CSCI 3171 Network Computing Module 1 PDF

CSCI 3171 Network Computing MODULE 1: PART 1 1 Topics that we will cover in this module Network Topologies Interconnection Devices PART 1 The Structure of the Internet Switching...

CSCI 3171 Network Computing MODULE 1: PART 1 1 Topics that we will cover in this module Network Topologies Interconnection Devices PART 1 The Structure of the Internet Switching Addressing PART 2 Performance CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 2 Definition of a network An interconnected collection of autonomous devices (workstations, laptops, tablets, mobile devices, sensors, etc.) that can exchange information (text, voice, video, image, sensor data) using specific protocols (e.g., TCP/IP) over different media (wireline and wireless) and across different platforms (Unix, Linux, Windows, Mac, legacy systems, etc.). CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 3 Classification of networks A Local Area Network (LAN) is typically a network that connects hosts within an office building or an organization or a campus. The geographical diameter of a LAN is usually less than a few km. A Metropolitan Area Network (MAN) connects hosts across a city or across multiple branch offices of an organization. The geographical diameter of a MAN is usually 10’s to 100’s of kms. A Wide Area Network (WAN) is a network that connects hosts anywhere in the world. The Internet is the largest WAN in operation today. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 4  Network topologies Any network can be built using two types of basic building blocks: Nodes Hosts (PCs, workstations, servers, audio-video equipment, mobile devices, etc.) Interconnection devices (repeaters, hubs, bridges, switches, routers) Links Twisted Pair Copper Cable, Coaxial cable, Optical fiber, Wireless, etc. The different ways of putting together these building blocks are referred to as network topologies or configurations. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 5  A) Two-node point-to-point topology Node Node Link Simple topology – just two nodes connected by one link. Can serve as a building block for other topologies. Also used in Wide Area Network (WAN) point to point connections. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 6  B) Linear topology A B C D Multiple point-to-point connections in a linear fashion. Drawbacks: Data transfer between nodes may need to go through other nodes. The bandwidth of a link is not shared uniformly by all nodes. Poor fault tolerance – the failure of a link can break the network communication. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 7  C) Bus topology Terminator Linear topology, but all nodes share a single link. Note that the electrical signal from a node travels in both directions along the link. Terminators are devices placed at each end to absorb the signals so that they are not reflected back onto the link. This topology provides better bandwidth utilization since the link is shared. However, a problem with this topology is collisions – if two nodes start transmitting simultaneously, the transmissions may collide. Solution: A special medium access control algorithm must be incorporated to deal with such collisions. Earlier Local Area Networks (LANs) were based on this topology. They were called the Classical or the Traditional Ethernets. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 8  D) Ring topology Token Multiple nodes share a single link connected as a ring. Orderly transmission without collisions by token passing mechanism. Token is a special bit pattern that rotates around ring. Only the node that captures the token can send the message. Network based on this topology - Token Ring Network. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 9  E) Dual ring topology Two counter-rotating rings Nodes are interconnected by two rings. One ring circulates a token in the clockwise direction. The other ring circulates another token in the counter- clockwise direction. This topology provides better fault tolerance than the single ring. The Fiber Distributed Data Interface (FDDI) was a network based on this topology. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 10  F) Star topology Hub A 6-port hub (Image source: cyberdata.net) Multiple nodes connected to a central interconnection device called a hub. A hub is like a collapsed bus –serves the same function à data is broadcast to all nodes. Advantages of the star topology over the bus: Easier to install than the bus topology. Has better fault tolerance than the bus topology. Current local area networks (LANs) or Ethernets are based on this topology. Note: In current networks, the hub is typically a switch. That is why current LANs are called Switched Ethernets. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 11 SWITCHED ETHERNET CONFIGURATION EXAMPLE CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 12  G) Mesh topology Multiple point-to-point links connected in an arbitrary topology. Can be a full mesh (every node is directly connected to every other node) or a partial mesh (some links may not be present). CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 13  We need to address two problems for building larger networks How can we increase the capacity (length of links, number of links, number of nodes) of the basic topologies? For example, the chances of the signal getting corrupted, or the signal voltage level falling are higher on longer links. As another example, if the number of nodes is increased in a bus topology, the number of collisions may increase and affect the performance. How can we interconnect two different topologies and/or different characteristics? For building heterogeneous networks, we need to interconnect a bus to a ring, a ring to a star, and so on. We will also need to interconnect networks of different bandwidths. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 14 The answer: Interconnection Devices Product Example Device Symbol Repeater/ Hub Bridge Switch Router Source: Google Images CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 15  Repeater/Hub: Distance Extension Device Simple distance extension device to extend the length of a network. In a typical LAN, repeaters are added at 250-meter or 500-meter intervals. A 2-port repeater receives signals on one port, removes the noise content, boosts the signal level and transmits it out on the other port. Wireless repeaters also serve the same purpose. A multi-port (more than two ports) repeater is called a hub. Adding more repeaters will not prevent collisions. The Ethernet standard limits to no more than 4 repeaters between any two hosts. Repeaters cannot interconnect LANs of different bandwidths or of different types. