View
250
Download
0
Embed Size (px)
Citation preview
DSL – ADSL and Wi - Fi
DSLADSLProtocolsSecurityWi-FiCable vs ADSL
DSL History• 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 ?• 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?• 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
• 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• 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)• 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• Others Discarded
ADSL MODEM
• What is it?• Routing• Security
• Firewall• NAT service
• Wireless Connection
ADSL Modem
Wi-Fi
• 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 key
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
• MAC address genereated
TKIP
WPA
802.1x
• 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• EAP Logoff• Port Unauthorized
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