04-network layer-intro by apcoms

8/14/2019 04-Network Layer-Intro by Apcoms

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Computer NetworksCPS 422

NETWORK LAYER

Faisal AmjadCPS 422

THE PERSPECTIVE

NETWORK LAYER

Internetworking

Packetizing

Addressing

Routing

Fragmenting

Faisal Amjad CPS 422

Faisal AmjadCPS 422

IntroductionSo far we have studied transmission across

individual networks

Now we take a conceptual LEAP to collect thediverse networking technologies into a coordinatedWhole

The primary Goal is a scheme that hides thedetails of underlying network hardware whileproviding universal communication services

The primary Result is a high level abstraction thatprovides the framework for all design decisions


Interconnecting the Networks

Application Level Interconnectiono Application programs used to handle heterogeneity

o The application program on each machine in the networkunderstands the network connections for that machineand interoperate across the connections

o At first this seems natural, but is limited andcumbersome in its approach

o Adding new functionality to the system means buildingnew application program for each machine

o Adding new hardware means modifying or creating newprograms for every possible application

o When an intermediate program fails, source anddestination are unable to detect or control the problem

Faisal AmjadCPS 422

Interconnecting the Networks

Network Level Interconnectiono The alternative to application level interconnection

o Provides a mechanism that delivers packets fromoriginal source to ultimate destination

o It detaches the notion of communication from thedetails of networking technologies

o It also hides the low-level details from the applicationsand the user


Need for Network Layer

We can now conclude that:o To solve the problem of delivery through several links,

the Network Layer was designed

o It is responsible for

routing packets through routers and switches and host-to-host delivery


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Faisal AmjadCPS 422

Internet Architecture

We have seen how machines connect to individualnetworks

Now we will see how networks can beinterconnected to form an Internetwork orInternet

Two networks can only be connected by acomputer that attaches to both of them

The inter-connecting computer must be willing tocooperate with other such computers in order toshuffle packets from one network to another

Such computers are called Internet Gateways orInternet Routers


Net 1 Net 2Router

Two physical networks interconnected by a Router

Router between Net 1 and Net 2 must

capture packets destined for each

other and transfer them

Faisal AmjadCPS 422

Interconnection through IP Routers

When internet connections become more complex,routers need to know about the topology beyondthe network to which they connect


Net 1 Net 2R1

Three Networks interconnected by two Routers

Net 3R2

R1 must transfer from Network 1to Network 2 all packets destined

for Network 2 or network 3

Important Point

Routers use the destination network, not the destination host, whenrouting a packet

Faisal AmjadCPS 422

Network Layer at Source

Responsible to create packets that carry universaladdresses (source and destination)

Receives data from transport layer

Adds universal addresses

Ensures it is of correct size for passage throughnext link (fragments it if required)

May add field for error control

Delivers packet to the Data link layer


Network Layer at Routers

Responsible for routing packets

Finds out the interface through which the packetmust be forwarded

May further resort to fragmentation


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Faisal AmjadCPS 422

Network Layer at Destination

Receives packet from data link layer

Responsible for address verification

Checks if the packet has been corrupted duringtransmission

If packet has been fragmented, then waits for allthe fragments and re-assembles them

Delivers the packet to the transport layer


Internet

The users view

Internet

The physical structure of Networksand Routers

FINALLY

04-network layer-intro by apcoms

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