Ch1_Introduction.pdf

CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 1

San Jose State University

College of Engineering

Computer Network Design (CmpE 206)

by

Rod Fatoohi, Ph.D.

Note: These course notes are provided exclusively for the

students convenience to follow the presentations. They cannot

be reproduced without a written permission from the author.

Some of these materials are from the following textbooks:

Computer Networks, 5th ed., 2011, Tanenbaum & Wetherall,

Prentice-Hall.

Data and Computer Communications, 9th ed., 2011, Stallings,

Prentice-Hall.


Overview

Protocol Hierarchies

Reference Models

Network Classifications

Internet Architecture

Standards

Units

Chapter 1


Computer Network: collection of

interconnected computer systems w/ software

protocol structure that enables communication.

Protocol: agreement between communicating

parties on how communication is to be done.

It contains rules governing communication.

Introduction


Overview


Reference Models



Standards

Units

Chapter 1


Protocol Hierarchies (Layering):

Networks are in general organized as series of

layers, each one built upon one below it.

Each layer provides services to higher layers.

Service is set of primitives (operations) that

layer provides to layer above it (what the

layer does).

Between adjacent layers there is interface.


Interface specifies which primitive

operations & services lower layer offers to

upper layer

how above layer access that layer?

Peers are entities (active elements) in same

layer of different machines.

Network Architecture: set of layers &

protocols.


Communication:

Conceptually, peers assume that they are

communicating horizontally.

Actually, each layer passes data & control

information to layer below it (vertically), until

lowest layer is reached.


Service vs Protocol:

Protocol: set of rules governing format &

meaning of messages within layer.

Service defines operations that layer

provides to layer above it.

Service is like abstract data type or object

it defines operations but not implementation

Protocol relates to implementation of

service

its not visible to user.

Service vs Protocol



Advantages of Layering:

Divide & Conquer

Modularity

Well-defined interfaces (Ex. API).

Disadvantages of Layering:

Performance.


Overview


Reference Models



Standards

Units

Chapter 1


OSI Reference Model:

Developed by International Standards

Organization (ISO).

Called ISO OSI (Open Systems

Interconnection) Reference Model.

Open System: specifications are publicly

available.


OSI Reference Model:

The Physical Layer is concerned w/

transmission of raw bits over physical link.

The Data Link Layer provides reliable

transfer of frames across physical link.

The Network Layer is responsible for

establishing, maintaining & transmission

connections across networks.

The Transport Layer provides reliable

transparent transfer of data w/ error

recovery & flow control.


OSI Reference Model (cont)

The Session Layer is responsible for

establishing, managing & termination of

sessions between applications.

The Presentation Layer performs useful

transformations on data to provide

standardized application interface &

common communications services.

The Application Layer provides services

to users.


The Link Layer (Network Access Layer)

not well defined.

mainly concerned w/ exchange of data between

end system and network & between two end

systems attached to same network.

includes device driver in OS & corresponding

Network Interface Card (NIC).

The Network Layer (Internet Layer)

handles movement of packets around

network.

The TCP/IP Reference Model (Internet

Reference Model):


TCP/IP Reference Model (cont)

The Transport Layer (Host-to-Host

Layer) provides flow of data between two

end systems.

The Application Layer (Process Layer)

handles details of various user applications.


IEEE 802 Reference Model :

Physical Layer:

encoding/decoding of signals.

preamble generation/removal (synchronization)

bit transmission/reception.

transmission Medium.

Medium Access Control Sublayer:

assembling transmitting data into frames on

transmission w/ address & error-detection.

disassembling frames on reception & performing

address recognition & error detection.

governing access to LAN transmission medium

IEEE 802 vs OSI



IEEE 802 Reference Model (Cont.)

Logical Link Control

providing one or more Service Access Points

(SAPs).


Overview


Reference Models



Standards

Units

Chapter 1


(based on geographical scope)

Personal Area Networks

Local Area Networks

Metropolitan Area networks

Wide Area Networks

Internet


Network Classifications (2)



Personal Area Network (PAN):

Within range of a person

used to connect computer w/ its peripherals

Cover short distance (few meters) w/ low speed

May use master-slave paradigm

Ex: Bluetooth, RFID.

