Download network cards

COMP1321
Digital Infrastructure
Richard Henson
February 2016
Week 15: LANs

Objectives
– Explain functions of client-server networks
and network services
– Define networking standards
– Relate Lower OSI layers to technologies
and naming systems
The Client-Server Model

Centralisation of organisational
resources
– client can still hold resources
» a lot (fat client)
» Not much (thin client)

Microsoft model: called a domain
Request and response
1. All network users use clients
2. Client requests information…
2. Server processes the request, sends a response
back to the client
CLIENT
Client
Program
SERVER
REQUEST
RESPONSE
Send Request
Read Results
Server
Program
Process Request
Send Back Results
Networks need
management…

Two types emerged
– Client-Server Networks
» networked computers either clients or servers
– Peer-Peer Networks
» networked computers all of equal status
Requirements of
organisational networks

The server would be expected to offer
the following to its users:
– Network Access
– Access to “restricted” files
» users with permission directly access files on
the server
– Applications
– Printing
– Access to email & The Internet
Servers in Larger Networks

To fulfill multiple requirements, larger
networks have MANY servers
– University ITS network: at least 50

Functions can be distributed servers e.g:
– Login Server
– File and Print server
– Applications Server
– Internet Gateway
Login Servers
(the most crucial!)

Dedicated to logging on users
– database of usernames/passwords

Only allows a potential user to access the
network if both username and password
exactly correspond with entries in the
database
– in Windows networks known as Domain
Controllers
Peer-Peer networks
Also known as workgroups
 No central server
 Computer nodes can act as both clients
and servers
 No expensive powerful machine
dedicated to providing services

Peer-Peer networks

All users:
– have their own local storage capacity
– bear the following responsibilities…
» local security & network administration
» granting access to their computer’s services and
resources via the network
Advantages & disadvantages
Client-Server v Peer-peer

In groups…

don’t look at next
slides… yet!
Advantages of a client-server
network v workgroup

Centralised:
– security
– access to resources
– network administration

With more than about 10 users, much
easier to manage than a workgroup.
Can handle up to thousands of users
Disadvantages of client-server,
compared to a workgroup

Expensive:
– dedicated computer(s) not accessible to
users
– server operating system needed
– network management required
Reduces user autonomy
 If one server, and it goes down, the
network ceases to function!!!

Windows Networks

Peer-peer networks:
– workgroups
– limited resource sharing ability

Client-server networks:
– domains
– access to domain via domain controller(s)

Enterprise networks
– multiple domains logically linked in a hierarchy
Virtual (client) and Cloud
(server) Networks

Extension of client-server model…
– client-end less resource intensive
– most of resources & processing at
server end

Popular because clients need less
CPU power & less maintenance
– therefore lower cost…
Thin Client/Cloud v
conventional Local LAN
Advantages and disadvantages?
3 minutes….
What makes up a LAN (1)?

Hardware:
– computers and other network end devices
» e.g. printers, web cameras
– transmission media, e.g. cable, radio
waves
– network cards, and intermediate devices
which link the network devices to the
transmission media
What makes up a LAN (2)?

Software to (just a sample…)
–
–
–
–
–
send/receive data
provide an even flow of data between devices
make sure sent data goes to the right place
provide a path for data through the network
make sure data is checked for corruption as it
passes through the network
– anything else that may need to be done to the
data e.g. formatting, compression, encryption
Transfer of data
through LANs (1)

All done through electrical signals


Medium/media transport(s) the signals
– insulated copper wire (cheap but effective)
– fibre optic cable (expensive, high volume)
– wireless (microwaves that are sent out a
specific frequency)
Transfer of data
through LANs (2)

Cables designed from the start to
transmit high volumes of digital data

Network cards provide the computermedium interface:
– control flow rate and error checking of data
– send/receive data at high, and even
higher… speeds
Network Media

3 main types:
– standardised copper cabling
– standardised optical fibre cabling
– “wifi” (wireless: e/m radiation of a standardised
frequency)

If a cabled LAN connection exceeds:
– 100 metres (twisted pair cabling)
– 185 metres (coaxial cabling – rarely used now)
– then a repeater (booster) is needed
Network Adaptors

Generally fit inside the computer:
– either as a separate card
– or on the motherboard…
– have their own unique “MAC address”
– use own software (firmware)
» work with other connectivity software to
control the sending and receiving of data
Network Software

On a peer-peer network, connectivity
software is all that is needed…

If network is client-server…
– complex “server” software is needed at the
server end
– “client” software as peer-peer at the client
end
Client-Server Networks

A client requests services from a server
Client-server interprocess communication
(IPC) fast and reliable

Types of clients:

– computer workstation (“fat” client)
– computer with limited local storage and processing
(“thin” client)
– printer with processing ability
Workstations

