Wide Area Networks (WANs)
Chapter 7
Copyright 2003 Prentice-HallPanko’s Business Data Networks and Telecommunications, 4th edition
2
Figure 7.1: Wide Area Networks (WANs)
Chapters 4 and 5: LANs Customer premises operation, high speeds
Chapter 6: Telephony LAN building wiring
PSTN carrier service
Chapter 7: WANs WAN technology often is based on telephone
technology and services
3
Figure 7.1: Wide Area Networks (WANs)
WAN Purposes Link sites (usually) within the same corporation
Provide remote access to individuals who are off-site
Internet access
1. Link Sites 2.RemoteAccess
3.InternetAccess
4
Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and telephone modem.
Point-to-Point Leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
PSDN
VPN
5
Figure 7.1: Wide Area Networks (WANs)
High Speeds and Low Speeds High cost per bit transmitted compared to LANs
Lower speeds (mostly commonly 56 kbps to a few megabits per second)
LANs Cheap, WANs Expensive(per bit transmitted)
LANs Fast, WANs Slow
6
Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and telephone modem. (low-speed access only)
Point-to-Point Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
7
Figure 7.2: Telephone Modem Communication
PSTNClient A
Server A Telephone
Telephone33.6kbps
Modem
Binary Data Analog ModulatedSignal
Modem
Need Modem at Each End Up to 33.6 kbps
8
Figure 7.2: Telephone Modem Communication
PSTN
Client B
ServerBTelephone
Digital Access Line
56 kbpsModem
For 56 kbps Download SpeedServer Must Have a Digital Connection, Not a Modem
9
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
Asymmetric speed is good for WWW service.
Other party must have a digital connection to the PSTN
10
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
11
Figure 7.3: Telephone Modem Modulation Standards and Speeds
Compression V.92 modems usually use V.44 compression, which
downloads webpages twice as fast as the old standard for compression, V.42 bis
Data:112.5 kbps
Signal:33.6 kbps
12
Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Point-to-Point Network of leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
13
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
14
Figure 7.4: Leased Line Networks
Leased Line (Private Line or Dedicated Line) Point-to-point connection
Always on
Usually very fast (56 kbps or more)
Usually digital instead of analog
Lower cost per bit transmitted than dial-up serviceBut speeds are higher, so higher total cost
Must be provisioned (set up). Can take weeks or months
15
Figure 7.4: Leased Line Networks
Trunk Line-Based Leased Lines
Require expensive optical fiber or (for 56 kbps, 64 kbps, T1 and E1 lines,) expensive data-grade copper UTP
For data-grade UTP, need two pairs—one for transmission in each direction. Called four-wire circuits.
Data-GradeCopper UTP
16
Figure 7.4: Leased Line Networks
Trunk Line-Based Leased Lines
56 kbps Leased Lines
Fractional T1 lines offer low-speed choices between 56 kbps and T1, typically:
128 bps, 256 kbps, 384 kbps, 512 kbps, 768 kbps
T1 Leased Lines (1.544 Mbps)
T3 Leased Lines
SONET OC/SDM Leased Lines
HighestDemand
17
Types of Leased Lines
Trunk Line-BasedLeased Lines
(Optical Fiber orData-Grade UTP)
Leased Lines
DSLs(Voice-Grade UTP)
Cable Modem
SatellitesOr 3G
(Chapter 6)
18
Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs)
Broadband speeds over single pair of voice-grade copper UTP
Does not always work: distance limitations, etc.
Where it does work, much cheaper than trunk line-based leased lines
Existing Voice-Grade UTP
19
Figure 7.6: ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
1.Existing Pair ofVoice-GradeUTP Wires
PC
3. 4.2.
