1. ECE4605: Advanced Internetworking
Raghupathy Sivakumar

2. Administrative Information
Office: 5164 Centergy
Phone:
URL:
By appointment

3. ECE4605: Goals
To expose students to the state of the art in computer networking
Material used in course primarily tapped from research publications and new industry standards
Research oriented focus (includes project)
Suggested Textbook Reading: Computer Networks (Tanenbaum), TCP/IP Illustrated Volume 1 (Stevens), Advanced Internet Technologies (Black), Internetworking with TCP/IP (Comer)

4. Focus of this course … Network Quality of Service
OSI/TCP/IP
Network Quality of Service
Wireless and Mobile Networking
Peer-to-peer/Overlay networking
Network security
Miscellaneous topics
Puzzles!!

5. Grading for undergraduate and graduate students independent
Evaluation & Grading
Midterm 15%
Final 35%
Project 20%
Presentations
+ Reviews/Disc 30%
Grading for undergraduate and graduate students independent

6. Paper Presentations & Reviews
Reading list to be put up on Web
2 students per team
Send to me by FRIDAY midnight about any preferences for teams
Each team will present approximately 4 papers during the semester
ALL students will review ALL papers
Reviews to be turned in by before the first class after each set of presentations

7. Presentations & Reviews (contd.)
Introduction (setting up context and relating to lectures)
Concepts/Algorithms/Main body of work
Results/Performance Evaluation
Critique/Suggestions for Improvement
Discussions
Concepts not understood
Reviews
Summary of paper

8. Projects List to be put up shortly Teams of 2 students each
Students interested in other projects can talk to me
Different projects
Project-based meetings with me after the project assignment stage
Regular interaction with me encouraged

9. Examinations
Exams based on concepts in lectures/presentations/discussions
If student does critique honestly, exams should require minimal additional preparation

10. Timeline

11. Overview of OSI & TCP/IP

12. 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?

13. 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?

14. 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

15. OSI Protocol Standard
Physical: mechanical/electrical rules for transferring bits
Link Layer: flow control/error detection/error recovery
Network: routing/congestion control
Transport: end-to-end communication of data/reliability/sequencing/flow control/error control
Session: application specific functionality, but generic to multiple applications (e.g. security)
Presentation: Data formatting
Application: http, ftp, smtp

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

17. Data Link Layer Flow Control Error Detection Error Recovery
Stop and Go
Sliding Window
Error Detection
Parity Check
Cyclic Redundancy Check (CRC)
Checksum
Error Recovery
Stop and Wait ARQ
Go back N ARQ
Selective Reject ARQ

18. Medium Access Control
Multiple stations sharing a common medium. Resolution of who gets access to the medium.
ALOHA
Slotted ALOHA
CSMA (non-, 1-, p- persistant)
CSMA/CD

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

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

21. Overview of TCP/IP

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
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

24. 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

25. 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

26. 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

27. CSMA (contd.) 1-persistent CSMA p-persistent CSMA non-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

28. 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

29. CSMA/CD (Contd.)
When will the performance of CSMA/CD be the same as that of CSMA?
IEEE Ethernet LAN Standard
Full-duplex Ethernet

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

31. 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?

32. 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

33. 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

34. 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 …

35. 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

36. 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

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

38. 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

39. 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

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

41. 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)

42. 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

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

44. 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?

45. 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.

46. 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

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

48. 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

49. 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

50. 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)

51. 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

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

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

54. 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

55. 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

56. Puzzle 1 You have a chain consisting of 63 inter-linked gold links
You have to stay at a motel where the charge per day is 1 gold link
You do not trust the motel manager and neither does he trust you
What is the minimum number of links you need to break in order to stay for 63 days?
Clue: The manager will not sell the links till you check out