wide area networks (wans) chapter 7 copyright 2003 prentice-hall pankos business data networks and...
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Wide Area Networks (WANs)
Chapter 7
Copyright 2003 Prentice-HallPanko’s Business Data Networks and Telecommunications, 4th edition
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Figure 7.1: Wide Area Networks (WANs)
The Telephone Network WAN technology often is based on telephone
technology
WAN Purposes Link sites within the same corporation
Provide remote access to individuals who are off-site
Internet access
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.1: Wide Area Networks (WANs)
Low Speeds High cost per bit transmitted compared to
LANs
Lower speeds (mostly commonly 56 kbps to a few megabits per second)
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.2: Telephone Modem Communication
PSTN (Digital)Client A
Server A Telephone
Telephone33.6kbps
Modem
Digital Signal ModulatedSignal
Modem
Need Modem at Each End Up to 33.6 kbps
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Figure 7.2: Telephone Modem Communication
PSTN (Digital)
Client B
ServerBTelephone
Digital Access Line
56 kbpsModem
For 56 kbps Download SpeedServer Must Have a Digital Connection, Not a Modem
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Figure 7.3: Telephone Modem Modulation Standards and Speeds
V.34 Send and receive at up to 33.6 kbps
Fall back in speed if line conditions are not optimal
V.90 Receive at up to 56 kbps
Send at up to 33.6 kbps
Other party must have a digital connection to the PSTN
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Figure 7.3: Telephone Modem Modulation Standards and Speeds
V.92 Receive at up to 56 kbps
Send at up to 33.6 kbps or higher if the line permits
Other party must have a digital connection to the PSTN
Modem on hold: can receive an incoming call for a short time without losing the connection
Cuts call setup time in half
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Figure 7.3: Telephone Modem Modulation Standards and Speeds
V.92 Usually uses V.44 compression, which downloads
webpages twice as fast as the old standard for compression, V.42 bis
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.5: Trunk-Line Based Leased Line
ComputerTelephone
SwitchTelephone
SwitchTelephone
SwitchServer
AccessLine
T1 Trunk Line (1.544 Mbps)
T1 Leased Line (1.544 Mbps)End-to-End Circuit with Trunk Line Speed
TrunkLine
Extend trunk line speeds to end-to-end service
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Figure 7.4: Leased Line Networks
Leased Line (Private Line or Dedicated Line) Point-to-point connection
Always on
Lower cost per minute than dial-up service
Must be provisioned (set up)
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Figure 7.4: Leased Line Networks
Trunk Line-Based Leased Lines
Based on trunk lines discussed in the previous chapter
Extend standard trunk line speeds to end-to-end circuits between two customer premises
Require expensive data-grade copper or optical fiber
Data-Grade UTP
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Figure 7.4: Leased Line Networks
Trunk Line-Based Leased Lines
Fractional T1 lines offer low-speed choices between 56 kbps and T1, typically:
128 kbps
256 kbps
384 kbps
512 kbps
768 kbps
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Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs)
Broadband speeds over single pair of voice-grade copper
Does not always work: distance limitations, etc.
Where it does work, much cheaper than trunk line-based leased lines
Existing Voice-Grade UTP
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Figure 7.6: ADSL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
1.Existing Pair ofVoice-GradeUTP Wires
PC
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Figure 7.6: ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
PC
1.Data
256 kbps to1.5 Mbps
2.64 kbps to256 kbps
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Figure 7.6: ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
PC
1.Ordinary Telephone
Service
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Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs) Asymmetric DSL (ADSL)
Asymmetric speed Downstream (to customer): 256 kbps to over
1.5 Mbps Upstream (from customer): 64 kbps or higher
Simultaneous telephone and data service
DSL access multiplexer (DSLAM) at end telephone office
Speed not guaranteed
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Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs) HDSL
Symmetric speed (768 kbps) over one voice-grade twisted pair
HDSL2: 1.544 symmetric speed over one voice-grade twisted pair
Needed in business. (ADSL primarily for home and small business access.)
