Data communication and network Chapter - 2

Copyright revised for Zafar Ayub
Data Communication and Network

(zafar_ayub@hotmail.com)
Chapter - 2
Compile by Zafar Ayub

1

Network Protocol
A protocol is a set of rules that governs the communications
between computers on a network. In order for two computers to
talk to each other, they must be speaking the same language.
These rules include guidelines that regulate the following
characteristics of a network; access method, allowed physical
topologies, types of cabling, and speed of data transfer.
Many different types of network protocols and standards are
required to ensure that your computer (no matter which operating
system, network card, or application you are using) can
communicate with another computer located on the next desk or
half-way around the world.

2 Copyright revised for Zafar Ayub

Types of Network Protocols
¢ Network protocols also known as Network Technologies, the most
common network protocols are;
¢ Ethernet (LAN protocol; architecture developed by Xerox,
DEC, and Intel in 1976)
¢ Local Talk ( network protocol that was developed by Apple
Computer, Inc. for Macintosh computers)
¢ Token Ring ( patented by IBM in 1981, is a network protocol
that employs token-passing between computers arranged in a
logical ring network)

¢ FDDI (set of ANSI and ISO standards for data transmission on
fiber optic lines in a local area network (LAN) that can extend
in range up to 200 km (124 miles).
¢ ATM (ATM is a high-speed networking standard designed to
support both voice and data communications. ATM is normally
utilized by Internet service providers on their private long-
distance networks)

Ethernet Protocol
¢ The Ethernet protocol is by far the most widely used. Ethernet uses
an access method called CSMA/CD (Carrier Sense Multiple
Access/Collision Detection).
¢ This is a system where each computer listens to the cable before
sending anything through the network. If the network is clear, the
computer will transmit.
¢ If some other node is already transmitting on the cable, the
computer will wait and try again when the line is clear.
¢ Sometimes, two computers attempt to transmit at the same instant.
When this happens a collision occurs. Each computer then backs off
and waits a random amount of time before attempting to
retransmit.
¢ With this access method, it is normal to have collisions. However,
the delay caused by collisions and retransmitting is very small and
does not normally effect the speed of transmission on the network.
ring network)


Types of Ethernet
¢ 10 Base 5
Coaxial cable (10Base5)
Thicknet. (Bus Topology)
¢ 10 Base 2
Thin coax cable (10Base2)
Thinnet. (Bus Topology)
¢ 10 Base T
Twisted pair Ethernet (10BaseT)
Star Topology on HUBs
¢ 100 Base T (Fast Ethernet)
100BASE-TX: two pairs of high-quality twisted-pair wires
100BASE-T4: four pairs of normal-quality twisted-pair wires
100BASE-FX: fiber optic cables
100 Mbps speed on Star Topologies on HUBs (Twisted pair CAT-6
cable)

¢ Giga Base T / 1000 Base X
High speed Ethernet on layer 3 switches with twisted pair
and fiber cable
Name Medium Specified distance
1000BASE-CX Twinaxial cabling 25 meters
1000BASE-SX Multi-mode fiber 220 to 550 meters dependent on fiber
diameter and bandwidth

1000BASE-LX Multi-mode fiber 550 meters
1000BASE-LX Single-mode fiber 5 km
1000BASE-LX10 Single-mode fiber using 1,310 nm wavelength 10 km

1000BASE-ZX Single-mode fiber at 1,550 nm wavelength ~ 70 km

1000BASE-BX10 Single-mode fiber, over single-strand fiber: 10 km
1,490 nm downstream 1,310 nm upstream

1000BASE-T Twisted-pair cabling (Cat-5, Cat-5e, Cat-6, or 100 meters
Cat-7)

