2. What is Meant By LAN
Architecture?
• LAN architecture is the overall design of a LAN.
It includes:
– LAN hardware
– LAN software
– LAN topology
– Media access control (MAC) protocol
• The LAN’s network operating system is
sometimes also considered to be part of LAN
architecture
3. LAN Topologies
• There are two types of LAN topologies: physical
and logical
• Physical LAN topology refers to the physical
layout of the network
– The way in which the communication is configured and
how nodes attach to the network
– Because the focus is on physical connections among
hardware component, physical topologies correspond to
the physical layer of the OSI reference model
• Logical topology is concerned with how messages
are passed from node to node within the network
4. LLC and MAC Sublayers
• LANs employ two primary data link protocols:
contention and token passing
• In IEEE 802 standards, the data link layer is
divided into two sublayers LLC and MAC (see
Figure 4-1)
– LLC (logical link control) is responsible for flow
control, message sequencing, message
acknowledgement, and error checking
– MAC (media access control) enables network nodes to
access the communication medium via contention or
token passing
6. How Ethernet Works-CSMA/CD
• CSMA/CD (Carrier Sense Multiple Access and Collision Detection) is
most widely used contention-based MAC used in LANs
– It is the MAC protocol used in Ethernet LANs
• In a true contention MAC (like CSMA/CD), each node has equal
access to the medium
• As noted in Table 4-1, each node monitors the medium for data traffic
and if none is detected, it begins transmitting data
• A collision occurs when two or more nodes begin to transmit at the
same time
• To avoid collision recurrence, each node waits a random time interval
(hardwired in its NIC) before attempting to retransmit
8. 10Mbps Ethernet
• The four commonly used 10Mbps Ethernet
cabling systems are:
– 10Base5, or thicknet, which uses thick coaxial cable
– 10Base2, or thinnet, which uses thin coaxial cable
– 10BaseT, which uses unshielded twisted pair cable
– 10BaseFL, which uses single or multimode optical fiber
9. 10Base5 (Thicknet) Ethernet
• 10Base5 (thickenet) Ethernet has the following specifications:
– Maximum segment length 500 meters (1650 feet)
– Maximum taps 100
– Maximum segments 5
– Maximum segments with nodes 3
– Maximum distance between taps 2.5 meters (8.25 feet)
– Maximum repeaters 4
– Maximum overall length with repeaters 2.5 kilometers (1.5 miles)
– Maximum AUI drop cable length 50 meters (165 feet)
We use BNC connectors, DIX connectors, Transceiver, Transceiver cable,
BNC barrel connectors, one BNC terminator, one Grounded terminator.
10. 10Base2 (Thinnet Coax) Ethernet
• 10Base2 (Thinnet) Ethetnet has the following
specifications:
– Maximum segment length 185 meters (610.5 feet)
– Maximum segments 5
– Maximum segments with nodes 3
– Maximum repeaters 4
– Maximum devices per segments 30
– Maximum overall length with repeaters 925 meters (3052.5 feet)
The term 10Base2 is little misleading since the maximum length is not actually
200 meters (660 feet) but only 185 meters (610.5 feet). The specification of
thinnet is 50 Ohms RG-85A/U or RG-85 Coaxial cable. You use in thinnet BNC
connectors, T connectors, and two terminators at both ends
11. 10BaseT (Twisted-Pair) Ethernet
• 10BaseT(twisted-pair) Ethernet has the following
specifications:
– Maximum segments 1024
– Maximum segments with nodes 1024
– Maximum segment length 100 meters (330 feet)
– Maximum nodes per segments 2
– Maximum nodes per network 1024
– Maximum hubs in a chain 4
10BaseT is wired as a Star which means that each device has its own set
of wires connected directly to a hub. The connection to the hub and the
LAN cards is made with an RJ-45 connector. UTP cable is classified in
categories, Categories 1and 2 are voice grade cable, Categories 3, 4, and
5 are data-grade.
12. 10BaseFL
• 10BaseFL Ethernet has the following specifications:
– Maximum segments 1024
– Maximum segments with nodes 1024
– Maximum segment length 2000 meters
– Maximum nodes per segments 2
– Maximum nodes per network 1024
– Maximum hubs in a chain 4
10BaseFL (10Mbps data rate, baseband signaling over a fiber-optic
cable) uses light rather than electricity to transfer Ethernet frame.
10BaseFL is a Star-wired network because it requires a hub (also called
a concentrator) to receive the light signal from each network station and
send the same signal to all stations.