Voice andData
20
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
21
Figure 7.6: ASDL with Splitter
DataWAN
PSTN
DSLAM
ADSLModem
Splitter
Telephone
SubscriberPremises
Telephone CompanyEnd Office Switch
PC
1.Ordinary Telephone
Service
22
Figure 7.4: Leased Line Networks
Asymmetric DSL (ADSL) Summary 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
Designed as consumer service, so data speed is not guaranteed
23
Figure 7.4: Leased Line Networks
HDSL High-rate DSL
Symmetric speed (768 kbps both ways) over one voice-grade twisted pair
Designed for business use. (ADSL is designed for home use.)
Speed guaranteed
HDSL2 1.544 symmetric speed over one voice-grade
twisted pair
24
Figure 7.4: Leased Line Networks
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 Mbps
Speed guaranteed
25
Figure 7.7: Cable Modem Services
PCSubscriberPremises
5. CableModem
4. CoaxialCable toPremises
2. OpticalFiber to
Neighborhood
3.Neighborhood
Splitter
ISP
1. CableTelevisionHead End
6. Requires NIC or USB port
26
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
27
Figure 7.8: GEO Satellite System
2. Point-to-PointUplink
3.BroadcastDownlink
4.Footprint5. Earth Station A Earth Station B
1.Geosynchronous
Satellite
Satellite appears stationary in sky (35,785 km or 22,236 mi)Far, so earth station needs dish antenna
28
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 of km or miles (Low Earth Orbit) or tens of thousands of km (miles) (Medium Earth Orbit)
Closer than GEO, so omnidirectional transceivers can be usedUser is served by a succession of satellites
29
Figure 7.1: Wide Area Networks (WANs)
WAN Technologies
Ordinary telephone line and modem. (low-speed access only)
Point-to-Point network of leased lines
Public switched data networks (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
PSDN
30
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
31
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)
32
Figure 7.10: Leased Line versus Public Switched Data Networks
Leased Line Network Many leased lines Individual leased line spans long distances Company must plan, buy switching equipment, and
operate the network
Public Switched Data Network Only need one leased line from each site to a POP Few and short-distance leased lines PSDN carrier provides planning, switching, and
operation of the network
33
Figure 7.11: Popular PSDN Services
ServiceTypicalSpeeds
Circuit- orPacket-Switched
Reliable orUnreliable
VirtualCircuits?
RelativePrice
X.259,600 kbpsto about40 Mbps
Packet Reliable Yes Moderate
FrameRelay
56 kbpsto about40 Mbps
Packet Unreliable Yes Low
X.25 (Obsolete): Slow because of reliability
Frame Relay Dominates PSDNs TodayUnreliable for Lower Carrier Cost
Speed Range is in Main Range of Corporate Demand
34
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
ATM is Faster than Frame RelayShould Grow in Demand as Corporate Demand Outgrows FR
However, Ethernet MANs are AppearingShould Offer Lower Prices for Comparable Speeds
35
Frame Relay and ATM
FR and ATM are Not Competitors
Most PSDN carriers offer both so they can server any speed range
Many interconnect their FR and ATM services, so that individual sites can use whatever service is best for them
36
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
37
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
ISDN is Not PopularExpensive for its Slow Speed
Has Niche in Backup Connections BecauseDial-Up, So Only Pay for When Needed
38
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
ISDN “Modem”
39
Quiz
In ISDN, 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?
40
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
41
Figure 7.14: Pricing Elements in Frame Relay Service
Frame Relay Pricing Frame relay access device at site
CSU/DSU at physical layer (converts between internal, PSDN digital formats)
Frame Relay at the Data Link Layer
Leased line from site to POP
Port on the POP Pay by port speed Usually the largest price component
Permanent virtual circuits (PVCs) among communicating sites
Other charges
42
Figure 7.13: Access Devices
CSU/DSU Channel service unit (CSU) protects the access line
from unapproved voltage levels, etc. coming from the firm
Data service unit (DSU) converts between internal digital format and digital format of access link to Frame Relay network.
Different digital formats may have different baud rate, number of states, voltage levels, etc.
