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Topic 8: WAN- Chapter 11 & 12: Wide Area Networks

Business Data Communications, 4e

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LANs, WANs, and MANs

Ownership WANs can be either public or private LANs are usually privately owned

Capacity LANs are usually higher capacity, to carry

greater internal communications load

Coverage LANs are typically limited to a single location WANs interconnect locations MANs occupy a middle ground

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*Comparison ofNetworking Options

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Network Services Available for MAN and WAN

Dialed Circuit Services Direct Dialing (DD) & Wide Area Telephone Services (WATS)

Dedicated Circuit Services Voice-grade circuits Wideband Analog Services T-Carrier Circuits Synchronous Optical Network (SONET)

Circuit-Switched Services Integrated Services Digital Network (Narrowband &

Broadband) Packet-Switched Services

X.25, Frame Relay, ATM, SMDS, and Ethernet/IP

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*WAN Alternatives

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Types of WANs

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Switching Methods

Circuit Switching: Requires a dedicated communication path for duration of transmission; wastes bandwidth, but minimizes delays

Message Switching: Entire path is not dedicated, but long delays result from intermediate storage and repetition of message

Packet Switching: Specialized message switching, with very little delay

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Circuit-SwitchingDefinition: Communication in which a

dedicated communications path is established between two devices through one or more intermediate switching nodes

Dominant in both voice and data communications today e.g. PSTN is a circuit-switched network

Relatively inefficient (100% dedication even without 100% utilization)

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Circuit-Switching Stages

Circuit establishmentTransfer of information

point-to-point from endpoints to node internal switching/multiplexing among

nodes

Circuit disconnect

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Circuit Establishment

Station requests connection from node Node determines best route, sends

message to next link Each subsequent node continues the

establishment of a path Once nodes have established

connection, test message is sent to determine if receiver is ready/able to accept message

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Information Transfer

Point-to-point transfer from source to node

Internal switching and multiplexed transfer from node to node

Point-to-point transfer from node to receiver

Usually a full-duplex connection throughout

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Circuit Disconnect

When transfer is complete, one station initiates termination

Signals must be propagated to all nodes used in transit in order to free up resources

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Public Switched Telephone Network (PSTN)

Subscribers Local loop

Connects subscriber to local telco exchange

Exchanges Telco switching

centers Also known as end

office >19,000 in US

Trunks Connections between

exchanges Carry multiple voice

circuits using FDM or synchronous TDM

Managed by IXCs (inter-exchange carriers)

Services:1. Dial-up line2. Dedicated line

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Integrated Service Digital Network (ISDN) 1st generation: narrowband ISDN

Basic Rate Interface (BRI) two 64Kbps bearer channels + 16Kbps data channel

(2B+D) = 144 Kbps circuit-switched

2nd generation: broadband ISDN (B-ISDN) Primary Rate Interface (PRI) twenty-three 64Kbps bearer channels + 64 data

channel (23B+D) = 1.536 Mbps packet-switched network development effort led to ATM/cell relay

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Past Criticism of ISDN

“Innovations Subscribers Don’t Need” , “It Still Doesn’t Network” , “It Still Does Nothing”

Why so much criticism? overhyping of services before delivery high price of equipment delay in implementing infrastructure incompatibility between providers' equipment.

Didn’t live up to early promises

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ISDN Principles

Support of voice and nonvoice using limited set of standard facilities

Support for switched and nonswitched applications

Reliance on 64kbps connections Intelligence in the networks Layered protocol architecture (can be

mapped onto OSI model) Variety of configurations

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ISDN Network Architecture

Physical path from user to office subscriber loop, a.k.a. local loop full-duplex primarily twisted pair, but fiber use growing

Central office connecting subscriber loops B channels: 64kbps D channels: 16 or 64kbps H channels: 384, 1536, or 1920 kbps

