1. ICOM 6115©Manuel Rodriguez-Martinez ICOM 6115 – Computer Networks and the WWW Manuel Rodriguez-Martinez, Ph.D. Lecture 2

2. ICOM 6115©Manuel Rodriguez-Martinez Administrative Affairs Group composition –2-3 members preferably –2 members if necessary –4 is not happening Fill the group registration form Work will be done at Amadeus –Choose account From 6115_a1 through 6115_a50

3. ICOM 6115©Manuel Rodriguez-Martinez Lecture Objective Introduction to network hardware architecture Types of Networks –Broadcast vs Point-to-Point –Local Area Networks –Wide Area Networks –Subnet, switching and internets Read Chapter 1 of Book

4. ICOM 6115©Manuel Rodriguez-Martinez Data Exchange Convention Data is transmitted in small chunks of bytes called packets –Minimal unit of data management for most layers Data Link and above (Physical deals with bits) Packets can have variable size –Efficient usage of channel capacity Send only what you need –But have more processing overhead Need to identify start and end of packet Small fixed-sized packets are called cells –Very fast to handle because of fixed size –Might need to add padding bytes to fill a cell

5. ICOM 6115©Manuel Rodriguez-Martinez Broadcast Networks Features of Broadcast Networks –Host are connected to a single communications channel Wire, fiber or air (given frequency) –All packets are received by all hosts Each packet has a destination address –Host are supposed to Keep packets address to it Discard the rest –Security issue here!

6. ICOM 6115©Manuel Rodriguez-Martinez Broadcast Networks Ethernet Technology is a broadcast type network

7. ICOM 6115©Manuel Rodriguez-Martinez Additional addressing modes Broadcast address –Special addressing mode to make all hosts accept a given packet. Multicast address –Allows broadcasting to sub-groups of hosts with the network Need to identify the multicast group Efficient for multimedia services –Video and radio on the network –One packet is enough to serve all hosts

8. ICOM 6115©Manuel Rodriguez-Martinez Point-to-Point Networks Features of Point-to-Point Networks –Host have many communications channels between them –Packets might need to travel intermediate machines to reach their destinations Need to have special purpose machines to route packets from source to destination - Routers –Called packet forwarding Routing algorithms – used to create tables with routes to move packets

9. ICOM 6115©Manuel Rodriguez-Martinez Point-to-Point Networks

10. ICOM 6115©Manuel Rodriguez-Martinez Routing and Forwarding Routes –possible paths to move data from a source to a destination Routing tables - store route information Routing –the process by which the possible routes to move data between hosts are computed Forwarding –the process of directing a packet to its destination by looking up the routing tables

11. ICOM 6115©Manuel Rodriguez-Martinez Example Scenario Data from the sender reaches the receiver thanks to the forwarding done by the routers

12. ICOM 6115©Manuel Rodriguez-Martinez Technological Trade-offs Broadcast Networks –Simple and cheap –Can only be used on small area Limitations of signal propagation on medium –Signals tend to deteriorate Point-to-Point Networks –Complex to setup –More expensive Need routers –Can be used over longer areas Routers can strengthen the signal

13. ICOM 6115©Manuel Rodriguez-Martinez Local Area Networks (LANs) Privately owned networks –Connect hosts on a single building or campus Computers, printers, etc. connect to these –Range is often 10m – 1km Principal characteristics –Size –Transmission technology –Topology

14. ICOM 6115©Manuel Rodriguez-Martinez Characteristics of LANs Maximum size –Worst-case transmission time is bound Can estimate time to send a packet Transmission Technology –Wired - Single cable connects all hosts –Wireless - Same frequency used by all hosts –High Speed Can move millions of bits per second Low delay for bits to reach the destination Transmission errors are rare

15. ICOM 6115©Manuel Rodriguez-Martinez Characteristics of LANs Bandwidth –a measure of how much data can the network accommodate per unit of time –Measured in terms of bits per second. Examples: –Ethernet : 10Mbps, 100Mbps, 1000Mbps –Infrared: 2Mbps –Wireless Ethernet: 11Mbps, 54Mbps –Mbps is 1,000,000 bits not bits

