1 / 28

Review of Underlying Network Technologies

Review of Underlying Network Technologies. Chapter 2. Network Communication. Internet is not a new kind of physical network Method of interconnecting physical networks Set of conventions for using networks Communication networks can be divided into two basic types

psyche
Download Presentation

Review of Underlying Network Technologies

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. Review of Underlying Network Technologies Chapter 2

  2. Network Communication • Internet is not a new kind of physical network • Method of interconnecting physical networks • Set of conventions for using networks • Communication networks can be divided into two basic types • Connection-oriented (circuit-switched) • Connectionless (packet-switched)

  3. Connection-Oriented • Forms a dedicated connection or circuit between two points • Like U.S. telephone system • Guarantees capacity • Once circuit is established, no other network activity will decrease the circuit’s capacity • Disadvantage is cost • Circuit costs are fixed, regardless of use

  4. Connectionless • Data to be transmitted is divided into packets • Usually only a few hundred bytes • Carries identification information • Allows concurrent communication • Multiple computers over shared medium • Disadv: • As activity increases, given pair of computers receives less of the network capacity

  5. Who Wins? • Connectionless! • Despite not being able to guarantee capacity • Wins via cost and performance • Sharing network bandwidth means fewer connections are required • Performance ok since we can build high speed network hardware • Throughout the text, network means connectionless network

  6. WANs and LANs • WAN: spans large geographical distance • Sometimes called long-haul networks • Usually do not have any distance limit • Slower: 1.5 Mbps to 2.4 Gbps • More delay: few ms to several tenths of a second • Usually consists of a series of packet switches interconnected by long distance comm lines • Extend network by new switch and comm line • Computers added by attaching to a packet switch

  7. LAN: spans short geographical distance • Fast: 100 Mbps to 10 Gbps • Less delay: few tenths of ms to 10 ms • Each computer usually contains a Network Interface Card • Connects machine directly to network • Network is “dumb”; interface devices in the computers do the work • Every computer attached to a network has a unique address* • Sender must know recipient’s address • Hardware technology specifies address scheme *Will change this statement slightly soon!

  8. Ethernet Technology • Ethernet is a packet-switched LAN • Invented by Xerox in early 1970’s • Standardized by Xerox, Intel, and DEC in 1978 • IEEE standard number 802.3 • Many variants exist

  9. Original design known as 10Base5 • Uses coaxial cable approximately ½ inch in diameter and up to 500 meters long • Cable is completely passive • 10 Mbps • Original wiring scheme • Has been superseded

  10. Thin-wire Ethernet • Known as 10Base2 • Some original Ethernet disadvantages: • Transceiver has non-trivial cost • Transceivers located with cable • Cable difficult to install (thick shield; hard to bend) • Thinnet cable thinner, cheaper, more flexible • Computer has both the host interface and connection circuitry • Easy to connect and disconnect (no technician) • Less protection from interference; shorter distances; fewer connections per network

  11. Twisted Pair Ethernet • Known as 10Base-T • Popular, current technology • Uses conventional unshielded copper wire • Cheaper and easier to install • Each computer connects to a hub over 4 pairs of wires • Only 2 pairs of wires used • Same communication capability as thick or thin Ethernet; just alternate wiring scheme

  12. Fast Ethernet • Thick, thin, twisted pair: 10 Mbps • Faster processors  Ethernet became bottleneck • Developed 100Base-T (100 Mbps) • Uses same twisted pair wires • Gigabit Ethernet • Known as 1000Base-T (1 Gbps, copper)) • 1000Base-X – uses fiber optics • Fiber is much faster • Developing 10 and 40 Gbps Ethernet technologies

  13. 10/100/1000 Ethernet • Allows compatibility with either 10Base-T, 100Base-T, or 1000Base-T • Can use for computer interfaces or hubs • Computer with 10/100/1000 interface card can attach to any of the 3 configurations • Hardware automatically detects speed • No hardware or software reconfiguration required

