![ITS 413 - Network Technologies 37
Wireless Transmission
• An even simpler model of wireless transmission:
• As IT professionals, we are interested in:
– Data Rate: how fast can we send the data? [bits per second]
– Transmission Range: how far can we send the data? [metres]
– Frequency: is it free or licensed? Who else may interfere? [Hertz]
– Transmit power: how much battery of our wireless device will it use? [Watts]
– (and of course, cost: different technologies will have different costs) [Baht]
Transmission Range
Data Rate
Frequency Receiver
Transmitter
Transmit power](https://image.slidesharecdn.com/network-technologies-220724105140-27b8537c/85/Network-Technologies-ppt-37-320.jpg)
Network-Technologies.ppt
- 1. Network Technologies Internet Technologies and Applications
- 2. ITS 413 - Network Technologies 2 Aim and Contents • Aim: – List and compare popular/future technologies for LANs, WANs; wired and wireless – Familiarise students with network technologies in use today • Contents: – Categorizing Networks: geography, users, medium, mobility – Wired Networks – Wireless Networks
- 3. ITS 413 - Network Technologies 3 Categorizing Networks • Based on geographical coverage: – Body Area Networks (BAN) – Local Area Networks (LAN) – Metropolitan Area Network (MAN) – Wide Area Network (WAN) WAN MAN LAN BAN Transmission media have different physical characteristics. Trade-off between data rate, distance, cost. Users of networks have different requirements.
- 4. ITS 413 - Network Technologies 4 Categorizing Networks • Based on users: – Access Network: end-users access network services – Core Network: traffic from between access and core networks transported • Related terms: Backbone Network, Transport Network Core Network (or Backbone/Transport Network) Core Network Core Network Core Network Core Network Access Network Access Network Access Network Access Network Access Network Access Network Access Network Access Network
- 5. ITS 413 - Network Technologies 5 Categorizing Networks • Based on users: – Access networks require capacity to support • Traffic between users within the same access network • Traffic from users in one access network to another – Core networks require capacity to support • Traffic between multiple access networks – Not all users send the same amount of data at the same time, • In access networks, the amount of traffic sent over time varies significantly; hence difficult to take advantage of statistical multiplexing • In core networks, the average traffic sent over time is stable; can take advantage of statistical multiplexing – Access networks are generally higher speed than core networks (for same cost)
- 6. ITS 413 - Network Technologies 6 Categorizing Networks • Based on transmission medium: – Wired • Easy to control signal transmission • Protect from interference from other transmitting sources • Higher data rates, less errors, more predictable – Wireless • Allows mobility • Allows convenience
- 7. ITS 413 - Network Technologies 7 Categorizing Networks • Based on link configuration: – Point-to-point (two devices) – Point-to-multipoint (shared among N devices) • Easier to allow multiple devices to communicate with each other • Harder to control the “sharing” of the medium
- 8. ITS 413 - Network Technologies 8 Categorizing Networks • Based on user mobility: – Fixed • Devices in the network are fixed (do not move) • Easier to design network; predict traffic requirements – Mobile • Devices may be move • Difficult to know how much capacity is needed in advance
- 10. ITS 413 - Network Technologies 10 Access Network Technologies • IEEE 802.3 Ethernet family • Copper (Telephone) Access • Coaxial and Optical Fibre Access • Wireless – IEEE 802.11 Wireless LAN family – Bluetooth (and other short range wireless)
- 11. ITS 413 - Network Technologies 11 IEEE 802.3 Ethernet Family • Very popular LAN technology – Originally point-to-multipoint, but now mainly point-to-point, switched communications – Data rates have been increased over time: 10Mb/s, 100Mb/s, 1Gb/s, 10Gb/s, … – Very cheap devices, easy to install network • Because of popularity, has been adapted to non-LAN applications: – Long distance links using 10Gb/s (MANs, WANs) – Interface between devices (router/switch, Storage Area Networks)
