Transcript Enterprise Internets

Wide Area Networks
Wide Area Networks (WANs)

WAN Technologies
 Ordinary
telephone line and telephone modem.
 Point-to-Point
 Public
Leased lines
switched data network (PSDN)
 Send
your data over the Internet securely, using Virtual
Private Network (VPN) technology
PSDN
VPN
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Evolution of WAN Technology
Layer
1: Leased line service and networks
Layer 2: Public switched data networks (PSDN)
Layer 3: Virtual Private Networks (VPN) over
the Internet and IP carrier networks
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Carriers

Organizations have the right to lay wires in their
premises

Organizations do not have right of ways between
sites

Organizations must turn to a transmission carrier

Carriers have rights of way. To compensate for
this power, they are regulated
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Transmission Carriers in the U.S.

Domestic Inter-LATA Carriers (U.S.)
 Domestic
means within a country
 Inter-LATA service
 Carriers
(between LATAs)
are called inter-exchange carriers (IXCs).
 Competition
has long existed in this arena.
IXC
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Transmission Carriers Between
Countries

International Carriers
 Called
International Common Carriers (ICCs)
 Each pair of countries negotiates on what ICCs to
allow, like we saw last class meeting.
 When you call internationally, you use one ICC, not
two--one at each end.
ICC
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POP

All competitors can interconnect their customers
into an integrated system

The key to competition
 Without
it, new competitors could not get a critical
mass of customers
 With
a POP, even a small customer base is no problems,
because these customers can reach any other telephone
customers in the world.

Trunk lines connect carrier switching offices
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Connecting to IXCs and ICCs
IXC
Switching
Office
Trunk Line
POP
at LEC
Switching
Office
IXC
Switching
Office
ICC
Switching
Office
The POP also links LEC and CAP subscribers to IXCs and ICCs.
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Circuit
 End-to-End
Connection Between Stations
 May
Pass through Several Switches
 May Go Through Multiple Transmission Media
 Maintained throughout the call

May flow through multiple carriers
 LEC,
ICC, etc.
Wire
Satellite
Wire
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Circuit Speeds

Voice Grade Circuits
 Ordinary
telephone line, except point-to-point
 Analog line: high error rate
 Requires modem
 Worst of all, slow: Under ~35 kbps
Analog
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Circuit Speeds

Digital
64 kbps
56 kbps
64 kbps Circuits
 Digital
line: low error rate
 If
you digitize an analog telephone system, it generates
64 kbps in data
 Used
to be sufficient for linking people from home
 Used
to be sufficient for linking branch offices
 Sometimes,
 Use
56 kbps
to be the most widely used digital circuit
 Inexpensive.
In range of most demand.
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Circuit Speeds

T1
1.544 Mbps
T1 Circuits
 1.544
Mbps
 Designed
 Can
DS1
to multiplex 24 digital voice lines
be used as a single high-speed data pipe
 Sufficient
 Also
for many uses to connect sites
called DS1 for the signaling format
 Very
widely used: In the critical speed range for many
“high speed” corporate uses and not too expensive
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Circuit Speeds

Fractional T1
128 kbps
256 kbps
384 kbps
768 kbps
Fractional T1 Circuits
 Many
 128
firms need between 64 kbps and T1 speeds
kbps, 256 kbps, 384 kbps, 768 kbps common
 Each
vendor only offers some options
 Different
 768
vendors offer different options
kbps usually is the fastest offering
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Circuit Speeds

T3
44.7 Mbps
T3 Circuits
 44.7
Mbps in U.S.
 For firms needing very high speeds
 Uncommon now but increasing

Other T-Series Speeds
 There
are faster T-series circuits, but they are rarely
used.
 There are T2 circuits, but they are not offered
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Circuit Speeds

E Series
2.048 Mbps
34.4 Mbps
E Series Circuits
 Used
in Europe, other areas
 Created
by CEPT (Conference of European Postal and
Telecommunications Authorities)
 E1:
2.048 Mbps (faster than T1)
 E3:
34.4 Mbps
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Circuit Speeds

Higher-Speed Digital Lines (SONET/SDH)
 Single
 In
world-wide standard for very high speeds
U.S., called SONET (Synchronous Optical Network)
 In
Europe, elsewhere called SDH (Synchronous Digital
Hierarchy)
 OC
circuit designations. Multiples of 51.84 Mbps
 OC3:
 OC12:
156 Mbps
622 Mbps
 Defined
SONET
SDH
up to a few Gigabits per second
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Types of Traditional Telephone
Circuits

Dial-Up Service (Any-to-Any)

