1. Guide to Networking Essentials, 6th Edition
Chapter 12: Wide Area Network Essentials

2. Objectives Describe the fundamentals of WAN operation and devices
Discuss the methods used to connect to WANs
Configure and describe remote access protocols
Describe the three major areas of cloud computing
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3. Wide Area Network Fundamentals
Internetworks and WANs can be described as two or more LANs connected together
Most obvious difference between internetworks and WANs is the distance between the LANs being connected.
They also differ in two other areas:
WANs use the services of carriers or service providers (phone companies and ISPs) for network connection
WANs use serial communication that can span miles compared to LAN technologies that span distances measured in hundreds of meters
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4. WAN Devices
WANs operate at the Data Link and Physical layers (Layers 2 and 1) of the OSI model
Several types of devices are likely to be used in WANS for media access, signal transmission, and reception and to connect a WAN to a LAN:
Modems
Channel service units/data service units
Routers
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5. Modems
A modem is a device that allows a computer (which works with digital signals) to communicate over lines that analog signals
A digital signal is a series of binary 1s and 0s represented by some type of signal that has two possible states (0v or 5v)
An analog signal varies over time continually and smoothly (transitions from 0v to 5v)
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6. CSU/DSUs
A channel service unit/data service unit (CSU/DSU) is a device that creates a digital connection between a LAN device (router) and the WAN link from the service provider
The WAN link is usually a T-carrier technology, such as a T1 or T3 (discussed later)
Similar to a modem, only all signals are digital
Converts one type of digital signal to another type of digital signal
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7. Routers
A router is responsible for getting packets from one network to another
In a WAN, it is usually the device connecting a LAN to the WAN service provider via a modem or CSU/DSU
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8. WAN Connection Methods
Many WAN technologies are available and differ in speed, level of security and reliability, and cost
Four most common connection methods:
Circuit-switched
Leased line
Packet-switched
VPN over the Internet
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9. Circuit-Switched WANs
A circuit-switched WAN creates a temporary dedicated connection between sender and receiver on demand
Analog example: a phone line connection from the PSTN, also known as plain old telephone service (POTS)
Digital example: Integrated Services Digital Network (ISDN)
Not as common today due to faster technologies but still in use in some areas
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10. Circuit-Switched WANs
Plain Old Telephone Service (POTS) – limited in bandwidth due to the digital-to-analog conversion that is performed, usually by modems
The conversion process degrades signal quality and limits data transfer speeds to about 56 Kbps
The most common modem standard for connecting to the Internet is V.92
V.92 modems use a technique called pulse code modulation (PCM) that digitizes analog signals and introduces less noise into the signal
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11. Circuit-Switched WANs
Modem communication using the V.92 standard
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12. Circuit-Switched WANs
Integrated Services Digital Network (ISDN) – a digital communication technology developed in 1984 to replace the analog phone system
Was not as popular as expected but can still be found in many US metropolitan areas and Western Europe
Defines communication channels of 64 Kbps
Two formats or rates:
BRI – Basic Rate Interface: consists of two B-channels (64 Kbps) and a D-channel (16 Kbps). B-channels are used for data transfer so BRI can operate at up to 128 Kbps
PRI – Primary Rate Interface (PRI): consists of 23 B-channels and a D-channel. Can provide up to Mbps
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13. Leased Lines
A leased line provides a dedicated point-to-point connection from the customer’s LAN through the provider’s network and the destination network
Provides permanent, secure, and dedicated bandwidth limited only by the provider’s technology and how much the customer is willing to spend
Most expensive WAN connectivity because it is dedicated
Should be considered:
When high quality, 24/7 access is needed
For mission-critical applications
When fast upstream as well as downstream communication is required
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14. Leased Lines
Leased lines are based on one of two types of digital technology: T-carriers and SONET
T-carriers
Typical lines are T1 and T3 that operate at Mbps and 44 Mbps, respectively
Derived from multiple 64 Kbps channels, making a T1 connection a grouping of 24 channels, and a T3 connection a grouping of 672 channels
Uses a signaling method called time division multiplexing (TDM): Allocates a time slot for each channel
If a portion of a T-carrier line is used for one purpose and a different portion for another purpose, the line has been fractionalized
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15. Leased Lines T-Carriers (cont.)
