This document provides an overview of WAN basics, including that a WAN covers a broad geographic area using devices like routers and switches. It describes the physical and data link layers that WANs operate on and common standards and protocols used at each layer like PPP, Frame Relay, and ISDN. Key concepts covered include the interfaces between the user (DTE) and provider (DCE), as well as encapsulation protocols for different WAN technologies like dedicated leased lines, circuit-switched, and packet-switched networks.

1. WAN Basics
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2. WAN - wide area networks - 1
A WAN is a data communications
network that covers a relatively
broad geographic area.
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3. WAN Devices
 Routers - provide services like
internetworking and WAN interface ports.
 Switches - for voice, data and video
communications.
 Modems - interface voice-grade services.
 Communication Servers - for dial-in and
dial-out services.
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4. WAN Technology Overview
 WAN operate at Physical and Data Link layers
(layers 1 and 2).
 Physical layer technologies describe electrical,
mechanical, operational, and functional
connections for WAN services.
 Data Link protocols describe how frames are
carried between systems on a single data link.
 Include protocols that operate over:
 Point-to-point (PPP).
 Multipoint,
 Frame Relay - multi-access switched service.
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5. WAN: Physical Layer - 1
 Describe interface between DTE and DCE.
 DCE is the service provider.
 DTE is the attached device.
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6. WAN: physical Layer - 2
 Physical Layer Standards:
 EIA/TIA-232 - RS232, speeds up to 64Kbps.
 EIA/TIA-449 - RS449, up to 2Mbps, longer cable runs
than RS232.
 V.24 - similar to RS232.
 V.35 - synchronous communications between network
access device and packet network (up to 48Kbps).
 X.21 - synchronous digital lines (Europe/Japan).
 G.703 - specs for connection between DTE & phone
company equipment using BNC, E1.
 EIA-530 - electrical implementation of RS449.
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7. WAN: Data Link Layer
 Common data link encapsulation
protocols for synchronous serial lines:
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8. ISDN - Integrated Services Digital Network
 Digital services that transmits voice and
data over existing phone lines.
 2 ISDN services: BRI & PRI
 BRI - basic rate interface - “2B+D”
B channel - 64Kbps for data
 D channel - 16Kbps for control.
 Total of 144 Kbps of bandwidth.
 PRI – “23B+D”
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9. WAN Terminology
 CPE - customer premises equipment
 all devices on subscriber’s premises.
 POP - point of presence
 where WAN provider services are connected at
the building.
 Demarcation (demarc)
 where CPE ends, and local loop begins, usually
at the POP.
 Central office (CO) switch
 switching facility of WAN service provider.
 Local Loop (last mile)
 cabling from demarc to CO.
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10. Interfacing WAN Service Providers
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11. User to Provider Interface - DTE/DCE
 DTE - the user end of the WAN connection.
 DCE - provider’s end - converts user data into a
form for WAN transmission - e.g. modem,
CSU/DSU, TA/NT1, Frame relay switch.
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12. WAN Encapsulation Protocols
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13. Dedicated (Leased lines)
 Long connect times
 Guaranteed bandwidth
 Short distance
 Usually synchronous (Clock)
 Physical standards
 EIA/TIA-232
 EIA/TIA-449
 V.35
 X.21
 EIA-530 13

14. Circuit Switched Networks - 1
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15. Circuit Switched Networks - 2
 Types:
 Asynchronous serial.
 ISDN, Basic Rate Interface (BRI), and ISDN Primary
Rate Interface (PRI).
 Uses/features:
 Guaranteed bandwidth for ISDN.
 Readily available (Especially Async)
 Typically lower bandwidth than leased lines.
 Flag fall and connect time billing.
 Good backup connection.
 A connection from a small remote site.
 Short-term on-demand access is required. 15

16. Packet Switched Networks - 1
 Uses virtual circuits within the Carriers
network.
 Doesn’t offer a strictly guaranteed bandwidth
as customers share the switched network. 16

17. Packet Switched Networks - 2
Efficient use of the carriers network
usually results in lower tariffs for a given
bandwidth.
 High bandwidths available.
 For highly meshed networks, virtual
circuits are considerably cheaper than
leased lines.
 Suited to long connect times and
distances.
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18. Packet switched vs Circuit switched
 Frame relay is packet switched, i.e. on a PVC
packets are transmitted. PVC is the link, line
or channel and data is switched on the line.
 ISDN is circuit switched, i.e. the link or line is
connected when needed, then data is sent.
 Generally low bandwidth.
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19. WAN Links
 Dedicated (leased) lines or switched
connections.
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