This document discusses wide area networks (WANs) and the various technologies used to connect locations over long distances. It covers both analog technologies like PSTN lines as well digital technologies including T-carrier lines, frame relay, ATM, and packet switching networks. Specific details are provided on connection speeds, reliability, and costs to consider for each technology. Equipment required at each location is also outlined, such as CPE, DCE, DTE, and wiring closets.

1. Chapter 12
Wide Area Networks
Networking Concepts – Eric Vanderburg ©2005

2. WANs
 WANs
look just like LANs to the end
user except accessing them is slower.
 WAN communication links:
 Packet-switching
networks
 Fiber-optic
cable
 Microwave transmitters
 Satellite links
 Cable television coax systems
Networking Concepts – Eric
Vanderburg ©2005

3. Considerations
 Speed
 CIR
(Committed Information Rate) – The
minimum guaranteed transmission rate
 Reliability
 Cost
 Availability
Networking Concepts – Eric
Vanderburg ©2005

4. WAN Technologies
 Analog
 Digital
 Packet
Switching
Networking Concepts – Eric
Vanderburg ©2005

5. Analog
PSTN (Public Switched Telephone Network) &
POTS (Plain Old Telephone System) – circuit
switched – worse connection over longer distance
PSTN Line Types:


1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Voice Only
Voice with minimal quality control
Voice and radio with tone conditioning
Less than 1200bps data applications
Basic data
Voice and data over trunk circuits
Voice and data over private lines
Voice and data over trunks between computers
Voice and video
Application relays, quality data
Networking Concepts – Eric
Vanderburg ©2005

6. Analog (continued)
 Lease
analog circuit to improve quality
and speed. No dial on demand lag
 Line conditioning – involves testing and
line upgrades to maintain a quality
standard
 consistent
transmission rate, improved
signal quality, & reduced interference and
noise
 C1 - C8 & D
Networking Concepts – Eric
Vanderburg ©2005

7. Analyzing analog needs
 How
often do you need the connection?
– always on, sometimes…
 Bandwidth
 Availability
 Best
for intermittent connections
Networking Concepts – Eric
Vanderburg ©2005

8. Digital Connectivity

DDS (Digital Data Service) – All digital WAN solutions






Synchronous dedicated point to point circuits with few errors
2.4, 4.8, 9.6, or 56 Kbps with nearly 99% error-free
transmission
ISDN
T-Carrier (also E & J) *see handout* 64k per channel
Switched 56k
CSU/DSU (Channel Service Unit/Data Service Unit) –
WAN communication device for digital connections –
hands data off to bridge or router
Networking Concepts – Eric
Vanderburg ©2005

9. T Carrier
 Multiplexing
(muxing) - Combining server
communication streams into one.
 DS specifications
DS-0 – 1 channel, 64kbps
 DS-1 – T1, 24 channels, 1.544Mbps
 DS-1c – 2 T1’s, 3.152Mbps
 DS-2 – T2 (4 T1’s), 6.312Mbps
 DS-3 – T3 (28 T1’s), 44.736Mbps, fractional T3
lines go in 6 Mbps sets
 DS-4 – T4 (168 T1’s), 274.76Mbps, requires fiber

Networking Concepts – Eric
Vanderburg ©2005

10. Other Digital technologies

Switched 56k






Charged per minute
Dial on demand
Faster because it is digital when analog did not support 56k
ISDN
B-ISDN (Broadband ISDN) – Data transfers over fiber
and works with ATM, SONET & Frame Relay to give
between 64k & 100Mbps
Packet Switching (Internet) – data is broken into
packets and then sequenced and sent to the
destination on the best path
Networking Concepts – Eric
Vanderburg ©2005

11. Virtual Circuits
 Virtual
Circuits – logical dedicated
pathways between points (created
during the negotiation stage – Session
layer)
 SVC
(Switched Virtual Circuit) – set up and
taken down as needed (on demand)
 PVC (Permanent Virtual Circuit) – created
and maintained indefinitely
Networking Concepts – Eric
Vanderburg ©2005

12. X.25
 SVC
connection, originally used for
mainframe to terminal connections
 64kbps-2Mbps
 Equipment
 X.25
NIC
 PAD (Packet Assembler/Disassembler)
 LAN/WAN X.25 Gateway
Networking Concepts – Eric
Vanderburg ©2005

13. Frame Relay
 Uses
PVC’s
 No error checking
 Faster performance
 Variable length frames
 Less expensive carrier type compared to ATM,
T1
 Layer 2 technology
 Purchased in 64k increments
 Requires CSU/DSU
Networking Concepts – Eric
Vanderburg ©2005

14. ATM

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

Can be used for voice, data, & fax
Can use SVC or PVC
Layer 2
Transport steps



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
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Header (first 5 bytes) is read to virtual circuit
Virtual circuit is used to as the pathway
Receiving node gets the cell and analyzes the header to see who it is
for
Versatile like Ethernet is
Max bandwidth is 2.4Gbps
ATM central connecting devices are all called switches that
operate like:


Hubs to forward data from one computer to another within a network.
Router-like devices to forward data at high speeds to remote
networks.
Networking Concepts – Eric
Vanderburg ©2005

15. Others
 FDDI
 SONET
 SMDS
(Switched Multimegabit Data Service) –
1.544Mbps – 45Mbps
Uses cells (53bytes)
 No error checking
 802.6 MAN standard along with billing services
 uses the DQDB (Distributed Queue Dual Bus) as
the interface and access method for the network.
SMDS is a dual-bus topology that forms a ring that
is not closed

Networking Concepts – Eric
Vanderburg ©2005

16. Equipment
 CPE
(Customer Premises Equipment) – The
equipment located at the customer site. Ex:
routers, modems, CSU/DSU
 Demarcation Point – the spot where the CPE
ends and the ISP’s responsibility begins
 Local Loop/Last Mile – The cabling between
the demarcation point and the CO (Central
Office) or POP (Point of Presence)
Networking Concepts – Eric
Vanderburg ©2005

17. Equipment
 DCE
(Data Circuit-Terminating
Equipment/Data Communications
Equipment) – sends and receives data
from the local loop/last mile.
 DTE (Data Terminal Equipment) – The
device that sends data from the
customer network to the DCE
 Router
or Bridge
Networking Concepts – Eric
Vanderburg ©2005

18. Wiring Closets
 MDF
(Main distribution
facility) – Central wiring
closet when more than
one is used
 IDF (Intermediate
distribution facility) –
wiring closets off the
MDF
Networking Concepts – Eric
Vanderburg ©2005