© 2009 pearson education, inc. publishing as prentice hall wide area networks (wans) chapter 7...

© 2009 Pearson Education, Inc. Publishing as Prentice Hall

Wide Area Networks(WANs)

Chapter 7

Panko’sBusiness Data Networks and Telecommunications, 7th edition © 2009 Pearson Education, Inc. Publishing as Prentice Hall

May only be used by adopters of the book

© 2009 Pearson Education, Inc. Publishing as Prentice Hall 7-2

Orientation

• Single Networks

– Layers 1 and 2 (so OSI standards dominate)

– Chapters 4-7: Local to long-distance for single networks

• Chapter 4: Wired Ethernet LANs

• Chapter 5: Wireless LANs (WLANs)

• Chapter 6: Telecommunications (and Internet Access)

• Chapter 7: Wide Area Networks (WANs)

• Chapter 8: TCP/IP Internetworking– To link multiple single networks


7-1: Wide Area Networks (WANs)

• Wide Area Networks (WANs)

– Connect different sites

• WANs and the Telephone Network

– Use the PSTN transport system for transmission

– Add switching and management to create a WAN

• WAN Purposes

– Provide remote access to individuals who are off site

– Link sites within the same corporation

– Provide Internet access

7-3

2



• Evolution of WAN Technology

– Layer 1: Leased line service and networks

– Layer 2: Public switched data networks (PSDNs)

– Layer 3: Virtual Private Networks (VPNs) over the Internet and IP carrier networks

7-4



• Carriers

– Beyond their physical premises, companies must use the services of regulated carriers for transmission

– Companies are limited to whatever services the carriers provide

– Prices for carrier services change abruptly and without technological reasons

– Prices and service availability vary from country to country

7-5



• High Costs and Low Speeds

– High cost per bit transmitted, compared with LANs

– Consequently, lower speeds (most commonly 256 kbps to about 50 megabits per second)

7-6


7-2: Leased Line Networks for Voice and Data

7-7


7-2: Leased Line Networks for Voice and Data

7-8


7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks

Full Mesh Topology

OC3 Leased Line

T1LeasedLine

Site A Site B

Site C Site D

T1LeasedLine

T3LeasedLine

T3LeasedLine

In a full mesh topology,there is a leased line

between each pair of sites

Highly reliableHighly expensive


7-3: Full Mesh and Pure Hub-and-Spoke Topologies for Leased Line Data Networks

7-10

In a pure hub-and-spoke topology, there is only

one leased line from thehub site to each other site.

Very inexpensive.Very unreliable.

Few companies use either of these extreme topologies.They have some backup links.

1


Leased Lines

Layer 1 Carrier WAN Service

7-11


Leased Lines

• Circuits between Two Sites

• Always On

• All digital

• High Speeds

• Physical layer operation

7-12


7-4: Leased Line Speeds

7-13

Line Speed Typical Transmission Medium

56 kbps or 64 kbps (rarely offered)

56 kbps or 64 kbps *2-Pair Data-Grade UTP

T1 1.544 Mbps *2-Pair Data-Grade UTP

Fractional T1 128 kbps, 256 kbps, 384 kbps, 512 kbps,

768 kbps

*2-Pair Data-Grade UTP

Bonded T1s (multiple T1s acting as a single line)

Small multiples of 1.544 Mbps

*2-Pair Data-Grade UTP

T3 44.736 Mbps *Optical Fiber

North American Digital Hierarchy

*Usually must be pulled to the customer’s premises.*This is expensive,


7-4: Leased Line Speeds

7-14

Line Speed (Mbps) Typical Transmission Medium

OC3/STM1 155.52 Optical Fiber

OC12/STM4 622.08 Optical Fiber

OC48/STM16 2,488.32 Optical Fiber



SONET/SDH Speeds

Above 50 Mbps, the world uses the same standard,which has two slight variations: SONET and SDH.These two variants interoperate without problems.


7-5: Connecting to a Leased Line

7-15

Routers need CSU/DSUs to connect to leased lines.The CSU terminates the telephone line; protects the telephone

system from harmful voltages and signals.

The DSU converts between the router’s signals and the signalsthat the PSTN is expecting to receive from the firm.

Conversion is needed because digital signals can varyalong several dimensions.


Figure 7-6: ADSL versus Business-Class Symmetric Digital Subscriber Line (DSL) Services

7-16

ADSL HDSL HDSL2 SHDSLUses existing 1-pair voice-grade UTP telephone access line to customer premises?*

Yes* Yes* Yes* Yes*

Target Market Residences Businesses Businesses BusinessesDownstream Throughput

A few megabits per second

768 kbps 1.544 Mbps 384 kbps–2.3 Mbps

Upstream Throughput Slower than downstream

768 kbps 1.544 Mbps 384 kbps–2.3 Mbps

Symmetrical Throughput?