Designed to work with other computers on
a peer-peer network
– include the basic networking software
required:
» to allow connection to the network structure
» to communicate effectively with other network nodes

All computers in a peer-peer network are
workstations
Servers

High-powered computers
– high storage capacity
– a lot of memory

Provide network services which are access by
users through clients
– requires highly specialized software collectively
called a Network Operating System (NOS)
Servers in small networks

Scenario: a single server is the central
controlling point

The server also looks after security on the
network:
– only allows valid users to log on
– only allows access to resources for users that
have logged on
– stores appropriate “user rights” for access to its
files and directories
Network Layer
User Specifies
Service
Transport
Layer
Network
Service
Network
Layer
Network provides
Service
Network layer service definitions
Data Link Layer



Responsible for error free transmission, using data
frames
A frame is a basic unit for network traffic, and has a
highly structured format
Mechanism:
– data from the upper layers (ie the network layer) is converted
by the data link layer into frames
– groups raw data bits received via the physical layer into
frames, for passing on to the upper layers
– may include an error recovery mechanism and also a flow
control mechanism, although this may be done at the
transport layer

Bridges operate up to this level
Physical Layer





Responsible for communicating with the network
media
Bits are converted into electrical signals and vice
versa
Issues include modulation of signals and timing
Manages the interface between a computer and the
network medium, but cable type and speeds of
transmission are deliberately omitted to allow future
technology to be easily included
Repeaters work only at this level
Network Hardware
Nodes: computers/ other intelligent
devices with MAC addresses
 Repeaters: boost weak digital signals
 Hubs: link devices through a cabling or
wireless system

– most hubs are also repeaters

Bridges
– OSI level 2 devices that can process and
filter the data in various ways, whilst hubs
just send it on
More Network Hardware

Switches
– OSI level 2/3 devices
– also used to set up virtual LANs

Routers
– Level 3 devices with routing protocols for
network/Internet packet routing

Gateways/Firewalls
– Level 4-7 devices with software allowing
conversion between protocols & control of
services
IEEE 802 Specifications and
Layers 1&2 of the OSI model

Emerged from IEEE/OSI meeting: February ‘80
– applied mainly to lower level OSI layers (1/2)
– found it necessary to extend the data link layer into
two parts
– Essential for development of LANs

Definitions used by manufacturers for hardware
and software of network interface cards
– origin of the MAC address…
Effect of IEEE 802
on the OSI model

To cover engineering issues, IEEE
divided the Data Link Layer into two sublayers:
– Layer 2 (upper): Logical Link Control –
IEE 802.1 & 802.2
– Layer 2 (lower): Media Access Control –
IEEE 802.3, 4, 5, 11, 12, etc.
Layer 2 (upper)
Logical Link Control

Focuses on IEEE 802.1 & 802.2

Controls transfer of data to the network layer

Uses logical interface points called SAPs
(service access points)
Layer 2 (lower)
Media Access Control

Direct communication with the network card
– provides packets with MAC address



Focuses on IEEE 802.3, 4, 5, 11, 12…
Provides shared access for multiple network
interface cards to the physical layer
Responsible for ensuring error-free
communication across the network
OSI layer software and
Network cards


Layer 1 and 2 software supplied with the
network card
– card itself should contain software (on ROM)
that conforms to one of the sixteen IEEE 802
specifications
Cards for wired connections have connectors
for cables:
– usually IEEE 802.3
– more rarely… IEEE 802.5

Wireless Cards
– usually based on IEEE802.11
“Binding” Network Card Software

OSI Level 3
software
binding

OSI Level
1/2
software

Data received by the
network card needs to be
passed on to level 3
software
Normally held on the
computer hard disk
Configuration:
– level 2 software needs to
combine with level 3
– achieved through “binding”
IP addresses

For packets to move between devices, each
device must have an IP address
– e.g. 192.168.2.22

Three ways to allocate an IP address:
– manually… just type it in
– from DHCP server (between fixed range)
– Through autoconfig (randomly allocated from a
range of IP addresses)
Switches and IP addresses
Switches (and routers) link devices together
 By default, a switch will create a virtual
LAN (VLAN)

– allows communication between devices on
same subnet (e.g. 192.168.1.0-255)
– fine for small networks
– regular cause of lack of connectivity!
Configuring Switches
Come with default configurations for
VLANs
 May need changing…
 IP address needs to be consistent with
devices being connected

– need IP addresses on the same subnet
Check your PC’s IP address
Access the Windows CLI
 Type ipconfig

Where has IP address come from?
 What is the IP address that it connects to?
 Is it on the same subnet?

Practical… LANs
connectivity with Switches
Simulation
Using Packet Tracer
after the break…