Wide Area Networks (1.2 & 2.4) Flashcards
WANs
▪ In the early 1990s, computer-networking design guides commonly invoked the Pareto principle (80-20 rule)
▪ Concept is that 80% of traffic stays on the LAN, while only 20% of traffic goes to WAN
▪ Today, most network traffic leaves the LAN and travels across the WAN
WAN Connection Types
▪ Dedicated leased line
▪ Circuit-switched connection
▪ Packet-switched connection
Dedicated Leased Line
▪ Logical connection that connects two sites through a service provider’s facility or telephone company’s central office
▪ More expensive than other WAN technologies because a customer doesn’t share bandwidth with other customers
Circuit-Switched Connection
▪ Connection is brought up only when needed, like making a phone call
▪ On-demand bandwidth can provide cost savings for customers who only need periodic connectivity to a remote site
Packet-Switched Connection
▪ Always on like a dedicated leased line, but multiple customers share the bandwidth
▪ SLAs used to guarantee a certain quality (5mbps at least 80% of the time)
▪ Virtual circuits are represented as dashed lines
Packet-Switched Connection
▪ Always on like a dedicated leased line, but multiple customers share the bandwidth
▪ SLAs used to guarantee a certain quality (5mbps at least 80% of the time)
▪ Virtual circuits are represented as dashed lines
WAN Physical Media
▪ Copper Wires
● Unshielded twisted-pair (UTP)
● Shielded twisted pair (STP)
● Coaxial cable
o Support both analog and digital connections
▪ Fiber-optic cable
● High bandwidth, long distance, and no EMI
▪ Electric power lines
● Broadband over Power Lines (BPL)
● Supports up to 2.7 Mbps
● Utilizes extensive infrastructure already in place (Power lines)
WAN Wireless Media
▪ Cellular (Phones and Hot Spots)
● 1G
o Communicated using a frequency of 30 KHz and had a bandwidth of about 2 kbps
● 2G
o Communicated over a GSM network using the 1800 Mhz frequency band
o Used multiplexing
o First to have SMS and text messages and international roaming
● 3G
o Support 144 Kbps
o Use a wider frequency band with frequencies from 1.6 Ghz to 2 Ghz
▪ WCDMA ● Wideband Code Division Multiple Access ● Could reach data speeds of up to 2 Mbps ● The slowest of the 3G technologies ▪ HSPA ● High Speed Packet Access standard ● Could reach speeds of up to 14.4 mbps ● Referred to as 3.5G ▪ HSPA+ ● High Speed Packet Access Evolution ● Brought speed up to around 50 mbps ● Referred to as 3.75G
● 4G
o Introduction of multiple input multiple output, or MIMO
o Uses an even wider frequency band, covering frequencies from 2 to 8 Ghz
o Often called 4G LTE, or 4G Long Term Evolution
o It was improved and became LTE Advanced or LTE-A
● 5G
o Reach speeds up to 10 Gbps using high-band 5G frequencies
o 5G is split into 3 frequency bands
▪ Low-band Frequencies
● Operates between 600-850 MHz and provide us with speeds of 30-250 Mbps
▪ Mid-band Frequencies
● Operate between 2.5 to 3.7 Ghz and supports higher data rates of 100-900 Mbps
▪ High-band Frequencies
● Operate between 25-39 Ghz
Global System for Mobile Communications (GSM)
o A cellular technology that takes your voice during a call and converts it to digital data
o A SIM card is used to identify yourself to the network
● Code-Division Multiple Access (CDMA)
o A cellular technology that uses, code division, to split up the channel
o For every call that is made, the data is encoded with a unique key and then all the data streams can be transmitted at once in a single channel
Microware
▪ A microwave link is a communication system that use a beam of radio waves in the microwave frequency range to transmit information between two fixed locations
▪ Frequencies ranges from 300 Mhz to 300 Ghz
● WiMax
o Worldwide Interoperability for Microwave Access
o Requires an antenna be installed on the roof of your home or office
o WiMAX is faster than GSM (2G), UMTS (3G), HSPA (3.5G)
● Satellite
o Used for remote areas
o Flying and Shipboard use
o Expensive in comparison to cellular, cable, or fiber connections
● Radio
o Implementation varies country to country based on frequencies
Dedicated Leased Line
▪ Point-to-point connection between two sites
● All bandwidth on line is available all the time
▪ Digital circuits are measured in 64-kbps channels called Digital Signal 0 (DS0)
● Channel Service Unit / Data Service Unit (CSU/DSU) is used to terminate the digital signals at customer’s demarcation point
▪ Common digital circuits include T1, E1, T3, and E3 circuits
Examples of Digital Signal Levels (Pictures Below)
Metro Ethernet
▪ Service providers are beginning to offer Ethernet interfaces to their customers
▪ Less expensive and more common than specialized serial ports used in a CSU/DSU
▪ Technology used by service provider is hidden from customer and they only need to connect their network’s router to a Smart Jack
Point-to-Point Protocol (PPP)
▪ Commonly used Layer 2 protocol on dedicated leased lines to simultaneously transmit multiple Layer 3 protocols (IP, IPX)
▪ Each Layer 3 control protocol runs an instance of PPP’s Link Control Protocol (LCP)
● Multilink interface
o Allows multiple physical connections to be bonded together into a logical interface
● Looped link detection
o Layer 2 loop can be detected and prevented
● Error detection
o Frames containing errors can be detected and discarded
● Authentication
o Device on another end can authenticate the link
▪ PPP Authentication Methods
● Password Authentication Protocol (PAP)
o Performs one-way authentication between client & server
o Credentials sent in clear-text
● Challenge-Handshake Authentication Protocol (CHAP)
o Challenge-Handshake Authentication Protocol
o Performs one-way authentication using a three-way handshake
o Credentials are hashed before transmission
Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP)
o Microsoft Challenge-Handshake Authentication Protocol
o Microsoft-enhanced version of CHAP, includes two-way authentication
PPP over Ethernet (PPPoE)
▪ Commonly used with DSL modems
▪ PPPoE encapsulates PPP frames within Ethernet frames
▪ Allows for authentication over Ethernet
Digital Subscriber Line (DSL)
▪ Asymmetric DSL (ADSL) ● Maximum distance to DSLAM: 18,000 feet ● Voice and Data on same line ● Downstream: Up to 8 Mbps ● Upstream: Up to 1.544 Mbps ▪ Symmetric DSL (SDSL) ● Maximum distance to DSLAM: 12,000 feet ● No simultaneous voice and data on same line ● Downstream: 1.168 Mbps ● Upstream: 1.168 Mbps ▪ Very High Bit-Rate DSL (VDSL) ● Maximum distance to DSLAM: 4,000 feet ● Downstream: Up to 52 Mbps ● Upstream: Up to 12 Mbps
Cable Modems
▪ Hybrid Fiber-Coax (HFC) distribution network is a cable television infrastructure containing both coaxial and fiber-optic cabling
▪ Specific frequency ranges are used for upstream and downstream data transmission as determined by Data-Over-Cable Service Interface Specification (DOCSIS)
● Upstream (5 MHz to 42 MHz)
● Downstream (50 MHz to 860 MHz)
▪ Transmits and receives over cable television infrastructure
