Presentation on theme: "Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge"— Presentation transcript:
1 Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links1.3 Network corecircuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 History
2 A closer look at network structure: network edge: applications and hostsaccess networks, physical media: wired, wireless communication linksnetwork core:interconnected routersnetwork of networks
3 The network edge: end systems (hosts): client/server model run application programse.g. Web,at “edge of network”peer-peerclient/serverclient/server modelclient host requests, receives service from always-on servere.g. Web browser/server; client/serverpeer-peer model:minimal (or no) use of dedicated serverse.g. Skype, BitTorrent
4 Access networks and physical media Q: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networksKeep in mind:bandwidth (bits per second) of access network?shared or dedicated?
5 Residential access: point to point access Dialup via modemup to 56Kbps direct access to router (often less)Can’t surf and phone at same time: can’t be “always on”DSL: digital subscriber linedeployment: telephone company (typically)up to 1 Mbps upstream (today typically < 256 kbps)up to 8 Mbps downstream (today typically < 1 Mbps)dedicated physical line to telephone central office
6 Access networks There are three ways to provide access to the internet to homeOver the telephoneADSL-based modemsOver the television plantCable-based modemsOver an optical fiberPassive Optical Networks (APON or EPON)
7 The ADSL-based access network is one of the access technologies thatCan be used to convert the telephone lineinto a high-speed digital linkis a part of a family of technologies calledThe x-type digital subscriber line (x-DSL)Where x takes on different values
8 X-DSL data rates ADSL modem is the most commonly used Rates Downstream: 8 MbpsUpstream: 800 Kbps – 1 Mbps
9 Bandwidth vs. distance VDSL ADSL 52 Mbps/6.4 Mbps up to 1000 feet (300 m)13 Mbps/1.6 Mbps up to 5000 feet (1.5 km)ADSLDownstream2 Mbps up to 5.4 Km8 Mbps up to 2.7 KmUpstream64 Kbps to 800 Kbps
11 Digital subscriber line Some of the key featuresDSL allows analog voice signals and digital dataTo be sent over the same local loop wiringThe local loop must be connected to sthg besidesA traditional voice switch at the end officeA device called DSL access multiplexer (DSLAM) is usedProvides high speed access to end usersDSL was designed to provide high speed access.
13 ADSL equipmentA telephone company technician must install a Network Interface Device on the customer’s permises. This small plastic box marks the end of the telephone company’s property and the start of the customer’s property. Close to the NID is a splitter, that separates the Hz band used by the POTS from data. The POTS signal is routed to the existing telephone or fax machine and the data signal is routed to an ADSL modem.
14 ADSL deployment: at the customer’s permise ADSL Transmission Unit at the customerpremises endADSL + POTS signalsTravel together down the twisted pairUsing filter you will be isolating each signal
15 ADSL access multiplexer Transmission between the end office and customeris done using the ADSL layerSpeeds are limited to 1.5 Mbps
16 Discrete multi-tone technique The twisted pair bandwidthextends to 1.1 Mbpsis divided into 256 sub-channelsEach occupying KHzSub-channel 0 is reservedFor the voice band regionSub-channels 1-5 separate data and POTS signalThe remaining sub-channels are used by ADSL
17 Upstream and upstream data In ADSLBoth the upstream and downstream dataAre sent over the same twisted pairThis can be implemented usingFrequency division multiplexing (FDM)Up to 32 sub-channels for the upstream directionUp to 218 downstream sub-channels
18 Discrete multi-tone technique What it does is to divide the available 1.1 Mhz spectrum on the local loop into 256 independent channels of 4 Khz each. Channel 0 is used for POTS (Plain Old Telephone Service). Channels 1-5 are not used to keep the voice signal and data signals from interfering. The rest are available for user data. In its ADSL version 32 channels are used for upstream and the rest downstream. The ADSL standard allows speeds of as much as 8 Mbps downstream and 1 Mbps in the upstreamADSL8 Mbps in the downstream1 Mbps in the upstream
19 The ADSL reference model architecture DSLAM can supportUp to 64 homes
20 Residential access: cable modems HFC: hybrid fiber coaxasymmetric: up to 30Mbps downstream, 2 Mbps upstreamnetwork of cable and fiber attaches homes to ISP routerhomes share access to routerdeployment: available via cable TV companies
26 Company access: local area networks company/univ local area network (LAN) connects end system to edge routerEthernet:10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernetmodern configuration: end systems connect into Ethernet switchLANs: chapter 4
27 Physical Media Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps EthernetCategory 5: 100Mbps EthernetBit: propagates between transmitter/rcvr pairsphysical link: what lies between transmitter & receiverguided media:signals propagate in solid media: copper, fiber, coaxunguided media:signals propagate freely, e.g., radio
28 Physical Media: coax, fiber Fiber optic cable:glass fiber carrying light pulses, each pulse a bithigh-speed operation:high-speed point-to-point transmission (e.g., 10’s-100’s Gps)low error rate: repeaters spaced far apart ; immune to electromagnetic noiseCoaxial cable:two concentric copper conductorsbidirectionalbaseband:single channel on cablelegacy Ethernetbroadband:multiple channels on cableHFC
29 The Network Coremesh of interconnected routersthe fundamental question: how is data transferred through net?circuit switching: dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete “chunks”