Computer Network Unit 1 q what are the topologies in computer n/w ?

Unit 5
Q 1.what is X-25 network ?
Ans: An X.25 network is an older packet-switched network based on Open System Interconnection (OSI) network architecture rather than on TCP/IP architecture. It is mostly used for commercial networks. It allows WAN-to-WAN or LAN connectivity at up to 2Mbps (megabits per second), but due to heavy error-checking protocols, its effective network speed is very slow. A newer network standard known as Frame Relay is derived from the X.25 networking standard.


Q 2. What do you understand by high speed network?
Ans: "high-speed" access to the Internet, because it usually has a high rate of data transmission. In general, any connection to the customer of 256 kbit/s (0.25 Mbit/s) or greater is more concisely considered broadband Internet access.


Q 3. Role of application layer in OSI model ?

Ans: The application layer serves as the window for users and application processes to access network services. This layer contains a variety of commonly needed functions: 

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  Resource sharing and device redirection
  
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  Remote file access
  
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  Remote printer access
  
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  Inter-process communication
  
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  Network management
  
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  Directory services
  
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  Electronic messaging (such as mail)
  
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  Network virtual terminals
  

Q 4. What do you mean by FDDI ?
Ans: FDDI (Fiber Distributed Data Interface) is a set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network


Q 5. Difference between routers and gateway ?
Ans: routers send data to a specific location based on a address for the network segment. The benefit is the ability for a router to search routing tables and find the shortest path to the destination. The downside to routers is that they are protocol dependent and therefore can only route data between network segments using the same protocol. Today this is a moot because everyone uses TCP/IP and has an open architecture. This is why, for example, data can be sent between a Windows NT network and a Netware network.

Here's how a router works: When it receives a packet and sees a MAC address (hardware address) that is not on the local segment, it strips away the MAC address, looks at the IP address (software address), searches its routing table, and then sends the packet based on the IP address to the router that's connected to the segment that contains that address.

Gateways are network points that acts as an entrance to another network. On the Internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of Internet users and the computers that serve pages to users are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.

In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. A gateway is often associated with both a router, which knows where to direct a given packet of data that arrives at the gateway, and a switch, which furnishes the actual path in and out of the gateway for a given packet.

All gateways are routers, but not all routers are gateways.

Routers "route" traffic from one network to another. They can be used to connect different IP ranges/segments of larger networks together. Commonly used in wide area networks, and larger networks with multiple IP ranges spread out...such as campus networks, large enterprise companies that are spread out across several buildings, etc. You may have a building where all the pcs are 10.50.1.xxx, and another building where all the pcs are 10.50.2.xxx, and another building where all the pcs are 10.50.3.xxx. Each building would have a router that connects the building to the central part of the network..where one big router takes connections from all the other buildings (like a star-hub layout)..and makes one big network out of it...and also gives everyone internet access.

Gateways usually refer to a router that performs the job of connecting the network to the internet. It's still a router, because it's connecting one network (the private network) to another network (the internet). When you talk about home grade broadband routers, or SOHO/SMB routers..they're usually running "gateway mode" by default. You can take many consumer grade routers and configure them into "router" mode..and use them in larger networks such as described in the above paragraph. In the web administration you'll commonly find a configuration section for this.