Physical RAN

We are now ready to replace the emulated RAN with physical gNBs and real UEs. You will need to edit hosts.ini to reflect the Aether cluster you want to support, where just a single server is sufficient and there is no reason to include nodes in the [gnbsim_nodes] set. We also assume you start with a variant of vars/main.yml customized for running physical 5G radios, which is easy to do:

$ cd vars
$ cp main-gNB.yml main.yml

The following focuses on a single gNB, which we assume is connected to the same L2 network as the Aether cluster. In our running example, this implies both are on subnet 10.76.28.0/24.

Troubleshooting Hint

Physical gNBs connect to SD-Core (both the AMF in the control plane and the UPF in the user plane) in exactly the same way as external instances of gNBsim. Going through the process of bringing up gNBsim in a second server, as described in the previous section, is a good way to validate that your Core is “gNB-ready”.

Modify Configuration

Modify the core section of vars/main.yml to match the following, substituting your local details for ens18 and 10.76.28.113. Of particular note, setting ran_subnet to the empty string indicates that the gNB is connected to the same physical L2 network as your Aether cluster, and the new values_file is tailored for a physical RAN rather than the emulated RAN we’ve been using.

core:
    standalone: "true"
    data_iface: ens18
    values_file: "deps/5gc/roles/core/templates/radio-5g-values.yaml"
    ran_subnet: ""
    helm:
        chart_ref: aether/sd-core
        chart_version: 0.12.6
    upf:
        ip_prefix: "192.168.252.0/24"
    amf:
        ip: "10.76.28.113"

Prepare UEs

When selecting UEs to connect to Aether, be aware that not all phones support the CBRS frequency bands that Aether uses. For band n78, Aether is known to work with recent iPhones (11 and greater), Google Pixel phones (4 and greater), OnePlus phones, and Moto G 5G phones. For band n48, Aether is known to work with Moto G 5G and OnePlus phones; Pixel 7 phones are purported to work as well. Another option is to use a 5G dongle connected to a Raspberry Pi as a demonstration UE. This makes it easier to run diagnostic tests from the UE. For example, we have used APAL’s 5G dongle with Aether.

5G-connected devices must have a SIM card, which you are responsible for creating and inserting. You will need a SIM card writer (these are readily available for purchase on Amazon) and a PLMN identifier constructed from a valid MCC/MNC pair. For our purposes, we use two different PLMN ids: 315010 constructed from MCC=315 (US) and MNC=010 (CBRS), and 00101 constructed from MCC=001 (TEST) and MNC=01 (TEST). You should use whatever values are appropriate for your local environment. You then assign an IMSI and two secret keys to each SIM card. Throughout this section, we use the following values as exemplars:

• IMSI: each one is unique, matching pattern 315010********* (up to 15 digits)

• OPc: 69d5c2eb2e2e624750541d3bbc692ba5

• Key: 000102030405060708090a0b0c0d0e0f

Note that the actual config files distributed with OnRamp have IMSIs constructed using PLMN id 00101. Both sets of examples are taken from working deployments (315010 for a 4G/eNB and 00101 for a 5G/gNB), so in principle either should work as a model you can emulate in your deployment. As a practical matter, however, it is certainly easiest (and safest) to start with the existing code.

After inserting the SIM card into the device and powering it up, log into the phone, select Network Settings > SIMs and create a new Access Point Name (APN), configured as shown in Figure 53. The entry name (TEST SIM in the example) is arbitrary and the MCC/MNC pair is set automatically based on the newly inserted SIM card. The important value is the APN, which is set to internet. This value corresponds to variable dnn (Data Network Name) defined in deps/5gc/roles/core/templates/radio-5g-values.yaml. Loosely speaking, the role the APN plays in the mobile network is similar to the role an SSID plays in a WiFi network.

Figure 53. Configure an Access Point Name (APN) for the new SIM card on the UE.

Finally, modify the subscribers block of the omec-sub-provision section in file deps/5gc/roles/core/templates/radio-5g-values.yaml to record the IMSI, OPc, and Key values configured onto your SIM cards. The block also defines a sequence number that is intended to thwart replay attacks. For example, the following code block adds IMSIs between 315010999912301 and 315010999912310:

subscribers:
- ueId-start: "315010999912301"
  ueId-end: "315010999912310"
  plmnId: "315010"
  opc: "69d5c2eb2e2e624750541d3bbc692ba5"
  key: "000102030405060708090a0b0c0d0e0f"
  sequenceNumber: 135

Further down in the same omec-sub-provision section you will find two other blocks that also need to be edited. The first, device-groups, assigns IMSIs to Device Groups. You will need to reenter the individual IMSIs from the subscribers block that will be part of the device-group:

device-groups:
- name:  "5g-user-group1"
   imsis:
       - "315010999912301"
       - "315010999912302"
       - "315010999912303"

The second block, network-slices, sets various parameters associated with the Slices that connect device groups to applications. Here, you will need to reenter the PLMN information, with the other slice parameters remaining unchanged (for now):

plmn:
    mcc: "315"
    mnc: "010"

Aether supports multiple Device Groups and Slices, but the data entered here is purposely minimal; it’s just enough to bring up and debug the installation. Over the lifetime of a running system, information about Device Groups and Slices (and the other abstractions they build upon) should be entered via the ROC, as described the section on Runtime Control. When you get to that point, Ansible variable standalone in vars/main.yml (which corresponds to the override value assigned to provision-network-slice in radio-5g-values.yaml) should be set to false. Doing so causes the device-groups and network-slices blocks of radio-5g-values.yaml to be ignored. The subscribers block is always required to configure SD-Core.

