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RFC2001: TCP Slow Start, Congestion Avoidance, Fast Retransmit,
and Fast Recovery Algorithms
...
3. Fast Retransmit
Modifications to the congestion avoidance algorithm were proposed in
1990 [3]. Before describing the change, realize that TCP may
generate an immediate acknowledgment (a duplicate ACK) when an out-
of-order segment is received (Section 4.2.2.21 of [1], with a note
that one reason for doing so was for the experimental fast-
retransmit algorithm). This duplicate ACK should not be delayed.
The purpose of this duplicate ACK is to let the other end know that a
segment was received out of order, and to tell it what sequence
number is expected.
Since TCP does not know whether a duplicate ACK is caused by a lost
segment or just a reordering of segments, it waits for a small number
of duplicate ACKs to be received. It is assumed that if there is
just a reordering of the segments, there will be only one or two
duplicate ACKs before the reordered segment is processed, which will
then generate a new ACK. If three or more duplicate ACKs are
received in a row, it is a strong indication that a segment has been
lost. TCP then performs a retransmission of what appears to be the
missing segment, without waiting for a retransmission timer to
expire.
Change-Id: Ie2cbcecab507c3d831f74390a6a85e0c5c8e0652
Signed-off-by: chao.an <anchao@xiaomi.com>
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|---|---|---|
| .. | ||
| arp | ||
| bluetooth | ||
| can | ||
| devif | ||
| icmp | ||
| icmpv6 | ||
| ieee802154 | ||
| igmp | ||
| inet | ||
| ipforward | ||
| local | ||
| mld | ||
| neighbor | ||
| netdev | ||
| netlink | ||
| pkt | ||
| procfs | ||
| route | ||
| sixlowpan | ||
| socket | ||
| tcp | ||
| udp | ||
| usrsock | ||
| utils | ||
| Kconfig | ||
| Makefile | ||
| net_initialize.c | ||
| README.txt | ||
README
======
Directory Structure
===================
nuttx/
|
`- net/
|
+- arp - Address resolution protocol (IPv4)
+- bluetooth - PF_BLUETOOTH socket interface
+- devif - Stack/device interface layer
+- icmp - Internet Control Message Protocol (IPv4)
+- icmpv6 - Internet Control Message Protocol (IPv6)
+- ieee802154 - PF_IEEE802154 socket interface
+- inet - PF_INET/PF_INET6 socket interface
+- ipforward - IP forwarding logic
+- local - Unix domain (local) sockets
+- mld - Multicast Listener Discovery (MLD)
+- neighbor - Neighbor Discovery Protocol (IPv6)
+- netdev - Socket network device interface
+- netlink - Netlink IPC socket interface
+- pkt - "Raw" packet socket support
+- sixlowpan - 6LoWPAN implementation
+- socket - BSD socket interface
+- route - Routing table support
+- tcp - Transmission Control Protocol
+- udp - User Datagram Protocol
+- usrsock - User socket API for user-space networking stack
`- utils - Miscellaneous utility functions
+-------------------------------------------------------------------++------------------------+
| Application layer || usrsock daemon |
+-------------------------------------------------------------------++------------------------+
+-------------------------------------------------------------------++----------------+ +-----+
| Socket layer (socket/) || /dev/usrsock | | |
+-------------------------------------------------------------------++----------------+ | |
+------------++--------------------------------------------------++-------------------+ | |
| Network || Protocol stacks (arp, ipv6, icmp, pkt, tcp, udp) || usrsock/ | | |
| Device |+--------------------------------------------------++-------------------+ | |
| Interface |+------------------------------------++---------------------------------+ | |
| (netdev/) || Network Device Interface (devif/) || Utilities | | |
+------------++------------------------------------++---------------------------------+ | |
+----------------------------------------------------------------+ | |
| Network Device Drivers | | HAL |
+----------------------------------------------------------------+ +-----+
+----------------------------------------------------------------+ +--------------------------+
| Networking Hardware | | Hardware TCP/IP Stack |
+----------------------------------------------------------------+ +--------------------------+