QOS over half-duplex GBICS

[mdrichards]

I have a question regarding a project that I'm about to start. There will be several 3524's stacked and looped together using GigaStack GBICs (WS-X3500-XL) in half-duplex mode. There will be only one GBIC per 3524. An AVVID phone system is planned for the near future. Is the QOS going to be satisfactory for VOIP if these connections are running in half-duplex mode? Or, do I need to add more GBICS and configure the links to run in full-duplex mode? Please advise.

[jim.down]

For any IP Telephony installation you must have full duplex to guarantee timely packet delivery.

You will therefore need to install additional GigaStack modules such that you have a point to point link between switches i.e. for a stack of 3 switches you will need 4 GigaStack modules.

[tom.mckenzie]

As soon as you introduce a third switch using gigastack modules the boxes will drop to half duplex and will not properly support QoS. You will need to gigastack groups of two switches to ensure continued full-duplex operation. Use GBIC's to uplink to the next level of the network.

IF AVVID is being introduced in the near future, you should consider introducing 3524PWR switches so the IP phones do not need external power supplies.

If these are not 3500PWR switches then check the level of code to ensure QoS is available.

Tom.

[jim.down]

Further to my previous response I believe that to stack 3 switches using GigaStack modules and to maintain full deuplex connectivity, 4 GigaStack modules are requried i.e. 1 in the top switch, 2 in the central switch and 1 in the bottom switch. The switches should not be daisy chained using the 2 ports of a single GigaStack module (e.g. in the centre switch)

[vcornett]

One other thing you need to be aware of using Gigastacks is that they are NOT hot swappable. To me that is worth the extra $ to buy SX GBICS. Cisco needs make the Gigastack hot swappable.

[tom.mckenzie]

I have just been involved in implementing an IPT solution with 3000 nodes supported using 3524's at the access layer. These were gigastacked in no more than pairs as Cisco confirmed adding a third would introduce half duplex functionality and therefore QoS would not be available. The alternative (as mentioned in a response below) is to use a 3508 which will allow a full-duplex config using several 3524's connected into it in a star topo.

[rmg]

Cisco do not recommend the use of Gigastack GBIC's when transporting IPT. You should think about star wiring to a 3508. See this note.

http://www.cisco.com/univercd/cc/td/doc/product/voice/ip_tele/avvidqos/qoscamps.htm#xtocid269428