11/30/2016

Last-Mile Network Broadband and Last Mile Networks

Design Concerns History: Dial-up

• Infrastructure Cost • First public Internet service used telephone lines • Throughput: Upstream and Downstream • Telephone lines: broadly available, low infrastructure cost • Packet or Circuit Switching • Phone modem encoded/decoded data in voiceband • Congestion Control • Dial-up: call a phone number, get Internet • Latency

• Result: different networks used in different scenarios

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History: DSL History: Cable Broadband

• Digital Subscriber Line: improvement on dial-up • Growth of Internet required greater throughput • Used extra bandwidth on telephone line • Use extra bandwidth in existing cable TV networks • Always on, circuit-switched • Higher throughput, but along shared medium • Allowed concurrent use of phones • Primary standard is DOCSIS • Faster than dial-up, but slower with distance • Still used in rural areas due to low infrastructure cost

DOCSIS DOCSIS Architecture (DOCSIS 3.0)

• Data Over Cable Service Interface Specifications • Formed by industry consortium, maintained by CableLabs • Combined 2 earlier, proprietary standards • Physical layer from Motorola CDLP • MAC layer from LANcity

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Physical Infrastructure Transmission

• Coaxial cable or hybrid fiber-coaxial (HFC) network • Radio frequency transmission • Fiber for trunk network, coaxial (RF) for client access • Downstream bandwidth: 108 MHz – 1002 MHz • Coaxial cables easy to install near metal objects • Upstream bandwidth: 5 MHz – 42 MHz or 85 MHz selectable • Cable Modem Termination System (CMTS) • Bandwidth divided into 6 MHz channels (NTSC) • Evolved from headend for cable TV distribution • 38 Mbps downstream throughput per channel • Handles the MAC layer and content distribution for an area • 9 Mbps (DOCSIS 1.0) or 27 Mbps (2.0) upstream throughput per channel • Interface to wide area network • Quadrature amplitude modulation (QAM) • Client Cable Modem • 2 carrier signals: phase difference encodes data • Performs demodulation of RF signal into usable data. • Channel bonding (3.0): use multiple channels for more throughput • Connects to network via coaxial cable (usually RG-6)

CMTS MAC Protocols

• Core • Cable is shared medium • Downstream transmitter, upstream receiver • Upstream: FDMA/TDMA or S-CDMA • Modulation and demodulation of data • All users transmit upstream on same channels • Packet forwarding between Network Side Interface & upstream RF Interface • Downstream: Request-Grant model • Timing module: maintains transmission timing requirements • Clients use certain channel(s), request packet from CMTS • EQAM (3.0): Handles downstream RF interfaces for channel bonding • Packet sequence number to maintain order at receiver • Provisions client modems (CM) • Upper layer protocols • CM acquires 1 downstream channel, gets init data from CMTS • SNMP for CM management • CM contacts CMTS by “ranging” upstream channel • TFTP for configuration • CM authentication, encryption, MAC layer initialization • DHCP for IP management

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Packet Headers Alternative: Satellite Broadband Frame Layout: MAC Header Layout: • Wireless broadband: access by satellite or broadcast tower • Little infrastructure needed • Satellite • Satellite dish at client location • Issues with latency • Dish -> satellite -> headend -> Internet takes time FC_PARM specifies type of packet: • Affected by weather, satellite location • Timing • MAC Management • Request Frame • Fragmentation • Concatenation

Upcoming: Fiber-Optic Cable Last-mile network comparisons

• Encode data in light DSL: on its way out Cable (DOCSIS): current standard • Lower latency, less interference, higher throughput than cable • Longer transmission distances possible than cable • Lowest infrastructure cost • Low infrastructure cost (cable TV (phone lines) lines) • Current providers: Google Fiber, Verizon FiOS • Pre-existing infrastructure • Pre-existing infrastructure • Adoption blocker: cost of new infrastructure • No pre-existing last-mile fiber-optic network • Circuit-switched • Shared medium • Used mainly for trunk networks • Low bandwidth • Higher bandwidth • Requires planning, permits, construction work • Limited effective range • Longer effective range • Planned to supersede cable • Still used in rural areas • Widely used in urbanized areas

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Last-mile network comparisons

Fiber-optic cable: the future Satellite: when wires don’t work • High infrastructure cost • Low infrastructure cost • No pre-existing infrastructure • Pre-existing infrastructure • Shared medium (satellites) • Very high bandwidth • Can offer good bandwidth • Very low latency • Significant latency issues • Long range • Long range • Growing adoption in urban areas • Used in remote areas

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