Connectionless vs Connection-oriented ServiceTCP/IPs fundamental
delivery service is connectionlessIndividual packets travel
independently and contains information that identifies the intended
recipientA reliable connection-oriented service is added on top of
the underlying connectionless service
Datagram forwarding across heterogeneous networksHeterogeneous
networks use different frame formatsRouter cannot forward a frame
from one type of network to another without modificationTwo
networks may use incompatible address formats (ie. address in a
frame may make no sense on another network).
IP Datagrama universal, virtual, hardware-independent internet
packet consisting of an IP header followed by data (fig
20.1)FSource and destination addresses in the datagram header are
IP addressesThe size of an IP datagram(version 4) can vary from 1
byte of data to 64k bytes.
Routing/Forwarding of Datagramsprocess of using a routing table
(fig 20.3) to select a next hop for a given datagramdatagram with
destination address D is masked with the i-th entry in the routing
table to determine next hop address if ((Mask[i] & D ) ==
Destination[i] )then forward to NextHop[i]
IP Datagram HeaderIP datagram header format (fig 20.4)Data
header contains the ultimate destination, not the frame headerWhen
a router forwards the datagram to another router, the IP address of
the next hop does not appear in the datagram headerThe address of
the next hop is used to translate to a corresponding hardware
address for transmission (ARP).
Unreliable Datagram DeliveryIP makes a best-effort attempt to
deliver each datagramNo guarantee of datagram deliveryProblems that
can occur at layer 3datagram duplication due to excessive
delayout-of-order delivery data corruption datagram loss Higher
layers of protocol software are needed to handle these errors.
