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1999, Cisco Systems, Inc.www.cisco.com
Module 6:WAN Basics
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6-2CSE: Networking FundamentalsWAN Basics 1999, Cisco Systems, Inc.www.cisco.com
Agenda
WAN Basics
Transmission Options
WAN Requirements &
Solutions
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WAN Basics
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A network that serves users across a broadgeographic area
Often uses transmission devices providedby public carriers (Pacific Bell, AT&T, etc.)
This service is commonly referred to asplain old telephone service (POTS)
WANs function at the lower three layers ofthe OSI reference model
Physical layer, data link layer, and networklayer
What Is a WAN?
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WAN Devices
WAN Switch Switches traffic such as Frame Relay,X.25, and SMDS, and operates at thedata link layer
Modem Interprets digital and analog signals,
enabling data transmission overtelephone lines
Access Server A concentration point for dial-in anddial-out connections
CSU/DSU Adapts a terminal physical interface to a
switch interface in a switched-carriernetwork
ISDN Terminal Connects ISDN Basic Rate Interface(BRI) to other interfaces, such asEIA/TIA-232
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WAN Terminating Equipment
Modem
Data Terminal EquipmentDTE
Data Circuit-Terminating Equipment
The Service ProvidersEquipment
DCE
EIA/TIA-232V.35X.21HSSI
To CorporateNetwork
The Customers
Equipment
WAN Provider(Carrier) Network
Physical Cable Types
Usually on the
CustomersPremises
Router
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Dedicated physical circuit established, maintained,and terminated through a carrier network for eachcommunication session
Datagram and data stream transmissions
Operates like a normal telephone call
Example: ISDN
WANModem Modem
Circuit Switching
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Network devices share a point-to-point link totransport packets from a source to a destination
across a carrier network
Statistical multiplexing is used to enable devices toshare these circuits
Examples: ATM, Frame Relay, SMDS, X.25
WAN
Modem Modem
Multiplexing Demultiplexing
Packet Switching
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A logical circuit ensuring reliablecommunication between two devices
Switched virtual circuits (SVCs)
Dynamically established on demand Torn down when transmission is complete
Used when data transmission is sporadic
Permanent virtual circuits (PVCs)
Permanently established
Save bandwidth for cases where certainvirtual circuits must exist all the time
Used in Frame Relay, X.25, and ATM
WAN Virtual Circuits
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OSI Reference Model
PhysicalLayer
DataLink
Layer
Network Layer
LLCSublayer
MACSublayer
S
MDS
X.21bis
EIA/TIA-232EIA/TIA-449V.24 V.35
HSSI G.703EIA-530
HDLC
PPP
WAN Protocols
LAPB
X.25PLP
FrameRela
y
SDLC
WAN Protocols
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SDLC IBMs SNA data link layer communicationsprotocol
HDLC Bit-oriented synchronous data link layer protocol
LAPB Data link layer protocol in the X.25 protocol stack
PPP Provides router-to-router and host-to-networkconnections over sync and async circuits
X.25 Defines connections for remote terminal accessand computer communications in PDNs
ISDN Permits telephone networks to carry data, voice,
and other source traffic
Frame Relay Switched data link layer protocol that handlesmultiple virtual circuits using HDLC; replacingX.25 due to higher efficiency
WAN Protocols
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TransmissionOptions
1999, Cisco Systems, Inc. www.cisco.com
T i i O ti WAN
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Transmission Options or WANServices
Type of Service Analog or Digital Permanentor Temporary
POTS
ISDN
Leased line T1/E1
Frame Relay
X.25
Analog
Digital
Digital
Digital
Digital
Temporary
Permanent
Temporary
Permanent
Permanent
DSL Digital Temporary
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POTS Using Modem Dialup
Widely available
Easy to set up
Dial on demand
Asynchronous transmission
Low cost, usage-based
Lower bandwidth access requirements
Telecommuters
Mobile
Users
Modem
Corporate Network
Server
ModemAccess Router
BasicTelephone
Service
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Integrated Services DigitalNetwork (ISDN)
High bandwidth
Up to 128 Kbps per basic rate interface
Dial on demand
Multiple channels Fast connection time
Monthly rate plus cost-effective,usage-based billing
Strictly digital
LANServer
Company Network
Telecommuter/After-
Hours, Work-at-Home
BRI2B+D
BRI/PRI23B+D
30B+D (Europe)
ISDN
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ISDN
One physical connectionto the ISDN network
23 logical connections
(U.S./Canada) 30 logical connections
(Europe)
Used at central site
Primary Rate Interface (PRI)
1.536Mbps
23B
30B
D
64 Kbps
64 Kbps}
One physical connectionto the ISDN network
Two logical connections
Used at remotetelecommuter site
64 Kbps
64 Kbps
16 Kbps
144Kbps
2B
D}
{
Basic Rate Interface (BRI)
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Leased Line
One connection per physical interface Bandwidth: 56 kbps1.544 Mbps
T1/E1 and fractional T1/E1
Cost effective at 46 hours daily usage
Dedicated connections with predictablethroughput
Permanent
Cost varies by distance
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Frame Relay
Permanent, not dialup
Multiple connections perphysical interface(permanent virtual circuits)
Efficient handling ofbursty (peak performanceperiod) data
Guaranteed bandwidth(typical speeds are
56/64 Kbps, 256 Kbps,and 1.544 Mbps)committed informationrate (CIR)
Cost varies greatly by region
Permanent Virtual Circuit (PVC)
Connecting Offices with Frame
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Free If
Available
Traffic
Time
Peak
CIRWhat YouPay For {
{
FrameRelay
Connecting Offices with FrameRelay
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X.25
Very robust protocol for low-quality lines
Packet-switched
Bandwidth: 9.6 kbps64 kbps
Well-established technology;large installed base
Worldwide availability
X.25DCE
DTE DTE
DCE
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DSL
Modem
End User
DSL
Modem
DSL
DSL is a pair of modems on each end of a copper wire pair
DSL converts ordinary phone lines into high-speed data conduits
Like dial, cable, wireless, and T1, DSL by itself is a transmission
technology, not a complete end-to-end solution End-users dont buy DSL, they buy services, such as high-
speed Internet access, intranet, leased line, voice, VPN, and videoon demand
Service is limited to certain geographical areas
Copper Loop
Ethernet ATM
Digital Subscriber Line (xDSL)
Server
CorporateNetwork
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DSL TechnologyMax. Data Rate
Down/Uplink (bps)Line CodingTechnology
BasebandVoice?
