Group Members
Monday, September 7, 2015
Wednesday, September 2, 2015
Network Topologies
TOPOLOGIES
There are two types of
Local Area Network Topologies. They fall into the following categories:
·
Logical topology
·
Physical topology
Logical
Topologies
When interviewing Warren
on 25 August 2015, (DUT student) stated that:
“A logical topology is a concept in networking that
defines the architecture of the communication mechanism for all nodes in a
network. Using network equipment such as routers and switches, the logical
topology of a network can be dynamically maintained and reconfigured. Logical
topologies contrasts with physical topologies, which refer to the physical
interconnections of all devices in the network.”
A more condensed and precise definition of a logical topology is that the term logical topology refers to the way data is transmitted between nodes. A logical topology may also be called a network transport system. (Y.Xin et al. 2003: 904).
There are two most
popular logical topologies which are:
·
Broadcast (Ethernet)
·
Token Ring
Tuesday, September 1, 2015
Ethernet
Ethernet
·
Shah (2013: 2) states that the term
Ethernet refers to the family of local- area network (LAN). A local-area
network (LAN) protocol developed by Xerox Corporation in cooperation with DEC
and Intel in 1976. Ethernet uses a bus or star topology and supports data
transfer rates of 10/100/1000 Mbps. Ethernet defines the lower two layers of
the OSI Reference Model. Ethernet network operates logically as a bus but is
organised by the devices connecting to a hub in a physical star. (Type of
networks topology 2007).
·
Shah (2013: 3) The Ethernet specification
served as the basis for the IEEE 802.3 standard, which specifies the physical
and lower software layers. Ethernet uses the CSMA/CD access method to handle
simultaneous demands. Ethernet, like other local area networks, falls in a
middle ground between long-distance, low-speed networks that carry data for
hundreds or thousands of kilometres, and specialized, very high speed
interconnections that are generally limited to tens of meters.
·
Evidence given by the System Software 1
Lecturer, Mr TP Govendor (2015, pers. comm. 07 August) A host broadcasts a message to all hosts on the same
network segment. There is no order that hosts must follow to transmit data.
Messages are sent on a First In, First Out (FIFO). Ethernet is based on this
topology
Monday, August 31, 2015
Token Ring
Token Ring
·
Network Topologies were discussed (Type of
networks topology 2007) Token Ring operates as a logical ring but the devices
are all connected to a hub-like device called a Multi-Station Access Unit
(MSAU) which makes its physical topology a star. Sheesley (2008) stated that Token
Ring was developed in the early 1980's by IBM as a way to connect PCs together.
It was a direct competitor to the Ethernet standard that we use today and the
ARCnet standard that disappeared in the mid-80's.
·
In token ring, Data being transmitted
sequentially from one ring station to the next with a control token circulating
around the ring controlling access. Token passing mechanism is shared by
ARCNET, token bus, and FDDI, and has theoretical advantages over the stochastic
CSMA/CD of Ethernet. A token ring network is wired as a star, with hubs and
arms out to each station and the loop going out-and- back through each. Cabling
is generally "Type-1" shielded twisted pair, with unique
hermaphroditic connectors, commonly referred to as IBM data connectors in
formal writing or colloquially as Boy George connectors Shah (2013: 22)
Other Logical Topologies:
Local
Talk
– it is a logical topology designed by Apple Computer, Inc. specifically for
networking Macintosh computers. A case in which Local Talk may be appropriate
is for a home network that requires simple configuration and does not require a
high output. Local Talk uses a transmission method called Carrier Sense Multiple Access/Collision
Avoidance (CSMA/CA). It is similar to the CSMA/CD used in
Ethernet networks, except that a node on a Local Talk network signals
its intent to transmit before it actually does so. Through this, collisions and
the need for the re-transmitting of data are usually avoided. (Y.Xin et al. 2003: 904).
Token Ring Explained
Sunday, August 30, 2015
Physical Topologies
PHYSICAL
TOPOLOGIES
BUS TOPOLOGY AND RING TOPOLOGY
BUS TOPOLOGY
Dania in Tech (2015: 08) online says it is a network topology in which nodes are directly
connected in common linear (or branched) half duplex link. Network cabling in
which all computers and devices (nodes) are connected to a single cabling so
that all nodes receive the message at the same time. Typically, the cable in
the bus topology can have two terminals in there to dampen the signal so that
it does not keep moving from one end to the other.
Linear or Distributed (types)
Linear implies that there is just one line associated
with two distinct end points, whereas Distributed there may be more than one
linear pattern connected to the network.
ADVANTAGES
Dania (2015)
·
Easy to implement and extend.
·
Well situated for temporary networks.
·
Initially less expensive than other
topologies.
·
Cheap.
DISADVANTAGES Dania (2015)
·
Difficult to troubleshoot or administer.
·
Limited cable length and number of
situations.
·
If there are problem with the cable, the
entire network goes down.
·
Maintenance costs may be higher in the
long run.
·
Performance degrades as add, frontal
computers are added/ heavy traffic.
·
Low security (all computers on the bus can
sell data transmissions).
·
One virus in the network will affect all
of them (but not as much as ring or star network).
·
If one node fails, the whole network will
shut down.
·
Proper termination id required.
·
If many computers are attached the amount
of data flowing causes the network to flow down.
Bus topology: Jibesh Sitikhu
Saturday, August 29, 2015
Ring Topology
RING
TOPOLOGY
Dania
in Tech (2015) think it is a network in which each node connects to exactly two
other nodes, forming a single continuous pathways for signals through each
node. Data travels from node to node, which each node along the way handling
every packets. Ring can be unconditional with all traffic either clockwise or
anticlockwise around the ring, or bidirectional (as in SONET/SDH). Unidirectional
ring network can be disrupted by failure of a single link.
ADVANTAGES
Dania (2015)
·
Data is quickly transferred without a
‘bottle neck’ (very fast, all data traffic is in the same direction).
·
Transmission of data is relatively simple
as packets travel in one direction only
·
Adding additional has very little impact
on bandwidth
·
Prevents network collision because of
media access method
DISADVANTAGES
Dania (2015)
·
It is difficult to troubleshoot the ring
·
Total dependence upon the cable
·
Data packets must pass through every
computer between sender and recipient therefore this takes it slower
·
If any of the nodes fail then the ring is
broken and cannot be transmitted successfully
·
If order for all computers to communicate
with each other, all computers must be turned out
·
Because all stations are wired together,
to add a station you must shut down the network temporarily.
Ring topology: google.com/photos/xmattytv1/albums (2014) Matty-tv
Friday, August 28, 2015
Star Topology
STAR
Topology
Vangie (2013) explains that with Star topology every node
connects to a central hub, switch or computer; the hub acting as a server and
the peripheral devices as clients.
Star Topology processes were discussed (Defining network topology 2011) the
data on the star topology passes through the central device before reaching the
intended destination. Hub acts as a junction to connect different nodes present
in Star Network, and at the same time it manages and controls whole of the
network. Depending on which central device is used, “hub” can act as repeater
or signal booster. Central device can also communicate with other hubs of
different network.
Disadvantages
Disadvantages
- Reliance on central device
- Higher costs
- Limited capacity for nodes by Penna Sparrow (2011)What you must know about a star topology is if the hub fails, all of the connected devices are disconnected.
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