No Yes Yes Yes

QoS Throughput Guarantees?

No Yes Yes Yes

*By definition,•ALL DSLs use 1-pair voice-grade UTP residential access lines.


Public Switched Data Networks (PSDNs)

Layer 2 Carrier WAN Services

7-17


Public Switched Data Networks (PSDNs)

• Leased Line Data Networks– Use many leased lines, which must span long distances

between sites

– This is very expensive

– Company must design and operate its leased line network

• Public Switched Data Networks– Carrier does more of the operational and management

work

– Total cost of technology, service, and management usually lower than leased line networks

1


7-8: Public Switched Data Network (PSDN)

Site A Site B

Site DSite C

One PrivateLine AccessLine per Site

Public Switched DataNetwork (PSDN)

Site E

POP POP

POPPOPPoint of Presence

In Public Switched Data Networks,the PSDN carrier handles all switching.Reduces the load on the network staff.

The PSDN central core is shown as a cloudto indicate that the user firm does not

have to know how the network operates.


7-8: Public Switched Data Network (PSDN)

Site A Site B

Site DSite C

One PrivateLine AccessLine per Site

Public Switched DataNetwork (PSDN)

Site E

POP POP

POPPOPPoint of Presence

In Public Switched Data Networks,the customer needs a single leased line

from each site to one of the PSDN carrier’spoints of presence (POPs)


7-7: PSDNs

• Service Level Agreements (SLAs)

– Guarantees for services

– Throughput, availability, latency, error rate, etc.

– An SLA might guarantee a latency of no more than 100 ms 99.99 percent of the time

• SLA guarantees no worse than a certain worst-case level of performance


7-10: Frame Relay

• There are several PSDN services

– Frame Relay

– ATM

– Metropolitan area Ethernet

7-22


7-10: Frame Relay

• Frame Relay is the Most Popular PSDN Service Today

– 56 kbps to 40 Mbps

– This fits the range of greatest corporate demand for WAN speed

– Usually less expensive than a network of leased lines

– Grew rapidly in the 1990s, to be come equal to leased line WANs in terms of market share (about 40%)

– Carriers have raised prices, reducing growth


7-11: Frame Relay Network Elements

SwitchPOP

Customer Premises B

Customer Premises C

1.Access DeviceCustomer

Premises A



SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

2.Leased Access

Line to POP



SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

3.Port

SpeedCharge at

POPSwitch

POP has a switch with ports

The port speed charge is basedon the port speed used

The port speed charge usuallyIs the biggest part of PSDN costs


7-12: ATM

• For Speeds Greater than Frame Relay Can Provide

– 1 Mbps up to several gigabits per second

• Not a Competitor for Frame Relay

– Most carriers provide both FR and ATM

– May even interconnect the two services

7-27


7-12: ATM

• Short Frames

– Most frames have variable length

– All ATM frames are a very short 53 octets in length

• 5 octets of header

• 48 octets of data (payload)

• No trailer

• 53 octets total

– Short length minimizes latency (delay) at each switch

7-28


7-12: ATM

• ATM Has Strong Quality of Service (QoS) Guarantees for Voice Traffic

– Not surprising because ATM was created for the PSTN’s transport core

– For pure data transmission, ATM does not provide QoS guarantees

• Data gets whatever is left over.

7-29


7-12: ATM

• Manageability, Complexity, and Cost

– Very strong management tools for large networks (designed for the PSTN)

– Too complex and expensive for most firms

• ATM’s Future?

– May flourish after firms outgrow Frame Relay speeds

– However, metropolitan area Ethernet should be a strong competitor

– ATM is flourishing in a different market, the PSTN core

7-30

1


7-13: Metropolitan Area Ethernet

• Metropolitan Area Network (MAN)

– A carrier network limited to a large urban area and its suburbs

– Metropolitan area Ethernet (metro Ethernet) is available for this niche

– Metro Ethernet is new, but is growing very rapidly

7-31



• Attractions of Metropolitan Area Ethernet

– Low prices

– High speeds

– Familiar technology for networking staff

– Rapid provisioning

7-32



• Carrier Class Service

– Basic Ethernet standards are insufficient for large WANs (wide area networks)

– Quality of service and management tools must be developed

– The goal: to provide carrier class services that are sufficient for customers

7-33



• Carrier Class Service

– 802.3ad standard

• Ethernet in the first mile

• Standard for transmitting Ethernet signals over PSTN access lines

• 1-pair voice-grade UTP, 2-pair data-grade UTP, optical fiber

7-34


Layer 3 Carrier WAN Service

IP Carrier Networks

The Internet withVirtual Private Networks

7-35


7-14: The Internet versus IP Carrier Networks

• IP Is Increasingly Important

– Companies know it and are comfortable with it

– There are two ways to use IP at Layer 3 for WAN transmission:

