Introduction to Networking What is a computer network

Introduction to Networking • • • What is a computer network? Internet Architecture Statistical multiplexing and packet switching Connection-oriented vs Connectionless Fundamental issues in computer networking • Readings – Sections 1. 1 -1. 5, 2. 5. 4, 2. 5. 5 Computer Science, FSU 1

What is a Computer Network? • Network provides connectivity – A set of computers/switches connected by communication links • Many topologies possible • Many different physical media – Coaxial cable, twisted pair, fiber optic, radio, satellite • Local area networks vs Wide area networks Computer Science, FSU 2

Elements of a Network • hosts, end-systems – pc’s, workstations, servers – PDA’s, phones, toasters running network apps • communication links router server local ISP – Point-to-point, multiaccess – fiber, copper, radio, satellite workstation mobile regional ISP • routers: forward packets (chunks) of data thru network • internet: network of networks • Internet is a specific internet company network Computer Science, FSU 3

What is The Internet? • The Internet : – collection of networks and routers that span the world and use the TCP/IP protocols to form a single, cooperative virtual network • intranet: connection of different LANs within an organization – – private may use leased lines usually small, but possibly hundreds of routers may be connected to the Internet (or not), often by firewall Computer Science, FSU 4

Internet Architecture NAP International lines regional network national network ISP company LANs on-line services ISP university company Computer Science, FSU access via modem 5

NAPs, NSPs, ISPs • NSP: National Service Provider (Tier 1 Backbones) – Example: Verizon, At&T • NAP: National Access Point National Provider NAP NAP National Provider Regional Provider customers Computer Science, FSU 6

NAP and Private Peering Computer Science, FSU 7

Sprint network Computer Science, FSU 8

Another Interesting figure about Internet found from the Internet http: //www. cs. fsu. edu/~zzhang/Internet_map. pdf Computer Science, FSU 9

Fundamental Issues in Networking • Naming/Addressing – How to find name/address of the party (or parties) you would like to communicate with – Address: byte-string that identifies a node • Routing/Forwarding: process of determining how to send packets towards the destination based on its address – Finding out neighbors, building routing tables • Resource sharing – Fundamentally, all nodes use a shared infrastructure to send/receive information. If all nodes becomes aggressive, everybody will be hurt. Computer Science, FSU 10

Multiplexing Strategies • Sharing of network resources among multiple users • Common multiplexing strategies • Time Division Multiplexing (TDM) • Frequency Division Multiplexing (FDM) • These two strategies are circuit switching technology Computer Science, FSU 11

Circuit Switched Networks • All resources (e. g. communication links) needed by a call dedicated to that call for its duration – Example: telephone network Computer Science, FSU 12

Statistical Multiplexing • • • Time division, but on demand rather than fixed Reschedule link on a per-packet basis Packets from different sources interleaved on the link Buffer packets that are contending for the link Buffer buildup is called congestion This is packet switching, used in computer networks Computer Science, FSU 13

Packet Switched Networks • Data entering network is divided into chunks called “packets” • Store-and-forward approach: packets buffered before transmission • Packets traversing network share resources with other packets – On demand resource use: statistical resource sharing • Fewer resources: queuing delay, packet loss Computer Science, FSU 14

Why Statistically Share Resources • Efficient utilization of the network • Example scenario – Link bandwidth: 1 Mbps – Each call requires 100 Kbps when transmitting – Each call has data to send only 10% of time • Circuit switching – Each call gets 100 Kbps: supports 10 simultaneous calls • Packet switching – Supports many more calls with small probability of contention • 35 ongoing calls: probability that > 10 active is < 0. 00044! Computer Science, FSU 15

Circuit Switching vs Packet Switching Item Circuit-switched Packet-switched Dedicated “copper” path Yes No Bandwidth available Fixed Dynamic Potentially wasted bandwidth Yes No Store-and-forward transmission No Yes Each packet follows the same route Yes No Call setup Required Not Needed When can congestion occur At setup time On every packet Effect of congestion Call blocking Queuing delay Computer Science, FSU 16

Connection-Oriented Service • Sender – – Requests “connection” to receiver Waits for network to form connection Leaves connection in place while sending data Terminates connection when no longer needed • Network – – Receives connection request Establishes connection and informs sender Transfers data across connection Removes connection when sender requests Computer Science, FSU 17

Connectionless Service • Sender – Forms packet to be sent – Places address of intended recipient in packet – Transfers packet to network for delivery • Network – Uses destination address to forward packet – Delivers the packet to destination Computer Science, FSU 18

Connection-Oriented vs Connectionless • Connection-Oriented • Telephone System, Virtual Circuit Model – Path is setup before data is sent – Data identifies the connection – All data follows the same path • Connectionless • Postal System, Datagram Model – No path setup before transmitting data – Packet contains identification of destination – Each packet handled independently Computer Science, FSU 19

Connection-Oriented vs Connectionles • Connection-Oriented – Connection setup overhead – State in packet switches – Can reserve bandwidth • Connectionless – Stateless and less overhead – Resource reservation not possible – Allows broadcast/multicast Computer Science, FSU 20

Fundamental Problems in Networking • What can go wrong? – Bit-level errors: due to electrical interferences – Packet-level errors: packet loss due to buffer overflow/congestion – Out of order delivery: packets may takes different paths – Link/node failures: cable is cut or system crash • What can be done? – Add redundancy to detect and correct erroneous packets – Acknowledge received packets and retransmit lost packets – Assign sequence numbers and reorder packets at the receiver – Sense link/node failures and route around failed links/nodes • Goal: to fill the gap between what applications expect and what underlying technology provides Computer Science, FSU 21

Summary • The pieces of a network – Internet architecture • Packet switching vs circuit switching – Statistical multiplexing • Connection-oriented vs connectionless • Fundamental issues in networking – Addressing/Naming and routing/forwarding – Error/Flow/Congestion control Computer Science, FSU 22