Chapter SevenChapter SevenWANs and Remote WANs and Remote

ConnectivityConnectivity

WAN EssentialsWAN Essentials

Wide Area NetworkWide Area NetworkWAN linkWAN link Connection between one WAN site and Connection between one WAN site and

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

Examples: p. 309Examples: p. 309

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 to connection uses a PSTN or other line to access remote servers via modems at both the access remote servers via modems at both the source and destinationsource and destination

The The Federal Communications Commission Federal Communications Commission (FCC)(FCC) sets standards and policy for sets standards and policy for telecommunications transmission equipment in the telecommunications transmission equipment in the United StatesUnited States Even with 56 Kbps modems, FCC limits PSTN lines to 53 Even with 56 Kbps modems, FCC limits PSTN lines to 53

Kbps to reduce crosstalkKbps to reduce crosstalk

The place where two telephone systems meet is the The place where two telephone systems meet is the point of presencepoint of presence (POP)(POP) LD to local, etc.LD to local, etc.

PSTNPSTN

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

Discussed on bottom of p. 311

X.25 and Frame RelayX.25 and Frame Relay

X.25X.25 Analog, packet-switched LAN technology optimized for long-distance data transmissionAnalog, packet-switched LAN technology optimized for long-distance data transmission Mid-70s 64Kbps – 1992 2.048 MbpsMid-70s 64Kbps – 1992 2.048 Mbps Developed as a more reliable connection for mainframes to remote terminalsDeveloped as a more reliable connection for mainframes to remote terminals Not widely accepted in U.S.Not widely accepted in U.S.

Frame RelayFrame Relay Updated, digital version of X.25 that also relies on packet switchingUpdated, digital version of X.25 that also relies on packet switching Standardized in 1984Standardized in 1984 1.544 or 45 Mbps1.544 or 45 Mbps Being replaced by newer, faster technologiesBeing replaced by newer, faster technologies Depicted as clouds in diagramsDepicted as clouds in diagrams

X.25 and Frame RelayX.25 and Frame Relay

Contract with telecommunications company Contract with telecommunications company states:states: EndpointsEndpoints Amount of bandwidthAmount of bandwidth Less expensive than a dedicated T1Less expensive than a dedicated T1

Figure 7-3: A WAN

using frame relay

X.25 and Frame RelayX.25 and Frame Relay

SVCs (switched virtual circuits)SVCs (switched virtual circuits) Connections Connections establishedestablished when parties need to when parties need to

transmit, then transmit, then dismantleddismantled once the transmission is once the transmission is completecomplete

PVCs (private virtual circuits)PVCs (private virtual circuits) Connections Connections establishedestablished before data needs to be before data needs to be

transmitted and transmitted and maintainedmaintained after transmission is after transmission is completecomplete

Not dedicated like T-carrier servicesNot dedicated like T-carrier services

CIR (committed information rate)CIR (committed information rate) Guaranteed minimum amount of bandwidth selected Guaranteed minimum amount of bandwidth selected

when leasing a frame relay circuitwhen leasing a frame relay circuit

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

International standard for transmitting data International standard for transmitting data over digital linesover digital linesEstablished by the ITUEstablished by the ITUAll 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

Circuit-switching – max 64 Kbps, multiple channelsCircuit-switching – max 64 Kbps, multiple channels The The D channelD channel is the “data” channel is the “data” channel

Packet-switching – max 16 or 64 Kbps, single channelPacket-switching – max 16 or 64 Kbps, single channel

Two types of ISDN connection: BRI & PRITwo types of ISDN connection: BRI & PRI

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

Average monthly cost - $100-$250Average monthly cost - $100-$250

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

The The Network Termination 1 (NT1)Network Termination 1 (NT1) device connects twisted- device connects twisted-pair wiring at customer’s building with ISDN pair wiring at customer’s building with ISDN terminal terminal equipment (TE)equipment (TE) via RJ-11 or RJ-45 data jacks via RJ-11 or RJ-45 data jacks

A A terminal adapter (TA)terminal adapter (TA) converts digital signals into analog converts digital signals into analog signals for use with ISDN phones and other analog devicessignals for use with ISDN phones and other analog devices

Figure 7-4: A BRI link

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

A variety of ISDN using 23 B channels and one A variety of ISDN using 23 B channels and one 64-Kbps D channel, as represented by the 64-Kbps D channel, as represented by the following notation:following notation: 23B+D23B+D

PRI links use same kind of equipment as BRI PRI links use same kind of equipment as BRI links, but require the services of an extra links, but require the services of an extra network termination device—called a network termination device—called a Network Network Termination 2 (NT2)Termination 2 (NT2)—to handle multiple ISDN —to handle multiple ISDN lineslines

Can achieve 1.544 MbpsCan achieve 1.544 Mbps

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 (from customer (from customer to POP)to POP) portion of a WAN link due to 18,000 linear feet limitation portion of a WAN link due to 18,000 linear feet limitation

Figure 7-5: A PRI link

T-CarriersT-Carriers

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

technologies generally capable of reaching or technologies generally capable of reaching or exceeding 1.544 Mbps throughputexceeding 1.544 Mbps throughput

Cable, DSL, & T-carriersCable, DSL, & T-carriers

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

standards for T1s, fractional T1s, T1Cs, T2s, T3s, or standards for T1s, fractional T1s, T1Cs, T2s, T3s, or T4sT4s

T1 – 24 channels x 64 Kbps = 1.544 MbpsT1 – 24 channels x 64 Kbps = 1.544 Mbps AT&T developed in 1957AT&T developed in 1957

