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

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

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 (ramanuja79@gmail.com) and me the group information, please do so by tonight!

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

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

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

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?

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

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

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

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

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

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

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

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)

Address Classes Class A Class B Class C 0 netId hostId 7 bits 24 bits 1 0 netId hostId 14 bits 16 bits 1 1 0 netId hostId 21 bits 8 bits

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

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?

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 : 127.0.0.0 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.

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

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

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

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

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)

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 = 1500 MTU=500 IP fragmentation

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

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

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

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

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?)