CS-09 – Data Communications and Networks

AGENDA (Session 2)

Quiz

Network Software & Protocol Hierarchy

Network Design Issues

Network Layers, Interfaces and Related Terms

Connection-Oriented/Connectionless services

Operations during Information Transfer

Services Vs. Protocols

OSI Model

TCP/IP Model

TCP/IP Vs OSI

Standards and Standards Organisations

Quiz

1. A computer network Connects

a) Terminals with its main computer.

b) Two nodes with capability of processing.

c) Two or more microprocessor devices.

d) Two or more autonomous computers

2. On Internet transmission technology is ‘point-to-point’ communication and not ‘broadcast based communication. TRUE/FALSE

3. A network spread of ‘1m to 1Km’ would be termed as a

a) LAN

b) WAN

c) MAN

d) Ethernet

4. UTP stands for

a) Unterminated Twin Pair

b) Unshielded Twisted Pair

c) Under Testing PC

d) Unshielded Terminal Point

5. DQDB (Distributed Queue Dual Bus) technology allows

a) Less collision than bus topology in a LAN.

b) Fast Query of any Database.

c) Distribution of processing load in various computers.

d) A connection to switched network.

6. Subnet is a

a) Pre-designated part of any Network

a) Collection of routers and transmission system between routers.

b) Small computer network connected to a bigger network.

c) A type of network topology.

7. Internet is a

a) Internetwork of incompatible networks.

b) WAN of compatible networks.

c) Connection of only computers worldwide.

d) Connection of computers that exists in two or more countries.

8. What out of following network usage could result in major cost saving for companies.

a) Using Mirrored Servers.

b) Providing Employee-to-Employee communication.

c) Running Application Servers.

d) Providing company-wide Internet access.

Network Software

· Computer programs that run a network

· Organised as layers to form a structured design

Network Architecture = Set of Layers & Protocols

Layer Protocol = Virtual Communication between peers

Layer Interface Protocol = Actual communication across Interface

Protocol = Syntax (Structure) + Semantics (Interpretation Rules)

+ Timing (Flow speed and Events)

Information Flow Mechanism

Networks Design Issues

· Mechanism to Identify sender/receiver (addressing scheme).

· Rules of Data Transfer (Simplex, Half-Duplex, Full-Duplex).

· Logical Channels and priorities.

· Error Control (Most Physical Medium are not perfect)

· Sender receiver shall agree on common method

· Receiver tells correctness of data

· Order of message parts are to be restored on receiving side

· Handling the issue of fast/slow sender/receiver (Buffering)

· Handling variety in message length (disassembling, reassembling required)

· Inefficiency due to packetisation.

· Common channel usage requirement for unrelated messages (For cost saving) – Multiplexing – De-Multiplexing.

· Selection of Route between multiple available paths.

· Susceptibility to hacking and virus attacks.

ULTIMATE DESIGN AIMS OF INFORMATION TRANSFER

· ERROR FREE (Reliable, secure)

o Failure Frequency

o Recovery from failure

o Handling of Catastrophe

· EFFICIENT (Performance)

o No. of Users

o Medium

o Hardware

o Software

· ECONOMICAL (Low Cost Transfer)

o Medium Rentals

o Equipment costs

Layer Interfaces, Services & Related Terminology

	Peer Entity

N-PDU (Protocol Data Unit) – Division of SDU for protocol purposes

Connection Oriented / Connection-less services

Connection Oriented

· Modeled after Telephone system

· Sender pushes information – Receiver collects in same order.

· Connection is established prior to information transfer

· E.g. Remote Login.

Connectionless

· Modeled after postal system

· Sender sends information with address – information routed on various routers, receiver collects and assembles.

· Datagram Services (like telegrams)

· Acknowledged Datagram (Like registered A/D letter)

QUALITY of SERVICE QoS issue

· Reliable service – Acknowledgement of receipt of each message. E.g. File Transfer. DELAY inevitable.

§ Message Boundaries Preserved

§ Message Boundary Unknown

· UnReliable Service – Where some Data Noise is acceptable but delay is not acceptable. Audio/Video Transfer.

Basic Operations in Information Transfer Services

· Known as Service Primitives.

· Available to user or other network entity

Classes of Service Primitives

· Request : Some service wanted

· Indication: Event Information

· Response : wants to respond

· Confirm: Acknowledgement

			Connection Indication (Ring)
					Connect Response (Pick)
		Connection Confirmation (Ring Stop)
			Data Indication
						Data Request
			Disconnect Indication (HangUp)

Services Vs. Protocols

Service

· Defines feature made available to upper layer

· Service may not change with protocol changes.

· Like an abstract data type or object in programming languages.

Protocol

· Rules defining frames, packets exchanges between peer entities.

· Protocol also used to implement service definitions.

· Like a function in programming languages.

OSI (Open System Interconnection) Model

· ISO standard

Principles:

· Abstraction between Layers

· Well Defined Function of Layer

· Internationally Standardised protocol

· Layer Boundary should minimise data flow across interface

TCP/IP Model

FTP = File Transfer protocol, SMTP = Simple Mail Transfer Protocol, DNS = Domain Name System, HTTP = Hyper Text Transfer Protocol, NNTP = Network News Transfer Protocol, TCP = Transmission Control Protocol, UDP = Universal Datagram Protocol, IP = Internet Protocol.

OSI Vs. TCP

· OSI defines Services, Interfaces and Protocols explicitly. TCP/IP doesn’t

· Layering concept is a post idea for TCP while OSI starts with this idea.

· OSI allows generic explanation of other protocols.

· TCP/IP doesn’t differentiate between Physical Layer and Data-link rules.

· Host to Network in TCP/IP is an unclear definition that doesn’t precisely cover network to D/L connection.

· TCP/IP is popular due to internet.

· OSI is unpopular because of Bad Timing, Bad technology (Unclear Upper Layers) , Bad Implementation (Connection vs. Receive Primitive) and Bad Politics (European Vs. US).

Standards and Standards Organisations

Standards

· De-facto (By Fact)

o Proprietary (Organisation Specific)

o Non-proprietary (Public Domain)

· De-jure (By Law)

o By an standards organisation.

Standards Organisations

(Committees, Forums, Regulatory Agencies)

· ISO (International Standards Organisation)

o 1947, Voluntary Organisation of Member Nations

o BIS Represents India in ISO

· ITU-T (International Telecomm Union – Telecom Stds Sect)

o Earlier CCITT (Consultative Committee on International Telegraph and Telephony)

o Famous for V (V.24, V.32, V.42) and X (X.25, X.28, X.400) series

o ISDN and B-ISDN also defined.

· IEEE (Institute of Electrical and Electronics Engineers)

o Famous for project 802 (LAN)

o Largest Professional Engineering Society

· EIA (Electronics Industries Association)

o Famous for RS-232-C and RS-449 etc.

· ISOC (Internet Society)

o IETF (Internet Engineering Task Force) part of IAB.

o TCP/IP in form of RFCs.

Others Like BIS, ANSI, ETSI, FR Forum, ATM Forum, FCC, TRAI are also there.