What are the differences between bridges and repeaters?

Bridges and repeaters are both important devices in the field of telecommunications and computer networking. In this article we discuss about these two and differences between them. 

- The repeaters are deployed at the physical layer whereas one can find bridges at the MAC layer. 

- Thus, we called repeaters as the physical layer device. 

- Similarly, bridge is known as the MAC layer device. 

- Bridge is responsible for storing as well forwarding the data packets in an Ethernet.

- Firstly, it examines the header of the data frame, selects few of them and then forwards them to the destination address mentioned in the frame. 

- Bridge uses the CSMA/CD for accessing a segment whenever the data frame has to be forwarded to it.

- Another characteristic of a bridge is that its operation is transparent. 

- This means that the hosts in the network do not know that the bridge is also present in the network. 

- Bridges learn themselves; they do not have to be configured again and again. 

- They can be simply plugged in to the network. 

- Installing a bridge causes formation of LAN segments by breaking a LAN. 

- Packets are filtered with the help of bridges. 

- The frames that belong to one LAN segment are not sent to the other segments. 

- This implies separate collision domains are formed. 

The bridge maintains a bridge table consisting of the following entries:

1. LAN address of the node
2. Bridge interface
3. Time stamp
4. Stale table entries

- Bridges themselves learn that which interface can be used for reaching which host. 

- After receiving a frame, it looks for the location of the sending node and records it.

- It keeps the collision domains isolated from one another thus, giving the maximum throughput. 

- It is capable of connecting a number of nodes and offer limitless geographical coverage. 

- Even different types of Ethernet can be connected through it. 

- Even the repeaters are plug and play devices but they do not provide any traffic isolation. 

- Repeaters are used for the purpose of regenerating the incoming signals as they get attenuated with time and distance. 

- If physical media such as the wifi, Ethernet etc. is being used, the signals can travel only for a limited distance and after that their quality starts degrading. 

- The work of the repeaters is to increase the extent of the distance over which the signals can travel till they reach their destination. 

- Repeaters also provide strength to the signals so that their integrity can be maintained. 

- Active hubs are an example of the repeaters and they are often known as the multi-port repeaters. 

- Passive hubs do not serve as repeaters. 

- Another example of the repeaters are the access points in a wifi network. 

- But it is only in repeater mode that they function as repeaters. 

- Regenerating signals using repeaters is a way of overcoming the attenuation which occurs because of the cable loss or the electromagnetic field divergence. 

- For long distances, a series of repeaters is often used. 

- Also, the unwanted noise that gets added up with the signal is removed by the repeaters. 

- The repeaters can only perceive and restore the digital signals.

- This is not possible with the analog signals. 

- Signal can be amplified with the help of amplifiers but they have a disadvantage which is that on using the amplifiers, the noise is amplified as well. 

- Digital signals are more prone to dissipation when compared to analog signals since they are completely dependent up on the presence of the voltages. 

- This is why they have to be repeated again and again using repeaters. 

What are different tips for testing GUI on smart devices?

WHAT ARE SMART DEVICES?
- Smart devices are most popularity gaining devices in today’s world.
- Though being a small cordless electronic device, it is capable of serving us many purposes.
- It is highly portable and can be connected anywhere to a network like 2G, 3G, 4G, Wi-Fi etc.
- You can have a voice and video communication and browse internet.
- Smart devices in the coming years are going to outnumber many other devices like cell phones and laptops.
- These devices exhibit quite appraisable artificial intelligence and ubiquitous computing factors.

But, what makes these smart deices so popular among users except their features?
It is their user friendly GUI (graphical user interface).
- The abstraction feature of the OOP is employed here in hiding the interactions between the user and the computer.
- These devices are able to optimize themselves according to the environment in which they operate.
- To some extent these devices are self governed.

GRAPHICAL USER INTERFACE ON SMART DEVICES
- The GUI of these devices is vigorously tested to maintain the standard.
- GUIs are a bridge between the software system and the user.
- When agitated, the interface responds to the user’s activity like click or mouse movement.
- GUI makes it easy to implement the software code and also for users to interact with the device.
- GUIs form a major percentage of the program code.
- A lot of time is devoted in developing graphical user interface and testing it. - GUIs account for the usability of the device.
- The current GUI testing methodologies are mostly manual and ad hoc in nature.
- The tools used for GUI testing record the test case execution and captures screen shots during testing.
- The recorded sessions are played again and the input test data is manipulated. - This methodology requires a large effort.

