A Little More on Chapter 7 And Start Chapter 8 TCP/IP

1. A Little More on Chapter 7And Start Chapter 8 TCP/IP

2. 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 Today

3. 7.7 Model for Quality of Service Analysis by Traffic Management 1 N-1 N 2 … Figure 7.41

4. (a) FIFO Queueing. (b) FIFO with 2 classes (a) Packet buffer Arriving packets Transmission link Packet discard when full (b) Packet buffer Arriving packets Transmission link Class 1 discard when full Class 2 discard when threshold exceeded Figure 7.42

5. Priority Queueing Packet discard when full High-priority packets Transmission link Low-priority packets When high-priority queue empty Packet discard when full Figure 7.43

6. Sorting packets according to priority tag Sorted packet buffer Arriving packets Tagging unit Transmission link Packet discard when full Figure 7.44

7. 7.8 Congestion Control Router 4 is overloaded. Requests for retransmissions compound the problem. Congestion 3 6 1 4 8 2 7 5 Multitasking computers can have the same type of queueing model, and the same type of saturation. Figure 7.50

8. 7.8 Congestion Control Open loop vs. closed loop methods Controlled Throughput Uncontrolled Due to "thrashing" Offered load Figure 7.51

9. Open Loop Control depends controlling or shaping entry to the system. One techniques is smoothing the variations in flow with the “leaky bucket” approach Water poured irregularly Leaky bucket Water drains at a constant rate Leaky bucket model for monitoring access controlled traffic and for smoothing bursty traffic Figure 7.53

10. Incoming packets are classified as conforming or non-conforming depending on whether they cause the bucket to overflow Nonconforming Packet arrival Time L+I Bucket content I Time * * * * * * * * * Leaky bucket used to identify non-conforming packets. Marked for deletion Figure 7.55

11. Traffic shaping. Output of leaky bucket with buffer looks more like (a) 10 Kbps (a) 0 1 2 3 Time 50 Kbps (b) 0 1 2 3 Time 100 Kbps (c) 0 1 2 3 Time Figure 7.58

12. 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. TCP uses Closed Loop Congestion Control

13. 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 How Does the Congestion Window Work?

14. The congestion window seeks the optimum level just before congestion occurs Congestion occurs Congestion 20 avoidance First threshold 15 Congestion window Threshold 10 Slow start 5 0 Round-trip times Figure 7.63

15. 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) Material in Chapter 8

16. Application Application TCP UDP ICMP IP ARP RARP Physical network Figure 8.1

17. HTTP Request Header contains source and destination port numbers TCP Header 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. Machine B Machine A Application Application Transport Transport Router/Gateway Internet Internet Internet Network Interface Network Interface Network Interface Network 1 Network 2 Figure 8.3

19. IP Packet Design: Fields Defined on next two slides 0 4 8 16 19 24 31 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 Figure 8.4

20. 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. IP Packet Fields

21. 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 IP Packet Fields, Continued

22. Varieties of IP addresses Bit position: 0 1 2 3 8 16 31 Class A 0 Net ID Host ID Class B 1 0 Net ID Host ID Class C 1 1 0 Net ID Host ID Class D 1 1 1 0 Multicast address Class E 1 1 1 1 Reserved for experiments Figure 8.5

23. Original 1 0 Net ID Host ID address Subnetted 1 0 Net ID Subnet ID Host ID address Figure 8.6

24. H1 H2 150.100.12.154 150.100.12.176 150.100.12.128 150.100.12.129 150.100.0.1 R1 To the rest of H3 H4 150.100.12.4 the Internet 150.100.12.55 150.100.12.24 150.100.12.0 150.100.12.1 R2 H5 150.100.15.54 150.100.15.11 150.100.15.0 Figure 8.7