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LAb 1 computer network

Prashant Kumar . … CTS 2

Question 1.1: What is the internal design of a “thinwire” Ethernet cable (10BASE2 standard)? The 10Base2 also supports 10 Mbps baseband transmission, the standard specifies zero point two five inch coaxial cable known as cheapernet or thin Ethernet. So here the coaxial cable is of cheaper variety which is used in cable TV which is 0.25 inches in diameter and that’s why it is also called chapernet because of its lower cost and also it is called thin Ethernet because this diameter is thinner than the standard 10Base5.

185 m is the maximum segment length and up to five cable segments can be connected using repeaters with maximum length of 925 m. So in this way with five repeaters you can have 925 m and total number of computers is the same which is 1024. This is connected in this manner

Question 1.2: What is the maximum transmission rate and maximum cable length specified for the 10BASE2 standard? Are there further limitations?
the maximum transmission rate is 10 MBps
10Base2 there is always a problem of loose connection, cut and other problems and for that purpose time domain reflectometry is used for detection of fault which is very time consuming. So, that problem can be avoided in case of this hub based 10BaseT Ethernet network wherein it is very easy to maintain and diagnose a fault. That’s why this particular topology has become very popular.

Question 1.3 : What is a UTP cable and how is it constructed?
Twisted-pair can be used for both analog and digital communication. The data rate that can be supported over a twisted-pair is inversely proportional to the square of the line length. Maximum transmission distance of 1 Km can be achieved for data rates up to 1 Mb/s. For analog voice signals, amplifiers are required about every 6 Km and for digital signals, repeaters are needed for about 2 Km. To reduce interference, the twisted pair can be shielded with metallic braid. This type of wire is known as Shielded Twisted-Pair (STP) and the other form is known as Unshielded Twisted-Pair (UTP).

in case of unshielded twisted pair apart from these two conductors and insulators there is a protective plastic cover, there is no other conductor or shielding
Now this is sufficient for ordinary telephone wire telephone network but however as there is no protective shield it is subjected to external electromagnetic interference. That means whenever this twisted pair of wire is taken through some industrial environment where lots of sparks and other things are going on then it creates a problem. So it is induced and that’s why whenever lightning occurs or there is some spark or a car is moving close by that signal is induced in this unshielded twisted pair of wire.

Question 1.4: What UTP standards are there and which maximum transmission rates and cable lengths do they specify?

the inner conductor that is used there is an insulator. This inner conductor diameter is specified here 18 gauge, 22 gauge, 24 gauge and twenty six gauge and here the diameters are given in inches 18 gauge corresponds to 0.0403 inch.
On the other hand 26 gauge has diameter 0.0159 gauge. So it is quite obvious that higher the diameter of the conductor lesser will be the attenuation. So 18 gauge wire gives you lesser attenuation compared to 26 gauge and obviously the 18 gauge wire will be costlier than 26 gauge. These are the common wire diameters and the gauge of wire given here and as we can see attenuation is given in dB per meter and here is the frequency. So at higher frequencies the attenuation increases for UTP.

Apart from increase in attenuation at higher frequencies as the length of the wire increases the attenuation also increases. It has been found that the attenuation is proportional to 1 by distance square so attenuation is proportional to proportional to distance square. Therefore as distance increases the attenuation becomes more and in such a situation as you know we can use repeater to amplify the signal and regenerate it and resend it if necessary. The twisted pair UTP is the simplest and possibly the cheapest guided media used in many application.

One of the most common application is local loop in telephone lines. That means in a telephone network the connection that you are getting to your home from the local exchange the wire that is used is your UTP and it is also used in Digital Subscriber Line DSL. Nowadays DSL is becoming more popular. We shall discuss about it in more detail. In DSL also the UTP is used. the maximum transmission rate for transfer is are capable of transporting 1 gigabit per second or 1,000 megabits per second (1 Gb/s or 1,000 Mb/s).

