- Networking function discussed
so far:
- Physical layer:
- Transmits data (signals) between neighbor nodes
- Datalink layer:
- Ensure reliable transfer of data between neighbor nodes
- Network layer:
- Transmits data (packets) between any pair of nodes
- Physical layer:
- Transport Layer:
- Transport lyare =
the first
user level layer in the
OSI architecture
I.e.:
- The Transport layer provides communication services that a user (i.e.: you) can use
- Transport lyare =
the first
user level layer in the
OSI architecture
-
To understand the
services provided by
the Transport Layer,
you need to
keep this in
mind
- Transport layer provide
communication functions to
user programs
- Different (user) programs have
different needs:
- Most program require
reliable data communication
- E.g.: web browser, email, etc.
- Some programs can
tolerate some
data loss but
need
speedy packet delivery
- E.g.: audio chat tool
- Most program require
reliable data communication
- There are multiple user programs running on a single computer !!!
- Transport layer provide
communication functions to
user programs
- Catering to
different needs of
the user programs:
- There are multiple Transport Layers available !!!
- The well-known
Transport Protocols are:
- TCP (Transmission Control Protocol)
- A heavy-weight (= lots of overhead) protocol that provide reliable transfer over the IP protocol
- UDP (User Datagram Protocol)
- A light-weight (= minimal overhead) protocol that allow users to transmit packets as quickly as possible over the IP protocol
- TCP (Transmission Control Protocol)
- A lesser know
Transport Protocol:
- XTP (Xpress Transport Protocol):
- A high speed protocol that
was promoted by the
XTP forum to
replace
the TCP protocol
Wikipedia: click here
- A high speed protocol that
was promoted by the
XTP forum to
replace
the TCP protocol
- XTP (Xpress Transport Protocol):
- Useful functions
provided by the Transport Layer:
- Reliable transfer:
- The Transmission Control Protocol (TCP) provides reliable communication between 2 user application programs
- Multiplexing:
- Every transport protocol provide multiplexing
- Reliable transfer:
- Fact:
- The network layer
establishes a
communication path between
two computers
- Packets transmitted on this
communication path are
identified by:
- The source IP address and
- The destination IP address
Graphically:
- The network layer
establishes a
communication path between
two computers
- Recall:
- There are
multiple application programs
running on a single computer:
- There are
multiple application programs
running on a single computer:
- Notice that:
- Different
user application programs
must be able to
communicate with
each other
- Different
user application programs
must be able to
communicate with
each other
- Therefore:
- The Transport layer must
provide
different communication "channels"
inside the
(single)
network path
to each pair of applications:
- The Transport layer must
provide
different communication "channels"
inside the
(single)
network path
to each pair of applications:
- We call this multiplexing because:
- The different applications are sharing the single network connection bestablished by the Network Layer....
- Other important functions
in the Transport layer
deals with
efficient operation:
- Flow control:
- Ensure
that the sender's
transmission speed
do not exceed
the
receive capability
of the receiver
- We make sure that the receiver buffers are not depleted...
- Ensure
that the sender's
transmission speed
do not exceed
the
receive capability
of the receiver
- Congestion control:
- The congestion control
mechanism
will
adjust
the transmission rate
(of the sender)
according to the
current state
of the network
- The goals of
congestion control:
- Transmit
as fast as possible
- While not causing congestion in the network.
- Transmit
as fast as possible
This is quite a "balancing act"... (discussed later)
- The congestion control
mechanism
will
adjust
the transmission rate
(of the sender)
according to the
current state
of the network
- Flow control: