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

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)

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


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


Low Speeds High cost per bit transmitted compared to

LANs

Lower speeds (mostly commonly 56 kbps to a few megabits per second)

5


WAN Technologies





6

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

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


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


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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WAN Technologies





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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

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


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


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


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

DataWAN

PSTN

DSLAM

ADSLModem

Splitter

Telephone

SubscriberPremises

Telephone CompanyEnd Office Switch

1.Existing Pair ofVoice-GradeUTP Wires

PC

18

Figure 7.6: ASDL with Splitter

DataWAN

PSTN

DSLAM

ADSLModem

Splitter

Telephone

SubscriberPremises


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


PC

1.Ordinary Telephone

Service

20


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


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

22


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

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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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

26

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

27


WAN Technologies



Public switched data networks (PSDN)


28

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

29


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)

30


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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Ethernet10 Gbps and 40 Gbps

Packet Unreliable NoProbablyLow

ATM1 Mbpsto about156 Mbps

Packet Unreliable Yes High

ServiceTypicalSpeeds

Circuit- orPacket-Switched

Reliable orUnreliable

VirtualCircuits?

RelativePrice

33


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)

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

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


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

37


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

38


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)

41


SwitchPOP

Customer Premises B

Customer Premises C

1.Access DeviceCustomer

Premises A

42


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

2.T1 Leased Access

Line to POP

43


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

CIR = 56 kbpsABR = 1 Mbps

3.Port

SpeedCharge

44


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

45


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

5.Sometimes

TrafficCharges and

Other Charges6. Management

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


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

48


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

49


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

50


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

51


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

52


WAN Technologies



Public switched data networks (PSDN)


53


WAN Technologies





54

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

55

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

56


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

57

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

58


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

59


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

60

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

61

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

62


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

63


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 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

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

Documents

line private line

modem slide

trunk line speed trunk

line conditions

pstn slide

pstn modem

standard trunk line

bis slide