1. Raghupathy Sivakumar http://www.ece.gatech.edu/research/GNAN
ECE4605: Scheduling & IP
Raghupathy Sivakumar

2. Puzzle
Two threads. Each thread will burn completely in 1 hour when lit from an end.
Rate of burn variable and non-uniform (e.g. a thread cut in half will not burn in 30 minutes)
How will you time 45 minutes?
Light one thread from 2 ends, and one thread from 1 end. When
the thread lit from both ends burns out, light the other end of
the other thread

3. Announcements 2 students per group
Same group for both project and paper presentations
Either both should be undergraduate students, or both should be graduate students
If you have not sent Ram and me the group information, please do so by tonight!

4. Groups Group 1 Niranjan Mysore, Radhika Woo, Dong Hyuk
Group 2 Ahmed, Zaheer Seshadri, Shyam S.
Group 3 Lakshmanan, Sriram Zhuang, Zhenyun
Group 4 Chakraborty, Devpratim Lalani, Ayaz A.
Group 5 Jain, Neha Yadav, Shashwat

5. Reading List Up on our class website
Group 1 will present paper 1, etc.

6. Presentations Plan for 25-30 minutes 18-20 slides Introduction
setting up context
relating to lectures
Concepts/Algorithms/Main body of work
Results/Performance Evaluation
Critique/Suggestions for Improvement
Questions (at least 5 per presentation, distributed along talk)
Rehearse if possible

7. Scheduling
When a station gets to transmit, the protocol that determines which packet gets to be transmitted
Fairness the primary consideration
Weighted fairness … an extension
Default scheduling in today’s Internet?

8. Scheduling Policies … FCFS Priority GPS Packetized GPS
Weighted round-robin

9. Scheduling (Contd.) Weighted Round Robin Simpler approximation of WFQ
Assumes constant packet sizes
Can cause unfair delay A
Fixed Tx Schedule:
C C C B B A A B C

10. Scheduling (Contd.) WRR with WFQ Spread
For each flow k with weight wk generate wk elements of the form (1/wk,k), (2/wk,k), …, (wk/wk,k)
Sort all such elements from all competing flows in lexicographic order
Extracting the second element of each pair from the resulting sorted list gives the WRR with WFQ spread

11. WRR with WFQ Spread A (1) (1,A) B (2) (1/2,B), (1,B) C (3)
(1/3,C), (2/3,C), (1,C)
Lexicographically Sorted: (1/3,C), (1/2,B), (2/3,C), (1,A), (1,B), (1,C)
Schedule: C B C A B C

12. Other scheduling policies…
Deficit Round Robin (DRR)
Handles varying size packets
Frame of N bits split among the competing flows in the ratio of their weights
Flows get to transmit HOL packet only when they have accumulated packet-length number of bits
Class based queuing (CBQ)
General scheduling and link-share scheduling
Greater flexibility to control scheduling policy

13. TCP/IP Protocol Suite Physical layer Data-link layer – ARP, RARP, SLIP
Network layer – IP, ICMP, IGMP, BootP
Transport layer _ TCP, UDP, RTP
Application layer – http, smtp, ftp

14. Internet Protocol (IP)
Addressing
Routing
Fragmentation and Reassembly
Quality of Service
Multiplexing and Demultiplexing

15. Addressing
Need unique identifier for every host in the Internet (analogous to postal address)
IP addresses are 32 bits long
Hierarchical addressing scheme
Why?
Conceptually …
IPaddress =(NetworkAddress,HostAddress)

16. Address Classes Class A Class B Class C 0 netId hostId
7 bits 24 bits
netId hostId
14 bits 16 bits
netId hostId
21 bits 8 bits

17. IP Address Classes (contd.)
Two more classes
1110 : multicast addressing
1111 : reserved
Significance of address classes?
Why this conceptual form?

18. Addresses and Hosts
Since netId is encoded into IP address, each host will have a unique IP address for each of its network connections
Hence, IP addresses refer to network connections and not hosts
Why will hosts have multiple network connections?

19. Special Addresses hostId of 0 : network address
hostId of all 1’s: directed broadcast
All 1’s : limited broadcast
netId of 0 : this network
Loopback :
Dotted decimal notation: IP addresses are written as four
decimal integers separated by decimal points, where each
integer gives the value of one octet of the IP address.

20. Exceptions to Addressing
Subnetting
Splitting hostId into subnetId and hostId
Achieved using subnet masks
Useful for?
Supernetting (Classless Inter-domain Routing or CIDR)
Combining multiple lower class address ranges into one range
Achieved using 32 bit masks and max prefix routing

21. Weaknesses Mobility Switching address classes
Notion of host vs. IP address

22. IP Routing Direct Indirect
If source and destination hosts are connected directly
Still need to perform IP address to physical address translation. Why?
Indirect
Table driven routing
Each entry: (NetId, RouterId)
Default router
Host-specific routes

23. IP Routing Algorithm RouteDatagram(Datagram, RoutingTable)
Extract destination IP address, D, from the datagram and compute the netID N
If N matches any directly connected network address deliver datagram to destination D over that network
Else if the table contains a host-specific route for D, send datagram to next-hop specified in table
Else if the table contains a route for network N send datagram to next-hop specified in table
Else if the table contains a default route send datagram to the default router specified in table
Else declare a routing error

24. Routing Protocols Interior Gateway Protocol (IGP)
Within an autonomous domain
RIP (distance vector protocol), OSPF (link state protocol)
Exterior Gateway Protocol (EGP)
Across autonomous domains
BGP (border gateway protocol)

25. IP Fragmentation
The physical network layers of different networks in the Internet might have different maximum transmission units
The IP layer performs fragmentation when the next network has a smaller MTU than the current network
MTU = MTU=500
IP fragmentation

26. IP Reassembly Fragmented packets need to be put together
Where does reassembly occur?
What are the trade-offs?

27. Multiplexing Web Email MP3 Web Email MP3 TCP UDP TCP UDP IP IP
IP datagrams
IP datagrams

28. IP Header Used for conveying information to peer IP layers Source
Destn
Application
Application
Transport
Router
Router
Transport IP IP IP IP
DataLink
DataLink
DataLink
DataLink
Physical
Physical
Physical
Physical

29. IP Header (contd.) 4 bit version 4 bit hdr length 16 bit total length
TOS
16 bit identification
3 bit
flags
13 bit fragment offset
8 bit TTL
8 bit protocol
16 bit header checksum
32 bit source IP address
32 bit destination IP address
Options (if any) (maximum 40 bytes)
data

30. Puzzle Man in a boat floating in a swimming pool 
He has a large solid iron ball
If he drops the ball into the water, what happens to the level of water in the swimming pool? (increases, decreases, stays the same?)