ccna exp4 - chapter01 - introduction to wans

8/3/2019 CCNA Exp4 - Chapter01 - Introduction to WANs

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Chapter 1 – Introduction to WANs

CCNA Ex loration 4.0

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Introduction

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What is a WAN?

• A WAN is a data communications network that operates beyond the geographic scopeof a LAN.

• WANs generally carry a variety of traffic types, such as voice, data, and video.

• Here are the three major characteristics of WANs:

1. Connect devices that are separated by a broader geographical area.

2. Use the services of carriers, such as telephone companies…

3. Use serial connections




Why Are WANs Necessary?


• There are business needs that require communication among remote sites, including thefollowing: – People in the regional or branch offices of an organization need to be able to

communicate and share data with the central site. – Organizations often want to share information with other organizations across large

distances. – Employees who travel on company business frequently need to access informationthat resides on their corporate networks.

– It is now common in many households for consumers to communicate with banks,stores, and a variety of providers of goods and services via computers.

– Students do research for classes by accessing library indexes and publicationslocated in other parts of their country and in other parts of the world.



The Evolving Enterprise

Businesses and Their Networks

• As companies grow, they hire more employees, open branch offices,and expand into global markets. These changes also influence their

requirements for integrated services and drive their networkrequirements.

Small Office (Single LAN)





Campus (Multiple LANs)

• As the business has expanded, the network has also grown. Instead of a singlesmall LAN, the network now consists of several subnetworks, each devoted to

a different department.• These multiple LANs are joined to create a company-wide network, or campus,

which spans several floors of the building.





Branch (WAN)

• Another five years later, Span Engineering has been so successful with itspatented process that demand for its services has skyrocketed, and new

projects are now being built in other cities.• To ensure that all parts of the business are able to access the same services

and applications regardless of where the offices are located, the company nowneeds to implement a WAN.





Distributed (Global)

• Span Engineering has now been in business for 20 years and has grown to thousands ofemployees distributed in offices worldwide.

•The company is also encouraging teleworking and virtual teams. Web-basedapplications, including web-conferencing, e-learning, and online collaboration tools, arebeing used to increase productivity and reduce costs.

• Site-to-site and remote access Virtual Private Networks (VPNs) enable the company touse the Internet to connect easily and securely with employees and facilities around the


.



The Evolving Network Model

The Hierarchical Design Model

• The hierarchical network model is a useful high-level tool for designinga reliable network infrastructure.

• It provides a modular view of a network, making it easier to design andbuild a scalable network.





The Hierarchical Network Model

• As you may recall from CCNA Exploration: the hierarchical network modeldivides a network into three layers:

1. Access layer-Grants user access to network devices.2. Distribution layer-Aggregates the wiring closets.

3. Core layer (also referred to as the backbone) - A high-speed

backbone that is designed to switch packets as fast as possible.


The figure represents the

Hierarchical Network Model in

campus environments.




The Enterprise Architecture

• This architecture is designed to provide network planners with a roadmap for networkgrowth as the business moves through different stages

• The following are some examples of the modules within the architecture that arerelevant to the Span Engineering scenario described earlier:

1. Campus Architecture

2. Branch Architecture

3. Data Center Architecture


4. Teleworker Architecture



The Enterprise Architecture


• The Cisco Enterprise Architecture consists of modules representing focused views that target eachplace in the network.

– Each module has a distinct network infrastructure with services and network applications that

extend across the modules.

• The Cisco Enterprise Architecture includes the following modules:

1. Enterprise Campus Architecture

2. Enterprise Edge Architecture

3. Enterprise Branch Architecture

4. Enterprise Data Center Architecture5. Enterprise Teleworker Architecture



The Topology




Extra: Campus Infrastructure Module




2. Enterprise Edge Architecture

• This module offers connectivity to voice, video, and data servicesoutside the enterprise.

• This module enables the enterprise to use Internet, partner resources,

and provide resources for its customers…




Extra: Enterprise Edge Module




3. Enterprise Branch Architecture

• This module allows businesses to extend the applications and servicesfound at the campus to thousands of remote locations and users or to asmall group of branches.




4. Enterprise Data Center Architecture

• Data centers are responsible for managing and maintaining the manydata systems that are vital to modern business operations. Employees,partners, and customers rely on data and resources in the data center

to effectively create, collaborate, and interact




5. Enterprise Teleworker Architecture

• Many businesses today offer a flexible work environment to theiremployees, allowing them to telecommute from home offices.




