Networking concepts – part 1

Networking concepts – part 1

Types of networks

  • LAN – Local area network
    • All users must be trusted
    • Owned by a single entity
  • MAN – Metropolitan area Network
    • City/town-wide network
    • hospitals / corporation offices
  • WAN – Wide area network
  • Internet
  • PAN – Personal area network

Physical and Logical topologies

Physical topologies

How the network is connected together? via cables or wireless

Types of physical topologies

Bus topology
  • All systems are attached to the same cable segment.
  • Rarely used today because of fault tolerance, poor reliability, poor traffic isolation capability and limited scalability.
  • It’s very hard to secure because all devices can see all the traffic.
Ring topology
  • Each system has two connections to the network.
  • The system transmits a message from one side, receives from the other one.
  • Not secure, messages are going for a full loop until it reaches destination.

Star topology

  • The most commonly used topology today.
  • All systems are connected to a central device (hub or switch).
  • Sender –> Center Point –> Receiver
  • A switched star network is the only topology that can prevent other users from eavesdropping on traffic sent between two hosts.

Logical Topologies

These protocols are responsible for making sure that a signal sent by a system finds its way to its destination.

There are two general ways systems can communicate on a network:

  • Shared segment (Ethernet)
  • Allocated time (Token ring)

Ethernet

  • Layer 2 protocol.
  • Only one should be transmitting a frame (a chunk of data) at a time.
  • Collisions happen when multiple systems are transmitting simultaneously.
  • A collision occurs can cause both signals to fail and require systems to re-transmit their frames again.
  • CSMA/CD Protocol (Carrier Sense Multiple Access/Collision Detection)

Token ring and FDDI

  • Not so popular

Token ring

Token Ring

FDDI

FDDI_Dual_Token_Ring

fddi_basic2

Asynchronous Transfer Mode (ATM)

Establishing a channel for each connection allows ATM to provide Quality of Service (QoS). When setting up a virtual circuit, switches along the path can be requested to allocate the desired amount of bandwidth ” I need 1MB to support a video conference, Do you have that much available?” If the answer is “Yes” then a virtual circuit is created, if the answer is “No” we search for another switch.

  • Expensive to set up.
  • Not frequently used on LANs.
  • Good fit for a network that needs low-latency traffic such as video streaming.
  • Connection-oriented, so before systems can communicate, they must establish a virtual-circuit connection between them.
  • The virtual circuit is torn down at the end of the connection.
Types of ATM
  • PVC (Permanent Virtual Circuit)

PVC is set up in advance usually manually.

  • SVC (Switched Virtual Circuit)

Is established automatically on the fly

Wan Technologies

  • Point to point communication over a dedicated line.
  • high cost.
  • Confident as you run solely on the line.

Allowing n sites to directly communicate with each one another would require n+1 links. In such a situation it’s better to use Packet-Switched technology. e.g Frame Relay

Frame Relay

It’s a wan technology similar to Ethernet and Token Ring in that it’s based on packet switching.

Lowering the costs of the WAN instead of using dedicated direct links between sites, you will use the Frame Relay Cloud.

MPLS (Multi-protocol Label Switching)

  • Layer 2.5 in the OSI model.
  • Supports IP traffic including IPv6, VoIP, IP Video.
  • Used as a replacement for Frame Relay and ATM.

ISDN, DSL, Cable Modems

  • Connecting throw telephone companies and ISP (Internet service providers)

ISDN

  • Use the “dial-up” connection over the phone to connect to only SPID (Service profile identifier).
  • Used mainly as a backup.
  • Sometimes can connect with any remote caller, so it can be used as a backdoor.

DSL (Digital Subscriber Line)

  • High-speed network access over traditional telephone lines.
  • Operates on the regular telephone line with a different modulation frequency, so it can be used at the same time with the telephone service.

Cable modems

  • Delivered by cable television companies.
  • Using DOCSIS (Data Over Cable Interface Specification).Network design

Network design

network_design

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