Abstract

Traffic prioritization gives network managers greater control over campus networks by providing a means to establish policies for bandwidth use. Such policies preserve the throughput characteristics of mission critical traffic in the face of increased demand from non-critical data. Without session prioritization, mission critical transaction-based traffic will suffer severe performance degradation — in both throughput and response times — when contending for bandwidth against other traffic types. 

Depending upon network infrastructure and design, network managers can deploy traffic prioritization from end systems, to net- work devices such as layer 2, or layer 3 switches. Extending prioritization to the desktop is critical to ensuring the highest level of service for strategic applications. Furthermore, given that virtually every net- work has components from multiple vendors, standards-based prioritization is essential. 

Until now, there have been few workable schemes for prioritizing critical traffic and improving end-to-end response times in frame-based networks. Although low-speed LAN-to-WAN bridges offered prioritization schemes, they were a far cry from end- to-end prioritization. Early attempts were, by definition, based on proprietary schemes since industry-standard prioritization has only recently been ratified. The existence of the IEEE 802.1p and 802.1Q standards changes that by offering a vendor-independent method for assigning priority to frames and thereby prioritizing traffic streams. 

3Com Corp. commissioned The Tolly Group to evaluate end-to-end IEEE 802.1p prioritization as implemented in its CoreBuilder 3500 switch and Fast EtherLink XL 10/100 Adapter with 3Com’s DynamicAccess software. 

The Tolly Group quantified how the invocation of 3Com’s Class of Service could enhance the throughput of Windows NT-based, client-server traffic. 3Com’s end-to-end prioritization utilizes Fast EtherLink adapters using 3Com’s DynamicAccess software which “tags” each frame transmitted from an end-station with an 802.1 p/Q VLAN field — consisting of a 4-byte extension to the Ethernet MAC header. Three bits within this tag are reserved for use as priority indicators and can be adjusted by Fast EtherLink 10/100 XL adapters to set network manager-defined priority settings for various application traffic types. The CoreBuilder 3500 reads these bits and queues traffic accordingly. Testing was performed in April to June 1998. 

Test results show that 3Com’s 802.1p/Q standards-based prioritization, as implemented as part of its policy-based networking scheme in the CoreBuilder 3500 switch and the Fast EtherLink 10/100 XL Fast Ethernet adapters, effectively prioritized mission-critical transaction-based sessions that otherwise would have suffered severe performance degradation due to contention with backbone traffic.