Bring Up Aether

You are now ready to bring Aether on-line. We assume a fresh install by typing the following:

$ make aether-k8s-install
$ make aether-5gc-install

You can verify the installation by running kubectl just as you did in earlier stages. Note that we postpone bringing up the AMP until later so as to have fewer moving parts to debug.

gNodeB Setup

Once the SD-Core is up and running, we are ready to bring up the physical gNB. The details of how to do this depend on the specific device you are using, but we identify the main issues you need to address using SERCOMM’s 5G femto cell (as distributed by MosoLabs) as an example. That particular device uses either the n48 or n78 band and is on the ONF MarketPlace, where you can also find a User’s Guide that gives detailed instructions about configuring the gNB.

Further Reading

MOSO CANOPY 5G INDOOR SMALL CELL.

Troubleshooting Hint

The product data sheet shows support for frequency bands n78/n48/n77, but individual devices do not necessarily support all three. For example, we have experience with an n78 device and an n48 device, with the latter (n48) now becoming the default. For that band, PLMN id 00101 is currently recommended.

For the purposes of the following description, we assume the gNB is assigned IP address 10.76.28.187, which per our running example, is on the same L2 network as our Aether server (10.76.28.113). Figure 54 shows a screenshot of the SERCOMM gNB management dashboard, which we reference in the instructions that follow:

Figure 54. Management dashboard on the Sercomm gNB, showing the dropdown Settings menu overlayed on the NR Cell Configuration page (which shows default radio settings).

1. Connect to Management Interface. Start by connecting a laptop directly to the LAN port on the small cell, pointing your laptop’s web browser at the device’s management page (https://10.10.10.189). You will need to assign your laptop an IP address on the same subnet (e.g., 10.10.10.100). Once connected, log in with the credentials provided by the vendor.

2. Configure WAN. Visit the Settings > WAN page to configure how the small cell connects to the Internet via its WAN port, either dynamically using DHCP or statically by setting the device’s IP address (10.76.28.187) and default gateway (10.76.28.1).

3. Access Remote Management. Once on the Internet, it should be possible to reach the management dashboard without being directly connected to the LAN port (https://10.76.28.187).

4. Connect GPS. Connect the small cell’s GPS antenna to the GPS port, and place the antenna so it has line-of-site to the sky (i.e., place it in a window). The Status page of the management dashboard should report its latitude, longitude, and fix time.

5. Spectrum Access System. One reason the radio needs GPS is so it can report its location to a Spectrum Access System (SAS), a requirement in the US to coordinate access to the CBRS Spectrum in the 3.5 GHz band. For example, the production deployment of Aether uses the Google SAS portal, which the small cell can be configured to query periodically. To do so, visit the Settings > SAS page. Acquiring the credentials needed to access the SAS requires you go through a certification process, but as a practical matter, it may be possible to test an isolated/low-power femto cell indoors before completing that process. Consult with your local network administrator.

6. Configure Radio Parameters. Visit the Settings > NR Cell Configuration page (shown in the figure) to set parameters that control the radio. It should be sufficient to use the default settings when getting started.

7. Configure the PLMN. Visit the Settings > 5GC page to set the PLMN identifier on the small cell (00101) to match the MCC/MNC values (001 / 01 ) specified in the Core.

8. Connect to Aether Control Plane. Also on the Settings > 5GC page, define the AMF Address to be the IP address of your Aether server (e.g., 10.76.28.113). Aether’s SD-Core is configured to expose the corresponding AMF via a well-known port, so the server’s IP address is sufficient to establish connectivity. The Status page of the management dashboard should confirm that control interface is established.

9. Connect to Aether User Plane. As described in an earlier section, the Aether User Plane (UPF) is running at IP address 192.168.252.3. Connecting to that address requires installing a route to subnet 192.168.252.0/24. How you install this route is device and site-dependent. If the small cell provides a means to install static routes, then a route to destination 192.168.252.0/24 via gateway 10.76.28.113 (the server hosting Aether) will work. If the small cell does not allow static routes (as is the case for the SERCOMM gNB), then 10.76.28.113 can be installed as the default gateway, but doing so requires that your server also be configured to forward IP packets on to the Internet.

Troubleshooting Hint

For the SERCOMM gNB, if you elect to enable GPS, then Setting > Sync_Settings > Sync_Mode should be set to TIME. With GPS and PTP disabled, Setting > Sync_Settings > Sync_Mode should be set to FREE_RUNNING.

