Calculating DSP Requirements for SBC SWe Lite

Introduction

This document describes how to determine vCPU and RAM resources required for an 

 to process planned SIP-based traffic models. Because many deployments are limited due to constraints imposed by existing equipment, it is important to understand and configure your system for media manipulation.

Purpose

This document is intended to help partners and customers who employ a VM (Virtual Machine) hosting an instance of the SBC SWe Lite:

• Identify the number of media sessions requiring manipulation supported by a given vCPU and RAM configuration of an 

• Identify the number of vCPU and RAM resources to be provisioned to an  to address a given number of media sessions requiring manipulation

Both goals support a partner/customer's effort to ensure traffic processing expectations are met in an 

 deployment.

The available 

 configurations ("Partner Configurator"), which includes a description of embedded features and options, is available behind the partner portal.

Definitions and Terminology

 

Concepts and Definitions

RTP Direct Media Mode Sessions

Definition

A media session that does not flow through the 

. These flows are common with endpoints that reside within the same physical premises (such as a single branch office) where there is no need for any manipulation of any aspect of the media flow (such as codecs, headers, and encrypting/decrypting) The implications of such sessions on the  are:

• • The 
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     does not consume any RAM or vCPU resources processing the direct media mode sessions.
  • Partners/customers do not need to consider direct media mode sessions when determining an appropriate vCPU and RAM assignment to a given 
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    .

Licensing

The 

 supports a single media session on a 1:1 basis with an associated SIP signaling session. Note the following:

• The 

 requires a license to enable a given quantity of SIP signaling sessions.
• The  supports a single media session on a 1:1 basis with an associated SIP signaling session without further licensing. Specifically:

• A direct media mode session will be supported without any additional licensing licensing beyond the corresponding SIP session license.
• Multiple direct media mode session streams (audio, video, and so on) may be associated with a given SIP session, and will not require additional licensing unless identified elsewhere.
• Only one mode of media is supported against a given SIP session. For example, you cannot have one stream of media in direct media mode, one stream of media in RTP proxy media mode, and both associated with the same SIP signaling session.

Refer to Obtaining and Installing a SWe Lite License and Working with Licenses or a description of available 

 session and feature licenses.

RTP Proxy Media Mode Sessions

Definition

A media session that flows through the 

 but does not require media manipulation. These flows may be common with endpoints that may not reside within the same physical premises, but do reside within the same enterprise. If these sessions require access to a public SIP trunk (call flows out of the corporate WAN), there may be a need for encryption/decryption and IP address manipulation services, as many public carriers do not support the forwarding of encrypted media or private IP addresses. However, complex media manipulation such as transcoding will not be required due to enterprise-wide policies surrounding codec usage being in force. The implications of such sessions on the  are:

1. The 

 consumes RAM and vCPU resources processing the RTP proxy media mode sessions
2. Consumption of RAM and vCPU resources is less than the consumption of RAM and vCPU resources associated with media manipulation mode sessions
3. Partners/customers need to consider RTP proxy media mode sessions when determining an appropriate vCPU and RAM assignment to a given 

RTP Proxy Media Mode Sessions – Licensing

The 

 supports a single RTP proxy media mode session on a 1:1 basis with an associated SIP interworking session. Note the following regarding RTP proxy media mode session:

• An RTP proxy media mode session will be supported without any additional licensing beyond the corresponding SIP session license if encryption/decryption services are not required. Services the SBC is capable of applying to such media streams include:

• The modification of IP address and other data within the S/RTP, UDP, IP and other header data as provisioned by the user
• The pass-through of encrypted media traffic (SRTP ↔ SRTP) where no change is required to the previously applied encryption

• An RTP proxy media mode session requiring encryption/decryption services will require additional licensing beyond the corresponding SIP session license. Encryption/decryption services means:

• An RTP proxy media mode session that requires the SBC support RTP ↔ SRTP conversions
• An RTP proxy media mode session that requires SRTP ↔ SRTP changes, such as a cipher change, and authentication algorithm change as the media flow transits the SBC

Other considerations:

• Multiple RTP proxy media mode session streams (audio, video, and so on) may be associated with a given SIP session, and will not require additional licensing unless identified elsewhere
• Only ONE mode of media is supported against a given SIP session; for example, you cannot have one stream of media in direct media mode, one stream of media in RTP proxy media mode, both associated with the same SIP signaling session

Refer to Obtaining and Installing a SWe Lite License and Working with Licenses for a description of available 

 session and feature licenses, including instructions on how to enable RTP proxy encryption/decryption services. 

