Local and Corporate Networks 2010
Unit 3 Multi-segment LAN Networks
2.2 Levels of Interconnection.
Internetworking techniques facilitate the movement of information among different networks. They are
used to interconnect two or more different types of networks, and this involves performing some form
of data conversion. Such conversion may be as simple as amplification, as in the case of a repeater;
or as complex as transforming an entire stack of protocols; or for passing from the OSI to the SNA
model, for example, thus requiring a Gateway.
Internetworking techniques connect two different types of networks
depending on the type of conversion needed, a different device is used
Application
Application
Gateway
SAP
Presentation
The Gateway
Uses the 7
layers for
SAP
Session
conversion
Transport
from one
network type
to another
SAP
SAP
Presentation
SAP
Session
SAP
Transport
SAP
SAP
Network
Router
Switch
SAP
Link
Bridge
Network
SAP
Link
SAP
SAP
Physical
Repeater
Physical
With internetworking via Bridges, we find that better performance is delivered for connections
between LANs at a single location. Bridges work well in low LAN interconnection environments.
These structures are simple to manage, but are not very secure.
Routers support more complex network structures, facilitate better bandwidth use, and are useful in
filtering and containing traffic in confined portions of a network. Filters also enable a high level of
security. Routers are very useful for interconnecting remote LANs.
Switches perform the same function as bridges with routine traffic, and function like routers with new
traffic. Since a switch works at the level of hardware and a router at the level of software, a switch is
much faster.
Whether a bridge, a router, or a switch is used depends on the protocols used for the required traffic
load, the transference relationship, the sensitivity of applications to delays, and network topology.
Designs steps:
The advantages and disadvantages of using bridges, routers, or switches should be weighed, as
should the advantages and disadvantages of solutions from different vendors and products.
An Enterprise network addressing structure should be developed.
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Local and Corporate Networks 2010
Unit 3 Multi-segment LAN Networks
The following should be established:
The choice of cost-effective strategies for transmission.
The choice of topology and architecture options for each network at each site.
The choice of Software, Hardware, and Management platforms.
Integrated network management and the number and types of protocols used as well as cost.
2.3 Interconnectivity.
Bridges and routers can be built to support multi-protocol operation on a single network, but cannot
support multiple network architectures. The central problem with this restriction lies in the way each
architecture defines its Domains and in the protocol exchange mechanism on which the routing tables
are built.
Bridges and routers can be used on network that operate with multiple protocols
Bridges and routers cannot interconnect with networks that have different
architectures
IP Nodes IP can communicate with one another, but not with AppleTalk or SNA Nodes
Gateways facilitate connection to networks with different architectures
SNA
Host
Gateway
TCP/IP
Nodes
Gateway
Protocol Converter
There are various types of Gateways, depending on the combination of
protocol to be used in terms of both architecture and applications.
A gateway can perform conversions among the different levels of OSI model
To interconnect networks of different architectures, Gateways–which perform complete functional
conversion from one protocol to another equivalent protocol–must be used, either in the same layer or
via the required conversion of layers. If, for example, a protocol in a particular architecture belongs to
layer 4 but its functions include layer 4 and 5 functions of another architecture, the Gateway will
functionally break down the source protocol and will generate layer 4 and 5 protocols of the other
architecture.
2.4 The Network Card.
The Network Interface Card (NIC) is responsible for interconnecting a PC with the network's physical
communication environment. Interconnection is secured between the computer's internal bus, where
data travel in parallel, and some type of cable (copper, coaxial, or fiber), where data travel in series.
Making this connection requires a transceiver with capability to transmit and receive simultaneously
and to convert data from parallel to serial and vice versa.
NICs are exclusive that is, they are made for a particular computer and for a particular type of
network. We thus have NICs for PCs, for Macintosh, for Sun, etc.; as well as NICs for Ethernet, for
Token Ring; or for the network standard that is used. The proper NIC is therefore needed for a
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Unit 3 Multi-segment LAN Networks
particular Computer and Network under discussion. Taking the most popular market conditions, we
view the NIC as a PC board with Ethernet Bus network outlet.
Every interface card must include a single Layer 2 network address for that card. That address can
be configured manually, as it was in the old ARCNET network, or fixed internally in a ROM, as is in
Ethernet networks.
NICs should also be adjusted to the computer bus, and thus there will NICs for PCI, EISA, or ISA, on
PCs, or appropriate buses for other computer architectures.
