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Internet infrastructure and access
Henning Schulzrinne
Dept. of Computer Science
Columbia University
Fall 2003
Internet backbones
Classify ISPs into tiers– tier 1: global reach, about 40
British Telecom (BT), Cable & Wireless, Global Crossing, Level 3, Sprint, MCI (UUnet), Verio (NTT), …
– tier 2: regional– tier 3: local
Tier-1’s typically use railroad tracks or pipelines as right-of-way
– some also lease (some) circuits from other providers– at least 20,000 fiber miles
Connect to local circuits via points-of-presence (POP)
Internet backbones
OC-3 (155 Mb/s), OC-12 (622 Mb/s), OC-48 (2.4 Gb/s) or OC-192 (10 Gb/s)
Usually, WDM or D-WDM (e.g., 16 λ x 2.5 Gb/s, up to 40 λ)
– 50 or 100 GHz optical spacing Fiber: about $30,000-$50,000/mile, almost all
construction Transport: POS (packet over SONET), MPLS, ATM,
FR (edges) Backbone utilization: no more than 30% typical
– needed for fault recovery
Network utilization
local phone line: 4% U.S. long distance switched voice: 33% Internet backbones: 10-15% private line networks: 3-5% LANs: 1%
ISPs
America Online dial 25.3
MSN dial 8.7
United Online (Juno) dial 5.2
Earthlink dial 5.0
Comcast cable 4.4
SBC DSL 2.8
Verizon DSL 1.9
Cox cable 1.7
Charter cable 1.3
BellSouth DSL 1.2
Many dial-up ISPs don’t own modems use wholesale providers
DSL + cable modem modems are always
oversubscribed (10:1?)
Residential broadband
Quick review: DSL
Uses spectrum from 25 kHz to 1.1 MHz ATM cells Ethernet PPP DSLAM aggregates circuits US local loops can be up to 18 kft long ADSL+: 16 Mb/s @ 4 kft, 10 Mb/s @ 6 kft
(1.1 mi) downstream
Commercial international backbone
Internet2 backbone (Abilene)
Internet2 (Abilene) 10 Gb/s network
Peering
Exchange of traffic between ISPs– autonomous systems (AS)– private peering vs. public peering– public peering at MAE-East, MAE-West, AMS-IX, …– either a LAN or mesh of ATM/FR VCs
Sender keeps all (SKA) = only pay for rack space, not traffic
Alternative: transit payment (tier2 tier1)
Peering points: AMSIX in Amsterdam
Peering point: AMSIX
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