RTP Media Manipulation Mode Sessions

Definition

A media session requires media manipulation is considered a media manipulation mode session. Such flows may be common with endpoints that may communicate across enterprise and public boundaries. The common call types that require media manipulation services include the following (not an exhaustive list):

1. 1. Sessions that require transcoding, such as G.711 (common codec in enterprises) ↔ G.729ab (common codec in public networks) translation, G.711 A-law ↔ G.711 µ-law, and so on. Please refer to Protocols and Protocols and Functions Supported for the list of codecs supported by the 
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      .
   2. Transrating, that is, call legs that carry a different time sample size of media, where the 
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       performs the translation. Used often when enterprises or the service provider is looking to save bandwidth by reducing packet count at the expense of voice quality (should a packet be dropped).
   3. Silence suppression, where the 
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       looks to remove/insert RTP packets carrying no meaningful media, again to save packet traffic;
   4. Fax calls.
      
      1. Fax tone detection and interworking to T.38 (T.38 support will be available in a future release of the 
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         )
      2. G.711 fax media pass-through, as DSP intervention reduces the likelihood of in-band fax signaling/media issues
         
         
   5. Any call flow where in-band ↔ out-of-band interworking is required. Examples:
      1. In-band DTMF tone detection interworking with out-of-band RFC 4733 (supersedes RFC 2833)
      2. In-band DTMF tone detection interworking with SIP INFO messages
      3. Interworking RTP dynamic payload types, required when the subtended SBC peers use differing payload type identifiers from the dynamic RTP payload range (for example 96 - 127) to identify a common payload format (in other words,  codec)
         
         
   6. Any form of media that originates from the SBC in support of call developments. For example:
      • Announcement playback
      • Local ringback tone
      • Music on Hold
      • Comfort noise
      
      
   7. Jitter compensation, to maximize user experience with voice quality.
   8. Certified Skype for Business Phones and Devices interworking with non-certified endpoints. With DSP intervention, 
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      s can address media incompatibility issues that at first glance may not be apparent between certified Skype for Business Server endpoints (as documented at https://technet.microsoft.com/en-us/office/dn947482) and other SIP-based client endpoints, such as RTCP reporting interval mismatch, and unrecognized in-band supplementary service requests.

The implications of media manipulation mode sessions on the 

 are:

• The
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   consumes RAM and vCPU resources processing media manipulation mode sessions
• Consumption of RAM and vCPU resources is higher than the consumption of RAM and vCPU resources associated with RTP proxy media mode sessions
• Partners/customers need to consider media manipulation mode session density when determining an appropriate vCPU and RAM assignment to a given 
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Media Manipulation Mode Sessions – Licensing

The 

 supports a single media manipulation mode session on a 1:1 basis with an associated SIP signaling session. Note the following regarding licensing implications:

• A media manipulation mode session requires additional licensing beyond the corresponding SIP session license. Refer to the section above for an example of services available with a media manipulation mode-related license.

• A media manipulation mode session supports encryption/decryption services. Encryption/decryption services means:

• An RTP proxy media manipulation mode session that requires that the SBC support RTP ↔ SRTP conversions.
• An RTP proxy media manipulation mode session that requires SRTP ↔ SRTP changes, such as a cipher change, authentication algorithm change, and so on as the media flow transits the SBC.

Other considerations:

• Multiple media manipulation mode session streams (such as audio) may be associated with a given SIP session, and will not require additional licensing unless identified elsewhere.
• Only one mode of media is supported against a given SIP session. For example, you cannot have one stream of media in media manipulation mode session mode, one stream of media in RTP proxy media mode, both associated with the same SIP signaling session.
Refer to Obtaining and Installing a SWe Lite License and Working with Licenses for a description of available

 session and feature licenses, including instructions on how to enable RTP proxy encryption/decryption services. 

Session Density Map

The table below is a guide to the maximum capacity of an  

 configured into a VM (Virtual Machine) with a given set of vCPU and RAM resources.  The maximum number of the following items vary depending upon a given VM resource profile:

• RTP Media manipulation mode sessions;
• RTP proxy session mode sessions requiring encryption/decryption services;
• RTP proxy session mode sessions not requiring encryption/decryption services;
• Direct media mode sessions (not presented in the table, but equivalent to RTP proxy session mode sessions not requiring encryption/decryption services;
• SIP registrations.