- 12. ITS 413 - Network Technologies 12 Copper (Telephone) Access • Telephone networks have provided connectivity to users for decades – The network that connects users across countries, and between countries, is called the Public Switched Telephone Network (PSTN) – The service delivered to the end user is called the Plain Old Telephone Service (POTS) – The access line in most telephone networks is a twisted pair copper cable between a local telephone exchange and the home (or apartment/office) – Wide availability of telephones meant data communications adapted to make use of the network • Dial up Internet Access • Integrated Services Digital Network (ISDN) • Digital Subscriber Line technologies – ADSL, HDSL, VDSL, …
- 13. ITS 413 - Network Technologies 13 PSTN • Multiple users connect to a local exchange via Unshielded Twister Pair • Exchanges are connected in a hierarchy across cities, countries and the world – Originally using copper, but now using coaxial, satellite and fibre Bangkadi Exchange Bangkok Central Exchange Chiang Mai Central Exchange Chiang Mai Local Exchange 600 voice circuits 3600 voice circuits 60 voice circuits UTP telephone line UTP telephone line
- 14. ITS 413 - Network Technologies 14 PSTN Users Local Telephone Exchanges City Telephone Exchange Traffic from 1 user Traffic from all users connect to exchange Traffic from all local exchanges
- 15. 15 Dial Up Access • Dial-up access over telephone lines – Modem converts digital data from computer into analog signal to be sent over telephone line (instead of analog voice) • Telephone system limits bandwidth to 4kHz (although copper cable can carry more) • Maximum data rate 56kb/s Bangkadi Exchange Bangkok Central Exchange Chiang Mai Central Exchange Chiang Mai Local Exchange 600 voice circuits UTP telephone line Computer Modem The Internet Dial Up Server Internet Service Provider (ISP)
- 16. ITS 413 - Network Technologies 16 Digital Subscriber Line • Copper line can actually transmit about 1MHz spectrum – DSL technologies make use of most of this 1MHz (except the 4kHz for voice) – Digital signals are sent from home (modem) to exchange (multiplexer) – Different types of standards ADSL Example use of copper line spectrum
- 17. ITS 413 - Network Technologies 17 Digital Subscriber Line ISP Network Internet Public Switched Telephone Network Customer Premises (e.g. house) ADSL Modem ADSL Filter ADSL Multiplexer (e.g. DSLAM) Exchange/Central Office
- 18. ITS 413 - Network Technologies 18 Digital Subscriber Line • Asymmetric Digital Subscriber Line (ADSL) – Larger bandwidth (and hence data rate) for downstream (exchange to you) than upstream (you to exchange) traffic • ADSL Multiplexers (in exchange) can support larger bandwidths on transmission • Well suited to many Internet applications, e.g. web browsing, email – ADSL can adapt data rate depending on amount of noise on line • Lower speeds for longer distances and poor quality copper cables – Key Features: • Makes use of widely installed telephone network • Supports basic voice and video applications
- 19. ITS 413 - Network Technologies 19 Digital Subscriber Line • Other DSLs: – ADSL2, ADSL2+ – High Data Rate DSL (HDSL) – Symmetric (High-Speed) DSL (SDSL, SHDSL) – Very High Speed DSL (VDSL, VDSL2) Technology Downlink Uplink ADSL 512kb/s 256kb/s ADSL 1.5Mb/s 512kb/s ADSL 8Mb/s 820kb/s ADSL2 12Mb/s 1Mb/s ADSL2+ 24Mb/s 3.5Mb/s Technology Speed Use HDSL 1.5Mb/s Alternative of T1/E1 SHDSL 5.6Mb/s Home/ business VDSL 100Mb/s FTTC
- 20. ITS 413 - Network Technologies 20 Coaxial Cable Access • Coaxial cables have been used to deliver cable TV to many homes – Cable operator has a separate physical network than telephone network • Coaxial cable network can be used to deliver data to a home – Coaxial cables typically shared medium between homes in neighbourhood • Point-to-multipoint topology • More people using at the same time, the lower throughput for you – DOCSIS is standard for Data over Cable Service Interface Specification – Data rates (down/up) : • 6Mb/s / 768kb/s • 30Mb/s / 1Mb/s • Key features: – Generally faster than ADSL, although shared medium – Can avoid paying for telephone line (if use Voice over IP)
- 21. ITS 413 - Network Technologies 21 Optical Fibre Access • Optical fibre mostly used in core (not access) networks • However, delivering fibre to the end user is possible – Instead of (or as well as) copper and coaxial cables – Referred to as Fibre To The Home (FTTH) or Premise (FTTP) or Building (FTTB) – Point-to-multipoint topology • Single optical fibre to a building (or multiple buildings) is shared by 10 to 30 users – Typical speeds offered are 100Mb/s (but shared between users) • Key features: – Allow much higher data rates than copper and coaxial cable – Support data (Internet), voice and video (e.g. digital TV) – Requires installation of optical fibre