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ISDN B ChannelBasic user channel (aka “bearer

channel”)Can carry digital voice, data, or mixture

Mixed data must have same destination

Four kinds of connections possible Circuit-switched Packet-switched Frame mode Semipermanent

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ISDN D Channel

Carries signaling information using common-channel signaling call management billing data

Allows B channels to be used more efficiently

Can be used for packet switching

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ISDN H Channel

Only available over primary interface

High speed ratesUsed in ATM

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ISDN Basic Access

Basic Rate Interface (BRI) Two full-duplex 64kbps B channels One full-duplex 16kbps D channel Framing, synchronization, and overhead

bring total data rate to 192kbps Can be supported by existing twisted pair

local loops 2B+D most common, but 1B+D available

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ISDN Primary Access

Primary Rate Interface (PRI) Used when greater capacity required No international agreement on rates

US, Canada, Japan: 1.544mbps (= to T1) Europe: 2.048mbps

Typically 23 64kbps B + 1 64kbps D Fractional use of nB+D possible Can be used to support H channels

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Wide Area Networking Issues

Trend towards distributed processing architectures to support applications and organizational needs.

Expansion of wide area networking technologies and services available to meet those needs.

Dedicated vs. Switched WAN Services

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X.25

The oldest packet switched service is X.25, a standard developed by ITU-T. X.25 offers datagram, switched virtual circuit, and permanent virtual circuit services (Data link layer protocol: LAPB (Link Access Procedure-Balanced), network layer protocol PLP).

Although widely used in Europe, X.25 is not widespread in North America. The primary reason is transmission speed, now 2.048 Mbps (up from 64 Kbps).

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Frame Relay Characteristics

Frame relay is a packet switching technology that transmits data faster than X.25. It differs from X.25 and traditional networks in three important ways:1. Frame relay only operates at the data link layer.2. Frame relay networks do not perform error control.3. Frame relay defines two connection data rate that are

negotiated per connection and for each virtual circuit as it is established: Committed information rate (CIR) and Maximum allowable rate (MAR).

Transmission speeds: 56 Kbps to 45 Mbps. Frame relay lacks of standards.

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Frame Relay

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Traditional Packet Switching

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Frame Relay Operation

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Frame Relay Architecture

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Asynchronous Transfer Mode (ATM)

ATM has four important differences from frame relay:

ATM uses fixed packet lengths of 53 bytes (5 bytes of overhead and 48 bytes of user data), which is more suitable for voice transmissions.

ATM provides extensive quality of service information that enables the setting of very precise priorities among different types of transmissions (i.e. voice, video & e-mail; services include CBR, VBR, ABR & UBR).

ATM is scaleable. It is easy to multiplex basic ATM circuits into much faster ATM circuits.

ATM provides connection-oriented services only.

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Virtual Channels & Virtual Paths

Logical connections in ATM are virtual channels analogous to a virtual circuit in X.25 or a

frame relay logical connection used for connections between two end

users, user-network exchange (control signaling), and network-network exchange (network management and routing)

A virtual path is a bundle of virtual channels that have the same endpoints.

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Advantages of Virtual Paths

Simplified network architecture Increased network performance

and reliabilityReduced processing and short

connection setup timeEnhanced network services

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*ATM Cell Format

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ATM Bit Rate Services

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T Carrier Circuits

T Carrier circuits are dedicated digital circuits and are the most commonly used form of dedicated circuit services in North America today.

Instead of a modem, a channel service unit (CSU) or data service unit (DSU) are used to connect the circuit into the network.

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T Carrier Circuits

T-1 circuit (a.k.a. a DS-1 circuit) provides a data rate of 1.544 Mbps. T-1’s allow 24 simultaneous 64 Kbps channels (with TDM) which transport data, or voice messages using pulse code modulation. (64Kbps x 24 = 1.536Mbps)

T-2 circuit (6.312 Mbps) is basically a multiplexed bundle of four T-1 circuits.

