Wide Area Networks (WANs) Chapter 7 Copyright 2003 Prentice-Hall Panko’s 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)

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


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


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


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


WAN Technologies

Ordinary telephone line and telephone modem. (low-speed access only)

Point-to-Point Network of leased lines



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

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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


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


WAN Technologies

Ordinary telephone line and modem. (low-speed access only)




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


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


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

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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


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

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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


DataWAN

PSTN

DSLAM

ADSLModem

Splitter

Telephone

SubscriberPremises


PC

1.Data

256 kbps to1.5 Mbps

2.64 kbps to256 kbps

21


DataWAN

PSTN

DSLAM

ADSLModem

Splitter

Telephone

SubscriberPremises


PC

1.Ordinary Telephone

Service

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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


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


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

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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

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


WAN Technologies

Ordinary telephone line and modem. (low-speed access only)

Point-to-Point network of leased lines

Public switched data networks (PSDN)


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


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


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

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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

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Ethernet10 Gbps and 40 Gbps

Packet Unreliable NoProbablyLow

ATM1 Mbpsto about156 Mbps

Packet Unreliable Yes High




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


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





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


SwitchPOP

Customer Premises B

Customer Premises C

1.Access DeviceCustomer

Premises A

45


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

2.T1 Leased Access

Line to POP

46


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

CIR = 56 kbpsABR = 1 Mbps

3.Port

SpeedCharge

47


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


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


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


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


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


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


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


WAN Technologies Ordinary telephone line and modem. (low-speed

access only)


Public switched data networks (PSDN)


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


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


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


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


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


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


IP Security (IPsec) Security associations:

Governed by corporate policies

List ofAllowableSecurity

Associations

List ofAllowableSecurity

Associations

Party B Party A

IPsec Policy Server

Documents

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