Here we are going to discuss some tips regarding GUI testing of smart devices.

- The effectiveness of GUI testing depends on the ability of the tester to develop new interactions between the user and the software.
- The best advice for graphical user testing will be to use an automated test generating tool.
- This will save you much time and effort.
- Before using an automated test generator, you should code for all possible interactions.

Even though the automated test generator provides a great help, there are many decisions that it misses out.

To compensate for this, the better option is to release the beta copy of the GUI and let the users test it and give you the feedback. More the number of testers, more effective will be the testing.

Here we are listing some tips for making GUI testing more effective:

- Having a defined coverage criterion will make it easy for you to decide what to test first.

- Prepare documentation for the test cases that have to be executed. In this documentation, define the test input data to be used for each test case. The input test data should be related to the requirements specifications of the software system.

- Compare the actual output with the expected output and decide what can be done to get the desired output if the two don’t match.

- After you have predicted the outputs for the test cases, execute them one by one and verify the output.

- Most importantly ask yourself questions like:

a) “how to improve the interaction of the user and the system?”
b) “how to make it easier for the user to access various features of the device through GUI”, “what are the possible where bugs can be found?”
c) “is this GUI compatible with the environment in which it is to be used?”
d) “what are the features that should be compulsorily incorporated in to the GUI?”.

Overview of LocalTalk Protocol

LocalTalk refers to the physical networking -- that means the built-in controller in many Apple computers, the cables and the expansion cards required on some systems. The "official" Apple cabling system typically uses a "bus topology" where each device in the network is directly connected to the next device in a daisy chain. The illustration on the Farallon book cover below gives an idea of how a bus looks.
Ethernet is the most-used method of Macintosh networking and all new Macs sport an Ethernet port, but the longevity of Macs mean there's still a bunch out there with serial ports (i.e., LocalTalk support) but no Ethernet. New iMacs and G4s lack serial ports, so can't network directly with older LocalTalk Macs and printers.

LocalTalk implementation utilized the Mac's RS-422 printer port with twisted-pair cabling and 3-pin DIN connectors. Systems were daisy-chained together and required adapters to work with the Mac's onboard DB-9 or 8-pin DIN connectors. LocalTalk provided a fairly speedy 230.4 kbps networking speed, very useable for file sizes and traffic levels of the day - compare this to the still used 56 kbps modem.

A variation of LocalTalk, called PhoneNet used standard unshielded twisted pair telephone wire with 6 position modular connectors (same as used in the popular RJ11 telephone connectors) connected to a PhoneNet transceiver, instead of the expensive shielded twisted-pair cable. In addition to being lower cost, PhoneNet-wired networks were more reliable due to the connections being more difficult to accidentally disconnect.
A LocalTalk-to-Ethernet Bridge is a network bridge that joins the physical layer of the AppleTalk networking used by previous generations of Apple Computer products to an Ethernet network. Some LocalTalk-to-Ethernet Bridges only performed Appletalk bridging. Others were also able to bridge other protocols. For example: TCP/IP in the form of MacIP.

Transparent Bridging

Transparent bridges are devices which connects more than one network segments with other bridges to make all routing decisions.Transparent bridges are sometimes called learning bridges. When they are turned on and receive data packets from a network segment they:
- Learn the relation between MAC address and segment/port, and
- Forward the packet to all other segments/ports.

There are two types of Transparent Bridge Modes:
- Store-and-Forward: Stores the entire frame and verifies the CRC before forwarding the frame. If a CRC error is detected, the frame is discarded.
- Cut-Through: Forwards the frame just after it reads the destination MAC address without performing a CRC check.

Transparent bridges are so named because their presence and operation are transparent to network hosts. When transparent bridges are powered on, they learn the workstation locations by analyzing the source address of incoming frames from all attached networks.