- 22. ITS 413 - Network Technologies 22 Summary: Wired Access Networks • Ethernet is the most common wired access network technology – Almost all computing devices have (or can support) Ethernet cards • From building (home/office) to other core networks, common to make use of existing telecommunication networks: – Dial-up, DSL using the telephone network (PSTN) – Coaxial used cable TV network • Optical fibre to the building is becoming more popular – Higher speeds, but costly to deploy
- 23. ITS 413 - Network Technologies 23 Core Network Technologies • Telephone-based Digital circuits – Leased Lines, Digital Hierarchies: PDH, SDH/SONET – Point-to-point topology • Packet Switching WANs – X.25, Frame Relay, ATM • IP Networks • Wireless Networks – Point-to-point microwave, satellite
- 24. ITS 413 - Network Technologies 24 Telephone Based Digital Circuits • Telephone networks (PSTN) use circuit switching • Telephone companies originally designed their core networks to carry digitized voice calls (later extended to carry data) – Hence most data rates measured in multiples of 64kb/s (or voice circuits) • Using PCM to sample voice at 8000 samples per second, 8 bits per sample • The circuit switched network of telephone companies can also be used to provide private (dedicated) circuit networks between end- points – Typically point-to-point topology, but can be extended to mesh, star and ring topologies
- 25. ITS 413 - Network Technologies 25 Telephone Based Digital Circuits • Plesionchronous Digital Hierarchy (PDH) – Originally point-to-point links using copper lines – Differences between European and US standards PDH is used to connected between sites and usually leased (rented) from a telecommunications company on a monthly basis. For example, if CAT had a copper cabling between Bangkadi and Rangsit, SIIT could lease a PDH circuit, such as E1 at 2Mb/s.
- 26. ITS 413 - Network Technologies 26 Telephone Based Digital Circuits • Synchronous Digital Hierarchy (SDH) – Developed for increased data rates and overcome limitations of PDH – Uses optical fibre – SDH is “International” standard; SONET is the US version
- 27. ITS 413 - Network Technologies 27 Packet Switching WANs • Several packet switching network technologies have been developed and used over past 30 years – A telecommunications company (or large organisation) deploy their own transmission media (copper cables or optical fibre) and run a packet switching service • Virtual Circuit Packet Switching – X.25 – Frame Relay – ATM • Datagram Packet Switching – IP
- 28. ITS 413 - Network Technologies 28 X.25 • ITU-T standard for interface between host and packet switched network – Developed in 1970’s; initiated by telephone carriers – there was a need to provide WAN connectivity over public data networks – Designed to transmit over error-prone analog links – Today, largely replaced by other technologies (frame relay, IP over SONET, …) • Legacy networks mainly support transaction-oriented application (e.g. financial) • Still used in developing countries • Defines three layers – Physical – Link – Packet (like Network layer) • Typical speed is 64kb/s; up to 2Mb/s
- 29. ITS 413 - Network Technologies 29 Frame Relay • Developed in late 1980’s, early 1990’s • Designed to eliminate most X.25 overhead • A single user data frame is sent from source to destination – There are no Acknowledgements for hop-by-hop (Layer 2) flow control or error control • But since many communication links are very reliable now, this is not a big issue – Fewer overheads than X.25. Frame Relay is more efficient • Provides data rate of 1.5Mb/s, extended to 44Mb/s
- 30. ITS 413 - Network Technologies 30 Frame Relay Network Example: this may be a network owned and operated by an ISP. SIIT pays the ISP to carry traffic to other networks (e.g. Rangsit, other Uni’s, the Internet) Example: this may be the SIIT Bangkadi LAN These are Frame Relay switches