1000BASE-TX Twisted-pair cabling (Cat-6, Cat-7) 100 meters


¢ 10G Base Ethernet
For core network backbone and submarine cables

Name Medium Specified distance

10GBASE-SR Multi-mode fiber 100 meters

10GBASE-LR Single-mode fiber 10 km

10GBASE-LRM Multi-mode fiber 300 meters

10GBASE-ER Single-mode fiber 40 Km

10GBASE-ZR Single – mode fiber 80 km

10GBASE-LX4 Single-mode fiber at 1,550 nm wavelength 10 km

10GBASE-T Twisted pair 100 m


Standard of Ethernet
¢ 10 Base T
10 Mbps (Half Duplex)
IEEE 802.3 at Data Link Layer / Layer 2
¢ 100 Base T (Fast Ethernet)
100 Mbps (Half Duplex / Full Duplex)
IEEE 802.3u at Data Link Layer / Layer 2
¢ Giga Ethernet
1000 Mbps (Full Duplex )
IEEE 802.3z at Data Link Layer / Layer 2
¢ 10 Giga Ethernet
10000 Mbps (Full Duplex)
IEEE 802.3ae at Data Link Layer / Layer 2


CSMA / CD
¢ Carrier Sense: wait till medium is idle before sending frame.

¢ Multiple Access: multiple computers use the same shared media.
Each uses same access algorithm.

¢ Collision Detection: Listen to medium – detect if another station’s
signal interferes – back off and try again later.


CSMA / CD - Transmitting


¢ When Ethernet network determine transmission of data, data
broken into packet, and packed into frames.
¢ Maintain queued for transmission, usually this process occur on
NIC.
¢ Before transmission, transceiver listen on medium is used or not, if
free then start transmission, other wise wait for an algorithm.
¢ The listing process through out whole cable transceivers.
¢ It is possible that two or more of them sense simultaneously, and
began transmitting, cable medium is shared medium; so possibly two
or more transmission frames collapse with each other.
¢ Collapse known as collision.
¢ When transmission began, sender station continuously monitor the
medium, and when collision is occur, then transmit “Jam Signal”.
¢ At this stage all station which are involved in this collision, began
“evasive action”, is an algorithm for waiting of random period of
time.


¢ If collision occurs: wait a random time t1 - 0< t1<d.
D depends on transmission speed – time for frame width or 512
bits.
¢ If second collision occurs, wait a random time t2 - 0< t2<2d.
Double range for each successive collision.
¢ If collision occur its maximum value, transmission aboard.
¢ And if no collision, then again listen cable that is busy or not.


CSMA / CD - Receiving


¢ Each station on the medium, listen incoming frames and check for
fragments; fragments are partial frame (faulty or collision occur
frames).
¢ In first step, check frame size, valid Ethernet frame has
approximately size is 64 bytes.
¢ If frame is shooter, then assumed that collision may occur, then not
further process, and try again.
¢ In second step, station also check MAC address of destination
frame, if this address is not match, then start receiving again.
¢ And if address match, then check series of various elements, like
receiving frame not too long, conditionally length is 1518 bytes, if
exceed assumed that frame is faulty, and transmission terminate due
to over size of frame.
¢ If over size test is clear, then check CRC formula, and comparing
result value with receiving frame value.
¢ if comprising value checked then, and result is match then
disassemble frame, and successful receiving.


¢ If length field is not match, then aboard receiving.
¢ And CRC not match, then check extra bit (check sum), if no extra
bit then end of receiving due to CRC error.
¢ And If add extra value in CRC, then again aboard receiving due to
alignment error.


Token Ring Protocol
¢ Initially used only in IBM computers in 1981, it was eventually
standardized with protocol IEEE 802.5.
¢ Token ring technology is a local area network protocol which
resides at the data link layer (DLL 2 layer) of the OSI model.
o It uses a special three-byte frame called a token that travels around
the ring.
o Active monitor grants the possessor permission to transmit on the
medium.
o Token ring frames travel completely around the loop.
o Like Ethernet any computer start transmitting at every time; not
possible, either wait for special frame “token”, and when it get on
wire and if is token is empty then copy their data on it, and passing
through forward.
o This token traveling method is clockwise and called as token passing
method.


Token Ring Topology
¢ Ring topology is used for token ring protocol; but actually physically
star topology and logically ring topology are used.


¢ In token ring protocol, ring topology used MSAU as central device,
CAT-3 (4Mbps to16Mbps), and IBM token ring adapter.
¢ MSAU (Multi Station Access Unit) just like Ethernet hub, but every
computer linked with two UTP / STP cables, one for received and
second for transmit.
¢ These short cable which are attached with computer to MSAU, is
called Lobe.
¢ There are two types of computers on token ring topology, only one
at ring is active monitor, and all other reaming are standby monitor.
¢ Active monitor responsible for generating token and passing
through on network in clock wise.
¢ Standby monitors just like clients which are directly connected on
ring , waiting for token for data transmission at its own parity.
¢ Active monitor selection is done by automatically by an election
method, and if within 10 millisecond, active monitor is out of
response, automatically election generated and new computer
active monitor.


