Thursday, February 5, 2009

Internet Technologies and Tools - Introduction to Internet and Its Applications

CHAPTER 1
1. Explain Satellite technology for communication across large distances. [8]


Satellite Microwave
• Satellite is relay station
• Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency
• Requires geo-stationary orbit
o Height of 35,784km
• Television
• Long distance telephone
Private business networks

2. Working of Digital Subscriber lines

• Digital Subscriber Line (DSL) technology is a modem technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, such as multimedia and video, to service subscribers.
Advantages:
1. You can leave your Internet connection open and still use the phone line for voice calls.
2. The speed is much higher than a regular modem (1.5 Mbps vs. 56 Kbps)
3. DSL doesn't necessarily require new wiring; it can use the phone line you already have.
4. The company that offers DSL will usually provide the modem as part of the installation
disadvantages:
• A DSL connection works better when you are closer to the provider's central office.
• The connection is faster for receiving data than it is for sending data over the Internet.
• The service is not available everywhere
Types of DSL:

1. Asymmetric Digital Subscriber Line (ADSL)
ADSL technology is asymmetric. It allows more bandwidth downstream---from an NSP's central office to the customer site---than upstream from the subscriber to the central office. This asymmetry, combined with always-on access (which eliminates call setup), makes ADSL ideal for Internet/intranet surfing, video-on-demand, and remote LAN access. Users of these applications typically download much more information than they send. ADSL transmits more than 6 Mbps to a subscriber, and as much as 640 kbps more in both directions (shown in Figure 15-1). Such rates expand existing access capacity by a factor of 50 or more without new cabling. ADSL can literally transform the existing public information network from one limited to voice, text, and low-resolution graphics to a powerful, ubiquitous system capable of bringing multimedia, including full motion video, to every home this century.

Figure 15-1: The components of a ADSL network include a telco and a CPE.

2. Very-High-Data-Rate Digital Subscriber Line (VDSL)
VDSL transmits high-speed data over short reaches of twisted-pair copper telephone lines, with a range of speeds depending on actual line length. The maximum downstream rate under consideration is between 51 and 55 Mbps over lines up to 1000 feet (300 m) in length. Upstream rates in early models will be asymmetric, just like ADSL, at speeds from 1.6 to 2.3 Mbps. Both data channels will be separated in frequency from bands used for basic telephone service and Integrated Services Digital Network (ISDN), enabling service providers to overlay VDSL on existing services.
Figure 15-5: This diagram provides an overview of the devices in a VDSL network.




3. Working of Client/Server architecture

Client-server architectures are sometimes called two-tier architectures.
In a two tier architecture the workload is divided between the server (which hosts the database) and the client (which hosts the User Interface). In reality these are normally located on separate physical machines but there is no absolute requirement for this to be the case. Providing that the tiers are logically separated they can be hosted (e.g. for development and testing) on the same computer (Figure 1).

Figure 1: Basic Two-Tier Architecture
The distribution of application logic and processing in this model was, and is, problematic. If the client is 'smart' and hosts the main application processing then there are issues associated with distributing, installing and maintaining the application because each client needs its own local copy of the software. If the client is 'dumb' the application logic and processing must be implemented in the database and then becomes totally dependent on the specific DBMS being used. In either scenario, each client must also have a log-in to the database and the necessary rights to carry out whatever functions are required by the application

5. What does DNS stand for? What is its main purpose?

Domain Name System (or Service or Server), an Internet service that translates domain names into IP addresses. The Domain Name System (abbreviated DNS) is an Internet directory service. DNS is how domain names are translated into IP addresses, and DNS also controls email delivery. If your computer cannot access DNS, your web browser will not be able to find web sites, and you will not be able to receive or send email.
The DNS system consists of three components: DNS data (called resource records), servers (called name servers), and Internet protocols for fetching data from the servers. . Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

5. Write a note on how Domain Name System (DNS) Servers work.
When you set up your machine on the Internet, you (or the software that you installed to connect to your ISP) had to tell your machine what name server it should use for converting domain names to IP addresses. On some systems, the DNS is dynamically fed to the machine when you connect to the ISP, and on other machines it is hard-wired. If you are working on a Windows 95/98/ME machine, you can view your current name server with the command WINIPCFG.EXE (IPCONFIG for Windows 2000/XP). On a UNIX machine, type nslookup along with your machine name. Any program on your machine that needs to talk to a name server to resolve a domain name knows what name server to talk to because it can get the IP address of your machine's name server from the operating system.
The browser therefore contacts its name server and says, "I need for you to convert a domain name to an IP address for me." For example, if you type "www.howstuffworks.com" into your browser, the browser needs to convert that URL into an IP address. The browser will hand "www.howstuffworks.com" to its default name server and ask it to convert it.
The name server may already know the IP address for www.howstuffworks.com. That would be the case if another request to resolve www.howstuffworks.com came in recently (name servers cache IP addresses to speed things up). In that case, the name server can return the IP address immediately. Let's assume, however, that the name server has to start from scratch.
A name server would start its search for an IP address by contacting one of the root name servers. The root servers know the IP address for all of the name servers that handle the top-level domains. Your name server would ask the root for www.howstuffworks.com, and the root would say (assuming no caching), "I don't know the IP address for www.howstuffworks.com, but here's the IP address for the COM name server." Obviously, these root servers are vital to this whole process, so:
• There are many of them scattered all over the planet.
• Every name server has a list of all of the known root servers. It contacts the first root server in the list, and if that doesn't work it contacts the next one in the list, and so on.
Here is a typical list of root servers held by a typical name server:
; This file holds the information on root name servers
; needed to initialize cache of Internet domain name
; servers (e.g. reference this file in the
; "cache . " configuration file of BIND domain
: name servers).
;
; This file is made available by InterNIC registration
; services under anonymous FTP as
; file /domain/named.root
; on server FTP.RS.INTERNIC.NET
; -OR- under Gopher at RS.INTERNIC.NET
; under menu InterNIC Registration Services (NSI)
; submenu InterNIC Registration Archives
; file named.root
;
; last update: Aug 22, 1997
; related version of root zone: 1997082200
;
The formatting is a little odd, but basically it shows you that the list contains the actual IP addresses of 13 different root servers.
The root server knows the IP addresses of the name servers handling the several hundred top-level domains. It returns to your name server the IP address for a name server for the COM domain. Your name server then sends a query to the COM name server asking it if it knows the IP address for www.howstuffworks.com. The name server for the COM domain knows the IP addresses for the name servers handling the HOWSTUFFWORKS.COM domain, so it returns those. Your name server then contacts the name server for HOWSTUFFWORKS.COM and asks if it knows the IP address for www.howstuffworks.com. It does, so it returns the IP address to your name server, which returns it to the browser, which can then contact the server for www.howstuffworks.com to get a Web page.
One of the keys to making this work is redundancy. There are multiple name servers at every level, so if one fails, there are others to handle the requests. There are, for example, three different machines running name servers for HOWSTUFFWORKS.COM requests. All three would have to fail for there to be a problem.

