5 ways to enhance your WAN VoIP Topology

By the time you finish reading this post, “CM VoIP Resource Allocation Best Practices,” you have learned 5 ways to configure the Avaya Communications Manager and allocate the VoIP Resources based on location or geographical region.  This helps to load-balance the WAN traffic, enhance the performance of the voice delivery and allows the Media Gateways to handle the RTP/SDP Media and DSP utilization.

Not so long ago, I was assisting a customer troubleshoot issues with fax transmissions. The problem started happening after the fax service was updated from H.323 to a SIP-based service. As I reviewed some of the system configurations, I noticed conflicts between the codec types implemented.

Here are the 5 ways:

• 1.- Gather  the customer’s WAN Configuration
• 2.- Allocate and configure
• 3.- Review the implemented elements
• 4.- Assess the utilization of the VoIP Resources
• 5.- Test the VoIP Resources

1.- Gather the Customer WAN Configuration

The main key here is understanding the call flow, how many hops before the call gets to its destination and where do the MGs (Media Gateways) reside.

As you enter the discovery process, you have to ask for diagrams, and IP Spreadsheets that can help you understand IP Routes and Network Subnets participating in the call flow.

Another consideration is knowing the amount of calls (bandwidth) made per location and which voice compression are they using.

While you are analyzing the VoIP routing between locations, it is good to know the type and model of network switches are in production, which voice tagging mechanism is being implemented for the voice VLAN. Find out the DHCP Scope Options for both Data and Voice DHCP Pools.

Note – It is not recommended to have QoS assigned on the Network interfaces (NICs) corresponding to the Avaya Gear (MGs /MedPros/IPOffice/C-LANs/among others.). As the traffic leaving each interface has been tagged with DCSP Value of 46/EF. Not tagging these interfaces it helps reducing the overhead or computing from the switch.

2.- Allocate and Configure

Now that you understand which elements and which VoIP-Resources are utilized per IP Network Region you can start the process of “allocate and configure” those VoIP-Resources.

Allocate – Run a trunk/traffic analysis per location to give you a better idea how many channels are needed.

Direct Connected vs WAN/WAN-Direct Connected – Those IP Network Regions or locations without VoIP-Resources you can have a direct connection to another region with enough VoIP-Resources capacity.

The same can be use for load-balancing your VoIP-Resources through a WAN Direct/Non-Direct connection.

Communication manager uses its algorithm to decide where to pull the VoIP-Resources when necessary, to exclude the PROC-R IP-NR it is recommended to have PROCR assigned to a neutral IP-Network-Region.

Configuration best practices – Each Media Gateway has sockets to allow the connection of the VoIP-Resource or Media-Coder. Keep in mind that each Media Gateway has its maximum capacity.

Media Servers (AMS) is a software-based voip-engine that acts similar to a MP120/MP160, etc. decoding/encoding the SDP/RTP Media.

For legacy system using Port Networks, the analogy stays the same, where MedPros and Crossfires are the VoIP Engines providing Media Processors similar to the H.248 MGs/AMS. And unlike the MG/AMS, these TN Circuit Packs get configured individually and need to be physically connected to the LAN and following the same port speed and duplex guidelines that Avaya recommends (100 Mgb / Full Duplex).

Another element to consider is the IP Subnet size when configuring and designing these interfaces.

Per VLAN Avaya recommends a /24 bit subnet to limit the ARP  broadcast traffic per subnet, to keep the voip-resources and TDM Time Slot resources balanced in the legacy PNs.

3.- Review Communication Manager Configuration

Now that you know the amount of calls traveling through the WAN link, it is time to assign and configure the IP-Codecs. Here, you get to compress the RTP-Streams (voice) from a G.711 to a G.729, among others codec types. For fax transmission it is a good practice to offer the same codecs and t.38 signaling mechanism supported by the Fax Vendor.

Some fax providers might want to see the fax transmission presented different. In some cases, G.711 will do, and in other cases you can just set it as Pass-Through or T.38-Standard-Fallback.

In the illustration above you can see how t.38 is the primary signaling mechanism with G711 as a fallback option. I find this to be most stable option when not knowing what to send to the Fax.

Applying the IP-Codec – The codec-type gets applied to the corresponding IP-Network-Region. To apply the codecs to the WAN connection, you have to navigate to the third or fourth page of the form, depending on the version of CM.

WAN/Virtual Regions vs Direct Connected Regions

Direct Connected NRs have a higher priority over the Virtual NRs when reserving and allocating VoIP-Resources resources.

IP-Network-Region 241 is reserved for Processor Ethernet (PROCR). NR-240 is the first Virtual Region, 239 is the second, 238 is the third, all the way down to 221. 220 thru 201 are allocated for SIP Trunking, 200 – 11 for Media Gateways (Legacy Port Networks are assigned to NR-11 through NR-64).

NRs 1 through 10 are reserved for the Core/Data-Center

4.- Validate the VoIP Resources

One way to validate and review the usage of the Media Processors is by entering the “List Measurement” commands. These reports provide you with the necessary information to analyze the amount of VoIP-Resources used. The report breaks down the different categories.

list measurements ip dsp-resources gw summary today – As shown below. You can see a full report of the amount of voip-resources available per Media Gateway, total voip-resource used based on the scheduled reporting timeframe, and so on.

Another way to review them it is by connecting to the Media Gateway and running the “show voip-parameters” command. This shows the active and idle Media sessions. It also displays if there are any faults, the version of the Media Processor, and much more.

5.- Test the VoIP-Resources

To ensure the VoIP-Resources are working properly, there are a couple of quick maintenance commands that you can run.

From the Media Gateway you can run “test voip-dsp 1” to test the first socket. Each Media Processor has banks of DSP Channels from 1 through 4, this depends on the MP size.

When the Media Gateway has more than one Media Processor, you can run the command “campon-busyout voip-dsp 1” to gracefully busyout the first VoIP engine. You can reset then release it to bring it back.

Port Networks/Legacy, it is very similar “campon-busyout media-processor 01a14” is the command.

I hope this post has helped you in some way, but before you go, I want to ask you a quick question. – When working with audio problems, which command do you execute when troubleshooting speech quality?

Resources

Avaya – List Measurements IP dsp resources feature description