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DSL – ADSL and Wi - Fi DSL ADSL Protocols Security Wi-Fi Cable 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 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 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 • • • • 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