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Computer Networks. Chapter 1 Introduction Prof. Jerry Breecher CSCI 280 Spring 2002. The Weeks Ahead. Date. Lecture. Lab/Project. Jan 14 - 16. Introduction. Start Proj. 0. Project 0 Due. Jan 21 - 23. The Physical Layer. Start Project 1. Project 1 Checkin. Jan 28 - 30.

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Computer networks l.jpg

Computer Networks

Chapter 1

Introduction

Prof. Jerry Breecher

CSCI 280

Spring 2002


The weeks ahead l.jpg
The Weeks Ahead

Date

Lecture

Lab/Project

Jan 14 - 16

Introduction

Start Proj. 0

Project 0 Due

Jan 21 - 23

The Physical Layer

Start Project 1

Project 1 Checkin

Jan 28 - 30

Medium Access Layer

Feb 4 - 6

Medium Access Layer

Project 1 Checkin

Chap. 1 - Introduction


Chapter overview l.jpg
Chapter Overview

1.1 Introduction

1.2 Network Hardware

1.3 Network Software

1.4 Reference Models

1.5 Example Networks

1.6 Example Data Communication Services

1.7 Network Standardization

Chap. 1 - Introduction


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What You Will Learn

  • Terminology

  • Communication basics

    • Media and signals

    • Binary numbering system

    • Data transmission characteristics

      • asynchronous and synchronous communication

      • serial and parallel transmission

      • bandwidth, throughput and noise

      • multiplexing

Chap. 1 - Introduction


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What You Will Learn

  • Networking and Network Technologies

    • Packet Switching, Circuit Switching

    • Protocols and Layering

    • Network Addressing

    • Interconnection (bridges, switches, routers)

    • Topologies (star, ring, bus, mesh)

    • Routing

    • Flow, Error and Congestion Control

Chap. 1 - Introduction


Introduction l.jpg

The Big Picture: Where are We Now?

Introduction

1.1 Introduction

1.2 Network Hardware

1.3 Network Software

1.4 Reference Models

1.5 Example Networks

1.6 Example Data Communication Services

1.7 Network Standardization

Some of the overall issues we’ll be dealing with in this course.

Chap. 1 - Introduction


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Introduction

Motivation for Networks

  • Information Access

  • Sharing of Resources

  • Facilitate Communications

What A Network Includes

  • Transmission hardware

  • Special-purpose hardware devices

    • interconnect transmission media

    • control transmission

    • run protocol software

  • Protocol software

    • encodes and formats data

    • detects and corrects problems

Chap. 1 - Introduction


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Introduction

What A Network Does

  • Provides communication that is

    • Reliable

    • Fair

    • Efficient

    • From one application to another

  • Automatically detects and corrects

    • Data corruption

    • Data loss

    • Duplication

    • Out-of-order delivery

  • Automatically finds optimal path from source to destination

Chap. 1 - Introduction


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Lingo

Introduction

Where are we going: This chapter is basically an overview of the course. Before we get mired down in details, we want to get a general idea of what this whole course is about. Here are the kind of issues we’ll be dealing with.

Broadcast Networks -

Single channel with multiple machines connected to it.

Point-to-point -

Individual connections between pairs of machines.

Mostly EE issues.

Packets -

Messages - the "chunk" of data transmitted from one machine to the next.

Addressing -

+ One to one: Packet contains specific target address.

+ Broadcasting: All machines on the network receive and

process the packet.

+ Multicasting: A subset of machines receive and process the packet.

Chap. 1 - Introduction


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Lingo

Introduction

Can also view messaging in terms of the distance of transmission:

0.1 meter Single processor

1 meter Multiprocessor

10 meter Room

100 meter Building -- Local area network

1 kilometer Campus

10 kilometer City -- Metropolitan area network

100 kilometer Country

1K kilometer Continent -- Wide area network

10K kilometer Planet -- Internet

Serial:

Parallel:

Chap. 1 - Introduction


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Dedicated

fixed bandwidth

route fixed at setup

idle capacity wasted

network state

Lingo

Introduction

Packet Switching

Circuit Switching

  • Best Effort

    • end-to-end control

    • multiplexing technique

    • re-route capability

    • congestion problems

Chap. 1 - Introduction


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The Big Picture: Where are We Now?

