Networking (Tutorial-7) Networking Device

Networking Device

Introduction

• Network Segments 
• NICs 
• Repeaters 
• Hubs 
• Bridges 
• Switches 
• Routers and Brouters 
• Gateways

Extending Networks

Extending Networks

Network Segments

• No exact definition, usually an area of a LAN, the cable connecting two devices 
• “The area of the network bound by bridges or switches where collisions are propagated, or the area bound by a router to prevent the propagation of broadcasts” 
• The more devices which are added to the network the more traffic – solution use a device to ‘filter’ the traffic. 
• Such a device reduces congestion, and improves overall performance .
• Dividing a network in to segments allows the majority of traffic to stay remain local.

Broadcast

• A broadcast is a signal sent by one device and read by all other devices on the network 
• Can be used to send a message to all users, may be used by network to find the identity of all the computers on the network 
• Consumes bandwidth, problem quickly becomes evident as more devices are added to the network 
• Broadcast Domain – defines the boundary of broadcasts, some devices stop a message passing through (edge of domain), others pass the message on (hubs)

Collision Domains

• Collisions occur when two or more devices transmit at the same time. 
• This causes the electrical charge of the signal to increase – a collision 
• All devices in the same collision domain cease transmitting for a random amount of time – to ensure they do not all attempt to start transmitting at the same time again 
• Network, broadcast and collision domains are no longer the same since the introduction of switches

Network Interface Card (NIC)

At source:

• Receives the data packet from the Network Layer 
• Attaches its the MAC address to the data packet 
• Attaches the MAC address of the destination device to the data packet 
• Converts data in to packets suitable for the particular network (Ethernet, Token Ring, FDDI) 
• Converts packets in to electrical, light or radio signals 
• Provides the physical connection to the media

As a destination device

• Provides the physical connection to the media 
• Translates the signal in to data 
• Reads the MAC address to see if it matches its own address 
• If it does match, passes the data to the Network Layer

Repeater

• Allows the connection of segments 
• Extends the network beyond the maximum length of a single segment 
• Functions at the Physical Layer of the OSI model 
• A multi-port repeater is known as a Hub 
• Connects segments of the same network, even if they use different media 

Has three basic functions

• Receives a signal which it cleans up 
• Re-times the signal to avoid collisions 
• Transmits the signal on to the next segment

Hub

• A central point of a star topology 
• Allows the multiple connection of devices 
• Can be more than a basic Hub – providing additional services (Managed Hubs, Switched Hubs, Intelligent Hubs) 
• In reality a Hub is a Repeater with multiple ports 
• Functions in a similar manner to a Repeater
• Works at the Physical Layer of the OSI model 
• Passes data no matter which device it is addressed to 
• This feature adds to congestion 
• Use large Hubs (24 port), or stacking them exacerbates this negative feature

Hub Features

• Type of media connection needed 
• Number of ports 
• Speed 
• Managed or Unmanaged 
• Requirement for Uplink Port ? (allows two Hubs to be connected using a patch cable – crossover cable) 
• Token Ring Hubs are known as MAUs

Bridge

• Like a Repeater or Hub it connects segments 
• Works at Data Layer – not Physical 
• Uses Mac address to make decisions 
• Acts as a ’filter’, by determining whether or not to forward a packet on to another segment
• Builds a Bridging Table, keeps track of devices on each segment 
• Filters packets, does not forward them, by examining their MAC address 
• It forwards packets whose destination address is on a different segment from its own 
• It divides a network in to multiple collision domains – so reducing the number of collisions
• Uses the Spanning Tree Protocol (STP) – to decide whether to pass a packet on to a different network segment 

Switch

• A multiport Bridge, functioning at the Data Link Layer 
• Each port of the bridge decides whether to forward data packets to the attached network 
• Keeps track of the Mac addresses of all attached devices (just like a bridge) 
• Similarly priced to Hubs – making them popular 
• Acts like a Hub, but filters like a Bridge 
• Each port on a Switch is a collision domain

Brouter

• Functions both as Bridge and a Router – hence name 
• Can work on networks using different protocols 
• Can be programmed only to pass data packets using a specific protocol forward to a segment – in this case it is functioning in a similar manner to a Bridge 
• If a Brouter is set to route data packets to the appropriate network with a routed protocol such as IP, it is functioning as a Router.

Router

• Works at Network Layer in an intelligent manner 
• Can connect different network segments, if they are in the same building or even on the opposite side of the globe 
• Work in LAN, MAN and WAN environments 
• Allows access to resources by selecting the best path 
• Can interconnect different networks – Ethernet with Token Ring 
• Changes packet size and format to match the requirements of the destination network
• Two primary functions – to determine the ‘best path’ and to share details of routes with other routers 
• Routing Table – a database which keeps track of the routes to networks and the associated costs 
• Static Routing – routes are manually configured by a network administrator 
• Dynamic Routing – adjust automatically to changes in network topology, and information it receives from other routers 
• Routing Protocol – uses a special algorithm to route data across a network eg RIP

Gateway

• Allows different networks to communicate by offering a translation service from one protocol stack to another 
• They work at all levels of the OSI model – due to the type of translation service they are providing 
• Address Gateway – connects networks using the same protocol, but using different directory spaces such as Message Handling Service 
• Protocol Gateway – connects network using different protocols. Translates source protocol so destination can understand it 
• Application Gateway – translates between applications such as from an Internet email server to a messaging server

Wireless Media

Wireless LAN or WLAN

• Wireless local area network that uses radio waves as its carrier 

Wi-Fi ("Wireless Fidelity“)

• A set of standards for WLANs based on IEEE 802.11

Wi-Max

• Emerging technology that can cover ranges up to 10 miles or more 

Satellite/Microwave

• High speed media used for longer distances and remote locations 

Advantages and Disadvantages

Repeater

• Advantages – Can connect different types of media, can extend a network in terms of distance, does not increase network traffic 
• Disadvantages – Extends the collision domain, can not filter data, can not connect different network architectures, limited number only can be used in network

Hub

• Advantages – Cheap, can connect different media types 
• Disadvantages – Extends the collision domain, can not filter information, passes packets to all connected segments.

Bridge

• Advantages – Limits the collision domain, can extend network distances, uses MAC address to filter traffic, eases congestion, can connect different types of media, some can connect differing architectures 
• Disadvantages – Broadcast packets can not be filtered, more expensive than a repeater, slower than a repeater – due to additional processing of packets.

Switch

• Advantages - Limits the collision domain, can provide bridging, can be configured to limit broadcast domain 
• Disadvantages – More expensive than a hub or bridge, configuration of additional functions can be very complex.

Router

• Advantages – Limits the collision domain, can function in LAN or WAN, connects differing media and architectures, can determine best path/route, can filter broadcasts. 
• Disadvantages – Expensive, must use routable protocols, can be difficult to configure (static routing), slower than a bridge.