January-2004 [18]
7. Explain how Domain Names are allocated with special reference to special domain names. [18]
When someone wants to create a new domain, he or she has to do two things:
Find a name server for the domain name to live on.
Register the domain name.
Technically, there does not need to be a machine in the domain -- there just needs to be a name server that can handle the requests for the domain name.
There are two ways to get a name server for a domain:
You can create and administer it yourself.
You can pay an ISP or hosting company to handle it for you. . This type of machine is called a virtual Web hosting machine and is capable of hosting multiple domains simultaneously. Five-hundred or so different domains all shared the same processor.

The COM, EDU and UK portions of these domain names are called the top-level domain or first-level domain. There are several hundred top-level domain names, including COM, EDU, GOV, MIL, NET, ORG and INT, as well as unique two-letter combinations for every country.
Within every top-level domain there is a huge list of second-level domains. For example, in the COM first-level domain, you've got:
• howstuffworks
• yahoo
• msn
To create a domain, you fill out a form with a company that does domain name registration (examples: register.com, verio.com, networksolutions.com). They create an "under construction page," create an entry in their name server, and submit the form's data into the whois database. Twice a day, the COM, ORG, NET, etc. name servers get updates with the newest IP address information. At that point, a domain exists and people can go see the "under construction" page. All of these machines run name server software called BIND. BIND knows about all of the machines in our domain through a text file on the main server that looks like this:
@ NS auth-ns1.howstuffworks.com.
@ NS auth-ns2.howstuffworks.com.
@ MX 10 mail

mail A 209.170.137.42

vip1 A 216.183.103.150
www CNAME vip1
Decoding this file from the top, you can see that:
The first two lines point to the primary and secondary name servers.
The next line is called the MX record. When you send e-mail to anyone at howstuffworks.com, the piece of software sending the e-mail contacts the name server to get the MX record so it knows where the SMTP server for HowStuffWorks is (see How E-mail Works for details). Many larger systems have multiple machines handling incoming e-mail, and therefore multiple MX records.
The next line points to the machine that will handle a request to mail.howstuffworks.com.
The next line points to the IP address that will handle a request to oak.howstuffworks.com.
The next line points to the IP address that will handle a request to howstuffworks.com (no host name).
You can see from this file that there are several physical machines at separate IP addresses that make up the HowStuffWorks server infrastructure. There are aliases for hosts like mail and www. There can be aliases for anything. For example, there could be an entry in this file for scoobydoo.howstuffworks.com, and it could point to the physical machine called walnut. There could be an alias for yahoo.howstuffworks.com, and it could point to yahoo. There really is no limit to it. We could also create multiple name servers and segment our domain.
As you can see from this description, DNS is a rather amazing distributed database. It handles billions of requests for billions of names every day through a network of millions of name servers administered by millions of people. Every time you send an e-mail message or view a URL, you are making requests to multiple name servers scattered all over the globe. What's amazing is that the process is usually completely invisible and extremely reliable!
Every name in the COM top-level domain must be unique, but there can be duplication across domains. For example, howstuffworks.com and howstuffworks.org are completely different machines.
In the case of bbc.co.uk, it is a third-level domain. Up to 127 levels are possible, although more than four is rare. Because all of the names in a given domain need to be unique, there has to be a single entity that controls the list and makes sure no duplicates arise. For example, the COM domain cannot contain any duplicate names, and a company called Network Solutions is in charge of maintaining this list. When you register a domain name, it goes through one of several dozen registrars who work with Network Solutions to add names to the list. Network Solutions, in turn, keeps a central database known as the whois database that contains information about the owner and name servers for each domain. If you go to the whois form, you can find information about any domain currently in existence.
While it is important to have a central authority keeping track of the database of names in the COM (and other) top-level domain, you would not want to centralize the database of all of the information in the COM domain. Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS. Name servers do two things all day long:
• They accept requests from programs to convert domain names into IP addresses.
• They accept requests from other name servers to convert domain names into IP addresses.
3. b) What are the essential functions that the router must perform to achieve internetworking among dissimilar subnetworks? [6]

2. b) Write and Explain the procedure for translating a domain name into an equivalent IP address. What are two performance optimizations techniques used by DNS server? [9]

Client wants IP for www.amazon.com; 1st approx:
 Client queries a root server to find com DNS server
 Client queries com DNS server to get amazon.com DNS server
 Client queries amazon.com DNS server to get IP address for www.amazon.com
DNS: distributed db storing resource records (RR)
 Type=A
– name is hostname
– value is IP address
 Type=CNAME
– name is alias name for some “cannonical” (the real) name
www.ibm.com is really
servereast.backup2.ibm.com
– value is cannonical name
 Type=NS
– name is domain (e.g. foo.com)
– value is IP address of authoritative name server for this domain
 Type=MX
– value is name of mailserver associated with name
Example: just created startup “Network Utopia”
Register name networkuptopia.com at a registrar (e.g., Network Solutions)
– Need to provide registrar with names and IP addresses of your authoritative name server (primary and secondary)
– Registrar inserts two RRs into the com TLD server:
(networkutopia.com, dns1.networkutopia.com, NS)
(dns1.networkutopia.com, 212.212.212.1, A)
 Put in authoritative server Type A record for www.networkuptopia.com and Type MX record for networkutopia.com
 How do people get the IP address of your Web site?
Questions: Name, type fields or a query
Responses: RRs in reponse to query
Authority: records for authoritative servers
Additional information: additional “helpful” info that may be used
The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map
people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.
DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record. Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times.

3. c) Explain the differences between Routing and Switching? [6]
Switching involves moving packets between devices on the same network. Conversely, routing involves moving packets between different networks. Switches operate at layer 2 of the OSI Model. A switch, also referred to as a multi-port bridge, is able to determine where a packet should be sent by examining the MAC address within the data link header of the packet (the MAC address is the hardware address of a network adapter). A switch maintains a database of MAC addresses and what port they are connected to. Routers, on the other hand, operate at layer 3 of the OSI Model. A router is able to determine where to send a packet using the Network ID within the Network layer header. It then uses the routing table to determine the route to the destination host. Routing is based upon IP address and switching is based upon hardware MAC address.