Network Hardware

1.1 Introduction

1.2 Network Hardware

1.3 Network Software

1.4 Reference Models

1.5 Example Networks

1.6 Example Data Communication Services

1.7 Network Standardization

The various possible hardware structures that are possible. LANs, MANs, WANs and all that.

Chap. 1 - Introduction


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Network Hardware

LOCAL AREA NETWORKS

  • LANs are:

    • Privately owned. Can be up to several kilometers long;

    • Restricted so worst case transmission time can be contained.

    • Run at speeds of 10, 100, or more Mbps.

    • Low delay. High reliability.

    • Requires collision arbitration.

  • Ethernet:

    • IEEE 802.3.

    • Bus based broadcast network with decentralized control at 10 or 100 Mbps.

  • Token Ring:

    • IEEE 802.5

    • Ring based broadcast network with token arbitration at 4 or 16 Mbps.

Chap. 1 - Introduction


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Network Hardware

METROPOLITAN AREA NETWORKS:

MANS are:

Larger version of LAN ("city" wide).

Public or private / data or voice.

Broadcast - no switches.

Can be distinguished from LANs based on wiring mechanism.

Chap. 1 - Introduction


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Network Hardware

WIDE AREA NETWORKS

WANS are: Networks spanning large distances.

Hosts or End Systems -

Machines running user applications.

(Communication) Subnet -

Connections between hosts - transmission lines + switches.

A "locality" understanding each other's addresses.

Circuits/Channels/Trunks -

Transmission lines move the bits.

Packet switching nodes/Intermediate systems/Data switching exchanges

Specialized computers moving data between several inputs

to several outputs.

Chap. 1 - Introduction


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Network Hardware

WIDE AREA NETWORKS

WANS are: Networks spanning large distances.

Router - Generic term for switching computers.

Point-to-point/Store-and-forward/Packet-switched -

Moving through a series of routers, packets are received at a router, stored there, then forwarded to the next router.

Topologies -

Chap. 1 - Introduction


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Network Hardware

Media

Wireline

String

Garden Hose

Copper

Twisted Pair

Coax

Optical Fiber

Wireless

Sound

Light and mirrors

Infrared

RF

Microwave

Chap. 1 - Introduction


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Network Hardware

WIRELESS NETWORKS

  • What are they: Used where computer is mobile or far away from wires.

  • Only 1 - 2 Mbps / higher error rates / interference.

  • Wireless Mobile Applications

  • NO NO Stationary workstations in offices.

  • NO YES Using portable in hotel.

  • YES NO LANs in unwired buildings.

  • YES YES Portable office; PDA.

  • INTERNETWORKS:

  • ( or internet )

  • Collection of interconnected networks.

  • internet ( lower case i ) is generic term.

  • Internet ( upper case I ) is worldwide connection to all kinds of machines.

Chap. 1 - Introduction


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The Big Picture: Where are We Now?

Network Software

1.1 Introduction

1.2 Network Hardware

1.3 Network Software

1.4 Reference Models

1.5 Example Networks

1.6 Example Data Communication Services

1.7 Network Standardization

This covers the way the software is put together. It talks about the philosophy of connecting together two entities.

“Layering” is the key word.

Chap. 1 - Introduction


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PROTOCOL HIERARCHIES

Network Software

Layers -

The concept that network software is organized functionally into levels. A level on one host talks to the same level on another host (its peer).

Protocol -

The protocol is the convention or standard that a layer uses to talk to the other layer. An agreement or standard on the conversation.

Physical Medium -

Underneath the layers is the wire or fiber or whatever.

Interface -

Defines the services that one layer offers another (either up or down.)

Important to keep this simple and clean.

Important that each layer perform specific actions.

Chap. 1 - Introduction


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PROTOCOL HIERARCHIES

Network Software

  • Network architecture -

  • A set of layers and protocols. It contains details on what happens in the layer and what the layers says to its peer.

  • Functional interfaces and implementation details are not part of the spec, since that's not visible outside the machine.

