http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/hardware/module/guide/03instal.html#wp1037598
WS-X4448-GB-RJ45, WS-X4548-GB-RJ45, and WS-X4548-GB-RJ45V Gigabit Ethernet Switching Modules
The WS-X4448-GB-RJ45, WS-X4548-GB-RJ45, and WS-X4548-GB-RJ45V switching modules 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.