Token Passing
¢ The first computer set its NIC default value.
¢ In second perform lobe test, transmit and receive cables initially
connected with MSAU, in this test computer send single on their
transmit cable and listening back same signal at its receiving cable.
¢ If successful communication occur then other process shall be
start, other wise computer goes to fail for ring attachment; this test
called loopback test.
¢ In next stage computer place current (phantom current) on cable
ring, which cause this lobe is active on MSAU, otherwise MSAU
assume this computer is going switch off.
¢ After this network adapter now checks to insure that its MAC
address is unique on network; for this its send special signal
(destination its own MAN address) if no computer set an indicator
flag on this frame, then its assume its address is unique, otherwise
remove from network until anyone reconfigure its MAC address.
¢ Within seven second, a ring poll occur, by this every computer get
know its upstream neighbor address.

¢ Ring poll: ring polling occur every seven second, by this process
every computer aware of its next upstream neighbor MAC address.
All of this value also be save at active, and in every seven second
every computer listen that active monitor is present or not other
wise again election shall be occur.
¢ By clearing all test computer become full flag member of ring.
¢ Lets start a ring which have five computer A to E, where A is a
active monitor.
¢ Computer A is automatically elected by an election, now B
required to send data to E, then when token is pass through at B
computer, its check if token is empty then he copy their data into
empty token.
¢ Token is now moving forward C; again C check that this token is
for its or not, forward it, token forward to D; again this process
happened, and when this token at E, this computer NIC check that
destination MAC is match, if yes then copy all data and copied
flagged is down means off.

¢ Again token forwarding back to A, after reaching A computer check
if copy flag is down or off then again up this flag and assume that
data has been copied other wise again transmit in ring.
¢ When this happen means data has been copied, A also up all
reaming flags; like token is empty, data copy, and if any error then
remove from frame.
¢ Then A again transmit this token on ring, when its pass through by
B, computer B check and if token empty flag is up then computer B
able to copy their data on this token, and computer B copy their
data on exiting pervious computer A data.
¢ Token priority / flag: There are 8 priority / flags on token ring
transmission; from 0-7, every flag represent any one operation like
token is empty, data has been copied or error, etc.


Active Monitor: Every station in a token ring network is either an
active monitor (AM) or standby monitor (SM) station. However, there
can be only one active monitor on a ring at a time. The active monitor
is chosen through an election or monitor contention process.
The monitor contention process is initiated when
•a loss of signal on the ring is detected.
•an active monitor station is not detected by other stations on
the ring.
•a particular timer on an end station expires such as the case
when a station hasn't seen a token frame in the past 7 seconds.
When any of the above conditions take place and a station decides
that a new monitor is needed, it will transmit a "claim token" frame,
announcing that it wants to become the new monitor. If that token
returns back to the sender, it is OK for it to become the monitor. If
some other station tries to become the monitor at the same time
then the station with the highest MAC address will win the election
process. Every other station becomes a standby monitor. All stations
must be capable of becoming an active monitor station if necessary.

The active monitor performs a number of ring
administration functions.
•The first function is to operate as the master clock
for the ring in order to provide synchronization of the
signal for stations on the wire.
•Another function of the AM is to insert a 24-bit delay
into the ring, to ensure that there is always sufficient
buffering in the ring for the token to circulate.
•A third function for the AM is to ensure that exactly
one token circulates whenever there is no frame being
transmitted, and to detect a broken ring.
•Lastly, the AM is responsible for removing circulating
frames from the ring.


