Modem Passthrough over Voice over IP

The Modem Passthrough over VoIP feature performs the following functions:

• Represses processing functions like compression, echo cancellation, high-pass filter, and voice activity detection (VAD).

• Issues redundant packets to protect against random packet drops.

• Provides static jitter buffers of 200 milliseconds to protect against clock skew.

• Discriminates modem signals from voice and fax signals, indicating the detection of the modem signal across the connection, and placing the connection in a state that transports the signal across the network with the least amount of distortion.

• Reliably maintains a modem connection across the packet network for a long duration under normal network conditions.

For further details, see the following functions of the Modem Passthrough over VoIP feature:

Modem Tone Detection

The gateway is able to detect modems at speeds up to V.90.

Passthrough Switchover

When the gateway detects a data modem, both the originating gateway and the terminating gateway roll over to G.711. This disables the high-pass filter, disables echo cancellation, and disables VAD. At the end of the modem call, the voice ports revert to the prior configuration and the digital signal processor (DSP) goes back to the state before switchover. You can configure the codec by selecting g711alaw or g711ulaw options of the codec command.

Tips You need to configure Modem Passthrough in both the originating gateway and the terminating gateway for the Modem Passthrough over VoIP to operate. If you configure only one of the gateways in a pair, the modem call will not connect successfully.

Redundancy can be enabled in one or both of the gateways. When only a single gateway is configured for redundancy, the other gateway receives the packets correctly, but does not produce redundant packets.

See the following sections for the Modem Passthrough over VoIP feature configuration:

To configure Modem Passthrough over VoIP for all the connections of a Cisco AS5300 Universal Access Server gateway, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)#voice service voip	Enters the voice-service configuration mode. Configures voice service for all the connections for the gateways.
Step 2	Router(conf-voi-serv)#modem passthrough {nse [payload-type number] codec {g711ulaw | g711alaw} [redundancy] [maximum-sessions value]}	Configures Modem Passthrough over VoIP for the Cisco AS5300 Universal Access Server gateways. The default behavior is no modem passthrough. The payload-type is an optional parameter for the nse keyword. Use the same payload-type number for both the originating gateway and the terminating gateway. The payload-type number can be set between 96 and 119. If you do not specify the payload-type number, it defaults to 100. When the payload-type is 100, and you use the show running-config command, the payload-type parameter does not appear. Use the same codec type for both the originating gateway and the terminating gateway. g711ulaw codec is required for T1, and g711alaw codec is required for E1. The redundancy keyword is an optional parameter for packet redundancy for modem traffic. The maximum-sessions is an optional parameter for the modem passthrough command in the voice-service configuration mode. This parameter determines the maximum simultaneous Modem Passthrough sessions. The recommended value for the maximum-sessions is 16. The value can be set from 1 to 26.
Step 3	Router(conf-voi-serv)#exit	Exits from voice-service configuration mode.
Step 4	Router(config)#exit	Exits the global configuration mode.

• Configure globally in the voice-service configuration mode

• Configure individually in the dial peer configuration mode on a specific dial peer

The default behavior for the voice-service configuration mode is no modem passthrough. This implies that Modem Passthrough is disabled for all dial peers on the gateway by default.

To enable Modem Passthrough on the VoIP dial peers on both the originating and terminating gateway, configure Modem Passthrough globally or explicitly on the dial peer.

For the Modem Passthrough to operate, you must define VoIP dial peers on both gateways to match the call, for example, by using a destination-pattern. The Modem Passthrough parameters associated with those dial peers then will apply to the call.

Note   When Modem Passthrough is configured individually for a specific dial peer, that configuration for the specific dial peer takes precedence over the global configuration.

To configure Modem Passthrough over VoIP for a specific dial peer, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	Router(config)#dial-peer voice number voip	Enters the dial-peer configuration mode. Configures a specific dial peer in dial-peer configuration mode.
Step 2	Router(config-dial-peer)#modem passthrough {nse [payload-type number] codec {g711ulaw | g711alaw} [redundancy]} | system}	Configures Modem Passthrough over VoIP for a specific dial peer. The default behavior for the Modem Passthrough for VoIP in dial-peer configuration mode is modem passthrough system. As required, the gateway defaults to no modem passthrough. The payload-type is an optional parameter for the nse keyword. Use the same payload-type number for both the originating gateway and the terminating gateway. The payload-type number can be set between 96 and 119. If you do not specify the payload-type number, it defaults to 100. When the payload-type is 100, and you use the show running-config command, the payload-type parameter does not appear. Use the same codec type for both the originating gateway and the terminating gateway. g711ulaw codec is required for T1, and g711alaw codec is required for E1. The redundancy keyword is an optional parameter for packet redundancy for modem traffic. When the system keyword is enabled, the following parameters are not available: nse, payload-type, codec, and redundancy. Instead the values from the global configuration are used.
Step 3	Router(config-dial-peer)#Exit	Exits from dial-peer configuration mode and returns to the global configuration mode.
Step 4	Router(config)#exit	Exits the global configuration mode.