13. 100VG-AnyLAN
• 100VG-AnyLAN (aka 100BaseVG) is capable of transporting both IEEE
802.3 and IEEE 802.5 frames
• It is faster
• It provides a mechanism for interconnecting 100 Mbps token ring and
100BaseT Ethernet LANs via specialized hubs and routers (see Figure 4-2)
– 100VG-AnyLAN-compliant adapters are also needed
• It uses demand priority access (DPA) rather than CSMA/CD as the MAC
protocol in order to enable real-time voice and video frames to be given
priority over other data frames
• Hubs can filter individually addressed frames for enhanced privacy.
100VG-anyLAN can use over Categories 3, 4, and 5 Twisted-pair and Fiber-
optic cables. It uses a Star topology and defines how child hubs can be
connected to a parent hub to extend the network. Several Hubs are cascaded
in Figure 4-3.
16. 100BaseT Ethernet
• 100BaseT, also called Fast Ethernet, is simply regular Ethernet
run at a faster data rate over category 5 twisted-pair cable.
100BaseT uses the CDMA/CD protocol in a star wired bus as
10BaseT.
100BaseT has been specified for three media types:
– 100BaseT4 (four pairs categories 3, 4, and 5 UTP or STP)
– 100BaseTX (two pairs category 5 UTP or STP)
– 100BaseFX (two-strand fiber-optic cable)
In addition to the faster data rate and the higher quality cable required,
100BaseX has the same advantages and drawbacks as 10BaseT.
17. Segmentation
• Segmentation is the process of splitting a
large Ethernet network into two or more
segments linked by bridges or router.
18. Token Passing
• Token passing is the other major MAC protocol found in LANs
• It is used in token ring and FDDI LANs and other networks with
logical ring topologies
• The token is a pre-defined bit pattern that is passed among network
attached computers until one of them wants to use the medium to
transmit data
• Token passing is summarized in Table 4-2
• In token ring networks that resemble physical star topologies, token
passing takes place within MAUs (see Figure 4-7)
• Token passing can be used in bus topologies as well as in physical ring
topologies.
• Table 4-3 compares token passing and CSMA/CD
20. IEEE 802.5 and 802.6 LANs
• The most widely used microcomputer ring network is the
token passing ring. It conforms to the IEEE 802.5 standard
• Token ring networks physically look like a star topology,
but technically they are physical rings
– Token ring nodes attach to multistation access units (MAUs) – see
Figure 4-4
– MAUs can be described as “a ring in a box”, because nodes attach
to the physical ring by connecting to the MAU (see Figure 4-5)
– MAUs can be interconnected to form larger rings (see Figure 4-6)
• IEEE 802.6 addresses dual-ring metropolitan area network
(MAN) architectures.
26. Cabling for Token Ring
• Type 1: STP cable used to connect terminals and distribution panel and to run through walls to
wiring closets in the same building. It is two twisted pairs of solid core 22 gauge copper wire
surrounded by a shield.
• Type 2: It is made just as type1 cable with the exception that it incorporates four twisted pairs of
telephone wires.
• Type 3: UTP cable with four pairs, each twisted two time for every 3.6 meters (12feet) of length. It
is cheaper than Type 1 and 2. It is made of either 22 or 24-gauge wire.
• Type 5: Optical cable used only on the main ring path. It consists of 62.5-micron diameter or 100-
micron diameter fiber-optic cable.
• Type 6: STP cable that does not carry signals as for as Type 1 and 2. It is generally used only as
patch cable or as extensions in wiring closets. It is made with 26-gauge copper wire twisted together
in shielded jacket.
• Type 8: Used for runs under carpets. Likes Type 6 cable, it is made of two 26-gauge stranded-core
wires twisted together.
• Type 9: Basically the fire-retardant version of Type 6 cable. It is made with two 26-gauge stranded-
core copper wires twisted together in a shielded jacket.
27. Token Ring
Token Ring has the following specification:
Cable type UTP, STP, or Fiber-optic
Maximum MSAUs 33
Maximum Nodes 260
Maximum distance between 45.5 meters (150 feet) for UTP; up to
nodes and MSAU 100 meters (330 feet) for STP or Fiber-Optic
cable
Maximum patch cable distance 45.5 meters with UTP cable; 200 meters
connecting MSAUs (660 feet) with STP, 1 kilometer (0.6 mile)
with Fiber-optic cable.
Minimum patch cable 2.5 meters (8 feet)
distance connecting MASUs
Maximum cumulative patch cable 121.2 meters (400 feet) with UTP cable;
distance connecting all MSAUs Fiber-optic cabling can span several
kilometers
28. How token Ring Works
Active Monitor and Standby Monitors
• Active Monitor in a Token Ring network (usually the device
that has been operating on the network for the longest time)
that periodically checks the status of the network and monitors
for the network errors. Whereas Standby Monitor in Token
Ring network monitors the status and may become the active
monitor in the case of failure of the active monitor.
