top button
Flag Notify
    Connect to us
      Facebook Login
      Site Registration Why to Join

Facebook Login
Site Registration

why MME will query for PGW prior to SGW

+1 vote
1,475 views

Hi Friends,
I saw somewhere that MME will also do a DNS query for P-GW. As i know S-Gw will do a query for P-Gw address. Is there any situation that MME will do a query for P-GW address using APN? and after this query how MME will use the P-Gw Address.

and is there any possibility of Doing DNS query by P-Gw to get any other nodes Ips and under what conditions P-Gw will do a DNS query?

posted Feb 9, 2015 by Srinivas Sambari

Share this question
Facebook Share Button Twitter Share Button LinkedIn Share Button

2 Answers

+2 votes

MME only knows for which APN, UE is trying to connect. MME will get the PDN information(based on APN - PDN Address/ PDN host name) from HSS in diameter ULA(Update Location Answer) message. if MME receives PDN host name, then MME will resolve this host name from DNS server and will get PDN IP address. this PDN IP adress will share with SGW in create session request to which PGW, SGW will contact for this UE. Based on tracking Area(TA) SGW will be selected by MME. So, if TA changed, then SGW may change for this UE. but for each APN there will be fixed set of PDN's(IPv4, IPv6, IPv4v6) mapped at HSS.

answer Jun 27, 2018 by Althi Rajeswararao
+1 vote

Selection of the PGW is done by the MME based on the APN not by the SGW, process is something like this -

  1. During UE attach the MME query the DNS Server to select the PGW where a requested (subscribed) PDN connectivity (APN) is located. Selection can be based on the information provided to the MME, when the UE attaches to the network.
  2. Following the PGW selection, the MME query the DNS Server to select an available SGW to serve the UE using the TAC, which in most cases is based on network topology and the location of the UE within the network, so that the best SGW is selected.
answer Feb 9, 2015 by Salil Agrawal
Similar Questions
+1 vote

GTP tunnel id is a 32-bit long value over one IP address combination. Suppose there are two nodes A and B which has IP addresses X and Y respectively. Is it possible when first GTP tunnel id range gets exhausted then both the nodes starts using different IP address combination and again GTP tunnel id range can be re-used ? If it is impossible then what could be the reason ?

Contact Us
+91 9880187415
sales@queryhome.net
support@queryhome.net
#280, 3rd floor, 5th Main
6th Sector, HSR Layout
Bangalore-560102
Karnataka INDIA.
QUERY HOME
...