Networks

1
Networks

• Jay Ho
• Jeff Keenan
• Tiffany McKnight

2
What is a Network?

• A network is a series of points or nodes
  interconnected by communication paths
• A computer network allows us to easily share and
  distribute data between different machines

3
Local Area Network (LAN)

• A group of computers and associated devices that
  share a common communications line and typically
  share the resources of a single processor or
  server within a small geographic area

4
LAN Components

• Dumb Terminals a simple I/O device processing
  limited to presentation of information to screen
• X-Terminal Terminal with a few megabytes of
  memory that can handle displaying windows and
  mouse and keyboard input.

5
LAN Components

• Workstation single-user computer systems
• Range in complexity from simple personal
  computers to advanced processors with
  sophisticated graphics and vector processing
  capabilities
• Some allow many users to log in simultaneously

6
LAN Components

• Servers Provide a service to the other nodes
  shared by many users
• NFS Network File System
• Printers
• Compute Server
• E-mail
• Gateways Interface to another network

7
Accessing Terminal Services

• rlogin Remote Login
• Simple terminal protocol, used when little
  control is needed between host and client
• telnet
• Gives more customization than rlogin
• ssh Secure Socket Shell
• Encrypts commands and passwords, uses digital
  certificates for authentication

8
(No Transcript)
9
ETHERNET

• Developed at Xerox PARC in the 1970s.
• Key innovation was building a system in which a
  network node could sense when the network was in
  use.
• The technology was designed from an earlier
  network called AlohaNet.

10
ETHERNET

• All machines are connected to a central point,
  usually a hub or a switch.
• Each machine has a Network Interface Card (NIC)
  that attaches it to the network.
• The network of stations are usually connected by
  twisted pair copper wire.
• This wire is the same type of wire used in phone
  lines, but has 2 wire pairs instead of 1.

11
ETHERNET
12
ETHERNET

• Standard Ethernet uses 10baseT with a transfer
  rates of 10 Megabits per Second (Mbps).
• FastEthernet uses 100baseTX, with the transfer
  rates of 100 Mbps.
• The wire is connected to each machine with a
  RJ-45 jack.
• Each machine has a 6 byte Ethernet address.

13
ETHERNET

• To send data
• sender send message out via NIC
• HUB receives message and repeats it out on all
  Ports, so it is sent to every machine on the LAN.
• Machine to which message is address reads the
  message from the network, all others will ignore
  it.
• All the message are sent in a small group called
  packet.
• A packet is a group of bits that includes a
  header, payload, and control elements that are
  transmitted together

14
ETHERNET

• A packet is a group of bits that includes a
  header, payload, and control elements that are
  transmitted together
• You can think of a packet as one sentence or a
  group of numbers being sent at the same time.
• The payload is the part that contains the actual
  data being sent.
• The header contains information about the type of
  data in the payload, the source and destination
  of the data, and a sequence number so that data
  from multiple packets can be reassembled at the
  receiving computer in the proper order.

15
ETHERNET

• Collisions occur when 2 machines try to send data
  at the same time, and both pockets are discarded.
• In order to avoid collisions, machines has to
  always check to see if network is clear before
  transmitting.
• Even when the machine is transmitting, it has to
  constantly monitor the network to make sure its
  clear, so that no two machine will transmit at
  the same time and interfere with each other.

16
ETHERNET

• If a collision occurs, both machines wait a
  random amount of time before they try sending the
  data again.
• However, collisions can be reduced with the used
  of a switch instead of a hub.
• A switch only repeats messages to the intended
  recipient instead of to all connected machines,
  hence reducing network traffic.
• Switches are often called smart hubs.

17
TOKEN PASSING NETWORK

• Machines are organized in a logical ring.
• The Token is a special packet that is passed from
  one machine to the next on the network on a
  regular interval.
• A machine may only transmit if it has a token.

18
TOKEN PASSING NETWORK

• Each machine may only hold the token for a set
  amount of time.
• Hence, if the token doesnt reach a machine after
  Token_Holding_Timenodes, it is assumed that the
  machine holding the token has died, and the
  network resets itself and creates a new token.

19
TOKEN PASSING NETWORK

• Transmitting a message
• sender receives token
• sender transmits to next node on the ring.
• Each node that receives a message looks to see if
  it is the intended recipient.
• If so, it reads the message, else it will just
  ignore it.
• Message is then send on to the next machines in
  the ring.
• When the message gets back to the sender, the
  sender takes off the ring.

20
HARDWARE

• Conductors
• twisted pair copper wire (Category 5) 150 Mbps
• coaxial cable (BNC) 10 million bps
• fiber optic 1300 Mbps

21
HARDWARE

• Other hardware
• Network interface card (NIC)
• Hub
• Switch
• Router

22
HARDWARE

• router
• If two LANs are built around the same
  communication rules, then they can be connected
  with a router.
• A router is a more complicated device that stores
  the addressing information of each computer on
  each LAN and uses this information to act like an
  electronic post office, sorting data and sending
  it along the most expedient route to its
  destination.
• Routers send packets only to the desired
  network, reducing overall net-work traffic.

23
HUBS
24
SWITCH
25
NIC
26
ROUTER
27
Internet Protocol (IP)

• Allows Interconnection of Networks via the
  Internet
• Uniquely Identifies every machine with an IP
  Address
• Fragments data and routes it across the network

28
IP Address

• 32-bit Address, written as dotted-quad
• Example 128.163.215.165
• Certain Ranges reserved for Private Intranets
• 10.0.0.0 10.255.255.255
• 172.16.0.0 172.31.0.0
• 192.168.0.0 192.168.255.255
• IPv6 will expand to 128-bit Address

29
IP Address Classes

• Class A Large Networks
• network.local.local.local
• Class B Medium Size Networks
• network.network.local.local
• Class C Small Networks (less than 256 nodes)
• network.network.network.local

30
Net Masking

• Necessary due to shortage of Class C address
• Netmask XOR IP Address removes network part of IP
  address and leaves local address
• Example
• Netmask 255.255.255.0
• IP Address 198.93.72.146
• Host Address 0.0.0.146

31
Delivering the Data

• IP is a Connectionless Protocol
• No continuing connection between endpoints
• Data placed in IP datagram along with address
• Large data can be fragmented to be sent over
  small packet networks
• No built in error checking other than header
  checksum
• Packet routed from sender to receiver

32
IP Header Format
33
Source Host 198.93.72.146
Gateway
Router 2
Gateway
Router 1
Router 3
Gateway
Router 4
Dest. Host 128.163.215.165
34
Transmission Control Protocol

• Used to send data in the form of messages over IP
• Connection Oriented
• Uses Source and Destination IP and Port to
  identify connections
• Sender divides data into packets which are
  wrapped in an IP datagram
• Receiver re-assembles packets and delivers to
  application layer

35
TCP Packet Format
36
Transmission Control Protocol

• Built in Reliability
• Every message must be Acked
• Checksums protect against corrupted data
• Flow Control
• Prevents Sender from overloading Receiver
• Congestion Control
• Gives all users fair share of network bandwidth

37
TCP/IP Applications

• HTTP Hypertext Transfer Protocol
• FTP File Transfer Protocol
• SMTP Simple Mail Transfer Protocol
• Telnet/SSH
• DNS Domain Name Service
• Maps URLs to IP Address