Transcript Network protocols

MAKERERE UNIVERSITY
College of Computing and Information Sciences
School of Computing and Informatics Technology
BIT 1102: COMMUNICATIONS TECHNOLOGY
AND THE INTERNET
6.LAN ACCESS METHODS/NETWORK PROTOCOLS
Network Protocol
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 Just like Human beings communicate using
languages such as English, French or
Swahili, Computers / Nodes on a network
need to follow a standard in order to
transmit to each other.
 So, a network protocol can be defined as a
set of rules (a language) governing devices
communicating on a network.
BIT 1102: Communications Technology & the Internet
Network Protocol
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 It is a formal description of digital message
formats and the rules for exchanging those
messages in or between computing systems
and in telecommunications.
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What’s a protocol?
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.
Hi
TCP connection
req
Hi
TCP connection
response
Got the
time?
2:00pm
<file>
time
Qn: Other human protocols?
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Who develops these Standards?
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 Several international bodies are dedicated to developing
acceptable standard standards for communicating on the
network. These include,
 IEEE: Institute of Electrical and Electronic Engineers
(www.ieee.org)
 IETF = Internet Engineering Task Force (www.ietf.org)
 ITU: International Tele Communications
Union(www.itu.int).
 ANSI= American National Standards
Institute(www.ansi.org).
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Network protocols
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 There are many protocols currently in use for various
purposes such as:
 LAN access methods


Ethernet
Token ring
 TCP
 IP
 SMTP and many more.
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Access Control Methods
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 A LAN Access method describes how the
devices access the network and share the
transmission facilities
 Two primary access control methods exist
for computers to communicate with each
other over the network
 Token
based access
 Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)