Syntax Description

nse	Named Signaling Events (NSE).
payload-type	(Optional) NSE payload-type.
number	The value of the payload-type (96 - 119).
codec	Codec selections for upspeed.
g711ulaw	Codec G.711 U-Law 64000 bps for T1.
g711alaw	Codec G.711 A-Law 64000 bps for E1.
redundancy	Packet redundancy for modem traffic.
maximum-sessions	(Optional) Maximum simultaneous Modem Passthrough sessions.
value	The number of simultaneous Modem Passthrough sessions. The minimum value is 1 and the maximum value is 26. The default is 16 calls.

Defaults

Disabled

Command Modes

Voice-service configuration mode

Command History

Release	Modification
12.1(3)T	This command was introduced for the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the modem passthrough command to configure Modem Passthrough over VoIP for the Cisco AS5300 Universal Access Server gateway. The default behavior for voice service voip command is no modem passthrough.

The payload-type is an optional parameter for the nse keyword. Use the same payload-type number for both the originating gateway and the terminating gateway. The payload-type number can be set between 96 and 119. If you do not specify the payload-type number, it defaults to 100.

Use the same codec type for both the originating gateway and the terminating gateway. g711ulaw codec is required for T1, and g711alaw codec is required for E1.

The redundancy keyword is an optional parameter for packet redundancy for modem traffic.

The maximum-sessions is an optional parameter for the modem passthrough command. This parameter determines the maximum simultaneous Modem Passthrough sessions. The recommended value for the maximum-sessions is 16. The value can be set from 1 to 26.

Examples

The following example shows modem pass though configuration in voice service configuration mode:

Router(conf-voi-serv)# modem passthrough nse payload-type 101 codec g711ulaw redundancy maximum-session 1

Related Commands

Command	Description
voice service voip	Enters the voice-service configuration mode and specifies the voice encapsulation type.

Syntax Description

nse	Named signaling event.
payload-type	NSE payload-type.
number	The value of the payload-type (96 - 119).
codec	Voice compression for speech or audio signals. Codec selections for upspeed.
g711ulaw	Codec G.711 U-Law 64000 bps for T1.
g711alaw	Codec G.711 A-Law 64000 bps for E1.
redundancy	Packet redundancy for modem traffic.
system	Defaults to the global configuration.

Defaults

Defining system as the method in dial peer points to the voice service VoIP configuration default and is intended to simplify gateway configuration. The default is modem passthrough system. As required, the gateway defaults to no modem passthrough.

Command Modes

Dial-peer configuration mode

Command History

Release	Modification
12.1(3)T	This command was introduced for the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the modem passthrough dial-peer configuration command to configure Modem Passthrough over VoIP for a specific dial peer. The payload-type is an optional parameter for the nse keyword. Use the same payload-type number for both the originating gateway and the terminating gateway. The payload-type number can be set between 96 and 119. If you do not specify the payload-type number, it defaults to 100.

Use the same codec type for both the originating gateway and the terminating gateway. g711ulaw codec is required for T1, and g711alaw codec is required for E1.

The redundancy keyword is an optional parameter for packet redundancy for modem traffic.

When the system keyword is enabled, the following parameters are not available: nse, payload-type, codec, and redundancy. Instead the values from the global configuration are used.

Examples

The following example shows how Modem Passthrough over VoIP is configured for a specific dial peer in the dial-peer configuration mode:

Router(config-dial-peer)# modem passthrough nse ?
Router(config-dial-peer)# modem passthrough nse codec g711ulaw redundancy 16

Related Commands

Command	Description
dial-peer voice	Enters dial-peer configuration mode.

Syntax Description

voice	Specifies that the active call table displays voice call information.
brief	(Optional) Displays a truncated version.

Defaults

No default behavior or values.

Command Modes

Privileged EXEC

Command History

Release	Modification
11.3(1)T	This command was introduced.
12.0(4)XJ	This command was modified for Store and Forward Fax.
12.1(3)T	This command was modified for Modem Passthrough over Voice over IP on the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the show call active privileged EXEC command to display the contents of the active call table. If you use the voice keyword, the active call table displays information about all the voice calls currently connected through the router or access server.