6. c) Home based Internet services can be established using analog modems, IDSN, cable modems, ADSL and hi-speed wireless links. Compare their advantages and disadvantages [8]

July-2005 [50]
1. d) Write any three features of intranet that differences it largely from Internet. [4]

Intranets have become increasingly popular in the corporate environment because they offer inexpensive, easy-to-use data access environments which are platform independent. They are defined as company-internal networks using Internet communications hardware and software and restricting communication with the Internet. Internet content is largely static, designed to please, and is not sensitive, intranet content can be sensitive or even confidential, is more dynamic, and focuses on productivity and information exchange. Comparing information delivery, network performance (bandwidth), GUI components, platform inadequacies, and interactivity further set intranets apart from the Internet. A centrally formulated corporate information policy constitutes an advantage over the Internet's unregulated structure and allows for more rapid development of networking tools. The major difference between the Internet and previous networks is that it is not owned or operated by anyone. In this sense it is an 'open' network. The Internet is huge

2. b) Explain the difference of functioning between Bridges and Routers. [6]

A bridge is a device that connects and passes packets between two network segments that use the same communications protocol. Bridges operate at the data link layer (layer 2) of the OSI reference model. A bridge will filter, forward or flood an incoming frame based on the MAC address of that frame. A router is an intelligent connecting device that can send packets to the correct LAN segment to take them to their destination. Routers link LAN segments at the network layer of the OSI Reference Model for computer to computer communications. The networks connected by routers can use similar or different networking protocols. The most popular interior routing protocol is OSPF and the most popular exterior routing protocol is BGP.
A bridge does not look at protocols and a router does. Bridges need to examine every packet whereas routers only look at packets addressed to it. Since the time involved in scanning
every packet is enormous, bridges must make use of specially designed hardware. But as bridges attempt to look deeper into each packet to perform such functions as security and access controls, their throughput will drop. As routers use faster technology (i.e. 68020) and special purpose hardware, their throughput should rise.

c) Write a short note on baseband technology and broadband technology, with a special reference to advantages and the latest status of broadband in India. [6]

A baseband transmission sends one type of signal using a medium's full bandwidth, as in 100BASE-T Ethernet. Broadband in data communications refers to data transmission where multiple pieces of data are sent simultaneously to increase the effective rate of transmission, regardless of actual data rate. In network engineering this term is used for methods where two or more signals share a medium
• Rapid loading of web pages and e-mail (as much as 100 times faster)
• Equally fast downloading of files, programs, and computer updates
• More efficient use of time online -- no more waiting for pages to load
• ...and no more dropped telephone signals!
• No need to tie up a telephone line or support the cost of a second telephone line
• An always-on connection, ready when you are to access the outside world
• The ability to easily stream video and music -- this could be a whole new experience for many people
• More efficient delivery of photos and other large e-mail attachments
• The ability to enable Vonage, Skype or other low-cost (or no-cost) voice-over-IP telephone communications systems
• Technology which enables people to work from home

3. ISDN [6]

Integrated Services Digital Network(ISDN) is a state-of-the-art Public Switched Digital Network for provisioning of different services – voice, data & image transmission over the telephone line through the telephone network. 1. Single connection can support both voice and data.
2. High quality services being digital right from subs, premises (End to End).
3. Eight terminals can be connected on a single line.
4. High speed data transfer from PC to PC is possible – 64 Kbps against existing 9.6 Kbps (6
times faster).
5. Two calls can be established simultaneously on a single pair of wires.
6. The call set time is very short (1-2 seconds).
7. A number of supplementary services are supported like in pots.
Calling Line Identification , Call Forwarding , Call Forwarding on busy signal , Call Forwarding on no reply , Call Forwarding unconditional , Advice of Charge , Terminal Portability , Multiple Subscriber Number , Closed User Group

7. a) With reference to various applications of Internet in our daily life, explain, how Internet has revolution the area of Learning? [8]

- Accessibility is one of the main advantages of e-learning courses. OHNs will be able to access courses from anywhere in the country, whereas at the moment they are only offered in a few universities, and often require expensive travel and lengthy periods away from work. This adds to the costs - which many companies are not willing to pay - resulting in a shortage of well-qualified practitioners.
- Reduced costs - see above
- Easy access to other resources, materials and subject experts
- Ability to study in own time and not within university, travel and work time constraints
- Flexible programmes that are more suited to individual needs
The internet revolution has created a new underclass of people in rural and remote areas who are being excluded from the brave new world of teleworking, virtual shopping and online public services by lack of access to technology.

b) Suppose a network uses distance vector routing. What happens if the router sends a distance vector with all 0’s(Zero)? [5]

Most routing protocols fall into one of two classes: distance vector or link state. The name distance vector is derived from the fact that routes are advertised as vectors of (distance, direction), where distance is defined in terms of a metric and direction is defined in terms of the next-hop router. For example, "Destination A is a distance of 5 hops away, in the direction of next-hop router X." As that statement implies, each router learns routes from its neighboring routers' perspectives and then advertises the routes from its own perspective. Because each router depends on its neighbors for information, which the neighbors in turn may have learned from their neighbors, and so on, distance vector routing is sometimes facetiously referred to as "routing by rumor."
Distance vector routing protocols include the following:
• Routing Information Protocol (RIP) for IP
• Xerox Networking System's XNS RIP
• Novell's IPX RIP
• Cisco's Internet Gateway Routing Protocol (IGRP)
• DEC's DNA Phase IV
• AppleTalk's Routing Table Maintenance Protocol (RTMP)