WAN Technology Overview

WANs and the OSI Model

• As described in relation to the OSI reference model, WAN operationsfocus primarily on Layer 1 and Layer 2.

• WAN access standards typically describe both physical layer deliverymethods and data link layer requirements, including physicaladdressing, flow control, and encapsulation.




WAN Physical Layer Concepts

WAN Physical Layer Terminology

• The figure illustrates the terminology commonly used to describe physical WANconnections, including:

– Customer Premises Equipment (CPE)

– Data Communications Equipment (DCE)

– Data Terminal Equipment (DTE)

– Demarcation Point

– Local Loop

–





WAN Devices

• WANs use numerous types of devices that are specific to WANenvironments, including:

– Modem – CSU/DSU

– Access server

– WAN switch


– Router – Core router



Extra: Network Access Server





WAN Physical Layer Standards

• WAN physical-layer protocols describe how to provide electrical,mechanical, operational, and functional connections for WAN services.

The WAN physical layer also describes the interface between the DTEand the DCE.





WAN Physical Layer Standards




WAN Switching Concepts

Data Link Protocols

• Data link layer protocols define how data is encapsulated for transmission to remotesites and the mechanisms for transferring the resulting frames. A variety of differenttechnologies, such as ISDN, Frame Relay, or ATM, are used.

• The most common WAN data-link protocols are: – HDLC

– PPP

– Frame Relay


– ATM




WAN Encapsulation

• Data from the network layer is passed to the data link layer for deliveryon a physical link, which is normally point-to-point on a WAN

connection.• The data link layer builds a frame around the network layer data so that

the necessary checks and controls can be applied.





WAN Frame Encapsulation Formats

• The frame always starts and ends with an 8-bit flag field. The bit pattern is01111110.

– The address field is not needed for WAN links, which are almost alwayspoint-to-point.

• The control field is protocol dependent, but usually indicates whether thecontent of the data is control information or network layer data.





WAN Frame Encapsulation Formats





Circuit Switching

• A circuit-switched network is one that establishes a dedicated circuit(or channel) between nodes and terminals before the users may

communicate.• The internal path taken by the circuit between exchanges is shared by

a number of conversations. Time division multiplexing (TDM) giveseach conversation a share of the connection in turn. TDM assures that


a fixed capacity connection is made available to the subscriber.




Packet Switching

• In contrast to circuit switching, packet switching splits traffic data intopackets that are routed over a shared network. Packet-switching

networks do not require a circuit to be established, and they allowmany pairs of nodes to communicate over the same channel.

• There are two approaches to this link determination, connectionless orconnection-oriented.




WAN Link Connection Options




Dedicated Connection Link Options

Leased Lines

• When permanent dedicated connections are required, a point-to-point link is used toprovide a pre-established WAN communications path from the customer premisesthrough the provider network to a remote destination. Point-to-point lines are usually

leased from a carrier and are called leased lines.




Dedicated Connection Link Options

Line Types and Bandwidth




Extra: Leased Line Services over ATM and SHDSL

• RAD’s LA-110 integrated access devices and ACE-2002EATM multiservice access concentrator support structuredAAL1 over a V.35 interface.




Extra: 64 kbps Leased Lines Services

• RAD's ASM-31 2-wire multi-rate short range modemprovides cost-effective remote access, operating in full-duplex mode over 2-wire twisted pair lines, at selectable

data rates from 1.2 kbps to 128 kbps (or 38.4 kbps inasynchronous mode) over distances up to 5.4 kilometers(3.4 miles).




Circuit Switched Connection Options

Analog Dialup

• When intermittent, low-volume data transfers are needed, modems andanalog dialed telephone lines provide low capacity and dedicated

switched connections. Traditional telephony uses a copper cable,called the local loop, to connect the telephone handset in thesubscriber premises to the CO.

• The physical characteristics of the local loop and its connection to the


PSTN limit the rate of the signal to less than 56 kb/s.



Circuit Switched Connection Options

Integrated Services Digital Network

• Integrated Services Digital Network (ISDN) is a circuit-switching technology thatenables the local loop of a PSTN to carry digital signals, resulting in higher capacityswitched connections.

• SDN cahnges the internal connections of the PSTN from carrying analog signals totime-division multiplexed (TDM) digital signals.