The table will be used extensively to identify and plan the required resource configuration for a given deployment of an 

 to address a partner/customer's expected SIP traffic flow.

¹G.722 (AMR) reduces values by 30%.

²SWe Lite supports 25 video streams per vCPU to a maximum of 100 streams. Exceeding 4 vCPUs will not allow more than 100 video streams.

How to Determine vCPU and RAM Requirements

Follow these steps to determine the number of vCPUs and RAM required for your 

 deployment.

1. Determine the number of RTP media manipulation mode sessions needed (taking into account future growth): From Table 3, identify the required minimum quantity of vCPUs and RAM to address your required capacity, and then record the values.

2. Determine the additional RTP proxy session mode sessions requiring encryption/decryption services for your 

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    deployment (taking into account future growth):

   Step	Action
   a	From Table 3, identify the maximum available RTP proxy session mode session capacity (with encryption/decryption services) available with the quantity of of vCPUs and RAM recorded from Step 1.
   b	Determine if the maximum available RTP proxy session capacity from (a) above is larger than your required capacity of additional RTP proxy session mode sessions requiring encryption/decryption services: If... Then Capacity from (a) is larger Proceed to step 3, using the quantity of vCPUs and RAM determined from point 1 above. Capacity from (a) is smaller Review Table 3 and increase the quantity of vCPUs and RAM until you arrive at a quantity of both that supports an RTP proxy session capacity (with encryption/decryption services) equal to/greater than your required number of sessions. Record these values.

3. Determine the additional RTP proxy session mode sessions not requiring encryption/decryption services for your 

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    deployment (taking into account future growth):
   
   

   Step	Action
   a	From Table 3, identify the total number of RTP media sessions available with the quantity of vCPUs and RAM recorded from point 2(a) or 2(b) above. This value can be found in the Maximum SIP with corresponding RTP Sessions column.
   b	Add the number of required RTP media manipulation mode sessions and RTP proxy session mode sessions requiring encryption/decryption services and record the value.
   c	Subtract the value recorded in 3(b) from the value recorded in 3(a).
   d	Determine if the value in (c) above is greater than/equal to the required additional RTP proxy session mode sessions not requiring encryption/decryption services for your Unable to show "metadata-from": No such page "_space_variables" deployment.    If... Then The value in (c) above is greater than/equal to Proceed to step 4, using the quantity of vCPUs and RAM determined from point 3(a) above. The value in (c) above is less than Review Table 3 and increase the quantity of vCPUs and RAM and repeat steps 3(a) through 3(c) until you arrive at a quantity of both that supports an overall session capacity greater than your total required number of sessions across all modes. Record these vCPU and RAM values.

4. Prepare to configure your 
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    with the required number of vCPUs and RAM by referring to Configuring the SBC Edge and SBC SWe Lite.

Examples

Calculating the vCPU and RAM Resource Requirements for a Low-Density 

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 Deployment

1. I need 15 RTP media manipulation mode sessions (sessions will be equivalent to the Default Media Manipulation Scenario defined above). From Table 3 I see a single vCPU and 1 GiB of RAM will support this capacity. I record these values as the potential number of vCPU and RAM resources to assign to my 

.

2. I need 35 additional RTP proxy session mode sessions requiring encryption/decryption services. From Table 3 I see a single vCPU and 1 GiB of RAM will support up to 100 RTP proxy session mode sessions requiring encryption/decryption services  I continue to use the number of vCPU and RAM resources from point 1 to assign to my .

3. I need 50 additional RTP proxy session mode sessions not requiring encryption/decryption services.

(a) From Table 3, I see a single vCPU and 1 GiB of RAM will support a maximum of 100 total sessions.
(b) The sum from adding the required media manipulation mode sessions plus RTP proxy session mode sessions requiring encryption/decryption services is 50.
(c) The difference from subtracting 3(b) from 3( a) results in 50 sessions.
(d) As 3(c) is equal to the 50 RTP proxy session mode sessions not requiring encryption/decryption services, I continue to use the number of vCPU and RAM resources determined from point 2 above to assign to my 

.

