1. Wide Area Networks (WANs)
Chapter 7
Copyright 2003 Prentice-Hall Panko’s Business Data Networks and Telecommunications, 4th edition

2. 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

3. 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

4. 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)

5. 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

6. Figure 7.2: Telephone Modem Communication
Need Modem at Each End Up to 33.6 kbps
Modulated
Signal
Digital Signal
Modem
Telephone
33.6
kbps
Modem
Telephone
Server A
Client A
PSTN (Digital)

7. Figure 7.2: Telephone Modem Communication
PSTN (Digital)
Digital Access Line
Server B
56 kbps
Modem
Telephone
Client B
For 56 kbps Download Speed
Server Must Have a Digital Connection, Not a Modem

8. 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

9. 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

10. 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

11. 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

12. Extend trunk line speeds to end-to-end service
Figure 7.5: Trunk-Line Based Leased Line
T1 Trunk Line (1.544 Mbps)
Computer
Telephone
Switch
Server
Access
Line
Trunk
Line
T1 Leased Line (1.544 Mbps)
End-to-End Circuit with Trunk Line Speed
Extend trunk line speeds to end-to-end service

13. 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)

14. 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

15. 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

16. 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

17. Figure 7.6: ADSL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
ADSL
Modem 1.
Existing Pair of
Voice-Grade
UTP Wires PC
DSLAM
Splitter
PSTN
Telephone

18. Figure 7.6: ASDL with Splitter1.
Data
256 kbps to
1.5 Mbps
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN 2.
64 kbps to
256 kbps
ADSL
Modem PC
DSLAM
Splitter
PSTN
Telephone

19. Figure 7.6: ASDL with Splitter
Subscriber
Premises
Telephone Company
End Office Switch
Data
WAN
ADSL
Modem PC
DSLAM
Splitter
PSTN 1.
Ordinary Telephone
Service
Telephone

20. 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

21. Figure 7.4: Leased Line Networks
Digital Subscriber Lines (DSLs)
HDSL
Symmetric speed (768 kbps) over one voice-grade twisted pair
HDSL2: symmetric speed over one voice-grade twisted pair
Needed in business. (ADSL primarily for home and small business access.)
Speed guaranteed

22. 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

23. Sharing Neighborhood Capacity
Figure 7.7: Cable Modem Services
6. To Other Subscribers
Sharing Neighborhood Capacity
Subscriber
Premises
ISP
4. Coaxial
Cable to
Premises
2. Optical
Fiber to
Neighborhood
5. Cable
Modem 3.
Neighborhood
Splitter PC
1. Cable
Television
Head End
6. Requires NIC or USB port

24. Figure 7.4: Leased Line Networks
Cable Modem
Delivered by cable television operator
High asymmetric speed
Up to 10 Mbps downstream
64 kbps to 256 kbps upstream
Speed is shared by people currently downloading in a neighborhood
In practice, medium ADSL speed or higher

25. Figure 7.8: GEO Satellite System1.
Geosynchronous
Satellite
2. Point-to-Point
Uplink 3.
Broadcast
Downlink 4.
Footprint
5. Earth Station A
Earth Station B
Appears stationary in sky (36,000 km or 22,300 mi)
Far, so earth station needs dish antenna

26. Figure 7.9: LEO and MEO Satellite Systems
1. Currently Responsible LEO or MEO
2. Next Responsible
LEO or MEO
3. Small
Omnidirectional
Transceiver
A few thousands (LEO) or tens of thousands of km (miles) (MEO)
Closer, so omnidirectional transceivers can be used

27. 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

28. Figure 7.10: Leased Line versus Public Switched Data Networks
Multisite Leased Line Mesh Network
Site B
Site A
OC3 Leased Line
T3 Lease
Line
T1 Leased
Line
56 kbps
Leased
Line
56 kbps
Leased
Line
Site C
T1 Leased
Line
56 kbps
Leased
Line
Site D
Site E