DSU
43
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)
44
Figure 7.14: Pricing Elements in Frame Relay Service
SwitchPOP
Customer Premises B
Customer Premises C
1.Access DeviceCustomer
Premises A
45
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
46
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
47
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
48
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
49
Figure 7.15: Frame Relay Pricing Details
To Determine Needs for Each Site
Step 1: Determine PVC Needs Determine needed speed from this site to each
other site
You will need a virtual circuit to serve the needed speed to each other site
Sum all the virtual circuit speeds
NewNot in Book
Site BeingAnalyzed
30 kbps needed56 kbps PVC
800 kbps needed, 1 Mbps PVC
Sum1,056 kbps
50
Figure 7.15: Frame Relay Pricing Details
Step 2: Determine Port Speed You need a port speed equal to or greater than the
sum of the PVCs
You can get by with 70%
70% of 1,056 kbps is 739 kbps
Next-higher port speed may be 1 Mbps
Don’t overdo port speed because port speed is most expensive component
NewNot in Book
51
Figure 7.15: Frame Relay Pricing Details
Step 3: Determine Leased Line Speed 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
If port speed is 1 Mbps, leased line should be T1 with 1.544 Mbps capacity
NewNot in Book
52
Figure 7.15: Frame Relay Pricing Details
Example The Situation
Headquarters and two branch offices.Branches communicate with HQ at 200 kbpsBranches communicate with each other at 40
kbps
HQ
B1
B2
NewNot in Book
53
Figure 7.15: Frame Relay Pricing Details
Example For HQ
How many connections will HQ need?
What are their speeds?
What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps)
If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed?
What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
HQ
NewNot in Book
54
Figure 7.15: Frame Relay Pricing Details
Example For Each Branch
How many links will the branch need?
What are their speeds?
What will be their PVC speeds (0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps)
If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed?
What leased line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?
B1
NewNot in Book
55
Figure 7.1: Wide Area Networks (WANs)
WAN Technologies Ordinary telephone line and modem. (low-speed
access only)
Point-to-Point Network of leased lines
Public switched data networks (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
VPN
56
Figure 7.17: Virtual Private Network
VPN Server
Corporate Site A
VPN Server
CorporateSite B
2. RemoteCustomer PC
(or site)
3. RemoteCorporate PC
Tunnel
Internet
ExtranetRemote
Access forIntranet
1.Site-to-Site
57
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
Only good for internal corporate communication
But Internet reaches almost all sites in all firms
Low transmission cost per bit transmitted
58
Figure 7.16: Virtual Private Network (VPN) Issues
VPN Problems Latency and Sound Quality
Internet can be congestedCreates latency, reduces sound qualityUse a single ISP as for VoIP (see Chapter 6)
SecurityPPTP for remote access is popular IPsec for site-to-site transmission is popular
59
Figure 7.18: ISP-Based PPTP Remote Access VPN
RADIUSServer
PPTPRAS
Internet ISPPPTP
AccessConcentrator
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. Allows or rejects connection
Secure Tunnel
Unsecure TCPControl Channel
60
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
Some security limitationsNo security between user site and ISPNo message-by-message authentication of userUses unprotected TCP control channel
New
61
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
62
Figure 7.19: IPsec in Transfer 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
63
Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec)
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
64
Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec) At internet layer, so protects information at higher
layers
Transparent: upper layer processes do not have to be modified
Internet Layer with IPsec Protection
TCP UDP
HTTP SMTP FTP SNMP
Protected
65
Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec) Security associations:
Agreement on how security options will be implemented
May be different in the two directions
Security Association (SA1) for TransmissionsFrom A to B
Security Association (SA2) for TransmissionsFrom B to A
Party B Party A
66
Figure 7.16: Virtual Private Network (VPN) Issues
IP Security (IPsec) Security associations:
Governed by corporate policies
List ofAllowableSecurity
Associations
List ofAllowableSecurity
Associations
Party B Party A
IPsec Policy Server
Top Related