Created doc "NextEPC Splitting Network Elements"

Outlining basic requirements of each network element and interfaces and how to break up the network.

docs/_docs/guide/03_splitting_network_elements.md

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+# NextEPC Splitting Network Elements
+In a production network network elements would typically not all be on the same machine, as is the default example that ships with NextEPC.
+
+NextEPC is designed to be standards compliant, so in theory you can connect any core network element (MME, PGW, SGW, PCRF, HSS) from NextEPC or any other vendor to form a functioning network, so long as they are 3GPP compliant. 
+
+To demonstrate this we will cover isolating each network element onto it's on machine and connect each network element to the other. For some interfaces specifying multiple interfaces is supported to allow connection to multiple
+
+In these examples we'll be connecting NextEPC elements together, but it could just as easily be EPC elements from a different vendor in the place of any NextEPC network element.
+
+| Service        | IP           | Identity |
+| ------------- |:-------------:|:-------------:|
+| P-GW | 10.0.1.121 | pgw.localdomain |
+| S-GW | 10.0.1.122 | |
+| PCRF | 10.0.1.123 | pcrf.localdomain |
+| MME | 10.0.1.124 | mme.localdomain |
+| HSS | 10.0.1.118 | hss.localdomain |
+
+# External MME
+In it's simplest form the MME has 3 interfaces:
+ * S1AP - Connections from eNodeBs
+ * S6a - Connection to HSS (Diameter)
+ * S11 - Connection to S-GW (GTP-C)
+
+
+
+# External P-GW
+In it's simplest from the P-GW has 3 interfaces:
+ * S5 - Connection to home network S-GW (GTP-C)
+ * Gx - Connection to PCRF (Diameter)
+ * Sgi - Connection to external network (Generally the Internet via standard TCP/IP)
+ 
+### S5 Interface Configuration
+Edit ```/etc/nextepc/pgw.conf```and change the address to IP of the server running the P-GW for the listener on GTP-C and GTP-U interfaces.
+
+```
+
+pgw:
+
+    freeDiameter: pgw.conf
+      
+    gtpc: 
+    
+      addr:
+      
+        - 10.0.1.121
+        
+     gtpu: 
+    
+      addr:
+      
+        - 10.0.1.121
+        
+ ```
+
+
+
+
+### Gx Interface Configuration
+Edit ```/etc/nextepc/freeDiameter/pgwd.conf```
+
+Update ```ListenOn``` address to IP of the server running the P-GW:
+
+``` ListenOn = "10.0.1.121"; ``` 
+
+Update ConnectPeer to connect to the PCRF on it's IP.
+
+```ConnectPeer = "pcrf.localdomain" { ConnectTo = "10.0.1.123"; No_TLS; };```
+
+
+### Restart Services
+Restart NextEPC PGW Daemon:
+
+``` $ sudo systemctl restart nextepc-pgwd ```
+
+
+# External S-GW
+In it's simplest form the S-GW has 2 interfaces:
+ * S11 - Connection to MME (GTP-C)
+ * S5 - Connection to the home network P-GW (GTP-C)
+
+### S5 Interface Configuration
+Edit ```/etc/nextepc/sgw.conf```and change the address to IP of the server running the S-GW for the listener on GTP-C interface.
+
+```
+sgw:
+
+    freeDiameter: pgw.conf
+      
+    gtpc: 
+    
+      addr:
+      
+        - 10.0.1.122
+        
+ ```
+ 
+ Restart NextEPC SGW Daemon:
+
+``` $ sudo systemctl restart nextepc-sgwd ```
+
+
+# External PCRF
+In it's simplest from the PCRF has 1 network interface:
+ * Gx - Connection to P-GW (Diameter)
+
+### Gx Interface Configuration
+Edit ```/etc/nextepc/freeDiameter/hss.conf```
+
+Update ```ListenOn``` address to IP of the server running the HSS on it's IP:
+
+``` ListenOn = "10.0.1.123"; ``` 
+
+Update ConnectPeer to connect to the MME.
+
+```ConnectPeer = "pgw.localdomain" { ConnectTo = "10.0.1.121"; No_TLS; };```
+
+### MongoDB Interface Configuration (NextEPC HSS only)
+Edit ```/etc/nextepc/freeDiameter/hss.conf``` and change the ```db_uri:``` to point at the HSS: ```db_uri: mongodb://10.0.1.118/nextepc``` 
+
+Restart NextEPC PCRF Daemon:
+
+``` $ sudo systemctl restart nextepc-pcrfd ```
+
+# External HSS
+In it's simplest form the HSS has 1 network interface:
+ * S6a - Connection to MME (Diameter)
+
+### S6a Interface Configuration
+Edit ```/etc/nextepc/freeDiameter/hss.conf```
+
+Update ```ListenOn``` address to IP of the server running the HSS on it's IP:
+
+``` ListenOn = "10.0.1.118"; ``` 
+
+Update ConnectPeer to connect to the MME.
+
+```ConnectPeer = "mme.localdomain" { ConnectTo = "10.0.1.124"; No_TLS; };```
+
+Restart NextEPC HSS Daemon:
+
+``` $ sudo systemctl restart nextepc-hssd ```
+
+### MongoDB Interface Configuration (NextEPC specific)
+If you are using NextEPC's HSS you may need to enable MongoDB access from the PCRF. This is done by editing ''/etc/mongodb.conf'' and changing the bind IP to:
+``` bind_ip = 0.0.0.0 ```
+
+Restart MongoDB for changes to take effect.
+
+``` $ /etc/init.d/mongodb restart ```
+
+
+# External MME
+### S11 Interface Configuration
+Edit ```/etc/nextepc/mme.conf```, filling the IP address of the S-GW and P-GW servers.
+```
+sgw:
+
+    gtpc:
+    
+      addr: 10.0.1.122
+
+
+pgw:
+
+    gtpc:
+    
+      addr:
+      
+        - 10.0.1.121
+```
+
+### S6a Interface Configuration
+Edit ```/etc/nextepc/freeDiameter/mme.conf```
+
+Update ```ListenOn``` address to IP of the server running the MME:
+
+``` ListenOn = "10.0.1.124"; ``` 
+
+Update ConnectPeer to connect to the PCRF on it's IP.
+
+```ConnectPeer = "hss.localdomain" { ConnectTo = "10.0.1.118"; No_TLS; };```
+
+
+### Restart Services
+Restart NextEPC MME Daemon:
+
+``` $ sudo systemctl restart nextepc-mmed ```
+