COS 338 Day 11. 2 DAY 11 Agenda Questions? Capstone Proposal Overdue 3 accepted, 2 in mediation, 1 MIA Assignment 3 Due 1 B, 2 C’s, 1 F and 2 MIA Assignment

COS 338

Day 11

2

DAY 11 Agenda

Questions? Capstone Proposal Overdue

3 accepted, 2 in mediation, 1 MIA

Assignment 3 Due 1 B, 2 C’s, 1 F and 2 MIA

Assignment 4 Posted Due Oct 20

Lab 4 is on Oct 20 OpNet lab 3 – Evaluating WAN Performance

Lab 5 is on oct 24 (after exam) OpNet Lab 4 – Large WAN

Exam 2 is on Oct 24 Chap 4-7, open book, open notes, 60 min, 25 M/C questions

Today is Lecture on WAN’s

Wide Area Networks (WANs)

Chapter 7

Copyright 2005 Prentice-HallPanko’s Business Data Networks and Telecommunications, 5th edition

4

Wide Area Networks (WANs)

Chapters 4 and 5: LANs LANs for customer premises operation, high

speeds (Ethernet and WLANs)

Chapter 6: Telephony PSTN carrier service

Chapter 7: WANs WAN technology often is based on telephone

technology and services

5

Figure 7-1: Wide Area Networks (WANs)

WAN Purposes

1. Link sites (usually) within the same corporation

2. Remote access for individuals who are off-site

3. Internet access for individuals or firms

6

Figure 7-1: Wide Area Networks (WANs), Continued

Technologies for Individual Internet Access and remote access to Corporate Networks Telephone modems DSL lines Cable modems Wireless Internet access

Site-to-Site Transmission within a Firm Private line networks Public switched data networks (PSDNs) Virtual Private Networks (VPNs)

Propagation over the Internet with added security Low cost per bit transmitted

7

Figure 7-1: Wide Area Networks (WANs), Continued

High Costs and Therefore Low Speeds High cost per bit transmitted compared to LANs

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

Typical WAN speeds:56 kbps to a few megabits per second.

Individual Internet Access:Telephone Modems

9

Telephone Modem Communication

Computers are digital sources

Telephone transmission lines are analog

A modem converts between the two

Client ATelephone56 kbps

Modem

DigitalComputer

Signal

AnalogSignal

10

Figure 7-2: Amplitude Modulation

LowAmplitude

(0)

HighAmplitude

(1)

AmplitudeModulation

(1011)

Amplitude (low)

Amplitude (high)

11

Figure 7-3: Telephone Modem Communication

PSTN

Client ATelephone

Digital Access Line

56 kbpsModem

For 56 kbps Download SpeedISP Must Have a Digital Connection, Not a Modem

ISP

Digital Subscriber Lines (DSLs)

DSLs provide data over the existing 1-pair voice-grade access line that already goes to residences and small businesses

13

Digital Subscriber Lines (DSLs)

DSLs provide digital data transmission over the single-pair voice-grade local loop that already runs to residential customer premises.

These lines are already installed, so no cost to run new access lines (as there is with private lines).

Single-pair voice-grade UTP was not meant to carry data. Sometimes it works. Other times, it does not. Depends primarily on whether distance to the nearest end office is too far.

14

Figure 7-4: Digital Subscriber Lines (DSLs)

Asymmetric DSL (ADSL) Asymmetrical throughput

Downstream speed of 512 kbps to 1.5 MbpsUpstream speeds of 90 kbps to 384 kbpsGood for Web access with large downloadsSufficiently fast for e-mail

Aimed at residential customersThroughput is NOT guaranteedDSLAM (discussed later) often oversubscribed,

slowing access

15

Figure 7-4: Digital Subscriber Lines (DSLs), Continued

Symmetric DSL Services Speed is symmetric

Same upstream and downstream

Aimed at business customersThroughput IS guaranteed

Several Types of Symmetric DSLHDSL (768 kbps): Half of a T1 private line (later)HDSL2 (1.544 kbps): Full T1 private line speedSHDSL: Flexible (384 kbps to 2.3 Mbps)

16

Figure 7-5: Asymmetric Digital Subscriber Line (ADSL)

DataWAN

PSTN

6. DSLAM

ADSLModem

2. Splitter

Telephone

SubscriberPremises

Telephone CompanyEnd Office Switch

1.Existing 1-PairVoice-Grade

UTP

PC

5.Ordinary Telephone

Service

3.Downstream Data

512 kbps to1.5 Mbps

4.Upstream

90 kbps to 384 kbps

17

Fiber to the Home (FTTH)

Single-pair voice-grade copper running to residences is limited in the speed it can provide for data transmission

Fiber to the home (FTTH) will bring optical fiber to each home

Higher speeds for data transmission, video, etc.

