|
|
8.2 | |
TCP/IP Suite Control Messages | |
| 8.2.8 | |
Congestion and flow control messages |
|
If multiple computers try to access the
same destination at the same time, the destination computer can be
overwhelmed with traffic. Congestion can also occur when traffic from
a high speed LAN reaches a slower WAN connection. Dropped packets
occur when there is too much congestion on a network. ICMP
source-quench messages are used to reduce the amount of data lost. The
source-quench message asks senders to reduce the rate at which they
are transmitting packets. In most cases, congestion will subside after
a short period of time, and the source will slowly increase the
transmission rate as long as no other source-quench messages are
received. Most Cisco routers do not send source-quench messages by
default, because the source-quench message may itself add to the
network congestion.
A small office home office (SOHO) is a
scenario where ICMP source-quench messages might be used effectively.
One such SOHO could consist of four computers networked together using
CAT-5 cable and Internet connection sharing (ICS) over a 56K modem. It
is easy to see that the 10Mbps bandwidth of the SOHO LAN could quickly
overwhelm the available 56K bandwidth of the WAN link, resulting in
data loss and retransmissions. With ICMP messaging, the host acting as
the gateway in the ICS can request that the other hosts reduce their
transmission rates to a manageable level, thus preventing continued
data loss. A network where congestion on the WAN link could cause
communication problems is shown in Figure
|
.
Web Links