Introduction and Overview of Network and Telecommunications (contd.)

Reading for next class Ch 4.1 – 4.23: Internet applications

Review: Internet protocol stack Application: 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 ”

TCP vs. UDP: Two Communication Paradigms StreamMessage Connection-orientedConnectionless 1-1 communication1-1, 1-many, many-many Sequence of bytesSequence of messages Arbitrary length transferLimited to 64K bytes Widely usedMultimedia applications Based on TCP (Guaranteed) Built on UDP (Not Guaranteed)

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

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

Some Examples ApplicationTCP or UDP? TCP Remote terminal accessTCP WebTCP File transferTCP Streaming multimediaUDP, TCP Internet telephonyUDP, TCP Name translationTypically UDP Remote file serverTypically UDP TCP today: >95% Internet traffic ~75% on-demand and live streaming

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

Hello World! TCPHTTP message TCPHTTP messageIP TCPHTTP messageIP TCPHTTP messageIP TCPHTTP messageIP TCPHTTP message Wire HTML Example HTTP message

Another Illustration Think of these nesting dolls:

Why Using Packets?

Connections between Computers n(n-1)/2 Overhead Telephone and Telegraph Wires in Broadway, 1890 From Book of Old New York. Henry Collins Brown. 1913

Switch Model: Reducing the Mess Analogy – Airport hubs

Tie-1 ISP: e.g., Sprint

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?

An Analogy State CollegePhillyNYCBoston Local host: Alice Remote host: Jack

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.

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

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

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

Traceroute Question 2 How many hops does this route have?

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

Traceroute Question 4 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? Local host: Alice Remote host: Jack 1 hop 2 hop 3 hop N-1 hop N hop

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

Traceroute Example 1 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net ( ) 4 339ms 279ms 279ms Allspice.lcs.mit.edu ( ) 3 delay measurements

Traceroute Question 6 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net ( ) 4 339ms 279ms 279ms Allspice.lcs.mit.edu ( ) How many computers are there in this route? How many hops?

Traceroute Question 7 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net ( ) 4 339ms 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 )?

Traceroute Question 8 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net ( ) ms 120ms 140ms New-York2.t3.ans.net ( ) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net ( ) 4 339ms 279ms 279ms Allspice.lcs.mit.edu ( ) What’s the average round trip time form local host to Cambridge1.bbnplanet.net?

Traceroute Example 2 C:\> tracert ms 1 ms 1 ms ms 11 ms 9 ms c hsd1.pa.comcast.net [ ] 3 11 ms 10 ms 10 ms te sur02.statecollege.pa.pitt.comcast.net [ ] 4 17 ms 15 ms 15 ms be-3-ar03.lowerpaxton.pa.pitt.comcast.net [ ] 5 21 ms 21 ms 27 ms he ar01.pittsburgh.pa.pitt.comcast.net[ ] 6 45 ms 31 ms 32 ms be-7016-cr01.newyork.ny.ibone.comcast.net [ ] 7 29 ms 28 ms 29 ms ae12.edge1.NewYork2.level3.net [ ] ms 302 ms 306 ms ae-4-4.car1.Manchesteruk1.Level3.net [ ] ms 210 ms 207 ms ae-4-4.car1.Manchesteruk1.Level3.net [ ] ms 103 ms 106 ms ms 107 ms 107 ms ae29.erdiss-sbr1.ja.net [ ] ms 106 ms 106 ms ae31.londpg-sbr1.ja.net [ ] ms 109 ms 109 ms ae21.read-rbr3.ja.net [ ] ms 117 ms 105 ms ae1.read-rbr2.ja.net [ ] ms 107 ms 107 ms ae2.oxfo-rbr2.ja.net [ ] ms 107 ms 107 ms Oxford-University-2.ja.net [ ] ms 110 ms 108 ms csurb.backbone.ox.ac.uk [ ] ms 110 ms 110 ms boucs.backbone.ox.ac.uk [ ] ms 107 ms 107 ms boucs-lompi1.sdc.ox.ac.uk [ ] ms 109 ms 108 ms aurochs-web-154.nsms.ox.ac.uk [ ] Trace complete. Level3: Trans-atlantic link comcast Janet: UK’s research network oxford

Try it yourself Step 1: Start  Run  cmd Step 2: Trace route to – Somewhere 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?