) How many packets are sent by local host? How many packets are forwarded by New York (New-York2.t3.ans.net )?

34 Traceroute Question 8 C:\> tracert allspice.lcs.mit.edu1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) ms 280ms 260ms Cambridge1.bbnplanet.net ( ) ms 279ms 279ms Allspice.lcs.mit.edu ( ) What’s the average round trip time form local host to Cambridge1.bbnplanet.net?

35 Traceroute Example 2 C:\> tracert www.oxford.ac.uk comcastms ms ms ms ms ms c hsd1.pa.comcast.net [ ] ms ms ms te sur02.statecollege.pa.pitt.comcast.net [ ] ms ms ms be-3-ar03.lowerpaxton.pa.pitt.comcast.net [ ] ms ms ms he ar01.pittsburgh.pa.pitt.comcast.net[ ] ms ms ms be-7016-cr01.newyork.ny.ibone.comcast.net [ ] ms ms ms ae12.edge1.NewYork2.level3.net [ ] ms ms ms ae-4-4.car1.Manchesteruk1.Level3.net [ ] ms ms ms ae-4-4.car1.Manchesteruk1.Level3.net [ ] ms ms ms ms ms ms ae29.erdiss-sbr1.ja.net [ ] ms ms ms ae31.londpg-sbr1.ja.net [ ] ms ms ms ae21.read-rbr3.ja.net [ ] ms ms ms ae1.read-rbr2.ja.net [ ] ms ms ms ae2.oxfo-rbr2.ja.net [ ] ms ms ms Oxford-University-2.ja.net [ ] ms ms ms csurb.backbone.ox.ac.uk [ ] ms ms ms boucs.backbone.ox.ac.uk [ ] ms ms ms boucs-lompi1.sdc.ox.ac.uk [ ] ms ms ms aurochs-web-154.nsms.ox.ac.uk [ ] Trace complete. comcast Level3: Trans-atlantic link Janet: UK’s research network oxford

36 Try it yourself Step 1: Start  Run  cmd Step 2: Trace route toSomewhere in the U.S. Somewhere outside U.S. Discuss the results with classmates next to you How may hops are there in the path? What’s the average delay from you computer to the remote host? How many networks does the path traverse?