WANs and Remote WANs and Remote ConnectivityConnectivity

ObjectivesObjectives

Identify network applications that require WAN Identify network applications that require WAN technologytechnology

Describe a variety of WAN transmission and Describe a variety of WAN transmission and connection methodsconnection methods

Identify criteria for selecting an appropriate WAN Identify criteria for selecting an appropriate WAN topology, transmission method, and operating systemtopology, transmission method, and operating system

Understand the hardware and software requirements Understand the hardware and software requirements for connecting to a network via modemfor connecting to a network via modem

Install and configure simple remote connectivity for a Install and configure simple remote connectivity for a telecommunicating clienttelecommunicating client

WAN EssentialsWAN Essentials

WAN linkWAN link Connection between one WAN site and Connection between one WAN site and

another siteanother site A WAN link is typically described as point-to-A WAN link is typically described as point-to-

pointpoint

Dedicated lineDedicated line Continuously available link that is leased Continuously available link that is leased

through another carrierthrough another carrier

WAN EssentialsWAN Essentials

Figure 7-1: Differences in LAN and WAN connectivity

PSTNPSTN

Public Switched Telephone NetworkPublic Switched Telephone Network

Refers to the network of typical telephone Refers to the network of typical telephone lines and carrier equipment that service lines and carrier equipment that service most homesmost homes

Also called Also called plain old telephone service plain old telephone service (POTS)(POTS)

PSTNPSTN

A A dial-updial-up connection uses a PSTN or other line connection uses a PSTN or other line to access remote servers via modems at both to access remote servers via modems at both the source and destinationthe source and destination

The place where two telephone systems meet is The place where two telephone systems meet is the the point of presencepoint of presence (POP)(POP)

PSTNPSTN

Figure 7-2: A typical PSTN connection to the Internet

ISDN (Integrated Services Digital ISDN (Integrated Services Digital Network)Network)

International standard for transmitting data International standard for transmitting data over digital linesover digital lines

Established by the ITUEstablished by the ITU

All ISDN connections are based on two types All ISDN connections are based on two types of channels:of channels: The The B channelB channel is the “bearer” channel is the “bearer” channel The The D channelD channel is the “data” channel is the “data” channel

BRI (Basic Rate Interface)BRI (Basic Rate Interface)

A variety of ISDN using two 64-Kbps bearer A variety of ISDN using two 64-Kbps bearer (B) channels and one 16-Kbps data (D) (B) channels and one 16-Kbps data (D) channel, as indicated by the following channel, as indicated by the following notation:notation: 2B+D2B+D

Through Through bondingbonding, the two 64-Kbps , the two 64-Kbps channels can be combined to achieve an channels can be combined to achieve an effective throughput of 128-Kbpseffective throughput of 128-Kbps

PRI (Primary Rate Interface)PRI (Primary Rate Interface)

It is only feasible to use ISDN for the It is only feasible to use ISDN for the local looplocal loop portion of a WAN linkportion of a WAN link

Figure 7-5: A PRI link

T-CarriersT-Carriers

BroadbandBroadband Group of network connection types or Group of network connection types or

transmission technologies generally capable transmission technologies generally capable of exceeding 1.544 Mbps throughputof exceeding 1.544 Mbps throughput

T-carriersT-carriers Term for any kind of leased line that follows Term for any kind of leased line that follows

the standards for T1s, fractional T1s, T1Cs, the standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4sT2s, T3s, or T4s

Types of T-CarriersTypes of T-Carriers

The most common T-carrier implementations are The most common T-carrier implementations are T1T1 and and T3T3

Signal levelSignal level ANSI standard for T-carrier technology that refers to ANSI standard for T-carrier technology that refers to

its Physical layer electrical signaling characteristicsits Physical layer electrical signaling characteristics

DSO (digital signal, level 0)DSO (digital signal, level 0) Equivalent of one data or voice channelEquivalent of one data or voice channel

Fractional T1Fractional T1 Arrangement allowing an organization to use only Arrangement allowing an organization to use only

some channels on a T1 line, paying for what they usesome channels on a T1 line, paying for what they use

T-Carrier ConnectivityT-Carrier Connectivity

WiringWiring Can use unshielded or shielded twisted-pair copper wiringCan use unshielded or shielded twisted-pair copper wiring

CSU/DSU (Channel Service Unit/Data Service Unit)CSU/DSU (Channel Service Unit/Data Service Unit) CSUCSU provides termination for the digital signal and ensures provides termination for the digital signal and ensures

connection integrity through error correction and line monitoringconnection integrity through error correction and line monitoring DSUDSU converts the digital signal used by bridges, routers, and converts the digital signal used by bridges, routers, and

multiplexers into the digital signal sent via the cablingmultiplexers into the digital signal sent via the cabling