Calculating the vCPU and RAM Resource Requirements for a High-Density 

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 Deployment

1. I need 100 RTP media manipulation mode sessions (sessions will be equivalent to the RTP Default Media Manipulation Scenario defined above). From Table 3, I see 2 vCPU and 1.5 GiB of RAM will support this capacity. I record these values as the potential number of vCPU and RAM resources to assign to my 

2. I need 400 additional RTP proxy session mode sessions requiring encryption/decryption services. From Table 3, I see 2 vCPU and 1.5 GiB of RAM will support up to 1,000 RTP proxy session mode sessions requiring encryption/decryption services alongside a maximum of 100 media manipulation mode sessions. I continue to use the number of vCPU and RAM resources from point 1 to assign to my 

.

3. I need 500 additional RTP proxy session mode sessions not requiring encryption/decryption services.

(a) From Table 3, I see 2 vCPU and 1.5 GiB of RAM will support up to 1,000 total sessions.

(b) The sum of adding the required media manipulation mode sessions and RTP proxy session mode sessions requiring encryption/decryption services is 500.

(c) The difference from subtracting 3( b) from 3(a) is 500 sessions.

(d) As 3(c) is equal to the 500 RTP proxy session mode sessions not requiring encryption/decryption services, I continue to use the number of vCPU and RAM resources (2 vCPUs, 1.5 GiB RAM) determined from point 2 above to assign to my 

.

Calculating the vCPU and RAM Resource Requirements for a High-Density SIP Registration 

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 Deployment

The required vCPU and RAM for a high capacity SIP Registration deployment are relatively simple: if the number of SIP registrations exceeds 1,000 endpoints, please configure the VM with a minimum of 4 vCPUs and 2.5 GiB RAM. If less/equal to 1,000, the RAM is defined by the required session capacity.

Considerations for Media Manipulation Session Mode versus RTP Proxy Session Mode

SIP Signaling Group Considerations

SIP Signaling groups (provisioning constructs that represent a connection between the 

 and another SIP based peer) can be configured to use either media manipulation session mode or a RTP proxy session mode. Note the following:

• Preference can be set so that either media manipulation session mode or RTP proxy session mode is preferred, but not required.

• If RTP proxy session mode is configured as preferred by both signaling groups, the call proceeds using RTP proxy session mode.

• If media manipulation session mode is configured as preferred by both signaling groups, the call proceeds in media manipulation session mode.

• If one signaling group is configured as media manipulation session mode preferred, and the other signaling group is configured as RTP proxy session mode preferred, the selection of mode is based on the preference of the signaling group associated with the party initiating the call. If media manipulation session mode is preferred but there is no available resource for the initiating party, the initiating party will fall back to attempt the call using RTP proxy session mode.

• After a media path is established between the SIP client and the 

 in either media manipulation session mode or RTP proxy session mode, 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 emphasizes the importance of understanding the network deployment/architecture. It simply means that the network deployment/architecture needs to be understood.

• If media manipulation session mode is preferred but not required, and if the other signaling group is configured for RTP proxy session mode only, the call goes through using RTP proxy session mode. This improves preservation of the media manipulation session mode resource for calls which require the resources most. However, keep in mind that there is no support for a mid-call dynamic switch to change mode, including the case of call transfer and conference. This is not necessarily a limitation. This also emphasizes the importance of understanding the network deployment/architecture.

• If media manipulation session mode is either required or preferred and a RTP proxy session mode route is not possible, the 

 must have an available media manipulation session mode resource – otherwise, the call will fail.

Considerations for DTMF

There are several alternatives for DTMF calls:

• When a DTMF call is received, the 

 terminates the call and transmits G.711. Other codec types may also be used. However, types such as G.723.1 may be less reliable.

• When a DTMF call is received, the 

 terminates the call and transmits the signals as out-of-band RFC 2833/4733 compliant messages or out-of-band SIP INFO messages.

• A signaling group can be provisioned to transmit in-band signals as voice, RFC 2833/4733, or SIP INFO messages. There is no fall-back function.

• In the case of RTP proxy session mode, the 

 does not process the DTMF.

Considerations for Video Interworking in Non-DSP Mode

SWe Lite supports 25 video streams per vCPU to a maximum of 100 streams. Exceeding 4 vCPUs will not allow more than 100 video streams.