- end-devices - cable - software
- intermediary devices - wireless
It is refers to hosts and it can be sender or receiver.
- Every host in the network is identified by an address so the host
( sender ) uses the address of the destination host (receiver)to send the message.
Example : PCs, IP phones, PDAs
devices provide connectivity in the network, ensure that data flows across the network and connect end devices or networks .
Example:
- network access devices ( Hubs, switches, wireless pointes)
- internetworking devices (routers)
-communication servers and modems
-security devices (firewall)
-
Functions :
Regenerate and retransmit data signals
-
Maintain information about what pathways exist through
the network and internetwork
-Notify other devices of errors and communication failures
-Direct data along alternate pathways when there is a link failure
-
Classify and direct messages according to QoS priorities
-
Permit or deny the flow of data, based on security settings

A collision domain ; is a section of network where packet collisions can occur if two nodes attempt to communicate at the same time
A broadcast domain : includes all of the hosts that a broadcast frame transmitted by a single host can reach.
All hosts in a broadcast domain share a common Layer 3 network address.
In TCP/IP terminology this means that they are on the same subnet.
Hub it used to connect computers on a network so as to communicate with each other.
Ea ch computer plugs into the hub with a cable, and information
sent from one computer to another through the hub.
A hub do not read any of the data passing through it and
can't identify the source or destination of the information it receives,
so it sends the information to all of the computers connected to it, including the
one that sent it.
-A hub can send or receive information, but it can't do both at the same time.
Hubs are classified as Layer 1 (physical layer) devices in the
OSI model
Switch
It is a small hardware device that joins multiple computers together within one local area network (LAN). witch divides a LAN so that each host has its own segment.
A twisted pair cable with RJ45 connectors connected to ports on a switch.
A switch can have as many as 96 ports.
Switches filter traffic based on MAC address. A unicast frame will only be
forwarded to the port that connects to the host with the destination MAC
address. To hosts on all other ports of the switch, it appears as though there is no network traffic.
Only when two separate hosts attempt to communicate with the same third host
do collisions occur.
Switches learn which MAC addresses are associated with particular ports by noting source addresses as frames enter the switch
Broadcast frames are forwarded to all ports of a switch.
Hubs are classified as Layer 2 (data link layer) devices in the
OSI model
Router

Routers are used to move packets from one broadcast domain to another and it manage traffic at layer 3.
- router use destination IP address to decide where to send packets .
routing tables , inform routers of the location of other networks.
- it can be ( static router ) or ( dynamic router ).
A -routing protocol is a protocol that specifies how routers communicate with each
Other disseminating information that enables them to select routes then any two
nodes on a computer network (e.g. RIP, OSPF, IGRP).
Proxy server
-A proxy server is an intermediary between Clients and Internet as NAT
router
-It operates at an application Layer
What happen with unregistered client
Unregistered clients whose have not public IP address sends their internet access request to the Proxy serve
The proxy server sends identical request to server on the Internet
As the proxy receives response from the Internet server, it forwards back to the requested clients on the unregistered network it is functions
-A pr oxy server is an intermediary between Clients and Internet as NAT router
-It supports all major applications on the Internet
-
It enables administrator to exercise significant control of all downloads or uploads of clients over the Internet
It enables large numbers of unregistered network to access the
Internet or registered networks
-It provide high degree of protection of the private network and represent
a secured Firewall to protect the private network s when it access the Internet
Modem
-
A modem is a device for making an analog connection between computers over a telephone line, effectively making a WAN connection between computers or networks
Types of modems:
DSL Cable Modem function bandwidth
Uses phone lines that
deliver voice services not shared transmits signals to/from Internet
points using broadband
Cable TV network shared media access
bandwidth

LECTURE 6
What is a network design
Traditional design New design based on a set of general rules QoS and functionalities
focused on capacity planning Refer to plan, design and
Implementation
Design requirements time
(have specified reliability) (specified capacity) (specified delay requirements)
__________________________________________________________
Mission-critical applications controlled-rate applications real-
Network Design Goals
__________________________________________________________
Scalability Adaptability CostControl
ability to address the needs accommodate new services without Financial
an increasing number of users significant considerations
Logical design: refers to logical layout. It is show IP address associated with each part of the network.
-Physical design: refers to physical layout of network.( cables, switches)
-Routing: it is refers the way of forwarding the packets between network sections. It based on routing table also it routing protocols with transport protocols (TCP/IP) that assigned to the phase.
-Addressing: determine the private and public IP and also subnet classes.
-Simulation: evaluate the performance of design topology in simulation phase.
-Implementation and Test: refers to real-time hardware and software implementation , testing and evaluation .

Network services
What the network can provide to user
__________________________________________________________
Social network service cloud computing
-online services
-site that focuses on building and reflecting of social network or relation among people
-examples : e-banking, ecommerce, e-learning
-internet-based computing whereby shared resources, software and information are provided to computers or devices on demand.
-example: electricity grid
Network services
Defined as a levels
__________________________________________________________
Performance functions
( capacity, delay, reliability) (security, accounting, billing)
Services performance requirement
__________________________________________________________
Reliability capacity delay