• There are two types of ISDN interfaces:

1. Basic Rate Interface (BRI)


2. Primary Rate Interface (PRI)



Packet Switched Connection Options

Common Packet Switching WAN Technologies

• The most common packet-switching technologies used in today's enterpriseWAN networks include Frame Relay, ATM, and legacy X.25.

X.25

• X.25 is a legacy network-layer protocol that provides subscribers with a

network address. Virtual circuits can be established through the network withcall request packets to the target address. X.25 link speeds vary from 2400 b/s


. .

S C O




Frame Relay

• Frame Relay differs from X.25 in several ways. Most importantly, it is amuch simpler protocol that works at the data link layer rather than the

network layer. Frame Relay implements no error or flow control. FrameRelay offers data rates up to 4 Mb/s, with some providers offering evenhigher rates.


P k S i h d C i O i




ATM

• Asynchronous Transfer Mode (ATM) technology is capable oftransferring voice, video, and data through private and public networks.

It is built on a cell-based architecture rather than on a frame-basedarchitecture. ATM cells are always a fixed length of 53 bytes.

• ATM was designed to be extremely scalable and can support linkspeeds of T1/E1 to OC-12 (622 Mb/s) and higher.


I t t C ti O ti



Internet Connection Options

Broadband Services

• Broadband connection options are typically used to connect telecommuting employees toa corporate site over the Internet. These options include cable, DSL, and wireless.

DSL

• DSL technology is an always-on connection technology that uses existing twisted-pairtelephone lines to transport high-bandwidth data, and provides IP services to subscribers


The ADSL spectrum

E t DSL T h l O ti



Extra: DSL Technology Options

Family ITU Name Ratified MaximumSpeed capabilities

ADSL G.992.1 G.dmt 1999 7 Mbps down

800 kbps up

ADSL2 G.992.3 G.dmt.bis 2002 8 Mb/s down

1 Mbps up

ADSL2plus G.992.5 ADSL2plus 2003 24 Mbps down

1 Mbps up


ADSL2-RE G.992.3 Reach Extended 2003 8 Mbps down

1 Mbps up

SHDSL

(updated 2003)

G.991.2 G.SHDSL 2003 5.6 Mbps up/down

VDSL G.993.1 Very-high-data-rateDSL

2004 55 Mbps down

15 Mbps up

VDSL2 -12 MHzlong reach

G.993.2 Very-high-data-rateDSL 2

2005 55 Mbps down

30 Mbps up

VDSL2 - 30 MHz

Short reach

G.993.2 Very-high-data-rateDSL 2

2005 100 Mbps up/down





Cable Modem

• Coaxial cable is widely used in urban areas to distribute television signals. Networkaccess is available from some cable television networks. This allows for greaterbandwidth than the conventional telephone local loop.






Broadband Wireless

• Wireless technology uses the unlicensed radio spectrum to send and receive data. Theunlicensed spectrum is accessible to anyone who has a wireless router and wirelesstechnology in the device they are using.

• The following new developments in broadband wireless technology are changing thissituation:

– Municipal WiFi

– WiMAX

–






VPN Technology

• A VPN is an encrypted connection between private networks over apublic network such as the Internet. Instead of using a dedicated Layer

2 connection such as a leased line, a VPN uses virtual connectionscalled VPN tunnels, which are routed through the Internet from theprivate network of the company to the remote site or employee host.

VPN Benefits


– Cost savings – Security

– Scalability

– Compatibility with broadband technology





Site-to-site VPNs

• Site-to-site VPNs connect entire networks to each other, for example,they can connect a branch office network to a company headquarters

network, as shown in the figure.






Remote-access VPNs

• Remote-access VPNs enable individual hosts, such as telecommuters,mobile users, and extranet consumers, to access a company network

securely over the Internet.






Metro Ethernet

• Metro Ethernet is a rapidly maturing networking technology that broadens Ethernet to thepublic networks run by telecommunications companies.

• IP-aware Ethernet switches enable service providers to offer enterprises converged

voice, data, and video services such as IP telephony, video streaming, imaging, and datastorage.

Benefits of Metro Ethernet include:

• Reduced expenses and administration


• Easy integration with existing networks

• Enhanced business productivity






Choosing a WAN Link Connection





• The figure compares the advantages and disadvantages of the WANconnection options that we have discussed in this chapter.





Extra: Steps in WAN design



Extra: Steps in WAN design


Extra: WAN Topologies



Extra: WAN Topologies


Star or Hub-and-SpokeFull-Mesh

Partial-Mesh

Chapter Lab



p


Summary



y


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