Cisco Call Manager groups can be used to specify a prioritized list of up to three Call Manager with which Cisco IP Phones can register. You assign a Call Manager to a device through a Device Pool
During a failover transition , active calls are preserved and phones will re-register once the existing calls are complete.
You use Regions to specify the codec and the maximum video bandwidth that can be used on calls between devices .
Every device is in one Region, and you assign a device to a Region by specifying a Region within a Device Pool and then assigning a Device Pool to a device
As you have probably seen it during the last days , I’ve put a lot of QoS information. Indeed ,QoS is not my preferred area so I’ve put all my attention to this topic to have a better understanding of all QoS mechanisms and it is successful as QoS is less nebulous now … We will see in the future.
Now , as I have finished all CCVP guides, I will begin again with the CCIE Quick References Sheet …. Time is decreasing hardly now so I’m in the starting blocks for the exam next week.
🙂
Another QoS mechanism that is useful for slower link speeds is LFI which will fragment larger payload to specified fragment sizes and then interleave the smaller payloads in among the fragments, reducing then the serialization delay.
There are three primary LFI mechanisms supported by Cisco are as follows:
- Multitlink PPP (MLP) : used on PPP links
- FRF.12 : used on Voice over IP over Frame-Relay (VoIPovFR) links
- FRF.11 Annex C : used on voice ov Frame-Relay (VoFR) links
In MLP mode , then you define the maximum serialisation delay that you wnat on your link and under FRF.12, you define the maximum size of the fragment that you want on your link.
To make more efficient the use of your bandwidth on slow-speed links, we can use 2 types of compression.
- Payload compression : Reduces the payload size, using approaches such as STAC, predictor or MPPC
- Header compression : Reduces the size of the TCP and RTP headers
The goal of compressions technologies is to increase the throughput over a WAN link while we are reducing the delay.
However , especially with payload compression approaches , the time that is required by lower-end routers to run the compression algorithm can increase the overall delay so in order to avoid this , you still can equip your router with a compression module like the CAIM.
With header compression , a header typically is reduced from approximately 40 bytes to 3 up to 5 bytes for TCP header compression or 2 up to 4 bytes for RTP header compression.
However, the routers technically are not doing real compression. Rather, these routers cache information that does not change during a conversation, such as source and destination IP address and TCP/UDP port numbers. The compressed header then carries such information as UDP checksums and a session context ID (CID) which identifies which flow the packet is a part of.
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