- 31. ITS 413 - Network Technologies 31 Asynchronous Transfer Mode • In 1980’s, as Internet grew, people wanted faster methods than IP datagram switching (and routing) – Routers performing forwarding/routing in software were slow for large networks • Developed ATM, with the intention that it could be used as a fast WAN and LAN technology – Virtual circuit based packet switching • Use fixed size (53 byte) packets, or ATM cells: 48 bytes of data and 5 bytes of header – Better support for voice, video and data: Quality of Service control (wasn’t available in IP at the time) – Support data rates from 25Mbs up to 622Mb/s (now even faster) • Current status: – ATM WANs are today used by telecommunication companies to connect their networks (e.g. within ISPs, across cities, between cities) • In the future, may be replaced with IP over optical networks (SDH/SONET) – ATM LANs were not successful: Ethernet is the dominant LAN standard
- 32. ITS 413 - Network Technologies 32 Layers in Packet Switching Technologies Application Transport Network Data Link Physical X.25 Packet LAPB/HDLC X.21, RS232 LAPF Many … ATM ATM PHY, SDH Internet Layered Model X.25 Frame Relay ATM Circuit switching (PDH, SDH) can be considered to be at the Physical layer
- 33. ITS 413 - Network Technologies 33 Summary: Wired Core Networks • Circuit Switching technologies – Make use of existing telecommunication networks • Packet Switching technologies – More efficient than circuit switching for data traffic • Many of the technologies are used together – ATM can use SDH as a physical layer
- 35. ITS 413 - Network Technologies 35 Wireless Communications • Benefits – Untethered communications (no wires) • In some cases, can enable quick installation • Deploying and maintaining cables is expensive – Mobility of users and devices • Challenges – Wireless channel is not as robust as wired • More errors, therefore more losses and retransmissions, less throughput • Higher delays, therefore must wait long time for retransmissions, less throughput • Varying conditions due to mobility and environment – Example: timeout based retransmissions can lead to poor performance – Radio spectrum is limited (cannot just add more wires) • Therefore must efficiently “share” the spectrum amongst all users – Many Internet protocols designed assuming a “perfect link” • For examples, sometimes TCP may perform poorly over wireless link – Physical security is difficult (e.g. cannot easily limit the transmissions to a building) • Hence, extra network security is needed
- 36. ITS 413 - Network Technologies 36 Wireless Transmission • A simple model of wireless transmission: – The amount of power lost between transmitter and receiver depends on: • Distance, frequency, size of antenna, directionality of antenna, obstructions – The encoding of bits (0’s and 1’s) into an analog signal, and decoding at receiver, determines the data rate that can be used it particular environment – A receiver can only successfully decode (“understand”) a signal received above a certain power level Receiver Transmitter Transmitted signal, power Pt Received signal, power Pr Distance, d Power of the signal is lost during transmission
- 37. ITS 413 - Network Technologies 37 Wireless Transmission • An even simpler model of wireless transmission: • As IT professionals, we are interested in: – Data Rate: how fast can we send the data? [bits per second] – Transmission Range: how far can we send the data? [metres] – Frequency: is it free or licensed? Who else may interfere? [Hertz] – Transmit power: how much battery of our wireless device will it use? [Watts] – (and of course, cost: different technologies will have different costs) [Baht] Transmission Range Data Rate Frequency Receiver Transmitter Transmit power
- 38. ITS 413 - Network Technologies 38 Spectrum, Frequency and Bandwidth • A signal is sent at some frequency f with bandwidth b – The set of all frequencies available is called the spectrum • Why is the frequency (and bandwidth) important? – Data rate • A higher bandwidth (and frequency) generally leads to higher data rate – Transmission range • Higher frequency leads to shorter range • Different frequency signals are affected by obstacles in different ways – E.g. some frequencies are affected by rain, some frequencies will pass through walls, others wont, … – Interference • If other people/technologies use the same frequency, they may interfere, causing lower data rates – E.g. some cordless home phones may interfere with wireless LAN – Cost • The spectrum is limited and managed by national/international organisations • Some frequencies are free to use by anybody (within some rules) – E.g. most wireless LANs operate at the free Industrial Scientific Medical (ISM) frequency • Other frequencies you need a license to use – The license may be expensive, e.g. companies in Germany spent 2 trillion Baht (2,000,000,000,000) on licenses to use spectrum for 3G mobile networks
