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The following sections describe the configurations that directly enable or disable MSRP and MSRP multiplexing on the SBC. Also described are other SBC configurations that impact MSRP sessions and therefore should be evaluated if you enable MSRP support in your network. Refer to MSRP Support for more information.

Enabling MSRP Support

MSRP support is enabled or disabled on a per-trunk-group basis using the SIP trunk group media option called "msrp." By default, MSRP is enabled. The CLI syntax appears below:

% set addressContext <addressContextName> zone <zoneName> sipTrunkGroup <trunkGroupName> media msrp <enabled | disabled>

Refer to SIP Trunk Group - Media - CLI or SIP Trunk Group - Media (EMA) for more information.

Enabling MSRP Multiplexing

MSRP multiplexing (reuse of existing TCP connections for multiple MSRP sessions) is enabled or disabled on a per-trunk-group basis using the media option called “msrpMux.” By default, MSRP multiplexing is disabled. The CLI syntax appears below:

% set addressContext <addressContextName> zone <zoneName> sipTrunkGroup <trunkGroupName> media msrpMux <enabled | disabled>

Refer to SIP Trunk Group - Media - CLI or SIP Trunk Group - Media (EMA) for more information.

Source Address Filtering

The SBC supports source address filtering in which the SBC filters out media packets that do not match the expected IP address. If enabled, for an MSRP session the SBC compares the IP address of the incoming MSRP connect request with the IP address received in the SDP offer or answer from the peer. The SBC only allows the connection if they are same. If disabled, the SBC does not perform any source address validation before accepting a TCP connection. This option is enabled by default. The CLI syntax appears below.

% set addressContext <addressContextName> zone <zoneName> sipTrunkGroup <trunkGroupName> media sourceAddressFiltering <enabled | disabled>

Refer to SIP Trunk Group - Media - CLI or SIP Trunk Group - Media (EMA) for more information.

TCP Listener Port Range

The configured TCP port range determines on which ports the SBC can accept TCP connections. A unique unused port from this range is included in the SDP media line in the offer or answer towards the MSRP UAs. The SBC uses a port from this range, per MSRP call leg, when it takes the TCP server role in establishing a TCP connection. The default range is from 1024 to 65535. The CLI syntax appears below:

% set system media tcpPortRange baseServerPort <1 to 65534> maxServerPort <1 to 65534>

To create the TCP port range, use baseServerPort and maxServerPort to specify the minimum and maximum values:

  • baseServerPort – Base port number (inclusive) for TCP media server (range: 1-65534 / default = 1024).
  • maxServerPort – Maximum port number (inclusive) for TCP media server (range: 1-65534 / default = 65534).

Refer to Media System - CLI or System - Media - TCP Port Range (EMA) for more information.

DSCP Marking for MSRP Packets

Differentiated Services Code Point (DSCP) values are included in an IP packet field to assign different levels of service to network traffic. In the Quality of Service (QoS) settings of a Packet Service Profile, you can specify the DSCP marking to use for MSRP packets egressing the SBC. The CLI syntax appears below. The default value is "0". 

% set profiles media packetServiceProfile <profileName> qosValues msrpDscp <0 to 255>

Refer to  Packet Service Profile - CLI or Media Profiles - Packet Service Profile (EMA) for more information.

Reserving Interface Bandwidth for MSRP Packets

By default values, 95% of the bandwidth across all interfaces is available for RTP traffic. MSRP and other non-RTP media share the remaining 5% bandwidth with signaling. This amount may not be sufficient for MSRP support. MSRP traffic can consume significant bandwidth depending upon the application. For example, a large number of MSRP sessions or a UA transferring a file using MSRP can potentially use a significant amount of bandwidth.

The SBC provides a configuration option to specify the amount of interface bandwidth across all physical interfaces to reserve for non-RTP media. This value is specified as a percentage (up to 50%). The default value is 0%.  Specifying a non-zero value reduces the available bandwidth for RTP from 95% accordingly. However, it also ensures that aggregate MSRP traffic usage does not exceed the reserved bandwidth, thereby not interfering with RTP or signaling. The CLI syntax appears below.

Note

Configure dedicatedBWForNonRTPMedia to a non-zero value to reserve a percentage of NIF bandwidth for non-RTP calls.

% set system media dedicatedBWForNonRTPMedia <0 to 50>

Refer to Media System - CLI or System - Media (EMA) for more information.

MSRP Call Admission Control

The number of active TCP sessions allowed on the SBC can be restricted using the following CLI command. This limit includes MSRP sessions. The active session limit can be specified per trunk group (default value is unlimited). Once this configured limit is reached, no new MSRP sessions are accepted. Instead, the SBC rejects the INVITE request with a 488 response code.

% set addressContext <addressContextName> zone <zoneName> sipTrunkGroup <trunkGroupName> cac tcpMediaLimit <0 to 5000, unlimited>

Refer to SIP Trunk Group - CAC - CLI or SIP Trunk Group - CAC (EMA) for more information.

Direct Media Support

Similar to audio or video sessions, the SBC supports MSRP sessions when it is configured for direct media. If the IP peers (through their Packet Service Profiles) and the SIP trunk groups associated with an MSRP session are configured for direct media, MSRP packets are exchanged directly between the UAs without traversing the SBC. However, the SIP session is still established through the SBC and exists in the signaling path until the SIP session is torn down. To enable the use of direct media for MSRP sessions, take the following steps:

  • Enable direct media in the Packet Service Profiles of the IP peers involved with the MSRP sessions. In the following example, the profile "DEFAULT" is assigned to both IP peers. If using different Packet Service Profiles on each leg of the session, you must enable direct media in both profiles. 
% set profiles media packetServiceProfile DEFAULT flags useDirectMedia enable
% commit
  • Enable direct media on the SIP trunk groups used for each leg of the MSRP session. For example:
% set addressContext default zone PUBLIC sipTrunkGroup PUBLIC_TG media directMediaAllowed enabled
% set addressContext default zone PRIVATE sipTrunkGroup PRIVATE_TG media directMediaAllowed enabled 
% commit

Refer to the following pages for more information: