Tcp Ip Service Programs Appl

8/6/2019 Tcp Ip Service Programs Appl

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TCP/IP service programs and applications

RA22236EN10GLS0 2009 Nokia Siemens Networks

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Contents

1 TCP/IP service programs 3

1.1

Ping 4

1.2 Tracert 6

1.3 PathPing 8

2 Remarks on TCP 11

2.1 Slow start and congestion avoidance 12

3 Remarks on FTP 15

4 WWW 21

5 Exercise 25

6 Solution 29

TCP/IP service programs and

applications


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2009 Nokia Siemens Networks2


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3

1 TCP/IP service programs


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1.1 Ping

The command Ping can be used to check the network connection to one or severalremote hosts. The command runs an application which generates an ICMP (InternetControl Message Protocol) Echo Request data packet (this is an IP packet withProtocol = 1, Type field = 8) which is sent to the host. An Echo Reply is expectedfrom the host (this is an IP packet with Protocol = 1, Type field = 0).

In the Windows Ping, after 1 second a new packet is sent again. As a default, 4packets, each having 32 bytes data, are sent. The sent and received data arecompared. The length of the data sent can be modified with the command ping [l] tomaximum 65527 bytes. In the output of the ping command the number of sent,received, and lost packets as well as the ping delay is given.

The following figure shows an example:


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Fig. 1 An example for the ping command


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1.2 Tracert

The Tracert (trace route) tool checks the route to a destination by sending ICMP(Internet Control Message Protocol) Echo Request data packets with different TTL(time to live) values starting with TTL=1 for the first packet, then TTL=2 for the nextpacket,

Each node decreases the TTL value by 1 before further transmitting the data packet.

If the TTL value of a data packet reaches value 0, the corresponding node sendsback an error message ("time exceeded"). By checking these error messages, theTracert tool checks the route to the destination.



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Fig. 2 An example for the tracert command


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1.3 PathPing

The tool PathPing extends the features of the Ping and Tracert commands and offersmore information than those commands do.

During a certain time, data packets are sent to each node contained in the path to acertain destination. Statistics are calculated based on the data packets which aresent back from these nodes. Since the PathPing command shows losses of packetsfor each of the nodes and each connection, this command can be used to localizethose nodes and/or connections making problems.


Fig. 3 Part 1 of an example for the pathping command


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Fig. 4 Part 2 of an example for the pathping command


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2 Remarks on TCP


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Since many applications are running based on TCP (Transmission Control Protocol)we want to shortly mention in this chapter some problems arising from the usage ofTCP.

2.1 Slow start and congestion avoidance

In TCP the transmission performance in the beginning of a data transmission andafter a congestion situation is characterized by the so called slow start phase.

During slow start, the initial size of the so called congestion window, which is usedby the sender for flow control, is usually one segment only. Each time anacknowledgement is received by the sender, the size of the congestion window isdoubled during slow start phase, i.e. the amount of transmitted data startsexponentially. At a certain point, when the congestion window becomes too large,congestion occurs and data packets are discarded.

The initial slow start threshold, which is set to 65535 bytes, is reset to one half of thereceiver's window size. If now the congestion window is less or equal to this resetslow start threshold, then TCP restarts with slow start.

If the congestion window size reaches the slow start threshold again, TCP changesfrom the slow start to the so called congestion avoidance phase. In this phase, thecongestion window is not increased exponentially but linearly: Each time anacknowledgement is received, the congestion window is increased by 1 step, butcannot be increased more than the value suggested by the receiver.

In case of congestion, the slow start threshold is reset to half of its actual value and

the congestion window is reset to 1 segment.


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8,760

Slow start threshold, start value = 65535

congestion occurs

Slow start threshold, readjusted value

receivers window seize

cwnd

readjustment

of slow start

threshold

first phase:

slow start,

exponential growth

second phase:

slow start,

exponential growth

third phase:

congestion avoidance,

linear growth

Fig. 5 Slow start and congestion avoidance


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3 Remarks on FTP


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With FTP (File Transmission Protocol) , files can be transferred between computers.

FTP is standardized in RFC 959.

A FTP session requires two programs:

On the server side: A FTP server implementation.

On the client side: A FTP client program which, on most PC systems, is availableunder the command "ftp".

A FTP session is started from the client side by the ftp command with the name orthe IP number of the (remote) server. The server requires an identification andauthentication from the client and therefore prompts the client for the username andpassword. After the login procedure has been successful, the client can access theservers file system and enter commands for the transfer of files.


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User command meaning

User login with user namedir show directory content

ls list directory content

Pwd print working directory

Cd change dir

get get file

put put file

mget get several files(*)

mput put several files(*)

send send file

receive receive file

binary use transparent transmission

text use text transmission (ascii)

? show available commands (help)

! go to local shell

rmdir remove directory

open open connection to host

quit end connection

bye end connection

status show current status

remotehelp help from remote server

hash generates a # symbol on the screen for

every 2 kbytes transmitted


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Fig. 6 Download of a file with 100 KBytes using FTP and CS2


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Fig. 7 Download of a file with 500 KBytes using FTP and CS2 (3 timeslots)


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Fig. 8 Download of a file with 1Mbyte using FTP and MCS9 (2 timeslots)


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4 WWW


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The success of the Internet during the last years arises mainly from one applicationcalled WWW (World Wide Web). One has to distinguish the application WWW fromthe internet itself.

The WWW as a protocol standard was developed in the CERN research center inGeneva. Scientists developed the HTTP (Hypertext Transfer Protocol) which allowsan easy transmission of information containing not only text, but also pictures,programs, sound files links to other information etc.

An example for the download of an Internet page using a (3+1) GPRS mobile is givenin the following picture:


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Fig. 9 Example for the download of an Internet page


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5 Exercise


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Exercise

Title: Throughput when using FTPObjectives: Understanding of different throughput rates when using FTP

Pre-requisite: none

Task

Answer the following questions

Query

Consider the screenshot of Figure 6. How many bytes are received by the (3+1)

GPRS mobile in 28.89 seconds?

Consider the screenshot of Figure 7. How many bytes are received by the (3+1)GPRS mobile in 133.75 seconds?

Concerning FTP, why is the throughput usually higher when downloading larger files?


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6 Solution


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Tcp Ip Service Programs Appl

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