The document discusses various topics related to sharing resources and internet applications. It begins by covering medium access control protocols like ALOHA, CSMA, and CSMA/CD. It then discusses congestion control, including max-min fairness, router queuing strategies, and window-based congestion control. Finally, it summarizes several internet applications - DNS, email protocols like SMTP, and the basic web client-server architecture.
Fourth lesson of the Computer Networking class. Covers reliable transport principles and the introduction for sharing resources (MAC and congestion control)
Part 5 : Sharing resources, security principles and protocolsOlivier Bonaventure
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Fourth lesson of the Computer Networking class. Covers reliable transport principles and the introduction for sharing resources (MAC and congestion control)
Part 5 : Sharing resources, security principles and protocolsOlivier Bonaventure
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Beyond TCP: The evolution of Internet transport protocolsOlivier Bonaventure
The transport layer is one of the key layers of the Internet protocol stack. It enrichs the network layer service to make it suitable for applications. Almost 40 years after its initial design, TCP remains the most widely used transport protocol. In the early 2000s, SCTP was proposed as an alternative to TCP. Despite a clean and extensible design and many useful features, it did not reach wide deployment. This failure is mainly caused by middleboxes. We'll describe their operation and explain why Multipath TCP, which is a backward compatible evolution to TCP, has better chances of being deployed. We'll explain the main principles behind Multipath TCP and the lessons that can be drawn from its design. We'll then analyse why Internet giants like Google and Microsoft now consider application-layer solutions like QUIC to replace standard protocols like TCP.
Presentation given at MPLS+SDN+NFVWORLD 2019 in Paris that shows how network architects can leverage the support for IPv6 Segment that is included in the Linux kernel to develop new end-to-end services that use IPv6 Segment Routing on clients, routers and servers.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Many applications are network I/O bound, including common database-based applications and service-based architectures. But operating systems and applications are often untuned to deliver high performance. This session uncovers hidden issues that lead to low network performance, and shows you how to overcome them to obtain the best network performance possible.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Beyond TCP: The evolution of Internet transport protocolsOlivier Bonaventure
The transport layer is one of the key layers of the Internet protocol stack. It enrichs the network layer service to make it suitable for applications. Almost 40 years after its initial design, TCP remains the most widely used transport protocol. In the early 2000s, SCTP was proposed as an alternative to TCP. Despite a clean and extensible design and many useful features, it did not reach wide deployment. This failure is mainly caused by middleboxes. We'll describe their operation and explain why Multipath TCP, which is a backward compatible evolution to TCP, has better chances of being deployed. We'll explain the main principles behind Multipath TCP and the lessons that can be drawn from its design. We'll then analyse why Internet giants like Google and Microsoft now consider application-layer solutions like QUIC to replace standard protocols like TCP.
Presentation given at MPLS+SDN+NFVWORLD 2019 in Paris that shows how network architects can leverage the support for IPv6 Segment that is included in the Linux kernel to develop new end-to-end services that use IPv6 Segment Routing on clients, routers and servers.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Many applications are network I/O bound, including common database-based applications and service-based architectures. But operating systems and applications are often untuned to deliver high performance. This session uncovers hidden issues that lead to low network performance, and shows you how to overcome them to obtain the best network performance possible.
MAC stands for Media Access Control. A MAC layer protocol is the protocol that controls access to the physical transmission medium on a LAN.
It tries to ensure that no two nodes are interfering with each other’s transmissions, and deals with the situation when they do.
Distributed coordinate function: ad hoc mode
Virtual and physical carrier sense (CS)
Network allocation vector (NAV), duration field
Binary exponential backoff
RTS/CTS/DATA/ACK for unicast packets
Broadcast packets are directly sent after CS
Takes time for every node to increase CW
Especially if traffic is spatially-correlated and bursty
Waste backoff slots if collisions cause CW to increase
Now let’s look at how this works in practice.
