Net essentials6e ch12

Guide to Networking Essentials, 6th Edition

Chapter 12: Wide Area Network Essentials

Copyright © 2012 Cengage Learning. All rights reserved. 2

Objectives

2

• 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


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


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


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)


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

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


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


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



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


Modem communication using the V.92 standard




• 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 1.544 Mbps


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


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 1.544 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


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

Leased Lines



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


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


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)


X.25 Networks

• Packet-switching technology developed in themid-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


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

Frame Relay Networks


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


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


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


WAN Connections Methods


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)



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

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


WAN Equipment

A WAN connection showing the CPE, demarcation point, and local loop


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


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”


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


Remote Access Networkingvia 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


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


Cloud Computing

• There are three primary categories of cloud computing:– Hosted applications– Hosted platforms– Hosted infrastructure


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


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


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



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


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

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


Net essentials6e ch12

Technology

Transcript of Net essentials6e ch12