The network layer provides two main services: connectionless and connection-oriented. Connectionless service routes packets independently through routers using destination addresses and routing tables. Connection-oriented service establishes a virtual circuit between source and destination, routing all related traffic along the pre-determined path. The document also discusses store-and-forward packet switching, where packets are stored until fully received before being forwarded, and services provided to the transport layer like uniform addressing.

1. Network Layer

2. Network Layer Design Issues
1. Store-and-Forward Packet Switching
2. Services Provided to the Transport Layer
3. Connectionless Service
4.Connection-Oriented Service
5. Comparison of virtual circuits and datagram
networks

3. 1.Store and Forward Packet
switching
The environment of the network layer protocols.
fig 5-1

4. 1.Store and Forward Packet switching
 A host with a packet to send transmits it to
the nearest router by using its own LAN or
Point to point link to the ISP . The packet
is stored until it fully arrive and link has
finished its processing by verifying the
checksum. Then it is forwarded to the next
route along the path until it reaches the
destination host when it is to be delivered
this mechanism is called store and forward
packet switching

5. 2. Services provided to the
transport Layer
1.The services should be independent of the
router technology.
2. The transport layer should be shielded from
the number, type, and topology of the routers
present.
3.The network addresses made available to the
transport layer should use a uniform
numbering plan, even across LANs and WANs

6. 3. Connectionless Service
Routing within a diagram subnet.

7. 3. Connectionless Service
-> Packets are injected into the network
individually and routed independently of each
other . Packets are called as Datagrams
-> Destination and outgoing line table is
maintained at every router
Internal router table will guide where to send
the packets from the different available
possibilities for reaching the destination
-> Incoming packets checksum verified before
forwarding to the next link

8. 4. Connection-Oriented Service
Routing within a virtual-circuit subnet.

9. 4. Connection-Oriented Service
 Connection is established a route from the source
machine to the destination machine is chosen as part
of the connection set up and stored in tables inside the
routers that route is used for all traffic flowing over the
connection when the connection is released virtual
circuit will be terminated
Eg: Telephone Lines

10. 5.Connectionless VS. Connection-Oriented