1 / 85

INFO 330 Computer Networking Technology I

INFO 330 Computer Networking Technology I . Chapter 1 Networking Overview Glenn Booker. Computer Networks. A network is the structure that allows computer applications to communicate with each other The applications could be executed by the user, or part of the operating system

paul
Download Presentation

INFO 330 Computer Networking Technology I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. INFO 330Computer Networking Technology I Chapter 1 Networking Overview Glenn Booker Chapter 1

  2. Computer Networks • A network is the structure that allows computer applications to communicate with each other • The applications could be executed by the user, or part of the operating system • Not every computer system is designed to allow networking • Microsoft DOS had no native networking ability; it was added after the need arose Chapter 1

  3. The Internet • The Internet is the primary model for understanding networking concepts because, well, nearly every computer and many other things could be connected to it Chapter 1

  4. The Internet • Key parts of any network include • Hosts or end systems, which are the computers and other things with which most people interact • End user computers, workstations, and servers are all considered hosts • As of July 2008 there were about 600 million hosts on the Internet! Chapter 1

  5. The Internet • Communication links, which are the wired or wireless means used to connect to the network • Packet switches, which help guide information between hosts • Routers and link-layer switches are the primary types of packet switches Graphics are taken from the text’s lecture notes Chapter 1

  6. The Internet • The network sends chunks of information called packets along a route or path to get from one host to another • The speed at which it does so is the transmission rate, typically in bits per second (bps) Chapter 1

  7. The Internet • The control over choosing the path is known as packet switching • End systems connect to the Internet through an Internet Service Provider (ISP) • ISPs provide many levels of service • Residential or business service, typically from 56kb dialup to DSL, FIOS, or cable modems Chapter 1

  8. The Internet • The packets are defined and handled according to protocols, most notably the Transmission Control Protocol (TCP) and Internet Protocol (IP) • A protocol is a language for communication Chapter 1

  9. Protocols • In order for it to work, both parties (e.g. hosts, switches, etc.) need to speak the same language oder Sie werden einander nicht verstehenor they won’t understand each other • Some protocols use a handshake concept • Like saying Hi as a greeting, special messages are defined that request a connection, and reply to accept the connection Chapter 1

  10. Protocols • More formally, then, protocols define • The format of messages (like the spelling of words) • The order of messages (the syntax of sentences, or else your messages like Yoda will sound) • Much of understanding networking is understanding how these protocols work Chapter 1

  11. Source of Protocols • Internet protocols are defined by the Internet Engineering Task Force (IETF) • The IETF was created by the Internet Architecture Board (IAB) and also reports to the Internet Society (ISOC) • The Request For Comments (RFCs) define the actual protocols • The first RFC was dated April 1969 • As of September 2009, there are over 5700 RFCs Chapter 1

  12. Internet vs Intranet • The Internet (a proper noun, hence is capitalized) is the public network of zillions of computers, toasters, etc. • An intranet (not a proper noun) is the generic term for a local private network that uses the same protocols as the Internet Chapter 1

  13. Type of Internet Service • The Internet runs distributed applications • The World Wide Web, instant messaging, distributed games, etc. are all distributed applications • These applications are developed using an Application Programming Interface (API) to connect to the Internet Chapter 1

  14. Type of Internet Service • There are two choices for the type of service provided by an Internet connection • A connection-oriented, reliable service • A connection-less, unreliable service • Neither guarantees how fast a message will get from host A to host B Chapter 1

  15. Connection-oriented, Reliable Service • This establishes a loose connection between client and server, but not to the switches between them • Key traits needed from this are • Reliable data transfer – every little bit counts • Flow control to keep from overwhelming hosts • Congestion control to avoid Internet gridlock • TCP provides this service (see RFC 793) Chapter 1

  16. Connection-less, Unreliable Service • This service has no handshaking – it just sends packets of data • Don’t know if packets ever got there • No flow or congestion control • Handled by User Datagram Protocol (UDP), RFC 768 • Use when speed is critical, such as video conferencing or Internet telephone Chapter 1

  17. The Edge of the Network • Now we’ll examine the contents of the Internet from the outside in – from the “edge” to the “core” • Hosts (end systems) can be divided into clients and servers • Clients are computers that request services from Servers • One computer (host) can be multiple clients and servers at once (esp. in peer-to-peer applications) Chapter 1

  18. Access Networks • To get from a host to a distant part of the Internet, you need to pass through the access network • Access networks get residential, business, and wireless users connected • Types of connections include • 56 kbps dial-up modem, an analog connection over a voice phone line • Typically get 40-42 kbps due to line noise Chapter 1

  19. Access Networks • Digital subscriber line (DSL) gives a dedicated connection, with different upstream and downstream rates • DSL uses FDM • Downstream/upstream rates are typically values like 768k/128k, 3.0M/768k, etc. • Business connections may use dedicated T1 lines (1.536 Mbps), ISDN connections, and other options Chapter 1

