ProtocolsProtocols Used for communications between Used for communications between

entities in a systementities in a system Must speak the same languageMust speak the same language EntitiesEntities

User applicationsUser applications E-mail facilitiesE-mail facilities TerminalsTerminals

SystemsSystems ComputerComputer TerminalTerminal Remote sensorRemote sensor

Protocol ContProtocol Cont Protocol:Protocol:

A set of rules and conventionsA set of rules and conventions Governs how computers exchange information over Governs how computers exchange information over

a shared/network medium. a shared/network medium. Used for communications between entities in a Used for communications between entities in a

systemsystem Defines :Defines :

What is communicatedWhat is communicated How it is communicatedHow it is communicated When it is communicatedWhen it is communicated

Varieties of communication protocols exist.Varieties of communication protocols exist. LAN protocols, WAN protocols, Network LAN protocols, WAN protocols, Network

protocols, Routing protocols etc. protocols, Routing protocols etc.

Key Elements of Protocol Key Elements of Protocol Syntax:Syntax:

Refers to structure or format of the data (the order Refers to structure or format of the data (the order they are presented)they are presented)

Example - data format, codingExample - data format, coding

Semantics:Semantics: Refers to the meaning of each section of the bitsRefers to the meaning of each section of the bits Example - data information, control informationExample - data information, control information

Timing:Timing: Refer to synchronousRefer to synchronous

When data should be sentWhen data should be sent How fast they can be sentHow fast they can be sent

Example sequencing, speed/delay matchingExample sequencing, speed/delay matching

Protocol ArchitectureProtocol Architecture Protocols in networking follows ‘layered’ Protocols in networking follows ‘layered’

architecturearchitecture

Purpose of this layered architecture: Purpose of this layered architecture: functions necessary for transfer of data are functions necessary for transfer of data are

grouped into layers.grouped into layers. a set of/each task(s) is separated from others.a set of/each task(s) is separated from others. several protocols at each layer, each suitable several protocols at each layer, each suitable

for a different situation.for a different situation. work that must be done in networking is work that must be done in networking is

broken down into manageable units. broken down into manageable units.

Protocol ArchitectureProtocol Architecture Task of communication broken up into Task of communication broken up into

modules, for example file transfer could modules, for example file transfer could use three modulesuse three modules File transfer applicationFile transfer application Communication service moduleCommunication service module Network access moduleNetwork access module

A simplified architecture A simplified architecture for file transfer for file transfer

Three-layered ModelThree-layered Model

Network Access LayerNetwork Access Layer Exchange of data between the computer Exchange of data between the computer

and the networkand the network Sending computer provides address of Sending computer provides address of

destination computer.destination computer. May invoke levels of serviceMay invoke levels of service Dependent on type of network used Dependent on type of network used

(LAN, packet switched etc.) (LAN, packet switched etc.)

Cont…Cont…

Transport LayerTransport Layer Reliable data exchangeReliable data exchange Independent of network being usedIndependent of network being used Independent of application Independent of application

Application LayerApplication Layer Support for different user applicationsSupport for different user applications E.g. e-mail, file transfer E.g. e-mail, file transfer

Protocols in simplified Protocols in simplified architecture architecture

Addressing Addressing RequirementsRequirements

Two levels of addressing requiredTwo levels of addressing required Each computer needs unique Each computer needs unique

network addressnetwork address Each application on a (multi-tasking) Each application on a (multi-tasking)

computer needs a unique address computer needs a unique address within the computerwithin the computer The service access point or SAPThe service access point or SAP The port on TCP/IP stacksThe port on TCP/IP stacks

Protocol Data UnitProtocol Data Unit At each layer, protocols are used to At each layer, protocols are used to

communicatecommunicate Control information is added to user data Control information is added to user data

at each layerat each layer Transport layer may fragment user dataTransport layer may fragment user data Each fragment has a transport header Each fragment has a transport header

addedadded Destination SAPDestination SAP Sequence numberSequence number Error detection codeError detection code

This gives a transport protocol data unitThis gives a transport protocol data unit

Protocol Data UnitsProtocol Data Units

Network PDUNetwork PDU

Adds network headerAdds network header Network address for destination computerNetwork address for destination computer Facilities requestsFacilities requests

Standardized Protocol Standardized Protocol ArchitecturesArchitectures

Required for devices to communicateRequired for devices to communicate Vendors have more marketable productsVendors have more marketable products Customers can insist on standards based Customers can insist on standards based

equipmentequipment Two standards:Two standards:

OSI Reference modelOSI Reference model Never lived up to early promisesNever lived up to early promises

TCP/IP protocol suiteTCP/IP protocol suite Most widely usedMost widely used

Also: IBM Systems Network Architecture Also: IBM Systems Network Architecture (SNA)(SNA)

