- Designers of TCP:
- TCP was developed by a team led by
Vint Cerf
and
Bob Kahn
Read more on Vinton Cerf (and other Internet pioneers): click here
- TCP was developed by a team led by
Vint Cerf
and
Bob Kahn
- First adoption:
- TCP was adopted in
1982 for use in the Internet.
The 1982 version of TCP did not include congestion control
- TCP was adopted in
1982 for use in the Internet.
- First major improvement:
- In 1987, congestion control was added to the TCP protocol (by Van Jacobson).
- The TCP protocol is documented in the Internet standard RFC 793: click here
- TCP provides:
- Multiplexing
(same as
UDP)
- End-to-end reliable communication
(using Go-back-N)
- Flow control
- Congestion control - added in 1987 by Van Jacobson and others.
- Multiplexing
(same as
UDP)
- Multiplexing
in TCP
is implemented
in the
same way
as in UDP:
- The TCP protocol
also provides
216 (65536)
communication ports
for use to application programs
- User applications
select and associate with a
TCP port#
- TCP packets contains TCP port numbers to identify the messages from different user applications
- The TCP protocol
also provides
216 (65536)
communication ports
for use to application programs
- NOTE:
- TCP ports and
UDP ports
are different entities
inside one computer
- There are 65536 UDP ports and 65536 TCP ports inside one computer
- TCP ports and
UDP ports
are different entities
inside one computer
- Reliable transfer:
- TCP uses the sliding window protocol (with some tweeks) to provide reliable communication
- Tweeks:
- Some tweeks are necessary due to a hostile operational environment
- Difference
in operational environment
between
Transport layer (TCP) and
Datalink layer:
- Delay over a
single hop in
the datalink layer is
relatively constant:
- Timeout values (for frame retransmission) can be set very accurately
- Delay over a
multiple hops in
the Transport Layer is
extremely variable
(due to congestion):
- Timeout values (for packet retransmission) must be adjusted continuously !!!!
- Delay over a
single hop in
the datalink layer is
relatively constant:
- Flow control:
- Flow control = controlling the transmission rate at the source so that the packet arrivals can be buffered by the receiver
Example:
- Suppose the receiver can process
maximum
1000 packets per second
- If
the sender transmits
more than
1000 packets per second (for
a prolonged period of time), then:
- The receiver's buffer will eventually overflow
- Congestion:
- Congestion occurs when the input rate exceeds the output rate for some period of time
Example 1: a slower link
Example 2: concentrated flows
- Solving the
congestion problem:
- The answer
on how to solve
the congestion problem is
easy:
- Reduce the transmission rate....
- Unfortunately, we do
not know the
answers to:
- When do we
reduce
the transmission rate ?
- Congestion detection !!!!
- How much ???
- Transmission rate adjustment
If we reduce the transmission rate by too much, the bandwidth will be wasted (idle !!!)
- When do we
reduce
the transmission rate ?
- The answer
on how to solve
the congestion problem is
easy:
- The congestion control
mechanism
of TCP will be
discussed much later...