Question 1.5: What is the difference between STP and UTP?
1. STP cables are shielded while UTP cables are unshielded
2. STP cables are more immune to interference and noise than UTP cables
3. STP cables are better at maximizing bandwidth compared to UTP cables
4. STP cables cost more per meter compared to UTP cables
5. STP cables are heavier per meter compared to UTP cables
6. UTP cables are more prevalent in SOHO networks while STP is used in more high-end applications

  • ●  Question 1.6: Why are termination resistors needed for data cables e.g. Ethernet cables?
  • ●  Because each differential pair of wires is a transmission line, you must properly terminate the line to prevent reflections. A common method of terminating a two-wire multidrop RS-485 network is to install terminating resistors at each end of the multidrop network. If you daisy-chained multiple instruments together, you need a terminating resistor at only the first and last instruments. The terminating resistor should match the characteristic impedance of the transmission line (typically 100–120 Ohms). National Instruments offers an optional DB-9 RS-485 termination connector that contains embedded terminating resistors for easy termination.

  • ●  Question 1.7: What does the reflected signal look like when compared with the input


● The reflection is cause due the different impendence’s. When electrons from the higher impedance wire attempt to travel through the lower impedance wire, some of them can’t make it and are reflected back, destroying the signal.
Question 1.12: Search on the internet for a description of the commands ping, pathping

and traceroute. What is the difference between ping and pathping (Linux: traceroute) and which protocol do they use?
Applies To: Windows Server 2008
The ping command helps to verify IP-level connectivity. When troubleshooting, you can use ping to send an ICMP echo request to a target host name or IP address. Use ping whenever you need to verify that a host computer can connect to the TCP/IP network and network resources. You can also use ping to isolate network hardware problems and incompatible configurations.

Follow this sequence to diagnose network connectivity:

  1. Ping the loopback address to verify that TCP/IP is configured correctly on the local

    computer. ping

  2. Ping the IP address of the local computer to verify that it was added to the network

    correctly. ping IP_address_of_local_host

  3. Ping the IP address of the default gateway to verify that the default gateway is

    functioning and that you can communicate with a local host on the local

    network. ping IP_address_of_default_gateway

  4. Ping the IP address of a remote host to verify that you can communicate through a

    router. ping IP_address_of_remote_host

The following table shows some useful ping command options.

-n Count
-w Timeout milliseconds). The default is 4,000 (a

4-second timeout).

/? Provides command Help.

By default, ping waits 4,000 milliseconds (4 seconds) for each response to be returned before displaying the “Request Timed Out” message. If the remote system being pinged is across a high-delay link, such as a satellite link, responses might take longer to be returned. You can use the -w (wait) option to specify a longer timeout.

-l Size
-f packet. By default, the ping packet allows

Determines the number of echo requests to send. The default is 4 requests.

Enables you to adjust the timeout (in

Enables you to adjust the size of the ping packet. The default size is 32 bytes.

Sets the Do Not Fragment bit on the ping fragmentation.

A response of “Destination net unreachable” means there was no route to the destination. You need to check the routing table on the router listed in the “Reply from” address in the “Destination net unreachable” message. For more information about the routing table, see Manage the IPv4 Routing Table .

A response of “Request timed out” means that there was no response to the ping in the default time period (1 second). You can check for the following:

  • ●  The ping command is blocked at the corporate or personal firewall level.Configure the corporate firewall to allow the ping command network access. Configure the personal firewall to allow ICMP Echo and Echo Reply packets.
  • ●  A router is down.To check the routers in the path between the source and the destination, use the tracert command.
  • ●  The destination host is down.Physically verify that the host is running or check connectivity through another protocol.
  • ●  There is no route back to your computer.If the host is running, you can check for a return route by viewing the default gateway and local routing table on the destination host.
  • ●  The latency of the response is more than one second.Use the -w option on the ping command to increase the timeout. For example, to allow responses within 5 seconds, use ping-w 5000 .

    The ping command uses Windows Sockets-style name resolution to resolve a computer name to an IP address, so if pinging by address succeeds, but pinging by name fails, then the problem lies in address or name resolution, not network connectivity.
    Provides information about network latency and network loss at intermediate hops between a source and destination. Pathping sends multiple Echo Request messages to each router between a source and destination over a period of time and then computes results based on the packets returned from each router. Because pathping displays the degree of packet loss at any given router or link, you can determine which routers or subnets might be having network problems. Pathping performs the equivalent of the tracert command by identifying which routers are on the path. It then sends pings periodically to all of the routers over a specified time period and computes statistics based on the number returned from each. Used without parameters, pathping displays help.

