39.1. Overview

39.1. Overview
	Chapter 39. NPV - New Packet Voice

The NPV stands for the New Packet Voice and it's the new way Abilis used for its proprietary Voice over IP.

NPV has been introduced in addition to the "old" PV, thus permitting perfect coexistence of the two as well as a smooth migration if desired.

The comparison between NPV and PV are summarized in the following table.

Table 39.1. NPV vs PV

	NPV	PV
Encapsulation	IP/UDP, ISDN B-CH	IP/UDP, ISDN B-CH, Frame Relay, ATM, Leased line
Number of links	Default 256, with licence 1000	256
UDP local port	ONE for all links. Default 38383.	One for every PV
Backup	Pool of max-bck channels [0..250]	One for every PV
Authentication	By Abilis-ID or user defined key or both together. Uses RSA encryption to secure the authentication.	No
Roles	Peer, Client, Server	STD, EXT, EXT-CLIENT, EXT-SERVER
IP address filtering	Yes	Yes
NAT traversal	Yes (client/server)	Yes (ext-client/ext-server)
Double path (ART)	Yes	Yes
Voice packets redundancy	Yes	Yes
Link state check	Yes, with peer states alignment and burst options	Yes
TOS/DS configuration	Yes	Yes
Cryptography	RC6 with 256 bits dynamic keys	RC6 with 128/192/256 static keys
CTIL parameters	Included in NPVL configuration	Separated in CTIL table
Extensive logging	Yes	No
Configuration	Simplified	Complex
Configuration resources	One resource with up to 1000 links	One per every link

Some key notes about the NPV resource:

Role: For the IP section of NPV we can have following possible scenario.

Both Abilis have a static and "not natted" IP address and UDP port.
In this case, both Abilis can be configured as PEER or CLIENT/SERVER, the choice is free.
One Abilis has a static and "not natted" IP address and UDP port, the other has a dynamic IP address or it's behind NAT.
In this case, the Abilis with static and "not natted" IP address and UDP port must be configured as SERVER while the Abilis with dynamic/natted IP must be configured as CLIENT.
Both Abilis have dynamic IP addresses.
In this case NPV cannot be used.
One Abilis has static and natted IP address, the other has a dynamic IP address or it's behind NAT.
In this case the Abilis with static and natted IP must be configured as SERVER , the other as CLIENT.

Table 39.2. Role

Role	Description
`PEER`	Allowed only when both Abilis have a static and "not natted" IP Address and UDP port.
`CLIENT/SERVER`	Allowed in any situation. The role CLIENT is required on the side with dynamic or natted IP.

	Warning
	Backup links aren't affected by Role setting.

ART Protocol: “Abilis Redundant Tunneling” sends the same information on two different lines. The receiving Abilis discards the packet which arrives second (out-of sequence). The probability that the same packet is lost on both links equals the product of the original probabilities. Example: two links with 10% failure rate (a very high one!) ends up with 1%, which is normally negligible.
Tip
It's advisable to use ART ONLY with lines with the same speed. In case of lines with different speeds, the packets are sent with the maximum speed of the slower line.
VRED Protocol: Abilis “Voice Redundancy” duplicates VOICE and/or FAX packets by repeating a packet when the subsequent one has to be sent. This method is similar to the redundancy used in SIP for T38 packets. The receiving Abilis discards the packet which arrives second (out-of sequence). The probability that the same packet is lost in two different moments is therefore reduced.
Link Check: it's a procedure used to detect end-to-end link real functioning, regardless of the lower protocol layers states.
Backup over ISDN: in case of failure of the permanent IP connection, the Abilis NPV links can be instantaneously switched onto ISDN backup lines.
Encryption: it activates the cryptography of the voice/fax sent on the NPV link, IP and ISDN backup, using RC6 cipher with a 256 bit cryptography key, randomly generated at every connection.

	Tip
	It's advisable to use ART ONLY with lines with the same speed. In case of lines with different speeds, the packets are sent with the maximum speed of the slower line.