29. Figure 7.10: Leased Line versus Public Switched Data Networks
Public Switched Data Network (PSDN)
Site A
Site B
Public Switched Data
Network (PSDN)
POP
POP
POP
POP
Point of Presence
One leased
line per site
Site D
Site E
Site C

30. 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

31. Figure 7.11: Popular PSDN Services
Typical
Speeds
Circuit- or
Packet-
Switched
Reliable or
Unreliable
Virtual
Circuits?
Relative
Price
ISDN
Two 64 kbps
B channels
One 16 kbps
D channel
Circuit
Unreliable No
Moderate
X.25
9,600 kbps
to about
40 Mbps
Packet
Reliable
Yes
Moderate
Frame
Relay
56 kbps
to about
40 Mbps
Packet
Unreliable
Yes
Low

32. Figure 7.11: Popular PSDN Services
Typical
Speeds
Circuit- or
Packet-
Switched
Reliable or
Unreliable
Virtual
Circuits?
Relative
Price
ATM
1 Mbps
to about
156 Mbps
Packet
Unreliable
Yes
High
Ethernet
10 Gbps
and
40 Gbps
Packet
Unreliable No
Probably
Low

33. 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

34. Figure 7.12: Integrated Services Digital Network (ISDN)
Personal
Computer 2.
64 kbps B Channel
Digital Signal
On Serial Cable
(1010) 1.
3 Multiplexed
Channels on
One Pair of
Telephone Wires
(2B+D)
ISDN
Wall
Jack
(RJ-45) 3.
64 kbps B Channel
Analog Voice Signal
On Telephone Wires 4.
16 kbps D channel is for
Supervisory
signaling
2B+D
Desktop Telephone

35. 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?

36. Figure 7.12: Integrated Services Digital Network (ISDN)
Internal DSU
Converts Serial Port
Signal to Digital
B Channel
Signal at 64
kbps
(1010)
Personal
Computer
64 kbps B Channel
Digital Signal
On Serial Cable
(1010)
ISDN
Wall
Jack
(RJ-45)
“ISDN Modem”
All-digital
Service
( )
The Data Channel
Uses 232 Serial Cable
Desktop Telephone

37. Figure 7.12: Integrated Services Digital Network (ISDN)
Personal
Computer
The Voice Channel
Uses Home Telephone Cord
ISDN
Wall
Jack
(RJ-45)
“ISDN Modem”
64 kbps B Channel
Analog Voice Signal
On Telephone Wires
All-digital
Service
( )
Internal Codec
Converts
Analog Voice
Signal to Digital
B Channel
Signal at 64 kbps
( ))
Desktop Telephone

38. Figure 7.12: Integrated Services Digital Network (ISDN)
Internal DSU
Converts Serial Port
Signal to Digital
B Channel
Signal at 64
kbps
(1010)
Personal
Computer
64 kbps B Channel
Digital Signal
On Serial Cable
(1010)
ISDN
Wall
Jack
(RJ-45)
All-digital
Service
( )
“ISDN Modem”
Bonding
Use Both B Channels for Data
Send and Receive at 128 kbps
Desktop Telephone

39. 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 POP
Pay by port speed
Usually the largest price component
Permanent virtual circuits (PVCs) among communicating sites
Other charges

40. Figure 7.13: Access Devices
(Frame Relay
Access Device)
T1 CSU/DSU at
Physical Layer
Site A
T1 Line
Frame Relay at
Data Link Layer PC
Access Device
(Router)
Site B
T3 CSU/DSU at
Physical Layer
T3 Line
ATM etc. at
Data Link Layer
Server

41. Figure 7.14: Pricing Elements in Frame Relay Service1.
Access Device
Customer
Premises A
Switch
POP
Customer
Premises B
Customer
Premises C

42. Figure 7.14: Pricing Elements in Frame Relay Service
Customer
Premises A 2.
T1 Leased Access
Line to POP
Switch
POP
Customer
Premises B
Customer
Premises C