Personal Area Network Example



Local Area Network (LAN):

within building: home, office, factory,

owned & operated by single organization

used to connect PCs & other devices

used to share resources & exchange information

Early wired LANs were broadcast shared medium; currently mostly switching

Wired LANs run at speeds of 100 Mbps to 10 Gbps w/ low latency & very low error rate

Ex: Ethernet & WiFi.

Local Area Network Examples



Metropolitan Area Network (MAN):

Within a city or a metropolitan area

Larger than LAN but smaller than WAN

Evolved w/ technologies used

Early example: Distributed Queue Dual Bus (IEEE 802.6) obsolete

Currently: Cable TV, WiMAX (IEEE 802.16)

Metropolitan Area Network Example



Wide Area Network (WAN):

cover large geographical area (country).

relay mainly on circuits provided by common

carrier (leased).

have many interconnected switching elements.

traditionally provide modest data rates to

customers, higher rates to business

traditionally have long delay & relatively high

error rates to customers

more scalable

Ex: Frame Relay (1.5 Mb/s), ATM (155 Mb/s

& 622 Mb/s).

Wide Area Network Example


Internet

internet (internetworking): collection of interconnected networks using common protocol suite.

Internet collection of ISP (Internet Service Provider) networks to connect companies, universities, government offices, and private individuals & uses TCP/IP protocol suite.



Overview


Reference Models



Standards

Units

Chapter 1



Tiered hierarchy of Internet Service Providers (ISPs)

At the top tier-1 ISPs, Internet backbone operators

operate large networks w/ fast routers (forwarding

packets at high rates) & high-speed links ( 622 Mbps)

directly connected to each other at private peering points

& Network Access Points (NAPs) network of switches

& routers that exchange large quantities of traffic

Connected to & provide services to tier-2 ISPs

small number ( dozen): AT&T, Sprint, Level 3 Comm,

Internet Architecture (2)



Internet Architecture (3)

Next, tier-2 ISPs, regional providers

Connected to & costumers to a few tier-1 ISPs

Might be directly connected to other tier-2 ISPs

Next, lower-tier ISPs & access ISPs

Connected to & costumers to higher-tier ISPs

Service providers to users & content providers

ISPs are connected to each others at Points of Presence (POPs) collection of routers at which routers of other ISPs can connect


Rules for Data Transfer

Simplex Communication

Data travel in one direction only.

Half-duplex Communication:

Data can travel in either direction but not simultaneously

Full-duplex Communication:

Data can travel in both directions at once.

Types of Networks

Circuit-Switched:

has three phases: connection establishment, data

transfer & connection termination.

Channel capacity must be available & reserved

between end systems during connection.

All packets follow the same path

Data transferred at fixed rate w/o delay except

propagation delay.

In heavy traffic, some calls are blocked.

Unused bandwidth during connection is wasted.

charging based on time & distance

Ex: Telephone network, PBX. CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 41

Types of Networks (2)

Packet-Switched: Data are transferred in blocks called packets.

Larger messages are divided into many packets.

Packets can follow different paths.

Re-assembly at destination might be needed

Channel efficiency is high since it can be dynamically shared by packets.

Data rate conversion is possible.

In heavy traffic, packets are accepted but more delay

Better fault tolerant (w.r.t switches crash).

charging based on volume of traffic.

Ex: LANs. CmpE 206 Copyright 2013 by Fatoohi, All Rights Reserved 42

Circuit Switching vs Packet Switching


Circuit Switching vs Packet Switching (2)


Circuit Switching vs Packet Switching (3)



Types of Network Services:

Connection-oriented Service:

has three phases: connection establishment,

data transfer & connection termination.

modeled after telephone system.

usually sending host sends stream of data

Communication doesnt have to be continuous.

data ordering preserved

provides information in case of failure.

uses some resources

Ex: TCP


Connectionless Service:

modeled after postal system.