T-3 circuit (44.376 Mbps) is equal to the capacity of 28 T-1 circuits (672 64Kbps channels).

T-4 circuit (274.176 Mbps) is equal to the capacity of 178 T-1s.Fractional T-1, (FT-1) offers portions of a 1.544 Mbps T-1 for a

fraction of its full costs.

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T Carrier System

T-Carrier Designation DS DesignationSpeed

T-1

T-2

T-3

T-4

DS-0

DS-1 (24 DS-0)

DS-2 (96 DS-0)

DS-3 (672 DS-0)

DS-4 (178 T-1)

64 Kbps

1.544 Mbps

6.312 Mbps

44.375 Mbps

274.176 Mbps

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*Digital signal X (DS-x) A term for the series of standard digital transmission rates or levels based on DS0, a transmission rate of 64 Kbps, the bandwidth normally used for one telephone voice channel.

Both the North American T-carrier system and the European E-carrier systems of transmission operate using the DS series as a base multiple. The digital signal is what is carried inside the carrier system.

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*E Carrier Circuits (European Standard)

E1 - 2.048 Mbps (32 DS-0). E1 carries at a higher data rate than T-1 because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal. E1 and T-1 can be interconnected for international use.

E2 - 8.448 Mbps. E3 - 16 E1 signals, 34.368 Mbps. E4 - four E3 channels, 139.264 Mbps. E5 - four E4 channels, 565.148 Mbps.

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Synchronous Optical Network (SONET)

An Optical Network for Dedicated Connection Services.

SONET has been accepted by the U.S. Standards Agency (ANSI) as a standard for optical (fiber) transmission at gigabits per second speed.

The International Telecommunications Standards Agency (ITU-T) also standardized a version of SONET under the name of synchronous digital hierarchy (SDH). The two are very similar and can be easily interconnected.

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SONETSONET Designation SDH Designation Speed

OC-1

OC-3

OC-9

OC-12

OC-18

OC24

OC-36

OC-48

OC-192

STM-1

STM-3

STM-4

STM-6

STM-8

STM-12

STM-16

51.84 Mbps

155.52 Mbps

466.56 Mbps

622.08 Mbps

933.12 Mbps

1.244 Gbps

1.866 Gbps

2.488 Gbps

9.952 Gbps

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*Switched Multimegabit Data Service (SMDS)

Characteristics of SMDS: Uses ATM-like 53-byte cells, but a different address

format. Provides datagram-based transmission services. So, it is

a connectionless service. Data unit is large enough to encapsulate frames of

Ethernet, token ring and FDDI. An unreliable packet service like ATM and frame relay.

Like ATM and frame relay, SMDS does not perform error checking; the user is responsible for error checking.

Speed ranging 56kbps - 44.375Mbps. Not yet a widely accepted standard. Its future is uncertain.

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*SMDS Network Components

SNI: Subscriber network interfaceCPE: Customer premises equipment

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*SMDS Interface Protocol (SIP)SIP is used for communications between CPE and SMDS carrier equipment

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Ethernet/IP Packet Network

A MAN/WAN service started in 2000 X.25, ATM, frame relay and SMDS use

traditional PSTN and thus provided by the common carrier such as AT&T and BellSouth. ISP with Ethernet/IP packet service laid their own gigabit Ethernet fiber-optic networks in large cities.

All traffic entering the network must be Ethernet using IP.

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Multiprotocol Label Switching (MPLS)

MPLS is a standards-approved technology for speeding up network traffic flow and making it easier to manage.

MPLS sets up a specific path for a given sequence of packets, identified by a label put in each packet, thus saving the time needed for a router to look up the address to the next node to forward the packet to.

MPLS is called multiprotocol because it works with the IP, ATM, and frame relay network protocols.

MPLS allows most packets to be forwarded at the layer 2 (switching) level rather than at the layer 3 (routing) level.

In addition to moving traffic faster overall, MPLS makes it easy to manage a network for quality of service (QoS).