  • Protocol stack -

  • A list of protocols used by a system, one protocol per layer.

  • Information flow -

  • "Send_to_peer" rather than "call_next_layer_down".

Chap. 1 - Introduction


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DESIGN ISSUES FOR THE LAYERS

Network Software

Both Directions Simultaneous

Simplex No No

Half duplex Yes No

Full duplex Yes Yes

o Number of logical channels per connection (for priority purposes)

o Error control. (garbled or missing.)

o Preservation of message ordering.

o Flow control.

o Breaking up messages into a smaller chunks (and reassembly.)

o Multiplexing messages on same connection.

o Routing - how to get from one host to another.

That word “Multiplexing”:

Chap. 1 - Introduction


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Network Software

INTERFACES AND SERVICES

Purpose of each layer is to provide services to the layer above it.

Entities / Peer entities -

Active element in each layer (process/IO chip).

Peer entity = layer N entity <--> layer N entity.

Layer N entity provides service for layer N + 1.

Service providers and users -

Layer N is a provider for user N + 1.

SAPs (Service Access Points) -

Entry points in N that layer N + 1 can access.

Has an address that uniquely identifies it.

IDUs (Interface Data Unit) -

The information from N + 1 provided at the SAP.

Made up of SDU + control information.

Chap. 1 - Introduction


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Network Software

INTERFACES AND SERVICES

Purpose of each layer is to provide services to the layer above it.

SDUs (Service Data Unit) -

The portion of the IDU that will be passed up to the peer entity.

PDUs (Protocol Data Unit) -

The SDU may be broken up into PDUs, that being the chunk size for

further transmission.

Rolled up in

this figure:

Chap. 1 - Introduction


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Network Software

CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:

  • Connection oriented service -

  • Like the phone system. The system establishes a connection, uses it, and closes it. Acts like a tube. Data comes out the other end in the same order as it goes in.

    • Connection Setup

    • Data Transfer

    • Connection Termination

  • Connectionless service -

  • Like the post office. Each message has the entire address on it. Each

    • message may follow a different route to its destination. Ordering not

    • maintained.

      • Data Transfer

  • Chap. 1 - Introduction


    Connection oriented connectionless services26 l.jpg

    Network Software

    CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:

    Quality of service -

    Will the message arrive??

    A reliable connection-oriented service guarantees success.

    o Message sequence - message boundaries and order are maintained.

    o Byte streams - messages are broken up or combined; flow is bytes.

    Can pair mechanism with upper-layer requirements.

    Chap. 1 - Introduction


    Connection oriented connectionless services27 l.jpg

    Network Software

    CONNECTION-ORIENTED / CONNECTIONLESS SERVICES:

    Datagram Service -

    Like junk mail. It's not worth the cost to determine if it actually arrived. Needs a high probability of arrival, but 100% not required. Connectionless, no acknowledgment.

    Acknowledged datagram service -

    As above, but improved reliability via acknowledgment.

    Request-reply service -

    Acknowledgment is in the form of a reply.

    Summarized in this Table.

    Chap. 1 - Introduction


    Service primatives l.jpg

    Network Software

    SERVICE PRIMATIVES:

    Primitives are:

    The operations available to an entity. Possibilities include:

    Request -- An entity want some work done.

    Indication -- An entity is told about an event.

    Response -- An entity wants to respond to an event.

    Confirm -- Response to earlier request has come back.

    Example of Connectionless Protocol:

    Unitdata.request |--------->| Unitdata.indication

    Unitdata.indication |<---------| Unitdata.request

    Example of Connection-oriented Protocol:

    Connect.request |--------->| Connect.indication

    Connect.confirm |<---------|

    Data.request |--------->| Data.indication

    Data.indication |<---------| Data.request

    Disconnect.request |--------->| Disconnect.indication

    Disconnect.confirm |<---------|

    Chap. 1 - Introduction


    Service primatives29 l.jpg

    Network Software

    SERVICE PRIMATIVES

    THE RELATIONSHIP OF SERVICES TO PROTOCOLS:

    Services are primitives that a layer provides for the layer above it.

    Protocols are rules governing the meaning of frames/packets/messages

    exchanged with the peer entity.

