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Showing posts with label UDP. Show all posts
COMPUTER NETWORKS-I × UDP
Remote Procedure Call
Mechanisms
• Client process calls the client
stub
• Marshalling-packing the
parameters
• Kernel receives from client
stub and sends to server machine
• Kernel on server OS passes the
message to server stub
• The server stub processes it
and the reply follows the same path in the other
direction
Problems may occur in RPC
• Passing pointer parameters from
client place to server space
• weakly typed language- C may
not be suitable
• Type conversion
• Use of global variables –since
two different space involved
Still UDP is commonly used in RPC
Another application of UDP a protocol
uses UDP
(a) The position
of RTP in the protocol stack.
(b) Packet
nesting.
RTP Real time
transport protocol
• UDP is used with real time
multimedia applications
• the applications are: internet
radio, internet telephony, music on demand, video
on demand, video conferencing
• RTP is used for different
formats like GSM, MP3 for sound and MPEG and
H.263 for video
• The basic function of RTP is to
multiplex several real time data stream onto
single stream of UDP packets. The
UDP stream can be sent to single destination
(unicast) and multiple
destination (multicast)
RTP Header
details
• P padded bit
• X extension header present or
not
• CC contributing sources
• M marker bit
• Version field
• Payload type
• Seq no
• Time stamp
• Synchronization and
contributing source identifier
RTP Header
COMPUTER NETWORKS-I × UDP
• Inward and Outward data
collection/dissemination
– SNMP for network management
– RIP routing table updates
– NFS remote file server
• Request-Response
– Eg. DNS uses UDP for name
translation
• Real time application
– Streaming multimedia and
internet telephony
– Video conferencing
The following are the port numbers of
some applications commonly used
• Both TCP and UDP use port
(or socket) numbers to pass information to the upper
layers.
• Port numbers are used to keep
track of different conversations that cross the
network at the same time.
• Application software developers
have agreed to use the well-known port numbers
that are defined in RFC1700.
• The range of numbers are below 255 for TCP and UDP
appilcations.
COMPUTER NETWORKS-I × UDP
Internet
Protocols
• Internet transport services:
• reliable, in-order unicast
delivery (TCP)
congestion
flow control
connection setup
• unreliable (“best-effort”),
unordered unicast or multicast delivery: UDP
services not available:
real-time
bandwidth guarantees
reliable multicast
UDP
•“no frills,” “bare bones”
Internet transport protocol
• “best effort” service, UDP
segments may be:
– lost
– delivered out of order to
applications
• connectionless:
– no handshaking between UDP
sender, receiver
– each UDP segment handled
independently of others
Why is there a
UDP?
• no connection establishment
(which can add delay)
• simple: no connection state at
sender, receiver
• small segment header
• no congestion control: UDP can
blast away as fast as desired
UDP header
Header details
• Source and destination port
numbers
• The source and destination
processes
• Length = length of header +
data
• Checksum covers header and data
• Optional in UDP but mandatory
in TCP
UDP Checksum
Sender:
• treat segment contents as
sequence of 16-bit integers
• checksum: addition (1’s
complement sum) of segment contents
• sender puts checksum value into
UDP checksum field
Receiver:
• compute checksum of received
segment
• check if computed checksum
equals checksum field value:
– NO - error detected
– YES - no error detected
