1. Basic Network Messages GryphonTech Day 2

2. How is it like a …. In your engineering notebooks, describe how a computer network is like the weather. http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Composition_book.jpg/150px-Composition_book.jpg

3. Today’s Goal Understand how a computer network puts packets together to send a message. We will look at layer 2 and 3 of the network protocol stack.

4. Protocol Stack A protocol is a code of procedures or behaviors in any group, organization, or situation. In information technology (IT) a network protocol stack provides the rules for how each part of the network talks to each other. http://cdn.sheknows.com/articles/2011/01/Kids_shaking_hands.jpg

5. What does that mean? Application layer StoryBrowser, ….What device uses it? Transport layer Words, …TCP, or SMTP, or … Network layer Letters, numbers, special characters IPRouter Link layerShapesEthernetSwitch Physical layerGraphite and paperThe cable that connects one machine to another Hub

6. Ethernet Frame IEEE 802.3 64 to 1518 bytes long because (see later slide) Preamble is 10101010 …DATA… is packet from next higher protocol level (IP Packet) FCS is a checksum Padding, between this frame and next http://telecom.tbl.net/novphy2.gif

7. Ethernet Protocol 1. Listen to the wire 2. If there is nothing on the wire, send something 3. If there is something on the wire, listen until it is free. 4. If collision go to, wait a random amount of time and then go to #2 http://checkerautobody.com/images/collision.jpg

8. Limits allow Ethernet to work 1. Minimum frame length (64 bytes) to ensure I can see if something is on the wire 2. Maximum wire length (100 meters or 325 feet) to ensure I can see if something is on the wire

9. Simulation A 6 sided die to ensure randomness A metronome to set the timing Four pairs of volunteers to talk Follow Ethernet protocol ◦ Listen ◦ Say two sentences ◦ Don’t talk if someone else is talking ◦ If two people start to talk at the same time, roll the dice and see who goes first.

10. Brainstorm 1. What can go wrong with Ethernet?

11. IP Addresses My network. my computer Depends on size of network 255.255.255.255 or 11111111.11111111.1111111.11111111 Only the parts that talk directly to the Internet needs to have Internet unique addresses. Everything else can be aliased.

12. IP Packet Header Followed by its package (the TCP packet…) http://ptgmedia.pearsoncmg.com/images/chap3_0672323516/elementLinks/03table02.gif

13. IP Packets are used by Routers Makes sure the header checksum is good. Decrease the time to live so a packet that cannot be delivered does not stay around forever. Looks at the IP address to decide which of its cables to send the packet over. Give it a new Destination Ethernet address. Compute the new checksum on Ethernet frame. And does a few other things….

14. Is IP like a Post Office? 1.Need a sending and receiving address? 2.Package has a size? 3.See if the outside of the package is OK? 4.Sent to a more central location if it is not a local package? 5.Doesn’t care what is inside? 6.Does a few other things? http://www.greeleycounty.org/images/postoffice.jpg

15. Simulate IP traffic Each table is a subnet. The pole stand has your subnet address on it. You have one router, represented by a whiteboard and marker. You are connected to the routers on each side of you, represented by rope. You an only send a message to someone by passing it through connections. On the whiteboard 1.Write down the addresses of all the other subnets 2.Figure out the fastest way to get a message to them 3.Write down which router the message will go to next Table 8 has a connection to the Internet

16. Simulate IP traffic, cont Pass a few messages around ◦ From Address ◦ To Address ◦ Time to live What happens when the network changes?

17. Brainstorm What can go wrong with IP?

18. Ticket Out  Draw an Ethernet Frame (envelope)  That contains an IP Packet (letter)  That contains the message, such as “hello”  Assume each letter in the message takes one byte for the purpose of counting.  Write down the names of the fields with the contents below it. Destination address 192.168.5.83

19. Bibliography - Content “Ethernet frame”, Wikipedia, the free encyclopedia. Wikimedia Foundation, Inc., 7/23/2011 Web. 7/23/2011. “IP Packet Structure”, Connected: An Internet Encyclopedia. Connected. 4/1997. Web. 7/6/2011. “MAC addresses”, Wikipedia, the free encyclopedia. Wikimedia Foundation, Inc., 7/13/2011. Web 7/13/2011.

20. Bibliography - Images Kids Shaking Hands, 2/16/2001, She Knows Parenting, Web 7/13/2011, http://cdn.sheknows.com/articles/2011/01/Kids_shaking_hands.jpg http://cdn.sheknows.com/articles/2011/01/Kids_shaking_hands.jpg Collision, n.d. Checker Auto Body Repair, Inc. Web. 7/13/2011. http://checkerautobody.com/images/collision.jpg http://checkerautobody.com/images/collision.jpg Ethernet Frame. 10/25/2004. Tampa Bay Interactive, Inc. Web. 7/14/2011. http://telecom.tbl.net/novphy2.gifhttp://telecom.tbl.net/novphy2.gif IP Packet Header. 8/23/2002. informIT. Web. 7/14/2011. http://ptgmedia.pearsoncmg.com/images/chap3_0672323516/eleme ntLinks/03table02.gif http://ptgmedia.pearsoncmg.com/images/chap3_0672323516/eleme ntLinks/03table02.gif Post Office. n.d. Greeley County, Kansas. Web. 7/14/2011. http://www.greeleycounty.org/images/postoffice.jpg http://www.greeleycounty.org/images/postoffice.jpg Composition Book, 5/17/2011 Wikipedia, The Free Encyclopedia/ Web. 8/1/2011.