Common Characteristics
A typical distance vector routing protocol uses a routing algorithm in which routers periodically send routing updates to all neighbors by broadcasting their entire route tables.3
The preceding statement contains a lot of information. Following sections consider it in more detail.
Periodic Updates
Periodic updates means that at the end of a certain time period, updates will be transmitted. This period typically ranges from 10 seconds for AppleTalk's RTMP to 90 seconds for Cisco's IGRP. At issue here is the fact that if updates are sent too frequently, congestion may occur; if updates are sent too infrequently, convergence time may be unacceptably high.
Neighbors
In the context of routers, neighbors always means routers sharing a common data link. A distance vector routing protocol sends its updates to neighboring routers4 and depends on them to pass the update information along to their neighbors. For this reason, distance vector routing is said to use hop-by-hop updates.
Broadcast Updates
When a router first becomes active on a network, how does it find other routers and how does it announce its own presence? Several methods are available. The simplest is to send the updates to the broadcast address (in the case of IP, 255.255.255.255). Neighboring routers speaking the same routing protocol will hear the broadcasts and take appropriate action. Hosts and other devices uninterested in the routing updates will simply drop the packets.
Full Routing Table Updates
Most distance vector routing protocols take the very simple approach of telling their neighbors everything they know by broadcasting their entire route table, with some exceptions that are covered in following sections. Neighbors receiving these updates glean the information they need and discard everything else.
Routing by Rumor
Figure 4.3 shows a distance vector algorithm in action. In this example, the metric is hop count. At time t0, routers A through D have just become active. Looking at the route tables across the top row, at t0 the only information any of the four routers has is its own directly connected networks. The tables identify these networks and indicate that they are directly connected by having no next-hop router and by having a hop count of 0. Each of the four routers will broadcast this information on all links.
Figure 4.3 Distance vector protocols converge hop-by-hop.
At time t1, the first updates have been received and processed by the routers. Look at router A's table at t1. Router B's update to router A said that router B can reach networks 10.1.2.0 and 10.1.3.0, both 0 hops away. If the networks are 0 hops from B, they must be 1 hop from A. Router A incremented the hop count by 1 and then examined its route table. It already knew about 10.1.2.0, and the hop count (0) was less than the hop count B advertised, (1), so A disregarded that information.
Network 10.1.3.0 was new information, however, so A entered this in the route table. The source address of the update packet was router B's interface (10.1.2.2) so that information is entered along with the calculated hop count.
Notice that the other routers performed similar operations at the same time t1. Router C, for instance, disregarded the information about 10.1.3.0 from B and 10.1.4.0 from C but entered information about 10.1.2.0, reachable via B's interface address 10.1.3.1, and 10.1.5.0, reachable via C's interface 10.1.4.2. Both networks were calculated as 1 hop away.
At time t2, the update period has again expired and another set of updates has been broadcast. Router B sent its latest table; router A again incremented B's advertised hop counts by 1 and compared. The information about 10.1.2.0 is again discarded for the same reason as before. 10.1.3.0 is already known, and the hop count hasn't changed, so that information is also discarded. 10.1.4.0 is new information and is entered into the route table.
The network is converged at time t3. Every router knows about every network, the address of the next-hop router for every network, and the distance in hops to every network.
Time for an analogy. You are wandering in the Sangre de Cristo mountains of northern New Mexico—a wonderful place to wander if you aren't lost. But you are lost. You come upon a fork in the trail and a sign pointing west, reading "Taos, 15 miles." You have no choice but to trust the sign. You have no clue what the terrain is like over that 15 miles; you don't know whether there is a better route or even whether the sign is correct. Someone could have turned it around, in which case you will travel deeper into the forest instead of to safety!
Distance vector algorithms provide road signs to networks.5 They provide the direction and the distance, but no details about what lies along the route. And like the sign at the fork in the trail, they are vulnerable to accidental or intentional misdirection. Following are some of the difficulties and refinements associated with distance vector algorithms.
Route Invalidation Timers
Now that the internetwork in Figure 4.3 is fully converged, how will it handle reconvergence when some part of the topology changes? If network 10.1.5.0 goes down, the answer is simple enough—router D, in its next scheduled update, flags the network as unreachable and passes the information along.
But what if, instead of 10.1.5.0 going down, router D fails? Routers A, B, and C still have entries in their route tables about 10.1.5.0; the information is no longer valid, but there's no router to inform them of this fact. They will unknowingly forward packets to an unreachable destination—a black hole has opened in the internetwork.
This problem is handled by setting a route invalidation timer for each entry in the route table. For example, when router C first hears about 10.1.5.0 and enters the information into its route table, C sets a timer for that route. At every regularly scheduled update from router D, C discards the update's already-known information about 10.1.5.0 as described in "Routing by Rumor." But as C does so, it resets the timer on that route.
If router D goes down, C will no longer hear updates about 10.1.5.0. The timer will expire, C will flag the route as unreachable and will pass the information along in the next update.
Typical periods for route timeouts range from three to six update periods. A router would not want to invalidate a route after a single update has been missed, because this event may be the result of a corrupted or lost packet or some sort of network delay. At the same time, if the period is too long, reconvergence will be excessively slow.
Split Horizon
According to the distance vector algorithm as it has been described so far, at every update period each router broadcasts its entire route table to every neighbor. But is this really necessary? Every network known by router A in Figure 4.3, with a hop count higher than 0, has been learned from router B. Common sense suggests that for router A to broadcast the networks it has learned from router B back to router B is a waste of resources. Obviously, B already knows about those networks.
A route pointing back to the router from which packets were received is called a reverse route. Split horizon is a technique for preventing reverse routes between two routers.
Besides not wasting resources, there is a more important reason for not sending reachability information back to the router from which the information was learned. The most important function of a dynamic routing protocol is to detect and compensate for topology changes—if the best path to a network becomes unreachable, the protocol must look for a next-best path.
Look yet again at the converged internetwork of Figure 4.3 and suppose that network 10.1.5.0 goes down. Router D will detect the failure, flag the network as unreachable, and pass the information along to router C at the next update interval. However, before D's update timer triggers an update, something unexpected happens. C's update arrives, claiming that it can reach 10.1.5.0, one hop away! Remember the road sign analogy? Router D has no way of knowing that C is not advertising a legitimate next-best path. It will increment the hop count and make an entry into its route table indicating that 10.1.5.0 is reachable via router C's interface 10.1.4.1, just 2 hops away.
Now a packet with a destination address of 10.1.5.3 arrives at router C. C consults its route table and forwards the packet to D. D consults its route table and forwards the packet to C, C forwards it back to D, ad infinitum. A routing loop has occurred.
Implementing split horizon prevents the possibility of such a routing loop. There are two categories of split horizon: simple split horizon and split horizon with poisoned reverse.
The rule for simple split horizon is, When sending updates out a
The routers in Figure 4.4 implement simple split horizon. Router C sends an update to router D for networks 10.1.1.0, 10.1.2.0, and 10.1.3.0. Networks 10.1.4.0 and 10.1.5.0 are not included because they were learned from router D. Likewise, updates to router B include 10.1.4.0 and 10.1.5.0 with no mention of 10.1.1.0, 10.1.2.0, and 10.1.3.0.
Figure 4.4 Simple split horizon does not advertise routes back to the neighbors from whom the routes were learned.
Simple split horizon works by suppressing information. Split horizon with poisoned reverse is a modification that provides more positive information.
The rule for split horizon with poisoned reverse is, When sending
In the scenario of Figure 4.4, router C would in fact advertise 10.1.4.0 and 10.1.5.0 to router D, but the network would be marked as unreachable. Figure 4.5 shows what the route tables from C to B and D would look like. Notice that a route is marked as unreachable by setting the metric to infinity; in other words, the network is an infinite distance away. Coverage of a routing protocol's concept of infinity continues in the next section.
Figure 4.5 Split horizon with poisoned reverse advertises reverse routes but with an unreachable (infinite) metric.
Split horizon with poisoned reverse is considered safer and stronger than simple split horizon—a sort of "bad news is better than no news at all" approach. For example, suppose that router B in Figure 4.5 receives corrupted information causing it to believe that subnet 10.1.1.0 is reachable via router C. Simple split horizon would do nothing to correct this misperception, whereas a poisoned reverse update from router C would immediately stop the potential loop. For this reason, most modern distance vector implementations use split horizon with poisoned reverse. The trade-off is that routing update packets are larger, which may exacerbate any congestion problems on a link.
Counting to Infinity
Split horizon will break loops between neighbors, but it will not stop loops in a network such as the one in Figure 4.6. Again, 10.1.5.0 has failed. Router D sends the appropriate updates to its neighbors router C (the dashed arrows) and router B (the solid arrows). Router B marks the route via D as unreachable, but router A is advertising a next-best path to 10.1.5.0, which is 3 hops away. B posts that route in its route table.
Figure 4.6 Split horizon will not prevent routing loops here.
B now informs D that it has an alternative route to 10.1.5.0. D posts this information and updates C, saying that it has a 4-hop route to the network. C tells A that 10.1.5.0 is 5 hops away. A tells B that the network is now 6 hops away.
"Ah," router B thinks, "router A's path to 10.1.5.0 has increased in length. Nonetheless, it's the only route I've got, so I'll use it!"
B changes the hop count to 7, updates D, and around it goes again. This situation is the counting-to-infinity problem because the hop count to 10.1.5.0 will continue to increase to infinity. All routers are implementing split horizon, but it doesn't help.
The way to alleviate the effects of counting to infinity is to define
This method is also how routers advertise a network as unreachable. Whether it is a poisoned reverse route, a network that has failed, or a network beyond the maximum network diameter of 15 hops, a router will recognize any 16-hop route as unreachable.
Setting a maximum hop count of 15 helps solve the counting-to-infinity problem, but convergence will still be very slow. Given an update period of 30 seconds, a network could take up to 7.5 minutes to reconverge and is susceptible to routing errors during this time. The two methods for speeding up reconvergence are triggered updates and holddown timers.
Triggered Updates
Triggered updates, also known as flash updates, are very simple: If a metric changes for better or for worse, a router will immediately send out an update without waiting for its update timer to expire. Reconvergence will occur far more quickly than if every router had to wait for regularly scheduled updates, and the problem of counting to infinity is greatly reduced, although not completely eliminated. Regular updates may still occur along with triggered updates. Thus a router might receive bad information about a route from a not-yet-reconverged router after having received correct information from a triggered update. Such a situation shows that confusion and routing errors may still occur while an internetwork is reconverging, but triggered updates will help to iron things out more quickly.
A further refinement is to include in the update only the networks that actually triggered it, rather than the entire route table. This technique reduces the processing time and the impact on network bandwidth.
Holddown Timers
Triggered updates add responsiveness to a reconverging internetwork. Holddown timers introduce a certain amount of skepticism to reduce the acceptance of bad routing information.
If the distance to a destination increases (for example, the hop count increases from 2 to 4), the router sets a holddown timer for that route. Until the timer expires, the router will not accept any new updates for the route.
Obviously, a trade-off is involved here. The likelihood of bad routing information getting into a table is reduced but at the expense of the reconvergence time. Like other timers, holddown timers must be set with care. If the holddown period is too short, it will be ineffective, and if it is too long, normal routing will be adversely affected.
Asynchronous Updates
Figure 4.7 shows a group of routers connected to an Ethernet backbone. The routers should not broadcast their updates at the same time; if they do, the update packets will collide. Yet this situation is exactly what can happen when a several routers share a broadcast network. System delays related to the processing of updates in the routers tend to cause the update timers to become synchronized. As a few routers become synchronized, collisions will begin to occur, further contributing to system delays, and eventually all routers sharing the broadcast network may become synchronized.
Figure 4.7 If update timers become synchronized, collisions may occur.
Asynchronous updates may be maintained by one of two methods:
• Each router's update timer is independent of the routing process and is, therefore, not affected by processing loads on the router.
• A small random time, or timing jitter, is added to each update period as an offset.
If routers implement the method of rigid, system-independent timers, then all routers sharing a broadcast network must be brought online in a random fashion. Rebooting the entire group of routers simultaneously could result in all the timers attempting to update at the same time.
Adding randomness to the update period is effective if the variable is large enough in proportion to the number of routers sharing the broadcast network. Sally Floyd and Van Jacobson6 have calculated that a too-small randomization will be overcome by a large enough network of routers and that to be effective the update timer should range as much as 50% of the median update period.

