- Service
provided by the UDP protocol:
- Multiplexing
(yep, nothing else...)
- Multiplexing
- UDP messages are
carried inside
IP packets:
Yes, yet another encapsulation....
- Note:
- Each transport layer defines its own format !!!
- The UDP message format:
Notes:
- Source Port#
= port number
used
by the sender
(application program)
- Dest Port#
= port number
used
by the receiver
(application program)
- CheckSum
= checksum
to protect the UDP packet
- PacketLength = length of user data portion (in #bytes)
- Source Port#
= port number
used
by the sender
(application program)
- The complete picture:
UDP in IP
- Multiplexing in UDP:
- The UDP protocol
provide 216 (65536)
different
port numbers
(16 bits)
- UDP messages from a user (application) program is identified by a unique UDP port number
- And vice versa:
- Received UDP messages are delivered to the user application program that own that UDP port#
- The UDP protocol
provide 216 (65536)
different
port numbers
(16 bits)
- Example:
- Program P2 communicates
with program P4
through UDP:
- Each program
must pick an
UDP port#:
- P2 transmits
a UDP message to the
UDP port# (9000)
of P2:
The UDP layer will insert the UDP port# 5000 used by P2 as the source port#
- The UDP message is
encapsulated inside
an IP packet (by the
IP layer):
- The IP packet is
forwarded
using only the
destination IP address !!!
- The UDP message is
delivered to
the port #9000 own by
the program P4:
- Program P2 communicates
with program P4
through UDP:
- Strength
of the UDP protocol
- UDP is very light weight and has almost no processing overhead !!!
- Weakness
of the UDP protocol:
- UDP does
not
provide
any additional service
- Writing application programs with UDP is very difficult !!!
(Prof. Mandelberg once said that macho programmers use UDP :))
- UDP does
not
provide
any additional service
- Fact:
- The UDP protocol is
ideally suited for:
- Network research that want to experiment with novel network techniques
because the UDP layer adds very little processing overhead
Reason:
- Researchers who wants to
implement new protocols
do not want:
- the
transport level software
to
add extra overhead
(Will give biased performance results)
(So that the performance of the experimental protocol can be measured accurately)
- the
transport level software
to
add extra overhead
- The UDP protocol is
ideally suited for:
- Some network research
that had used UDP:
- IP Multicast
(Steve Deering)
In fact, multicast communication is only avaliable in UDP (and not in TCP)
- Reliable multicast group (CCF)
In 1997, Professor Sunderam lead a project called CCF (Cooperative Collaboration Framework)
The CCF project implemented a multicast transport layer (without using IP-multicast) using UDP
- Many video and audio tools uses UDP.
- IP Multicast
(Steve Deering)