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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3Switch

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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

11 22Trunk Line

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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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5

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3Decision

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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5

4

7

3Decision

DecisionDecision

Decision

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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