## (10) LAN Pros & cons:

### Highlight's & Comprimises:

#### Physical Topology (& Wiring Plan)

- 3 IDF's were chosen & placed - one for each of the three main (imaginary) faculties
  - each faculties is responsible for it's own IDF

pros:

- This scheme increases overall simplicity & management
  - MDF connects to admin, servers & (obviously) IDFs - it does not directly connect with any curriculum computers
  - IDFs connect with all curriculum (& teacher) computers
- Any expansions can be easily incorporated, with minimal cable length
  - Any extra demountables should be easily in reach of an IDF.
- Cumulative cable lengths have been reduced slightly
- Network is functional, scalable, adaptable, and manageable.

cons:

- The school was just small enough to begin with to have just a single MDF & no IDFs
  - A single MDF could have reached all classrooms (without repeaters)
  - Using a single MDF, teachers could have been placed on a separate subnet (different switches) to students.
- VLANs would then become unnecessary.
- i.e. The network would be much simpler & ACLs would control all access rights.
- More IDFs means more wiring cabinets means greater expense.
  - In retrospect, three IDFs is probably overkill (although at least one IDF for the demountables makes sense).
- Many classrooms are closer to the MDF than the IDF they are attached too - i.e. more wire length than necessary.
- This is an expensive solution as multiple switches are used.
- This extended star topology allows a major point of failure at the router - if the router fails curriculum students won't be able to access the dns server, and no-one will be able to access outside the school.

Logical Topology

- Subnet scheme

- 1 subnet = main admin section, servers & teachers

- 2 subnets = curriculum
- 1 subnet = *spare

- VLAN scheme:

- VLAN1 (default) = students
- VLAN2 = teachers
- VLAN1&2 = admin & servers……… (allowing admin access to teachers & students)

pros:

- This chosen logical scheme increases simplicity
- 2 subnets (508 hosts) are more than enough for teachers & curriculum.
- The spare subnet will come in useful if another building (needing an IDF) is built
- The VLAN scheme was essential to isolate teachers & students (since they connect to the same switches in the IDFs)
- Very short, efficient ACLs permit curriculum access to the main enterprise server, but deny them access to admin.
- From the main admin section broadcasts can be sent to all admin, teachers and/or students - (e.g. network administrator may wish to netsend important messages to all computers)

cons:

- Using this VLAN scheme, teacher computers cannot access student computers - teachers must go to the main admin section (& a vacant admin computer) to do that.
- Under the current configuration, the 3 student cables running into each room are configured as VLAN1. Meaning that, if a printer is put in a classroom & connected to one of the three switches, it will effectively be VLAN 1 and therefore will be inaccessible by the teacher computer in the same room.

#### Electronics

pros:

- Collisions are minimised due to all devices being switches or routers which creates micro-segmentation
  - Our origional plan was to use 3 hubs per classroom (to provide for 24 stdudent computers), but we discovered very cheep ($120) hubs which servered the same purpose, but were better.
- Estimated bandwidth for all hosts (teachers, students & admin) is 100Mbps - which is 100 times larger than the requirement
- Our expendature comes to about $86,000 US (including all components cable) - well under budget.
  - In general, we found the cheapest component for each device - which means sacrificing quality.

cons:

- No layer 1 hubs were used in this design - switches were used instead, and this cost us slighly more
- Our router and router modules in the MDF, although on of the cheepest available, set us back $20,000 - 10% of our budget gone already

#### Media

pros:

- Our chosen media accounts for all requirements
- Each MDF to IDF backbone include 4 fibre optic runs - two of them spare

cons:

- Our pricing of cables is not certain - we suspect we have made mistakes **

### Impact of Collisions on Bandwidth

- Due to the way this network is microsegmented with switches, there will be very few collisions within this network.
  - Using SPX (Sequenced Packet Exchange) service, the IPX network becomes connection-oriented and any collisions or buffer overflows will result in retransmission.
- The estimated minimum bandwidth per student computer is 100 Mbps - to see the calcualtion click "see it all working together" (in the menu bar)