  20. Access Networks • Cable modems use hybrid fiber-coaxial cable (HFC) to connect to special cable modems • HFC is a variant on the same cable used for cable TV service • HFC is a shared medium – if all your neighbors are online, your connection speed will suffer! • Dial-up connections are only present when needed; DSL and cable modems are always on (we hope) Chapter 1

  21. Access Networks • Fiber to the home (FTTH) is fiber optic Internet connection for residential use • There are two kinds of FTTH • Active optical networks (AONs) are switched Ethernet • Passive optical networks (PONs) are used by Verizon’s FIOS service • Typically about 100 homes share a connection from the provider’s central office (CO) INFO 320 week 1

  22. Wired access • Local area networks (LANs) generally use Ethernet for wired connections • Ethernet speeds of 10-1000 Mbps are common, up to 10 Gbps for servers and routers INFO 320 week 1

  23. Wireless Access • Wireless devices connect through wireless access points (base station) on a LAN • Then the LAN uses some other access connection to get to the Internet • Wireless devices use the IEEE 802.11 family of technologies • 802.11a supports up to 54 Mbps @ 5 GHz • 802.11b supports 5.5 and 11 Mbps @ 2.4 GHz • 802.11g supports up to 54 Mbps @ 2.4 GHz Chapter 1

  24. Why Does Frequency Matter? • Wireless signals can be interfered with by other devices; when that occurs, they detune their speed • 802.11a has seven (48, 36, 24, 18, 12, 9, and 6 Mbps) • 802.11b has three lower data rates (5.5, 2, and 1 Mbps) • 802.11g has a range of lower speeds • The 802.11b and 802.11g standards use the 2.4 GHz (gigahertz) frequency range • This frequency range is used by other networking technologies, microwave ovens, 2.4GHz cordless phones (a huge market), and Bluetooth devices • The 5 GHz frequency range for 802.11a is relatively clear, so it’s less likely to have interference (so far) Chapter 1

  25. Wireless Network Example Chapter 1

  26. WiMAX • The next generations of wireless communication are a battle between advanced cell technologies (3G and 4G protocols) and WiMAX • WiMAX is IEEE 802.16, and promises 5-10 Mbps speed over ranges of tens of km INFO 320 week 1

  27. Physical Media • Physical media used for connecting networks can be guided or unguided • Guided media use something solid – wires, coaxial cable, fiber-optic cable, etc. • Unguided media use electromagnetic waves of some kind – wireless LAN signals, satellite channels, etc. Chapter 1

  28. Physical Media • Specific kinds of physical media include • Twisted pair copper wire • Coaxial cable • Fiber optics • Terrestrial radio channels • Satellite radio channels Chapter 1

  29. Twisted pair copper wire • Most common physical medium, has multiple coated wires wrapped around each other • Includes phone lines, which have four thin wires with RJ-11 plugs on the end • Ethernet cables have eight wires, and RJ-45 plugs on the end, so they’re wider than phone plugs • Can handle Gbpsspeeds over distances of about a hundred yards Chapter 1

  30. Coaxial cable • Coaxial (coax) cable has a copper wire core, and a copper cylinder around it – they share the same axis of rotation, hence the name • Handles multiple Mbps speeds for miles • There are only two conductors, which is why it’s a shared medium – everyone shares the same resources Chapter 1

  31. Fiber optics • Fiber optics use hollow fibers to guide light pulses • Handles hundreds of Gbps speeds up to 100 km • Most international phone lines, and the Internet backbone, are fiber optic cables • Used on high speed LANs – 1 to 10 Gbps Chapter 1

  32. Terrestrial radio channels • These include the wireless network channels discussed previously, plus radio signals used to beam networks between buildings • Can reach long distances with the latter, but signals can be intercepted, bounce, fade, and have interference from other signals Chapter 1

  33. Satellite radio channels • Consist of geostationary satellites and low-altitude satellites • Geostationary satellites hover 24,000 miles above the Earth’s surface, and are used to relay TV channels and parts of the Internet backbone • Low altitude satellites (LEO, low-Earth orbiting) orbit much faster, so you need several to be able to find one at any given time; are not used for networks Chapter 1

  34. Psst – what Internet Backbone? • The Internet is a network of many networks • It was designed that way to be redundant in the event of war – if one part of it was no longer usable (nice euphemism!), the rest of the network would still work • At its heart are many Tier-1 ISPs • Sprint, MCI, WorldCom, AT&T, etc. are all Tier-1 • They run extremely fast “backbone” connections (622 Mbps to 10 Gbps) Chapter 1

  35. Internet Backbone • The Tier-2 ISPs are regional or national in scope, and connect to Tier-1 and Tier-2 ISPs • Points where ISPs connect to each other are Points Of Presence (POPs) • Don’t confuse with Post Office Protocol (POP) • They may also connect at Network Access Points (NAPs) to local telecom companies or Tier 1 ISPs Chapter 1

