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3550-12T and 4900

Hello all experts,

I want to know the difference on the QOS features

between 3550-12T(Rel. 12.1(4)EA1) and 4900 (Rel 6.3).

The document in 4900 is much shorter than that in 3550-12T. Can I get the same feature set from these

two modules? (Such as the classification/marking/

shaping, etc.)

Thanks in advance.

Community Member

Re: 3550-12T and 4900


I assume that you are referring to 3com 4900 switch.

Here is some information I could find. Please do further research on both the products

3Com 4900 switches are incapable of classifying or reclassifying data on a per port basis as well as any data-specific criteria. These switches simply honor the 802.1p CoS tags and offer no intelligence to do the tagging or change the tagging within the switch. This "solution" is not secure or scalable because it is totally reliant on NICs and their associated software to do all of the network's priority decision making. This implementation requires all NICs in a network to be 3Com NICs. In the event of a software bug, software upgrade, or policy change, all NICs in the network must be upgraded—a very time-consuming process.

Additionally, this implementation is very prone to rogue users changing policy settings for all data transmitted from their stations.

Cisco QoS strategy is much different and much more practical than that of 3Com. The intelligence necessary to classify and reclassify data is at the switch level and accomplished in hardware. The Catalyst 3550-12T offers superior Layer 2 through 4 QoS features to ensure that network traffic is classified, prioritized, and congestion is avoided in the best possible manner. Packet classification allows the network elements to discriminate between various traffic flows and enforce policies based on Layer 2 802.1p CoS field and/or Layer 3 Differentiated Services Code Point (DSCP). Classification and reclassification can be based on criteria as specific as the IP or MAC source and destination or the Layer 4 TCP/UDP ports. Control plane and data plane ACLs are supported on all ports to ensure proper policing and marking on a per packet basis.

The SuperStack 3 4900 also falls short of the Catalyst 3550-12T when comparing how each switch handles priority traffic. The four egress queues of the 3Com SuperStack 3 4900 are hard-coded to specific CoS values—resulting in limited flexibility for the network administrator. Additionally, the SuperStack 3 4900 implements the most limited form of scheduling—strict priority scheduling. This type of scheduling may lead to the starvation of the lower priority queues and the dropping of all best efforts traffic. Lastly, 3Com offers no support for congestion avoidance controls such as Weighted Random Early Detection (WRED). The lack of QoS support on the SuperStack 3 4900 clearly makes this switch unsuitable for environments that experience or may experience congestion as the user base grows or applications demanding more bandwidth become relevant.

The Catalyst 3550-12T supports four egress queues per port—and these may be custom-tailored to the CoS ranges appropriate for a specific network. Contrary to the SuperStack 3 4900, the Catalyst 3550-12T performs advanced scheduling and congestion control. With Weighted Round Robin (WRR) scheduling, the Catalyst 3550-12T ensures that the lower priority packets are not entirely starved for bandwidth and are serviced without compromising the priority settings administered by the network manager. In conjunction with scheduling, the Catalyst 3550-12T supports congestion control via WRED. WRED avoids congestion by setting thresholds at which packets are dropped before over-congestion occurs.

Hope this helps.

Community Member

Re: 3550-12T and 4900

Hi Balaji, thanks for the valuable input. Now I know why Cisco is much better...

Sorry for the typo: what I mentioned though was the catalyst 4000.


I only see the configuration about WRR. There is no CAR/Shaping, WRED, Cos-DSCP-IPPrecedence map etc.

But from,

I can see a whole set of QoS feature.

So do you recommend 3550-12t if I want these QoS?

And, how about the cat 2948G-L3, it uses IOS 12.0 but

also has a limited feature set.

But, Cat5000 uses release 6.3 which looks much powerful than the rel6.3 used in cat4000. Is there a real difference between cat4900 and cat5000 from the software point of view?

(sorry, i'm a little confused:

==========IOS12.0/12.1=======CAT Rel6.3






Which point am I missing here?)

Thanks again for your suggestion,


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