Protocol Layering Chapter 11: Protocol Layering. D.E.Comer. “Internetworking with TCP/IP:...

Protocol Layering

Chapter 11: Protocol Layering.D.E.Comer. “Internetworking with TCP/IP: Principles, Protocols and Architecture”, Vol. 1, Prentice Hall, 2000

Presented by Wuilbert Jaramillo

2CMPT 880. Protocol Layering – by Wuilbert Jaramillo, [email protected]. Fall 2003

Outline

Part 1– Network problems, protocol and layering concepts– Need for protocols and layering

Part 2 – ISO/OSI and TCP/IP models– Comparison– Common points– Final remarks


Outline Part 1

Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?


Outline Part 2

Example: ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary


Existing Problems in Communication Networks

Hardware failure– Hosts, routers

Network congestion– Networks have finite capacity

Packet delay Data corruption

– Electric, magnetic interferences– HW failure

Data duplication


Complexity of networks

Networks are complex !!!Networks are complex !!! Parts of a network:

– Hosts– Routers– Media– Applications– Hardware– Software– Different OS– Different protocols

Is there a Solution? Is there a Solution?

Organize all the elements under a same agreement

Better yet, use a divide and conquer approach

Result: the concept of a communications protocol


Outline Part 1

Existing problems in communication networks Protocol -definitionProtocol -definition The need for protocols Set of protocols: Layering What is Layering? Why Layering?


Some definitions for Protocol

an original draft, minute, or record of a document or transaction

a code prescribing strict adherence to correct etiquette and precedence (as in diplomatic exchange and in the military services)

a set of conventions governing the treatment and especially the formatting of data in an electronic communications system


Protocol

Agreement about communication Specifies

– Format of messages– Meaning of messages– Rules for exchange– Procedures for handling problems

Protocols allow to specify or understand communication without knowing the details of a particular hardware


Outline Part 1

Existing problems in communication networks Protocol -definition The need for protocolsThe need for protocols Set of protocols: Layering What is Layering? Why Layering?


Need for Protocols

Hardware is low level Many problems can occur

– Bits corrupted or destroyed– Entire packet lost– Packet duplicated– Packets delivered out of order


Need for Protocols(continued)

Need mechanisms to distinguish among – Multiple computers on a network– Multiple applications on a computer– Multiple copies of a single application on a computer– Different Operating Systems (OS)


Outline Part 1

Existing problems in communication networks Protocol -definition The need for protocols Set of protocols: LayeringSet of protocols: Layering What is Layering? Why Layering?


Set of Protocols

Work together Each protocol solves part of a communication

problem Known as

– Protocol suite– Protocol family

Designed in layers


Plan for Protocol Design

Intended for protocol designers Divides protocols into layers Each layer is devoted to one sub-problem


Outline Part 1



What is layering?

A technique to organize a network system into a succession of logically distinct entities, such that the service provided by one entity is solely based on the service provided by the previous entity.


Conceptual Layers of Protocol Software

Layer n

…

Layer 2

Layer 1

Layer n

…

Layer 2

Layer 1

Sender Receiver

Network

The modules of Protocol SW are on each machine stacked vertically into layers


Conceptual/Realistic view

High Level

Protocol Layer

Internet

Protocol Layer

Network

Interface Layer

Conceptual Layers Software Organization

Protocol 1Protocol 2

Protocol 3

Interface 1Interface 2

Interface3

IP Module


Example: Internet Protocol Layers

Five layers– Application: supporting

network applications ftp, smtp, http

– Transport: host-host data transfer

tcp, udp– Network: routing of a

datagram from source to destination

ip,routing protocols– Link: data transfer between

neighboring network elements ppp, ethernet

– Physical: bits “on the wire”

Application

Transport

Network

Link

Physical


Protocol Layering and Data

Application

Transport

Network

Link

Physical

M

MH

MHH

MHHH

Message

Segment

Datagram

Frame


Layers and packet headers

Each layer – Appends header to outgoing packet– Removes header from incoming packet

Receiver uses header as demultiplexing key– Sender Multiplexes among several layers

MHHH


Outline Part 1



Why layering?

Dealing with complex systems:– Explicit structure allows identification of complex

system’s pieces– Modularization eases developing, maintenance,

updating of system Change of implementation of layer’s service transparent to

rest of system


Example: No layering

TelnetFTP

HTTP

Coaxial cable

Fiber optic

Packet radio

Application

TransmissionMedia

No layering: each new application hast to be re-implemented for every network technology!


