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DSL – ADSL and Wi - Fi
DSL
ADSL
Protocols
Security
Wi-Fi
Cable vs ADSL
DSL History
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Dial Up too slow
Pay for the connection time
Telephone occupied
VLSI advancements ( 1990 )
• DSLAM ( DSL Access Multiplexer )
• DSL modem cheaper
• Deployed over existing cable
• Installing Fiber Optic Cable expensive
• Competition in DSL drop prices
What is DSL ?
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Digital Subscriber Line
Splitter ( Client )
Splitter ( Service Provider)
DSLAM
• Fast Network Connection ( Fiber Optic )
• Switch
• PSTN (Public Switched Telephone Network )
ADSL Frequencies
ADSL
• Asymetric Digital Subscriber Line
• Asymetric -> Downstream != Upstream
• 1 * Downstream = 4 * Upstream
How does it work?
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Upstream / Downstream bands
25.875 kHz to 138 kHz Upstream
138 kHz – 1104 kHz Downstream
4.3125 kHz pieces ( 26 – 224 )
Acceptable signal-to-noise ratio
Distance – Electrical Noise
Splitter
• DSLAM
• PSTN
DSL
DSLAM
xDSL
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High Data Rate DSL (HDSL)
Symetric DSL (SDSL)
Asymetric DSL (ADSL)
Rate – Adaptive DSL (RADSL)
Very-high-bit-rate DSL (VDSL)
Very-high-bit-rate DSL2 (VDSL2)
Symetric High-speed DSL (G.SHDSL)
Powerline DSL (PDSL)
Speed Dependencies
• ADSL – 5km, 128kbps / 8mbps
• ADSL2 – 2.5km, 12mbps ( Framing – Err. Corr)
• ADSL2+ - 1.5, 24mbps ( 2.2 MHz )
Protocols
• PPPoE
• DHCP
• Bridging
• Transparent Bridging
• Source Route Bridging
PPPoE
• Point to Point Protocol over Ethernet
• PPP -> Dial Up
• Encapsulate PPP frames in Ethernet
frames
• Clasical connection
• Username
• Password
• IP assaign -> Connection Open
• Reuse of IP
DHCP
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Dynamic Host Configuration Protocol
Request and obtain internet address
DHCP client -> Query -> DHCP server
Immediately after Booting
IP address
Subnet Mask
DNS server ( Domain Name System Server )
Default Gateway info.
DHCP
Network Bridge
• Network Switch
• Broadcast Message
• Transparent Bridging
• Forwarding Database
• Recieved Frames Addresses
• Broadcast Message
• Store route in D.B.
Network Bridge
• Source Route Bridging
• Single Route frames (SR)
• Fixed destinations
• All Route frames (AR)
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Find routes
Broadcast frame -> All Ports
Register each step
Max. Hop Count
• Diameter of Network Graph
• Decrement by each Bridge
• Hop Count = 0 -> Discard
• First AR frame -> Best Route
ADSL MODEM
• What is it?
• Routing
• Security
• Firewall
• NAT service
• Wireless Connection
ADSL Modem
Wi-Fi
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SSID (Service Set Identifier)
Broadcast SSID
Beacon packets
100 ms
Same SSID -> Signal Strength
Lowest 1 Mbit/s
Wireless Protocols
Wireless Security
• Access Control
• MAC address check
• Allow
• Ban
• WEP
• WPA
• 802.1x
Access Control
WEP(Wired Eqivalent Privacy)
• IEEE 802.11 standard
• RC4
• Stream Cipher
• Block Cipher ?
• RC4 for confidentiality
• CRC-32 checksum for integrity
WEP(Wired Eqivalent Privacy)
• 64 BIT WEP – 40 BIT Hex – 4 * 10 = 40
• 128 BIT WEP – 104 BIT Hex – 4 * 26 =
104
• 256 BIT WEP – 232 BIT Hex – 4 * 58 =
232
• + 24 BIT Initialazition Vector (block of BIT exe S.C. Or
B.C)
• Stream Chiper
• Block Cipher
WEP
Wi-Fi Protected Access (WPA)
• Key Recovery Attacks on WEP
• Keys unknown but
• Mathematical relation between keys known
• Temporal Key Integrity Protocol ( TKIP )
• Per-packet key mixing
• a message integrity check and
• re-keying mechanism
• Every data packet -> unique encryption
key.
• Message Integrity Check
TKIP
WPA
802.1x
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Data – Link Layer
Closed Wireless Access Points
Detection -> Port on switch Unauthorized
Authenticator -> EAP Request ->
Supplicant
• Supplicant -> EAP Response ->
Authenticator
• Authenticator -> EAP Responce ->
Authentication Server
802.1x
802.1x
Cable vs ADSL
• SPEED
• Cable upto 2 times faster than ADSL (
3.0Mbps – 1.5Mbps)
• Shared bandwidth
• SHARING AND SECURITY
• Cable modem -> Pay for each extra client
• ADSL -> No Limitations
• Both very secure
Cable vs ADSL
• Price