    Chap. 1 - Introduction


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    The Big Picture: Where are We Now?

    Reference Models

    1.1 Introduction

    1.2 Network Hardware

    1.3 Network Software

    1.4 Reference Models

    1.5 Example Networks

    1.6 Example Data Communication Services

    1.7 Network Standardization

    There are two competing models for how the software is layered. These are the OSI and the TCP models. We talk about each of these here.

    Chap. 1 - Introduction


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    Layering

    Reference Models

    Chap. 1 - Introduction


    Reference models32 l.jpg

    Headers, Data, and Trailers

    Reference Models

    Encapsulation

    Chap. 1 - Introduction


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    THE OSI REFERENCE MODEL

    Reference Models

    OSI == Open Systems Interconnection

    Developed by ISO == International Standards Organization

    Principles used to develop OSI Layering:

    1. Need a layer for each different level of abstraction.

    2. Each layer performs a well defined function.

    3. Each layer should be standard-izable.

    4. Layer boundaries should minimize data flow across those boundaries.

    5. The right number of layers - don't put too many functions together, but not too many layers either.

    Chap. 1 - Introduction


    Reference models34 l.jpg

    THE OSI REFERENCE MODEL

    Reference Models

    Physical Layer -

    Purpose -- Transmits raw bits across a medium.

    Electrical -- Concerns are voltage, timing, duplexing, connectors, etc.

    Where Taught -- Differentiates an EE course from a CS course.

    Data Link Layer -

    Framing -- Breaks apart messages into frames. Reassembles frames into messages.

    Error handling -- solves damaged, lost, and duplicate frames.

    Flow control -- keeps a fast transmitter from flooding a slow receiver.

    Gaining Access -- if many hosts have usage of the medium, how is access arbitrated.

    Chap. 1 - Introduction


    Reference models35 l.jpg

    THE OSI REFERENCE MODEL

    Reference Models

    Network Layer -

    Routing -- What path is followed by packets from source to destination. Can be based on a static table, when the connection is created, or when each packet is sent.

    Congestion -- Controls the number packets in the subnet.

    Accounting -- Counts packets/bytes for billing purposes.

    Heterogeneity -- Interfacing so one type of network can talk to another.

    Chap. 1 - Introduction


    Reference models36 l.jpg

    THE OSI REFERENCE MODEL

    Reference Models

    Transport Layer -

    Reliability -- Ensures that packets arrive at their destination. Reassembles out of order messages.

    Hides network -- Allows details of the network to be hidden from higher level layers.

    Service Decisions -- What type of service to provide; error-free point to point, datagram, etc.

    Mapping -- Determines which messages belong to which connections.

    Naming -- "Send to node xyzzy" must be translated into an internal address and route.

    Flow control -- keeps a fast transmitter from flooding a slow receiver.

    Chap. 1 - Introduction


    Reference models37 l.jpg

    THE OSI REFERENCE MODEL

    Reference Models

    Session Layer -

    Sessions -- Provides services that span a particular message. For instance, a login session could be logged.

    Synchronization-- Provide way to subdivide a long mechanism for reliability.

    Presentation Layer -

    Prettiness -- Syntax and semantics of information transmitted. Understands the nature of the data being transmitted. Converts ASCII/EBCDIC, big endian/little endian

    Application Layer -

    Interfacing -- Terminal type translation.

    File transfer -- Programs able to understand directory structures and naming conventions and map them onto various systems.

    Chap. 1 - Introduction


    Reference models38 l.jpg

    THE OSI REFERENCE MODEL

    Reference Models

    Data Transmission in the OSI Model -

    Chap. 1 - Introduction


    Reference models39 l.jpg

    THE TCP/IP REFERENCE MODEL

    Reference Models

    Used in the Arpanet and in the Internet. Common mechanism that is gaining on/surpassing the OSI Model.

    Host to Network Layer -

    This lowest level is not defined in this model. Various mechanisms abound.

    Internet Layer -

    Connector -- Provides packet switched connectionless service.

    Routing -- The IP (Internet Protocol) does delivery and congestion control.