Troubleshooting Hint

For the SERCOMM gNB, we recommend the following when the gNB’s addresses is acquired via DHCP, assuming that address is unlikely to change. When configuring the WAN (via the LAN), start with DHCP enabled. Note the IP address the gNB has been assigned, and then after disconnecting from the LAN, connect to the GUI via this address. You will be on the same L2 subnet as the Aether server, which you should be able to ping using the gNB’s diagnostic tool. The default gateway DHCP returns does not know how to route data packets to the UPF. To fix this, modify the WAN settings to use a static IP, with the DHCP-provided IP used as the gNB’s static address. Then set the default gateway to the IP address of your Aether server.

Run Diagnostics

Successfully connecting a UE to the Internet is not a straightforward exercise. It involves configuring the UE, gNB, and SD-Core software in a consistent way; establishing SCTP-based control plane (N2) and GTP-based user plane (N3) connections between the base station and Mobile Core; and traversing multiple IP subnets along the end-to-end path.

The UE and gNB provide limited diagnostic tools. For example, it’s possible to run ping and traceroute from both. You can also run the ksniff tool described in the Networking section, but the most helpful packet traces you can capture are shown in the following commands. You can run these on the Aether server, where we use our example ens18 interface for illustrative purposes:

$ sudo tcpdump -i any sctp -w sctp-test.pcap
$ sudo tcpdump -i ens18 port 2152 -w gtp-outside.pcap
$ sudo tcpdump -i access port 2152 -w gtp-inside.pcap
$ sudo tcpdump -i core net 172.250.0.0/16 -w n6-inside.pcap
$ sudo tcpdump -i ens18 net 172.250.0.0/16 -w n6-outside.pcap

The first trace, saved in file sctp.pcap, captures SCTP packets sent to establish the control path between the base station and the Mobile Core (i.e., N2 messages). Toggling “Mobile Data” on the UE, for example by turning Airplane Mode off and on, will generate the relevant control plane traffic.

The second and third traces, saved in files gtp-outside.pcap and gtp-inside.pcap, respectively, capture GTP packets (tunneled through port 2152 ) on the RAN side of the UPF. Setting the interface to ens18 corresponds to “outside” the UPF and setting the interface to access corresponds to “inside” the UPF. Running ping from the UE will generate the relevant user plane (N3) traffic.

Similarly, the fourth and fifth traces, saved in files n6-inside.pcap and n6-outside.pcap, respectively, capture IP packets on the Internet side of the UPF (which is known as the N6 interface in 3GPP). In these two tests, net 172.250.0.0/16 corresponds to the IP addresses assigned to UEs by the SMF. Running ping from the UE will generate the relevant user plane traffic.

If the gtp-outside.pcap has packets and the gtp-inside.pcap is empty (no packets captured), you may run the following commands to make sure packets are forwarded from the ens18 interface to the access interface and vice versa:

$ sudo iptables -A FORWARD -i ens18 -o access -j ACCEPT
$ sudo iptables -A FORWARD -i access -o ens18 -j ACCEPT

Support for eNBs

Aether OnRamp is geared towards 5G, but it does support physical eNBs, including 4G-based versions of both SD-Core and AMP. It does not support an emulated 4G RAN. The 4G scenario uses all the same Ansible machinery outlined in earlier sections, but uses a variant of vars/main.yml customized for running physical 4G radios:

$ cd vars
$ cp main-eNB.yml main.yml

Assuming that starting point, the following outlines the key differences from the 5G case:

1. There is a 4G-specific repo, which you can find in deps/4gc.

2. The core section of vars/main.yml specifies a 4G-specific values file:

   values_file: "deps/4gc/roles/core/templates/radio-4g-values.yaml"

3. The amp section of vars/main.yml specifies that 4G-specific models and dashboards get loaded into the ROC and Monitoring services, respectively:

   roc_models: "deps/amp/roles/roc-load/templates/roc-4g-models.json"

   monitor_dashboard:  "deps/amp/roles/monitor-load/templates/4g-monitor"

4. You need to edit two files with details for the 4G SIM cards you use. One is the 4G-specific values file used to configure SD-Core:

   deps/4gc/roles/core/templates/radio-4g-values.yaml

   The other is the 4G-specific Models file used to bootstrap ROC:

   deps/amp/roles/roc-load/templates/radio-4g-models.json

5. There are 4G-specific Make targets for SD-Core (e.g., make aether-4gc-install and make aether-4gc-uninstall), but the Make targets for AMP (e.g., make aether-amp-install and make aether-amp-uninstall) work unchanged in both 4G and 5G.

The Quick Start and Emulated RAN (gNBsim) deployments are for 5G only, but revisiting the other sections—substituting the above for their 5G counterparts—serves as a guide for deploying a 4G version of Aether. Note that the network is configured in exactly the same way for both 4G and 5G. This is because SD-Core’s implementation of the UPF is used in both cases.