Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies CS490 Chapter 7b, Leon-Garcia Packet Switching Networks

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Today’s Outline 7.3 Datagrams vs. Virtual Circuits (a little more) Plus Definition of ATM 7.4 Routing in Packet Networks –Distance Vector, Link State, Flooding, Deflection Routing, Source Routing 7.5 Shortest Path Algorithms –Bellman Ford Algorithm –Construction of Routing Table and Updates –(On the blackboard) –We will not cover Dijkstra's algorithm in detail

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Figure 7.2 Physical layer Data link layer Physical layer Data link layer End system  Network layer Network layer Physical layer Data link layer Network layer Physical layer Data link layer Network layer Transport layer Transport layer Messages Segments End system  Network service Network service

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Medium A B C End system  End system  Network 1 2 Physical layer entity Data link layer entity 3 Network layer entity 3 Transport layer entity 4 Figure 7.3

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Comparison of Virtual Circuit and Datagram Subnets

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies IP Internet Protocol (Network Layer) Actually most information on IP is in Chapter 8 on TCP/IP Here we should just know that IP is a datagram service, packets are routed independently of one another It is not connection-oriented at the network layer, but can be at the transport layer above The IP packet has a header of bytes including source and destination addresses, CRC, and various option and control fields. Details in 8.2. The total length of a packet, including info, can be up to 65K bytes, but transit of Ethernet LANs often limits to 1500 bytes

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Asynchronous Transfer Mode Definition We will skip 7.6 as far as the exam is concerned, but here is a concise definition of ATM (p 483) Connection oriented in network layer Short (48 info bytes) fixed length packets called “cells” Cells contain short (5 byte) headers that point to connections ATM uses fast hardware switches up to 10,000 ports with up to 150Mbps each ATM has some of the best features of circuit switching and packet switching. Asychronous = no master clock

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Combinations of Service and Subnet Structure Type of Subnet (Network Layer)

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 7.4 Routing in Packet Switched Networks Net = Routers (or Switches) and links Routing involves –Setting up routing tables –Forwarding packets Routing Algorithm tries to set up “best” routes –minimize hops or –minimize delay or –maximize bandwidth or... The Routing Algorithm needs global info about net

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Goals of Routing Algorithm Rapid and Accurate Delivery of Packets Adapt to Failure of Node or Link Adapt to Change in Traffic Loads Determine Connectivity of Network Low Overhead

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Classification of Routing Algorithms Static vs. Dynamic (Adaptive) Centralized vs. Distributed Decisions for each Packet vs. at Connection Time

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies A B Switch or router Host Figure 7.23 Example of a Packet-Switched Network: Topology for Example

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies A B C D Figure 7.24 Virtual Circuit Packet Switching Note: VC numbers change at each router. Route on top (thin line) changes from 1 to 2 to 7 to 8. Next slide has routing tables.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Incoming Outgoing node VC A A A A 5 Incoming Outgoing node VC Incoming Outgoing node VC 3 7 B B 5 B B Incoming Outgoing node VC C C 6 Incoming Outgoing node VC Incoming Outgoing node VC 4 5 D 2 D Node 1 Node 2 Node 3 Node 4 Node 6 Node 5 Figure 7.25 Follow that circuit from A via VC Nos. 1, 2, 7,8 to B in Routers 1, 3, and 6.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Node 1 Node 2 Node 3 Node 4 Node 6 Node Destination Next node Destination Next node Figure 7.26 Routing Tables for a Datagram Network. Same Topology.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Hierarchical Addresses in the Internet Actually the book covers TCP/IP together in Chapter 8 Here (p 488) it points out that routing is simplified if hosts within a domain have the same prefix (network address). Then routers outside the domain only have to examine (and store) the prefix Thus IP addresses are always divided into a network address and a host address. (Usually there are three levels, often: network address, LAN address, host address) See Fig 7.27

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies R1R1 R2R (a) R1R1 R2R … … … … (b) Figure 7.27 Fig Advantage of Hierarchical Routing b. Non - Hier. a. Hierarchical -

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Figure 7.28 Fig Sample net with costs. We will use this net for a detailed example on the blackboard But, first let's finish talking about different types of routing.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Figure 7.29 Results of Bellman-Ford Algorithm: Shortest path tree for this network. Our bird's eye view of the net allows us to easily see that this is the lowest cost solution, but it's not so easy for the routers to do this automatically. They only have information measured by other routers to use.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Shortest Path Routing Approaches Distance Vector (original Internet approach, uses only one metric, often hops, uses Bellman-Ford, has count-to- infinity problem, RIP still used in internets) Link State (now most common in Internet, uses Dijkstra,can use multiple cost functions, avoids count-to- infinity)

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Other Routing Approaches Flooding Deflection Routing Source Routing

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (a) Figure Part 1 of 3 Flooding Routing Algorithm Send incoming packets on all output ports, except the one it came in on. First step.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (b) Figure Part 2 of 3 Second Step of Flooding

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (c) Figure Part 3 of 3 Third step of Flooding. Need control to prevent saturation of network. Use "time-to-live" field

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 0,00,10,20,3 1,01,11,21,3 2,02,12,22,3 3,03,13,23,3 Figure 7.34 Hot Potato or Deflection Routing

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies 0,00,10,20,3 1,01,11,21,3 2,02,12,22,3 3,03,13,23,3 busy Figure 7.35 Routers can do without buffers. Pure switch can be used. (0,2) wants to send to (1,0), but (0,1) is busy. Deflect to right.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies A B Source host Destination host 1,3,6,B 3,6,B 6,B B Figure 7.36 Source Routing

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Congestion Figure 7.50

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Offered load Throughput Controlled Uncontrolled Figure 7.51

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Time Bits per second Peak rate Average rate Figure 7.52

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

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Arrival of a packet at time t a X’ = X - (t a - LCT) X’ < 0? X’ > L? X = X’ + I LCT = t a conforming packet X’ = 0 Nonconforming packet X = value of the leaky bucket counter X’ = auxiliary variable LCT = last conformance time Yes No Yes No Figure 7.54

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies I L+I Bucket content Time Packet arrival Nonconforming ********* Figure 7.55

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Time MBS TLI Figure 7.56

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Tagged or dropped Untagged traffic Incoming traffic Untagged traffic Leaky bucket 1 PCR and CDVT Leaky bucket 2 SCR and MBS Tagged or dropped Figure 7.57

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Time Kbps Time Kbps 100 Kbps (a) (b) (c) Figure 7.58

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Incoming traffic Shaped traffic Size N Packet Server Figure 7.59

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Incoming traffic Shaped traffic Size N Size K Tokens arrive periodically Server Packet Token Figure 7.60

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies b bytes instantly t r bytes per second Figure 7.61

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies A(t) = b+rt R(t) No backlog of packets bRbR b R - r (a) (b) Buffer 1 0 empty t t Figure 7.62

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Congestion window Round-trip times Slow start Congestion avoidance Congestion occurs Threshold Figure 7.63

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Medium A B C End system  End system  Network 1 2 Physical layer entity Data link layer entity 3 Network layer entity 3 Transport layer entity 4 Figure 7.3