    Chap. 1 - Introduction


    Reference models40 l.jpg

    THE TCP/IP REFERENCE MODEL

    Reference Models

    Transport Layer -

    Allows peer entities to communicate.

    TCP -- Transmission Control Protocol provides a reliable connection oriented protocol that delivers a byte stream from one node to another. Guarantees delivery and provides flow control.

    UDP -- User Datagram Protocol provides an unreliable connection-less protocol for applications that provide their own.

    Application Layer -

    Terminal -- Telnet

    File transfer -- FTP

    The Web -- HTTP

    Chap. 1 - Introduction


    Reference models41 l.jpg

    COMPARISON OF REFERENCE MODELS

    Reference Models

    OSI has good definition of service, interface, and protocol as discussed before. Fits well with object oriented programming concepts. Protocols are better hidden.

    With TCP, the protocols came first; model was just a description of the protocols. But then the model isn't good for any other protocols.

    LAYERS

    Transport Network

    OSI Connectionless

    Connection-Oriented Connection-Oriented

    TCP Connectionless Connectionless

    Connection-Oriented

    Allows connectionless applications!

    Chap. 1 - Introduction


    Reference models42 l.jpg

    THE TCP/IP REFERENCE MODEL

    Reference Models

    • A CRITIQUE OF OSI:

    • Bad Timing -

    • TCP already in use by the time OSI came along.

    • Bad Technology -

    • Layers don't match reality . Chosen because IBM's SNA has seven layers.

    • Dominated by phone company mentality.

    • Bad Implementation -

    • Huge, unwieldy, slow.

    • A CRITIQUE OF TCP/IP:

    • Doesn't separate spec from implementation.

    • Model is only good for describing TCP.

    • Doesn't specify physical and data link layers.

    • THE HYBRID REFERENCE MODEL:

    • 5 Application

    • 4 Transport

    • 3 Network

    • 2 Data Link

    • 1 Physical

    Chap. 1 - Introduction


    Example networks l.jpg

    The Big Picture: Where are We Now?

    Example Networks

    1.1 Introduction

    1.2 Network Hardware

    1.3 Network Software

    1.4 Reference Models

    1.5 Example Networks

    1.6 Example Data Communication Services

    1.7 Network Standardization

    This section talks about some real networks.

    Chap. 1 - Introduction


    Example networks44 l.jpg
    Example Networks

    • NOVELL NETWARE:

    • Heavily used in PC world.

    • Proprietary protocol stack

    • Network layer -- IPX - unreliable connectionless

    • Transport layer -- NCP (Network Core Protocol)

    • - connection oriented

    • - other services

    • Naming and Addressing --

    • SAP (Service Advertising Protocol) - Servers advertise their address to router machines. Clients, when booted, ask for location of nearest server.

    • THE ARPANET:

    • 1968 Originally intended as reliable network, with multiple routing.

    • Used TCP/IP precursor, which got built into early UNIX.

    Chap. 1 - Introduction


    Example networks45 l.jpg
    Example Networks

    NSFNET:

    Late 1970s - Many other folks wanted to get on the net, but Arpanet was essentially limited to military contractors. NSF set up another network to handle this need. Started at 448 Kbps and by 80's upgraded to 1.5 Mbps.

    1990 Formed ANS (Advanced Networks and Services) -- MERIT, MCI, IBM

    took over from the government running at 45 Mbps.

    1995 ANSNET sold to AOL, who now runs it.

    THE INTERNET:

    Growing exponentially.

    All nodes run TCP/IP. Means that all nodes have an IP address by which they can be contacted.

    Services provided include:

    o e-mail o news o remote login o file transfer o the web

    GIGABIT TESTBEDS:

    Testing higher speed long distance nets. Typically 622 Mbps. While throughput improves, latency remains limited by the speed of light.

    Chap. 1 - Introduction


    Example data communications l.jpg
    Example Data Communications

    1.1 Introduction

    1.2 Network Hardware

    1.3 Network Software

    1.4 Reference Models

    1.5 Example Networks

    1.6 Example Data Communication Services

    1.7 Network Standardization

    These are public networks owned by the phone companies and offered to the public - thus called public networks.