  14. Power over Ethernet • Small amount of power • Sent over same copper cable • Power does not degrade data transmission • Can power small devices with one cable

  15. Two facts about increased capacity • (1) Few computers can sustain 1 Gbps data rate • (2) New versions did not change standards • Max packet size same as for 10Base-T • Higher-speeds not optimized for highest possible computer-to-computer throughput • Allows more stations and more total traffic

  16. Ethernet properties • Shared bus that supports broadcast • All stations connect to single shared channel • All stations receive every transmission • Uses best-effort delivery • Sender gets no information about packet delivery • Distributed access control • No central authority to grant access to shared channel • Carrier Sense Multiple Access with Collision Detect (CSMA/CD) • Host listens before transmit; sends if idle • Maximum packet size limits transmission time • Must observe minimum idle time between sends

  17. Collision detection and recovery • Signals travel at approx 70% speed of light • Stations can begin transmitting simultaneously (or almost simultaneously) • Results in a collision • Each station monitors cable while transmitting • If detect collision: host stops, waits, retries • Uses binary exponential backoff policy • Sender delays random time; doubles on second collision; quadruples on third collision; and so on • If network busy, retransmit attempts quickly spread over a reasonably long period

  18. Wireless Ethernet • Several wireless standards related to Ethernet • 802.11b (Wi-Fi) • Up to 11 Mbps; usually 2.5 – 4 Mbps • 802.11a and 802.11g • Up to 54 Mbps • 802.16 (Wi-Max) • Above three for point-to-point or with base • 802.16 is for point-to-point only • 802.11n • 540 Mbps • 802.11i • Standard for security

  19. Ethernet addressing and frames • Each computer has a 48-bit address • Checked in interface hardware, not computer’s CPU • When sending, specifies destination: • Single, broadcast, or multicast • Addresses associated with the interface hardware • Move/change interface; new machine physical address • Transmitted data viewed as a frame • Variable length; 64 octets to 1518 octets • Besides data, contains: • Preamble, destination and source addresses • Frame type • Cyclic Redundancy Check (CRC)

  20. Ethernet bridges • Bridge • Connects two Ethernets; passes frames • Operates on packets vs signals • Bridge follows CSMA/CD rules, so (almost) arbitrary number can be added • Ethernet switch is like a multi-port bridge • Adaptive or learning bridges • Can decide which frames to forward • Usually very sophisticated and robust • Important point: • Bridges hide the interconnection details • Set of bridged segments acts like single Ethernet

  21. Asynchronous Transfer Mode • ATM is connection-oriented • Designed for extremely high speed data switching • Operate at gigabit speeds • Needs complex, expensive hardware • One or more high speed switches • Optical fiber for all connections • Uses fixed-size frames called cells

  22. Connection-oriented networking • Not like packet-switched networks • Must first establish a connection to the destination computer • ATM switch finds path from sender to receiver • Waits on remote computer to accept the request • Local ATM switch selects identifier for the connection and passes it to the computer • Computer sends using identifier • When done, connection must be broken

  23. Wide Area Point-to-Point Networks • WANs formed by leasing data circuits • Digital circuits initially used for digitized voice • Data came later, so data rates are not powers of 10 • Are powers of 64 Kbps due to PCM • 8000 samples/sec; each sample 8 bits • T1: 1.544 Mpbs; T2: 6.312; T3: 44.736; T4: 274.760 • Lower data rates use copper; higher data rates need fiber circuits • Point-to-point “network” • When system connects exactly two computers • “Network” is a stretch; viewed as such for consistency • Main point: do not need hardware addresses

  24. Dialup IP • Another example of a point-to-point network • Typically from modem (residence) to ISP • TCP/IP view: • Placing call is like running a wire • Connection is made; stays as long as needed

  25. Summary • Reviewed several network hardware technologies • General idea: • TCP/IP protocols are extremely flexible • Almost any underlying technology can be used to transfer TCP/IP traffic

More Related