Chapter 8
Wide Area Networks
Announcements and Outline
Announcements
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Outline
8.1 Introduction
8.2 Services
8.21 Circuit-Switched Networks
8.22 Dedicated-Circuit Networks
8.23 Packet-Switched Networks
8.24 Virtual Private Networks
8.3 Best practice MAN/WAN design
8.4 Improving MAN and WAN Performance
8.5 Implications for Management
Copyright 2010
John Wiley & Sons, Inc
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8.1 Introduction
Wide area networks (WANs)
Typically built by using leased circuits from common
carriers such as AT&T
8.1 Introduction (Cont.)
Regulation of services
 Federal Communications Commission (FCC) in the US
 Canadian Radio Television and Telecomm Commission (CRTC)
in Canada
 Public Utilities Commission (PUC) in each state
Common Carriers
 Local Exchange Carriers (LECs) like Verizon
 Interexchange Carriers (IXCs) like Sprint
8.2 MANs/WANs Services
1) Circuit-Switched Networks
2) Dedicated-Circuit Networks
3) Packet-Switched Networks
4) Virtual Private Networks
8.21 Circuit Switched Networks – Architecture
8.21 Circuit Switched Networks
Oldest and simplest WAN approach
Uses the Public Switched Telephone Network (PSTN), or
the telephone networks
Provided by common carriers
Basic types in use today:
 POTS (Plain Old Telephone Service)
• Via use of modems to dial-up and connect to ISPs
 ISDN (Integrated Services Digital Network )
• Basic Rate Interface (BRI) – 128 Kbps
• Primary Rate Interface (PRI) – 1.5 Mbps
8.21 Circuit Switched Services
Simple, flexible, and inexpensive
 When not used intensively
Main problems
 Varying quality
• Each connection goes through the regular telephone network
on a different circuit,
 Low Data transmission rates
• Up to 56 Kbps for POTS, and up to 1.5 Mbps for ISDN
An alternative
 Use a private dedicated circuit
• Leased from a common carrier for the user’s exclusive use 24
hrs/day, 7 days/week
8.22 Dedicated Circuit Services – Basic Architecture
8.22 Dedicated Circuits
9 - 10
8.22 Ring Architecture
• Reliability
• Performance
8.22 Star Architecture
Easy to manage
Reliability
Performance
8.22 Mesh Architectures
8.22 Dedicated Services - T-Carrier
Most commonly used dedicated digital circuits in North
America
Units of the T-hierarchy
• T-1
• T-2
• T-3
• T-4
8.22 T-Carrier Digital Hierarchy
T-Carrier
Designation
DS Designation
Data Rate
DS-0
64 Kbps
T-1
DS-1
1.544 Mbps
T-2
DS-2
6.312 Mbps
T-3
DS-3
44.376 Mbps
T-4
DS-4
274.176 Mbps
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8.22 Dedicated Services - Synchronous Optical Network (SONET)
ANSI standard for optical fiber transmission in Gbps range
 Similar to ITU-T-based, synchronous digital hierarchy (SDH)
 SDH and SONET can be easily interconnected
SONET hierarchy
 Begins with OC-1 (optical carrier level 1) at
51.84 Mbps
 Each succeeding SONET hierarchy rate is defined
as a multiple of OC-1
8.22 SONET Digital Hierarchy
SONET Designation
SDH Designation
Data Rate
OC-1
STM-0
51.84 Mbps
OC-3
STM-1
155.52 Mbps
OC-9
STM-3
466.56 Mbps
OC-12
STM-4
622.08 Mbps
OC-18
STM-6
933.12 Mbps
OC-24
STM-8
1.244 Gbps
OC-36
STM-12
1.866 Gbps
OC-48
STM-16
2.488 Gbps
OC-192
STM-64
9.952 Gbps
8.23 Packet Switched Services – Basic Architecture
9 - 18
8.23 Packet Switched Services
Recap: In both circuit switched and dedicated services…
Packet switched services
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
9 - 19
8.23 Packet Switching
Interleave packets from separate messages for
transmission
 Most data communications consists of short burst of data
 Packet switching takes advantage of this burstiness
• Interleaving bursts from many users to maximize the use of
the shared network
8.23 Packet Switched - Service Protocols
• X.25
• Oldest packet switched service (widely used in Europe)
• Not in widespread use in North America
• Low data rates (64 Kbps) (available now at 2.048 Mbps)
• Asynchronous Transfer Mode (ATM)
• Newer than X.25; also standardized
• Data Rates
• Same rates as SONET: 51.8, 466.5, 622.08 Mpbs
• New versions: T1 ATM (1.5 Mbps), T3 ATM (45 Mbps)
• Provides extensive QoS information
• Enables setting of precise priorities among different types of
transmissions (i.e. voice, video & e-mail)
9 - 21
8.23 Packet Switched - Service Protocols
• Frame Relay
• Faster than X.25 but slower than ATM
• NO QoS support (under development)
• Common CIR speeds:
• 56, 128, 256, 384 Kbps, 1.5, 2, and 45 Mbps
• Ethernet Services
• Most organizations use Ethernet and IP in the LAN and BN.
• Currently offer CIR speeds from 1 Mbps to 1 Gbps at 1/4 the cost
of more traditional services
• No need to translate LAN protocol (Ethernet/IP) to the protocol
used in MAN/WAN services
• X.25, ATM, & Frame Relay use different protocols requiring
translation from/to LAN protocols
9 - 22
8.24 Virtual Private Networks
Provides equivalent of a private packet switched network
over public Internet
Provides low cost and flexibility
Disadvantages of VPNs:
9 - 23
8.24 VPN – Basic Architecture
8.24 Layer 3 VPN Using IPSec
9 - 25
8.24 VPN Types
Intranet VPN
Extranet VPN
Access VPN
9 - 26
8.3 WAN Design Practices
Difficult to recommend best practices
Factors used
Design Practices
9 - 27
8.3 MAN/WAN Services Summary
9 - 28
8.3 Recommendations Best Practices MAN/WAN
9 - 29
8.4 Improving Performance
MAN/WAN: Handled in the same way as improving LAN
performance
 By checking the devices in the network,
 By upgrading the circuits between computers
 By changing the demand placed on the network
Device:
• Upgrade the devices (routers) and computers that connect
backbones to the WAN
• Examine the routing protocol (static or dynamic)
• Dynamic routing
• Increases performance in networks with many possible routes
from one computer to another
• Better suited for “bursty” traffic
• Imposes an overhead cost (additional traffic)
– Reduces overall network capacity
– Should not exceed 20%
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8.4 Improving Circuit Capacity
9 - 31
8.4 Reducing Network Demand
9 - 32