What do the channel numbers in ssh error message refer to?

What do the channel numbers in ssh error message refer to?

In the example below what do the channel numbers correspond to, which are
on the server which are on the client.
$ ssh -L1570:127.0.0.1:8899 root@thehost
Password:
Last login: Fri Aug 9 13:08:44 2013 from theclientip
Sun Microsystems Inc. SunOS 5.10 Generic January 2005
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# channel 2: open failed: administratively prohibited: open failed
channel 3: open failed: administratively prohibited: open failed
channel 2: open failed: administratively prohibited: open failed
the ssh client is running on windows 7 and the server has a tomcat running
on port 8899.
Tomcat is not listening on 127.0.0.1 on the remote machine so if I change
the command to ssh -L1570:thehostpublicip:8899 root@thehost the port
forward works. So I know that port forwarding seems to be working just
fine on the server.
my sshd config file contains the following two lines
# Port forwarding
AllowTcpForwarding yes
# If port forwarding is enabled, specify if the server can bind to
INADDR_ANY.
# This allows the local port forwarding to work when connections are received
# from any remote host.
GatewayPorts yes
I am trying to setup port forwarding for another process not tomcat and I
get the error messages similar to the stuff above so I am trying to
understand the meaning of the error messages.