04-network Layer-intro By Apcoms
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Faisal Amjad CPS 422
CPS 422 Computer Networks
THE PERSPECTIVE
NETWORK LAYER
NETWORK LAYER
Routing
Internetworking
Addressing
Packetizing
Fragmenting
Faisal Amjad CPS 422
Interconnecting the Networks
Introduction So far we have studied transmission across individual networks Now we take a conceptual LEAP to collect the diverse networking technologies into a coordinated Whole The primary Goal is a scheme that hides the details of underlying network hardware while providing universal communication services The primary Result is a high level abstraction that provides the framework for all design decisions
Application Level Interconnection o Application programs used to handle heterogeneity o The application program on each machine in the network understands the network connections for that machine and interoperate across the connections o At first this seems natural, but is limited and cumbersome in its approach o Adding new functionality to the system means building new application program for each machine o Adding new hardware means modifying or creating new programs for every possible application o When an intermediate program fails, source and destination are unable to detect or control the problem
Faisal Amjad CPS 422
Faisal Amjad CPS 422
Need for Network Layer
Interconnecting the Networks Network Level Interconnection
We can now conclude that:
o The alternative to application level interconnection o Provides a mechanism that delivers packets from original source to ultimate destination o It detaches the notion of communication from the details of networking technologies o It also hides the low-level details from the applications and the user
Faisal Amjad CPS 422
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
Faisal Amjad CPS 422
1
Internet Architecture We have seen how machines connect to individual networks Now we will see how networks can be interconnected to form an Internetwork or Internet Two networks can only be connected by a computer that attaches to both of them The inter-connecting computer must be willing to cooperate with other such computers in order to shuffle packets from one network to another Such computers are called Internet Gateways or Internet Routers
Two physical networks interconnected by a Router
Net 1
Net 2
Router
Router between Net 1 and Net 2 must capture packets destined for each other and transfer them
Faisal Amjad CPS 422
Faisal Amjad CPS 422
Interconnection through IP Routers When internet connections become more complex, routers need to know about the topology beyond the network to which they connect
Three Networks interconnected by two Routers
Net 1
R1
Net 2
R2
Net 3
R1 must transfer from Network 1 to Network 2 all packets destined for Network 2 or network 3 Important Point Routers use the destination network, not the destination host, when routing a packet
Faisal Amjad CPS 422
Network Layer at Source
Faisal Amjad CPS 422
Network Layer at Routers
Responsible to create packets that carry universal addresses (source and destination) Receives data from transport layer Adds universal addresses Ensures it is of correct size for passage through next link (fragments it if required) May add field for error control Delivers packet to the Data link layer
Faisal Amjad CPS 422
Responsible for routing packets Finds out the interface through which the packet must be forwarded May further resort to fragmentation
Faisal Amjad CPS 422
2
FINALLY
Network Layer at Destination
The user’s view
Receives packet from data link layer Responsible for address verification Checks if the packet has been corrupted during transmission If packet has been fragmented, then waits for all the fragments and re-assembles them Delivers the packet to the transport layer
Faisal Amjad CPS 422
Internet
The physical structure of Networks and Routers
Internet
Faisal Amjad CPS 422
3
CPS 422 Computer Networks
THE PERSPECTIVE
NETWORK LAYER
NETWORK LAYER
Routing
Internetworking
Addressing
Packetizing
Fragmenting
Faisal Amjad CPS 422
Interconnecting the Networks
Introduction So far we have studied transmission across individual networks Now we take a conceptual LEAP to collect the diverse networking technologies into a coordinated Whole The primary Goal is a scheme that hides the details of underlying network hardware while providing universal communication services The primary Result is a high level abstraction that provides the framework for all design decisions
Application Level Interconnection o Application programs used to handle heterogeneity o The application program on each machine in the network understands the network connections for that machine and interoperate across the connections o At first this seems natural, but is limited and cumbersome in its approach o Adding new functionality to the system means building new application program for each machine o Adding new hardware means modifying or creating new programs for every possible application o When an intermediate program fails, source and destination are unable to detect or control the problem
Faisal Amjad CPS 422
Faisal Amjad CPS 422
Need for Network Layer
Interconnecting the Networks Network Level Interconnection
We can now conclude that:
o The alternative to application level interconnection o Provides a mechanism that delivers packets from original source to ultimate destination o It detaches the notion of communication from the details of networking technologies o It also hides the low-level details from the applications and the user
Faisal Amjad CPS 422
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
Faisal Amjad CPS 422
1
Internet Architecture We have seen how machines connect to individual networks Now we will see how networks can be interconnected to form an Internetwork or Internet Two networks can only be connected by a computer that attaches to both of them The inter-connecting computer must be willing to cooperate with other such computers in order to shuffle packets from one network to another Such computers are called Internet Gateways or Internet Routers
Two physical networks interconnected by a Router
Net 1
Net 2
Router
Router between Net 1 and Net 2 must capture packets destined for each other and transfer them
Faisal Amjad CPS 422
Faisal Amjad CPS 422
Interconnection through IP Routers When internet connections become more complex, routers need to know about the topology beyond the network to which they connect
Three Networks interconnected by two Routers
Net 1
R1
Net 2
R2
Net 3
R1 must transfer from Network 1 to Network 2 all packets destined for Network 2 or network 3 Important Point Routers use the destination network, not the destination host, when routing a packet
Faisal Amjad CPS 422
Network Layer at Source
Faisal Amjad CPS 422
Network Layer at Routers
Responsible to create packets that carry universal addresses (source and destination) Receives data from transport layer Adds universal addresses Ensures it is of correct size for passage through next link (fragments it if required) May add field for error control Delivers packet to the Data link layer
Faisal Amjad CPS 422
Responsible for routing packets Finds out the interface through which the packet must be forwarded May further resort to fragmentation
Faisal Amjad CPS 422
2
FINALLY
Network Layer at Destination
The user’s view
Receives packet from data link layer Responsible for address verification Checks if the packet has been corrupted during transmission If packet has been fragmented, then waits for all the fragments and re-assembles them Delivers the packet to the transport layer
Faisal Amjad CPS 422
Internet
The physical structure of Networks and Routers
Internet
Faisal Amjad CPS 422
3
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