Review of Review of Underlying Network Underlying Network

TechnologiesTechnologies

Chapter 2Chapter 2

Network CommunicationNetwork Communication

Internet is not a new kind of physical Internet is not a new kind of physical networknetwork Method of interconnecting physical networksMethod of interconnecting physical networks Set of conventions for using networksSet of conventions for using networks

Communication networks can be divided Communication networks can be divided into two basic typesinto two basic types Connection-oriented (circuit-switched)Connection-oriented (circuit-switched) Connectionless (packet-switched)Connectionless (packet-switched)

Connection-OrientedConnection-Oriented

Forms a dedicated connection or circuit Forms a dedicated connection or circuit between two pointsbetween two pointsLike U.S. telephone systemLike U.S. telephone systemGuarantees capacityGuarantees capacity Once circuit is established, no other network Once circuit is established, no other network

activity will decrease the circuit’s capacityactivity will decrease the circuit’s capacity

Disadvantage is costDisadvantage is cost Circuit costs are fixed, regardless of useCircuit costs are fixed, regardless of use

ConnectionlessConnectionless

Data to be transmitted is divided into Data to be transmitted is divided into packetspackets Usually only a few hundred bytesUsually only a few hundred bytes Carries identification informationCarries identification information

Allows concurrent communication Allows concurrent communication Multiple computers over shared mediumMultiple computers over shared medium

Disadv: Disadv: As activity increases, given pair of As activity increases, given pair of

computers receives less of the network computers receives less of the network capacitycapacity

Who Wins?Who Wins?Connectionless! Connectionless! Despite not being able to guarantee capacityDespite not being able to guarantee capacity

Wins via Wins via costcost and and performanceperformance Sharing network bandwidth means fewer Sharing network bandwidth means fewer

connections are requiredconnections are required Performance ok since we can build high Performance ok since we can build high

speed network hardwarespeed network hardware

Throughout the text, Throughout the text, networknetwork means means connectionless networkconnectionless network

WANs and LANsWANs and LANsWANWAN: spans large geographical distance: spans large geographical distance Sometimes called long-haul networksSometimes called long-haul networks Usually do not have any distance limitUsually do not have any distance limit Slower: 1.5 Mbps to 2.4 GbpsSlower: 1.5 Mbps to 2.4 Gbps More delay: few ms to several tenths of a secondMore delay: few ms to several tenths of a second Usually consists of a series of packet switches Usually consists of a series of packet switches

interconnected by long distance comm linesinterconnected by long distance comm lines Extend network by new switch and comm lineExtend network by new switch and comm line Computers added by attaching to a packet Computers added by attaching to a packet

switchswitch

LANLAN: spans short geographical distance: spans short geographical distance Fast: 100 Mbps to 10 GbpsFast: 100 Mbps to 10 Gbps Less delay: few tenths of ms to 10 msLess delay: few tenths of ms to 10 ms Each computer usually contains a Network Each computer usually contains a Network

Interface CardInterface CardConnects machine directly to networkConnects machine directly to networkNetwork is “dumb”; interface devices in the Network is “dumb”; interface devices in the computers do the workcomputers do the work

Every computer attached to a network has Every computer attached to a network has a unique addressa unique address** Sender must know recipient’s addressSender must know recipient’s address Hardware technology specifies address Hardware technology specifies address

schemescheme

*Will change this statement slightly soon!

Ethernet TechnologyEthernet Technology

Ethernet is a packet-switched LANEthernet is a packet-switched LAN

Invented by Xerox in early 1970’sInvented by Xerox in early 1970’s Standardized by Xerox, Intel, and DEC in 1978Standardized by Xerox, Intel, and DEC in 1978

IEEE standard number 802.3IEEE standard number 802.3

Many variants existMany variants exist

Original design known as Original design known as 10Base510Base5 Uses coaxial cable approximately ½ inch in Uses coaxial cable approximately ½ inch in

diameter and up to 500 meters longdiameter and up to 500 meters long Cable is completely passiveCable is completely passive 10 Mbps10 Mbps Original wiring schemeOriginal wiring scheme

Has been supersededHas been superseded

Thin-wire EthernetThin-wire Ethernet Known as Known as 10Base210Base2 Some Some originaloriginal Ethernet disadvantages: Ethernet disadvantages:

Transceiver has non-trivial costTransceiver has non-trivial costTransceivers located with cableTransceivers located with cableCable difficult to install (thick shield; hard to bend)Cable difficult to install (thick shield; hard to bend)

