CS代考 PROTOCOL ARCHITECTURE

PROTOCOL ARCHITECTURE
Open System Interconnect (OSI) TCP/IP

• LayeredArchitecture • OSILayers

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• TCP/IPLayers

Protocol Layering
• Protocollayeringenablesustodivideacomplextask into several smaller and simpler tasks
• Weusetheconceptoflayersinourdailylife.
– The process of sending a letter to a friend would be complex if there were no services available from the post office.

Protocol Layering – scenario1
• Face-to-facecommunication
• Eveninasimplescenarioofacandidconversation between friends, there are rules to follow
1. greeting each other when they meet.
2. confine vocabulary to the level of their friendship
3. refrain from speaking when the other party is speaking
4. conversation should be a dialog, not a monolog
5. exchange some nice words when they leave

Protocol Layering – scenario2
• Twopartiescommunicatingsecretmessagesabouta new business idea – using mail post letters

Principles of Protocol Layering
1. Forbidirectionalcommunication,weneedtomake each layer so that it is able to perform two opposite tasks, one in each direction, i.e. transmit/receive
2. objectsundereachlayershouldbeidentical
3. Assumethereisalogicalconnectionbetweeneach layer and its counterpart

Principles of Protocol Layering

The OSI Model
• OpenSystemsInterconnection(OSI).
• DevelopedbytheInternationalOrganizationfor Standardization (ISO).
• Modelforunderstandinganddevelopingcomputer-to- computer communication architecture that is flexible, robust and interoperable.
• Itisnotaprotocol.
• Developedinthe1980s.
• Dividesnetworkarchitectureintosevenlayers.

The OSI Model
• Eachlayerperformsasubsetoftherequired communication functions
• Eachlayerreliesonthenextlowerlayertoperformmore primitive functions
• Eachlayerprovidesservicestothenexthigherlayer
• Changesinonelayershouldnotrequirechangesinother layers

The OSI Model
• Layer1,2,3arethenetworksupportlayer,dealswiththe physical aspects of moving data from one device to another.
• Layer4ensuresthatwhatthelowerlayerhave transmitted is in a form that the upper layers can use.
• Layer5,6,7aretheusersupportlayer,allowthe interoperability among unrelated software.

OSI layers
1. Physical layer
2. Data Link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer

OSI layers

OSI layers

Protocol Data Units (PDU)
• Ateachlayer,protocolsareusedtocommunicate
• Controlinformationisaddedtouserdataateachlayer
– Example: the transport layer may fragment user data, each fragment has a transport header added
Destination Address Sequence number Error detection code
– This creates a transport protocol data unit (TPDU)

An exchange using the OSI model

L1: Physical Layer
• Thephysicallayerisresponsibleforcarryingindividual bits in a frame across the link
• Thephysicallayerisstillalogicalcommunication because there is another, hidden layer, the transmission media, under the physical layer
– the transmission medium does not carry bits; it carries electrical or optical signals
– There are several protocols that transform a bit to a signal – to be discussed..

L2: Data Link layer
• ResponsibleofHoptohopdelivery:
– Framing: divided the stream of bits received from the network layer manageable data units called frames.
– Physical address (MAC address).
– Flow control
– Error control: added trailer to the end of frame.
– Access control: multiple access control MAC

Data Link layer cont.
10110110101 01100010011 10110000001

Hop-to-Hop delivery

L3: Network Layer
• Thenetworklayerisresponsiblefor:
– Thedeliveryofindividualpacketsfromtheoriginal source to the final destination
– Logical addressing: if the packet passes the network boundary we need another addressing system that is universal
– Routing : route or switch the packet to final destination.
– Source-to-destination delivery, i.e. end-to-end

Network Layer cont.

Source-to-Destination delivery

L2 / L3 Devices – what is different
Switch is a L2 device Router is a L3 device

Network Layer Protocol Examples
• IP: Internet Protocol adds information about – source/destination addresses
– Type of service/traffic
– Checksum
– Time to live
– Optional extensions

Network Layer Protocol Examples
• ICMP: Internet Control Message Protocol: helps IP to
report some problems when routing a packet
• IGMP: Internet Group Management Protocol: helps IP in multitasking

Network Layer Protocol Examples
• ARP: Address Resolution Protocol: helps IP to find the link-layer address of a host or a router when its network-layer address is given
• RARP: Reverse Address Resolution Protocol: helps IP to find the network-layer address of a host or a router when its link-layer address is given

L4: Transport Layer
• Thetransportlayerisresponsiblefor:
– Service point or Port addressing
– Segmentation and reassembly: a message is divided into transmittable segments each segment containing a sequence no.
– Connection Control: connection oriented or connectionless.
– Flow control
– Error control

Transport Layer cont.

