1. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies A Little More on Chapter 7 And Start Chapter 8 TCP/IP

2. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Today C7: Count-to-Infinity Problem in Distance Vector Routing C7: Traffic management and Quality of Service C7:Congestion Control via Leaky Buckets and TCP Sliding Windows C8: Introduction to TCP/IP

3. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 1 2 NN-1 Figure 7.41 … 7.7 Model for Quality of Service Analysis by Traffic Management

4. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Packet buffer Transmission link Arriving packets Packet discard when full Packet buffer Transmission link Arriving packets Class 1 discard when full Class 2 discard when threshold exceeded (a) (b) Figure 7.42 (a) FIFO Queueing. (b) FIFO with 2 classes

5. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Transmission link Packet discard when full High-priority packets Low-priority packets Packet discard when full When high-priority queue empty Figure 7.43 Priority Queueing

6. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Sorted packet buffer Transmission link Arriving packets Packet discard when full Tagging unit Figure 7.44 Sorting packets according to priority tag

7. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 4 8 6 3 2 1 5 7 Congestion Figure 7.50 Router 4 is overloaded. Requests for retransmissions compound the problem. Multitasking computers can have the same type of queueing model, and the same type of saturation. 7.8 Congestion Control

8. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Offered load Throughput Controlled Uncontrolled Figure 7.51 7.8 Congestion Control Open loop vs. closed loop methods Due to "thrashing"

9. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Water drains at a constant rate Leaky bucket Water poured irregularly Figure 7.53 Open Loop Control depends controlling or shaping entry to the system. One techniques is smoothing the variations in flow with the “leaky bucket” approach Leaky bucket model for monitoring access controlled traffic and for smoothing bursty traffic

10. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies I L+I Bucket content Time Packet arrival Nonconforming ********* Figure 7.55 Incoming packets are classified as conforming or non- conforming depending on whether they cause the bucket to overflow Leaky bucket used to identify non-conforming packets. Marked for deletion

11. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Time0123 0123 10 Kbps Time0123 50 Kbps 100 Kbps (a) (b) (c) Figure 7.58 Traffic shaping. Output of leaky bucket with buffer looks more like (a)

12. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies TCP uses Closed Loop Congestion Control TCP provides end-to-end flow control to avoid overunning a slow receiver by a sliding window. Each byte is given a sequence number! The sender cannot send a new byte unless it is in the allowable “advertised window” However this advertised window does not prevent intermediate routers from overflowing due to congestion To try to optimize speed of transmission TCP establishes a second window called the “congestion window” At any time the window used is the smaller of the two.

13. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies How Does the Congestion Window Work? The size of the congestion window is automatically adjusted depending the experience of the receiver: It starts with a small value: one maximum length “segment,” which is the PDU at the transport level It then ramps up exponentially, doubling on each transmission until it reaches a congestion threshold-- initially "65K bytes." Graph shows 16 x 65K. It then goes up linearly until a time out is experienced -- assumed to be due to congestion The size of the congestion window is then cut back to its initial value and the congestion threshold is cut to half its initial value

14. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Congestion window 10 5 15 20 0 Round-trip times Slow start Congestion avoidance Congestion occurs Threshold Figure 7.63 The congestion window seeks the optimum level just before congestion occurs First threshold

15. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Material in Chapter 8 1. TCP/IP Architecture 2. Internet Protocol IP Version 4 3. IP Version 6 (skip) 4. Transport Layer Protocols (TCP and UDP) 5. DHCP and Mobile Internet (just a little) 6 Internet Routing 7. Multicast Routing (skip)

16. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Application TCPUDP IPICMPARPRARP Physical network Application Figure 8.1

17. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies HTTP Request TCP Header Header contains source and destination port numbers Header contains: source and destination IP addresses; transport protocol type IP Header Header contains: source and destination physical addresses; network protocol type FCS Ethernet Header Figure 8.2

18. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Application Transport Internet Network Interface Application Transport Internet Network 1 Network 2 Machine A Machine B Router/Gateway Network Interface Figure 8.3

19. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Version IHL Type of Service Total Length Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source IP Address Destination IP Address Options Padding 0 4 8 16 19 24 31 Figure 8.4 IP Packet Design: Fields Defined on next two slides

20. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies IP Packet Fields Version. mostly 4 or 6 Internet Header Length IHL in 32-bit words if no options are present IHL=5 Type of Service. (priority) Most routers ignore Total Length. No of bytes in IP packet including header and info. Max is 65,535. Usually less. Ethernet only allows 1500 bytes. ID, Flags, Frag Offset. Used in reassembling fragmented packets.

21. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies IP Packet Fields, Continued Time to Live TTL. Sending host sets. Decremented by one by each router. When field reaches zero, packet is discarded. Normally counts hops. Protocol that will receive packet. TCP=6, UDP=17, ICMP=1 Header checksum. Info part not checked. Since the TTL is decremented by each router, this has to recalculated by each router Source and Destination IP addresses 32 bits each. Options. Rarely used. Padding. used to make header a multiple of 32-bit words

22. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 0Net IDHost ID Net IDHost ID1 0 Net IDHost ID1 1 0 1 1 1 0Multicast address 1 1 Reserved for experiments Class A Class B Class C Class D Class E 0 1 2 3 8 16 31 Bit position: Figure 8.5 Varieties of IP addresses

23. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Original address Subnetted address Net IDHost ID1 0 Net IDHost ID1 0Subnet ID Figure 8.6

24. Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies R1 H1H2 H3H4 R2H5 To the rest of the Internet 150.100.0.1 150.100.12.128 150.100.12.0 150.100.12.176150.100.12.154 150.100.12.24 150.100.12.55 150.100.12.1 150.100.15.54 150.100.15.0 150.100.15.11 150.100.12.129 150.100.12.4 Figure 8.7