Technology Focus: Network and Communications Technology

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Major Network Categories

Major Network Types The Global Internet

Internal Corporate Networks

The Worldwide Telephone System

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Major Network Categories

Telecommunications Spans Two Concerns Voice and Video Communication vs

Data CommunicationAt least one party is a computer

The two are converging

Voice andVideo

DataCommunication

Telecommunications

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Network

A network is a system of hardware, software and transmission components that collectively allow two application programs on two different stations connected to the network to communicate well.

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Elements of a Network

ClientStation

Mobile ClientStation

ServerStation

ServerStation

Stations are computersand other devices

such as cellphones and PDAs

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Elements of a Network

ClientStation

Mobile ClientStation

ServerStation

ServerStation

Stations communicate bysending messages called

Frames

Frame

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Elements of a Network

Switch

Switch

Switch

Switch

Frames may passthrough multiple switches

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Elements of a Network

AccessLink

AccessLink

AccessLink

AccessLink

Access links connectstations to the

first switch

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Elements of a Network

TrunkLink

TrunkLink

Trunk Link

TrunkLink

TrunkLink

Trunk linksconnect switches

Higher capacitythan access links

Often opticalfiber

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Client/Server Architecture

Client PCServer

Network

Service

ClientsReceiveServices

ServersProvideServices

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Clients and Servers

Network Applications - File sharing, Network printing, Email, etc.

Clients – Access the server to perform an application

Most common desktop operating systems – Windows 95/98/XP (desktop)

Servers – Host one or more applications; Store application files; Respond to client requests

Common network operating systems: Microsoft Windows Server, Novell Network, UNIX, LINUX

A server is not a type of computer. Any computer can be changed from a workstation to a server. It is dependent on the operating system and application programs loaded onto the computer.

Since servers need to support simultaneous access from multiple clients and be operational 24x7, they tend to have greater power, storage capacity, and stability. Hence, computer companies label computers “servers”.

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Packets and Frames

Messages in Single Networks are Called Frames

Messages traveling across multiple networks (in Internets) are Called Packets

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Packet vs. Circuit Switching

Circuit switching: dedicated path between two nodes. Entire circuit must be available during the transmission. (Example: local telephone network.) Relatively inefficient for data transmission. (Why?)

Message switching: store-and-forward process. (Postal mail analogy)

Packet switching: also store-and forward, this time messages divided into packets of uniform length: Improved line utilization over message switching.

Key differences between circuit switching and packet switching: sharing of links, storing and forwarding, graceful degradation

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Packet Switching

Original Message

Computer X

PacketSwitch

APacket

SwitchingDecision

B

C

Computer Y

FE

D

1. Message Broken intoSmaller packets

2. Packets Routed individually

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Packet Switching

Packet Switching Reduces Trunk Line Costs Packets from several conversations are multiplexed

on trunk lines

Trunk LinkPacket from A to B Packet from C to D

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Packet Switching

Trailer HeaderData Field

AddressField

Message Structure

Packet

OtherHeaderField

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Quality of Service

It is not enough that networks work They must work well

Quality of Service (QoS) defines quantitative measures of service quality Speed and Delay (Latency) Reliability

Security (not a QoS measure but crucial)

Service Level Agreements (SLAs) Guarantees for various service parameters

Network provider pays performance penalties if guarantees are not met

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Quality of Service (QoS)

Data Transmission Rate Bits per second (bps) Multiples of 1,000 (not 1,024): kbps, Mbps, Gbps, Tbps

Congestion and Latency Congestion because traffic chronically or momentarily exceeds capacity

Latency (delay measured in milliseconds)

Especially bad for some services such as voice communication or highly interactive applications

Reliability Availability

Percentage of time the network is available to users for transmission and reception

Want 24 x 7 x 365 availability Telephone network: Five 9s (99.999%)

Error Rate % Lost or damaged messages or bits

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Geographic Scope

Local Area Network (LAN)

Limited geographical distance: home, office, building, campus, industrial part

Customer premises operationUser firm chooses technologyUser firm needs to manage on ongoing basis

Low cost per bit transmittedCompanies can afford high speed100 Mbps to the desktop is typical

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WAN

Geographic Scope

Wide Area Network (WAN) To link sites

Long distances

Requires the use of carriers to provide service Limited and complex choices but carrier manages

High cost per bit transmitted Companies cannot afford high transmission rates

Charges are distance dependent Typically transmit 1.544 Mbps or less Large organizations, like GMU, have bigger access links (Up

to 45 Mbps) Carriers have very large trunk links (155 Mbps – 10 Gbps)

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Internet

An internet is a group of networks linked together with routers in a way that allows an application program on any station on any network in the internet to be able to communicate with an application program on another station on any other network.

Network 1 Network 2

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An Internet

Routers

RouteNetwork 1

Network 3

Multiple Networks

Connected by Routers

Path of a Packet is its Route

Packet

Network 2

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An Internet

Single Networks Have Switches

Switches Connect Station-to-Router or Router-to-Router

Network X

Network Z Network Y

Switches

Routers

Switches

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Frame

Packet

Frames and Packets

Within a single network, the packet is carried in the data field of that network’s frame, probably across multiple switches

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Frames and Packets

Router removes packet from source network’s frame, sends back out in receiving network’s frame format

Frame

SamePacket

Different Frame Format

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Frames and Packets

Router removes packet from source network’s frame, sends back out in receiving network’s frame format

SamePacket

Different Frame Format

3d FrameFormat

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Frames and Packets

Like passing a shipment (the packet) from a truck (frame) to an airplane (frame) at an airport.

