Srivathsan Ananthachari wrote:
Hi,
This might have something to do with the protocol design . I was
wondering whether all the connection-oriented / reliable
protocols use
Windowing .
No, a lot of connection-oriented protocols and a lot of reliable protocols
don't use windowing. There are three separate issues here:
connection-oriented, reliability, and flow control. Those characteristics
can be combined in many ways, as in a protocol that is reliable, not
connection-oriented, and doesn't use flow control (such as TFTP); or a
protocol that is connection-oriented and reliable and doesn't use flow
control (like NetWare Core Protocol with no burst mode); or a protocol that
is connection-oriented but not reliable and doesn't do windowing, such as
Frame Relay. Wow, how many other combinations could I come up with? :-)
Connection-oriented means that there's some sort of formal establishment of
the connection. Examples are Frame Relay, ATM, TCP. Dare I bring up NetBIOS
again? :-) In a TCP/IP environment, NetBIOS depends on TCP for connection
establishment (and reliability and windowing flow control). In a NetBEUI
environment, NetBIOS handles reliability and connection establishment. It
also relies on LLC type 2 for those 2 things (it's pretty inefficient) and
windowing flow control. With NWLink (NetBIOS on IPX), NetBIOS does
connection establishment and realibility on its own, and has no windowing
flow control.
Reliable means that data delivery is guaranteed. This usualy requires
sequence numbers and ACKs. There are protocols that are reliable but not
connection-oriented and that don't use flow control. An example is OSPF when
it exchanges database description messages. This is a reliable protocol with
sequence numbers, but there's no formal connection establishment first.
Neighbors discover each other with hellos, but they don't establish a
connection. They don't use windowing either.
Many command/reply protocols, such as DNS, are reliable. The client
retransmits if it doesn't get an asnwer. But they aren't connection-oriented
and they don't use flow control.
Flow control coordinates the amount of data that can be sent to a receiver.
It can be handled in two different ways:
Stop-and-wait flow control: The sender waits for an ACK after every frame.
Examples of protocols that do this are Bysync (BSC), NetWare Core Protocol
when burst mode isn't used, Network File System (NFS), Trivial File Transfer
Protocol (TFTP). Some of those (like NCP) are connection-oriented and
reliable, but they don't use windowing. Some of them (like TFTP) are
reliable, but not connection-oriented.
Sliding window flow control: The sender can transmit several frames before
needing an ACK. TCP uses this, as does X.25, LLC Type 2, HDLC (though not
Cisco's HDLC), SDLC. Those are all connection-oriented and reliable also.
There are quite a few protocols that aren't connection-oriented or reliable
and don't do flow control: Ethernet, Token Ring, Cisco's HDLC, IP, UDP, etc.
Priscilla
Can the group add elaborate on this please..?
TIA
Srivathsan A
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