Speed guaranteed
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Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs) SHDSL
Super High rate DSL
Single voice-grade twisted pair; longer distances than ASDL, HSDL
Symmetric speed
Variable speed ranging from 384 kbps to 2.3 Mbps
Speed guaranteed
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Figure 7.7: Cable Modem Services
PC
SubscriberPremises
5. CableModem
4. CoaxialCable toPremises
2. OpticalFiber to
Neighborhood
3.Neighborhood
Splitter
ISP
1. CableTelevisionHead End
6. To Other SubscribersSharing Neighborhood Capacity
6. Requires NIC or USB port
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Figure 7.4: Leased Line Networks
Cable Modem
Delivered by cable television operator
High asymmetric speedUp to 10 Mbps downstream64 kbps to 256 kbps upstream
Speed is shared by people currently downloading in a neighborhood
In practice, medium ADSL speed or higher
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Figure 7.8: GEO Satellite System
2. Point-to-PointUplink
3.BroadcastDownlink
4.Footprint5. Earth Station A Earth Station B
1.Geosynchronous
Satellite
Appears stationary in sky (36,000 km or 22,300 mi)Far, so earth station needs dish antenna
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Figure 7.9: LEO and MEO Satellite Systems
3. SmallOmnidirectional
Transceiver
1. Currently Responsible LEO or MEO
2. Next ResponsibleLEO or MEO
A few thousands (LEO) or tens of thousands of km (miles) (MEO)Closer, so omnidirectional transceivers can be used
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data networks (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.10: Leased Line versus Public Switched Data Networks
T3 LeaseLine
Site C
Site A Site B
OC3 Leased Line
T1 LeasedLine
T1 LeasedLine
Site ESite D
56 kbpsLeased
Line
56 kbpsLeased
Line
56 kbpsLeased
Line
Multisite Leased Line Mesh Network
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Figure 7.10: Leased Line versus Public Switched Data Networks
Public Switched DataNetwork (PSDN)
POPPOP
POPPOP
Site A Site B
Point of Presence
One leasedline per site
Site D Site C Site E
Public Switched Data Network (PSDN)
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Figure 7.10: Leased Line versus Public Switched Data Networks
Leased Line Network Many leased lines
Individual leased line spans long distances
Company must buy switching, plan, and manage
Public Switched Data Network Only need one leased line from each site to a POP
Few and short-distance leased lines
PSDN carrier provides switching, planning, and management of the network
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Figure 7.11: Popular PSDN Services
ServiceTypicalSpeeds
Circuit- orPacket-Switched
Reliable orUnreliable
VirtualCircuits?
RelativePrice
ISDN
Two 64 kbpsB channelsOne 16 kbpsD channel
Circuit Unreliable No Moderate
X.259,600 kbpsto about40 Mbps
Packet Reliable Yes Moderate
FrameRelay
56 kbpsto about40 Mbps
Packet Unreliable Yes Low
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Figure 7.11: Popular PSDN Services
Ethernet10 Gbps and 40 Gbps
Packet Unreliable NoProbablyLow
ATM1 Mbpsto about156 Mbps
Packet Unreliable Yes High
ServiceTypicalSpeeds
Circuit- orPacket-Switched
Reliable orUnreliable
VirtualCircuits?
RelativePrice
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Figure 7.11: Popular PSDN Services
Most PSDNs are packet-switched, unreliable, and use virtual circuits All of these are designed to reduce carrier
transmission costs so that lower competitive prices can be set
Packet switching multiplexes trunk line transmissions, reducing trunk line costs
Unreliability and virtual circuits simply switching, reducing switching costs
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Figure 7.12: Integrated Services Digital Network (ISDN)
PersonalComputer
Desktop Telephone
3.64 kbps B ChannelAnalog Voice SignalOn Telephone Wires
2.64 kbps B Channel
Digital SignalOn Serial Cable
(1010)
1.3 MultiplexedChannels onOne Pair of
Telephone Wires(2B+D)
ISDNWallJack
(RJ-45)
4.16 kbps D channel
is forSupervisory
signaling
2B+D
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Quiz
How many bits per second are multiplexed over the single wire pair connected to the wall jack and to the single pair running from the customer premises to the carrier end office?
