Wide Area Network (WAN) Flashcards
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
WAN Physical Media: Copper Wires
● Unshielded twisted-pair (UTP)
● Shielded twisted pair (STP)
● Coaxial cable
o Support both analog and digital connections
WAN Physical Media: Fiber-optic cable
High bandwidth, long distance, and no EMI
WAN Physical Media: Electric power lines
Broadband over Power Lines (BPL)
● Supports up to 2.7 Mbps
● Utilizes extensive infrastructure already in place (Power lines)
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
Wide Area Network (WAN) Technologies: 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
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
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
Satellite Modems
▪ Used in remote, rural, or disconnected locations where other connections
are not available
▪ Provides relatively fast speeds like a DSL modem, but contain low
bandwidth usage limits and charge high costs for over limit usage
▪ Potential issues with Satellite communications:
● Delays - Time to satellite and back ( > !
“ second)
● Weather conditions
o Thunderstorms and snow can cause loss of connectivity
between satellite and receiver
Plain Old Telephone Service (POTS)
Public switched telephone network (PSTN) consists of telephone carriers
from around the world
▪ Analog connections (voice and/or data) using the PSTN
▪ Dial-up modems have a maximum bandwidth of 53.3-kbps because they
can only access one 64-kbps channel at a time
Integrated Services Digital Network (ISDN)
▪ Supports multiple 64-kbps B (Bearer) channels
▪ Older technology designed to carry voice, video, or data over B channels
▪ D channel (data or delta channel) existed for 64-kbps signaling data
Frame Relay
▪ Losing market share due to cable and DSL
● Frame Relay sites connected to virtual circuits (VC)
● VCs are point-to-point or point-to-multipoint
● Low cost and widely available
● Always-on or on-demand
● Layer 2 technology
Synchronous Optical Network (SONET)
▪ Layer 1 technology using fiber as media
▪ Transports Layer 2 encapsulation (like ATM)
▪ High data rates (155 Mbps to 10 Gbps)
▪ Covers large distances (20 km to 250 km)
▪ Physical topology can be a bus or ring
Asynchronous Transfer Mode (ATM)
Layer 2 WAN technology operating using Permanent Virtual Circuits
(PVCs) and Switched Virtual Circuits (SVCs)
▪ Similar to Frame Relay, except all frames are transferred as fixed-length
(cells) as its protocol data unit (PDU)
▪ Fixed-length cells of 53-bytes used to increase speed of transmissions
● Contains 48-byte payload and 5-byte header
o Generic Flow Control (GFC)
o Virtual Circuit Identifier (VCI)
o Virtual Path Indicator (VPI)
o Payload Type Indicator (PTI)
o Cell Loss Priority (CLP)
o Header Error Control (HEC)
ATM Virtual Circuits
User-Network Interface (UNI)
● Used to connect ATM switches and endpoints
Dynamic Multipoint Virtual Private Network (DMVPN)
Allow Internet to be used as WAN
connection for secure site-to-site
communication
▪ VPN tunnel has authentication and
encryption so users on the unsecure
network cannot read or decrypt the
traffic without proper keys
▪ Can connect remote locations with
low cost, instead of dedicated or leased-line access
Multiprotocol Label Switching (MPLS)
▪ Supports multiple protocols on the same network (used by service
providers)
▪ Support both Frame Relay and ATM on the same MPLS backbone
▪ Allows traffic to be dynamically routed based on load conditions and path
availability
▪ Label switching is more efficient than Layer 3 IP address routing
▪ Used by service providers for forwarding data in the backend, the
customer remains unaware of the details
WAN Data Rates
Bandwidth measured in Kbps, Mbps, & Gbps
▪ ATM and SONET measured by optical carrier
● OC levels are based off of OC-1 (51.84 Mbps)
● All others are multiples (OC-3 is 155.52 Mbps)
Software-Defined Wide Area Network (SDWAN)
▪ A virtual WAN architecture that allows enterprises to leverage any
combination of transport services to securely connect users to their
applications
▪ Uses a centralized control function to securely and intelligently redirect
the traffic across the WAN
▪ Enable cloud-first enterprises to deliver quality experiences to their users
▪ Allows your WAN environment to be more dynamic and efficient
▪ Reduces bottlenecks caused by your traditional, centralized WAN
architecture
Multipoint generic routing encapsulation (mGRE)
A protocol that can be used to enable one node to communicate with
many other nodes, essentially creating a point to multipoint link
▪ NOT limited to point to point connections
▪ Usually combined with the Dynamic Multipoint VPN, or DMVPN,
protocol, as well, for security