- 39. ITS 413 - Network Technologies 39 Spectrum, Frequency and Bandwidth
- 40. 40 Transmission Topology • Point-to-point – Transmit antenna points at receive antenna: directional – Signal power is concentrated between transmitter and receiver • Broadcast Radio (point-to-multipoint) – Transmitter sends signal in every direction: omni-directional – Anyone “within range” can receive the signal Transmitter Receiver Signal Signal Transmitter Receiver
- 41. ITS 413 - Network Technologies 41 Short Range Wireless Communications • Range: up to about 10 metres • Examples: Bluetooth, IrDA (infrared), ZigBee and IEEE 802.15.4, Ultra Wide Band (UWB) • Applications: connect electronic devices together – Wireless desktop: keyboard, mouse, PC, monitor connected without cables – Personal or Body Area Networks: devices carried with you (mobile phone, PDA, camera, watch, headset) connected – Automation: control and monitoring of devices (lights, machinery, A/C, entertainment) in homes, offices, factories, hospitals, … Technology Frequency Data Rate Power Bluetooth 2.4GHz <3Mb/s 1-3mW Range 1-10m ZigBee 915MHz/ 2.4GHz <250kb/s 1mW 10's m UWB 3-10GHz >100Mb/s ~1mW <10 m IrDA 350THz 115kb/s to < 4Mb/s ~1mW <1 m
- 42. ITS 413 - Network Technologies 42 Wireless LANs • Range: metres to 100’s of metres • Examples: IEEE 802.11 series (11b, 11a, 11g, 11n) • Applications: home/office LAN connectivity; city/public hot spots; … • Topology: point-to-multipoint (shared medium) Technology Frequency Data Rate 11b 2.4GHz 11Mb/s Range 20-300m 11a 5GHz 54Mb/s 15-30m 11g 2.4GHz 54Mb/s 25-75m 11n 5GHz 300Mb/s 20-60m
- 43. 43 Point-to-Point Fixed Wireless • Range: up to 10’s of kms • Examples: proprietary microwave products, IEEE 802.16 (WiMax), IEEE 802.11 • Applications: replacement for point-to-point WAN (core) links (e.g. alternative for PDH, SDH) • Typically fixed devices (e.g. antennas on towers), using highly directional antennas • WiMax (802.16) theoretically provides speeds up to 70Mb/s (or a range of 50km) – Symmetrical speeds, licensed spectrum Technology Frequency Data Rate 802.11b 2.4GHz 11Mb/s Range 10-20km 802.16 ~11GHz 10-20Mb/s 10-20km 802.16 2.3/2.5/ 3.5GHz 2Mb/s 10km Direction LOS LOS NLOS
- 44. ITS 413 - Network Technologies 44 Satellite • Range: 1000’s of kms • Examples: IPStar; CCSDS, SCPS, proprietary protocols • Applications: Internet access; TV/radio broadcasting; remote telephony • Satellite links range from Mb/s to 10’s of Gb/s (often shared amongst many users) Point-to-point topology Point-to-multipoint topology
- 45. ITS 413 - Network Technologies 45 Mobile Telephony • Range: km’s • Examples: – GSM derived: CSD, GPRS, EDGE, UMTS, HSPA, LTE – CDMAone derived: 1xRTT, EV-DO, UMB • Applications: mobile Internet access; voice/video over IP; data collection and monitoring • Mobile phone networks have progressively been updated to support both voice calls and data
- 46. ITS 413 - Network Technologies 46 Mobile Telephony ISP Core Network Mobile Phone Network Operators Core Network Base Station Internet Gateway PSTN PSTN Gateway Telephone calls Internet traffic
- 47. ITS 413 - Network Technologies 47 GSM Derived Data Technologies • Circuit Switched Data (CSD) 14 kb/s – Create a circuit-switched connection over original GSM voice call connection • General Packet Radio Service (GPRS) 60/40 kb/s • Enhanced Data Rates for GSM Evolution (EDGE) 240/120 kb/s – GPRS and EDGE are extensions to GSM; most networks support them with minor upgrades • Universal Mobile Telecommunication System (UMTS) 384 kb/s – A new system compared to GSM; most widely used 3G system • High Speed Packet Access – Extensions of UMTS to increase data rates – HSDPA (D = downlink) 14.4Mb/s – HSUPA (U = uplink) 5.7Mb/s – HSPA+ 42/22 Mb/s • Long Term Evolution (LTE) 326/86 Mb/s – A new system compared to UMTS
- 48. ITS 413 - Network Technologies 48 Summary: Wireless Networks • Wireless technologies can be used for both access and core networks – Access: WLAN, Bluetooth, Mobile Telephony, WiMax, Satellite • Mainly provide mobility to users or access in remote areas – Core: WiMax, Satellite, WLAN • Act as cable replacement where hard to deploy cables; typically fixed devices • Wireless technologies are typically lower data rates than similar cost wired technologies – WLAN (54Mb/s) vs Ethernet (100/1000Mb/s) – EDGE (240kb/s) vs ADSL (1.5Mb/s) – HSPA (~10Mb/s) vs Optical (100Mb/s) – WiMax (35Mb/s) vs Optical (1000Mb/s)