How Transparent Bridging Operates ?
The bridge uses its table as the basis for traffic forwarding. When a frame is received on one of the bridge’s interfaces, the bridge looks up the frame’s destination address in its internal table. If the table contains an association between the destination address and any of the bridge’s ports aside from the one
on which the frame was received, the frame is forwarded out the indicated port. If no association is found, the frame is flooded to all ports except the inbound port. Broadcasts and multi casts also are flooded in this way.
Transparent bridges successfully isolate intra-segment traffic, thereby reducing the traffic seen on each individual segment. This is called filtering and occurs when the source and destination MAC addresses reside on the same bridge interface.

Benefits of Transparent Bridging :
Transparent bridging can deliver many benefits including more efficient usage of finite network resources, improved responsiveness, reduced wait delays, fewer network errors resulting from collisions, plug ‘n’ play installation capabilities, reduced administrative managed requirements and overheads, superior network bandwidth allocation, reduced instances of the deleterious effects of broadcast storms, loop and redundancy issues.

Network Bridging

Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing, bridging makes no assumptions about where in a network a particular address is located. Instead, it depends on flooding and examination of source addresses in received packet headers to locate unknown devices. Once a device has been located, its location is recorded in a table where the MAC address is stored so as to preclude the need for further broadcasting. The utility of bridging is limited by its dependence on flooding, and is thus only used in local area networks.
A network bridge is a device which connects two parts of a network together at the data link layer (layer 2 of the OSI model).

Situations Where Bridging Is Appropriate :
- Connecting Networks.
- Filtering/Traffic Shaping Firewall.
- Network Tap.
- Layer 2 VPN : Two Ethernet networks can be joined across an IP link by bridging the networks to an EtherIP tunnel or a tap(4) based solution such as OpenVPN.
- Layer 2 Redundancy : A network can be connected together with multiple links and use the Spanning Tree Protocol to block redundant paths.

Advantages :
- Self-configuring.
- Isolate collision domain.
- Reduce the size of collision domain by micro segmentation in non-switched networks.
- Transparent to protocols above the MAC layer.
- LANs interconnected are separate, and physical constraints such as number of stations, repeaters and segment length don't apply.
- Helps minimize bandwidth usage.

Disadvantages :
- It does not limit the scope of broadcasts.
- It does not scale to extremely large networks.
- Buffering and processing introduces delays.
- Bridges are more expensive than repeaters or hubs.

Bridges - Basic Hardware Component

A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments.A network bridge connects multiple network segments at the data link layer (layer 2) of the OSI model. Bridges do send broadcasts to all ports except the one on which the broadcast was received.

Bridges inspect incoming traffic and decide whether to forward or discard it. Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges, though, support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.

Bridges come in three basic types:
- Local bridges: Directly connect local area networks (LANs)
- Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
- Wireless bridges: Can be used to join LANs or connect remote stations to LANs

Today, bridges are slowly but surely falling out of favor. Ethernet switches offer similar functionality; they can provide logical divisions, or segments, in the network. In fact, switches are sometimes referred to as multi-port bridges because of the way they operate.

Quick Tech Tip: InterNetworking

What are we talking about ? The interconnection of two or more networks, usually local area networks so that data can pass between hosts on the different networks as though they were one network. This requires some kind of router or gateway to facilitate the process of interconnecting two or more individual networks to facilitate communications among their respective nodes. Note: The interconnected networks may be different types. Each network is distinct, with its own addresses, internal protocols, access methods, and administration.
For different networks to interact, devices such as repeaters, bridges, routers, gateways are required. Repeaters are low level devices that just amplify or regenerate weak signals. They are needed to provide current to drive long cables. They copy individual bits between cable segments.
Unlike repeaters, bridges are store and forward devices. A bridge accepts the whole frame and passes it to the data link layer where the checksum is verified. Then the frame is sent down to the physical layer for forwarding on a different network.
Multiprotocol routers are conceptually similar to bridges, except that they are found in the network layer. They take incoming packets from one line to another, just as all routers do, but the lines may belong to different networks and use different protocols.
Transport gateways connect byte streams in the transport layer. Application gateways connects two parts of an application in the application layer.
When a gateway is between two WANs run by different organizations in different countries, the gateway is ripped apart in the middle and the two parts are connected with a wire.