Why we need SGW/PGW separately in LTE?

Question

Why we need SGW and PGW separately?
If it is for roaming then how it will be used at roaming condition?

Answer 1

Its not about LTE rather general Networking question.

Telecom network is a Hierarchical network, technically you can have all logical node functionality in a single box i.e. eNodeB. But assume that all eNodeB have big capability then how much will be the cost as eNodeB are many (in millions) and close to the UE. Also the level of connectivity is required to connect them O(n^2) where n is the number of nodes.

So to reduce the cost we break the functionality and move the functionality step by step away from UE in this way we reduce the cost of implementation drastically and ultimately the call rate. And while the designing any telecom system it is one of the prime factor (along with other i.e. backward compatibility, data-rate, cabling etc).

Answer 2

Both are the logical entities. It is not necessary that both should be in different hardware. There is a product called "EPC in a box" . In which all the nodes resides in same hardware.

With request your question in roaming scenario, UE sends attach request to visited network's MME and this MME talks to home HSS of UE to get subscription profile. In roaming scenarios, UE will use visited network SGW but pgw of its home network.

Comments

Answer is no way close to the question.

Answer 3

Hi. As per my knowledge LTE is not Hierarchical architecture instead it has flat architecture that's also one of the reason of giving less delay as compare to other generations.

Simple answer of above query. why we have two different logical entities SGW and PGW just not to mix the signalling data with user data.

3gpp had decided to take care of signaling separately and give the direct tunnel for the User packets.

Like in UMTS/GPRS every packet has to pass through from SGSN and then GGSN even though after signalling info SGSN had no work with user packets. That is the only reason they have separated them to remove unnecessary node from the architecture.

Answer 4

sort of load balancing, if SGW is not there performance of PGW node affect due to mobile signaling & handovers.

In roaming condition Visitor SGW communicate with Home PGW of roaming UE.

Usage data of visitor UE generated by SGW in roaming condition.