Intro to xdsl part 1

Attenuation vs. frequency

Maximum reach

• Length of cable for reliable communications
• ASSUMING ONLY THERMAL NOISE
• Bellcore study in residential areas (NJ) found
• -140 dBm / Hz
• white (i.e. independent of frequency)
• is a good approximation
• Real systems have other sources of noise,
• and thus have lower reach (Shannon!)
• We can compute the maximum reach from UTP attenuation

xDSL - Maximum Reach

Sources of Interference

• XMTR RCVR
• RCVR XMTR
• FEXT
• NEXT
• RCVR XMTR
• XMTR RCVR
• RF INGRESS

• THERMAL
• NOISE

Interference for xDSL

Examples of Realistic Reach

• More realistic design goals (splices, some xtalk)
• 1.5 Mbps 18 Kft 5.5 km (80% US loops)
• 2 Mbps 16 Kft 5 km
• 6 Mbps 12 Kft 3.5 km (CSA 50% US loops)
• 10 Mbps 7 Kft 2 km
• 13 Mbps 4.5 Kft 1.4 km
• 26 Mbps 3 Kft 900 m
• 52 Mbps 1 Kft 300 m (SONET STS-1 = 1/3 STM-1)

xDSL flavors

xDSL flavors

ITU G.99x standards

• G.991 HDSL (G.991.1 HDSL G.991.2 SHDSL)
• G.992 ADSL (G.992.1 ADSL G.992.2 splitterless ADSL
• G.992.3 ADSL2 G.992.4 splitterless ADSL2
• G.992.5 ADSL2+)
• G.993 VDSL (G.993.1 VDSL G.993.2 VDSL2)
• G.994 HANDSHAKE
• G.995 GENERAL (INFO)
• G.996 TEST
• G.997 PLOAM
• G.998 bonding (G.998.1 ATM G.998.2 Ethernet G.998.3 TDIM)

Bonding

• If we need more BW than attainable by Shannon bounds
• we can use more than one UTP pair (although XT may reduce)
• this is called bonding or inverse multiplexing
• There are many ways of using multiple pairs:
• ATM - extension of IMA (may be different rates per pair)
• cells marked with SID and sent on any pair
• Ethernet - based on 802.3(EFM)
• frames are fragmented, marked with SN, and sent on many pairs
• Time division inverse mux
• Dynamic Spectral Management (Cioffi)
• Ethernet link aggregation