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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

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INFO 330 Computer Networking Technology I

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  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

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