Wide Area Networks
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Transcript of Wide Area Networks
Wide Area NetworksWide Area Networks
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Wide Area Networks (WANs)Wide Area Networks (WANs)
WAN Technologies Ordinary telephone line and telephone modem.
Point-to-Point Leased lines
Public switched data network (PSDN)
Send your data over the Internet securely, using Virtual Private Network (VPN) technology
VPNPSDN
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Evolution of WAN TechnologyEvolution 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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CarriersCarriers
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.Transmission Carriers in the U.S.
Domestic Inter-LATA Carriers (U.S.) Domestic means within a country
Inter-LATA service (between LATAs)
Carriers are called inter-exchange carriers (IXCs).
Competition has long existed in this arena.
IXC
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Transmission Carriers Between Transmission Carriers Between CountriesCountries
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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POPPOP
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 ICCsConnecting to IXCs and ICCs
POPat LECSwitchingOffice
Trunk Line
IXCSwitchingOffice
IXCSwitchingOffice
ICCSwitchingOffice
The POP also links LEC and CAP subscribers to IXCs and ICCs.
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CircuitCircuit
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 WireSatellite
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Circuit SpeedsCircuit 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 SpeedsCircuit Speeds
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, 56 kbps
Use to be the most widely used digital circuit
Inexpensive. In range of most demand.
Digital64 kbps56 kbps
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Circuit SpeedsCircuit Speeds
T1 Circuits
1.544 Mbps
Designed to multiplex 24 digital voice lines
Can be used as a single high-speed data pipe
Sufficient for many uses to connect sites
Also called DS1 for the signaling format
Very widely used: In the critical speed range for many “high speed” corporate uses and not too expensive
T11.544 Mbps
DS1
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Circuit SpeedsCircuit Speeds
Fractional T1 Circuits Many firms need between 64 kbps and T1 speeds
128 kbps, 256 kbps, 384 kbps, 768 kbps common
Each vendor only offers some options
Different vendors offer different options
768 kbps usually is the fastest offering
Fractional T1128 kbps256 kbps384 kbps768 kbps
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Circuit SpeedsCircuit Speeds
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
T344.7 Mbps
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Circuit SpeedsCircuit Speeds
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
E Series2.048 Mbps34.4 Mbps
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Circuit SpeedsCircuit Speeds
Higher-Speed Digital Lines (SONET/SDH) Single world-wide standard for very high speeds
In U.S., called SONET (Synchronous Optical Network)
In Europe, elsewhere called SDH (Synchronous Digital Hierarchy)
OC circuit designations. Multiples of 51.84 Mbps
OC3: 156 Mbps
OC12: 622 Mbps
Defined up to a few Gigabits per second
SONETSDH
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Types of Traditional Telephone Types of Traditional Telephone CircuitsCircuits
Dial-Up Service (Any-to-Any)
Leased Lines Point-to-point only Cheaper for high volumes of use
Leased Line
SwitchedDial-UpService
Seattle
Washington, D.C.
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Leased Line ServiceLeased Line Service
Customer Premises A Customer Premises B
SwitchingOffice
SwitchingOffice
SwitchingOffice
TrunkLine
TrunkLine
LocalLoop Local
Loop
Leased LinesMay Pass ThroughMultiple Switches,
Even MultipleCarriers
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Leased LinesLeased 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
LeasedLine
Corporate-ownedSwitch
See this web site for price example
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Data NetworksData Networks
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
Data Network
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Circuit-Switched Data NetworksCircuit-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 NetworksCircuit-Switched Data Networks
Dedicated Capacity Circuit is maintained during the duration of the call
Capacity is always available
You must pay for this constant capacity
Most data transmission is burst, with long silences between transmission
Utilization of the line may be as low as 5%
So circuit-switched services is inherently expensive
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ADSL versus Business-Class Symmetric ADSL versus Business-Class Symmetric Digital Subscriber Line (DSL) ServicesDigital Subscriber Line (DSL) Services
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Packet-Switched Data NetworksPacket-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 SwitchesPacket Switches
Packet Switched Networks have Switches Route the packets through the network
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Packet Switching is EfficientPacket Switching is Efficient
Packets from several stations multiplexed over trunk lines between switches No costly dedicated transmission capacity
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Error Checking in Packet-Switched Data Error Checking in Packet-Switched Data NetworksNetworks
The Process
Sender transmits the packet
Sender maintains the packet in memory
Receiver checks the packet for errors
If there is an error, asks for a retransmission
Sender retrieves from memory, retransmits
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Error Checking in Packet-Switched Data Error Checking in Packet-Switched Data NetworksNetworks
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 NetworksReliable Packet-Switched Data Networks
Check for Errors at Each Hop Have reduced throughput Have latency (delays)
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ErrorCheck
ErrorCheck
ErrorCheck
ErrorCheck
ErrorCheck
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Unreliable Packet-Switched Data Unreliable Packet-Switched Data NetworksNetworks
No Error Check at Each Packet Switch Check only once, at receiving host Low latency, load on switches
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ErrorCheckNo Error Checks at Switches
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Unreliable ServiceUnreliable Service
Most Packet Switched Networks Today are Unreliable
Little Need: Error rates are low with modern lines, switches
Reduces delays: critical for some applications
Low load on the switches for high throughput
Better to check once, on the receiving host, than at every switch
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Connectionless ServiceConnectionless 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
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DecisionDecision
Decision
See some Level 3 services
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Connection-Oriented ServiceConnection-Oriented Service
Routing decision is made once, at start of connection
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DecisionDecision
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Connection-Oriented ServiceConnection-Oriented Service
First decision establishes a path (virtual circuit) All subsequent packets follow the virtual circuit
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Virtual Circuit
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Connection-Oriented Packet-Switched Connection-Oriented Packet-Switched Data NetworksData Networks
All Commercial Packet Switched Networks are Connection-Oriented Reduces loads on the switches for higher throughput
Lower 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 Connections in Packet-Switched Data NetworksNetworks
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
Site 1Site 1
Site 3Site 3 Site 4Site 4
Site 2Site 2PVC
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Connections in Packet-Switched Data Connections in Packet-Switched Data NetworksNetworks
Switched Virtual Circuits
Established at call setup
Only available in some packet switched networks
Will provide the any-to-any flexibility of circuit-switched data networks AND the efficiency of connection-oriented packet switching
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OSI LayeringOSI 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