Example: now with Layers

TelnetFTP

HTTP

Coaxial cableFiber optic

Packet radio

Application

Transport& Network

TransmissionMedia

Solution: introduce an intermediate layer that provides a common abstraction for various network technologies


Outline Part 2

ISO/OSI 7-layer modelISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary


ISO 7 layer model

Based on early work done by the International Organization for Standardization (ISO)

Reference Model of Open System Interconnection (OSI)

Contains 7 conceptual layers OSI: conceptually define service, interface,

protocol


OSI Model concepts***

Service –says what a layer does Interface –says how to access the service Protocol –says how the service is implemented

– A set of rules and formats that govern the communications between two peers


ISO/OSI Reference Model

Seven Layers– Lower three layers are hop-by-hop– Next four layers are end-to-end

Application

Presentation

Session

Transport

Network

Datalink

Physical

Application

Presentation

Session

Transport

Network

Datalink

Physical

Network

Datalink

Physical

Physical Medium


ISO Layers

Layer 1: Physical (underlying hardware) Layer 2: Data Link (hardware frame definitions) Layer 3: Network (packet forwarding, routing) Layer 4: Transport (reliability, end-to-end) Layer 5: Session (login and passwords, session and

connection coordination) Layer 6: Presentation (data representation) Layer 7: Application (individual application program)


ISO Graphical View

Layer 7 Application Message Passing

Layer 6 Presentation Encoding

Layer 5 SessionAuthentication &

Encryption

Layer 4 TransportStreams & Segments

Layer 3 Network Datagrams

Layer 2 Data Link Frames & Packets

Layer 1Physical

Hardware Signaling & Wiring


X.25 and its relation to the ISO model

Best known and most widely used– Established as a recommendation of the ITU– Specially popular en Europe

Operates much like a telephone system– Consists of complex packet switches– Hosts attach to one of the packet switches


X.25 and its relation to the ISO model


Outline Part 2

ISO/OSI 7-layer model TCP/IP 5 layer reference modelTCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary


TCP/IP History

It originated from research– Developed by the Department of Defense (DOD)– Network of networks

Network of lowest bidders– The Army puts a bid on a computer and DEC wins

the bid– The Air Force puts out a bid and IBM wins– The Navy bid is won by Unisys


The TCP/IP 5-Layer Reference Model

Physical

Conceptual Layer Objects PassedBetween Layers

Application

Transport

Internet

Network Interface

Messages or Streams

Transport Protocol Packets

IP Datagrams

Network-Specific Frames


TCP/IP Layer Description

Layer 5: Application– Used for communicating among applications

Layer 4: Transport– Provides reliable delivery of data

Layer 3: Internet– Defines uniform format of packets forwarded across networks of

different technologies and rules for forwarding packets in routers Layer 2: Network

– Defines formats for carrying packets in hardware frames Layer 1: Physical


TCP/IP practical overview

Physical

Application

Transport

Internet

Network Interface

Telnet, FTP, e-mail, etc.

TCP, UDP

IP, ICMP, IGMP

device driver and interface card


Two hosts running FTP


Two networks connected with a router


Mail with TCP/IP


A general background on TCP/IP


Outline Part 2

ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary


Layers in both ISO and TCP/IP

Physical

Application

Transport

Internet

Network Interface

Physical

Application

Presentation

Network

Datalink

Session

Transport


Comparison


Differences between ISO and TCP/IP

Reliability Locus of Authority and control


Reliability

ISO/X.25– Connection Oriented– Complex protocols

guarantee error free transport on every layer

– Retransmission of corrupted packages

– Flow control on every layer

TCP/IP– Connection less– Reliability is an end-to-end

problem– Freedom on handling

corrupted packets– Flow control on transport

layer


Locus of Authority and Control

ISO/X.25– Network layer is service to

transport layer– Network handles routing,

flow control, acknowledgements internally

– Complex independent systems working for simple hosts

TCP/IP– Host participates in

network protocols– Host participates in e.g.

routing, flow control– Simple package delivery

system with intelligent hosts


Outline Part 2

ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layeringCommon points in layering Summary


Protocol layering principle

Layered protocols are designed so that layer N at the destination receives exactly the same object sent by layer N at the source


Protocol layering

Application

Transport

Internet

Network Interface

Host A Host B

Application

Transport

Internet

Network Interface

Physical net

Identicalmessage

Identicalpacket

Identicaldatagram

IdenticalFrame


Protocol Layering with a router


Layering in the presence of Network substructure

Transport

Internet

Network

Interface

Intranet

Software OrganizationConceptual Layers

Protocol 1Protocol 2

Protocol 3

Interface 1Interface 2

Interface3

IP Module

Point-To-Point(Intranet)


Multiplexing and Demultiplexing

IP ModuleARP Module

RARP Module

Demultiplexing Based on Frame type

Frame arrives


More Demultiplexing

ICMP ProtocolUDP Protocol

TCP Protocol

IP Module

Datagram arrives


Outline Part 2

ISO/OSI 7-layer model TCP/IP 5 layer reference model ISO/OSI vs. TCP/IP Common points in layering Summary


Summary

Advantages– Breaks down complex

problem into more manageable components

– Implementation details of one layer are abstracted away from other layers

Disadvantages– Information hiding,

inefficient implementations– Can introduce overhead– Could lead to inefficiency

Protocol Layering Chapter 11: Protocol Layering. D.E.Comer. “Internetworking with TCP/IP:...

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