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Topic 8: WAN - Chapter 11 & 12: Wide Area Networks. Business Data Communications, 4e. 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

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lans wans and mans
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
network services available for man and wan
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
switching methods
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
circuit switching
Circuit-Switching
  • Definition: 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)
circuit switching stages
Circuit-Switching Stages
  • Circuit establishment
  • Transfer of information
    • point-to-point from endpoints to node
    • internal switching/multiplexing among nodes
  • Circuit disconnect
circuit establishment
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
information transfer
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
circuit disconnect
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
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)

Public Switched Telephone Network (PSTN)

Services:

1. Dial-up line

2. Dedicated line

integrated service digital network isdn
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
past criticism of isdn
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
isdn principles
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
isdn network architecture
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
isdn b channel
ISDN B Channel
  • Basic 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
isdn d channel
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
isdn h channel
ISDN H Channel
  • Only available over primary interface
  • High speed rates
  • Used in ATM
isdn basic access
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
isdn primary access
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
wide area networking issues
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
slide24
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).

frame relay characteristics
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.
asynchronous transfer mode atm
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.
virtual channels virtual paths
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.
advantages of virtual paths
Advantages of Virtual Paths
  • Simplified network architecture
  • Increased network performance and reliability
  • Reduced processing and short connection setup time
  • Enhanced network services
t carrier circuits
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.

t carrier circuits36
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.

t carrier system
T Carrier System

T-Carrier Designation DS Designation Speed

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

slide38

*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.

e carrier circuits european standard
*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.
synchronous optical network sonet
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.
sonet
SONET

SONET Designation SDH Designation Speed

OC-1

OC-3

OC-9

OC-12

OC-18

OC24

OC-36

OC-48

OC-192

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

STM-1

STM-3

STM-4

STM-6

STM-8

STM-12

STM-16

switched multimegabit data service smds
*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.
slide43

*SMDS Network Components

SNI: Subscriber network interface

CPE: Customer premises equipment

slide44

*SMDS Interface Protocol (SIP)

SIP is used for communications between CPE and SMDS carrier equipment

ethernet ip packet network
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.
multiprotocol label switching mpls
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).
slide49

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.

slide50

*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

cable wireless usa
*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.
more wan protocols
*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)
slide57

Abilene

vBNS (very high speed Backbone Network Services )

CA*Net 3

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

abilene
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.
slide59

ISP POP

Individual

Dial-up Customers

ISP Point-of Presence

Modem Pool

ISP POP

Corporate

T1 Customer

T1 CSU/DSU

Layer-2

Switch

ATM

Switch

ISP POP

Corporate

T3 Customer

T3 CSU/DSU

Remote

Access

Server

Corporate

OC-3 Customer

ATM Switch

NAP/MAE

Figure 9-2 Inside an ISP Point of Presence

slide60

Customer Premises

Individual Premise

Main

Distribution

Frame

Voice

Telephone

Network

DSL Modem

Line Splitter

Hub

Individual

Premise

Telephone

Wireless

Transceiver

DSL Access

Multiplexer

Individual

Premise

Computer

Computer

Wireless Access Office

Customer

Premises

Wireless

Transceiver

Router

Customer

Premises

ISP POP

Figure 9-9 Fixed wireless architecture

slide61

WAP Client

WAP Gateway

Web Site

WAE

User

Agent

Web Server

WAE

Requests

Wireless

Transceiver

Wireless Telephony

Application Server

WAE

Requests

WAE

Responses

(plus WML, etc.)

WAE

Responses

(plus WML, etc.)

WAE

Responses

(plus WML, etc.)

WAE

Requests

HTTP Requests

WAP Proxy

HTTP Responses

(plus HTML, jpeg, etc.)

Figure 9-10 Mobile wireless architecture for WAP applications

slide62

Sprint

Abilene

UUNet

CA*Net 3

Verio

DREN

WSU

Router

Boeing

Router

Router

Microsoft

U Idaho

Switch

Switch

Router

Router

Montana State U

HSCC

High-speed

Router

High-speed

Router

Router

AT&T

U Montana

Router

Switch

Switch

SCCD

Router

Sprint

U Alaska

U Wash

OC-48

OC-12

T-3

Portland POP

Figure 9-12 Inside the Pacific/Northwest Gigapop