2. a) What is Internet? Describe the Architecture of Internet. Explain how a router works. [6]


July-2006 [16]
1. f) Which transport technique is most appropriate for multimedia service: packet switching, circuit switching or ATM cell switching. Why? [4]



c) What is xDSL technology? [4]

4. a) What is ATM? Discuss the four types of services provided by it. [6]

5. b) Differentiate between multi-protocol router and a traditional single-protocol router. [6]

July-2007 [18]
4. a) Explain whether an ATM cell carries a source or destination address in its header or not. [6]

An ATM cell, UNI cell, and ATM NNI cell header each contain 48 bytes of payload. ATM Cell-Header Format
An ATM cell header can be one of two formats: UNI or the NNI. The UNI header is used for communication between ATM endpoints and ATM switches in private ATM networks. The NNI header is used for communication between ATM switches. Unlike the UNI, the NNI header does not include the Generic Flow Control (GFC) field. Additionally, the NNI header has a Virtual Path Identifier (VPI) field that occupies the first 12 bits, allowing for larger trunks between public ATM switches.
In addition to GFC and VPI header fields, several others are used in ATM cell-header fields.
• Generic Flow Control (GFC)---Provides local functions, such as identifying multiple stations that share a single ATM interface. This field is typically not used and is set to its default value.
• Virtual Path Identifier (VPI)---In conjunction with the VCI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.
• Virtual Channel Identifier (VCI)---In conjunction with the VPI, identifies the next destination of a cell as it passes through a series of ATM switches on the way to its destination.
• Payload Type (PT)---Indicates in the first bit whether the cell contains user data or control data. If the cell contains user data, the second bit indicates congestion, and the third bit indicates whether the cell is the last in a series of cells that represent a single AAL5 frame.
• Congestion Loss Priority (CLP)---Indicates whether the cell should be discarded if it encounters extreme congestion as it moves through the network. If the CLP bit equals 1, the cell should be discarded in preference to cells with the CLP bit equal to zero.
• Header Error Control (HEC)---Calculates checksum only on the header itself.

d) Explain the client server model of communication? What is the difference between client server architecture and web architecture? [4]
A network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers ). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power.
Web is a specialized version of client server network.
• Web is a special case of client server architecture in which fat clients are used to communicate with the server using variety of protocols and standards like HTTP, HTML, XML, SOAP etc.
• In client server architecture, both client and server exist within the walls of a single company, thus operates in a protected environment. Clients in that case become the trusted user. Web is different, since client can connect server from anywhere thus not a single connection can be treated as trusted.
• Because client server is typically within a company’s firewall, issues related to security are not as important as in Web applications.
• In client server architecture, clients are controlled as in who can access, how clients will communicate and use server’s resources etc. In Web, mostly anyone with a browser can connect to the Web.
• In client server architecture, every client is known; every request received by server will have information on who originated this request. In Web, users are anonymous thus pose a greater security risk.
• Web gives more opportunity to malicious users to tamper data at the client side as well as at the network level. Chances of data being tampered in the traditional client server architecture are much lesser as compare to Web.
• Number of clients that can be connected to the server is predictable and can be controlled in the traditional client server, but it can not be controlled in the Web.
• Clients are much more controlled in client-server. Which OS they will use, which platform they will run on, what browser will be used every thing can be controlled. In comparison to that, nothing can be controlled in Web.
• Business Logic: Mostly in the cases of Client-Server client side business logic needs to be tested which is mostly not needed in for the web-based applications.
• Platform / OS Dependence: The web based applications are O/S independent; they just need to be tested on different browsers. The Client-Server applications depend upon the Platform/ OS used, which accentuate their testing on different Platforms and OS.
• Scalability: Web based Application have to be tested for performance against thousands of simultaneous users. This number will be considerably less for Client Server application
• Security: This forms an integral part of web based applications but it might be relaxed just a bit for Client Server applications. The reason for this relaxation is based on the fact that the in case of Client-server interaction is taking place mostly between the trusted/known sources which is not the case for web based applications.


