Nortel Media Gateway 3200 User Manual page 97

H.248 User's Manual
The first three lines describe the voice stream, and can differ according to the user's
requirements. Attributes to the voice ('a' lines) should be added after the first 'm' line. The
'm=image' line, however, is mandatory, and should appear in the identical format to the
above.
The MG 3200 returns a fully specified line with the local port used for the T.38.
Fax redundancy can be requested by including the following attribute line after the
'm=image' line:
a=T38FaxUdpEC:T38UdpRedundancy
This parameter is only applicable for non-V21 packets. For V21 packets, the redundancy is
hard coded 4.
Two modes of fax support are available. The modes are chosen by the value of bit 2 (value
4) of the H.248 profiling parameter MGCPCompatibilityProfile. If this bit is not set, the MG
3200 uses a positive negotiation:
If the 'm=image' line is not received both in local AND in remote descriptors, the MG
3200 works with the defaults defined in the MG 3200. For example, if the MG 3200 is
configured to work with T.38 (default setting) and the 'm=image' line is received in the
local description only, the MG 3200 still works with T.38.
If the fax redundancy attribute line does not appear both in local and remote
descriptors, the MG 3200 uses the default value.
However, if bit 2 is set, the negotiation rules are as follows:
If the 'm=image' line is not received both in local AND remote descriptors, T.38 is NOT
used. In this case, if the local SDP "m=audio" line contains the G.711 coder, the fax
and modem mode is Bypass (VBD), and the G.711 payload type is used for the fax.
The modem payload type is still according to the ini file. If the G.711 coder is not
offered in the local SDP, the Fax and modem Transport Type is Transparent.
If the fax redundancy attribute line does not appear both in local and remote
descriptors, redundancy for non-V21 packets is NOT used.
7.2.2.13 Digits Collection Support
The following methods for digit collection are supported:
One by one collection using the single events in the 'dd' package (e.g., dd/d3).
Collection according to digit map. This includes the basic collection 'dd/ce' event
defined in the basic package and the 'xdd/xce' and 'edd/mce', both defined it
H.248.16. The maximal pattern length is 150 bytes, and the maximal collected
number is 30 digits. For the extended digit collection, the buffering of type ahead
digits continues up to the limit of 30 digits. New digits after that are lost.
7.2.2.14 Reporting Fax Events
Some of the Fax events can be reported using the packages from H.248.2: "CTYP" and
"IPFAX". The only Fax events reported by the "CTYP" package are the "V21flag" and
"cng", using the "ctyp/dtone" event.
The reported Fax states are "CONNECTED" and "EOF". "CONNECTED" is reported when
the H.248 application gets "EVENT_DETECT_FAX" from the board. "EOF" is reported
when the H.248 application gets "EVENT_END_FAX" from the board.
Version SN09 97
7. Standard Control Protocols
October 2006