Ethernet faces QoS barrier

(02/12/99) - While an Ethernet network has some measure of quality of service (QoS), the current lack of industry standards prevents interoperability between organisations and hinders end-to-end QoS connectivity.

QoS technologies identify packet applications and allocate priority to mission-critical information that can be defined via policies established by network administrators.

In an Ethernet-only network where the workgroup switches connect to backbone switches, a signaling protocol is necessary in order to guarantee the QoS required for the applications and users at both ends, said Hor Tuck Choy, technical marketing manager, Fore Systems.

Because such a signaling protocol is still being developed, it is difficult to implement a real end-to-end QoS in an Ethernet-only network, added Hor. "To make QoS meaningful, you need to have end-to-end, or QoS is useless to the user."

"In an Ethernet network, there's no real QoS mechanism, preventing it from transmitting other types of information [apart from data]," he explained. The industry is presently in the process of standardising mechanisms that govern end-to-end QoS within the LAN (local area network) environment, such as 802.1P and resource reservation protocol (RSVP), he added.

So while users within an organisation running on a pure-Ethernet network can still get QoS, the process is established through proprietary technology where network traffic cannot be prioritised when these users communicate outside the LAN, said Abdul Majid, senior consulting systems engineer, Greater Asia operations, Cisco Systems.

To implement QoS within an Ethernet environment, the network administrator needs to install application specific integrated circuits (ASICs) so the network has application and policy recognition capabilities, Majid explained.

Ethernet users supported by an asynchronous transfer mode (ATM) network in the backbone can also have some level of QoS through a process called LAN Emulation (LANE). LANE enables the Ethernet/ATM network to recognise Internet Protocol (IP) addresses, identify the type of application and carry out the appropriate QoS attached to the packet, Majid explained.

While QoS implementation over an Ethernet network is deployed more easily and costs less than over a ATM network, the latter is still the pioneer of QoS technology and provides a higher quality of traffic prioritisation, Majid said.

Only If Needed

"The quality of mapping Ethernet to ATM needs to be addressed," Kenny Ng, systems engineer, Xylan Asia-Pacific. "Right now they don't run on ATM quality standards."

"If you have an existing ATM network, then it would be useful to have some kind of interface for [Ethernet and ATM] to exist," said Andy Miller, network consultant, Cabletron Systems. "But the Ethernet QoS will never be the same as ATM QoS. And some applications may not require the type of QoS that ATM provides."

"With PNNI [Private Network-to-Network Interface], we can create meshed node-sharing between switches, or redundant switches," Miller said. "That's all standards based, and not logged into proprietary. So you know its a safe way to go if you adopt an ATM network."

PNNI is an ATM Forum specification that allows switches to automatically reconfigure routes around failures, carrying over ATM QoS features on those routes. But QoS should be deployed only if there is real network congestion and after the system administrators understand configuration procedures and policy management.

"If you want to prioritise all traffic, and want every user to have priority, then it will defeat the purpose of regulating network traffic," said Ng, and advised that QoS should be implemented only if necessary.

According to a survey conducted by Fore Systems and Informetics Research last year, network managers acquired LAN equipment to eliminate server bottleneck, increase network traffic and accommodate new high performance applications, said Hor.

"QoS is not the main reason for LAN purchases," he added. "It's quite low in priority compared to the others, so this is not a must-have thing. But it's a good-to-have thing because it allows the network managers to optimise network operations."

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