    You can use TRACERT to find out where a packet stopped on the network. In the following example, the default gateway has found that there is no valid path for the host on Probably, either the router has a configuration problem, or the network does not exist, reflecting a bad IP address.

    Pathping is a TCP/IP based utility (command-line tool) that provides useful information about network latency and network loss at intermediate hops between a source address and a destination address. It does this by sending echo requests via ICMP and analyzing the results. ICMP stands for Internet Control Message Protocol. ICMP is an extension to the Internet Protocol (IP – part of the TCP/IP protocol suite) defined by RFC 792 . ICMP supports packets containing error, control and informational messages. Pathping will send multiple echo request messages to each router between what you are attempting to ping – the source address. If your

destination is across a WAN link then it’s certain that you will be using some form of router, most likely two, which would mean that you could test pathping across a two hop network – two router hops. A typical network diagram is seen in the following illustration.

Question 1.13: Search on the internet for a description of the Domain Name Service, DNS. What is DNS for, how does it work?
A DNS server is any computer registered to join the Domain Name System. A DNS server runs special-purpose networking software, features a public IP address, and contains a database of network names and addresses for other Internet hosts.

Step 1: Request information

The process begins when you ask your computer to resolve a hostname, such as visiting http://www.prashant99.xyz The first place your computer looks is its local DNS cache , which stores information that your computer has recently retrieved.
If your computer doesn’t already know the answer, it needs to perform a DNS query to find out. Step 2: Ask the recursive DNS servers

If the information is not stored locally, your computer queries (contacts) your ISP’s recursive DNS servers . These specialized computers perform the legwork of a DNS query on your behalf. Recursive servers have their own caches, so the process usually ends here and the information is returned to the user.

Step 3: Ask the root nameservers
If the recursive servers don’t have the answer, they query the root nameservers . A nameserver is a computer that answers questions about domain names, such as IP addresses. The thirteen root nameservers act as a kind of telephone switchboard for DNS. They don’t know the answer, but they can direct our query to someone that knows where to find it.
Step 4: Ask the TLD nameservers
The root nameservers will look at the first part of our request, reading from right to left — http://www.prashant99.xyz — and direct our query to the Top-Level Domain (TLD) nameservers for .com . Each TLD, such as .com , .org , and .us , have their own set of nameservers, which act like a receptionist for each TLD. These servers don’t have the information we need, but they can refer us directly to the servers that do have the information. Step 5: Ask the authoritative DNS servers
The TLD nameservers review the next part of our request — http://www.prashant99.xyz — and direct our query to the nameservers responsible for this specific domain. These authoritative nameservers are responsible for knowing all the information about a specific domain, which are stored in DNS records . There are many types of records, which each contain a different kind of information. In this example, we want to know the IP address for http://www.prashant99.xyz , so we ask the authoritative nameserver for the Address Record (A) .
Step 6: Retrieve the record
The recursive server retrieves the A record for http://www.prashant99.xyz from the authoritative nameservers and stores the record in its local cache. If anyone else requests the host record for dyn.com , the recursive servers will already have the answer and will not need to go through the

lookup process again. All records have a time-to-live value, which is like an expiration date. After a while, the recursive server will need to ask for a new copy of the record to make sure the information doesn’t become out-of-date.
Step 7: Receive the answer
Armed with the answer, recursive server returns the A record back to your computer. Your computer stores the record in its cache, reads the IP address from the record, then passes this information to your browser. The browser then opens a connection to the webserver and receives the website.
This entire process, from start to finish, takes only milliseconds to complete.

Question 1.14: What does the computed TTL value reflect when considering the network connection between Ulm and Munich?
Pinging www.some-domain.com [XXX.XXX.XXX.XXX] with 32 bytes of

Reply from XXX.XXX.XXX.XXX: bytes=32 time=564ms TTL=237 Reply from XXX.XXX.XXX.XXX: bytes=32 time=555ms TTL=237 Reply from XXX.XXX.XXX.XXX: bytes=32 time=554ms TTL=237 Reply from XXX.XXX.XXX.XXX: bytes=32 time=548ms TTL=237

Ping statistics for XXX.XXX.XXX.XXX:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss) Approximate round trip times in milli-seconds:
Minimum = 548ms, Maximum = 564ms, Average = 555ms

It counts no of hops between router how many router is involved between connection so if we if we ping from different place it may be possible to have there might be more no of router involved between the route .