Being held back by high installation costs, which require provable strong demand

http://www.broadweave.com/home.htm

Cable Modem Service

19

Figure 7-6: Cable Modem Service

PCSubscriberPremises

6. CableModem

4. CoaxialCable to

Neighborhood

2. OpticalFiber to

Neighborhood

3.Neighborhood

Splitter

ISP

1. CableTelevisionHead End

7. PC needs NIC or USB portHybrid Fiber Cable (HFC)

5. CoaxialDrop Cable

20

Figure 7-6: Cable Modem Service, Continued

Cable Modem Delivered by cable television operator

Cable modems follow the Data-Over-Cable Interface Specification (DOCIS) standard

Up to 10 Mbps downstream128 kbps to 512 kbps upstreamHeavy users get throttled back by operator

Speed is shared in a neighborhoodOnly users sending and receiving simultaneously In practice, medium ADSL speed or higher

21

Figure 7-7: Wireless Access Systems

Wireless Access to the Internet Fixed Versus Mobile

FixedFor homes and offices (fixed locations)Use dish antennasHigher speeds

MobilePeople traveling within a city or fartherNeed omnidirectional antennasLower speeds

22

http://www.pwless.net/corporate/default.htm

23

Figure 7-7: Wireless Access Systems, Continued

Satellite Versus Terrestrial Wireless Satellite

Expensive because of transmission distanceExpensive because satellites are expensive

to launch and maintainCan cover large areas

TerrestrialEarth-based radio stationsService within a city

24

Figure 7-7: Wireless Access Systems, Continued

3G Cellular Service Telephone modem and DSL/cable modem speeds

802.16 WiMAX One of several terrestrial wireless access standards

under development

Fixed version being standardized first20 Mbps up to 50 km (30 miles)

Mobile version under development (802.16e)3 Mbps to 16 Mbps for mobile users

Site-to-Site Networking:Private Line Networks

26

Figure 7-8: Private Line Networks for Voice and Data

Connect sites via private lines

Perspective User firm must do all the planning and installation

User firm must operate and maintain the network

Labor-intensive site-to-site networking

27

Figure 7-8: Private Line Networks for Voice

T3 PrivateLine

Site C

Site A Site B

OC3 Private Line

T1 PrivateLine

T1 PrivateLine

Site ESite D

56 kbpsPrivate

Line

56 kbpsPrivate

Line

56 kbpsPrivate

Line

PBX Private Line Voice NetworksHave a PBX at Each Site

28

Figure 7-8: Private Line Networks for Data

T3 PrivateLine

Site C

Site A Site B

OC3 Private Line

T1 PrivateLine

T1 PrivateLine

Site ESite D

56 kbpsPrivate

Line

56 kbpsPrivate

Line

56 kbpsPrivate

Line

Router Private Line Data NetworksHave a Router at Each Site

29

Figure 7-9: Full Mesh Topology

Site C

Site A Site B

Site ESite D

Very ReliableVery Expensive

In a Full Mesh Topology,Each Site Connects

Directly to Each Other Site

30

Figure 7-9: Pure Hub-and-Spoke Topology

Site C

Site A Site B

Site ESite D

In a Pure Hub-and-SpokeTopology, There is OnlyOne Line for Each Site

Less Expensive, butNo Redundancy for Reliability

31

Figure 7-9: Pure Hub-and-Spoke Topology, Continued

T3 PrivateLine

Site C

Site A Site B

OC3 Private Line

T1 PrivateLine

T1 PrivateLine

Site ESite D

56 kbpsPrivate

Line

56 kbpsPrivate

Line

Most Firms Mix the Two TopologiesTo Balance Cost and Reliability

32

Figure 7-10: Private Line Speeds

Trunk Line Speed

North American Digital Hierarchy

56 kbps (DS0 Signaling)56 kbps

(sometimes 64 kbps)

T1 (DS1 Signaling) 1.544 Mbps

Fractional T1128 kbps, 256 kbps,384 kbps, 512 kbps,

and 768 kbps

Bonded T1s (multiple T1sacting like a single line)

Varies(usually up to 6 Mbps)

T3 (DS3 Signaling) 44.7 Mbps

Medium

2-pair DG* UTP

2-pair DG* UTP

2-pair DG* UTP

2-pair DG* UTP

Optical Fiber

*DG = Data Grade

33

Figure 7-10: Private Line Speeds, Continued

Trunk Line Speed

Japanese Multiplexing Hierarchy

64 kbps 64 kbps

J1 1.544 Mbps (same as U.S. T1)