ThinnetThinnet cable thinner, cheaper, more flexible cable thinner, cheaper, more flexible Computer has both the host interface and Computer has both the host interface and

connection circuitry connection circuitry Easy to connect and disconnect (no Easy to connect and disconnect (no

technician)technician) Less protection from interference; shorter Less protection from interference; shorter

distances; fewer connections per networkdistances; fewer connections per network

Twisted Pair EthernetTwisted Pair Ethernet Known as Known as 10Base-T10Base-T Popular, current technologyPopular, current technology Uses conventional unshielded copper wireUses conventional unshielded copper wire

Cheaper and easier to installCheaper and easier to install Each computer connects to a hub over 4 pairs of wiresEach computer connects to a hub over 4 pairs of wires

Only 2 pairs of wires usedOnly 2 pairs of wires used Same communication capability as thick or thin Same communication capability as thick or thin

Ethernet; just alternate wiring schemeEthernet; just alternate wiring scheme

Fast EthernetFast Ethernet Thick, thin, twisted pair: 10 MbpsThick, thin, twisted pair: 10 Mbps Faster processors Faster processors Ethernet became Ethernet became

bottleneckbottleneck Developed Developed 100Base-T 100Base-T (100 Mbps)(100 Mbps)

Uses same twisted pair wiresUses same twisted pair wires

Gigabit EthernetGigabit Ethernet Known as Known as 1000Base-T 1000Base-T (1 Gbps, copper))(1 Gbps, copper)) 1000Base-X1000Base-X – uses fiber optics – uses fiber optics

Fiber is much fasterFiber is much faster

Developing 10 and 40 Gbps Ethernet technologiesDeveloping 10 and 40 Gbps Ethernet technologies

10/100/1000 Ethernet10/100/1000 Ethernet Allows compatibility with either 10Base-T, Allows compatibility with either 10Base-T,

100Base-T, or 1000Base-T100Base-T, or 1000Base-T Can use for computer interfaces or hubsCan use for computer interfaces or hubs Computer with 10/100/1000 interface card Computer with 10/100/1000 interface card

can attach to any of the 3 configurationscan attach to any of the 3 configurations

Hardware automatically detects speedHardware automatically detects speed

No hardware or software reconfiguration No hardware or software reconfiguration requiredrequired

Power over EthernetPower over Ethernet Small amount of powerSmall amount of power Sent over same copper cableSent over same copper cable Power does not degrade data transmissionPower does not degrade data transmission Can power small devices with one cableCan power small devices with one cable

Two facts about increased capacityTwo facts about increased capacity (1) Few computers can sustain 1 Gbps data (1) Few computers can sustain 1 Gbps data

raterate (2) New versions did not change standards(2) New versions did not change standards

Max packet size same as for 10Base-TMax packet size same as for 10Base-T Higher-speeds not optimized for highest Higher-speeds not optimized for highest

possible computer-to-computer throughputpossible computer-to-computer throughputAllows more stations and more total trafficAllows more stations and more total traffic

Ethernet propertiesEthernet properties Shared bus that supports broadcastShared bus that supports broadcast

All stations connect to single shared channelAll stations connect to single shared channelAll stations receive every transmissionAll stations receive every transmission

Uses best-effort deliveryUses best-effort deliverySender gets no information about packet deliverySender gets no information about packet delivery

Distributed access controlDistributed access controlNo central authority to grant access to shared No central authority to grant access to shared channelchannelCarrier Sense Multiple Access with Collision Carrier Sense Multiple Access with Collision Detect (CSMA/CD)Detect (CSMA/CD)Host listens before transmit; sends if idleHost listens before transmit; sends if idleMaximum packet size limits transmission timeMaximum packet size limits transmission timeMust observe minimum idle time between sendsMust observe minimum idle time between sends

Collision detection and recoveryCollision detection and recovery Signals travel at approx 70% speed of lightSignals travel at approx 70% speed of light Stations can begin transmitting simultaneouslyStations can begin transmitting simultaneously

(or almost simultaneously)(or almost simultaneously)Results in a Results in a collisioncollision

Each station monitors cable while transmittingEach station monitors cable while transmittingIf detect collision: host stops, waits, retriesIf detect collision: host stops, waits, retries

Uses binary exponential backoff policyUses binary exponential backoff policy Sender delays random time; doubles on second Sender delays random time; doubles on second

collision; quadruples on third collision; and so oncollision; quadruples on third collision; and so on

If network busy, retransmit attempts quickly If network busy, retransmit attempts quickly spread over a reasonably long periodspread over a reasonably long period

Wireless EthernetWireless Ethernet Several wireless standards related to EthernetSeveral wireless standards related to Ethernet 802.11b (Wi-Fi)802.11b (Wi-Fi)

Up to 11 Mbps; usually 2.5 – 4 MbpsUp to 11 Mbps; usually 2.5 – 4 Mbps 802.11a and 802.11g802.11a and 802.11g

