ECE 4607: Mobile & Wireless Networks

1. ECE 4607: Mobile & Wireless Networks Raghupathy Sivakumar http://www.ece.gatech.edu/research/GNAN http://www.ece.gatech.edu/~siva/ECE4607

2. Guest Lectures • Professor Sivakumar traveling for a lecture at the WISARD (Wireless Systems: Advanced Research and Development) 2009 conference • Guest lectures on January 6th and 8th

3. e-Handouts (online) • Class information • Schedule

4. Goals • Fundamental concepts in wireless network protocols and algorithms • Impact of wireless networks on the different layers of the network protocol stack • Theoretical and practical exposure to problems and solutions in wireless network protocols

5. Requirements • Knowledge of the OSI protocol stack • Some knowledge of the TCP/IP protocol suite and associated protocols • Experience in programming for assignments & project

6. Administrative Information • Raghupathy Sivakumar • Room 5164, Centergy • Email : siva@gatech.edu • Office hours: By appointment • Class website • http://www.ece.gatech.edu/~siva/ECE4607/ • TA • TBD

7. Policies • Slides: Lecture slides available on website by 12noon on the day of class • Lecture slides are NOT comprehensive – students are expected to attend classes to “fill in” information • Classes: Miss classes at your own risk. Professor and TAs will not be responsible for any information you might not have because of a missed class. • Cheating: Zero tolerance policy toward cheating. You will receive an F for the entire class if you are found cheating in any exam or assignment. • Disturbance: No talking in class and disturbing other students when lecture is being delivered. Please turn OFF your cellphones before sitting down for lectures. You will be asked to leave the classroom if you violate this policy.

8. Textbook • No textbook • Primary material: • Class discussions + slides • Suggested reading • Supplementary reading to be suggested during lectures

9. Grading • Exams • 2 midterms (2 x 10% = 20%) • 1 final (1 x 30% = 30%) • Assignments • 3 paper presentations (3 x 5% = 15%) • 15 paper reviews (15 x 1% = 15%) • Project • 1 mini-project (1 x 15% = 15%) • Other • Class participation (1 x 5% = 5%) • Active participation required • Need to turn in a participation report at the end of the semester (make notes of interactions in class)

10. Paper Presentations • 3 paper presentations per group • Students to complete assignments in groups of 4* • 15% of your final grade • Papers to present will be put up on class website • All students have to review papers their group is not presenting (1% per paper) * Subject to change

11. Project • 1 mini-project • 15% of your final grade • Project will be defined for you • Deliverables: Preliminary report, demonstration and results, final report/presentation

12. Groups: Regular Students • Form groups of three • Try to choose students with complimentary skills • Send groups to TA (one email per group w/ subject: ECE 6610 Groups) by end of day Thursday, 1/20

13. References, Reading Material, and Lecture Notes • Most references – research papers in the concerned area. Available online. • Follow lecture slides and class discussions closely

14. OSI Model

15. Communication Networks • Broadcast networks • Each station can hear every other station in the network (fully connected network) • Switched networks • Stations interconnected through a (non-fully) connected mesh • Packet switched vs. Circuit switched What kind of a network is the Internet?

16. Communication Protocols • Rules used in communication • Monolithic vs. Layered • Protocol data units – used to exchange information between peer layers of protocol stack • Examples of communication protocols?

17. OSI • Open Systems Interconnection: ISO (International Standards Organization)’s standard for communication protocols • Also referred to as the OSI reference model or simply the OSI model • 7 layer protocol stack

18. OSI Protocol Stack • Physical • Data link • Network • Transport • Session • Presentation • Application

19. OSI (contd.) • Physical: mechanical/electrical rules for transferring bits • Data link: • flow control • error detection • error recovery

20. OSI (contd.) • Network • Routing • Congestion control • Quality of service • Transport • End-to-end communication of data • Reliability • Sequencing • Flow control • Congestion control

21. OSI (contd.) • Session • Application specific functionality • Still, generic to multiple applications (e.g. security) • Presentation • Data formatting • Application

22. TCP/IP Protocol Suite • Differences between OSI and TCP/IP? • 5 layers: • Physical • Data link/MAC (ARP, SLIP) • Network (IP, ICMP, IGMP) • Transport (TCP, UDP) • Application (http, ftp, telnet, smtp)

23. Medium Access Control

24. Overview • Medium Access Control • ALOHA, slotted-ALOHA, CSMA, CSMA/CD • Scheduling • FCFS, Priority scheduling • Fair queuing, Weighted fair queuing • Round robin, Weighted round robin • Deficit round robin • Class based queuing

25. Medium Access Control • When multiple stations share a common channel, the protocol that determines which station gets access to the shared channel • Key characteristics based on which MAC protocols are evaluated: utilization and fairness

26. ALOHA • ALOHA • When a station wants to transmit, it transmits … • Collisions detected at a higher layer and retransmissions done as required • Simple logic • Highly inefficient at large loads. Maximum utilization of 18% at a mean load of 0.5 transmissions/slot

27. Slotted ALOHA • Stations can transmit only at the beginning of pre-determined slots • Reduces the “vulnerable period” for collisions • More efficient • Maximum utilization of 36% at a mean load of 1 transmission/slot

28. Carrier Sense Multiple Access • Station wishing to transmit senses channel. If channel idle, transmits. Else, backs-off and tries later • Carrier sensing hardware required • More efficient than both versions of ALOHA • 3 flavors of CSMA

29. CSMA (contd.) • 1-persistent CSMA • On finding channel busy, station continues listening and transmits when channel becomes idle • p-persistent CSMA • On finding channel idle, station transmits with a probability of p, backs-off and tries again when channel is busy • non-persistent CSMA • On finding channel busy, station backs-off for a random amount of time and tries later

30. CSMA/CD • In CSMA, when there is a collision of two transmissions, it is detected only after the entire frames have been transmitted … irrespective of when the collision occurs • CSMA/CD includes a collision detection mechanism that can detect collisions even as stations are transmitting • Transmitting stations terminate transmissions upon collision detection and try later

31. CSMA/CD (Contd.) • When will the performance of CSMA/CD be the same as that of CSMA? • IEEE 802.3 Ethernet LAN Standard • 802.3u – fast ethernet • 802.3ab – gigabit ethernet • 802.3ae – 10G ethernet • Full-duplex Ethernet

32. Other MAC Schemes • Collision free protocols • Bit map protocol • Binary countdown protocol • Limited contention protocols • Adaptive tree walk protocol

33. Recap • Class goals and overview • Grading and other administrative stuff • Communication networks • OSI Protocol Stack

34. Scheduling

35. 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?

36. Scheduling Policies … • FCFS • 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

37. 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

38. 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 …

39. 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

40. 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

41. 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

42. 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

43. Internet Protocol (IP)

44. 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

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

46. 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)

47. 0 netId hostId 7 bits 24 bits 1 0 netId hostId 14 bits 16 bits 1 1 0 netId hostId 21 bits 8 bits Address Classes • Class A • Class B • Class C

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

49. 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?

50. 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.