How is End-to-End QoS maintained In LTE Network?

Question

For practical network installations, an eNodeB would be connected to SGW via some IP router. Similarly there can be IP router connection between SGW and PGW.

How is End-to-End QoS maintained between these routers?

Because as I see in specs, the QCI value is transmitted in GTP-C signalling messages between S5/S8, S11 interface: based on that QCI & other QoS parameters, the bearers are defined & GTP-U tunnels are made.

But, for in-between routers, how is QoS guaranteed?

Answer 1

Once a Packet is received by PGW. It takes the received IP packet as payload and prepares another IP packet for S5/S8 interface. While preparing IP packet, PGW updates DSCP flag of IP packet to meet required QCI.
Afterwards, IP packet routing mechanism will take care.

Answer 2

Just an addition to what Vimal has explained, downlink QoS is maintained/enforced at the PGW and uplink QoS is maintained/enforced at the eNodeB. However telecom nodes are responsible for the correct DSCP setting and IP network takes care of the routing/qos based on DSCP setting only.