Nstreme Protocol · Topic 2 of 3

Nstreme Configuration Options

Learn the Nstreme settings in RouterOS, including enable polling, disable csma, framer policy and framer limit, and how to set up an AP and a station.

5 min

In a nutshell

The settings are enable-polling, disable-csma, framer-policy and framer-limit.
They are set in the Nstreme submenu, after Nstreme is selected for the interface.
Polling avoids hidden node collisions, and each client waits longer when there are many clients.

What it is

The Nstreme configuration options are the settings that control framing, polling and CSMA on an Nstreme interface.

They sit in the Nstreme submenu of the wireless interface. A good choice depends on the size of the network, the traffic and the length of the link.

Wrong values do not break the link in an obvious way. They quietly cost throughput or add delay, so you need to understand what each one does.

How it works

You select the protocol, then set the framing and the access method on both ends.

The settings

The settings are set with one command:

/interface wireless nstreme set wlan1 enable-polling=yes disable-csma=no framer-policy=dynamic-size framer-limit=3200

Setting	Purpose
`enable-polling`	Turns on polling, so the access point controls who sends
`disable-csma`	Turns off the listen before talk rule
`framer-policy`	How frames are packed into larger frames
`framer-limit`	The size limit for the packed frames, in bytes

Before these settings take effect, the interface must use Nstreme. In RouterOS v6 that is wireless-protocol=nstreme, and older releases used enable-nstreme in the same submenu.

Enable polling

With enable-polling=yes, the access point polls its clients in turn. On a client, the same setting makes it answer polls. Polling is the main way to avoid hidden node collisions, and it is best for point to multipoint.

With few clients, polling gives a smooth and fair share. With many clients, each client waits longer for its turn, so the throughput per client falls.

Disable CSMA

disable-csma removes the listen before talk rule. It saves waiting time, and it is meant for polled links on a clean channel. If the channel is shared with other networks, leave CSMA on.

Combination	Effect
Polling on, CSMA on	Orderly turns, and the radio still listens first
Polling on, CSMA off	The most efficient, for a clean channel that you control
Polling off	Clients send in the usual way, and framing is the main gain

Framer policy

The framer-policy setting decides how frames are packed:

Value	Behaviour
`none`	No packing, each frame goes alone
`best-fit`	Packs as many frames as fit under the limit, without splitting a frame
`exact-size`	Fills the frame to the limit, and may split the last frame to do so
`dynamic-size`	Chooses the frame size dynamically, based on the traffic

best-fit and exact-size use the framer-limit as the target. A larger limit lets more frames pack together, with more saving, but it adds delay and costs more to repeat when lost.

dynamic-size is a sensible starting point. Move to a fixed policy only when a test shows a gain.

Framer limit

The framer-limit is the maximum size of a packed frame. A larger value suits steady bulk traffic on a clean link. A smaller value suits traffic that is sensitive to delay, such as voice, or a link with many losses.

Exam tip

Change one of these settings at a time, and compare the throughput and the retries before and after each change.

Configuring an access point and a station

Both ends must be set up to match:

# Access point
/interface wireless set wlan1 mode=ap-bridge ssid=Backhaul wireless-protocol=nstreme
/interface wireless nstreme set wlan1 enable-polling=yes framer-policy=dynamic-size

# Station
/interface wireless set wlan1 mode=station ssid=Backhaul wireless-protocol=nstreme
/interface wireless nstreme set wlan1 enable-polling=yes framer-policy=dynamic-size

The SSID, the band and the protocol must agree. The framing settings do not have to be identical, but a sensible match keeps behaviour predictable.

Choosing values

Network	Suggested approach
Point to point backhaul on a clean channel	Polling on, CSMA off, dynamic framing
Point to multipoint with many clients	Polling on, CSMA on, moderate framing
Delay sensitive traffic	Smaller framer limit
Bulk transfer	Larger framer limit

Checking the result

/interface wireless nstreme print
/interface wireless registration-table print detail
/tool bandwidth-test address=192.168.88.2 direction=both

The first command shows the settings that are in force. The registration table shows the state of the link. The bandwidth test shows the real throughput, so you can compare settings.

Watch out

Do not test on a live link in a busy hour. A bad setting can lower throughput for every user until you change it back.

What to remember for the exam

Six facts cover this topic.

The settings are enable-polling, disable-csma, framer-policy and framer-limit.
They are set in the Nstreme submenu, after Nstreme is selected for the interface.
Polling avoids hidden node collisions, and each client waits longer when there are many clients.
disable-csma is for polled links on a channel that you control.
The framer policies are none, best-fit, exact-size and dynamic-size.
A larger framer limit gives more saving and more delay.

Common mistakes

Four errors are typical.

CSMA off on a shared channel. The link interferes with other users.

A very large framer limit for voice. The delay becomes too high.

Setting only one end. The settings and the protocol must be right at both ends.

Changing many values at once. You cannot tell which one helped.

Check yourself

Work through these three questions.

Which setting turns on polling, and where is it set?
enable-polling turns it on, and it is set in the Nstreme submenu of the wireless interface, with /interface wireless nstreme set. The client also needs it set to answer polls.
What is the difference between best-fit and exact-size framing?
best-fit packs whole frames up to the limit without splitting any. exact-size fills the frame to the limit and may split the last frame.
When is it sensible to use disable-csma?
On a polled link on a clean channel that only you use. On a shared channel it interferes with other users.

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