TOBB ETÜ ELE46/ELE563Communications Networks

Lecture 01May 6, 2014

Fall 2011

Tuesday 10:30 – 12:20 (310)Thursday 15:30 – 17:20 (372)

İsrafil BahçeciOffice: 168

ibahceci@etu.edu.tr

Ders Bilgileri - I

Bu derste neler öğreneceğiz? İnternet olgusu hayatımızın çok önemli bir parçasıdır.

Her ne kadar bilgisayar ağı kavramı İnternetten ibaret olmasa da İnternet en önemli ve en yaygın bilgisayar ağlarının başında gelmektedir. Neden?

İnterneti olanaklı kılan teknolojiler ve yapı blokları nelerdir?

Bu yapı taşlarını kullanarak nasıl bir mimari oluşturulmuştur ki böylesi etkin ve yaygın bir iletişim sistemi ortaya çıkmıştır?

Bu sistemin eksikleri var mıdır? Varsa neledir?

Ders Bilgileri - II

Kaynak kitap Computer Networks, Andrew Tanenbaum , 5th Edition,

Prentice Hall 2011 Yarımdcı kitap

Computer Networks: A Systems Approach, 5th Edition, Morgan Kaufmann (an Elsevier Company) by L. L. Peterson and B. S. Davie

Ders Bilgileri - III

Notlandırma Arasınav: %30 Sonsınav: %60 Proje (seçmeli): %10

Objective of this Lecture

Requirements placed on the network The idea of network architecture Key elements in implementation of a network

architecture Key metrics to evaluate the performance of computer

networks

An Example URL (Uniform Resource Locator) HTTP (Hyper Text Transfer Protocol) Click in your browser “http://www.mkp.com/pd3e” One click and as many as 17 messages are exchanged

Assuming the web page can be downloaded with a single message

Six messages to translate www.mkp.com into 213.38.165.180 Three messages to set up TCP between the browser and the

server Four messages for the browser to send the HTTP “get” request

and the server to reply with the requested page (+ ACKs) Four messages to tear down the connection

Requirements: Connectivity:Links Nodes

(a)

(b)

Point-to-point

Multiple access

Scalability Link Node Indirect connectivity →

switching

Switched Network

Clouds Switched network Circuit switched (telephone system) Packet switched (computer networks) Packets, messages Store-and-forward

Interconnection of Networks

internetwork (internet) Router, gateway address routing Unicasting, broadcasting, multicasting

Requirements: Cost-effective resource sharing

Efficient utilization of the links Multiplexing Analogy: CPU TDM FDM More efficient multiplexing: statistical multiplexing

L2

L3

R2

R3

L1 R1

Switch 1 Switch 2

Multiplexing over a link

How to service packets FIFO Round robin Quality of Service (QoS) Congestion

■ ■ ■

Support for Common Services

Application processes are communicating Should each application perform all the complex

functionality to communicate ? Common services, hide complexity (abstraction) Application level process communicate over logical

channels What functionality should the logical channel provide?

Host

HostHost

Channel

Application

Host

Application

Host

Common Communication Patterns

Client/Server Request/reply channel

(small request message, large reply message) – a digital library

The opposite Message stream channel – video on demand Channel abstractions

Reliability

Networks can fail Bit errors Burst errors Buffer overload Software/OS errors Routing errors Human errors Others (power failure)

Network Architecture:Example of A Layered Network System

Abstraction Interface Hide complexity Decompose the problem Monolithic software Modularity

Application programs

Process-to-process channels

Host-to-host connectivity

Hardware

Protocols

Protocols Service interface Peer interface

Hardware

Host-to-host connectivity

Request/replychannel

Message streamchannel

Application programs

Service and Peer Interface

Host 1 Host 2

Serviceinterface

Peer-to-peerinterface

High-levelobject

High-levelobject

Protocol Protocol

Example of A Protocol GraphHost 1 Host 2

Fileapplication

Digitallibrary

application

Videoapplication

Fileapplication

Digitallibrary

application

Videoapplication

RRP: Request Reply Protocol

MSP: Message Stream Protocol

HHP: Host-to-Host Protocol

Protocols Protocol specification

Pseudo code State transition diagram Packet formats

Interoperability Independent implementation

Standardization bodies IETF (Internet Engineering Task Force) ISO (International Standards Organization) IEEE (Institute of Electrical & Electronics Engineers)

EncapsulationHost Host

Applicationprogram

Applicationprogram

RRP

Data Data

HHP

RRP

HHP

Applicationprogram

Applicationprogram

RRP Data RRP Data

HHP RRP Data Header Trailer Body Demultiplexin

g

OSI Reference Model

One or more nodeswithin the network

End host

Application

Presentation

Session

Transport

Network

Data link

Physical

Network

Data link

Physical

Network

Data link

Physical

End host

Application

Presentation

Session

Transport

Network

Data link

Physical

OSI (Open System Interconnection) Reference model

Client-server model

REQUEST and REPLY

Applications Business: Web, VoIP, e-commerce Home: Connectivity, instant

messaging, social network, wiki Mobility

Peer-2-peer model

Network Scale and Hardware Broadcast vs. Point-2-Point

(unicast) Scale of network

Bluetooth, medical devices, RFID

Enterprise, home, AP, wireless router, 802.11 (WiFi), 802.3 (Ethernet), Virtual LANs

City coverage, cable TV + internet, Wireless MAN (802.16 WiMax)

Large geographical area, country, continent

Network Scale and Hardware

PANLAN

MANWAN

Network Scale and Hardware

WAN-VPN WAN-ISP

• Transmission lines• Routers inter-communication: Routing, forwarding algorithms

• Wireless WANs• Satellite• Cellular network

Network of Networks ISP (Internet service provder)

networks to connect many different types of networks Subnet: collection of routers and

communication lines Hosts: connected to subnet

Gateway: interconnects different netwroks Hardware and software translator

Network Software Protocol: agreement between

communicating parties Protocol stack: Efficient simplified

implementation by layers Services to higher layers, similar to

virtual machine

5-layer protocol stack

Physical communication

Virtual communication

• Clear, modular interface design,

• Well-defined functions

Network Architecture

Set of protocol layers

Protocol stack: list of protocols used by a certain system

Network Architecture 2

Layer Design Software design for higher levels,

hardware/firmware design for lower layers Design issues

Error detection, error correction Path selection, routing Network evolution: protocol layering Packet aggregation/de-aggregation, addressing,

ordering Scalability Resource allocation, scheduling, statistical

multiplexing Flow control, congestion control Quality of service Confidentiality, authentication

Connection Type Connection-oriented service:

circuit switch Connectionless service: packet

switch

Service vs. Protocol Service: a set of operations that a layer

provides to the layer above it Protocol: set of rules for the formatting,

packetization, message bit generation Object operations vs. implementation

Network Architecture Examples

Open System Interconnection (OSI) Generic model, although protocol

layers are not directly used TCP/IP

Not a generic model, but widely implemented protocol layers

Reference Model 1: OSI

• Open Systems Interconnection (OSI) reference model

• ISO (revised in 1995)• Principles

• New layer for a different abstraction

• Well-defined functionality

• Internationally standardized protocols

• Minimize information flow across interface

• Distinct functions per layer

PHY: Raw bits over the air, cable, fiber Data Link: Free of error transmission,

ACK/NACK, MAC: medium access control

Network: Routing, QoS, heterogonous network Transport: Packets to arrive in order,

independent of hardware or device, service type (e.g. error free connection, or unguaranteed connection) True end-to-end layer

Session: Dialog control high-level communication sync

Presetation: Syntax and semantics

Reference Model 2: TCP/IP