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 16  Bridge/Switch: Distance Extension + Filtering Device Bridges/Switches can buffer messages, check them for errors and forward or discard them, i.e., filtering. Message1 is discarded at the bridge For example, a message from host A to host B will be dropped at Message1 from A to B the left input port of the bridge/switch, whereas a message from Message2 is transmitted by the bridge host A to host Y will be forwarded to the other side. Message2 from A Message2 from A to Y to Y Filtering will reduce unnecessary traffic and improve the network performance. Bridges/Switches can also provide the distance extension function A B X Y of repeaters. Bridges/Switches can interconnect networks of different bandwidths (for e.g., a 100Mbps LAN can connect to a 1 Gbps LAN). CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 17  Router: Distance Extension + Filtering + Interconnection of networks Y A B X Routers can not only provide distance extension and filtering, but also are able to interconnect two different topologies. For example, they can interconnect an Ethernet (bus topology) to a Token Ring network (ring topology). It does this by translating the “rules” of operation between different network topologies. A router can also interconnect networks of different bandwidths. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 18  Routers - Path Determination R3 Y R1 R4 A B R2 X C D Another important function of a router is path determination. Routers maintain routing tables. They perform a routing table lookup on incoming messages and forward them in the correct (usually shortest path) towards their destination on a hop by hop basis. For example, a message from host A to host Y is forwarded from router R1 to R3 to R4., whereas a message from A to D is forwarded from R1 to R2. It is this property that makes the router the classic and the most important of all interconnection devices on the Internet. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 19  Generic Network Network cloud (any basic topology) Interconnection Device (Repeater, Hub, Bridge, Switch, or Router) CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 20  The Internet: the largest interconnected collection of networks in operation NSP network NSP network ISP network Other ISPs ISP network Routers ISP:Internet Service Provider NSP:Network Service Provider (national backbone) Other Campus Campus campus backbones Backbone LAN Backbone LAN) Other Office LAN campus LANs. LAN Campus CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 21 A simplified view of a portion of the Internet ISP: Internet Service Provider NAP: Network Access Point POP: Point of Presence LAN: Local Area Network Source: Data and Computer Communications by W. Stallings, 10th edition CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 22 Practical Perspective: The traceroute utility traceroute is a command line utility for displaying the route and measuring transit times of packets from a source to a destination across the Internet. In Unix, Linux and Mac OS, the command is traceroute on the Terminal. In Windows, the command is tracert on the CommandPrompt Window. Many visual traceroute online tools are also available. One open source tool is at: https://visualtraceroute.net CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 23 traceroute Example CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 24  Traceroute example Command line entry Canonical name of IP Address of Round trip times of the first hop router the first hop router three packets, Hop Number respectively, from Srini’s machine to the first hop router Router at hop 18 did not respond IP address of Stanford’s web server CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 25  How does traceroute work and what information does it collect? traceroute uses a network management packet called ICMP echo request and manipulates a parameter called TTL (Time To Live) in the packet. Normally, the TTL value (default) is 64 when a packet starts its journey. Each router along the path decrements TTL by 1. If TTL = 0, the packet gets discarded and the node that discards the packet sends an ICMP Time Exceeded packet back to the source. TTL prevents a packet without a proper address from endlessly looping on the Internet. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 26 How does traceroute work and what information does it collect? (cont’d.) R1 R2 R3 R10 R11 A B traceroute first sends an ICMP echo request packet with TTL set to 1. The first router R1 along the path decrements TTL by 1. Thus the TTL becomes 0. R1 discards the packet and sends a reply back to the source. The source will record the IP address of the sender (R1) and also the round-trip time. The source then sends an ICMP echo request packet with TTL set to 2. This packet gets discarded by the second router R2. Thus the source is able to collect information about R2 along the path. It continues to do this until the packet reaches the destination. For every hop, it sends three packets for getting the average round trip time. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 27  S Study the following sample traceroute output and answer the questions below ! b) How many routers are there between the source and the destination? 12 c) How many packets in total were sent by the source?to the finaldestination 13 3 39 d) What is the average time taken for a packet to go from the source to the destination? me 6 4 11 11904 e) What is the largest value of TTL (time to live) used by the source? 13 CSCI 3171: Module 1 - Part 1 Srini Sampalli 8 Practical Perspectives: Explore further How do Internet packets travel across oceans? Is the route from a source to a destination across the Internet (normally) the same path? Is the path from a source to a destination across the Internet (normally) the shortest path? CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 29  Key Take-aways Any network can be built with just two building blocks: Nodes and Links Basic topologies for networks range from two-node point to point, linear, bus, ring, double ring, star and mesh. Interconnection devices help in extending the capacity of basic topologies, interconnecting different topologies and/or bandwidths. These devices are Repeaters/Hubs, Bridges, Switches and Routers. The Internet is just a collection of basic topologies interconnected by interconnection devices. The Router is the classic and the core interconnection device on the Internet. Hierarchical transmission on the Internet is key to reducing the transit time. traceroute is a practical utility for tracing a packet’s journey from a source to a destination. CSCI 3171: Module 1 Introduction to Networks – PART 1 Srini Sampalli 30