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