TCP/IP Tutorial and Technical Overview - IBM Redbooks

and allows WPT-TCP to send acknowledgements selectively, indicating what
data needs to be retransmitted. Implementation of this optimization is
required.
► Explicit congestion notification (ECN): Defined in RFC 2481, ECN allows a
WP-TCP receiver to notify the sender of the data of congestion in the
network. This allows the sender to reduce it’s congestion window.
Implementation of this optimization is optional.
18.9.3 Wireless Control Message Protocol (WCMP)
The Wireless Control Message Protocol (WCMP) very closes mirrors the
functionality of the Internet Control Message Protocol (ICMP) defined in RFCs
792 and 2463. Defined in the OMA WAP-202-WCMP-20010624-a specification,
it is used by the WDP to provide ICMP-like capability when using wireless
bearers that do not support IP. Specifically, WCMP is used to report problems
occurring when processing datagrams. Errors reported by WCMP messages can
be broken into six types, some of which can be further divided into codes. These
are listed in Table 18-2.
Table 18-2 WCMP types and codes
WCMP message WCMP type WCMP code
Destination unreachable 51
Communication administratively
prohibited
Address unreachable 3
Port unreachable 4
Parameter problem 54
Erroneous header field 0
Message too big 60 0
Reassembly failure 61
Reassembly time exceeded 1
Buffer overflow 2
Echo request 178 0
Echo reply 179 0
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