Beaconing :
• The process on Token Ring network by which a device, in the
event of a cable fault, determines the state of the network and
location of the fault. (If a station does not hear from its
upstream neighbor in the seven seconds, it assume
something bad has happened and acts on its own. This action
is called beaconing.) It occurs when the Nearest Active
Upstream Neighbor Notification (NAUN) fails.
29. Token Ring
Advantages:
• Unlike Ethernet, Token Ring continuous to operate reliably
under heavy loads.
• Built-in diagnostic and recovery mechanism, such as
beaconing and auto-configuration, makes the protocol more
reliable.
• Token Ring makes connecting a LAN to an IBM mainframe
easier since IBM created it and supports it.
• Fault-tolerance features are provided through ring
reconfiguration, called ring-wrap. A single cable can create a
ring when attached to two MSAUs.
Disadvantages
• Token Ring cards and equipment are more expensive than
Ethernet or ARCnet system.
• Token Ring can be very difficult to troubleshoot and requires
considerable experience.
32. Some Key Ethernet Implementations
• Particularly important Ethernet
implementations include:
– Fast Ethernet (e.g. 100BaseT and 100BaseFX)
• The IEEE 802.3u specification covers Fast Ethernet
– Gigabit Ethernet (e.g. 1000BaseT,
1000BaseSX, and 1000BaseLX)
• The IEEE 802.3z specification addresses Gigabit
Ethernet
33. FDDI LANs
• Fiber Distributed Data Interface (FDDI) was first
recognized in ANSI’s X3T9.5 specification
• Physically, it has a dual ring topology
• It has a sequential/ring logical topology and uses a
variation of token passing as the MAC protocol
• Key FDDI technologies are identified in Figure 4-8
– These include single attached stations (SAS), dual attached
stations (DAS), FDDI concentrators, and FDDI/Ethernet bridges
• FDDI is often used as a backbone network architecture.
35. ATM LANs
• ATM (asynchronous transfer mode) is a switched network
architecture that employs 53-octet cells to transmit data
• Two data link layers are defined:
– ATM adaptation layer (AAL)
– ATM
• ATM physical topologies are stars
• ATM NICs with 25 speeds of 25, 100, or 155 mbps are
available for workstations
• Ethernet and token ring LANs can interface with an
organization’s ATM backbone network via ATM
gateway/access switches (see Figure 4-9)
36. ATM
• ATM is a circuit-based network, in that a virtual circuit is
setup between two devices to communicate over the network.
There are two types of circuits in an ATM network.
– Permanent Virtual Circuit (PVC): A circuit that is setup once in the
switches to allow communication between two devices.
– Switch Virtual Circuit (SVC): A circuit that is temporarily setup
just for the duration of a communication between two devices.
Several Classes of service have been defined for ATM
- Circuit emulation with constant bit rate.
- Audio and/or video with a variable bit rate.
- Connection-oriented service for data transmission.
- Connectionless service for data transmission
38. Wireless LAN Architectures
• IEEE 802.11x standards are the most important wireless LAN
(WLAN) specifications that exist today (see Table 4-4)
• WLANs are typically implemented as physical stars
– Nodes connect to wireless hubs called access points
• CSMA/CA is the MAC protocol for IEEE 802.11-compliant LANs
• IEEE 802.11 addresses FHSS (frequency hopping spread spectrum),
DSSS (direct sequence spread spectrum), and diffuse infrared
transmission
– User “roaming” capabilities are also addressed
• WiFi (Wireless Fidelity) certification has been developed to promote
interoperability among WLAN products
• The WISPR (Wireless ISP Roaming) standard is designed to enable
users to roam from one publicly accessible WLAN to another
40. Choosing Among LAN
Architectures
• A number of factors should be considered when selecting among LAN
architectures
• Some of the major factors are described in Table 4-5.
• Especially important factors to consider include:
– Immediate and recurring LAN costs
– Total cost of ownership (TCO)
– Number of concurrent users that can be supported
– Transmission speed and data throughput
– Vendor support
– Manageability
– Scalability/expandability
– Security
– Adherence to widely accepted standards
42. CSMA/CA
• CSMA/CA (Carrier Sense Multiple Access and
Collision Avoidance) is a variation of CSMA/CD
used in wireless LANs because it is difficult to
detect collisions in such networks
• When CSMA/CA is used, each node must wait a
random time interval (hardwired in the wireless
NIC) after detecting a clear medium before
transmitting