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Figure 7.12: Integrated Services Digital Network (ISDN)
PersonalComputer
Desktop Telephone
“ISDN Modem”
64 kbps B ChannelDigital Signal
On Serial Cable(1010)
Internal DSUConverts Serial Port
Signal to DigitalB Channel
Signal at 64kbps
(1010)
All-digitalService
(1101001..)
ISDNWallJack
(RJ-45)
The Data ChannelUses 232 Serial Cable
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Figure 7.12: Integrated Services Digital Network (ISDN)
PersonalComputer
Desktop Telephone
64 kbps B ChannelAnalog Voice SignalOn Telephone Wires
“ISDN Modem”
Internal CodecConverts
Analog VoiceSignal to Digital
B ChannelSignal at 64 kbps
(000010000))
All-digitalService
(1101001..)
ISDNWallJack
(RJ-45)
The Voice ChannelUses Home Telephone Cord
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Figure 7.12: Integrated Services Digital Network (ISDN)
PersonalComputer
Desktop Telephone
“ISDN Modem”
64 kbps B ChannelDigital Signal
On Serial Cable(1010)
Internal DSUConverts Serial Port
Signal to DigitalB Channel
Signal at 64kbps
(1010)
All-digitalService
(1101001..)
ISDNWallJack
(RJ-45)
BondingUse Both B Channels for DataSend and Receive at 128 kbps
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Figure 7.14: Pricing Elements in Frame Relay Service
Frame Relay Pricing Frame relay access device at site
CSU/DSU at physical layer
Leased line from site to POP
Port on the POPPay by port speedUsually the largest price component
Permanent virtual circuits (PVCs) among communicating sites
Other charges
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Figure 7.13: Access Devices
Site A
Site B
PC
Server
T1 CSU/DSU atPhysical Layer
Frame Relay atData Link Layer
T3 CSU/DSU atPhysical Layer
ATM etc. atData Link Layer
T1 Line
T3 Line
Access Device(Frame Relay
Access Device)
Access Device(Router)
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Figure 7.14: Pricing Elements in Frame Relay Service
SwitchPOP
Customer Premises B
Customer Premises C
1.Access DeviceCustomer
Premises A
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Figure 7.14: Pricing Elements in Frame Relay Service
SwitchPOP
Customer Premises B
Customer Premises C
Customer Premises A
2.T1 Leased Access
Line to POP
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Figure 7.14: Pricing Elements in Frame Relay Service
SwitchPOP
Customer Premises B
Customer Premises C
Customer Premises A
CIR = 56 kbpsABR = 1 Mbps
3.Port
SpeedCharge
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Figure 7.14: Pricing Elements in Frame Relay Service
Switch
PVC 2
PVCs 1&2
POP
PVC 2 PVC 1
Customer Premises B
Customer Premises C
Customer Premises A
PVC 1
PVC 1
4.PVC
Charges
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Figure 7.14: Pricing Elements in Frame Relay Service
SwitchPOP
Customer Premises B
Customer Premises C
Customer Premises A
5.Sometimes
TrafficCharges and
Other Charges6. Management
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Figure 7.15: Frame Relay Pricing Details
Other Charges Flat rate versus traffic volume charges
Installation charges
Managed service charges
Service level agreement (SLA) charges
Geographical Scope Frame Relay systems with broader geographical
scope cost more
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Figure 7.15: Frame Relay Pricing Details
To Determine Needs
For Each Site Determine needed speed to each other site
You will need a virtual circuit of this speed
Sum all the virtual circuit speeds
You will need a leased line this fastActually, you usually can get by with a least line
70% this fast because not all virtual circuits will always be in use
NewNot in Book
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Figure 7.15: Frame Relay Pricing Details
To Determine Needs
For Each Site You need a port speed equal to or greater than the
sum of the PVCsAgain, you can get by with 70%
Remember that port speed is more expensive than leased line speeds
In general, don’t waste port speed by using a leased line much under its capacity
NewNot in Book
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Figure 7.15: Frame Relay Pricing Details
Example The Situation
Headquarters and two branch offices.Branches communicate with HQ at 256 kbpsBranches communicate with each other at 56
kbps
HQ
B1
B2
NewNot in Book
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Figure 7.15: Frame Relay Pricing Details
Example For HQ
How many PVCs will HQ need?