J3 32.1 Mbps

CEPT Multiplexing Hierarchy (Europe)

64 kbps 64 kbps

E1 2.048 Mbps

E3 34.4 Mbps

34


Trunk Line Speed

SONET/SDH*

OC3/STM1 156 Mbps

OC12/STM4 622 Mbps

OC48/STM16 2.5 Gbps

OC192/STM64 10 Gbps

OC768/STM256 40 Gbps

Notes: SONET and SDH speeds are multiples of 51.84 Mbps. (Figures listed are rounded off for readability)

OCx is the SONET designation.STMx is the SDH designation.

35


Perspective

Most the range of greatest demand for site-to-site transmission is 56 kbps to a few megabits per second

So the largest market for private lines consists of T1 and fractional T1 lines or the equivalent in various countries

Site-to-Site Networking:Public Switched Data Networks

37

Figure 7-11: Private Line versus Public Switched Data Networks

Public Switched DataNetwork (PSDN)

POPPOP

POPPOP

Site A Site B

Point of PresenceOne privateline per site

Site D Site C Site E

Public Switched Data Network (PSDN)

38

Figure 7-11: Private Line versus Public Switched Data Networks, Continued

Private Line Network Company must plan, buy switching equipment, and

operate the network. Requires much labor.

Public Switched Data Network PSDN carrier provides planning, switching, and

operation of the network. This greatly reduces corporate management labor.

PSDN drawn as a cloud to indicate that users do not need to understand it because the PSDN handles all of the details.

39

Figure 7-12: Virtual Circuit

PSDN Switches Are Arranged in Meshes Loops so multiple alternative paths between stations Switches must consider alternative paths This is complex, making switching expensive

40

Figure 7-12: Virtual Circuit, Continued

PSDNs Create Virtual Circuits Virtual circuit is a single path (data link) between two

stations Set up before transmission begins Only a single possible path, so switching is fast and

inexpensive

Virtual Circuit

Virtual Circuit

41

Figure 7-12: Virtual Circuit, Continued

PSDNs Create Virtual Circuits Switching table has virtual circuit instead of data link

layer addresses Frame header has a virtual circuit number,

NOT a destination address Virtual CircuitA . . .B . . .C . . .D . . .

Port1234

Site-to-Site Networking:Frame Relay (FR)

The most popular PSDN

43

Frame Relay (FR)

The most popular PSDN Today Speed range is 56 kbps to up to 40 Mbps

Matches main speed range of corporate WAN demand (56 kbps to a few megabits per second)

FR Switching is Designed to Minimize Cost Switching is unreliable to reduce the cost per frame

Switching uses virtual circuits to reduce cost

Cost minimization is important in WAN communication

44

Figure 7-13: Frame Relay Network

SwitchPOP

Customer Premises B

Customer Premises C

1.Access DeviceCustomer

Premises A

45

Figure 7-13: Frame Relay Network, Continued

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)

46


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 Or Private Line (teleco).

May have different baud rate, number of states, voltage levels, etc.

DSU

47


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

2.T1 Private Access

Line to POP

48


SwitchPOP

Customer Premises B

Customer Premises C

Customer Premises A

3.Port

SpeedCharge at

POPSwitch

49


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

50


Permanent Virtual Circuits (PVCs) Set up once, kept in place for months or years

Between a firm’s sites (which rarely change)

The most common form of virtual circuit today

Switched Virtual Circuits (SVCs) Set up at beginning of a communication session

Taken down at the end of the session

More expensive than PVCs, less common

51


Frame Relay Pricing Recap Frame relay access device at site (or router) Private line from site to POP Port on the POP

Pay by port speedUsually the largest price component

Permanent virtual circuits (PVCs) among communicating sites

Usually the second-largest component of prices

Other charges

52

Figure 7-14: Frame Relay Frame

Variable Length Frames Start flag (01111110) to signal start of frame Address field has variable length (2-4 octets) Information field to carry data (variable) CRC (Cyclical Redundancy Check) field to detect

errors (2 octets) If find errors, switch discards the frame

Stop flag (01111110) to signal end of frame

01111110 01111110Address Information CRC

53

Figure 7-14: Frame Relay Frame, Continued

Address Field of Frame Relay Frame Variable Length: 2-4 octets

Usually 2 octets (as shown below)

Data link control indicator (DLCI, pronounced dull’-see) is the virtual circuit number (10 bits long in 2-octet form)