Transport Layer Protocol Examples
TCP: Transmission Control Protocol
– Connection based, error detection/correction, flow
UDP: User Datagram Protocol
– Connectionless based, best effort, light weight, efficient
SCTP: Stream Control Transmission Protocol
– Based on UDP, designed to respond to new applications that are emerging in the multimedia

Reliable process-to-process connection

L5: Session Layer
• Dialogcontrol:establish,maintain,andsynchronizethe
interaction between communicating systems.
• Synchronization:itallowsaprocesstoaddcheckpoints or synchronization points to a data stream.

Session Layer

L6 :Presentation Layer
• Designtothehandlethesyntaxandsemanticofthe
information exchanged between 2 systems.
• datatranslation,encryption,decryption,and compression.

Presentation Layer

L7: Application Layer
• Theapplicationlayerisresponsibleforproviding services to the user.
• Mailservices
• Filetransfer,accessandmanagement
• Remotelog-inornetworkvirtualterminal
• AccessingtheWorldWideWeb
• Directoryservice

Application Layer
SMTP Telnet HTTP SMTP Telnet HTTP

Application Layer Examples
• HTTP: The Hypertext Transfer Protocol is a vehicle for
accessing the World Wide Web (WWW).
• SMTP: The Simple Mail Transfer Protocol is the main protocol used in electronic mail (e-mail) service.
• FTP: The File Transfer Protocol is used for transferring files from one host to another.

Application Layer Examples
• TheTerminalNetwork(TELNET)andSecureShell (SSH) are used for accessing a site remotely.
• SNMP: The Simple Network Management Protocol is used by an administrator to manage the Internet at global and local levels.
• DNS: The Domain Name System is used by other protocols to find the network-layer address of a computer from a URL (Uniform Resource Locator)

TCP/IP Protocol Suite
• TheTCP/IPprotocolsuiteisahierarchicalprotocol,
made of five layers: 1. Physicallayer
2. Datalinklayer
3. Networklayer
4. Transportlayer 5. Applicationlayer.

TCP/IP and OSI model

Some Protocols in TCP/IP Suite

TCP/IP PROTOCOL SUITE
• ThelayersintheTCP/IPprotocolsuitedonotexactly match those in the OSI model.
• TheoriginalTCP/IPprotocolsuitewasdefinedas having four layers: host-to-network, internet, transport, and application.
• However,whenTCP/IPiscomparedtoOSI,wecansay that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.

Addressing
• Fourlevelsofaddressesareusedinaninternet employing the TCP/IP protocols:
1. physicaladdress, 2. logicaladdress, 3. portaddressand 4. specificaddress.

Addressing
e.g. someorg.com

Multiplexing and Demultiplexing
Several applications are served by same transport protocol, a.k.a. multiplexing one at a time

Relationship of layers and addresses in TCP/IP
SCTP: Stream Control Transmission Protocol TCP: Transmission Control Protocol
UDP: User Datagram Protocol

Example L2 Addressing
• Anodewithphysicaladdress10sendsaframetoanode with physical address 87.
• Thetwonodesareconnectedbyalink(bustopologyLAN).
• thecomputerwithphysicaladdress10isthesender,andthe computer with physical address 87 is the receiver.

Example L3 Addressing
• Figureshowsapartofaninternetwithtworouters connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.

Figure IP addresses

Example L4 Addressing
• Figureshowstwocomputerscommunicatingviathe Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.

Figure 2.21 Port addresses

Network Devices
• Modem:adevicethatmodulatesadigitalsignalonto
analog signal for transmission over telephone lines. • Repeater:Re-generatesthesignalagain.

Network Devices
1. Hub, a distributor that has a lot of ports which connected to computers.
2. Switches, like a hub but it transmit packets to it destination
3. Bridge, it is used to connect two similar LANs.
4. Routers, choose the best path to transmit the packet.
5. Gateway, it is use to connect two deferent LANs and connect different application protocols.
6. Repeaters, repeats signals that travels via long distance

Network devices With Layer
Network Devices
Application Layer
Application gateway
Transport Layer
Transport gateway
Network Layer
Router and gateway
Data link layer
Bridge and Switch
Physical Layer
Repeater, Hub and Modem.

References
• DataCommunicationsandNetworking5thedition– 2013, Behrouz A. Forouzan; Chapter 2

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