    Chap. 1 - Introduction


    Example data communications47 l.jpg

    Public Networks

    Example Data Communications

    These are subnets, often owned by the phone companies, offered to subscribers.

    This is a public network.

    SMDS - SWITCHED MULTIMEGABIT DATA SERVICE

    Interconnects the LANs operating within a single company. Connects diverse branches.

    Chap. 1 - Introduction


    Example data communications48 l.jpg

    Public Networks

    Example Data Communications

    • X.25 NETWORKS

    • Developed during 70's. Interface between public packet-switched networks and customers.

    • Operate at 64 Kpbs, so are very slow and becoming outdated. However there are still many of them in operation.

    • Connection oriented. Uses:

    • Switched Virtual Circuit - established when the first packet is sent. Circuit remains for duration of session providing in-order delivery, and flow control.

    • Permanent Virtual Circuit - established by agreement between the customer and the carrier. Like a leased line.

    • PAD ( Packet Assembler Disassembler ) allows non-X.25-speaking terminals to connect to X.25.

    Chap. 1 - Introduction


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    Public Networks

    Example Data Communications

    • FRAME RELAY:

    • Takes advantage of modern high-speed reliable digital phone lines.

    • This allows simple protocols with work done by user computers rather than by the network. Runs at 1.5 Mbps with few features.

    • Customer leases a permanent virtual circuit between two points. This "virtual leased line" means that the wire is shared with other users at a great price reduction. Each is allowed some bursti-ness, but doesn't get the line all day.

    Chap. 1 - Introduction


    Example data communications50 l.jpg

    Public Networks

    Example Data Communications

    BROADBAND ISDN AND ATM:

    The above networks, together with a multitude of old versions, mean a major headache. Need a way to provide all of these, and many new services with a single high speed network.

    ISDN(Integrated Services Digital Network) will offer cable, video on demand, e-mail, etc. etc. etc.

    ATM (Asynchronous Transfer Mode) is underlying mechanism. Transmits in small fixed-size cells.

    5 48

    +---------+---------------------------------------+

    | Header | User Data |

    +---------+---------------------------------------+

    Chap. 1 - Introduction


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    Public Networks

    Example Data Communications

    ATM (Continued)

    Packet (cell) switching is dramatic change for phone companies.

    ATM is connection oriented; make connecting request first; then all cells follow the same path.

    Target is 155 Mbps and 622 Mbps. Allows TV transmission.

    See the ISDN ATM Reference Model below:

    Chap. 1 - Introduction


    Example data communications52 l.jpg

    Public Networks

    Example Data Communications

    • ATM promises much but will take a while to deliver.

    • Moving from circuit switching will take a long time.

    • Requires replacement of existing wires.

    ATM (Continued)

    Comparisons to other models.

    Chap. 1 - Introduction


    Example data communications53 l.jpg

    Public Networks

    Example Data Communications

    COMPARISONS:

    Here’s an overview of the properties of these Public Networks

    Chap. 1 - Introduction


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    The Big Picture: Where are We Now?

    Standards

    1.1 Introduction

    1.2 Network Hardware

    1.3 Network Software

    1.4 Reference Models

    1.5 Example Networks

    1.6 Example Data Communication Services

    1.7 Network Standardization

    Networks have more standards than any other area of the computer industry.

    The reason is because hardware/software from different manufactures must all play together - and you can’t do that unless the vendors get together and establish agreements about the behavior of this equipment.

    Chap. 1 - Introduction


    Standards55 l.jpg
    Standards

    Issues Include:

    de facto and de jure.

    Phone companies and the governments that regulate them.

    ISO (International Standards Organization)

    ANSI (American National Standards Institute)

    NIST (National Institute of Standards and Technology)

    IEEE (Institute of Electrical and Electronics Engineering)

    IAB (Internet Architecture Board)

    Chap. 1 - Introduction


    Summary l.jpg
    Summary

    We (and the text) use the Internet and ATM as examples.

    Architecture (not hardware) of physical Layer.

    Data Link Layer.

    MAC (Medium Access Layer) - part of Data Link Layer.

    Network Layer

    Transport Layer

    Application Layer (naming, mail, news, web, etc.)

    Chap. 1 - Introduction


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