Interconnect Network

Repeaters:

A repeater receives a signal, regenerates it, and passes it on. It can regenerate and
retime network signals at the bit level to allow them to travel a longer distance on
the media.
.‫ في الكابل عندما يكون طول الكابل محدود‬Signal ‫إلعادة توليد‬

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Hubs:

Hubs are actually multiport repeaters. The difference between hubs and repeaters is
usually the number of ports that each device provides. A typical repeater usually has
two ports. A hub generally has from 4 to 24 ports. Hubs are most commonly used in
Ethernet 10BASE-T or 100BASE-T networks.

The use of a hub changes the network from a linear bus with each device plugged
directly into the wire to a star topology. Data that arrives over the cables to a hub
port is electrically repeated on all the other ports connected to the network segment.

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Conclusion:

1. A hub is a box that contains a certain number of junctions (UTP outlets) to

which are connected different stations.

2. Belongs to layer 1 OSI (Physical layer).

3. A hub is a distributor to which are connected computers.

4. Each UTP outlet is controlled by LED.

5. A hub is responsible of the communication between different junctions.

6. Hub: 4 - 8 - 16 - 32 - 64 - 128 ports.

7. Hubs can be:

 Active: needs a continuous alimentation.
 Passive: Does not need a continuous alimentation.

Advantages:
1. Easy to install a hub.

2. A hub can ensure an electrical isolation between computers.

Disadvantages:
1. A hub cannot reduce data traffic on network.

2. Debit: 10MB/s - 100MB/s.

3. A hub cannot multiplexing the communication between stations. (If A and B

work together, others will be in pause mode).

4. If the hub is offline no network connection.

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The bridges:

There are times when it is necessary to break up a large LAN into smaller and more
easily managed segments.
This decreases the amount of traffic on a single LAN and can extend the
geographical area past what a single LAN can support.

The devices that are used to connect network segments together include bridges,
switches, routers, and gateways. Switches and bridges operate at the data link layer
of the OSI model.

The function of the bridge is to make intelligent decisions about whether or not to
pass signals on to the next segment of a network.

When a bridge receives a frame on the network, the destination MAC address is
looked up in the bridge table to determine whether to filter, flood, or copy the frame
onto another segment. This decision process occurs as follows:

 If the destination device is on the same segment as the frame, the bridge will
not send the frame onto other segments. This process is known as filtering.

 If the destination device is on a different segment, the bridge forwards the

frame to the appropriate segment.

 If the destination address is unknown to the bridge, the bridge forwards the
frame to all segments except the one on which it was received. This process is
known as flooding.

Switches:

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A switch is sometimes described as a multiport bridge. A typical bridge may have only two
ports that link two network segments. A switch can have multiple ports based on the
number of network segments that need to be linked. Like bridges, switches learn
information about the data frames that are received from computers on the network.
Switches use this information to build tables to determine the destination of data that is
sent between computers on the network.

Although there are some similarities between the two, a switch is a more sophisticated
device than a bridge. A bridge determines whether the frame should be forwarded to the
other network segment based on the destination MAC address. A switch has many ports
with many network segments connected to them. A switch chooses the port to which the
destination device or workstation is connected. Ethernet switches are popular connectivity
solutions because they improve network speed, bandwidth, and performance.

Switching is a technology that alleviates congestion in Ethernet LANs. Switches reduce

traffic and increase bandwidth. Switches can easily replace hubs because switches work
with the cable infrastructures that are already in place. This improves performance with
minimal changes to a network.

All switching equipment perform two basic operations. The first operation is called
switching data frames. This is the process by which a frame is received on an input
medium and then transmitted to an output medium. The second is the maintenance of
switching operations where switches build and maintain switching tables and search for
loops.

Switches operate at much higher speeds than bridges and can support new functionality,
such as virtual LANs.

An Ethernet switch has many benefits. One benefit is that it allows many users to
communicate at the same time through the use of virtual circuits and dedicated network
segments in a virtually collision-free environment. This maximizes the bandwidth available
on the shared medium. Another benefit is that a switched LAN environment is very cost
effective since the hardware and cables in place can be reused.

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Conclusion:

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1. Belongs to layer 2 OSI (Data link layer).

2. Switch 4, 8, 12, 16, 24, 32, 64, 128, ports.

3. Switch is a box that contains a certain number of junctions (UTP outlets) to

which are connected different stations.

4. Speed (debit): 100MB/s, 1GB/s, 10GB/s (N.T).

5. Switch can regularize and reduce data traffic on networks.

6. Switch is always active.

7. Switch can be programmable.

8. Switch is responsible of multiplexing the communication between stations (All

stations can work together.).

