QoS: Ethernet vs. Wi-Fi

Priority mapping available; traffic shaping joins WLAN

Industry analysis by expert Joanie Wexler, plus links to the day's wireless news headlines

Certain networking services work differently on the wired and wireless sides of enterprise networks. One discussed in the last newsletter is multicast. Multicast is basically non-existent for WLANs, though some vendors are enhancing their systems to better control content delivery over the airwaves.

Another capability that differs is quality of service (QoS). Ethernet has mechanisms such as 802.1p, which involves setting priority bits in a 3-bit frame header in an Ethernet packet and allows for eight levels of prioritization.

Ethernet everywhere!

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Certain networking services work differently on the wired and wireless sides of enterprise networks. One discussed in the last newsletter is multicast. Multicast is basically non-existent for WLANs, though some vendors are enhancing their systems to better control content delivery over the airwaves.

Another capability that differs is quality of service (QoS). Ethernet has mechanisms such as 802.1p, which involves setting priority bits in a 3-bit frame header in an Ethernet packet and allows for eight levels of prioritization.

Ethernet everywhere!

But Wi-Fi is half-duplex and relies on a collision-avoidance media access control mechanism, which renders prioritization more limited. 802.11e, the Wi-Fi standard for QoS, contains a component informally known as Wi-Fi Multimedia (WMM) that prioritizes traffic according to four access categories.

David Stiff, senior manager of product management in Cisco's wireless networking group, notes that Ethernet is full duplex and involves talking to one device at either end of the connection. "So there are tons of ways to queue [packets in Ethernet]. You don't have that level of granularity on Wi-Fi," he says.

Still, Cisco's Unified Wireless Network can map packet priorities from Ethernet to Wi-Fi under some conditions, he says.

Meanwhile, Meraki has added a new wireless QoS twist at the higher layers. The vendor, which offers a WLAN controller cloud service, has embedded Layer 7 deep packet inspection (DPI) and traffic shaping into each of the APs it sells. Typically, this type of activity has been restricted to the WAN, where limited bandwidth causes greater scrutiny of packet flows, policies and treatment.

Meraki's QoS move is aimed at differentiating among different types of HTTP traffic, much of which is recreational, says Sanjit Biswas, Meraki's CEO. Information about Wi-Fi traffic types can be aggregated and displayed through the cloud, allowing customers to then assign treatment priorities to each type.

For example, administrators could rate-limit low-priority traffic with a policy such as "no user can use more than a megabit per second of BitTorrent," Biswas explains.

Or such traffic can also be blocked from the Wi-Fi network entirely through the cloud service portal, he says.

Read more about wireless & mobile in Network World's Wireless & Mobile section.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.