What are their speeds?
If POP speeds are 56 kbps, 256 kbps, 512 kbps, what port speed will HQ need?
What leased lines will HQ need if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
HQ
NewNot in Book
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Figure 7.15: Frame Relay Pricing Details
Example For Each Branch
How many PVCs will the branch need?
What are their speeds?
If POP speeds are 56 kbps, 256 kbps, 512 kbps, what port speed will the branch need?
What leased lines will the branch need if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
B1
NewNot in Book
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data networks (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
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Figure 7.17: Virtual Private Network
VPN Server
Corporate Site A
VPN Server
CorporateSite B
RemoteCustomer PC
(or site)
RemoteCorporate PC
Tunnel
Internet
ExtranetRemote
Access forIntranet
Site-to-Sitefor Internet
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Figure 7.16: Virtual Private Network (VPN) Issues
Virtual Private Network (VPN) Transmission over the Internet with added security
Some analysts include transmission over a PSDN with added security
Why VPNs PSDNs are not interconnected
Internet reaches almost all sites
Low transmission cost per bit transmitted
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Figure 7.16: Virtual Private Network (VPN) Issues
VPN Problems Latency
Reduces by having all communication go through a single ISP
SecurityPPTP for remote access is popular IPsec for site-to-site transmission is popular
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Figure 7.18: ISP-Based PPTP Remote Access VPN
RADIUSServer
PPTPRAS
InternetISP
PPTPAccess
Concentrator
LocalAccess
RemoteCorporate
PCCorporate
Site A
Remote Access VPNs User dials into a remote access server (RAS) RAS often checks with RADIUS server for user
identification information
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Figure 7.16: Virtual Private Network (VPN) Issues
Point-to-Point Tunneling Protocol Available in Windows since Windows 95
No need for added software on clients
Provided by many ISPsPPTP access concentrator at ISP access point
Secure tunnel between access concentrator and RAS at corporate site
Some security limitationsNo security between user site and ISPNo message-by-message authentication of user
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Figure 7.16: Virtual Private Network (VPN) Issues
Site-to-Site VPNs and Extranets Site-to-site networks link sites within a single
companyOften part of an intranet—use of TCP/IP
transmission and applications internallyTCP/IP transmission is low in costTCP/IP applications are good, standardized, and
inexpensive
Extranet: communication with customers and suppliers with security over the Internet
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Figure 7.19: IPsec in Tunnel Mode
Tunnel OnlyBetween SitesHosts Need NoExtra Software
SecureTunnel
TunnelMode
IPsecServer
IPsecServer
LocalNetwork
LocalNetwork
No SecurityIn Site Network
No SecurityIn Site Network
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Figure 7.19: IPsec in Tunnel Mode
End-to-End (Host-to-Host)Tunnel
Hosts Need IPsec Software
SecureTunnel
TransferMode
IPsecServer
IPsecServer
LocalNetwork
LocalNetwork
SecurityIn Site Network
SecurityIn Site Network
Module F
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Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec) At internet layer, so protects information at higher
layers
Tunnel mode: sets up a secure tunnel between IPsec servers at two sites
No security within sitesNo need to install IPsec software on stations
Transfer mode: set up secure connection between two end hosts
Protected even on internal networksMust install IPsec software on stations
Module F
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Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec) Security associations:
Agreement on how security options will be implemented
Established before bulk of secure communication begins
May be different in the two directions
Governed by corporate policies
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Figure 7.20: Policy-Based Security Associations in IPsec
Security Association (SA1) for TransmissionsFrom A to B
Security Association (SA2) for TransmissionsFrom B to A
List ofAllowableSecurity
Associations
List ofAllowableSecurity
Associations
Party B Party A
IPsec Policy Server