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Chapter # 2: lecture 3 (06-02-2013)
lecture 4 (13-02-2013)
Networks and Protocols
By:
William Stalling
Data Communication
What is a network?
The ability to connect people and equipment no
matter where they are in the world.
– telephone
– computers
– television
Networking and Its Benefits
SOHO Network
– Small Office/Home Office
– sharing of resources
• Internet
• Printer
Networking and Its Benefits Define the components of an Information network
Hosts – PCs
– send and receive information across the network
– connected to a network device
Peripherals – not directly connected to the network, but connected
to hosts
Network devices – hub, switch, router
Network media – used to connect hosts/devices
Networking and Its Benefits Clients and servers
– software installed determines the role of a client or a
server
Server software
– enables the server to provide information to other
hosts
Client software
– enables the client to request and display information
from the server
– Example: Internet Explorer
Networking and Its Benefits Build computer peer-to-peer network and verify
The ability to act as both a client and server
Network Topologies Physical topology
– created to record where each host is on the network
– shows how each host is connected (media, devices,
etc)
Network Topologies
Logical topology
– how the host uses the network
– host names, addresses, groups, applications
Communication Protocols Primary purpose of a network – to communicate
Elements of communication
– Sender (source)
• has a need to communicate
– Receiver (destination)
• receives message and interprets it
– Channel
• pathway for information to travel
Successful delivery of the message
Rules (protocols) must be followed:
– Identification of the sender or receiver
– Channel in which to communicate (face-to-face)
– Mode of communication (written or spoken)
– Language
– Grammar
– Speed or timing
Communication Protocols Encoding vs. Decoding
Encoding
– Humans
• converting thoughts into language, symbols, or sounds
– Computers
• messages converted into bits by sending host
• each bit encoded into sound, light, or electrical impulses
• destination host then decodes the signal
Decoding
– reverse of encoding
Communication Protocols Message formatting and encapsulation
Message needs a specific format
Compare to parts of a letter – Identifier (recipient)
– Salutation
– Message
– Closing
– Identifier (sender)
Encapsulation – placing the letter into the envelope
De encapsulation – letter removed from the envelope
Communication Protocols Messages have size restrictions depending on the
channel used
If the message is broken into smaller pieces, it is
easier to understand
If the message is too long or too short, will be
considered undeliverable.
Communication Protocols Timing
– when to speak; how fast or how slow
– how long to wait for a response
Access Method – determines when someone is able to send a message
– can speak when no one else is talking, otherwise a COLLISON occurs
Flow Control – timing for negotiations
– sender might transmit messages faster than the user can handle
Response Timeout – how long should you wait for a response and what action to take
Acknowledgment – may be required to ensure message was delivered
Communication Protocols Message Patterns
Unicast – single destination
Multicast – same message to a group
Broadcast – all hosts need to receive the
message
Communication Across a Local Ethernet
Network
Computers must speak the same language in order to
communicate!!
Standards in technology Standards – rules by which equipment from
different vendors operate
Benefits of standards: – Facilitate design
– Simplify product development
– Promote competition
– Provide consistency
– Facilitate training
– More vendor choices for customers
Communication Across a Local Ethernet
Network
IEEE (Institute of Electrical and Electronic
Engineers)
– maintains networking standards
– 802.3 – Ethernet standard
A breakdown of terminology
– 100 Base-T
– 100 = Speed in Mbps
– Base = Baseband transmission
– T = Twisted Pair
Communication Across a Local Ethernet
Network
Physical addressing
MAC address (Media Access Control)
Ethernet communication
– each interface has a MAC address
– each device may look at the data, but only the
interface that matches the destination MAC will
respond
The Ethernet Frame Preamble – beginning of the timing
SFD (Start Frame Delimiter) – marks the end of the timing, but beginning of the frame
Destination MAC
Source MAC
Length/Type – Length – tells which protocol receives the data
– Type – number of bytes of data
Encapsulation – packet of information
FCS (Frame Check Sequence) – checks for damaged frames
The Hierarchical Design Structure
Smaller, more manageable groups allow traffic to
remain local on the networks
Divided into three layers
– Access Layer
• connection to the hosts
– Distribution Layer
• interconnects smaller networks
– Core Layer
• high speed connection between
distribution devices
Logical Addressing
MAC vs. IP
IP Address (Logical Address)
– assigned based on where the host is located
– assigned by the administrator
Parts of an IP address
– Network – same for all hosts connected to the LAN
– Host – unique to each host on the network
Access Layer Devices
Most basic level
Made up of:
– host devices
– first line of networking devices
– hub, switch, workstations
Access Layer Device – A HUB
Accepts data signal from one port and sends it
(regenerates) out all ports
– multiport repeater
Collisions
– results in message being garbled and unreadable
– occur when two or more hosts send a message at
the same time (undesirable in a network)
NOT VERY SMART
– a hub will not recognize there is a collision and send
it all ports
Access Layer Device – A SWITCH
SMARTER THAN A HUB
dedicated bandwidth out each port
no need to share with other ports (unlike a hub)
Can forward messages to a specific host by
looking in its MAC table If destination MAC is not in its MAC table, floods the network out
all ports looking for a response
Only the host with the correct MAC address will respond
More Stuff on Switches
How does the MAC table get built?
– keeps track of frames being sent between hosts
– records the information when there is a response
Collision Domains
– each port on a switch is its own collision domain
– 8 port switch = 8 collision domains
Broadcasts
If there is only one destination MAC in a message,
how can you contact everyone else?
– send a broadcast MAC
– hexadecimal digits
– FFFF.FFFF.FFFF
Useful when hosts need to send information but
don’t know what hosts are to receive it
Switches and hubs send the broadcast out to
everyone on their network. (Broadcast Domain)
ARP Request
Sent when the sending host knows the
destination IP, but not the MAC
Will discover the MAC address of any local host
on the network
Distribution Layer Devices and Communication
Methods
Responsible for making sure local traffic stays local on the
network
Traffic destined for other networks will be passed on.
Distribution Layer Devices—The Router
Routers – directs traffic based on the destination
IP address
Routers build routing tables; switches build MAC
tables
Routers decode packets, switches decode
frames
Look only the network portion of the IP address
– finds the best path to take to get to the destination
Routers do not forward broadcasts!!!
Default Gateway
Used when a host wants to send data to a host on
a different network.
Must be set on the workstation connected to the
routing device – the router interface connected to
the PC
Types of Routing
Dynamic – information is obtained from neighboring routers
Static – manually entered by the network administrator
What happen to a message that is not in the routing table? – It is dropped unless . . .
A default route is set – “last resort” type of router
– will send it to the router it thinks may be have the destination IP
Distribution Layer Devices and Communication
Methods
LAN – Local Area Network
Under the same administrative control
Plan, Implement and Verify a Local Network
Consider the following before beginning:
– Number and type of hosts
– Applications to be run on the network
– Data and devices to be shared
– Speed requirements (bandwidth)
– Level of security
– Reliability of the network
– Connectivity requirements
Building the Network Physical environment
– temperature control
– availability/placement of outlets
Physical configuration – location of devices
– how are devices connected
– location/length of cable runs
– hardware configurations (hosts, servers)
Logical configuration – size of broadcast & collision domains
– IP addressing scheme
– Naming
– Permissions
– Sharing