PROTOCOLS AND ARCHITECTURE

Lesson 2NETS2150/2850

Lesson Outcomes The need for a Protocol

Architecture Understand importance of OSI

Reference Model Overview of TCP/IP Suite – the

basis for the rest of this unit of study!

What’s a protocol? The set of rules or conventions

governing the exchange of data between two entities

Protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

All communication activity in Internet governed by protocols

What’s a protocol?

a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

Get http://www.awl.com/

TCP connection req

TCP connectionresponse

<file>time

Key Features of a ProtocolKey features of a protocol are: Syntax

Formats of the supported packet types Semantics

Definitions of each of the packet type and error codes

Timing Sequence in which packets are exchanged and

use of timers But, how to manage many related

protocols?!

Need For Protocol Architecture

Task broken into subtasks Implemented separately in layers as stack Functions needed in both systems Peer layers communicate E.g. File transfer

Source must activate comms. path or inform network of destination

Source must check destination is prepared to receive

File transfer application on source must check destination file management system will accept and store file for this user

May need file format translation

Standardized Protocol Architectures Required for devices to interoperate Vendors can have more marketable products Customers can insist on standards based

equipment Two standards:

OSI Reference model Never lived up to early promises de jure (i.e. by legislation)

TCP/IP Reference model Most widely used de facto (i.e. in reality)

OSI Reference Model Open Systems Interconnection Developed by the International

Organization for Standardization (ISO)

Seven layers A theoretical system delivered too

late!! TCP/IP is the de facto standard

OSI Reference Model II Each layer performs a subset of the

required communication functions Each layer relies on the next lower layer

to perform certain functions Each layer provides services through

primitives (operations) to the next higher layer

Changes in one layer should not require changes in other layers (modular, info hiding)

OSI Layers

Protocol Data Units (PDU) At each layer, there is a protocol Control data is added to user data at each

layer & certain functions performed E.g.: transport layer may fragment user data Each fragment has a transport header added

Destination SAP (i.e port #) Sequence number Error detection code

This gives a transport PDU

The OSI Environment

OSI as Framework for Standardization

Layer Specific Standards

Elements of Standardization Protocol specification

Operates between the same layer on two systems

May involve different operating systems Protocol specification must be precise

Format of data units (i.e. syntax) Semantics of all fields allowable sequence of PDUs (i.e timing)

Service definition Functional description of what is provided

Addressing Used by the higher layer, also known as SAP

OSI Layers (1) Physical

Physical interface between devices Mechanical Electrical Functional Procedural

Data Link Means of activating, maintaining and

deactivating a reliable link Error detection and control Higher layers may assume error free

transmission

OSI Layers (2) Network

Transfer of information Higher layers do not need to know about

underlying technology Not needed on direct links

Transport Exchange of data between end systems Error free In sequence No losses No duplicates

OSI Layers (3) Session

Provides control structure for communications Manages sessions between applications

Presentation Data formats and coding (big/little-endian) Data compression Encryption

Application Means for applications to access OSI environment Contains management functions and mechanisms

to support distributed applications

TCP/IP Protocol Architecture Developed by the US Defense Advanced

Research Project Agency (DARPA) for its packet switched network (ARPANET)

Used by the global Internet No official model but a working one!

Application layer Transport layer Internet layer or network layer Network access or data link layer Physical layer

Physical Layer Physical interface between data

transmission device (e.g. computer) and transmission medium or network

Characteristics of transmission medium

Signal levels Data rates

Network Access Layer Exchange of data between end

system and network Destination address provision

Physical address Invoking services like priority

Internet Layer (IP) Systems may be attached to

different networks Routing functions across multiple

networks Provides logical addressing

Implemented in end systems and routers

Transport Layer (TCP) Reliable delivery of data Ordering of delivery Provides application process

addressing (called port number)

Application Layer Support for user applications e.g. HTTP, FTP, Telnet, SMTP, SNMP

etc

OSI v TCP/IP

Encapsulation/Decap Process

TCP/IP Concepts

Addressing levels Level in architecture at which entity is

named Unique address for each end system and

router (i.e. physical address) Network level address (i.e. logical address)

IP or internet address (in TCP/IP) Network service access point or NSAP (in OSI)

Process within the system Port number (in TCP/IP) Service access point or SAP (in OSI)

Some Protocols in TCP/IP Suite

Intro Networking Video

Summary The needs for standardized

protocols and protocol architecture Discussed two layered models:

The OSI Reference Model TCP/IP protocol suite

Next: The mechanism of data transmission