Other methods will be explored in computer Networks
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Ethernet
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 Ethernet is one of the most common and
widely used network protocols that uses
methods known as
1. Carrier Sense Multiple Access with
Collusion Detection (CSMA/CD).
2. Carrier Sense Multiple Access with
Collision Avoidance (CSMA/CA).
BIT 1102: Communications Technology & the Internet
Carrier Sense Multiple Access(CSMA)
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 Multiple Access
 Any of the network devices can transmit data onto the
network at will; there is no central controller
 A broadcast network where all stations see all frames,
regardless of whether they represent an intended
destination
 Each station must examine received frames to determine if
the station is a destination. If so, the frame is passed to a
higher protocol layer for appropriate processing.
 Carrier Sense
 Before sending data, stations listen to the network to see if
it is already in use. If in use, the station wishing to transmit
waits, otherwise it transmits
BIT 1102: Communications Technology & the
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CSMA/CD
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 In this method, the computer “listens” to the
network before transmitting. If the network is
clear, the computer / node sends the
transmission.
 Sometimes
when using CSMA/CD, two
computers may begin transmitting at the same
time. When this occurs, there is data collision and
both computers back off and wait for a random
time to re-transmit. The delay however is minimal
and does not greatly affect the network speed.
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Ethernet cont’d
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 Ethernet protocol runs on topologies such as
Bus, tree and star. Fiber optic, Coaxial,
wireless and twisted pair are the main
channels supported by Ethernet at speeds of
10Mps .
 (Fast
Ethernet and Gigabit Ethernet
transmit at 100Mps and 1000 Mps
respectively)
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ii) Carrier Sense Multiple Access with
Collision Avoidance
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 Unlike CSMA/CD,
Carrier Sense Multiple access
with Collision Avoidance (CSMA/CA) involves
listening in to the network in order to “avoid”
collisions.
 In
CSMA/CA, before any actual transmission
occurs, the sender must broadcast an intension to
transmit, and only transmits when the network is
clear. If the network is busy, the sending computer
withdraws the transmission and re-broadcasts after
a pre defined interval.
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ii) Carrier Sense Multiple Access with
Collision Avoidance
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1. Sender send a request-to-send (RTS) frame to
receiver and indicates the time needed to
complete data transmission
2. Receiver send clear-to-send (CTS) frame,
indicates time to complete data transmission
and reserves channel for the sender
3. Sender transmits the data and receiver responds
with an ACK frame, ensuring reliable
transmission
4. RTS and CTS frames let other stations know of
the data transmission so that collision is avoided
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CSMA/CA cont’d
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 Local
talk protocol developed by Macintosh
computers is an example of a protocol that uses
CSMA/CA.
 CSMA/CA is also used on networks where by the
medium of transmission does not allow for collision
detection.
 In wireless LANs, for example, not all stations may be
able to detect each other so CSMA/CD is not an
option.
 CSMA/CA transmits at lower speeds of about 230kb/s
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Token Ring
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 How
does
Token
work?
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Ring
protocol
Token ring Explained
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 Developed by IBM, this protocol uses a special
electronic frame known as a token which is passed
from computers connected together in a logical “ring”.
 If a computer has data to transmit, the data is
attached to the token which is passed round the “ring”
until it reaches the destination. At this point, the
receiving computer captures the data and releases the
empty token.
 If the token arrives at a computer without anything to
transmit, it simply proceeds to the next computer.
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Token Ring cont’d
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 Though
once popular, the token ring
protocol has lost popularity to the Ethernet
protocol and is rarely used currently.
 Defined under IEEE 802.5.
 Token ring Networks Transmit between
4Mbps to 1GBps over twisted pair or fiber
optic cable
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FDDI
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 Developed by the ANSI, Fibre Distributed Data
Interface (FDDI) is a network protocol that
enables transmission over long distances. (It
generally connects two or more LANs) at high
speeds, mainly over fiber optic cable.
 FDDI uses Dual Ring topology using a Token
mechanism as discussed (see token ring)
 The “Dual” ring topology refers to two rings, one
of which will operate if there’s no problem on the
network. If there’s failure on the primary ring,
transmission then moves to the backup ring.
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Fiber-Distributed Data Interface (FDDI)
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 FDDI
provides a standard for data
transmission in a local area network that can
extend in range up to 200 kilometers (124
miles).
 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 (though it can use copper cable,
in which case one can refer to CDDI).
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Asynchronous Transfer Mode (ATM)
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 A highly complex network protocol that involves the
transmission of all data in packets of a fixed size (53
Bytes).
 ATM
protocols
are
connection-oriented
ie
transmission only starts when the channel is known to
be free.
 While ATM is wide spread in WANs, it has generally
failed to gain popularity as a LAN protocol.
 The MFA (Frame Relay Alliance) Forum (formerly
ATM Forum) is a Consortium regulating this protocol
(mfaforum.org)
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Internet Protocol (IP)
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 Internet protocol (IP): IP is used to transfer
data from one computer to another on a Network.
 IP is able to achieve this based on an IP address,
which is a Unique number assigned (Either
manually or automatically) to each computer on
the Network.
 IPV4 (version 4) in most use currently. IPV6 is
being migrated to in many organizations as well.
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Transport Control Protocol (TCP)
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 While IP is only concerned with delivering
data packets, the Transmission Control
Protocol (TCP) ensures reliable and accurate
delivery of the data packets across the
network.
 TCP and IP together (TCP/IP) form the
basic communication “language” or protocol
used on the Internet.
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Other Common protocols
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 Simple Mail Transfer Protocol (SMTP):
This protocol is used in sending and receiving
of Electronic mails (e-mail).
 Dynamic Host Configuration protocol:
This protocol is used to automatically assign
IP addresses to “hosts” or work stations on a
network. A DHCP server is normally
configured to perform this task.
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Other Common protocols cont’d
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 Hyper Text Transfer Protocol (HTTP):
This is a protocol used for exchanging information
on the World wide Web (www)
Its standards development has been coordinated by
the IETF and the W3C (World Wide Web
Consortium)
 Secure Socket Layer (SSL) protocol:
The predecessor to Transport Layer Security(TLS) ,
SSL is concerned with the security of a message
being relayed over a network e.g. the internet
(Security to be covered in a later chapter)
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Other Common protocols cont’d
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 The File Transfer Protocol (FTP):
Is used widely on the Internet for
transferring files to and from a remote
host.
 FTP is commonly used for uploading pages
to a Web site and for providing online file
archives.
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Thank you
BIT 1102: Communications Technology & the Internet