Truck

SameShipment

Airplane

Airport AirportTruck

Shipper Receiver

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The Internet: Universal Addressing Scheme

NetworkBrowser

Packet

Router

PacketRouter

Packet

Route

WebserverSoftware

Router

User PC(Host)IP Address=128.150.50.9

Webserver(Host)

IP Address=128.171.17.13Host name=voyager.cba.hawaii.edu

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Hosts

All computers connected to the Internet are hosts Server hosts (webservers, FTP servers, etc.)

Also client PCs at home, at school, and at work

Also PDAs and Internet-enabled cellphones

The Internet treats all hosts of all sizes as equals

Only application software distinguishes between them (browsers for client PCs, webserver applications for server hosts, etc.)

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Host Addresses and Host Names

Host IP Address Official address of host on the Internet

Every host must have an IP address, including client PCs and PDAs

32 bits long

Often expressed in dotted Decimal Notation for human reading (e.g., 128.171.17.13)

Hosts and routers work with 32-bit binary form

IP Address: 128.171.17.13

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Internet Service Providers (ISPs) and Internet Backbone Carriers

Internet Backbone(Multiple Carriers)

InternetService Provider

InternetService Provider

User PC Webserver

ISPISP

Router

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Wide Area Networks (WANs)

Organizations connect their computing resources locally through so-called LAN’s (Local Area Newtorks)

LAN’s are typically considered a local IT resource, internally owned and operated

So called WAN’s , wide area networks are needed to interconnect geographically distant computing resources (branches of a bank, factories and warehouses, production and R&D facilities etc) of a single organization

Businesses WAN connectivity options include: Connecting their corporate servers (and/or LAN’ s) together using

leased lines (i.e., building private WANs) Using the existing infrastructure owned by specialized providers:

Public switched data networks Using the Internet infrastructure (Virtual Private Network technology)

(VPN)

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Trunk-Line Based Leased Line

ComputerTelephone

SwitchTelephone

SwitchTelephone

SwitchServer

AccessLine

T1 Trunk Line (1.544 Mbps)

T1 Leased Line (1.544 Mbps)End-to-End Circuit with Trunk Line Speed

TrunkLine

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Leased Line Networks

Leased Line (Private Line or Dedicated Line) Point-to-point connection Always on (no dialing or other “call setup” procedures) If used extensively, lower cost per minute than dial-up service Must be provisioned (set up) ahead of time (instantaneous

provisioning not possible) T1s have historically been very expensive to lease. Lower-cost

alternatives include: Fractional T1

Lease a portion of the T1 (in DSO (64 Kbps) or 2-DSO (128 Kbps) increments). Common increments:

64 Kbps (Called a DS-0, not Fractional T1) 128 bps, 256 kbps, 384 kbps, 512 kbps, 768 kbps

Essentially, a leased line is a circuit switched service

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Alternative #1: Leased Line Corporate Data Network

T3 LeaseLine

Site C

Site A Site B

OC3 Leased Line

T1 LeasedLine

T1 LeasedLine

Site ESite D

56 kbpsLeased

Line

56 kbpsLeased

Line

56 kbpsLeased

Line

Multisite Leased Line Mesh Network

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Leased Line Trade-Offs

Leased Line Network Many leased lines, often span long distances

Pricing is distance-sensitive

Company must design/install the network, buy the switching equipment (e.g., Routers), order many leased lines, and maintain the network.

Pros: Control, Security, Predictable Performance

Cons: More expensive, more management and administration responsibilities scalability issues for large number of nodes

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Alternative #2: Corporate Use of a Public Switched Data Networks

Packet-Switched Network(Based on Frame Relay, SONET,

or other WAN technology)

POPPOP

POPPOP

Site A Site B

Point of Presence

One leased line per site. Typically in form of a “service” (not a ‘leased line’) that includes the physical layer protocol.

Site D Site C Site E

Alternative: Use a public Packet-Switched Network

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Public Switched Data Network Trade-Offs

Public Packet-Switched Network Owned and operated by the telecommunications Companies

(AT&T, Sprint UUNet etc.)

Only need one leased line from each site to a POP Short distances to the first available POP (intra-LATA)

Pricing is typically not distance sensitive Mostly it is based on requested data rate parameters

Business still needs one router per site and some maintenance, but bulk of the design, installation, equipment, and maintenance falls to the Communications Company.

Pros: Less expensive, less administration and management Cons: Less control, potential security issues, less

performance predictability

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Alternative #3: Corporate Customer orders Internet VPN services

Customer Premises C

Customer Premises B

Ethernet

Switch(es)LAN(s)

VPN connection

VPN connection

VPN connection

The Internet(A collection of networks owned by Communications Companies).

Customer connects to its ISP’s POPs. The ISPSends traffic over its own TCP/IP network or to other TCP/IP networks, as needed.

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What is ordered?

The customer orders (1) either:

Leased Lines from the telephone company to connect its sites to the ISP POPs; or

The physical line connection comes bundled with the ISP’s Internet VPN services

(2) VPN services

(3) A Service Level Agreement (SLA)