IP datagrams

Internet service paradigm:
TCP/IP supports both connectionless and connection-oriented services
fundamental delivery service is connectionless at the Internet layer
optional reliable connection-oriented service is layered on top of this at the transport layer

IP datagrams
Packets of data are sent across multiple physical networks via routers
Internet protocols define a universal virtual packet - the IP datagram
The amount of data carried in a datagram is not fixed and is determined by an application

Routers and routing tables:
Each router forwards a virtual packet by using a local routing table
Each entry is:
destination address
mask
next hop
IP address of a router or
Deliver direct
Then does address resolution


Best-effort delivery
IP attempts best effort delivery and does not guarantee to deal with:
datagram duplication
delayed or out of order delivery
corruption of data
datagram loss
These issues are dealt with other protocol layers

Encapsulation
When an IP datagram is sent across a physical network it is placed in the data area of a frame and the frame type is set to IP