43. Figure 7.14: Pricing Elements in Frame Relay Service
Customer
Premises A 3.
Port
Speed
Charge
CIR = 56 kbps
ABR = 1 Mbps
Switch
POP
Customer
Premises B
Customer
Premises C

44. Figure 7.14: Pricing Elements in Frame Relay Service
Customer
Premises A 4.
PVC
Charges
PVCs 1&2
Switch
POP
PVC 2
PVC 1
PVC 1
PVC 2
PVC 1
Customer
Premises B
Customer
Premises C

45. Figure 7.14: Pricing Elements in Frame Relay Service5.
Sometimes
Traffic
Charges and
Other Charges
Customer
Premises A
6. Management
Switch
POP
Customer
Premises B
Customer
Premises C

46. 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

47. Figure 7.15: Frame Relay Pricing Details
New
Not in Book
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 fast
Actually, you usually can get by with a least line 70% this fast because not all virtual circuits will always be in use

48. Figure 7.15: Frame Relay Pricing Details
New
Not in Book
To Determine Needs
For Each Site
You need a port speed equal to or greater than the sum of the PVCs
Again, 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

49. Figure 7.15: Frame Relay Pricing Details
New
Not in Book
Example
The Situation
Headquarters and two branch offices.
Branches communicate with HQ at 256 kbps
Branches communicate with each other at 56 kbps B1 HQ B2

50. Figure 7.15: Frame Relay Pricing Details
New
Not in Book
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

51. Figure 7.15: Frame Relay Pricing Details
New
Not in Book
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

52. 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

53. 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

54. Figure 7.17: Virtual Private Network
Site-to-Site
for Internet
VPN Server
Tunnel
Internet
VPN Server
Corporate
Site B
Corporate
Site A
Remote
Corporate PC
Remote
Customer PC
(or site)
Remote
Access for
Intranet
Extranet

55. Figure 7.16: Virtual Private Network (VPN) Issues
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

56. Figure 7.16: Virtual Private Network (VPN) Issues
VPN Problems
Latency
Reduces by having all communication go through a single ISP
Security
PPTP for remote access is popular
IPsec for site-to-site transmission is popular

57. Figure 7.18: ISP-Based PPTP Remote Access VPN
Remote Access VPNs
User dials into a remote access server (RAS)
RAS often checks with RADIUS server for user identification information
Local
Access
RADIUS
Server
PPTP
RAS
Internet
Remote
Corporate PC
ISP
PPTP
Access
Concentrator
Corporate
Site A

58. 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 ISPs
PPTP access concentrator at ISP access point
Secure tunnel between access concentrator and RAS at corporate site
Some security limitations
No security between user site and ISP
No message-by-message authentication of user

59. Figure 7.16: Virtual Private Network (VPN) Issues
Site-to-Site VPNs and Extranets
Site-to-site networks link sites within a single company
Often part of an intranet—use of TCP/IP transmission and applications internally
TCP/IP transmission is low in cost
TCP/IP applications are good, standardized, and inexpensive
Extranet: communication with customers and suppliers with security over the Internet

60. Figure 7.19: IPsec in Tunnel Mode
Server
IPsec
Server
Local
Network
Local
Network
Secure
Tunnel
Tunnel Only
Between Sites
Hosts Need No Extra Software
No Security
In Site Network
No Security
In Site Network

61. Figure 7.19: IPsec in Tunnel Mode
Module F
Transfer
Mode
IPsec
Server
IPsec
Server
Local
Network
Local
Network
Secure
Tunnel
Security
In Site Network
Security
In Site Network
End-to-End (Host-to-Host)
Tunnel
Hosts Need IPsec Software

62. 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 sites
No need to install IPsec software on stations
Transfer mode: set up secure connection between two end hosts
Protected even on internal networks
Must install IPsec software on stations
Module F

63. 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

64. Figure 7.20: Policy-Based Security Associations in IPsec
Security Association (SA1) for Transmissions
From A to B
Security Association (SA2) for Transmissions
From B to A
Party A
Party B
List of
Allowable
Security
Associations
List of
Allowable
Security
Associations
IPsec Policy Server