Wide Area Network (WAN)

Question 1

WAN Connection Types

Answer 1

Dedicated leased line
▪ Circuit-switched connection
▪ Packet-switched connection

Question 2

Dedicated Leased Line

Answer 2

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

Question 3

Circuit-Switched Connection

Answer 3

▪ 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

Question 4

Packet-Switched Connection

Answer 4

▪ 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

Question 5

WAN Physical Media: Copper Wires

Answer 5

● Unshielded twisted-pair (UTP)
● Shielded twisted pair (STP)
● Coaxial cable
o Support both analog and digital connections

Question 6

WAN Physical Media: Fiber-optic cable

Answer 6

High bandwidth, long distance, and no EMI

Question 7

WAN Physical Media: Electric power lines

Answer 7

Broadband over Power Lines (BPL)
● Supports up to 2.7 Mbps
● Utilizes extensive infrastructure already in place (Power lines)

Question 8

Global System for Mobile Communications (GSM)

Answer 8

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

Question 9

Code-Division Multiple Access (CDMA)

Answer 9

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

Question 10

Microware

Answer 10

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

Question 11

Wide Area Network (WAN) Technologies: dedicated leased line

Answer 11

▪ 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

Question 12

Metro Ethernet

Answer 12

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

Question 13

Point-to-Point Protocol (PPP)

Answer 13

▪ 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

Question 14

PPP Authentication Methods
● Password Authentication Protocol (PAP)

Answer 14

o Performs one-way authentication between client & server
o Credentials sent in clear-text

Question 15

PPP over Ethernet (PPPoE

Answer 15

Commonly used with DSL modems
▪ PPPoE encapsulates PPP frames within Ethernet frames
▪ Allows for authentication over Ethernet

Question 16

Digital Subscriber Line (DSL)

Answer 16

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

Question 17

Cable Modems

Answer 17

▪ 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

Question 18

Satellite Modems

Answer 18

▪ 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

Question 19

Plain Old Telephone Service (POTS)

Answer 19

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

Question 20

Integrated Services Digital Network (ISDN)

Answer 20

▪ 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

Question 21

Frame Relay

Answer 21

▪ 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

Question 22

Synchronous Optical Network (SONET)

Answer 22

▪ 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

Question 23

Asynchronous Transfer Mode (ATM)

Answer 23

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)

Question 24

ATM Virtual Circuits

Answer 24

User-Network Interface (UNI)
● Used to connect ATM switches and endpoints

Question 25

Dynamic Multipoint Virtual Private Network (DMVPN)

Answer 25

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

Question 26

Multiprotocol Label Switching (MPLS)

Answer 26

▪ 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

Question 27

WAN Data Rates

Answer 27

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)

Question 28

Software-Defined Wide Area Network (SDWAN)

Answer 28

▪ 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

Question 29

Multipoint generic routing encapsulation (mGRE)

Answer 29

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