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MPLS Services in the Market

In January 1999, AT&T announced the first VPN services to be based on MPLS --- its IP-Enabled Frame Relay service.Cable & Wireless and Cisco Systems conducted a trial of IP-VPN service based on MPLS with Hongkong Telecom in March, 1999. MCI/Worldcom Started to offer MPLS-based IP-VPN service in March, 1999.

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*Internet Backbone Networks-- Major companies

AT&T Network Services (http://www.ipservices.att.com/backbone/)BBN Planet (GTE)Cable & Wireless USA Sprintlink UUNET, a part of MCI WorldCom

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AT&T Network Service

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GTE BBN Planet

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Cable & Wireless USA

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*Cable & Wireless USA

Offers a world-wide voice, data, Internet and messaging services.

Its Internet backbones connects to 70+ countries.

Service area includes switched services from most of US cities to all 50 states, Puerto Rico, the Virgin Islands and more than 200 countries.

Private line and managed data services are available between most major US metropolitan areas and key business centers around the world.

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MCI UUNET

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*More WAN Protocols

ATM Encapsulation Methods (LANE) CDPD FUNI (to provide users with the ability to connect

between ATM networks and existing frame-based equipment (e.g., routers)

GPRS (allows GSM networks to be truly compatible with the Internet)

IP Switching Protocols SS7 Suite (Signaling System 7 by CCITT) Tag Switching Protocols (e.g. TDP - Tag Distribution Protocol) UMTS (a protocol for cellular network) Telephony Voice over IP (VoIP, enables users to carry voice traffic over an

IP network)

57Figure 9-11 Gigapops and high speed backbones of Internet 2/Abilene, vBNS, and CA*Net 3

AbilenevBNS (very high speed Backbone Network Services )CA*Net 3

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Abilene

Abilene is an advanced backbone network that supports the development and deployment of the new applications being developed within the Internet2 community. Abilene connects regional network aggregation points, called gigaPoPs, to support the work of Internet2 universities as they develop advanced Internet applications. Abilene complements other high-performance research networks.

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ISP Point-of Presence

Modem Pool

Individual Dial-up Customers

Corporate T1 Customer

T1 CSU/DSU

Corporate T3 Customer

T3 CSU/DSU

Corporate OC-3 Customer

ATM Switch

Layer-2 Switch

ISP POP

ISP POP

ISP POP

NAP/MAE

Figure 9-2 Inside an ISP Point of Presence

RemoteAccess Server

ATM Switch

60Figure 9-9 Fixed wireless architecture

Wireless Access Office

WirelessTransceiver

Customer Premises

Telephone

DSL Modem

Hub

Computer Computer

CustomerPremises

CustomerPremises

MainDistribution

Frame

VoiceTelephoneNetwork

DSL AccessMultiplexer

WirelessTransceiver

Router

Line Splitter

Individual Premise

IndividualPremise

IndividualPremise

ISP POP

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Web Server

Web Site

WAP Proxy

WAP Gateway

Wireless Telephony Application Server

HTTP Requests

HTTP Responses(plus HTML, jpeg, etc.)

Figure 9-10 Mobile wireless architecture for WAP applications

WAEResponses

(plus WML, etc.)

WAERequests

WAP Client

WirelessTransceiver

WAEUser

AgentWAE

Requests

WAEResponses

(plus WML, etc.)

WAERequests

WAEResponses

(plus WML, etc.)

62Figure 9-12 Inside the Pacific/Northwest Gigapop

Router

High-speedRouter

Abilene

DREN

WSU

Boeing

U Idaho

High-speedRouter

Router

Router

Montana State U

U Montana

U Alaska

Portland POP

Microsoft

Router Router

Switch

U Wash

Router

Switch Switch

CA*Net 3Sprint UUNet Verio

Router

AT&T

Sprint

Router

OC-48OC-12T-3

HSCC

Switch

SCCD