PROTOCOLS AND ARCHITECTURE Lesson 2 NETS2150/2850

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 Got the time? 2:00 Get TCP connection req TCP connection response time

Key Features of a Protocol Key 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