FDDI Protocol
¢ Fiber Distributed Data Interface (FDDI) provides a 100 Mbps
optical standard for data transmission in a local area network that
can extend in range up to 200 kilometers (120 mi).
¢ Although FDDI logical topology is a ring-based token network, it
does not use the IEEE 802.5 token ring protocol as its basis; instead,
its protocol is derived from the IEEE 802.4 token bus timed token
protocol.
¢ In addition to covering large geographical areas, FDDI local area
networks can support thousands of users. As a standard underlying
medium it uses optical fiber, although it can use copper cable, in
which case it may be referred to as CDDI (Copper Distributed
Data Interface). FDDI offers both a Dual-Attached Station (DAS),
counter-rotating token ring topology and a Single-Attached Station
(SAS), token bus passing ring topology


Network Topologies
A Network Topology is the layout pattern of interconnections of the
various elements (links, cables, devices, etc) of a computer system.
In network arrangement of computers or flow of network traffic,
known as Network Topology.
Means arrangement of device on network with structural (physical)
or virtual (logical) is Network Topology.


Types of Network Topologies
¢ Network topologies may be physical or logical with respect to their
functionality.
¢ Physical topology refers to the physical design of a network
including the devices, location and cable installation.
The shape of the cabling layout used to link devices is called the
physical topology of the network.This refers to
the layout of cabling
the locations of nodes
the interconnections between the nodes and the cabling
The physical topology of a network is determined by;
the capabilities of the network access devices and media
the level of control
fault tolerance desired
the cost associated with cabling or telecommunications
circuits.


¢ Logical topology refers to how data is actually transferred in a
network as opposed to its physical design.
The logical topology is define;
is the way that the signals act on the network media
the way that the data passes through the network from one
device to the next without regard to the physical interconnection of
the devices.
A network's logical topology is not necessarily the same as its
physical topology. For example;
the original UTP Ethernet using hubs / switches, but logically
connected bus topology layout.
Token Ring is a logical ring topology, but is wired a physical
star from the MSAU (Media Station Access Unit).
¢ In general physical topology relates to a core network whereas
logical topology relates to basic network.


BUS Topology
¢ A bus network topology is a network architecture in which a set of
clients are connected via a shared communications line / medium,
called a BUS topology.
¢ The bus topology is often referred to as a linear bus because the
computers are connected in a straight line. This is the simplest and
most common method of networking computers.
Advantages :
Easy to connect a computer or peripheral to a linear bus.
Easy to implement and extend
Well suited for temporary networks (quick setup)
Typically the cheapest topology to implement
Faster than a ring network.
If any node on the bus network fails, the bus its self is not effected.
Requires less cable length than a star topology.


Disadvantages :
Difficult to administer/troubleshoot
Limited cable length and number of stations
A cable break can disable the entire network
Maintenance costs may be higher in the long run
Performance degrades as additional computers are added or on
heavy traffic
Low security (all computers on the bus can see all data
transmissions)
One virus in the network will affect all of them (but not as badly as a
star or ring network)
Proper termination is required.(loop must be in closed path)
Significant Capacitive Load (each bus transaction must be able to
stretch to most distant link).


How it’s work?
¢ A Bus networks are the simplest way to connect multiple clients,
but may have problems when two clients want to transmit at the
same time on the same bus.
¢ The Ethernet is common protocol for bus topology.
¢ Thus systems which use bus network architectures normally have
some scheme of collision handling or collision avoidance for
communication on the bus, quite often using CSMA / CD(Carrier
Sense Multiple Access / Collision Detection).
¢ In Bus topology computers are connected with each other via cable,
called coax cable (thick net / thin net) with their NIC.
¢ NIC connect with cable via passive device called BNC -T(British
Naval Connector) / Transverse (DB-15) and at last of both cables
ends T-Connector or open loop must be closed.
¢ Bus topology has two basic types 10Base-2 and 10Base-5.


10Base-2
¢ In 10Base-2 coax cable used Thinnet cable (RG-58) 50 ohm.
¢ It is capable of covering up to 590 feet (180 meters) and is not
highly susceptible to noise interference.
¢ It transmits at 10Mbps megabits per second and can support up to
30 nodes per segment.
¢ This is a type of coax cable you can use for networks it’s a thinner
cable, like the one you find on your cable television.