Figure 7-6: A CSU/DSU connecting a T1

T-Carrier ConnectivityT-Carrier Connectivity

MultiplexerMultiplexer Device that combines multiple voice or data channels on Device that combines multiple voice or data channels on

one lineone line

Figure 7-7: Typical use of a multiplexer on a T1-connected data network

T-Carrier ConnectivityT-Carrier Connectivity

Routers and Routers and bridgesbridges

On a typical On a typical T1-connected T1-connected data network, data network, terminal terminal equipment will equipment will consist of consist of bridges, bridges, routers or a routers or a combination of combination of the twothe two

Figure 7-8: A router on a T1-connected network

DSLDSL

Digital Subscriber LinesDigital Subscriber Lines

Uses advanced data modulation techniques Uses advanced data modulation techniques to achieve extraordinary throughput over to achieve extraordinary throughput over regular phone linesregular phone lines

Like ISDN, DSL can span only limited Like ISDN, DSL can span only limited distances without the help of repeatersdistances without the help of repeaters

Types of DSLTypes of DSL

Term Term xDSLxDSL refers to all DSL varieties, of refers to all DSL varieties, of which at least eight currently existwhich at least eight currently exist

DSL types can be divided into two categories:DSL types can be divided into two categories: AsymmetricalAsymmetrical SymmetricalSymmetrical

To understand the difference between these To understand the difference between these two categories, you must understand the two categories, you must understand the concept of concept of downstreamdownstream and and upstreamupstream data transmissiondata transmission

DSL ConnectivityDSL Connectivity

DSL connectivity, DSL connectivity, like ISDN, depends like ISDN, depends on the PSTNon the PSTN

Inside carrier’s POP, Inside carrier’s POP, a device called a a device called a DSL access DSL access multiplexer multiplexer (DSLAM)(DSLAM) aggregates multiple aggregates multiple DSL subscriber lines DSL subscriber lines and connects them and connects them to a larger carrier or to a larger carrier or to the Internet to the Internet backbonebackbone

Figure 7-9: A DSL connection

DSL ConnectivityDSL Connectivity

Once inside Once inside the customer’s the customer’s home or office, home or office, the DSL line the DSL line must pass must pass through a through a DSL DSL modemmodem

Figure 7-10: A DSL modem

CableCableCable Cable connections connections require that the require that the customer use a customer use a special special cable cable modemmodem, a , a device that device that modulates and modulates and demodulates demodulates signals for signals for transmission transmission and reception and reception via cable wiringvia cable wiring

Figure 7-11: A cable modem

CableCable

Hybrid fiber-coax (HFC)Hybrid fiber-coax (HFC) Very expensive fiber-optic link that can support high Very expensive fiber-optic link that can support high

frequenciesfrequencies HFC upgrades to existing cable wiring are required before HFC upgrades to existing cable wiring are required before

current TV cable systems can serve as WAN linkscurrent TV cable systems can serve as WAN links

Cable dropCable drop Fiber-optic or coaxial cable connecting a neighborhood Fiber-optic or coaxial cable connecting a neighborhood

cable node to a customer’s housecable node to a customer’s house

Head-endHead-end Cable company’s central office, which connects cable Cable company’s central office, which connects cable

wiring to many nodes before it reaches customers’ siteswiring to many nodes before it reaches customers’ sites

CableCable

Figure 7-12: Cable infrastructure

SONET (Synchronous Optical SONET (Synchronous Optical Network)Network)

Can provide data Can provide data transfer rates from transfer rates from 64 Kbps to 39.8 64 Kbps to 39.8 Gbps using the Gbps using the same TDM same TDM technique used by technique used by T-carriersT-carriersKnown Known internationally as internationally as SDH SDH (Synchronous (Synchronous Digital Hierarchy)Digital Hierarchy)

SONET is SONET is self-self-healinghealing

Figure 7-13: SONET technology on a long-distance WAN

WAN Implementation:WAN Implementation:SpeedSpeed

Table 7-4b: A comparison of WAN technology transmission speeds

WAN Implementation:WAN Implementation:ReliabilityReliability

WAN implementations can roughly be divided as WAN implementations can roughly be divided as follows:follows: Not very reliable, suited to individual or unimportant Not very reliable, suited to individual or unimportant

transmissions:transmissions:PSTN dial-upPSTN dial-up

Sufficiently reliable, suited for day-to-day Sufficiently reliable, suited for day-to-day transmissions:transmissions:

ISDN, T1, fractional T1, T3, DSL, cable, X.25, and frame ISDN, T1, fractional T1, T3, DSL, cable, X.25, and frame relayrelay

Very reliable, suited to mission-critical applications:Very reliable, suited to mission-critical applications:SONETSONET

WAN Implementation:WAN Implementation:SecuritySecurity

Among other things, consider the following Among other things, consider the following issues:issues: WAN security depends in part on the encryption WAN security depends in part on the encryption

measures each carrier provides for its linesmeasures each carrier provides for its lines Enforce password-based authorization for LAN Enforce password-based authorization for LAN

and WAN access and teach users how to choose and WAN access and teach users how to choose difficult-to-decrypt passwordsdifficult-to-decrypt passwords

Take the time to develop, publish, and enforce a Take the time to develop, publish, and enforce a security policy for users in your organizationsecurity policy for users in your organization