16. ICOM 6115©Manuel Rodriguez-Martinez Characteristics of LANs Typically LANs are built out of broadcast networks –Ethernet, Token Ring Network Topology –Physical organization of LANs Most successful topologies –Bus – by far the most successful! Ethernet –Ring Token Ring and FDDI

17. ICOM 6115©Manuel Rodriguez-Martinez Typical LAN Topologies Bus LANRing LAN

18. ICOM 6115©Manuel Rodriguez-Martinez Bus LANs All machines connect to the same cable Channel allocation –Only one machine is allowed to transmit –Others must refrain from sending Otherwise signals interfere and get corrupted Need arbitration mechanism –Control access to the network –Resolve conflicts when two computer want to use the network at the same time

19. ICOM 6115©Manuel Rodriguez-Martinez Example Bus: Ethernet Any host can transmit at any time If two host send packets at the same time –A packet collision occurs Data is distorted –Network card can detect collision Collision detection –Host wait a random amount of time and re- transmit the packet Back-off algorithm

20. ICOM 6115©Manuel Rodriguez-Martinez Ring Network All machines connected to form a ring Bits are propagated independently –Travel around the ring back to the sender Typically one machine is allowed to send a group of bits at a time for given period Token based channel allocation –Host must have a token to use the network –Token is a special packet that moves around the ring

21. ICOM 6115©Manuel Rodriguez-Martinez Example: FDDI FDDI- Fiber Distributed Data Interface 100 Mbps LAN

22. ICOM 6115©Manuel Rodriguez-Martinez LAN Problem: Bandwidth Allocation Bus networks are the most popular –Ethernet But bandwidth must be shared by hosts Suppose N host can access the network with equal probability –Pr(access) = 1/N –Throughput = effective bandwidth per host –Throughput = bandwidth/N Decreases with increasing number of hosts!

23. ICOM 6115©Manuel Rodriguez-Martinez Example: 10Mbps Ethernet On a 5 host Ethernet segment Each host will see a throughput of 2Mbps

24. ICOM 6115©Manuel Rodriguez-Martinez Solution: Segment the network Old Ethernet Current Ethernet

25. ICOM 6115©Manuel Rodriguez-Martinez Fundamental Idea: Star Network Switch Hub Switch Star Configuration

26. ICOM 6115©Manuel Rodriguez-Martinez Example: Ethernet Switch Plug-in Card Backplane connects Plug-in Cards Forwarding Within the card Among cards (via backplane)

27. ICOM 6115©Manuel Rodriguez-Martinez Bridges and Switches Smart Devices that can forward packet inside the LAN LAN gets divided into segments –Traffic is isolated to particular segments –Bridges and switches allow traffic to pass between segments Communicating computers are on different segments of LAN LANs becomes a point-to-point network –Packet-switched LAN

28. ICOM 6115©Manuel Rodriguez-Martinez Routers, switches and bridges What is the difference? –Hard to tell –Some switches are also routers Possible interpretation –Switches - deal with packet forwarding at the Data Link Layer Limited to LANs –Routers – deal with packet forwarding at the Network layer Includes Wide-Area Networks (WANs)

29. ICOM 6115©Manuel Rodriguez-Martinez Wide Area Networks (WAN) Networks that span large geographical area –State, country, or continent WAN provide infrastructure to connect LANs with each other Subnet –Fundamental building block of a WAN Transmission Lines Routers

30. ICOM 6115©Manuel Rodriguez-Martinez WAN Architecture This would be equivalent to the UPR Network

31. ICOM 6115©Manuel Rodriguez-Martinez WAN Characteristics Most WANs are packet-switched –Point-to-point Each LAN has at least one router –Moves traffic in and out the LAN The are several lines connecting pairs of routers Forwarding must be used to –Move data between routers not directly attached

32. ICOM 6115©Manuel Rodriguez-Martinez Building bigger networks Subnets can be combined to built larger WANs –internets –World wide example: The Internet Often have backbone lines and routers –Not attached to any LAN –They connect subnets together NSFNET and ARPANET became the Internet

33. ICOM 6115©Manuel Rodriguez-Martinez Example internetwork Backbone