LTE Basics: Is only Radio Interface the one which is non-wired rest everything is connected through wire?

Question

As far as I know, radio Interface (AIR INTERFACE) is only between UE and ENODEB rest everything is connected through wire, Is my understanding correct?

If No, then please explain how other things are connected and how data is being transferred?
If Yes.. Then how Long Distance call been made?

Answer 1

Even I know the same thing that radio interface is between UE and eNodeB only and known as Uu interface. The complete LTE network is known as EPS system and it consists of EUTRAN + EPC. EnodeB resides in E-UTRAN and rest of the nodes reside in EPC side. Every operator uses its own private network so there is no worry about network congestion and they maintain in a well manner. Standard does not mention about anything related to distance between eNodeB and MME.

Now comes to your second question: How data flow in a lte network ?
- Once UE gets attached to network, it gets an IP address which is allocated by PGW.
- Downlink data is received by PGW and it forwards the data packet to SGW by using GTP-U tunnel.
SGW receives this packet and remove the GTP header and sends IP packet to eNodeB by putting another header.
- eNodeB removes the GTP header and its PDCP layer compress the IP packet using ROHC mechanism. After that , data flow to RLC, MAC and PHY layer and finally reaches to UE.

If you have any other doubt or concern, please ask.

Answer 2

Related to cell distance...
Distance of cell is depend upon the RACH preamble format used in the cell. Different preamble formats provides different guard period to accommodate round trip delay. RACH preamble format 4 provides max 716 micro sec guard period. Using this timer we can calculate cell radius as
radius = (speed of light * guard timer)/2.
This comes as 107 km. So LTE support max cell radius as ~100 KM.

Answer 3

Access network only provides the last mile (dont take in literal terms) connection while ENB to PGW is the mobile network, which can connect two mobile like they are in a circle (loosely saying).

In general other then Uu interface all interfaces are wired but it is not necessary it can be anything including the wireless only stuff is the network should expose IP interface.

Now coming to your last portion, as I said mobile network is a circle only call is taken care from one circle to another circle by NLD (national long distance carrier) or to another country by an ILD (International Long distance carreir).

Lets take the example one UE from Bangalore makes a call to another UE in Bihar, call originates from UE-->eNodeB-->SGW-->PGW from here it is handed over to an NLD which takes the call to Bihar and give it to PGW (I have assumed all IP case here otherwise it would be MSC-GMSC in place of SGW-PGW)