Access Networks and the Local Loop
Prof. Rami Langar LIGM/UPEM [email protected] http://perso.u-pem.fr/~langar
1 Access Networks Evolution o A large number of recent technologies:
n xDSL and unbundling of the local loop n CATV, HFC (Hybrid Fiber Coax) n FTTx, PON n Power Line Communication (PLC) n WLL (Wireless Local Loop) o 802.11 (WiFi) o 802.16 (Wimax) o Satellites (LEO/MEO/GEO) o 3rd Generation Mobile Systems (UMTS) o LTE, femtocells n …
2 The Local Loop solutions
100 ADSL 90 Mobile 3G Optical fiber 80 Cable modem 70 WiMAX
60
50 Satellite
Rural b Urban Suburban
40 urban Dense Sparsely populated Sparsely
30 100k Relative complexity/cost (%) complexity/cost Relative
20 Mobile 4G 10k
10 1k
0 0.1 1 10 100 1,000 10,000 100,000 3 Population density (per km2) Length of the wired Local Loop
France
4 Communication medium (wire)
5 xDSL access
6 Legacy wired DSL access infrastructure
STB
DSLAM modem ADSLF 1 F STB F Modem ADSL 34 Broadband F Network Internet servers STB - DSLAM modem ADSLF F 1 STB F Modem ADSL 34 F
STB
DSLAM modem ADSLF 1 F STB F Modem ADSL 34 F
STB
DSLAM modem ADSLF 1 F STB F Modem ADSL 34 F
7 The xDSL Loop
PABX (Tel) IP network
LAN xDSL Modem BAS PABX X X X X Data xDSL Network ATM/SDH Modem Network DSLAM GW PSTN
8 Legacy wired DSL access infrastructure (2)
PABX ADSL
DSLAM
ATM/SDH WDM
PABX ADSL ATM/SDH ATM/SDH
ATM/SDH DSLAM WDM
Typical infrastructure of incumbent telecom operators WDM: Wavelength Division Multiplexing SDH: Synchronous Digital Hierarchy; ATM: Asynchronous Transfer Mode DSL: Digital Subscriber Line à ATM/SDH aggregation being replaced by Giga Ethernet access 9 xDSL access evolution: ATM vs Ethernet
10 The ADSL modulation Discrete multitone modulation (DMT) modems (DSP-based) 20 canaux (~4 kHz/canal) 256 canaux (~4 kHz/canal) ~8 bits par intervalle d’horloge ~8 bits par intervalle d’horloge
⇒ ~ 20 x 4.000 x 8 = 640 kbit/s ⇒ ~ 256 x 4.000 x 8 = 8,2 Mbit/s
4 kHz
Up Down +- 3,5 dB/Hz
A DMT modem permanently evaluates the line quality, so as to adaptively recompute the power and the optimal capacity in bit/s per Hz to allocate to each channel 11 ADSL: bandwidth-distance constraints
Maximum capacity (in Mbit/s) ADSL PABX 100
10 ADSL
Data 1 Network 0 1 2 3 4 5 6 7 Distance (in kilometers)
PABX ADSL
Data Network
12 ADSL evolutions
o ADSL 2 n New coding and modulation techniques, leading to: o More bandwidth (maximum rate of 10Mbps downstream, apprx 1Mbps upstream) at a given distance o Or longer reachable distances (for a given rate) n Inverse Mux, possibility to use lower frequencies
o ADSL 2+ n Higher frequency range for download n leading to a maximum of 25 Mbps for download (for VERY short distances) n Same frequency range for upload. Still 1Mbps.
13 The DSL wiring and unbundling
ULL: Unbundling Local Loop (at the concentrator level or DSLAM level) 14 xDSL bandwidth-distance product
– ADSL (Asymmetric Digital Subscriber Line) – SDSL (Symmetric DSL) – HDSL (High-bit-rate DSL) – VDSL (Very-high-bit-rate DSL)
15 xDSL spectral utilization
25 kHz 1,1Mhz POTS (plain old tel. service) 2,2Mhz
upstream downstream ADSL ADSL2 ADSL2+
VDSL
12Mhz
10Khz 100Khz 1Mhz 10Mhz 16 FTTx
17 The Optical Loop o FITL (Fiber In The Loop) or FTTX (Fiber To The X) n X=C, Cabinet, Curb n X=N, Building n X=H, Home n X=T, Terminal o FTTX development examples n FTTH by Free (FR); FTTB by Numericable (FR), Fastweb (IT) n Future: FTTC + femtocell/WiMax Aps o FTTX usually based nowadays on Ethernet MAN with n Direct fiber connections n Use of Ethernet PONs (EPONs) (previously APON for ATM over PON) n Use of remote DSLAMs (e.g.VDSL)
18 PON (Passive Optical Network)
Unpowered optical splitters enable a single fiber to be used by multiple users.
• Downstream: broadcast to all • Upstream: TDMA (CSMA/CD not adapted to the speed of EPON)
• 3 types of PON: • ATM over PON (APON) • Ethernet PON (EPON) • Gigabit PON (GPON)
OLT: Optical Line Terminaison ONU/ONT : Optical Network Unit/Terminal 19 CATV cabling
20 The Cable Loop (CATV) o Reusing existing CATV equipment n Inexisting in some countries n Widely deployed in some others (north america) n Upload channel problem (usually TDMA as in PONs)
o DOCSIS standard uses slots nnumbred from 1 to 4096
o Up to 14 slots can be used per communication
o Slot reservation by sending a request on a random slot (Binary Exponential Backoff algorithm) n Large bandwidth (more than 800 MHz)
o Frequency multiplexing to handle different applications
21 THE WIRELESS LOOP
22 The Wire-Less Loop (WLL)
Data Network
No real applications in early 2000s Nowadays new products and protocols (4G, Wimax, LTE) à bypass DSL The Wire-Less Loop (2) o Cellular Network : n Up to 2Mbps (3G) n Up to 100 Mbps (4G) n Up to 1 Gbps (5G) o IEEE 802.11 (WiFi) n 11Mbps (11.b), 54Mbps(11.a et 11.g) , 100Mbps under investigation n Limited coverage o WiMax (IEEE 802.16) n 802.16a (deployed early 2005): o point to point connection up to 134Mbps. o Point-to-multipoint: up to 75Mbps for cells of several kms o Target: Fixed access n 802.16e: o Includes roaming (speed around 100km/h) o Target: mobile broadband access
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Femtocell and OFDMA spectrum sharing
• A femtocell is a small cellular base station typically designed for use in a home or small business. • It can connect to the Mobile Operator Network through Internet
25 The Satellite Loop
LEO (Low Earth Orbit) 500 – 1.500 km
MEO (Medium Earth Orbit) 5.000 – 12.000 km
GEO (Geostationary Earth Orbit) 36.000 km
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