Examples

This is sample output from the show call active voice command updated with the Modem Passthrough output:

Router# show call active voice
GENERIC:
SetupTime=104443 ms
Index=1
PeerAddress=50110
PeerSubAddress=
PeerId=100
PeerIfIndex=104
LogicalIfIndex=10
ConnectTime=104964
CallDuration=00:02:43
CallState=4
CallOrigin=2
ChargedUnits=0
InfoType=2
TransmitPackets=15720
TransmitBytes=2362904
ReceivePackets=15670
ReceiveBytes=2737904
TELE:
ConnectionId=[0x4B091A27 0x3EDD0003 0x0 0xFEFD4]
TxDuration=155310 ms
VoiceTxDuration=155310 ms
FaxTxDuration=0 ms
CoderTypeRate=g711ulaw
NoiseLevel=-75
ACOMLevel=11
OutSignalLevel=-13
InSignalLevel=-22
InfoActivity=2
ERLLevel=27
SessionTarget=
ImgPages=0
 GENERIC:
SetupTime=104648 ms
Index=1
PeerAddress=55240
PeerSubAddress=
PeerId=2
PeerIfIndex=105
LogicalIfIndex=0
ConnectTime=104964
CallDuration=00:02:47
CallState=4
CallOrigin=1
ChargedUnits=0
InfoType=2
TransmitPackets=16026
TransmitBytes=2608248
ReceivePackets=16075
ReceiveBytes=2609164
VOIP:
ConnectionId[0x4B091A27 0x3EDD0003 0x0 0xFEFD4]
RemoteIPAddress=1.14.82.14
RemoteUDPPort=18202
RoundTripDelay=2 ms
SelectedQoS=best-effort
tx_DtmfRelay=inband-voice
FastConnect=TRUE
 
SessionProtocol=cisco
SessionTarget=ipv4:1.14.82.14
OnTimeRvPlayout=40
GapFillWithSilence=0 ms
GapFillWithPrediction=0 ms
GapFillWithInterpolation=0 ms
GapFillWithRedundancy=0 ms
HiWaterPlayoutDelay=67 ms
LoWaterPlayoutDelay=67 ms
ReceiveDelay=67 ms
LostPackets=0 ms
EarlyPackets=0 ms
LatePackets=0 ms
VAD = enabled
CoderTypeRate=g729r8
CodecBytes=20
SignalingType=cas
 
Modem passthrough signaling method is nse:
Buffer Fill Events = 0
Buffer Drain Events = 0
Percent Packet Loss = 0
Consecutive-packets-lost Events = 0
Corrected packet-loss Events = 0
Last Buffer Drain/Fill Event = 157sec
Time between Buffer Drain/Fills = Min 0sec Max 0sec
 
 
Router# show call active voice brief 
<ID>: <start>hs.<index> +<connect> pid:<peer_id> <dir> <addr> <state> 
  dur hh:mm:ss tx:<packets>/<bytes> rx:<packets>/<bytes>
 IP <ip>:<udp> rtt:<time>ms pl:<play>/<gap>ms lost:<lost>/<early>/<late>
  delay:<last>/<min>/<max>ms <codec>
 MODEMPASS <method> buf:<fills>/<drains> loss <overall%> <multipkt>/<corrected>
   last <buf event time>s dur:<Min>/<Max>s
 FR <protocol> [int dlci cid] vad:<y/n> dtmf:<y/n> seq:<y/n>
  sig:<on/off> <codec> (payload size)
 ATM <protocol> [int vpi/vci cid] vad:<y/n> dtmf:<y/n> seq:<y/n>
  sig:<on/off> <codec> (payload size)
 Tele <int>: tx:<tot>/<v>/<fax>ms <codec> noise:<l> acom:<l> i/o:<l>/<l> dBm
 
3    : 104443hs.1 +521 pid:100 Answer 50110 active
 dur 00:03:28 tx:20151/3036404 rx:20102/3517936
 Tele 0:D:1: tx:199630/199630/0ms g711ulaw noise:-75 acom:11  i/0:-22/-13 dBm
 
3    : 104648hs.1 +316 pid:2 Originate 55240 active
 dur 00:03:28 tx:20102/3276712 rx:20151/3277628
 IP 1.14.82.14:18202 rtt:3ms pl:40/0ms lost:0/0/0 delay:67/67/67ms g729r8
 MODEMPASS nse buf:0/0 loss 0% 0/0  last 195s dur:0/0s 

Related Commands

Command	Description
show call history voice	Displays the Voice over IP call history table.
show dial-peer voice	Displays configuration information for dial peers.
show num-exp	Displays how the number expansions are configured in Voice over IP.
show voice port	Displays configuration information about a specific voice port.