2.
b) What are the advantages of ATM that uses small the fixed length packets? [6]

ATM was specified to use short fixed length cells to carry all traffic. The use of variable length packets has several important benefits over 53 byte cells:

• Lowers overhead. For typical Internet data the basic ATM overhead is 25%-30%. Variable length CIF packets can reduce this to 5%. This would be a major cost reduction on international trunks.
• Eliminates need for new Network Interface Cards (NIC’s) to attach workstations and servers. By permitting variable length Ethernet, Token Ring, and PPP packets to be used with all the features of ATM, CIF basically cuts in half the cost of workstation access by allowing the use of currently installed NIC’s.
• Eliminates the need for Segmentation and Reassembly (SAR) Hardware. This time consuming and expensive function can be avoided if variable length packets are used. Thus, CIF interfaces and NIC’s are inherently faster and less expensive than ATM interfaces where SAR’s are required.
• Fixed cell size to permit high speed switching in hardware. This was a benefit for the past decade, but today Ethernet switches have proved that with today’s silicon this is unnecessary for fast, inexpensive switching.
• Small cell size to reduce the delay for 64 Kilobit voice to 6 milliseconds for echo control. With variable length packets however, this capability is preserved.
• Small, fixed cell size has also been rumored to be important in reducing the delay of all traffic, but this has never been an issue for high-speed lines. CIF limits packet size to 1500 bytes like Ethernet and the delay variance which a full packet can cause other traffic is only one millisecond on a 10 Mbps Ethernet wire and is far less on OC-3 or OC-12 ATM trunks (voice and video need delay variance under 10-30 milliseconds). Thus, this is a non-issue for voice or video.
• Virtual Circuit (VC) Switching was chosen over Datagram switching, so as to permit fast switching speeds, enable call based QOS specification, and to enable call based flow control. The introduction of Tag Switching to IP is clear recognition that for high speed switching VC’s or tags are critical. The requirement of VC’s for QOS and flow control is only starting to be recognized. CIF keeps VC’s.
• Quality Of Service (QOS) signaling protocol so as to permit mixing of voice, video and data on the same wire with no degradation of the delay sensitive traffic. This is an important benefit available in ATM Forum SIG 4.0 not available in IP networks today. CIF maintains the full QOS of ATM.
• QOS based routing of traffic over network trunks to enable load balancing on trunks and to ensure all traffic is routed on paths capable of supporting the QOS and bandwidth. This is another important benefit available in ATM Forum PNNI 1.0 not available in IP networks today. CIF supports PNNI.
Low delay flow control was always recognized as a necessity for high speed switched networks. In order to control the data flow at greatly increased speeds, a much lower delay flow control, explicit rate, has been specified in ATM Forum TM 4.0, a capability not available in IP networks today. This not only reduces the buffer requirements and thus the cost of the switches but also dramatically decreases the time required for page accesses like WWW requests. CIF allows explicit rate flow control to be extended to the desktop economically over Ethernet or PPP dial-in.
4.
a) What are the benefits of DSL? How can a DSL line be shared among multiple users? [6]

• You can leave your Internet connection open and still use the phone line for voice calls.
• The speed is much higher than a regular modem (1.5 Mbps vs. 56 Kbps)
• DSL doesn't necessarily require new wiring; it can use the phone line you already have.
The company that offers DSL will usually provide the modem as part of the installation.

5) t’s the difference between forward lookup and reverse lookup in DNS? [6]
The Domain Name System (DNS) helps users to find their way around the Internet. Every computer on the Internet has a unique address - just like a telephone number - which is a rather complicated string of numbers. It is called its "IP address" (IP stands for "Internet Protocol"). IP Addresses are hard to remember. The DNS makes using the Internet easier by allowing a familiar string of letters (the "domain name") to be used instead of the arcane IP address. So instead of typing 207.151.159.3, you can type www.internic.net. It is a "mnemonic" device that makes addresses easier to remember.
What does it mean to "register" a domain name?
When you register a domain name, you are inserting an entry into a directory of all the domain names and their corresponding computers on the Internet.
When you register a domain name, you are inserting an entry into a directory of all the domain names and their corresponding computers on the Internet. This allows you to point (or forward) this domain name to your web site, and use it for email.

Domain names are registered for a specific period of time (usually in increments of one year) and must be renewed at the end of each registration period. You own the domain for the life of the registration only.

If you allow the domain to expire, it will no longer be active and you will not own the domain. If you do not renew the domain in time, after the allowed grace period, the domain may be auctioned, or deleted, in which case, it eventually becomes available to others to register.

Each registry has different rules for how long a domain may (or may not) be held during a grace period, allowing time for the previous registrant to renew the name.

You do not lose any time when you renew a domain early. The month and day will always stay the same. We highly suggest you keep track of your domain expiration dates, and renew well in advance of expiration to avoid unintentional down time or loss of the name.

IP address lookup is the process of translating between IP addresses and Internet domain/computer names. Forward IP address lookup :converts an Internet name to an
address. Reverse IP address lookup :converts the number to the name.

b) Discuss how a user gets connected to the Internet using an ISP. [6]

When you are connected to the Internet through your service provider, communication between you and the ISP is established using a simple protocol: PPP (Point to Point Protocol), a protocol making it possible for two remote computers to communicate without having an IP address.
In fact your computer does not have an IP address. However an IP address is necessary to be able to go onto the Internet because the protocol used on the Internet is the TCP/IP protocol which makes it possible for a very large number of computers which are located by these addresses to communicate.
So, communication between you and the service provider is established according to the PPP protocol which is characterised by:
• a telephone call
• initialisation of communication
• verification of the user name (login or userid)
• verification of the password
Once you are "connected", the internet service provider lends you an IP address which you keep for the whole duration that you are connected to the internet. However, this address is not fixed because at the time of the next connection the service provider gives you one of its free addresses (therefore different because depending on its capacity, it may have several hundreds of thousand addresses.).
Your connection is therefore a proxy connection because it is your service provider who sends all the requests you make and the service provider who receives all the pages that you request and who returns them to you.
It is for these reasons for example that when you have Internet access via an ISP, you must pick up your email on each connection because generally it is the service provider that receives your email (it is stored on one of its servers

