Lecture notes about the OSI model and it's seven layers.

1. The OSI Model
OSI (OpenSystemsInterconnection)
Opensystemisa model thatallowstwodifferentsystemstocommunicate regardlessof theirunderlying
architecture.
Peerto Peer
Layer x in sendingdevice communicateswithLayerx inreceivingdevice.
Physical Layer
Coordinatesthe functionrequiredtotransmitabitstreamovera physical medium.Itdealswiththe
mechanical andthe electrical specificationsof the interface andtransmissionmedium.Itdefinesthe
proceduresandfunctionsthatphysical devicesandinterfaceshave toperformfortransmissiontooccur.
The physical layerisconcernedwiththe following:
1. Physical Characteristicsof InterfacesandMedia
2. Representationof bits
3. Data TransmissionRate
4. Synchronizationof bits
5. Line Configuration
6. Physical Topology
7. TransmissionNode
Data Link Layer
The data linklayertransformsthe physical layertoa reliable linkandisresponsiblefornode tonode
delivery.Makesthe physical layerappearerrorfree tothe networklayer.
SpecificResponsibilitiesinclude the following:
1. Framing
2. Physical Addressing
3. Free FlowControl
4. Error Control
5. AccessControl
Network Layer
The networklayerisresponsible forthe source todestinationdeliveryof apacketpossiblyacross
multiple networks. If twosystemsare attachedtodifferentnetworkswithconnectingdevicesbetween
the network.There isoftenaneedforthe networklayertoaccomplishsource todestinationdelivery.
Responsibilitiesinclude:
1. Logical Addressing
2. Routing

2. Transport Layer
It ensuresthe whole message arrivesintactandinorder.Foraddedsecuritythe layermaycreate a
connectionbetweenthe twoendports.A connectionisasingle,logical pathbetweenthe source
and the destinationthatisassociatedwithall packets inamessage.
SpecificResponsibilities:
1. Service PointAddressing
2. SegmentationandRe-assembly
3. ConnectionControl
4. FlowControl
5. Error Control
SessionLayer
The networkdialogue controlleritestablishes,maintainsandsynchronizesthe interactionbetween
communicationsystems.
SpecificResponsibilities:
1. Dialogue Control
2. Synchronization
PresentationLayer
Thislayerisconcernedwiththe syntax andsemanticsof the informationexchangedbetweentwo
systems.
SpecificResponsibilities:
1. Translation
2. Encryption
3. Compression
ApplicationLayer
Enablesthe userto accessthe networkitprovidesuserinterfacesandsupportforservicessuchas
electronicmail,Remotefile accessandtransfer,share database managementandothertypesof
distributedinformation services.
SpecificResponsibilities:
1. NetworkVirtual Terminal
2. File transfer,Accessandmanagement
3. Mail Services
4. DirectoryServices