Up to 54 MbpsUp to 54 Mbps 802.16 (Wi-Max)802.16 (Wi-Max)

Above three for point-to-point or with baseAbove three for point-to-point or with base802.16 is for point-to-point only802.16 is for point-to-point only

802.11n802.11n540 Mbps540 Mbps

802.11i802.11iStandard for securityStandard for security

Ethernet addressing and framesEthernet addressing and frames Each computer has a 48-bit addressEach computer has a 48-bit address

Checked in interface hardware, not computer’s CPUChecked in interface hardware, not computer’s CPU When sending, specifies destination:When sending, specifies destination:

Single, broadcast, or multicastSingle, broadcast, or multicast Addresses associated with the interface Addresses associated with the interface

hardwarehardwareMove/change interface; new machine physical address Move/change interface; new machine physical address

Transmitted data viewed as a frameTransmitted data viewed as a frameVariable length; 64 octets to 1518 octetsVariable length; 64 octets to 1518 octetsBesides data, contains:Besides data, contains:

Preamble, destination and source addressesPreamble, destination and source addresses Frame typeFrame type Cyclic Redundancy Check (CRC)Cyclic Redundancy Check (CRC)

Ethernet bridgesEthernet bridges BridgeBridge

Connects two Ethernets; passes frames Connects two Ethernets; passes frames

Operates on packets vs signalsOperates on packets vs signals

Bridge follows CSMA/CD rules, so (almost) Bridge follows CSMA/CD rules, so (almost) arbitrary number can be addedarbitrary number can be added

Ethernet Ethernet switchswitch is like a multi-port bridge is like a multi-port bridge Adaptive or learning bridgesAdaptive or learning bridges

Can decide which frames to forwardCan decide which frames to forward

Usually very sophisticated and robustUsually very sophisticated and robust Important point:Important point:

Bridges hide the interconnection detailsBridges hide the interconnection details

Set of bridged segments acts like single EthernetSet of bridged segments acts like single Ethernet

Asynchronous Transfer ModeAsynchronous Transfer Mode

ATM is connection-orientedATM is connection-orientedDesigned for extremely high speed data Designed for extremely high speed data switchingswitching Operate at gigabit speedsOperate at gigabit speeds

Needs complex, expensive hardwareNeeds complex, expensive hardware One or more high speed switchesOne or more high speed switches Optical fiber for all connectionsOptical fiber for all connections Uses fixed-size frames called cellsUses fixed-size frames called cells

Connection-oriented networkingConnection-oriented networking Not like packet-switched networksNot like packet-switched networks Must first establish a connection to the Must first establish a connection to the

destination computerdestination computerATM switch finds path from sender to receiverATM switch finds path from sender to receiver

Waits on remote computer to accept the requestWaits on remote computer to accept the request

Local ATM switch selects identifier for the Local ATM switch selects identifier for the connection and passes it to the computerconnection and passes it to the computer

Computer sends using identifierComputer sends using identifier When done, connection must be brokenWhen done, connection must be broken

Wide Area Point-to-Point NetworksWide Area Point-to-Point Networks WANs formed by leasing data circuitsWANs formed by leasing data circuits Digital circuits initially used for digitized voiceDigital circuits initially used for digitized voice

Data came later, so data rates are not powers of 10Data came later, so data rates are not powers of 10Are powers of 64 Kbps due to PCMAre powers of 64 Kbps due to PCM

8000 samples/sec; each sample 8 bits8000 samples/sec; each sample 8 bits T1: 1.544 Mpbs; T2: 6.312; T3: 44.736; T4: 274.760T1: 1.544 Mpbs; T2: 6.312; T3: 44.736; T4: 274.760

Lower data rates use copper; higher data rates Lower data rates use copper; higher data rates need fiber circuitsneed fiber circuits

Point-to-point “network”Point-to-point “network”When system connects exactly two computersWhen system connects exactly two computers““Network” is a stretch; viewed as such for Network” is a stretch; viewed as such for consistencyconsistencyMain point: do not need hardware addressesMain point: do not need hardware addresses

Dialup IPDialup IP Another example of a point-to-point networkAnother example of a point-to-point network Typically from modem (residence) to ISPTypically from modem (residence) to ISP TCP/IP view:TCP/IP view:

Placing call is like running a wirePlacing call is like running a wire

Connection is made; stays as long as neededConnection is made; stays as long as needed

SummarySummary

Reviewed several network hardware Reviewed several network hardware technologiestechnologies

General idea:General idea: TCP/IP protocols are extremely flexibleTCP/IP protocols are extremely flexible Almost any underlying technology can be Almost any underlying technology can be

used to transfer TCP/IP trafficused to transfer TCP/IP traffic