0 7

DLCI (6 bits) C/R 0

DLCI (4 bits) FECN BECN DE 1

Bits

54

Frame Relay Design

Determine Needs for Each Site Site A to Site B needs 30 kbps Site A to Site C needs 800 kbps Site B to Site C needs 100 kbps

Design FR Requirements One Site at a Time

Site A

Site B

800 kbps needed

30 kbps needed

Site C

100 kbps needed

55

Frame Relay Design, Continued

Step 1: Determine the Site’s PVC Needs Determine needed speed from this site to each

other

You will need a PVC at least as high (vendors only offer some PVC speeds)

Sum all the virtual circuit speeds

Site BeingAnalyzed

30 kbps needed;Select 56 kbps PVC

800 kbps needed; Select 1 Mbps PVC

Sum of PVCs1,056 kbps

56


Step 2: Determine the Port Speed Required

For each private line connection to an FR switch, pay according to port speed

Usually the most expensive element in FR costs

Vendors usually offer only a few options for port speeds

Frame RelaySwitch

Port

Private Line

57


Step 2: Determine Port Speed Port speed must be equal to or greater than 70% of

the sum of the PVCs

This is called oversubscription70% reflects the fact that not all PVCs will be at

maximum speed all of the time

70% of 1,056 kbps is 739 kbps

Next-higher port speed may be 1 Mbps

Pick the minimum port speed that is as high or higher than your need

58


Step 3: Determine Private Line Speed Remember that port speed is more expensive than

private line speeds

In general, don’t waste port speed by using a private line much under its capacity

If port speed is 1 Mbps, the private line should be T1 with 1.544 Mbps capacity

Private Line ForMultiple PVCs

59


Some Frame Relay Vendors Use Multi-Tier Pricing

Committed Information Rate (CIR) Pretty much guaranteed

Excess Burst Speeds Faster bursts up to excess burst speeds are

available if there is capacity

If there is congestion, frames beyond CIR are eligible to be discarded

60


Example Firm needs four PVCs from a site

Each will have a CIR of 128 kbpsEach will have an excess burst speed of 256

kbps

Will pick a port speed of 4 x 128 kbps = 512 kbps or higher (based on CIR)

Note that oversubscription is not used when bursting is used. Port speed is the sum of the PVC CIRs

61


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

62


Example For HQ

How many connections will HQ need?

What are their speeds?

What will be their PVC speeds (if options are 0 kbps, 56 kbps, 256 kbps, 512 kbps, 1 Mbps)?

HQ

63


Example For HQ

If port speeds are 56 kbps, 256 kbps, 384 kbps, 512 kbps, what port speed will be needed?

What private line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?

HQ

64


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, or 1 Mbps)?

B1

65


Example For Each Branch

If port speeds are 56 kbps, 256 kbps, 384 kbps, or 512 kbps, what port speed will be needed?

What private line will be needed if speeds are 56 kbps, 256 kbps, 512 kbps, or T1?

B1

Site-to-Site Networking:Asynchronous Transfer Mode (ATM)

67

Asynchronous Transfer Mode (ATM)

ATM is a faster PSDN than Frame Relay Frame Relay: 56 kbps up to about 40 Mbps

ATM: 1 Mbps up to about 156 Mbps

Not Competitors. Most PSDN Vendors Offer Both to Customers FR for low-speed customer needs

ATM for higher speeds (at higher prices)

As corporate demand grows, ATM may increase its market share

68

ATM Cell

Fixed Length (53 octets) Frame Allows Simpler and Therefore Faster Processing at Switches

For instance, switch does not have to do calculations to figure out how much buffer space it will need for a cell, as is the case with Frame Relay’s variable-size frame.

53 Octets5 octets of header48 octets of payload (data)

Fixed length frames are called cells

69

ATM Cell, Continued

Short Cell Length Limits Latency at Each Switch Switches may have to wait until the entire frame

arrives before processing it and sending it back out.

With shorter frames, there is less latency at each switch along the path

Important in continent-wide WANs that require cells to pass through many switches

Especially important for voice, which is highly latency-intolerant (ATM was created for digitized voice)

70

ATM QoS

Quality of Service

ATM provides strong QoS guarantees for voice traffic (latency, jitter, etc.)