Leased Lines
 Point-to-point
only
 Cheaper for high volumes of use
Switched
Dial-Up
Service
Seattle
Leased Line
Washington, D.C.
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Leased Line Service
Switching
Office
Leased Lines
May Pass Through
Multiple Switches,
Even Multiple
Carriers
Trunk
Line
Switching
Office
Local
Loop
Customer Premises A
Trunk
Line
Switching
Office
Local
Loop
Customer Premises B18
Leased Lines
 Limited
to 2 points
 Cheaper
than dial-up on high-volume routes
 Companies
can build enterprise networks from
meshes of leased lines between sites
Corporate-owned
Switch
Leased
Line
See this web site for price example
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Data Networks
Data Network
 Data
Networking Alternatives
 Use
the telephone network and modems (slow)
 Lease lines, add own switching (complex)
 Data
Networks
 Optimized
for data transmission
 Customer only has to connect to the data network
 Carrier handles transmission, switching, management
 Shown as cloud to indicate lack of need to know details
 Two types: circuit-switched and packet-switched
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Circuit-Switched Data Networks

Switched for any-to-any communication

Just dial the number of the party being called

Very flexible
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Circuit-Switched Data Networks

Dedicated Capacity
 Circuit
is maintained during the duration of the call
 Capacity
 You
is always available
must pay for this constant capacity
 Most
data transmission is burst, with long silences
between transmission
 Utilization
 So
of the line may be as low as 5%
circuit-switched services is inherently expensive
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ADSL versus Business-Class Symmetric
Digital Subscriber Line (DSL) Services
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Packet-Switched Data Networks

Messages are Broken into Small Pieces (Packets)
 Flow
through the network more easily than long
messages, like sand in an hourglass
Packet
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Packet Switches

Packet Switched Networks have Switches
 Route
the packets through the network
Switch
1
3
2
4
6
5
7
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Packet Switching is Efficient

Packets from several stations multiplexed over
trunk lines between switches
 No
costly dedicated transmission capacity
1
2
Trunk Line
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Error Checking in Packet-Switched Data
Networks

The Process
 Sender
transmits the packet
 Sender
maintains the packet in memory
 Receiver
 If
1
2
checks the packet for errors
there is an error, asks for a retransmission
 Sender
retrieves from memory, retransmits
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Error Checking in Packet-Switched Data
Networks

Considerations in
 Adds
delay (latency) every time it is done
 Places
a heavy load on the switch, lowering throughput
 Not
often needed, because there are very few errors on
modern transmission lines.
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Reliable Packet-Switched Data Networks

Check for Errors at Each Hop
 Have
reduced throughput
 Have latency (delays)
Error
Check
Error
Check
Error
Check
Error
Check
Error
Check
1
2
3
4
5
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Unreliable Packet-Switched Data
Networks

No Error Check at Each Packet Switch
 Check
only once, at receiving host
 Low latency, load on switches
Error
Check
No Error Checks at Switches
1
2
3
4
5
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Unreliable Service

Most Packet Switched Networks Today are
Unreliable
 Little
Need: Error rates are low with modern lines,
switches
 Reduces
 Low
delays: critical for some applications
load on the switches for high throughput
 Better
to check once, on the receiving host, than at
every switch
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Connectionless Service
 Routing
Decision for each packet at each switch
 Places
a heavy load on switches
 Unnecessary work: subsequent packets usually travel
same path, because conditions rarely change between
packets
Decision
1
Decision
3
2
4
6
Decision
5
7
Decision
See some Level 3 services
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Connection-Oriented Service

Routing decision is made once, at start of
connection
Decision
1
Decision
3
2
4
6
Decision
5
7
Decision
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Connection-Oriented Service

First decision establishes a path (virtual circuit)
 All
subsequent packets follow the virtual circuit
1
3
2
4
6
Virtual Circuit
5
7
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Connection-Oriented Packet-Switched
Data Networks

All Commercial Packet Switched Networks are
Connection-Oriented
 Reduces
 Lower

loads on the switches for higher throughput
latency because of less work at each switch
When marketers say “packet switched,” they now
automatically include the concept of connection
orientation
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Connections in Packet-Switched Data
Networks

Permanent Virtual Circuits (PVCs)
 Established
for long durations
 Set up weeks or months ahead of time
 If your firm has four sites, need 6 PVCs
 Makes packet switched networks like network of leased
lines
PVC
Site 1
Site 2
Site 3
Site 4
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Connections in Packet-Switched Data
Networks

Switched Virtual Circuits
 Established
 Only
at call setup
available in some packet switched networks
 Will
provide the any-to-any flexibility of circuitswitched data networks AND the efficiency of
connection-oriented packet switching
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OSI Layering

Connectionless Service
 OSI
Layer 3 (Networking)
 Routing across a series of packet switches
 Alternative Routing

Connection-Oriented Service
 OSI
Layer 2 (Data Link)
 Reduces network to a single path
 Loses flexibility of alternative routing after virtual
circuit is established
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