The need for QoS, configuration on Extreme Aerohive
This blogpost will focus on the configuration of QoS policies on Extreme Cloud IQ (Portal). Aiming to provide a real scenario which led to the implementation of QoS for an organisation. Before diving into this I cannot stress on the point that QoS solution will be successful only if it is implemented end to end. The QoS marking and policing if not honoured by the subsequent hops in the access <> distribution <> core.
The Need for QoS
The issues arise when packets do not get prioritisation and are either dropped or queued. The network transmission quality is determined by latency, jitter and packet loss. It becomes even more crucial with Wi-Fi being a shared and half-duplex medium it becomes all the more necessary to mark and prioritise the relevant traffic on the network. One may have 10Gbps internet or more but AP are often the bottlenecks in the network. With the adaptation of VoIP/Skype/Zoom and similar RTP/SIP applications, there is a need to make sure voice/video traffic get priority over other traffic. Moreover, Wireless networks and protocols are mostly designed for data services… so it is normally not possible “ just to drop” Rich Media on top and expect positive results.
Extreme Cloud IQ configuration
Let’s start with looking at the Extreme Cloud IQ configuration.
QoS Classifier Maps > Classifier map is used to mark traffic with Extreme Network QoS classes by various QoS classification systems (802.1p/DiffServ/802.11e).
Incoming Traffic – AP prioritises and forwards the incoming traffic as determined by the mapped QoS level.
Outgoing Traffic – AP uses marker maps.
If you login and navigate to below for checking the first option of “Classifier Maps”.
Configure > Network Policies > Edit “Policy Name” > Additional Settings > QoS Options
The incoming traffic is mapped based on the network/application service defined in the classifier map. In the above screenshot you can see LYNC, LYNC AUDIO and others set as VOICE and action being PERMIT.
MAC OUIs and SSIDs
I haven’t used this in our config but one can choose to map traffic to classes based on either the source/destination MAC OUI in the packet or based on SSID
802.1p is a layer 2 prioritisation often described as Class of Service can be seen in the TCI field of the Ethernet frame. The 3 bits give 8 different classes as shown below. In my scenario I have used the DiffServ and 802.11e(WMM) for layer 3 QoS.
DiffServ is concerned with classifying packets as they enter the local network. This classification then applies to Flow of traffic where a Flow is defined by 5 elements; Source IP address, Destination IP, Source port, Destination port and the transport protocol. The DSCP QoS is retained end to end and one of the reason it is preferred more than 802.1p.
Before moving to 802.11e, let’s get basics correct.
802.11 use collision avoidance mechanisms unlike collision detection for Ethernet. The DCF (Distributed Coordinated Function) algorithm is used for media access. Regardless of any clients on the medium, a 802.11 WLAN device will wait for a DCF interframe space and then begin the transmission. Once the DIFS is counted down to 0, a random backoff timer is generated if the medium is not free.
QoS is not possible with DCF alone and hence 802.11e was ratified. The EDCA (Enhanced Distributed Channel Access) included 4 queues(Background, Best Effort, Video, Voice), AIFS (ACs) and a range of contention windows (CWmin and CWmax). Two additional 802.11e enhancements included TxOP and Call Admission Control (CAC)
For outgoing traffic, one can define marker maps to map classes to priority numbers in standard classification systems (802.11e, 802.1p, and DiffServ). After defining classifier and marker maps, you then define classifier and marker profiles that enable one or more of the methods defined in the maps. Finally, you associate those profiles with SSIDs or interfaces to apply the mappings to traffic arriving at or exiting those interfaces.
Verifying if WMM QoS is working
The QoS Data Frame includes the QoS Control field which provides the information in the Priority field.
Adding Custom Application for QoS Categorisation
Navigated to > Configure > Application > Add Custom
Helpful links for more reading