1. Scheduling, IP …

2. Puzzle Two glass marbles, identical properties
One building with 100 floors
Either marble, if thrown from a certain floor k or above will break, but will not break if thrown from floor k-1 or below
What is the minimum number of throws required to find k? (worst case scenario)
Once you break a marble, you cannot use it anymore

3. Scheduling Policies … FCFS Priority
Packets queued on a first-come-first-served basis
No fairness
Priority
Multiple queues with different priorities
Packets belonging to queue k served only when queues with higher priorities are empty

4. Scheduling (Contd.) Generalized Processor Sharing (GPS)
Ideal fair queuing approach based on a fluid flow system
Complex, idealistic
Packetized GPS (WFQ)
Packetized version of GPS (practical)
Finish times in a correponding GPS system used for prioritizing packets

5. Scheduling - WFQ 3 flows A, B, C Weights: A(1), B(2), C(3)
Assume same packet sizes 8 7
Complex overhead due to
computation of finishing times
Simpler approach? 5 4 6 3 2 1
Tx Schedule: C B C C B A C B …

6. Scheduling (Contd.) Weighted Round Robin A Fixed Tx Schedule:
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

7. 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

8. 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

9. 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

10. 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

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

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

13. 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

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

15. 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?

16. 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.

17. Exceptions to Addressing (norm today)
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

18. Examples Subnetting Supernetting 192.168.1.0/24 – class C network
/26 and /26 – 2 subnetworks with upto 62 stations each!
Supernetting
/24 and /24 – 2 class C networks
/23 – 1 super network with upto 126 stations!!

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

20. 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

21. 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

22. 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)

23. 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

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

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

26. 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

27. 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

28. Recap MAC Protocols: ALOHA, slotted-ALOHA, CSMA, CSMA/CD
Scheduling: FCFS, Priority, FQ, WFQ, WRR, CBQ
Internet Protocol: Addressing, Routing, Fragmentation & Reassembly, Mux/Demux

29. Puzzle You have a deck of 52 cards
You draw out 5 cards randomly and look at the cards
You can now show 4 of the cards to a friend, and the friend should identify the 5th card
How do you do this?

30. TCP/IP in relation to the OSI model
                                               
TCP/IP in relation to the OSI model