A timer value included in packets sent over TCP/IP-based networks that tells the recipients how long to hold or use the packet or any of its included data before expiring and discarding the packet or data. For DNS, TTL values are used in resource records within a zone to determine how long requesting clients should cache and use this information when it appears in a query response answered by a DNS server for the zone.

● ●

Done some lab work in MY MACBOOK apple ..

Exercise questions done in LAB ….

2. Connect a pulse generator which simulates the signal of an Ethernet adapter (rectangular pulse with
approx. 1 MHz repetition frequency, pulse width 0.5 s) to the first input of an oscilloscope. Divert the

signal from Channel 1 of the oscilloscope via a long coaxial cable of unknown length, and put the signal
on Channel 2. The impedance of the cable is 50Ω. Add a respective resistor at the end of the cable.

Question 1.8: How long may the cable be if the output power Pout of the cable is to be half that of
the input signal Pin?

Adb = 20log 10 (V1/V2); (1-2)
Adb=20*log 10 (1.5/0.5)= 9.542 db; – attenuation per cable(length 20 meters) 9.542/20 = 0.4771 – attenution per meter

In order to find the needed length of the cable we devide 3db by attenuation per meter

3db/ 0.4771 db=6,29 meters

There is difference propagation delay in pic we can see .. With Resistance 50 ohm

This is reflection in wave we can see without Resistance means value is infinity …

Wave formation With short circuit ..

Wave formation with Resistance more than <75 ohm

By pictures we can see that delay takes 2 squares on oscilloscope.

To calculate the length cable we multiply speed (2*108 m/s) on propagation delay time (2(squares)*0,5*10-6)

2*108*10-6* 2*0.5= 20 meters

Exercise 1.2 Transmit data via a serial link

Question 1.9: What kind of cable do you need and what is the difference between a null modem cable
without handshaking and a null modem cable with partial handshaking?

For this task we need RS232 Cable with no handshaking, since we need only to send and receive data

Null modem cable means that it`s a cable that can connect 2 computers without modem

Without handshaking means it`s able only to send and receive data. Other data lines are simply lost since this wire doesn`t transmit them

With partial handshaking allows also sending Request to Send(RTS) and Clear to Send(CTS) that allows to avoid data collision if the are send in the same time.

3. Type some text on one computer and read on the other. Increase the data transfer rate to 19’200 bps or 38’400 bps on one of the two computers (use a right mouse click on the title bar and choose “Change Settings”. What happens if you do not synchronize the data transfer rate on both computers?

Since one computer is sending data at one frequency and the other one is expecting to receive it in the other, the receiving computer interprets the signal input differently, giving a different output then the input of the first computer was giving.

Send a sequence of identical key strokes. Are you able to re-code the character by observing only the signal on the oscilloscope?

Here`s a bit sequence 0110011 of a lower letter “g” in 7-bit asci encoding

Question 1.10: What is software flow control and what advantages / disadvantages does software flow control have in comparison to hardware flow control (Internet research)?

– Less demand for hardware implementations
– no need for extra wire for hardware flow control Disadvantages

– Flow control may cause extra delays

– Requires at least 1 character to transmit

Question 1.11: How is the signal on the monitor re-coded to the respective ASCII character?
It sends first XON in order to prepare the receiving computer for a transmission, and then sends the ASCII code. In

our case XON command consisted of 1 bit

Exercise 1.3 Network configuration with Windows

Picture representation of proof….

Connection With Putty … Picture ….Repersentation ..#

connection between two system is done with connecting putty … typed in different system …

Exercise 1.4 Connect two computers by a direct link
Instruction to be followed in Exercise no 1.4 given in lab question . Proof Picture .

(configuration set up in linux seystem with cmd line interface ..)

connection set up with window PC sending file from Window to Linux PC

file received in linux operating system … after connection setup .. —