Cables de mando (FK nº)

Figure 5.4: SCW - Access Concentrator - High CPU Use

5.6 Deployment in SLL Network

The SLL testbed network is situated in rural Eastern Cape, the network is discussed in more detail in Section 2.11.2. Sta and students at the schools use the PCs in the computer labs. The schools are geographically dispersed and connected to each other via WiMAX technology. This system was successfully deployed to the SLL network and an overview of the network connecting the schools can be seen in Figure 5.5.

Figure 5.5 shows the single Internet connection, provided via VSAT, a satellite back- haul. The Internet connection is housed at Mpume, which is connected via a WiMAX network to the other schools. The WiMAX base station is located at Ngwane, while the other schools have WiMAX Customer Premise Equipment (CPE). DNS name resolution is provided by querying the ISP's (Telkom) DNS servers.

The VSAT provides a 3 GB monthly bandwidth capacity, with a maximum download throughput rate of 512 Kbps and upload rate of 128 Kbps [59]. Sharing this single Internet connection equitably between the schools was one of the goals of this project.

Before deployment, a procedure was created. The deployment procedure involved researching the layout of the SLL network (see Figure 5.6) and constructing a mock network in a lab environment. This mock network involved using the physical devices (two CAPs and the AC) which were to be deployed to the SLL. The SSL deployment is a six hour car trip from Rhodes University to the Dwesa-Cwebe region, and by conrming the devices were operating correctly before departing, the deployment process ran smoothly. The AC was deployed at Mpume, and the CAPs were deployed to Ngwane and Mthok- wane. Two other schools, Nondobo and Nqabara were not included in the deployment. Reasons for their exclusion from the deployment are further described in Section 2.11.2, in summary, Nondobo seldom use their computer lab and Nqabara has yet to be connected to the WiMAX network. The deployment procedure involved conrming conguration details of the existing AC at Mpume and then replacing it with the new system's AC.

5.6. Deployment in SLL Network 99

Figure 5.5: Overview of SLL Network

After this, the procedure was to replace the the previous routers with the CAPs at Ng- wane and then Mthokwane. The procedure also included labeling the various cables and how they plugged into the CAPs and AC. Labeling of the cables and the devices was to aid local support sta to reconnect a CAP or AC, in the event that they had become disconnected. It can help the SLL sta in ensuring that devices are connected correctly when troubleshooting network issues. Most importantly, labeling would ensure that net- work cables were connected to the correct network interface. A ow-chart was prepared, see Appendix C, to aid Ngwane and Mthokwane in troubleshooting network connectivity problems.

Each of the schools have a school server, which is an Edubuntu Linux Terminal Server Project (LTSP) server which boots thin client PCs [13]. The thin client PCs are low-cost or low-performance hardware and all processing is performed on the Edubuntu server. LTSP enables the use of older machines as thin clients, reducing hardware and administration costs, as administrators only have to maintain software on the server [13]. Using LTSP and thin clients also prolongs the life and usefulness of the thin clients as all applications are processed on the server and as such older PCs can be used as thin clients.

The physical layout of the SLL network is somewhat dierent to the logical layout and is described for clarity. The physical connections are described rst. Each school is connected via a WiMAX CPE to the WiMAX base station located at Ngwane. This provides TCP/IP connectivity between each of the schools via the WiMAX base station. The CAPs and AC's network interface which is facing the WiMAX network is in the range 169.254.0.0/16. This network provides a method to troubleshoot connectivity issues

5.6. Deployment in SLL Network 100

5.6. Deployment in SLL Network 101 Site Name PPP Address Subnet Connection Medium

Mpume n/a 192.168.1.0/24 Ethernet Ngwane 192.168.255.2 192.168.2.0/24 WiMAX Base Station Mthokwane 192.168.255.3 192.168.3.0/24 WiMAX CPE

Table 5.3: SLL - Deployed Sites Information and Requirements

between the schools and to facilitate PPPoE tunnels between the CAPs and AC. All communication from the CAPs, whether it is destined for the Internet or another school, is routed via the AC over their secure PPPoE tunnel. The AC routes trac destined for the Internet to the Mpume Server.

The network layout provided in Figure 5.6 shows how the network was logically struc- tured and what devices are present. The Mpume Edubuntu server boots the thin clients in their computer lab, and provides the gateway to the Telkom VSAT. The Mpume lab does not need to communicate with the AC for access to the Internet, as all their Internet based trac is routed directly to the VSAT. This is because there is no need for the con- nection to be encrypted using PPPoE as Mpume's Internet bound trac is not carried via the WiMAX network. Connected to the Mpume server is the AC, which provides connec- tivity to the Ngwane and Mthokwane schools. The AC, located at Mpume, connects to the WiMAX base station via its WiMAX CPE. Located at Ngwane is the WiMAX base station, terminating the WiMAX connections from the other two schools. Connected to the WiMAX base station is Ngwane's CAP and beyond that is the Ngwane server and computer lab. The Ngwane Edubuntu server boots thin clients for their computer lab. Lastly, Mthokwane is similar to Ngwane however the Mthokwane CAP connects to a WiMAX CPE.

The SLL network is dependent on other sites due to its physical layout and inherently has several points of failure. For example, Ngwane cannot access the Internet if the AC is down, if the Mpume Server is down or if the Telkom VSAT is down. While Mthokwane cannot access the Internet if the WiMAX base station at Ngwane is down, if the AC is down, if the Mpume Server is down or if the Telkom VSAT is down. Section 5.8 provides two recommendations to modify the structure of the SLL network to resolve these points of failure. The term down can refer to powered o, unreachable via the network or in a halted state (locked up or crashed).

Each of the three sites have a simple requirement, they require access to the Internet. As a result the CAPs and AC allow HTTP, HTTPS, SSH, ICMP and DNS trac only. This was achieved using an IPFW rewall ruleset, consult Appendix C. IPFW can be modied, if required, to allow additional services.

The system was deployed successfully in three days to the SLL network and encoun- tered only minimal setbacks during deployment which were quickly resolved. The rst

5.7. Results - SLL Network 102