Types of T-CarriersTypes of T-Carriers

The most common T-carrier implementations are The most common T-carrier implementations are T1T1 and and T3T3Signal levelSignal level ANSI standard for T-carrier technology that refers to ANSI standard for T-carrier technology that refers to

its Physical layer its Physical layer electrical signaling characteristicselectrical 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 International vs. NA standard - p. 318International vs. NA standard - p. 318

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

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

Types of T-CarriersTypes of T-Carriers

Figure 7-1: Carrier specifications

T-Carrier CostsT-Carrier Costs

T1T1 $500-$2,000 installation$500-$2,000 installation $500-$2,000 monthly access fees$500-$2,000 monthly access fees

Longer the distance, higher the access feesLonger the distance, higher the access fees

Fractional T1Fractional T1 Only lease needed channels – in 64 Kbps incrementsOnly lease needed channels – in 64 Kbps increments

T3T3 $3,000 installation$3,000 installation Monthly access fees based on usageMonthly access fees based on usage Full usage could max at $18,000/monthFull usage could max at $18,000/month

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 Uses advanced data modulationadvanced data modulation techniques 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

CostsCosts T-1 throughput - $100/monthT-1 throughput - $100/month Consumer-grade (1/2 bandwidth) - $20/monthConsumer-grade (1/2 bandwidth) - $20/month

Types of DSLTypes of DSL

Term Term xDSLxDSL refers to all DSL varieties, of which at refers to all DSL varieties, of which at least least eighteight currently exist currently existDSL types can be divided into two categories:DSL types can be divided into two categories:

Asymmetrical – different speed up & down streamAsymmetrical – different speed up & down stream Symmetrical – same speed up & down streamSymmetrical – same speed up & down stream

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

Downstream – Carrier’s POP to customerDownstream – Carrier’s POP to customer Upstream – Customer to Carrier’s POPUpstream – Customer to Carrier’s POP

Types of DSLTypes of DSL

Table 7-2: Comparison of DSL types

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 modemmodemVoice signals Voice signals use very use very small range small range of of frequencies frequencies between 0 between 0 and 35 KHzand 35 KHz

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 device , a device that that modulatesmodulates and and demodulatesdemodulates signals for signals for transmission and transmission and reception via reception via cable wiringcable wiring

Not a true modem Not a true modem – p. 327– p. 327

Figure 7-11: A cable modem

CableCable

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

frequenciesfrequencies HFC HFC upgradesupgrades to existing cable wiring to existing cable wiring are requiredare required before 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)

Developed in Developed in 1980s1980sCan provide data Can provide data transfer rates from transfer rates from 64 Kbps to 39.8 64 Kbps to 39.8 GbpsGbps using the using the same TDM same TDM technique used by technique used by T-carriersT-carriersKnown Known internationally as internationally as SDH (Synchronous SDH (Synchronous Digital Hierarchy)Digital Hierarchy)

SONET is SONET is self-self-healinghealing

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

Fiber-optics transmission media is used

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

Table 7-3: SONET OC levels

Data rate indicated by Optical Carrier (OC) level

WAN Implementation:WAN Implementation:SpeedSpeed

Table 7-4a: 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 reliableNot very reliable, suited to individual or unimportant , suited to individual or unimportant

transmissions:transmissions:PSTN dial-upPSTN dial-up

Sufficiently reliableSufficiently reliable, suited for day-to-day , 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 reliableVery reliable, suited to mission-critical applications:, 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 WAN security depends in part on the encryption encryption

measures each carriermeasures each carrier provides for its lines 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 policysecurity policy for users in your organization for users in your organization

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

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

VPNs are VPNs are wide wide area networks area networks logically defined logically defined over public over public transmission transmission systemssystems that that serve an serve an organization’s organization’s users, but users, but isolateisolate that that organization’s organization’s traffic from other traffic from other users on the users on the same public same public lineslines

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 (RAS) on the network (RAS)

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

pcAnywhere, MS System Management Server (SMS)pcAnywhere, MS System Management Server (SMS) Internet/Web interfaceInternet/Web interface

Through 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

Remote ConnectivityRemote Connectivity

ICA (Independent Computing Architecture) clientICA (Independent Computing Architecture) client Remote access client developed by Citrix Systems, Remote access client developed by Citrix Systems,

Inc.Inc. Enables remote users to use virtually any LAN Enables remote users to use virtually any LAN

application over any type of connection, public or application over any type of connection, public or privateprivate

Windows 2000 Terminal ServicesWindows 2000 Terminal Services

Remote Access Service (RAS)Remote Access Service (RAS) One of the simplest dial-in serversOne of the simplest dial-in servers This software is included with Windows 2000 ServerThis software is included with Windows 2000 Server

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

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

Serial Line Internet Protocol (SLIP)Serial Line Internet Protocol (SLIP)Can carry only IP packetsCan carry only IP packets

Supports only Supports only asynchronousasynchronous transmission transmission Data transmitted/received doesn’t conform to timing schemeData transmitted/received doesn’t conform to timing scheme Start and stop bitsStart and stop bits

Requires more configuration than PPP – rarely usedRequires more configuration than PPP – rarely used

SLIP and PPPSLIP and PPP

Point-to-Point Protocol (PPP)Point-to-Point Protocol (PPP)

Can carry many different types of Network layer Can carry many different types of Network layer packetspackets

Supports both Supports both asynchronousasynchronous and and synchronoussynchronous transmissiontransmission

Synchronous – data transmitted/received must conform Synchronous – data transmitted/received must conform to timing schemeto timing scheme

Uses timing – not start and stop bitsUses timing – not start and stop bits

Requires less configuration than SLIPRequires less configuration than SLIP