Maintain restricted access to network equipment Maintain restricted access to network equipment rooms and data centersrooms and data centers

WAN Implementation:WAN Implementation:Virtual Private Networks (VPNs)Virtual Private Networks (VPNs)

VPNs are wide VPNs are wide area networks area networks logically defined logically defined over public over public transmission transmission systems that systems that serve an serve an organization’s organization’s users, but isolate users, but isolate that that organization’s organization’s traffic from other traffic from other users on the users on the same public linessame public lines

Figure 7-14: An example of a VPN

Remote ConnectivityRemote Connectivity

Remote access methods:Remote access methods: Direct dial to the LANDirect dial to the LAN

The computer dialing into the LAN becomes a The computer dialing into the LAN becomes a remote remote nodenode on the network on the network

Direct dial to a workstationDirect dial to a workstationSoftware running on both remote user’s computer and LAN Software running on both remote user’s computer and LAN computer allows remote user to “take over” the LAN computer allows remote user to “take over” the LAN workstation, a solution known as workstation, a solution known as remote controlremote control

Internet/Web interfaceInternet/Web interfaceThrough a browser, a user at home or on the road connects Through a browser, a user at home or on the road connects to a LAN whose files are made visible to the Web through to a LAN whose files are made visible to the Web through Web server softwareWeb server software

Dial-Up NetworkingDial-Up Networking

Refers to the Refers to the process of process of dialing into a dialing into a LAN’s LAN’s (private) (private) access server access server or to an ISP’s or to an ISP’s (public) (public) access server access server to log onto a to log onto a networknetwork

Figure 7-15: Choosing a network connection type

SLIP and PPPSLIP and PPP

Serial Line Internet Protocol (SLIP)Serial Line Internet Protocol (SLIP) Communications protocol enabling a workstation to Communications protocol enabling a workstation to

connect to a server using a serial connectionconnect to a server using a serial connection Can carry only IP packetsCan carry only IP packets Supports only Supports only asynchronousasynchronous transmission transmission

Point-to-Point ProtocolPoint-to-Point Protocol Communications protocol enabling a workstation to Communications protocol enabling a workstation to

connect to a server using a serial connectionconnect to a server using a serial connection Can carry many different types of Network layer packetsCan carry many different types of Network layer packets Supports both Supports both asynchronousasynchronous and and synchronoussynchronous

transmissiontransmission

Chapter SummaryChapter Summary

WANs are distinguished from LANs by the fact WANs are distinguished from LANs by the fact that the former networks traverse a wider that the former networks traverse a wider geographical areageographical area

One WAN transmission method, PSTN, relies on One WAN transmission method, PSTN, relies on the network of telephone lines that typically the network of telephone lines that typically service homesservice homes

X.25 is an analog packet-switched technology X.25 is an analog packet-switched technology optimized for long-distance data transmissionoptimized for long-distance data transmission

Frame Relay is an updated, digital version of Frame Relay is an updated, digital version of X.25X.25

Chapter SummaryChapter Summary

Another WAN transmission method, ISDN, is an Another WAN transmission method, ISDN, is an international standard established by the ITU for international standard established by the ITU for transmitting data over digital linestransmitting data over digital lines

Two types of ISDN connections are commonly Two types of ISDN connections are commonly used in North America are BRI and PRIused in North America are BRI and PRI

Another WAN transmission method is digital Another WAN transmission method is digital subscriber line (DSL)subscriber line (DSL)

Cable is another option for high bandwidth local Cable is another option for high bandwidth local loop WAN transmissionloop WAN transmission

Chapter SummaryChapter Summary

T-carrier technology uses time division multiplexing T-carrier technology uses time division multiplexing (TDM) to divide a single channel into multiple channels (TDM) to divide a single channel into multiple channels for carrying voice, data, video, or other signalsfor carrying voice, data, video, or other signalsSONET can provide data transfer rates from 64 Kbps to SONET can provide data transfer rates from 64 Kbps to 39.8 Gbps using the same TDM technique employed by 39.8 Gbps using the same TDM technique employed by T-carriersT-carriersWhen installing or upgrading a WAN, consider its ability When installing or upgrading a WAN, consider its ability to integrate with your present LAN or WAN equipment, to integrate with your present LAN or WAN equipment, transmission speed required, security needed, transmission speed required, security needed, geographical distance the WAN must span, growth, and geographical distance the WAN must span, growth, and costcostVPNs represent one way to construct a WAN from VPNs represent one way to construct a WAN from existing public transmission systemsexisting public transmission systems

Chapter SummaryChapter Summary

Three ways remote users connect to Three ways remote users connect to LANs: LANs: Direct dial to the LANDirect dial to the LAN Direct dial to a workstationDirect dial to a workstation An Internet connection with a Web interfaceAn Internet connection with a Web interface

SLIP and PPP are communications SLIP and PPP are communications protocols enabling a workstation to protocols enabling a workstation to connect to a server using a serial connect to a server using a serial connectionconnection