Lesson 2 primarily focuses on the topology of a network, this can be split up into:
- Physical topology (architecture)
- Logical topology
The physical topology is how the network actually looks, how is has been laid out with cables etc.
The logical topology is the route that the data follows - this is what you can't see!
The physical topologies that we look at are:
- The Physical Bus topology
This is where nodes are arranged in a linear fashion - one after the other, each node is directly connected to the network cable (backbone) with a T-connector and then by a BNC connector directly to the node. Think of peer-peer. These types of networks are not very reliable as if there is a break in the cable, the entire network goes down, they are also typically slow and difficult to troubleshoot. The backbone must have terminators on each end so that when information is broadcast, it knows where to end! (can't use UTP in bus)
- Physical Star Topology
This type of architecture uses a central device from which all nodes branch off or connect. A device such as a HUB or Switch. When using a hub, the signal is broadcast to all, when using a switch there is some intelligence as the switch has record of where the nodes are situated on the physical topology. Thus it will be a bit faster.
- Physical Ring Topology
This is a layout whereby each node is connected to its nearest node and the signal travels like a dog chasing it's tail. Each node then amplifies the signal to the next node. The signal always travels in a clockwise direction around the ring. The nodes will have network cards with an "in' and "out" point which determines the upstream and downstream node. Failure of a node could potentially bring down the entire network.
- Physical Mesh Topology
This is when each nodes is connected to each and every other node
In this mesh topology, each node has 4 network cards in it, the mesh is very difficult to fail as it always has a redundancy to the entire network. In the Physical Mesh, the data will always follow OSPF - open, shortest path first! NB!!!
- Hybrid Topology
This is exactly as it says - it is a hybrid between two or more topologies.
The acronyms that we need to know and some other points to remember:
- T.T.L. - time to live (the amount of time given to a signal, its life)
- UTP - unshielded twist pair (cable) - Connects to a RJ45
- STP - shielded twisted pair (cable) - connects to a RJ45
- Coax - cable with a core and a protective sheath (like television cable)
- Fibre - shielded cable with a glass core
- CSMA/CD - carrier sense multiple access with collision detection (802.3) Ethernet
- CSMA/CA - carrier sense multiple access with collision avoidance (802.5)
- UTP - cannot be used in a bus topology
- In the exam, we will need to know and be able to draw the types of topologies!
- Below is some cable information:
No comments:
Post a Comment