2. Internet Infrastructure

2. a) Explain Satellite technology for communication across large distances. [8]
Satellite Microwave
• Satellite is relay station
• Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency
• Requires geo-stationary orbit
o Height of 35,784km
• Television
• Long distance telephone
• Private business networks
b) State the advantages and disadvantages of satellite microwave and optical fiber transmission. [10]
Microwave Advantages and Disadvantages
Advantages:
• No cables needed
• Multiple channels available
• Wide bandwidth
• Coverage over a large geographical area
• Can be cheaper over long distances
Disadvantages:
• Line-of-sight will be disrupted if any obstacle, such as new buildings, are in the way
• Signal absorption by the atmosphere. Microwaves suffer from attenuation due to atmospheric conditions. Noise and interference
• Towers are expensive to build. Huge initial cost
• Propagation delay
1.What are optical fibers? Write at least four advantages of fibers over conventional metal wires [4]

Compared to conventional metal wire (copper wire), optical fibers are:
• Less cost - Several miles of optical cable can be made cheaper than equivalent lengths of copper wire. This saves your provider (cable TV, Internet) and you money.
• Smaller-Thinner - Optical fibers can be drawn to smaller diameters than copper wire.
• Higher carrying capacity - Because optical fibers are thinner than copper wires, more fibers can be bundled into a given-diameter cable than copper wires. This allows more phone lines to go over the same cable or more channels to come through the cable into your cable TV box.
• Less signal degradation - The loss of signal in optical fiber is less than in copper wire.
• Light signals - Unlike electrical signals in copper wires, light signals from one fiber do not interfere with those of other fibers in the same cable. This means clearer phone conversations or TV reception.
• Low power Requirement - Because signals in optical fibers degrade less, lower-power transmitters can be used instead of the highvoltage electrical transmitters needed for copper wires. Again, this saves your provider and you money.
Digital signals - Optical fibers are ideally suited for carrying digital information, which is especially useful in computer networks.
• Non-flammable - Because no electricity is passed through optical fibers, there is no fire hazard.
• Lightweight - An optical cable weighs less than a comparable copper wire cable. Fiber-optic cables take up less space in the ground.
Flexible - Because fiber optics are so flexible and can transmit and receive light, they are used in many flexible digital cameras for the following purposes: Mechanical imaging –imaging - in bronchoscopes, endoscopes, laparoscopes inspecting mechanical welds in pipes and engines (in airplanes, rockets, space Plumbing - to inspect sewer lines Because of these shuttles, cars)

July-2005 [4]
1.
f) What media can be used for noise resistance? Briefly state its other advantages. [4]

January-2006 [6]
7.
b) Discuss the following techniques to ensure the data against accidental damage:
i) parity bits
A parity bit is a bit that is added to ensure that the number of bits with value of one in a given set of bits is always even or odd. Parity bits are used as the simplest error detecting code.
As for binary digits, there are two variants of parity bits: even parity bit and odd parity bit. An even parity bit is set to 1 if the number of ones in a given set of bits is odd (making the total number of ones, including the parity bit, even). An odd parity bit is set to 1 if the number of ones in a given set of bits is even (making the total number of ones, including the parity bit, odd). Even parity is actually a special case of a cyclic redundancy check (CRC), where the 1-bit CRC is generated by the polynomial x+1.
If the parity bit is present but not used, it may be referred to as mark parity, where the parity bit is always 1, or as space parity, where the bit is always 0. Therefore, parity bit is an error detecting code, but is not an error correcting code as there is no way to determine which particular bit is corrupted. The data must be discarded entirely, and re-transmitted from scratch.
There is a limitation to parity schemes. A parity bit is only guaranteed to detect an odd number of bit errors. If an even number of bits have errors, the parity bit records the correct number of ones, even though the data is corrupt.

ii) Checksum

A checksum is a form of redundancy check, a simple way to protect the integrity of data by detecting errors in data that are sent through space (telecommunications) or stored for some time. It works by adding up the basic components of a message, typically the assorted bits, and storing the resulting value. Anyone can later perform the same operation on the data, compare the result to the authentic checksum, and (assuming that the sums match) conclude that the message was most likely not corrupted.
An example of a simple checksum:
• Given 4 bytes of data (can be done with any number of bytes): 0x25, 0x62, 0x3F, 0x52
• Step 1: Adding all bytes together gives 0x118.
• Step 2: Drop the carry nibble to give you 0x18.
• Step 3: Get the two's complement of the 0x18 to get 0xE8. This is the checksum byte.
• Step 4: To test the checksum byte simply add it to the original group of bytes. This should give you 0x100.
• Step 5: Drop the carry nibble again giving 0x00. Since it is 0x00, this means no error was detected (although an undetectable error could have occurred). The simplest form of checksum, which simply adds up the asserted bits in the data, cannot detect a number of types of errors. Such a checksum, for example, is not changed by:
• Reordering of the bytes in the message.
• Inserting or deleting zero-valued bytes.
• Multiple errors which sum to zero.
These types of redundancy check are useful in detecting accidental modification such as corruption to stored data or errors in a communication channel.

iii) Cyclic redundancy Checks [6]
cyclic redundancy check (CRC) is a type of function that takes as input a data stream of any length, and produces as output a value of a certain space, commonly a 32-bit integer. A CRC can be used as a checksum to detect accidental alteration of data during transmission or storage. CRCs are popular because they are simple to implement in binary hardware, are easy to analyze mathematically.
A CRC is an error-detecting code. Its computation resembles a long division operation in which the quotient is discarded and the remainder becomes the result, with the important distinction that the arithmetic used is the carry-less arithmetic of a finite field. The length of the remainder is always less than or equal to the length of the divisor, which therefore determines how long the result can be. The definition of a particular CRC specifies the divisor to be used, among other things.
An important reason for the popularity of CRCs for detecting the accidental alteration of data is their efficiency guarantee. Typically, an n-bit CRC, applied to a data block of arbitrary length, will detect any single error burst not longer than n bits (in other words, any single alteration that spans no more than n bits of the data), and will detect a fraction 1-2-n of all longer error bursts. Errors in both data transmission channels and magnetic storage media tend to be distributed non-randomly (i.e. are "bursty"), making CRCs' properties more useful t han alternative schemes such as multiple parity checks.
To compute an n-bit binary CRC, line the bits representing the input in a row, and position the (n+1)-bit pattern representing the CRC's divisor (called a "polynomial") underneath the left-hand end of the row. Here is the first calculation for computing a 3-bit CRC:
11010011101100 <--- Input
1011 <--- divisor (4 Bits)
--------------
01100011101100 <--- result
If the input bit above the leftmost divisor bit is 0, do nothing and move the divisor to the right by one bit. If the input bit above the leftmost divisor bit is 1, the divisor is exclusive-ORed into the input (in other words, the input bit above each 1-bit in the divisor is toggled). The divisor is then shifted one bit to the right, and the process is repeated until the divisor reaches the right-hand end of the input row. Here is the last calculation:
00000000001110 <--- result of multiplication calculation
1011 <--- divisor
--------------
00000000000101 <--- remainder (3 bits)
Since the leftmost divisor bit zeroed every input bit it touched, when this process ends the only bits in the input row that can be nonzero are the n bits at the right-hand end of the row. These n bits are the remainder of the division step, and will also be the value of the CRC function (unless the chosen CRC specification calls for some postprocessing).