Syntax Description

voice	Specifies that the call history tables shows voice call information.
last number	(Optional) Displays the last calls connected, where the number of calls that appear is defined by the argument number. Valid values are from 1 to 2147483647.
brief	(Optional) Displays a truncated version of the call history table.

Defaults

No default behavior or values.

Command Modes

Privileged EXEC

Command History

Release	Modification
11.3(1)T	This command was introduced.
12.0(4)XJ	This command was modified for Store and Forward Fax.
12.1(3)T	This command was modified for Modem Passthrough over Voice over IP on the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the show call history voice privileged EXEC command to display the voice call history table. The call history table contains a listing of all calls connected through this router in descending time order since Voice over IP was enabled. You can display subsets of the call history table by using specific keywords. To display the last calls connected through this router, use the keyword last, and define the number of calls you want to see with the argument number. To display a truncated version of the call history table, use the brief keyword.

Examples

This is sample output from the show call history command updated with the Modem Passthrough over Voice IP feature.

Router# show call history voice 
GENERIC:
SetupTime=104648 ms
Index=1
PeerAddress=55240
PeerSubAddress=
PeerId=2
PeerIfIndex=105
LogicalIfIndex=0
DisconnectCause=10  
DisconnectText=normal call clearing.
ConnectTime=104964
DisconectTime=143329
CallDuration=00:06:23
CallOrigin=1
ChargedUnits=0
InfoType=speech
TransmitPackets=37668
TransmitBytes=6157536
ReceivePackets=37717
ReceiveBytes=6158452
VOIP:
ConnectionId[0x4B091A27 0x3EDD0003 0x0 0xFEFD4]
RemoteIPAddress=1.14.82.14
RemoteUDPPort=18202
RoundTripDelay=2 ms
SelectedQoS=best-effort
tx_DtmfRelay=inband-voice
FastConnect=TRUE
 
SessionProtocol=cisco
SessionTarget=ipv4:1.14.82.14
OnTimeRvPlayout=40
GapFillWithSilence=0 ms
GapFillWithPrediction=0 ms
GapFillWithInterpolation=0 ms
GapFillWithRedundancy=0 ms
HiWaterPlayoutDelay=67 ms
LoWaterPlayoutDelay=67 ms
ReceiveDelay=67 ms
LostPackets=0 ms
EarlyPackets=0 ms
LatePackets=0 ms
VAD = enabled
CoderTypeRate=g729r8
CodecBytes=20
cvVoIPCallHistoryIcpif=0
SignalingType=cas
 
Modem passthrough signaling method is nse
Buffer Fill Events = 0
Buffer Drain Events = 0
Percent Packet Loss = 0
Consecutive-packets-lost Events = 0
Corrected packet-loss Events = 0
Last Buffer Drain/Fill Event = 373sec
Time between Buffer Drain/Fills = Min 0sec Max 0sec
 
 
GENERIC:
SetupTime=104443 ms
Index=2
PeerAddress=50110
PeerSubAddress=
PeerId=100
PeerIfIndex=104
LogicalIfIndex=10
DisconnectCause=10  
DisconnectText=normal call clearing.
ConnectTime=104964
DisconectTime=143330
CallDuration=00:06:23
CallOrigin=2
ChargedUnits=0
InfoType=speech
TransmitPackets=37717
TransmitBytes=5706436
ReceivePackets=37668
ReceiveBytes=6609552
TELE:
ConnectionId=[0x4B091A27 0x3EDD0003 0x0 0xFEFD4]
TxDuration=375300 ms
VoiceTxDuration=375300 ms
FaxTxDuration=0 ms
CoderTypeRate=g711ulaw
NoiseLevel=-75
ACOMLevel=11
SessionTarget=
ImgPages=0
 
Router# show call history voice brief 
<ID>: <start>hs.<index> +<connect> +<disc> pid:<peer_id> <direction> <addr>
  dur hh:mm:ss tx:<packets>/<bytes> rx:<packets>/<bytes> <disc-cause>(<text>)
 IP <ip>:<udp> rtt:<time>ms pl:<play>/<gap>ms lost:<lost>/<early>/<late>
  delay:<last>/<min>/<max>ms <codec>
  MODEMPASS <method> buf:<fills>/<drains> loss <overall%> <multipkt>/<corrected>
   last <buf event time>s dur:<Min>/<Max>s
 FR <protocol> [int dlci cid] vad:<y/n> dtmf:<y/n> seq:<y/n>
  sig:<on/off> <codec> (payload size)
 ATM <protocol> [int vpi/vci cid] vad:<y/n> dtmf:<y/n> seq:<y/n>
  sig:<on/off> <codec> (payload size)
 Telephony <int>: tx:<tot>/<voice>/<fax>ms <codec> noise:<lvl>dBm acom:<lvl>dBm
 

Related Commands

Command	Description
show call active	Displays active call information for a call in progress.

