Overview of NV2 protocol
NV2 protocol is proprietary wireless protocol developed by MikroTik for use with Atheros 802.11 wireless chips. NV2 is based on TDMA (Time Division Multiple Access) media access technology instead of CSMA (Carrier Sense Multiple Access) media access technology used in regular 802.11 devices.
TDMA media access technology solves hidden node problem and improves media usage, thus improving throughput and latency, especially in PtMP networks.
NV2 is supported for Atheros 802.11n chips and legacy 802.11a/b/g chips starting from AR5212, but not supported on older AR5211 and AR5210 chips. This means that both - 11n and legacy devices can participate in the same network and it is not required to upgrade hardware to implement NV2 in network.
Media access in NV2 network is controlled by NV2 Access Point. NV2 AP divides time in fixed size "periods" which are dynamically divided in downlink (data sent from AP to clients) and uplink (data sent from clients to AP) portions, based on queue state on AP and clients. Uplink time is further divided between connected clients based on their requirements for bandwidth. At the begginning of each period AP broadcasts schedule that tells clients when they should transmit and the amount of time they can use.
In order to allow new clients to connect, NV2 AP periodically assigns uplink time for "unspecified" client - this time interval is then used by fresh client to initiate registration to AP. Then AP estimates propagation delay between AP and client and starts periodically scheduling uplink time for this client in order to complete registration and receive data from client.
NV2 implements dynamic rate selection on per-client basis and ARQ for data transmissions. This enables reliable communications across NV2 links.
For QoS NV2 implements variable number of priority queues with builtin default QoS scheduler that can be accompanied with fine grained QoS policy based on firewall rules or priority information propagated across network using VLAN priority or MPLS EXP bits.
NV2 protocol implementation status
As of version 5.0rc1 NV2 has the following features:
- TDMA media access
- WDS support
- QoS support with variable number or priority queues
Features that NV2 DOES NOT HAVE YET:
- data encryption
- RADIUS authentication features
- synchronization between NV2 APs
- some other features...
Compatibility and coexistence with other wireless protocols
NV2 protocol is not compatible to or based on any other available wireless protocols or implementations, either TDMA based or any other kind, including Ubiquiti Airmax and FreeBSD TDMA implementation. This implies that only NV2 supporting and enabled devices can participate in NV2 network.
Regular 802.11 devices will not recognize and will not be able to connect to NV2 AP. RouterOS devices that have NV2 support (that is - have RouterOS version 5.0rc1 or higher) will see NV2 APs when issuing scan command, but will only connect to NV2 AP if properly configured.
As NV2 does not use CSMA technology it may disturb any other network in the same channel. In the same way other networks may disturb NV2 network, because every other signal is considered noise.
The key points regarding compatibility and coexistence:
- only RouterOS devices will be able to participate in NV2 network
- only RouterOS devices will see NV2 AP when scanning
- NV2 network will disturb other networks in the same channel
- NV2 network may be affected by any (NV2 or not) other networks in the same channel