WS-X4548-GB-RJ45 Port contention and over subscription

[Rowan Smith]

Hi,

I have a WS-X4548-GB-RJ45 installed in a 4506E Chasis.  According to the Cisco documentation it states:

Bandwidth is allocated across six 8-port groups, providing 1 Gbps per port group

Slot Bandwidth = 6Gbps

My understanding is that this means each port in a group of 8 can talk to each other at line rate of 1Gbps.  However the combined throughput for those 8 ports, when talking to any other port on the device or when going to another slot is 1Gbps.

So firstly, can someone please explain what this actually means please is my interpretation correct?

Secondly, can someone please explain how I measure if this contention is being hit, eg, is there a SNMP object I can query, or a show interface statistic which can be looked at?

Finally, what are the groups of 8 ports is it 1-8, 9-16 etc? or some other grouping/allocation?

Thanks very much.

[wmorse]

• The 48 ports can burst to Gigabit Ethernet line rate and can share 12 Gbps of full-duplex bandwidth into the switching fabric
• amount of oversubscription can be controlled simply by varying the number of ports used at 1000 Mbps
• All ports use the standard IEEE 802.3x flow-control (pause frame) mechanism to control Gigabit Ethernet host traffic.
• The WS-X4548-GB-RJ45 switching module have 48 oversubscribed ports in six groups of eight ports each:

• Ports 1, 2, 3, 4, 5 ,6, 7, 8
• Ports 9, 10, 11, 12, 13, 14, 15, 16
• Ports 17, 18, 19, 20, 21, 22, 23, 24
• Ports 25, 26, 27, 28, 29, 30, 31, 32
• Ports 33, 34, 35, 36, 37, 38, 39, 40
• Ports 41, 42, 43, 44, 45, 46, 47, 48
• The eight ports within each group use common circuitry that effectively multiplexes the group into a single, nonblocking, full-duplex Gigabit Ethernet connection to the internal switch fabric. For each group of eight ports, frames received are buffered and sent to the common Gigabit Ethernet link to the internal switch fabric. If the amount of data received for a port begins to exceed buffer capacity, flow control sends pause frames to the remote port to temporarily stop traffic and prevent frame loss.