Functions of the NIC
Transceiver (Adaptation of Signal to specific medium)
Physical Address (MAC Address)
Signal Coding
Access to Medium
Frame Assembly
Connection to Physical Medium
CRC Assembly and Error Detection
Network Layer
Layer
Link Layer
Physical Layer
PC
I/O Bus
Station
Interface
Link Data Control
Data
encapsulation
Link
management
Physical Channel
Coaxial
Cable
Transmitter
and
Receiver
Coding
and
Decoding
Transceiver
Cable
Ethernet Controller Card
(NIC)
Transceiver
2.5 Repeaters.
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Local and Corporate Networks 2010
Unit 3 Multi-segment LAN Networks
These are used to extend the distance between computers on a LAN
They are used to adapt levels and impedances between different types of cables
A hub is a multiport repeater that provides centralized connectivity
of devices and enables the physical medium between them to be extended
It operates at the level of Layer 1, regenerating the bits received at a port, on another port
A repeater is unable to discriminate among packets, since it operates at the level of
individual bits
Successive passive repeaters connecting different network segments can be incorporated,
until the maximum distance possible in the system is reached
101010101010101
101010101010101
Repeater
Physical Layer
Repetition
A repeater is an electronic device whose function is to amplify (regenerate) a signal to ensure that it
has the proper amplitude values to be able to correctly detect the logical 'ones' and 'zeros' that are
transmitted over a network. Effort should be made to ensure that signal phase shifts (jitter) fall within
the allowable values, to prevent pulses from overlapping with one another in time.
The repeater is responsible for "repeating the signals" of a network segment on other segments
connected to the repeater. It removes the frame preamble entering the repeater and recreates it in the
frame it sends out with the usual 8 byte configuration: 1010 ... 1011. It expands frames with less than
32 bits to 96 bits, to get the smallest error frame size.
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Unit 3 Multi-segment LAN Networks
Floor n Cable
taps
Repeater
Repeater
Floor 2 Cable
Floor 1 Cable
Repeater
Stations
No more than two
repeaters can be
placed between
two computers
for a maximum
length of 1500m
Stations
Stations
Main Cable
Passive Elements that regenerate electrical signals from one cable to another
In small local area networks, as was the case with the early LANs, repeaters can be included to boost
signals on every floor on an office building. These repeaters will be connected to one another via
another cable connecting all of the repeaters. That kind of configuration is no longer in use, having
been replaced by Bridges or by Switches, but is noteworthy as a historical example of the use of
repeaters.
The repeater operates in Layer 1 and only provides boost for network signals, detecting incoming
signals, electronically regenerating them, converting the pulses to their initial values.
In a repeater, packets are not distinguished. Instead, they are all regenerated just the way they get to
a repeater. Through a repeater a signal can 'go further' and can form longer LANs.
Repeaters are also known as Hubs, since they perform the functions of cable 'hubs,' taking all cables,
from each station, to a single concentration point. The purpose of this concentration is both
technological (to amplify signals in one place) and administrative, to concentrate failure points at one
place and to monitor network wiring from a single point. All cables are vulnerable to rodent (rat)
activity, as these vermin tend to chew into wires, cutting them – and this produces failure points that
must then be found and repaired. Cables are installed along floors and walls that, though accessible,
are not part of an area for regular people traffic and must be accessed by specialized personnel.
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Local and Corporate Networks 2010
Unit 3 Multi-segment LAN Networks
For bus type interconnections,
a cable, or bus, running to
all the computers, was used at first
Later on, a more secure method
was found, involving a
connection centralizer
element, the hub
HUB
The hub provides a separate cable or
connection for each computer to
connect. If a cable or a
computer goes out of service,
it is simply disconnected
from the hub
The hub serves only to ensure connectivity, and it amplifies signals as well;
it does no processing with signals
They establish Electrical Connection to the Network for each machine
There are small, 5 to 8 port hubs for Workgroup
They usually have 8, 12, 16, 24, or 32 ports
Data are sent to all ports alike
They involve problems of inefficiency, collisions, and scalability
Interconnection among Hubs is limited
The 5-4-3 rule (no more than 4 hubs) should be used
Maximum cable length of 100 m with 11.5 dB attenuation
Chassis type Hubs allow a large number of ports to be hosted and a set of
interconnection facilities – such as fiber connection, implementation of routers,
bridges, gateways, central processors, and other components – to be shared
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