• Companies can use IP carrier networks just as they use PSDNs for Layer 2 WANs

– Reduces corporate labor– Usually are ISPs– Sometimes are PSDNs that offer Layer 3 IP carrier

service

• Companies can create their own IPsec VPNs

7-36



• Advantages using of the Internet as a WAN

– Low cost per bit transmitted because of economies of scale in the Internet

– Access to other companies, nearly all of which are connected to the Internet

– IP carrier networks can offer QoS SLAs

• IP is only a best-effort protocol

• But companies can engineer their networks for full QoS

• Customers must connect all sites to the same ISP for this to work

7-37



• Security

– If companies act on their own, they can add virtual private network (VPN) protection to their transmissions

– IP Carrier Network Security

• IP Carrier Networks have some inherent security

– Restrict access to business customers

• However, for real security, virtual private networks (VPNs) are needed

– IP carrier networks provide cryptographic equipment at each site

7-38


7-15: Route-Based Virtual Private Network (VPN) in an IP Carrier Network

7-39


7-16: Virtual Private Networks (VPNs)

CorporateSite A

VPNGateway

VPNGateway

RemoteAccessVPN

Tunnel

Internet

RemoteCorporate

PC

Site-to-SiteVPN

CorporateSite B

ProtectedClient

ProtectedServer

A VPN is communication over theInternet with added security

Host-to-HostVPN

Remote access VPNsprotect traffic for individual users


7-16: Virtual Private Networks (VPNs)

CorporateSite A

VPNGateway

VPNGateway

RemoteAccessVPN

Tunnel

Internet

RemoteCorporate

PC

Site-to-SiteVPN

CorporateSite B

ProtectedClient

ProtectedServer

A VPN is communication over theInternet with added security

Host-to-HostVPN

Site-to-site VPNsprotect traffic between sites

Will dominate VPN traffic


7-17: IPsec Transport and Tunnel Modes

Secure onthe Internet

SiteNetwork

SiteNetworkSecure Connection

Securein Site

Network

Securein Site

Network

Transport Mode

ExtraSoftware,

DigitalCertificate,and SetupRequired

ExtraSoftware,

DigitalCertificate,and SetupRequiredIPsec is the strongest VPN security technology.

IPsec transport mode gives host-to-host securityhowever, software must be added to each host,

each host must have a digital certificate,and each host must be setup (configured).

This is very expensive.


7-17: IPsec Transport and Tunnel Modes

IPsecGateway

Secure onthe Internet

SiteNetwork

SiteNetwork

IPsecGateway

TunneledConnection

NoSecurityin Site

Network

NoSecurityin Site

Network

Tunnel Mode

No ExtraSoftware,

DigitalCertificate,or SetupRequired

No ExtraSoftware,

DigitalCertificate,or SetupRequiredIn IPsec tunnel mode, there is only security over

the Internet between IPsec gateways at each site

No security within sites, butno software, setup or certificates on the individual hosts

Inexpensive compared to transport mode


7-18: SSL/TLS for Browser–Webserver

Communication

Webserverwith Built-in

SSL/TLS Support

PC withBrowser Already

Installed

1. SSL/TLS Operates at the Transport Layer

2.Protects All Application Layer Traffic

That Is SSL/TLS Aware(WWW and Sometimes E-Mail)

No additional software is needed on the user PC.

IPsec works at the internet layer.SSL/TLS works at the transport layer.

Only protects SSL/TLS-aware applications.This primarily means HTTP.

SSL/TLS is built into every browser and webserver.


Figure 7-20: Market Perspective

• Leased Line Networks

– Dominated WAN transmission until the 1990s

– But difficult to set up and expensive to run

– Recent spurt in use because of reduced leased line prices and rising Frame Relay prices

– Needed for access lines in PSDNs and VPNs anyway

7-45



• Frame Relay

– Grew explosively in the 1990s

– Became very widely used

– FR prices have risen recently in an effort by carriers to increase their profit margins

– Widely used and familiar, but now considered a legacy technology

7-46



• ATM

– Very high speeds, but very high price

– Not thriving in the corporate market

7-47



• Metro Ethernet

– Price and speed are very attractive

– Growing very rapidly

– Limited to metropolitan area networking, at least for now

– Still somewhat immature technically

7-48



• IP Carrier Networks and Internet Transmission with VPNs

– The Internet offers a very low cost per bit transmitted

• VPNs provide security for Internet transmission

– Companies can also subscribe to IP carrier services

• IP carrier services also offer QoS

– IP WAN usage is growing rapidly

7-49

© 2009 pearson education, inc. publishing as prentice hall wide area networks (wans) chapter 7...

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