I am trying to model queuing delays in ethernet switches. Can anyone guide which queuing model can be used to model the queuing delays in a switch ?
Most switches use multiple buffer queues for each port.
Each traffic class for QoS (frequently controlled by DiffServ) is mapped to one of the buffers. Buffers are then served in some priority pattern, e.g. 4:2:1 for a three-stage queue, aka weighted round robin.
Many switches allow you to configure the number of queues or even the priority pattern.
Minimum latency for non-congested forwarding is often provided in the device datasheet. Note that there's a distinction between last-bit-in-first-bit-out (LIFO) primarily for store-and-forward switching (with minimum frame size), and first-bit-in-first-bit-out (FIFO) for cut-through forwarding. When these are mixed, you can calculate the respetive counterpart by adding/subtracting the serialization delay for a minimum frame (72*8=576 bits).
As Ron has pointed out, buffering with common network speeds is necessarily shallow. A congesting 10 Gbit/s flow exhausts a fairly sized 12 MB (port-global!) buffer in 10 ms.