a) What are the types of wireless networks? [6]

Types of Wireless Networks and Usage
There are three primary usage scenarios for wireless connectivity.
• Wireless Personal Area Networking (WPAN)
• Wireless Local Area Networking (WLAN)
Wireless Wide Area Networking (WWAN)
WPAN describes an application of wireless technology that is intended to address usage scenarios that are inherently personal in nature. The emphasis is on instant connectivity between devices that manage personal data or which facilitate data sharing between small groups of individuals. An example might be synchronizing data between a PDA and a desktop computer. Or another example might be spontaneous sharing of a document between two or more individuals. The nature of these types of data sharing scenarios is that they are ad hoc and often spontaneous. Wireless communication adds value for these types of usage models by reducing complexity (i.e. eliminates the need for cables).
WLAN on the other is more focused on organizational connectivity not unlike wire based LAN connections. The intent of WLAN technologies is to provide members of workgroups access to corporate network resources be it shared data, shared applications or e-mail but do so in way that does not inhibit a user’s mobility. The emphasis is on a permanence of the wireless connection within a defined region like an office building or campus. This implies that there are wireless access points that define a finite region of coverage.
Whereas WLAN addresses connectivity within a defined region, WWAN addresses the need to stay connected while traveling outside this boundary. Today, cellular technologies enable wireless computer connectivity either via a cable to a cellular telephone or through PC Card cellular modems. The need being addressed by WWAN is the need to stay in touch with business critical communications while traveling.



b) What are EAP, LEAP, PEAP and EAP-TLS & EAP-TTLS? [6]

EAP-TLS
EAP-TLS (Extensible Authentication Protocol - Transport Layer Security) was created by Microsoft and accepted by the IETF as RFC 2716: PPP EAP TLS Authentication Protocol.. EAP-TLS is the de facto standard for authentication in 802.11i wireless LANs.
PEAP
Protected Extensible Authentication Protocol, Protected EAP, or simply PEAP (pronounced "peep"), is a method to securely transmit authentication information, including passwords, over wired or wireless networks. It was jointly developed by Cisco Systems, Microsoft, and RSA Security. Note that PEAP is not an encryption protocol; as with other EAP types it only authenticates a client into a network.
PEAP uses server-side public key certificates to authenticate the server. It then creates an encrypted SSL/TLS tunnel between the client and the authentication server. The ensuing exchange of authentication information to authenticate the client is then encrypted and user credentials are safe from eavesdropping.
PEAP is a joint proposal by Cisco Systems, Microsoft and RSA Security as an open standard. It is already widely available in products, and provides very good security. It is similar in design to EAP-TTLS, requiring only a server-side PKI certificate to create a secure TLS tunnel to protect user authentication.
EAP-TTLS
Tunneled Transport Layer Security (EAP-TTLS) is a proprietary protocol which was developed by Funk Software and Certicom, and is supported by Agere Systems, Proxim, and Avaya .
EAP-TTLS is being considered by the IETF as a new standard. The addition of EAP-TTLS to a wireless LAN protocol standard would enable wireless LANs to communicate securely without the use of encryption certificates.
PEAP and EAP-TTLS make it possible to authenticate wireless LAN clients without requiring them to have certificates.
PEAP and EAP-TTLS both utilize Transport Layer Security (TLS) to set up an end-to-end tunnel to transfer the user's credentials without having to use a certificate on the client
EAP
Extensible Authentication Protocol, or EAP, is a universal authentication framework frequently used in wireless networks and Point-to-Point connections Although the EAP protocol is not limited to wireless LANs and can be used for wired LAN authentication, it is most often used in wireless LANs. Recently, the WPA and WPA2 standard has officially adopted five EAP types as its official authentication mechanisms.
EAP is an authentication framework, not a specific authentication mechanism. EAP is not a wire protocol; instead it only defines message formats. Each protocol that uses EAP defines a way to encapsulate EAP messages within that protocol's messages. In the case of 802.1X, this encapsulation is called EAPOL, "EAP over LANs".
LEAP
The Lightweight Extensible Authentication Protocol (LEAP) is a proprietary wireless LAN authentication method developed by Cisco Systems. Important features of LEAP are dynamic WEP keys and mutual authentication (between a wireless client and a RADIUS server). LEAP allows for clients to reauthenticate frequently; upon each successful authentication, the clients acquire a new WEP key (with the hope that the WEP keys don't live long enough to be cracked).
Some 3rd party vendors also support LEAP through the Cisco Compatible Extensions Program

5.a) How does a router differ from a bridge? [6]

. Bridge connects two pieces of land together offering a path from one to another. Networks also can have bridges - they connect two networks making each accessable to the other. Bridges can be used to connect two different types of networks but are usually used to separate one large network into two smaller networks for performance purposes. A bridge knows all of the addresses on each side of the bridge and can send information accordingly.

Router is an intelligent bridge for large networks. A router can listen to the traffic on the entire network and determine the least congested route to its destination. Gateway gateway is used to connect different types or the same types of networks together. They can translate the different formats

6. Which switching technique performs error checking on the first 64 bytes of the frame? What are different processing methods used by switches to make switching decisions?[6]

LAN switches are characterized by the forwarding method that they support, such as a store-and-forward switch, cut-through switch, or fragment-free switch. In the store-and-forward switching method, error checking is performed against the frame, and any frame with errors is discarded. With the cut-through switching method, no error checking is performed against the frame, which makes forwarding the frame through the switch faster than store-and-forward switches.
Store-and-Forward Switching
Store-and-forward switching means that the LAN switch copies each complete frame into the switch memory buffers and computes a cyclic redundancy check (CRC) for errors. CRC is an error-checking method that uses a mathematical formula, based on the number of bits (1s) in the frame, to determine whether the received frame is errored. If a CRC error is found, the frame is discarded. If the frame is error free, the switch forwards the frame out the appropriate interface port. An Ethernet frame is discarded if it is smaller than 64 bytes in length, a runt, or if the frame is larger than 1518 bytes in length, a giant.