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 A CONVERGED NETWORK!!!

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 Protocols

PROTOCOLS = RULES TO FOLLOW

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

Hubs And Collision Domains

Collision domain – area where the collision has

occurred.

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

Routing Tables and ARP tables

Used by routers to store information

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

Sharing Resources Main reason for networking – sharing

resources

– File sharing

– Print sharing

Consider this before sharing:

– security issues

– permissions granted

Windows XP users

– use Simple File Sharing