¢ Thinnet cabling components include;
¢ BNC barrel connectors

¢ BNC T connectors

¢ BNC terminator


¢ 10Base-2 specification;

Category Notes

Maximum segment length 185 meters (607 feet)

Connection to network interface card BNC T connector

Trunk segments and repeaters Five segments can be joined using four repeaters

Computers per segment 30 computers per segment by specification

Segments that can have computers Three of the five segments can be populated

Total number of computers 90 computers

Maximum total network length 925 meters (3035 feet)


5-4-3 Rule:
A thinnet network can combine as many as five cable segments
connected by four repeaters; but only three segments can have
stations attached.
Thus, two segments are untapped and are often referred to as
"inter-repeater links." This is known as the 5-4-3 rule.


¢ There are five segments, four repeaters, and trunk segments 1, 2,
and 5 are populated (have computers attached to them).
¢ Trunk segments 3 and 4 exist only to increase the total length of
the network and to allow the computers on trunk segments 1 and
5 to be on the same network.
¢ Because normal Ethernet limits are too confining for a large
business, repeaters can be used to join Ethernet segments and
extend the network to a total length of 925 meters (3035 feet).
Note:
The 5-4-3-2-1 rule limits the range of a collision domain by limiting the
propagation delay to a "reasonable" amount of time. The rule breaks
down as follows:
5 - The number of network segments
4 - the number of repeaters needed to join the segments into one
collision domain
3 - the number of network segments that have active (transmitting)
devices attached
2 - the number of segments that do not have active devices attached
1 - the number of collision domains


Advantages:
Relatively inexpensive
Easy to install
Easy to configure

Disadvantages:
Limitation of computer till max 90 computers


10Base-5
¢ In 10Base-5 coax cable used Thicknet cable (RG-59) 50 ohm.
¢ Thick-net cable is often used as backbone in local area network
environment.
¢ It transmit data speed of 10Mbps covers distances of up to 1640
feet / 500 meters and accommodates up to 100 nodes per
segments.


¢ Thicknet cabling components include;
¢ Transceivers These are devices that can both transmit and receive,
provide communications between the computer and the main LAN
cable, and are located in the vampire taps attached to the cable

¢ Transceiver cables The transceiver cable (drop cable) connects the
transceiver to the NIC.


¢ DIX (or AUI) connectors These are the connectors on the
transceiver cable.


¢ N-series connectors, including N-series barrel
connectors, and N-series terminators


¢ 10Base-5 specification;
Category Notes
Maximum segment length 500 meters (1640 feet).

Transceivers Connected to the segment (in the tap).

Maximum computer-to-transceiver distance 50 meters (164 feet).

Minimum distance between transceivers 2.5 meters (8 feet).

Trunk segments and repeaters Five segments can be joined using four repeaters.

Segments that can have computers Three of the five segments can be populated.

Maximum total length of joined segments 2500 meters (8200 feet).

Maximum number of computers per segment 100 by specification.

Total number of computers 300 computers


5-4-3 Rule:
One thicknet Ethernet network can have a maximum of five
backbone segments connected using repeaters , of which up to
three can accommodate computers.
Figure shows how the 5-4-3 rules are applied to thicknet.


¢ The length of the transceiver cables is not used to measure the
distance supported on the thicknet cable; only the end-to-end
length of the thicknet cable segment itself is used.
¢ Between connections, the minimum thicknet cable segment is 2.5
meters (about 8 feet).
¢ This measurement excludes transceiver cables. Thicknet was
designed to support a backbone for a large department or an entire
building.
Note:
The 5-4-3-2-1 rule limits the range of a collision domain by limiting the
propagation delay to a "reasonable" amount of time. The rule breaks
down as follows:
5 - The number of network segments
4 - the number of repeaters needed to join the segments into one
collision domain
3 - the number of network segments that have active (transmitting)
devices attached
2 - the number of segments that do not have active devices attached
1 - the number of collision domains


Advantages:
Backbone cable
Covers distances of up to 1640 feet or 500 meters
Accommodates up to 100 nodes per segment

Disadvantages:
it’s very difficult to work
it transmits data at speeds of 10Mbps
A loose connection or missing terminator could cause erratic
network performance.
This will lead to reduced speed, error counts in high-frame
transmission or even a lack of network connectivity.
When using thin-net, a malfunction transceiver could also
cause excessive packet transmission or frame transmission
errors.


Data communication and network Chapter - 2

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Data communication and network Chapter - 2