In this section:
Introduction
This document describes how to calculate DSP resource requirements for the New Investment
Protection Configurations of the SBC 1000 using Release 3.2 and 4.0 software.
For earlier configurations please refer to the "Quick Guide to DSP Resource Requirements for the Sonus
SBC 1000 Session Border Controller: Older Configurations."
Purpose
This guide is intended to help partners and customers understand how to determine DSP resource requirements for their immediate needs and to support future growth.
How to Use This Guide
This guide is intended to be used in conjunction with the Partner Configurator to determine DSP
resource requirements for various codec/transcoding scenarios. This guide is not a replacement for the
Partner Configurator.
WHAT YOU NEED TO KNOW
Default transcoding scenario: The most common IP – IP transcoding scenario for SBC 1000 is from G.711 (RTP) to G.711 (SRTP). This is considered as the default transcoding scenario for SBC 1000 when calculating DSP resource requirements.
DSP resource requirement number: DSP resources is a unit of DSP processing required to transcode from one codec to another. For SBC 1000, 1 DSP resource is equal to the processing associated with 1 (one) transcoding session for the default transcoding scenario (described above). All calculations mentioned in this document build upon the default transcoding scenario mentioned above. For example, DSP resource requirement number for 100 IP-IP sessions for a default transcoding scenario is 100.
Special case for multiple low-bit rate codecs: In the case where two or more low-bit rate codecs (G.729ab, G.723.1, G.726, or T.38) will be used (IP-IP and/or TDM/IP) a 20% uplift is applied to the calculated results. For example, if several codecs will be used and this calculates to a DSP resource requirement of 100, then a 20% uplift is applied and the true DSP resource requirement will be
120. Note that this uplift requirement only applies for multiple low-bit rate codecs (G.729ab, G.723.1, G.726, or T.38). Combination of a single low-bit rate codec with G.711 does not require an uplift. It is also important to design for the most DSP intensive usage. Hence, where multiple codecs will be used
and the split among these codecs will vary be sure to calculate using the codec that is most DSP
intensive and then apply the 20% uplift.
Multiplication Factor: Multiplication factor when multiplied with your session requirement count gives you the total number of DSP resources required for those sessions.
Survivable Branch Appliance (SBA) and Cloud Connector Edition (CCE) applications from Microsoft®: Addition of the SBA does not affect DSP requirements.
DSP mode versus RTP Proxy (Media Pass Through): In the case of RTP Proxy media passes through the
SBC and does not use the DSP.
DSP MATRIX FOR IP-IP OPERATING MODE
The following table provides multiplication factor (to be used with IP-IP session count requirement) to determine DSP resource requirement. To determine the multiplication factor for your transcoding scenario, select from-codec ('codec type' column) and to-codec ('codec type' row) in the following table. The intersecting cell gives you your multiplication factor.
Table 1: IP – IP DSP resource consumption table
Note: Densities assume VAD on (60% silence during call), RTCP on, RFC2833 on, and 20ms packet size for all codecs (except 30ms for G.723.1), G.722.2 at 12.65 kbit/s, RTP (unless specified with SRTP).
DSP RESOURCE CONSUMPTION FOR TDM-IP OPERATING MODE
Resource requirements for TDM/FXx <> IP usage are measured to be 50% the usage of comparable IP <> IP flows, identified in Table 1, where the TDM/FXx leg of the call can be approximated as a G.711 non-encrypted SIP leg from a media services perspective. By way of example, assume the case of TDM/FXx – IP flow, where encryption on the IP media flow is required with the selection G.729ab .
Please note the above calculation scheme assumes VAD on (60% silence during call), RTCP on, RFC2833 on, and 20ms packet size for all codecs (except 30ms for G.723.1), G.722.2 at 12.65 kbit/s, RTP(unless specified with SRTP ), and standard Line Echo Canceller.
SBC 1000 CONFIGURATIONS AND DSP RESOURCE TO DSP SKU MAPPING
The SBC 1000 Release 6.1 customer orderable SKUs are pre-populated with DSP physical resources to support calls that require media services. The Depending upon the configuration, the SBC 1000 features one, two, or three DSPs (Digital Signal Processors). The mapping of available DSP resources to available DSPs is presented in table 3:
Table 3: DSPs to DSP resource mapping
Number of DSPs
Available DSP Resources
1
64
2
128
3
192
For the list of available customer orderable SKUs and available DSPs, please contact your Sonus sales representative.
CALCULATING DSP RESOURCE REQUIREMENTS
To determine the appropriate configuration and the number of DSPs you will need, please follow these steps:
DSPs will be needed to support your needs.
Example 1 - Calculating the DSP resource requirement for a simple low density IP – IP deployment
5. I also want 4 FXS – IP sessions, where the media on the IP legs will be encoded as G.729ab and encrypted. From table 1, the multiplication factor is 1.31*50%, or 0.66; therefore, my IP-IP DSP resource requirement number is 2 * 0.66 = 2 (round up from 1.31).
6. Simultaneous usage – total DSP resource requirement is 20 + 2 = 22.
7. 8. Based on the mapping table, I can select any SBC 1000 customer orderable SKU (as all SKUs feature at least one DSP, with a minimum available 64 DSP resources) with 4 FXS ports.
Example 2 - Calculating the DSP resource requirement for a medium density IP – IP & TDM - IP deployment
5. Regarding the TDM – IP flows, I also want 60 TDM to/from IP sessions, where the media on the IP legs will be encoded as G.722 and encrypted. From table 1, the multiplication factor is 1.95*50%, or 0.98; therefore, my IP-IP DSP resource requirement number is 60 * 0.98 = 59 (round up from 58.8).
6. Simultaneous usage: total DSP resource requirement is 59 + 57 = 116.
8. Based on the mapping table, I can select any SBC 1000 customer orderable SKU that features a minimum of 2 DSPs and 2 PRI links
Example 3 - Calculating the DSP resource usage possible in a high capacity IP – IP deployment
5. The simultaneous maximum number of calls subject to DSP intervention, worst case (G.723.1 – G.723.1), that may be supported across the system is 192 DSP resources divided by 2.64 = 72 (rounded down from 72.5)
6. The simultaneous maximum number of calls subject to DSP intervention, best case (all calls G.723.1 to/from G.711), that may be supported across the system is 192 DSP resources divided by 1.53 = 126 (rounded down from 126.3). The 1.53 multiplication factor was derived from table 1, and includes no uplift for multiple low bit rate codecs.
7. For clarity, please note an SBC 1000 (Release 6.1 and later hardware) can always support 192 total calls. Points 5 and 6 merely identify the maximum simultaneous quantity of calls that are subject to DSP intervention; additional calls are supported when running in direct media or RTP proxy mode.
BEHAVIOR WITH DSP MODE VERSUS RTP PROXY (MEDIA PASS THROUGH)
RTP Proxy was introduced on the Sonus SBC 1000 and Sonus SBC 2000 with Release 3.1. In the case of RTP Proxy media passes through the SBC and does not use the DSP. For clarity of understanding in this document the term media pass through mode is used and is the same as RTP Proxy.
those calls where the resource is truly needed. However, it is again important to keep in mind that there is no support for a mid-call dynamic switch to change mode, this
includes the case of call transfer and conference. This is not necessarily a limitation. It simply means that the network deployment/architecture needs to be understood.
SBC must have available DSP resource. Otherwise the call will fail.
Fax
transmission will be T.38.)
DTMF
2833/4733 or out of band using the INFO message.
INFO. There is no fallback function.