Multiplexing:enables several communication streams to travel simultaneously over the same cable segment
Require a CSU/DSU at each end of the link to convert the signals used by the T-carrier line into signals used by the LAN
T1 lines can use twisted-pair, coaxial or fiber-optic cabling
T3 lines can use coaxial or fiber-optic cabling
T1 lines are the most common WAN connection method in the US
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16. Leased Lines
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17. Leased Lines
Synchronous Optical Network (SONET) – flexible, highly fault-tolerant technology that can operate at different capacities over fiber cabling
Typical SONET rates are OC-3 (155 Mbps), OC-12 (622 Mbps), OC-48 (almost 2.5 Gbps), OC-192, and OC-768 (used by large ISPs)
SONET networks can carry traffic from a variety of other network types, such as T-carrier and ATM
SONET uses a dual-ring topology (like FDDI), making it very fault-tolerant
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18. Packet-Switched WANs
A packet-switched WAN does not create a dedicated connection between sender and receiver
Each packet is transmitted through the provider’s network independently (similar to LAN traffic)
Data shares bandwidth with your provider’s other customers
Most common packet-switched networks are:
X.25
Frame relay
ATM
MPLS
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19. Packet-Switched WANs
Virtual Circuits – a logical connection created between two devices in a shared network
No single cable exists between the two endpoints
Maps a path through the network of switches between two points
The pathway is created after sender and receiver agree on bandwidth requirements and request a pathway
Switched virtual circuit (SVCs): established when needed and then terminated when the transmission is completed
Permanent virtual circuit (PVCs): pathway between two communication points is established as a permanent logical connection (more expensive than SVCs)
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20. X.25 Networks
Packet-switching technology developed in the mid-1970s running over older copper phone lines
Offer both SVCs and PVCs – although not all X.25 providers offer PVCs
Earlier X.25 could only operate at 64 Kbps
A 1992 specification revision improved the maximum throughput of X.25 to 2 Mbps, but the new version was not widely deployed
Even though X.25 offers reliable and error-free communications, this technology has been largely replaced by other higher-speed technologies
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21. Frame Relay Networks
A PVC packet-switching technology that offers WAN communication over a fast, reliable digital link
Can maintain transmission rates from 64 Kbps to 44 Mbps (T3 speed)
Allows customers to specify the bandwidth needed
Charges depend on the PVC’s bandwidth allocation (known as Committed Information Rate [CIR])
CIR is the guaranteed minimum transmission rate
Connection is established by using a pair of CSU/DSUs with a router or bridge at each end to direct traffic on and off the WAN link
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22. Frame Relay Networks
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23. ATM Networks
Asynchronous Transfer Mode (ATM) – high-speed network technology designed for both LAN and WAN use
ATM bandwidth can be as low as a few Mbps up to 622 Mbps, but the most common speed is 155 Mbps
Cell-based packet switching technology
Cells are of a fixed length rather than typical packet-based systems that use variable length packets
Fixed length cells can be switched more efficiently than variable length packets
ATM is used quite heavily for the backbone and infrastructure in large communications companies
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24. Multiprotocol Label Switching (MPLS)
MPLS runs over ATM, frame relay, SONET, and even Ethernet
Creates a connection-oriented virtual circuit using labels assigned to each packet
The label is used to make packet-forwarding decisions within the MPLS network, making it unnecessary to view the contents of the packet
Capable of supporting different Layer 3 protocols, it is currently used exclusively in IP networks
Supports both IPv4 and IPv6
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25. WANs over the Internet
Using VPN connections over inexpensive Internet connections is becoming a popular WAN alternative
VPNs offer the following advantages over other WAN methods discussed:
Inexpensive: Cost of Internet access is much lower than leased lines or packet-switched WAN connections
Convenience: A VPN can be configured as soon as Internet access is established
Security: Advanced authentication and encryption protocols protect the integrity and privacy of VPN traffic
Flexibility: After a corporate VPN infrastructure is in place, it is available for WAN connections from branch offices as well as mobile users and telecommuters
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26. WAN Connections Methods
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27. WAN Equipment Customer Equipment
Customer Premises Equipment (CPE): The equipment at the customer site that’s usually the responsibility of the customer
Customer might own or lease the equipment from the provider
Usually includes routers, modems and CSU/DSUs
The demarcation point is the point at which the CPE ends and the provider’s responsibility begins (where the WAN connection is made)
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28. WAN Equipment Provider Equipment
The provider location nearest the customer site is usually referred to as the central office (CO)
Media (usually coax or fiber) runs from the customer site demarcation point to the CO of the WAN service provider
The connection between the demarcation point and the CO is called the local loop or last mile
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29. WAN Equipment Going the Last Mile