OSI Model OSI Model

The OSI Model The OSI Model A layered framework for network system A layered framework for network system

s design s design allows for communication across all type allows for communication across all type

s of computer systems s of computer systems consists of 7 layers consists of 7 layers each layer defines a segment of process each layer defines a segment of process

of moving information of moving information

Layered Architecture Layered Architecture

Please Do Not Touch Steve’s Pet Alligator

Application

Presentation

Session

Transport

Network

Data Link

Physical

- - Peer to Peer Processes- - Peer to Peer Processes

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

machineA

machineB

--- - -< peer to pee ---r process >

provides s ervices for

uses se rvices

provide d by

The OSI EnvironmentThe OSI Environment

Functions of the Layers Functions of the Layers

Physical Layer Physical Layer Transmits a bit stream over a physical link Transmits a bit stream over a physical link Deals with the mechanical and electrical spe Deals with the mechanical and electrical spe

cifications of the interface and transmission cifications of the interface and transmissionmediummedium

Specification Responsibilities : defines Specification Responsibilities : defines interface the devices and the transmission mediu interface the devices and the transmission mediu

mm data rates : # of bits sent each second data rates : # of bits sent each second synchronisation of bits : synchronises both side cl synchronisation of bits : synchronises both side cl

ocksocks

Physical Layer (Cont.) Physical Layer (Cont.)

Specification Responsibilities : defines ( Specification Responsibilities : defines (cont.)cont.) Line configuaration : Line configuaration :

concerns with the connection of devices to the m concerns with the connection of devices to the mediumedium

- - point to point configuration- - point to point configuration 2 devices are connected together through a link 2 devices are connected together through a link

multipoint configuaration multipoint configuaration a aaaa aa aaaaaa aaaaaaa aaaaaaa aaaaaaaa aaaa aa aaaaaa aaaaaaa aaaaaaa aaaaaaa

physical topology, defines physical topology, defines how devices are connected (mesh, star, etc.) how devices are connected (mesh, star, etc.)

Physical Layer (Cont.) Physical Layer (Cont.)

Specification Responsibilities : define Specification Responsibilities : define s (cont.) s (cont.)

Transmission mode, defines Transmission mode, defines 2direction of transmission between devices 2direction of transmission between devices

- -simplex, halfdupl ex, f ul l dupl ex - -simplex, halfdupl ex, f ul l dupl ex

Data Link Layer Data Link Layer - - node to node delivery- - node to node delivery fix the errors for the next layer fix the errors for the next layer Specification Responsibility Specification Responsibility

framing framing devides the stream of bits into frames devides the stream of bits into frames

physical addressing physical addressing add headers (souce address, destination address) add headers (souce address, destination address)

aaaa aaaaaaaaaaa aaaaaaa prevent overflow transmission prevent overflow transmission

aaaaa aaaaaaaaaaaa aaaaaaa add mechanism for detecting damages add mechanism for detecting damages

Data Link Layer Data Link Layer

Specification Responsibility (cont.) Specification Responsibility (cont.) access control access control

aaa a aaaaaaaaa aaaaaaaaaaaaaaaaa a aaaaaaaaa aaaaaaaaaaaaaa determines which device has control over the link determines which device has control over the link

at any given time at any given time

Responsible the delivery of packets b Responsible the delivery of packets b etween 2 systems on the same netwo etween 2 systems on the same netwo

rk link rk link

Network Layer Network Layer

- -Responsi bl e f or t he source t o dest - -Responsi bl e f or t he source t o dest i nat i on del i very of packet across i nat i on del i very of packet across

mul i t pl e net work l i nks mul i t pl e net work l i nks ensures t hat a packet get s f romi t ensures t hat a packet get s f romi t

ori gi n t o dest i nat i on ori gi n t o dest i nat i on Specification Responsibilities Specification Responsibilities

logicall addressing logicall addressing add source/destination addresses add source/destination addresses

routingrouting

Network Layer (cont.) Network Layer (cont.)

- - Responsible for end to end delivery of - - Responsible for end to end delivery of individual packet individual packet

each packet is treated independently each packet is treated independently gets the packet to the correct comput gets the packet to the correct comput

erer

Transport Layer Transport Layer

- - Responsible for source to destination ( - - Responsible for source to destination (- - end to end) delivery of- - end to end) delivery of entire message entire message

ensure that the whole message arrives int ensure that the whole message arrives int act and in order act and in order

Specification Responsibilities Specification Responsibilities - service point addressing- service point addressing

port address port address gets the entire message to the correct progra gets the entire message to the correct progra

m on the computer m on the computer

Transport Layer (cont.) Transport Layer (cont.)

