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WAN - wide area networks - 1
A WAN is a data communications
network that covers a relatively
broad geographic area.

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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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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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WAN: Physical Layer - 1
 Describe interface between DTE and DCE.
 DCE is the service provider.
 DTE is the attached device.

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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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WAN: Data Link Layer
 Common data link encapsulation
protocols for synchronous serial lines:

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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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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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Interfacing WAN Service Providers

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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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WAN Encapsulation Protocols

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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

Circuit Switched Networks - 1

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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

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

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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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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WAN Links
 Dedicated (leased) lines or switched
connections.

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