The device that sends data to the local loop is called the data circuit-terminating equipment (DCE): The CSU/DSU or modem
The device that passes data from the customer LAN to the DCE is called the data terminal equipment (DTE): Router or bridge that has one connection to the customer LAN and another connection to the DCE that makes the WAN connection
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30. WAN Equipment
A WAN connection showing the CPE, demarcation point, and local loop
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31. Remote Access Networking
Windows server OSs include the Routing and Remote Access Service (RRAS) that supports both dial-up remote access and VPN remote access
Users can dial in over POTS or use a VPN from any type of Internet connection
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32. Making a VPN Connection in Windows
In Windows 7, you create a new connection from the Network and Sharing Center by selecting “Set up a new connection or network”
This will start the “Set Up a Connection or Network Wizard”
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33. Making a Dial-Up Connection
All versions of Windows, starting with Windows 95, include Dial-Up Networking (DUN) software to make an RRAS connection
The protocol used is Point-to-Point Protocol (PPP) and is used to carry a variety of protocols over different types of network connections
Two protocols that are integral to PPP:
Link Control Protocol (LCP): Sets up the PPP connection and defines communications parameters and authentication protocols
Network Control Protocol (NCP): Encapsulates higher layer protocols such as IP and provides services such as dynamic IP addressing
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34. Remote Access Networking via the Web
Another remote access model is remote control of the desktop of your office computer using a Web browser
Several online services connect your Web browser to your desktop, including LogMeIn and GoToMyPC
A client component is installed on your computer and then log on to the online service which connects you
Uses authentication and encryption to maintain a secure connection
Third party software can also be used
Microsoft’s Terminal Services Gateway (TSG) allows remote connections by using SSL, the protocol that secures communication between Web browsers and Web servers
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35. Cloud Computing
Cloud computing is a computer networking model in which data, applications, and processing power are managed by servers on the Internet, and users of resources pay for what they use rather than for the equipment and software needed to provide the resources
Benefits:
Reduced physical plant costs
Reduced upfront costs
Reduced personnel costs
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36. Cloud Computing There are three primary categories of cloud computing:
Hosted applications
Hosted platforms
Hosted infrastructure
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37. Hosted Applications
Hosted applications are also referred to as on-demand applications or software as a service (SaaS)
Usually offered as a subscription based on the number of users
Customers can take advantage of new software editions much faster
Available anywhere the customer has a connection to the Internet
Most well-known example is Google Apps
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38. Hosted Platforms Hosted platform or platform as a service (PAAS)
A customer develops applications using the service providers development tools and infrastructure
Once developed, the applications can be delivered to the customer’s users from the provider’s servers
Most common hosted platforms available are Force.com’s Apex, Azure for Windows, Google’s AppEngine for Phython and Java, WaveMaker for Ajax, and Engine Yard for Ruby on Rails
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39. Hosted Infrastructure
Hosted infrastructure or infrastructure as a service (IaaS) allows a company to use storage or entire virtual servers
If a customer needs another 100 GB of space, they can pay for the space without worrying about how that space is actually provided
If a customer needs another server they pay for the amount of processing and storage the additional server actually requires
Customers rent the resources they are using
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40. Chapter Summary
The most obvious difference between internetworks and WANs is the distance between the LANs being connected
Several types of devices are likely to be used in WANs for media access, signal transmission, and reception and to connect a WAN to a LAN: Modems, CSU/DSU, and Routers
The methods used to make a WAN connection often dictate the technologies that can be used and the connection’s properties. The four most common are circuit-switched, leased line, packet-switched, and VPN over the Internet
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41. Chapter Summary
WAN equipment can be categorized into customer equipment, provider equipment, and the circuit that makes the connections between the demarcation point and the central office; called the last mile or local loop
Large and small businesses alike are leveraging fast, affordable remote access technologies that allow employees to access their office desktops and corporate resources from home and on the road
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42. Chapter Summary
Cloud computing is a computer networking model in which data, applications, and processing power are managed by servers on the Internet, and users pay for what they use rather than for the equipment and software needed to provide the resources
There are three primary categories of cloud computing: hosted applications, hosted platforms, and hosted infrastructure
Copyright © 2012 Cengage Learning. All rights reserved.