Specification Responsibilities (cont.) Specification Responsibilities (cont.) segmentation and reassembly segmentation and reassembly

devides message into segment (packet) devides message into segment (packet) addes a sequence number to each segment addes a sequence number to each segment

flow control flow control similar to the data link flow control similar to the data link flow control

perform end to end (machine) rather than across a link perform end to end (machine) rather than across a link

error control error control makes sure that the entire message arrives at the r makes sure that the entire message arrives at the r

eceiver without error (damage, loss, etc.) eceiver without error (damage, loss, etc.) retransmission mechanism retransmission mechanism

Session Layer Session Layer

The network dialog controller The network dialog controller Establishes, maintains, synchronise the int Establishes, maintains, synchronise the int

eraction between communication systems eraction between communication systems Specification Responsibilities Specification Responsibilities

dialog control dialog control - - agree to take either simplex, half duplex, full duplex - - agree to take either simplex, half duplex, full duplex

modemode synchronisationsynchronisation

allows a process to add checkpoints (synchronisatio allows a process to add checkpoints (synchronisatio n points in to a data stream) n points in to a data stream)

Session Layer (Cont.) Session Layer (Cont.)

a message of 1320 bytes

100

100

100

100

…...

checkpoint

synchronisation

Presentation Layer Presentation Layer

Concernswi t h t he synt ax and semant i cs of i Concernswi t h t he synt ax and semant i cs of i nformation exchanged between 2 sys nformation exchanged between 2 sys

t emst ems Specification Responsibilities Specification Responsibilities

translationtranslation character string character string numbers, etc. numbers, etc.

different computers use different encodi different computers use different encodi ng systems ng systems

Presentation Layer (Cont. Presentation Layer (Cont.))

Specification Responsibilities (cont.) Specification Responsibilities (cont.) responsible for interoperability between responsible for interoperability between

these different encoding methods these different encoding methods encryption encryption

aaa aaaaaaaaa aaaaaa aaaaaaaa aaaaaaaaa aaaaaa aaaaa aaaaaa aaaaa/ aaaaaa aaaaa/

compressioncompression reduce the number of bits to be transmitted reduce the number of bits to be transmitted

Application Layer Application Layer

Enables the user (human/software) t Enables the user (human/software) t o access the network o access the network

Specification Responsibilities Specification Responsibilities Applications : examples Applications : examples

aaaa aaa aaaaaaa aaaa aaaaaaaa aaa aaaaaaa aaaa aaaa to remote login to a remote machine to remote login to a remote machine

aaaa aaaaaaaaaaaa aaaaaaaa a aaa aaaaaaaaa aaa aaaaaaaa

TCP/IP Protocol Suite TCP/IP Protocol Suite

Used in the Internet Used in the Internet Developed before the OSI Model Developed before the OSI Model

do not match exactly with OSI Model do not match exactly with OSI Model 5 layers 5 layers

ApplicationApplication TransportTransport InternetworkingInternetworking NetworkNetwork PhysicalPhysical

TCP/IP Protocol Suite (Co TCP/IP Protocol Suite (Cont.)nt.)

Two main protocols Two main protocols Transmission Control Protocol Transmission Control Protocol aaaaaaaaa aaaaaa aaaaaaaaaaaaaaaaa aaaaaa aaaaaaaa

Many other protocols Many other protocols Hierarchical protocol Hierarchical protocol archi t ect ure archi t ect ure

made up f or i nt eract i ve modul es made up f or i nt eract i ve modul es - each upper level protocol is supported b - each upper level protocol is supported b

- y one or more lower level protocols - y one or more lower level protocols

TCP/IP Protocol Suite (Co TCP/IP Protocol Suite (Cont.)nt.)

AttheTransport l ayer, TCP/I P defi nes t w AttheTransport l ayer, TCP/I P defi nes t w o prot ocol s o prot ocol s

TCP TCP aaa aaaaa aaaaaaaa aaaaaaaaaaaa aaaaa aaaaaaaa aaaaaaaaa

At the Network layer At the Network layer IP IP

OSI vs TCP/IPOSI vs TCP/IP

TCP/IP and the OSI Model TCP/IP and the OSI Model

Physical

DataLink

Protocols defined b y the underlying ne

tworks

Network

ICMP IP

RARP

IGMP AR

P

Transport UDP TCP

ApplicationPresen

tationSession

ApplicationSMTP TELNET NFSFTP DNS SNMP

Addressing levelAddressing level Level in architecture at which entity is Level in architecture at which entity is

namednamed Unique address for each end system Unique address for each end system

(computer) and router(computer) and router Network level address Network level address

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

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

Trace of Simple Trace of Simple OperationOperation

Process associated with port 1 in host Process associated with port 1 in host A sends message to port 2 in host BA sends message to port 2 in host B

Process at A hands down message to Process at A hands down message to TCP to send to port 2TCP to send to port 2

TCP hands down to IP to send to host TCP hands down to IP to send to host BB

IP hands down to network layer (e.g. IP hands down to network layer (e.g. Ethernet) to send to router JEthernet) to send to router J

Generates a set of encapsulated PDUsGenerates a set of encapsulated PDUs

PDUs in TCP/IPPDUs in TCP/IP

Standard OrganizationsStandard Organizations

ISO ITU

IEEE

ANSI

EIA

State Department

Carriers Other org.