However, ATM usually offers few or no QoS guarantees for data traffic—get what is left over after capacity reserved for voice QoS

71

ATM QoS, Continued

Manageability Strong management tools (designed for the PSTN

transport core)

So it is very expensive for small and medium firms

Site-to-Site Networking:Metropolitan Area Ethernet

Ethernet is moving into metropolitan area networks

73

Metropolitan Area Ethernet

Ethernet is moving beyond the LAN Moving into the metropolitan area network (within a

single urban area)

New 802.3 standards (10 Gbps and 40 Gbps) being developed primarily for long distances of 10 km or more

E-Line service: to connect LANs at two sites

E-LAN service: to connect LANs at multiple sites

74

Metropolitan Area Ethernet, Continued

Cheaper than ATM for high speeds

Familiar technology so easy to manage

Still lacks standards for carrier-class service

New but growing rapidly compared to Frame Relay and ATM

Site-to-Site Networking:Virtual Private Networks (VPNs)

VPNs: Transmission over the Internet with added security

76

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? Lower transmission cost per bit transmitted than

PSDNs

Adequate security

77

Figure 7-16: Virtual Private Network (VPN)

VPN Server

Corporate Site A

VPN Server

CorporateSite B

3. Host-to-HostVPN

RemoteCorporate PC

Tunnel

Internet

2.Remote

Access VPN

1.Site-to-Site

VPN

78

VPN Technologies

SSL/TLS Limited to remote access VPNs SSL (Secure Sockets Layer) was its original name

IETF changed it to Transport Layer Security Created to protect HTTP traffic in e-commerce Built into every browser and webserver, so easy to

implement Good if all traffic over the VPN will be HTTP

Beginning to handle other applications (not in book)

Moderate security

79

VPN Technologies, Continued

Point-to-Point Tunneling Protocol (PPTP) For remote access VPNs Operates at the data link layer

Transparently provides security to all messages at higher layers

Software exists on all client PCs, but individual PCs must be configured to work with PPTP, and this is somewhat expensive

Good for remote access when not all traffic is HTTP

SSL/TLS has pushed PPTP almost entirely aside in the marketplace (New: Since book was written)

80

VPN Technologies, Continued

IPsec For all types of VPN (remote access, site-to-site,

host-to-host) Operates at the Internet layer

Transparently protects traffic at all higher layers Very strong security Requires digital certificates for all computers

Creating an infrastructure for certificates is expensive

Installation and setup on individual client PCs is expensive

81

IPsec in Tunnel Mode

Security Only Between SitesHosts Need No Extra Software

Only IPsec Gateways need Digital CertificatesEasier to Set Up than Transport Mode

SecureTunnel

TunnelMode IPsec IPsec

GatewayIPsec

GatewayLocal

NetworkLocal

Network

No SecurityIn Site Network

No SecurityIn Site Network

82

IPsec in Transport Mode

End-to-End (Host-to-Host)Tunnel

Each Host Needs IPsec SoftwareAnd Digital Certificate

SecureTunnel

TransportMode IPsec

IPsecGateway

IPsecGateway

LocalNetwork

LocalNetwork

SecurityIn Site Network

SecurityIn Site Network

Topics Covered

84

Topics Covered

Technologies for Individual Internet Access Telephone modems DSL lines Cable modems Wireless Internet access

Site-to-Site Transmission within a Firm Private line networks Public switched data networks (PSDNs) Virtual Private Networks

Propagation over the Internet with added security

85

Market Data

Individual Internet Access About two-thirds telephone modem access

About one-third broadband (DSL and cable modem)

Half broadband in large cities

Site-to-Site Networking Frame Relay: about 45% of the market

Private lines: about 45% of the market

VPNs: very small but growing rapidly

86

Key Points

WANs speeds are slow because long-distance transmission is costly Most WAN links are 56 kbps to a few megabits per

second

DSLs use the existing 1-pair UTP wiring that runs to residences and small businesses Limited transmission capability, but no cost to run

new wiring

87

Key Points

The most widely used private lines are Fractional T1 and T1

Because in the range of greatest corporate demand for WAN links

PSDNs have one private line running from each site to the PSDN cloud

Virtual circuits reduce cost No need to compute the best alternative path for

each frame separately

88

Key Points

Frame Relay Pricing

Multiple PVCs (one to each other site) are multiplexed over a site’s single private line and single POP port.

Port speed charges are the biggest price factor in Frame Relay pricing

PVC charges are the second biggest price factor

89

Key Points

Virtual private networks (VPNs) Communication over the Internet with added

security Why? Cheaper than other WAN alternatives

Moderate security for remote access VPNs SSL: simplest but limited to HTTP PPTP: protects all traffic above the data link layer

IPsec has the strongest VPN security But costly to set up because of digital certificates

Documents

COS 338 Day 11. 2 DAY 11 Agenda Questions? Capstone Proposal Overdue 3 accepted, 2 in mediation, 1 MIA Assignment 3 Due 1 B, 2 C’s, 1 F and 2 MIA Assignment