Internet Connections

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Internet Connections

• Gaining Access to Internet

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Three Types of Internet Connections

• 1 Direct Connection via LAN
• 2 Dialup Connection
• 3 Broadband Connection

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1 Direct Connection

• Permanent Connection, Always On
• Instantaneous Access to Internet
• Connection goes through a Router
• Connects to point in Internet via T lines
• T lines are digital transmission lines
• T1 line 1.5444 Mbps, 24 channels, 64 Kbps
• T3 line 44.736 Mbps, 672 channels

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2 Dialup Connection

• Temporary connection
• Initiate and terminate each session
• PPP governs establish of session
• Connect to ISP
• Connection via POTS or PSTN
• POTS Plain Old Telephone Service
• Public Switched Telephone Network

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2 Dialup Connection

• POTS or PSTN
• Twisted Pair Cable limited throughput
• Analog transmission lines built for Voice
• Limiting factor in speed of connection
• Modem 56K (Kbps)
• Converts digital to analog (sending end)
• Converts analog to digital (receiving end)

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2 Dialup Connection

• Actual Connection Speed
• 33 to 40 Kbps
• Modem technology is not the limiting factor
• POTS is the limiting factor
• Temporary connection
• IP address temporarily assigned to client by ISP
• IP address gets re-used in another client session

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3 Broadband Connection

• Two Transmission Methods
• Baseband Transmission (LANs)
• Transmitted signal consumes entire bandwidth
• Only one station can transmit at a time
• Why we need the network access protocols
• Broadband Transmission
• Transmitted signal does not consume the entire BW
• Cable can be subdivided into different channels

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3 Broadband Connection

• Broadband Transmission
• Can carry multiple signals at once
• Can carry a variety of signals
• Voice, Internet Data, Video, etc.
• Multiplexing
• Multiplexer (Mux) subdivides cable into channels
• Each channel can carry a different stream of data

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Multiplexing

• Frequency Division Multiplexing FDM
• Channels occupy different frequency ranges
• Analog Transmissions
• Time Division Multiplexing TDM
• Logical channels created by time slots
• Each time slot serves a particular source

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Figure 6.3 FDM
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Figure 6.12 TDM
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3 Broadband Connection

• Three types of Broadband service
• DSL Digital Subscriber Line
• Broadband Cable or Cable Modem technology
• Satellite
• Broadband service
• Permanent connection, instantly available

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DSL Digital Subscriber Line

• Traditionally the phone company
• Uses digital transmission facilities
• Twisted pair cable with an upgrade
• Subscriber needs DSL modem
• DSL modem encodes data into signals
• Not same encoding as 56K modem

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Figure 9.3 ADSL modem
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DSL Digital Subscriber Line

• A variety of DSL offerings
• Some for Business
• Some for Residential
• ADSL Asymmetrical DSL (Consumer)
• Throughput differs with direction
• Download more channels allocated
• More demand for downloading data

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DSL Digital Subscriber Line

• Asymmetrical DSL
• Download 1.5444 Mbps
• Upload 256 Kbps
• DSL Limitation
• Availability not available in all areas
• Performance degrades get further from CO

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Broadband Cable

• Traditionally Cable TV company
• Digital transmission facilities
• Uses mostly coaxial cable, some fiber optic
• Subscriber needs Cable modem
• Modem encodes data as signals
• Encoding different than DSL, Dialup
• Connection speed rivals or exceeds DSL

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Figure 9.8 Cable modem
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Broadband Cable

• Limitations
• Availability
• Cable is shared cable, all users on same cable
• Performance degrades as have more subscribers
• DSL over telephone network switched facility

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Satellite

• Similar concept to satellite TV service
• Earth stations require satellite dishes
• Signals are transmitted via satellites in orbit
• Two variations of service
• One-way service
• Two-way service

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Satellite

• One-way service
• Downloads signals via satellite link
• Uploads uses POTS (like dialup)
• Two-way service
• Both Downloads and Uploads use Sat link
• Expensive

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Satellite

• Best characteristic
• Available nearly anywhere
• Worst characteristic
• Propagation delay
• Satellites in geosynchronous orbit
• Approximately 22K miles from earth

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Comparing Internet Connections

• Time to download 10 MB (80 Mbits) file
• Dialup 23 min
• Satellite 3 min
• DSL 50 sec
• Cable 26 sec