9. Switch can control the task on networks.

10. Switch is an intelligent element.

11. Switch is auto learning the configuration of network.

Switch Hub
Intelligent element.
Debit 100MB/s - 1GB/s - 100GB/s (N.T) Debit 10MB/s, 100MB/s
Belongs to layer 2 OSI. Belongs to layer 1OSI.
Switch is always active. Hub can be active or passive.
4, 8, 12, 16, 24, 32, 64, 128 ports 4, 8, 16, 32, 64, 128 ports
Easy to install Easy to install
Switch regularize and reduce data traffic on Hub cannot regularize and reduce traffic on
network networks.
Switch can multiplexing the communication Hub cannot multiplexing the communication
between stations. between stations.
Hub sends the packets to all active units except the
Switch sends packets only to destination.
source.
Auto learning the configuration.
If the switch is offline no network
If the hub is offline no network connection.
connection.
Peer-To-Peer Network:

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When LAN and WAN technologies are used, many computers are interconnected to
provide services to their users. To accomplish this, networked computers take on different
roles or functions in relation to each other. Some types of applications require computers to
function as equal partners. Other types of applications distribute their work so that one
computer functions to serve a number of others in an unequal relationship.

Two computers generally use request and response protocols to communicate with each
other. One computer issues a request for a service, and a second computer receives and
responds to that request. The requestor acts like a client and the responder acts like a
server.

In a peer-to-peer network, networked computers act as equal partners, or peers. As peers,

each computer can take on the client function or the server function. Computer A may
request for a file from Computer B, which then sends the file to Computer A. Computer A
acts like the client and Computer B acts like the server. At a later time, Computers A and B
can reverse roles.

In a peer-to-peer network, individual users control their own resources. The users may
decide to share certain files with other users. The users may also require passwords before
they allow others to access their resources. Since individual users make these decisions,
there is no central point of control or administration in the network. In addition, individual
users must back up their own systems to be able to recover from data loss in case of
failures. When a computer acts as a server, the user of that machine may experience
reduced performance as the machine serves the requests made by other systems.

Peer-to-peer networks are relatively easy to install and operate. No additional equipment is
necessary beyond a suitable operating system installed on each computer. Since users
control their own resources, no dedicated administrators are needed.

As networks grow, peer-to-peer relationships become increasingly difficult to coordinate.

A peer-to-peer network works well with ten or fewer computers. Since peer-to-peer
networks do not scale well, their efficiency decreases rapidly as the number of computers
on the network increases. Also, individual users control access to the resources on their
computers, which means security may be difficult to maintain. The client/server model of
networking can be used to overcome the limitations of the peer-to-peer network.

Clients/Server Network:

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In a client/server arrangement, network services are located on a dedicated computer called

a server. The server responds to the requests of clients. The server is a central computer
that is continuously available to respond to requests from clients for file, print, application,
and other services. Most network operating systems adopt the form of a client/server
relationship.

Typically, desktop computers function as clients and one or more computers with
additional processing power, memory, and specialized software function as servers.

Servers are designed to handle requests from many clients simultaneously. Before a client
can access the server resources, the client must be identified and be authorized to use the
resource. Each client is assigned an account name and password that is verified by an
authentication service.

The authentication service guards access to the network. With the centralization of user
accounts, security, and access control, server-based networks simplify the administration of
large networks.

The concentration of network resources such as files, printers, and applications on servers
also makes it easier to back-up and maintain the data. Resources can be located on
specialized, dedicated servers for easier access.

Most client/server systems also include ways to enhance the network with new services
that extend the usefulness of the network.

The centralized functions in a client/server network has substantial advantages and some
disadvantages. Although a centralized server enhances security, ease of access, and control,
it introduces a single point of failure into the network.

Without an operational server, the network cannot function at all. Servers require a trained,
expert staff member to administer and maintain. Server systems also require additional
hardware and specialized software that add to the cost.

Figures and summarize the advantages and disadvantages of peer-to-peer and client/server
networks.

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Peer-to-peer Network

Advantages Disadvantages

Low cost. Does not scale to large network (max to computer)

No administrator need. Less secure.

Each user must be trained to perform

Easy to install.
administration tasks.

No administrator dedicated software.

Client/Server Network

Advantages Disadvantages
Easies to administrator when the network is
Require a professional administrator.
large.

All data can be backups on the server

Has a single point of failure.
central.

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10 base 2 10 base 5 10 base T 100 base TX 100 base FX

Max Length 185 m 500 m 100 m 100 m 400 m
Topology Bus Bus Star Star Star
Connectors BNC AUI RG 45 RG 45 ST | SC

Comparison Switching Techniques:

Packet Switching Circuit Switching Message Switching

One dedicated path between A message takes usually one
Several Possible Paths
sends and receiver path between tow hops.
Division of one message into One complete message is One complete message is
set of packets. sent sent.
Guarantee performance Message is checked for
Possible packets loss
QOS (Quality of service) errors (CRC).
Time delay (division and
Not time delay Time delay (Store and EWD)
reassembly of packets)

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