Multiplexing and de multiplexing, Computer Networking

Multiplexing  and De multiplexing

Another  critical set of services that are provided by the transport layer is that of application multiplexing and de multiplexing. This feature allows multiple applications to use the network simultaneously and ensure that the transport layer can differentiate  the data it receives from  the lower  layer according  to the application  or process to which  the data belong. To achieve this  segment headers at the data segment  headers at the transport layer have  a set of fields to determine the process to which the segment data are to be delivered. At the receiver these fields  are examined to determine the process to which  the data segment  belong  and the segment it then directed to that process. This functions at the receiver transport layer that  delivers the data it receivers to the correct application   process is called de multiplexing. The process at the sender where information about the   various  active processes is collected and the corresponding information is incorporated in the segment  headers to be given to  the lower layers  is called multiplexing

Transport  layer multiplexing  and de multiplexing that is extending the  host to host  delivery  service  provided  by the  network layer  to a process to process delivery  service  for application running  on the  hosts. At the destination host layer has the responsibility  of   delivering the data  in these segments to  the appropriation process  application process running  in the  host. As we have previously discussed that  a process as part of a network application  can have one or more sockets doors through which data passes from the network to the  layer in the receiving host does not actually deliver data  directly to a process but instead to an intermediary socket. Because at any given  time there  can be more than  one socket   in the  receiving host  each  socket  has a unique identifier. The  format  of the  identifier depends on whether the socket  in a UDP or in a TCP socket.


                                                                                   figure Multiplexing/ demultiplexing

Each transport layer  segment receiving  host  has a set  fields  in the segment for directs an  incoming  transport layer segments  to the appropriate socket. At the receiving  end the transport  layer examines  these fields  to identity  the  receiving socket and then  directs the segment to that socket this job of delivering the data  in a transport layer segment to the correct socket is called   de multiplexing . the job of gathering data chunks  at the  source host form  different  and passing the segments to  the network  layer is called multiplexing. Note  that the  transport  layer in  the middle  host  in figure must de multiplex  segments  arriving.

From the network  layer  bellow  to either process  p or p above  this is done  by directing the  arriving  segments  data the  to the  corresponding  process socket. The  transport  layer  in the middle  host  must also  gather  outgoing  data from  these  sockets, form  transport  layer  segments  and pass there  segments down  to the network  to the network  layer.

Let  us examine how transport layer  multiplexing and  de multiplexing is  actually done  in a host. We know  that  transport layer multiples in requires that sockets  unique  identifiers and that each segment have special fields that indicate the socket to which the  segment is to be delivered. These special fields illustrated in figure are the source  part number field  and the destination port number filed. The  port numbers ranging  from 1 to 1023 are called  well know  port numbers and are restricted which  means that they are reserved for use  by well know  application protocols  such as HTTP which  use post number 80  and FTP which use port number 21.

Service  of transport layer de multiplexing  each  socket in the host  can be assigned a port  number and when  a segment  arrives to the host the transport  layer  examines  the destination post number in the segment  and directs the  segments to the  corresponding  sockets. The  segments  data then  passes  through the sockets into the  attached process.


Posted Date: 3/9/2013 4:49:49 AM | Location : United States

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