  36. Internet Backbone • There are thousands of lower level ISPs, Tier-3, probably including your local ISP • For a packet to get from one host to another, it may pass through a variety of Tier-1, Tier-2, and Tier-3 ISPs, NAPs, POPs, etc. Chapter 1

  37. Circuit vs Packet Switching • In order to get a packet from host A to host B, two major approaches could be used • Both approaches send packets over communication lines • Circuit switching is what a traditional telephone system does • Reserve a path from A to B which is the circuit messages will follow, until the connection is closed • Packet switching is used by the Internet • Dump packets into the network with no reserved path, and make a best effort to get packet to destination Chapter 1

  38. Circuit Switching • To link host A and host B, each link between switches along the way must be reserved for the duration of that connection or circuit • There are two ways to share links with many circuits: • Frequency-division multiplexing (FDM) • Time-division multiplexing (TDM) Chapter 1

  39. FDM and TDM • FDM acts like FM radio – it divides the link by frequency ranges, and assigns a frequency range to each circuit • Typical frequency range, or bandwidth, is 4 kHz • This way one link can handle many circuits • TDM breaks the link into some number (n) of slots in a frame • Each slot is dedicated to one circuit, so that circuit has full attention of the link 100/n percent of the time Chapter 1

  40. Bits and Bytes • To review basic computer units • A bit is a binary digit – a 0 or 1 • Typically eight bits are a byte, the shortest word • Old ASCII text files may use seven bits per byte, so there are 27 = 128 ASCII characters • Transmission rate of data is given in bits per second (bps), or thousands or millions or billions of bits per second (kbps, Mbps, Gbps) • Data transfer = rate * time • Which has units of: bits = bits/sec * sec Chapter 1

  41. Key conversion point • In dealing with prefixes k, M, G, etc., in computer science they represent 2^(n*10) • k = 2^10, M = 2^20, G = 2^30, etc. • For our purposes, treat prefixes as their base 10 equivalents • k = 1000, M = 1,000,000, G = 1 billion INFO 320 week 1

  42. TDM Example • Suppose you have a 1.536 Mbps TDM connection, and want to send a 1 Mb (megabit) file; the connection has 12 links • How long does it take? • Your transmission speed is 1/12 of the 1.536 Mbps, or 0.128 Mbps • Time = data / rate = 1 Mb / 0.128 Mbps = 7.8125 seconds • This doesn’t include time to make the connection Chapter 1

  43. Packet Switching • Messages are divided into packets before going into the network • Most packet switches must receive an entire packet before forwarding it to the next switch • This store-and-forward transmission introduces delays while the switch waits for the entire packet to get there • If a packet size is L, and the transmission rate is R, the delay to receive one full packet is L/R Chapter 1

  44. Store and Forward Delay • Assume 1) no queuing delay, 2) no time to make a connection, and 3) no delay to propagate packets • Send a packet of L bits across a packet-switched network with Q links, all of which have a transmission rate of R bps • For each link, the store and forward delay of L/R seconds; this occurs Q times, for a total delay of Q*L/R seconds Chapter 1

  45. Packet Switching • Each switch typically connects to many links • For each link, there is an output buffer (or output queue) to hold packets waiting to go on that link • This introduces queuing delays, while a packet waits its turn • If the buffer is full, the packet can be lost – packet loss isn’t good! Chapter 1

  46. Statistical Multiplexing • Compare circuit to packet switching • Suppose users are active 10% of the time, sending 100 kbps of data, and not using the connection the other 90% of the time • If there’s a 1 Mbps connection available: • TDM circuit switching would need 10 slots to allow each user 100 kbps Chapter 1

  47. Statistical Multiplexing • Packet switching could handle 35 users total because the total number of active users will be 11 or more only 0.04% of the time (look up the binomial distribution for details) • The remaining 99.96% of the time, the total data rate is less than the 1 Mbps capacity of the connection • Hence sharing resources on demand (which is statistical multiplexing) allows the same performance 99.96% of the time, for over three times the number of users! Chapter 1

  48. Packet-Switched Networks • There are two major kinds of packet-switched networks – datagram networks and virtual-circuit networks • A datagram network forwards packets according to the host destination address • Hence the Internet is a datagram network • Routers forward packets to make a best effort to get them to the destination address Chapter 1

  49. Virtual Circuit Networks • A virtual circuit network forwards packets according to virtual circuit numbers • A virtual circuit (VC) is an imaginary connection between the source and destination hosts • Examples are X.25, frame relay, and asynchronous transfer mode (ATM) • Each packet has a VC identifier (VC ID) • Each packet switch indexes its VC translation table, and forwards the packet to the right outbound link Chapter 1

  50. Virtual Circuit Networks • A key difference between datagram and VC networks is that VC networks have to maintain state information about connections • Each new VC means a new entry has to be added to the VC translation table, and then is removed when the connection is ended • It also needs to keep a table to map VC numbers to output interface numbers Chapter 1

More Related