Internet Protocol:
Connectionless Datagram
Delivery
Chapter 7
Introduction
• An internet is an abstraction of physical networks
because it provides the same functionality:
– Accepting packets and delivering them
• Conceptual layers of internet services
Applications
Reliable Transport Service
Connectionless Packet Delivery Service
Connectionless Delivery System
• Service is defined as unreliable, best-effort,
connectionless packet delivery system
– Unreliable because delivery is not guaranteed
• the packet may be lost, duplicated, delayed, or delivered out of
order
• the service will not detect such conditions, nor will it inform
the sender or receiver - how will they know?
– Connectionless because each packet is treated
independently from all others
– Best-effort because bad things are not done
intentionally
Purpose of the Internet Protocol
• IP provides
– the basic unit of data transfer used in a TCP/IP internet,
and the format of all data
– IP software which performs the routing, the path over
which data is sent
– a set of rules for unreliable packet delivery: how
packets are processed, how and when error messages
are generated, when packets can be discarded
What is a Datagram?
• The basic unit of information passed across a
TCP/IP internet
IP datagram : internet = frame : physical network
• A datagram is separated into header and data areas
(like a frame) as shown in Figure 7.2
– The datagram header contains IP addresses
– The frame header contains hardware addresses
• See Figure 7.3
Summary
• IP formally specifies the format of internet
packets, called datagrams
• The IP datagram header contains
– source and destination IP addresses
– fragmentation information, precedence, and a checksum
for the header
– may contain options:
• record routing, timestamps
For Next Time
• Read Chapter 8
• What else?