Each message carries identification for routing.

Messages may get lost.

no reordering.

requires less initial overhead

can run faster

uses less resources

Ex: UDP


Overview


Reference Models



Standards

Units

Chapter 1


allow different devices to communicate

increase market share for standard products

2 categories: de facto from the fact & de jure

by law

Standard organizations for networking:

Telecommunications

International standards

Internet standards

Standards


International Telecommunications Union (ITU)

Standardize international telecommunications

UN specialized agency

State Dept. represents USA

many countries represented by Post, Telegraph &

Telephone (PTT) admin

Over 700 sector & associate members

3 main sectors:

Telecommunications standardization sector (ITU-T)

Radio-communications sector (ITU-R)

Development sector (ITU-D)


ITU-T

Formally known as International Telegraph & Telephone Consultative Committee (CCITT)

makes recommendations about telephone, telegraph & data communication

has 10 study groups

Over 3000 recommendations produced which become standards:

DSL

H.264 (MPEG-4 AVC)

X.509 public key certificates

International Standards

ISO (International Standards Organization)

voluntary organization whose members are national standard organizations of 157 countries.

over 200 technical committees on many subjects.

Over 17000 standards issued

member of ITU-T


International Standards (2)

ISO Standard Process:

1. Idea is assigned to technical committee

2. Committee assigns working group to study it & generates Committee Draft (CD)

3. CD is circulated for comments for 6 months

4. If idea is good & approved, Draft International Standard (DIS) generated for comments for 5 months.

5. If DIS approved*, Final DIS (FDIS) generated for approval within 2 months

6. If approved*, International Standard (IS) is generated.

*Approval for requires 2/3 majority



ANSI (American National Standards Institute)

private, nonprofit organization

member of ISO

its standards are frequently adopted by ISO

NIST (National Institute of Standards &

Technology)

US government agency.

Issues standards for US government.



IEEE (Institute of Electrical & Electronics

Engineers)

professional organization which develops

standards in EE & Computing.

IEEE 802 is key standard for LAN.


IEEE 802 Standards


IEEE 802 Standards (2)


Internet Standards

IAB

In 1979, ARPA formed Internet Control &

Configuration Board (ICCB) to coordinate

design of protocols & architecture of internet.

In 1983, ICCB was renamed Internet Activities

Board (IAB), then Internet Architecture Board.

Each of its ten members headed a task force.

met several times a year.

Volunteers did most of work.

Communication was done by a series of

technical reports called Request for Comments.


Internet Standards (2)

Request For Comments (RFCs)

numbered in chronological order of creation.

as short as one page & as long as 200 pages.

edited but not refereed.

cover a broad concept or details.

7359 issued (as of August 2014)

publicly available from several sites:

http://www.rfc-editor.org/rfc.html



IAB (2)

In 1989, IAB was reorganized into 2 groups: Internet

Research Task Force (IRTF) for long-term research &

Internet Engineering Task Force (IETF) for short-

term engineering issues.

Each group has a steering group: IRSG, IESG.

IETF was divided into over 70 working groups:

routing & addressing, security, network management,

user information, new applications,



Internet Society

professional society was formed in 1992 to

promote the Internet

W3C (World Wide Web Consortium)

Develops protocols & guidelines for the Web



Internet Standard Process:

An idea must be explained in an RFC &

generates sufficient interest to become

proposed standard.

There must be a working implementation in 2

independent sites to become draft standard for

at least 4 months.

If idea is sound & software works, IAB can

declare the RFC as Internet standard.



Overview


Reference Models



Standards

Units

Chapter 1

Data Rate Unit

used for speed of transmission line (ex: 1 kbps)


Data Rate Unit (2)


Capacity Unit

used for memory, disk, file & database sizes


Exp. Explicit Prefix

210 1,024 Kilo (KB)

220 1,048,576 Mega (MB)

230 1,073,741,824 Giga (GB)

240 1,099,511,627,776 Tera (TB)

Ch1_Introduction.pdf

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