VDSLVery-high-data-rate DSL
5155M / 1.62.3M13M / 1.62.3M
TBD Yes
ADSLAsymmetric DSL
8M / 1M1.5M / 640K
CAP, DMT,G.lite
Yes
IDSLISDN DSL
144K / 144K 2B1Q No
SDSLSymmetric DSL
768K / 768K 2B1Q/CAP No
HDSL2High-data-rate DSL
1.5M2M / 1.5M2M(T1E1 Symmetric)
OPTIS No
Trade-off is reach versus bandwidth
Reach numbers are best-case assuming clean copper
Different Layer 1 transmission technologies, need acommon upper protocol layer to tie them together
Max. ReachFeet (km)
1,000 (0.3)4,500 (1.5)
18,000 (5.5)
18,000 (5.5)+(w/repeaters)
22,000 (6.9)
15,000 (4.6)
Key Attributes
Very fastShort reachNo standard yet
Coexists with POTSTechnology of choice
for residential
Uses existing ISDN CPERelatively slow
SymmetricNo standard
Standard still underdevelopment
DSL Modem Technology
Asynchronous Transfer Mode
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Asynchronous Transfer Mode(ATM)
Technology capable of transferring voice, video, anddata through private and public networks
Uses VLSI technology to segment data, at highspeeds, into units called cells
5 bytes of header information 48 bytes of payload
53 bytes total
Cells contain identifiers that specify the data streamto which they belong
Capable of T3 (44 Mbps), E3 (34 Mbps), and SONETtransmission speeds (OC-1 at 51.84 Mbps to OC-12+)
Primarily used in enterprise backbones or WAN links
DataHeader
5 48
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??
Which Service?
Before deciding,determine the answersto some questions: Will employees use the Internet
frequently? Will the Internet be used for
conducting business?
Is a large volume of trafficbetween branch offices of the
business anticipated? Is videoconferencing or video
training needed betweenlocations?
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How Services Stack Up
Frame Relay 56,000 bps to 45,000,000 bps
ISDN BRI 56,000 to 128,000 bps
ISDN PRI 1,544,000 bps
T1/E1/DS1 1,544,000 bps/2,090,000 bps
Analog modems 33,600 bps
56K modems 56,000 bps
Cable modems 30,000,000 bps
ADSL modems 9,000,000 bps
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Wide-Area NetworkRequirements
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Wide-Area Network
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Wide Area NetworkRequirements
Minimize bandwidth costs
Maximize efficiency
Maximize performance
Support new/emerging applications
Maximize availability Minimize management and maintenance
Multiservice consolidation
Bandwidth efficiency
Performance and QoS guarantees
Emerging IP services
Carrier-class reliability
Ease of operation and management
Manage Bandwidth to
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Manage Bandwidth toControl Cost
Dial-on-demand routing
Bandwidth on demand Snapshot routing
IPX protocol spoofing
Compression
SoftwareCosts 2.7%
HardwareCosts 8.0%
Transmission Costs87.8%
Maintenance1.5%
Source: Data Communications
Dial on Demand Routing
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Dial-on-Demand Routing
Dials connection only when needed
Ideal for low-volume, periodic traffic
Controls usage costs
InterestingTraffic
Remote SiteMain OfficePSTN
Bandwidth-on-Demand
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Adds bandwidth when needed Configurable thresholds
Controls usage costs
Bandwidth-on-Demand
Start FileTransfer
Remote SiteMain Office PSTN
S h t R ti
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ISDNRouting
Table
Routing
Table Link Up
Update Request
Routing Updates
RoutingTable
Updated
Controls exchange of routing updates
Client initiates request
Server responds
Snapshot Routing
IPX P t l S fi
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IPX Protocol Spoofing
Without spoofing
With spoofing
LAN traffic can be very chatty
WAN links are expensive
Solution: Limit unnecessary traffic across WAN
High overhead traffic
across WAN
Spoofing SpoofingMuch reduced overheadacross WAN
Compression
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Compression
Three typesHeader
Link
Payload
Van Jacobson header compression
RFC 1144
Reduces header from 40 to ~5 bytes
Compression
Data
Data
CRC
CRC
TCP/IP Header
hdr
Dial Backup
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Dial Backup
If a primary link goes down or is too busy
Load balancing
Completely customizable
Secondary
Primary
Autodial
DSU/CSUX
WAN Summary
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Operate beyond the local LANs control
Customers pay telephone service providersfor WAN connections such as ISDN, xDSL,
Frame Relay, leased line, X.25, etc. Switching methods include point-to-point,
circuit switching, packet switching,dialup, and WAN virtual circuits
Key devices include WAN switches,access servers, modems, and CSU/DSUs
Bandwidth optimization features areessential for controlling WAN costs
WAN Summary
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