LAN Architectures

What are the 3 most common LAN architectures?
The 3 most common types of LAN architectures* are:
Ethernet
Token Ring
ArcNet
* These architectures are sometimes referred to as "lower-level protocols" because they represent the specifications for the IEE802 model which encompasses the physical (1st) and data link (2nd) layers of the OSI model.
What is Ethernet? What IEEE standard does it conform to?
Ethernet is a popular, relatively inexpensive, easy-to-install LAN architecture with the following characteristics:
Uses the CSMA/CD media access control.
Data transmission normally occurs at 10Mbps.
Typically implemented in a bus or star topology.
Ethernet LANs are normally distinguished by the type of cable they use (Thinnet, Thicknet, or Twisted Pair).
The Ethernet architecture conforms to most but not all of the IEEE 802.3 specification (the physical layers are identical but the MAC layers are somewhat different).
How does the nomenclature "10base2" describe Ethernet cable?
An Ethernet LAN is often described in terms of three parameters: transmission rate, transmission type, and segment distance.
"10base2" means:
10 - transmission rate or through put of 10Mbps
base - transmission type is baseband rather than broadband network (i.e., the signal is placed directly on the cable, one signal at a time)
2 - the maximum segment distance in meters times 100; in this case 200 meters (actually only 185 meters)
(In "10baseT," the T stands for twisted pair. Segment distance is 100 meters.)
What are the key characteristics of 10Base2 Ethernet.
A 10Base2 Ethernet LAN conforms generally to the IEEE 802.3 standard. Also known as Thinnet Ethernet, it has the following key characteristics:
Transmits at 10 Mbps
Uses Thinnet coaxial cable
Supports a maximum of 30 nodes per segment
Uses local bus topology
Minimum distance between computers is 0.5m (not including drop cables)
Maximum length of segment is 185m
Up to 5 segments can be connected (but only 3 can accommodate nodes)
Connected with BNC connectors (T-connectors)
Used primarily for smaller workgroups or departments

What is 100VG-AnyLAN?
· 100VG-AnyLAN. The VG stands for "Voice Grade" in recognition of the fact that it transmits at 100 Mbps over voice grade twisted-pair cable (Category 3).* Supports cable segments of only 100m. Uses a new media access control method called demand priority rather than the older CSMA/CD. IEEE standard 802.12.
· *100VG-AnyLAN can transmit on Category 3 cable because it uses all 4-wire pairs (quartet signaling). 10baseT uses only 2 of the wire pairs in Category 3 UTP.

What are the key characteristics of 10baseT Ethernet.
A 10baseT Ethernet LAN conforms generally to the IEEE 802.3 standard. Also known as Twisted Pair Ethernet, it has the following key characteristics:
Transmits at 10 Mbps
Normally uses UTP cable
Minimum grade of UTP cable is Category 3
Typically supports about 12 nodes per hub*
Uses star or bus topology
Minimum distance between nodes is 2.5m
Maximum length of segment is 100m
Most common type of Ethernet LAN; used in both small and large networks
*There is no hard and fast rule here. Hubs can be connected together so in total a 10BaseT LAN can support up to 1024 nodes without a bridge.
What is Token Ring? What IEEE standard does it conform to?
Token ring is a relatively expensive LAN architecture that is strongly influenced by IBM. It is very stable and can be expanded without a significant degradation in network performance.
Token ring uses the token passing media access control. Data transmission normally occurs at 4 or 16 Mbps depending on the cable.
Token ring is normally implemented in a logical ring/physical star topology with a MAU (Multistation Access Unit) as the hub. The maximum number of stations on one ring is 260 for shielded twisted pair and 72 for unshielded twisted pair (UTP). There can be up to 33 MAUs per ring.
Token Ring LANs normally use shielded twisted pair (STP) but may also use unshielded twisted pair (UTP) or fiber-optic cable. The maximum distance to the MAU from the workstation depends on the cable and varies from 45 meters for UTP to 100 meters for STP.
The Token Ring architecture conforms generally to the IEEE’s 802.5 specification
What is ArcNet? What IEEE standard does it conform to?
ArcNet (Attached Resource Computing Network) is a relatively inexpensive, reliable, and easy-to-install LAN architecture with the following characteristics:.
Additional workstations are easily added.
ArcNet is a baseband, token passing media access control architecture
ArcNet is relatively slow. Data transmission occurs at 2.5 Mbps. (20 Mbps for ArcNet Plus)
ArcNet can be implemented in a bus or star topology.
ArcNet LANs normally use coaxial cable but can also use twisted pair or fiber-optic cable. Maximum cable segment depends on the type of cable and hub connection (120m -600m)
The ArcNet architecture conforms very loosely to the IEEE’s 802.4 specification. ArcNet is a baseband star or bus and 802.4 defines a broadband bus.
What factors should be considered when selecting a LAN architecture?
The following factors should be considered when selecting a LAN architecture:
Cost - How much is available in the budget and what quantifiable benefits will the LAN provide?
Reliability - How dependent is the organization’s operations on the LAN?
Speed - How many concurrent users and how critical is response time?
Size - How many computers will be connected and what is the overall distance between them?
Security - How important is secure communications to the network?
Growth - What are the organization’s plans for growth?
Administration - How will the LAN be administered? Who will assume what responsibilities?


What is the most common bus topology normally used with the following architectures: 10base2, 10base5, 10baseT, Token Ring, and ArcNet?
Common LAN architectures and their topologies include:
Ethernet 10base2 - local bus
Ethernet 10base5 - regular bus
Ethernet 10baseT - bus or star
Token Ring - ring (physical star)
ArcNet - star or distributed star (interconnected)