Syntax Description

number	(Optional) A specific dial peer. By using this option, you can see configuration information for a single dial peer identified by the number argument. Valid entries are any integers that identify a specific dial peer from 1 to 32767.
summary	(Optional) Displays a summary of all voice dial peers.

Defaults

No default behavior or values.

Command Modes

Privileged EXEC

Command History

Release	Modification
11.3(1)T	This command was introduced.
11.3(1)MA	The summary keyword was added for the Cisco MC3810.
12.0(3)XG	This command was modified to support VoFR for the Cisco 2600 series and Cisco 3600 series routers.
12.0(4)T	Support was added for VoFR for the Cisco 7200 series routers.
12.1(3)T	This command was modified for Modem Passthrough over Voice over IP on the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the show dial-peer voice privileged EXEC command to display the configuration for all VoIP and POTS dial peers configured for the router. To show configuration information for only one specific dial peer, use the argument number to identify the dial peer.

Examples

This is sample output from the show dial-peer voice command for a POTS dial peer updated with the Modem Passthrough over Voice over IP feature:

Router# show dial-peer voice
VoiceEncapPeer100
        information type = voice,
        tag = 100, destination-pattern = \Q55250',
        answer-address = \Q', preference=0,
        numbering Type = \Qunknown'
        group = 100, Admin state is up, Operation state is up,
        incoming called-number = \Q', connections/maximum = 0/unlimited,
        DTMF Relay = disabled,
        huntstop = disabled,
        application associated: 
        type = pots, prefix = \Q55250',
        forward-digits default
        session-target = \Q', voice-port = \Q0:D',
        direct-inward-dial = disabled,
        digit_strip = enabled,
 
        register E.164 number with GK = TRUE
        Connect Time = 0, Charged Units = 0,
        Successful Calls = 0, Failed Calls = 0,
        Accepted Calls = 0, Refused Calls = 0,
        Last Disconnect Cause is "",
        Last Disconnect Text is "",
        Last Setup Time = 0.
VoiceOverIpPeer2
        information type = voice,
        tag = 2, destination-pattern = \Q55240',
        answer-address = \Q', preference=0,
        numbering Type = \Qunknown'
        group = 2, Admin state is up, Operation state is up,
        incoming called-number = \Q', connections/maximum = 0/unlimited,
        DTMF Relay = disabled,
        modem passthrough = nse, payload type = 117, codec = g711ulaw, redundancy,
        huntstop = disabled,
        application associated: 
        type = voip, session-target = \Qipv4:1.14.82.14',
        technology prefix: 
        settle-call = disabled
        ip precedence = 0, UDP checksum = disabled,
        session-protocol = cisco, session-transport = udp, req-qos = best-effort, 
        acc-qos = best-effort, 
        fax-rate = disable,   payload size =  20 bytes
        codec = g729r8,   payload size =  20 bytes,
        Expect factor = 10, Icpif = 30,
        Playout: Mode adaptive,
        Expect factor = 10, 
        Max Redirects = 1, Icpif = 30,signaling-type = cas,
 

Related Commands

Command	Description
show call active voice	Displays the Voice over IP active call table.
show call history voice	Displays the Voice over IP call history table.
show num-exp	Displays how the number expansions are configured in Voice over IP.
show voice port	Displays configuration information about a specific voice port.

Syntax Description

voip	Specifies Voice over IP encapsulation.

Defaults

No default behavior or values.

Command Modes

Global configuration

Command History

Release	Modification
12.1(1)XA	This command was introduced for VoATM on the Cisco MC3810 series.
12.1(2)T	This command was implemented in Cisco IOS Release 12.1(2)T on the Cisco MC3810 series.
121(3)T	This command was implemented in Cisco IOS Release 12.1(3)T for VoIP on the Cisco AS5300 Universal Access Servers.

Usage Guidelines

Use the voice service command to switch to the voice-service configuration mode from the global configuration mode and to specify a voice encapsulation type. Use the exit command to exit the voice-service configuration mode and return to the global configuration mode.

Examples

The following example shows how to access the voice-service configuration mode and specify VoIP voice encapsulation, beginning in global configuration mode:

Router(config)# voice service voip
Router(config-voice-service)#
 

Related Commands

Command	Description
modem passthrough	Configures Modem Passthrough over VoIP.