B hears A’s transmission, so when B’s chosen slot comes, it continues to wait.
In CSMA, each node picks a timeslot uniformly at random in the contention window.
This means that every slot has an equal chance of being chosen by a node.
However, if someone else starts transmitting before your chosen slot, you need to remain quiet.
Therefore…
SIFS : used by ACK, CTS, poll response(short)
PIFS : used by PC (point coordinator) when issuing polls(point)
DIFS : used by ordinary asynchronous traffic(distributed)
SIFS - 16 µsec. Slot Time - 9 µsec. AIFS[0] = (2 * 9) + 16 = 34 µsec = DIFS. AIFS[1] = (4 * 9) + 16 = 52 µsec (52 – 34) / 9 = 18/9 = 2 Slots ...
slot: 9us. SIFS: 16us. PIFS: 25us. DIFS: 34us. AIFS: >=34us.
SIFS : Short Interframe Space. – PIFS : PCF Interframe Space. – DIFS : DCF Interframe Space. – AIFS : Arbitration Interframe Space (used for QoS)
AIFS = SIFS + AIFSN * aSlotTime.
AIFS[0] = PIFS + 1 µs; AIFS[1] = PIFS + 5µs; AIFS[2] = DIFS; therefore, AIFS[0] < AIFS[1] < AIFS[2]; where PIFS = SIFS + SLOT = 25 µs and DIFS =SIFS + 2*SLOT = 34 µs.
Contention-based protocols (contd.)
MACAW — improved over MACA
RTS/CTS/DATA/ACK
Fast error recovery at link layer
IEEE 802.11 Distributed Coordination Function (DCF)
Largely based on MACAW
Called CSMA/CA
A and C want to send to B
A sends RTS (Request To Send) to B
B sends CTS (Clear To Send) to AC “overhears” CTS from B
C waits for duration of A’s transmission
A and C want to send data to B
A senses medium idle and sends data
C senses medium idle and sends data
Collision occurs at B
Contention-based protocols
CSMA — Carrier Sense Multiple Access
Ethernet (CSMA/CD) is not enough for wireless (collision at receiver cannot detect at sender)Packets which suffered collisions should be re-sent.
Ideally, we would want all packets to be sent collision-free, only once…
Ethernet Collisions
Node A needs to transmit data to Node D.
Node A builds a packet.
Checks to see if the cable plant is clear (no one else is currently transmitting).
Transmits packet while listening to the cable.
Before Node A’s transmission reaches node C, node C accomplishes the above steps and also starts to transmit.
There is a collision on the cable plant caused by node A and C.
All stations invoke the backoff algorithm.
This defe
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Part 10 : Routing in IP networks and interdomain routing with BGPOlivier Bonaventure
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
Slides supporting the "Computer Networking: Principles, Protocols and Practice" ebook. The slides can be freely reused to teach an undergraduate computer networking class using the open-source ebook.
6th International Conference on Machine Learning & Applications (CMLA 2024)ClaraZara1
6th International Conference on Machine Learning & Applications (CMLA 2024) will provide an excellent international forum for sharing knowledge and results in theory, methodology and applications of on Machine Learning & Applications.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
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Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
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Online aptitude test management system project report.pdfKamal Acharya
The purpose of on-line aptitude test system is to take online test in an efficient manner and no time wasting for checking the paper. The main objective of on-line aptitude test system is to efficiently evaluate the candidate thoroughly through a fully automated system that not only saves lot of time but also gives fast results. For students they give papers according to their convenience and time and there is no need of using extra thing like paper, pen etc. This can be used in educational institutions as well as in corporate world. Can be used anywhere any time as it is a web based application (user Location doesn’t matter). No restriction that examiner has to be present when the candidate takes the test.
Every time when lecturers/professors need to conduct examinations they have to sit down think about the questions and then create a whole new set of questions for each and every exam. In some cases the professor may want to give an open book online exam that is the student can take the exam any time anywhere, but the student might have to answer the questions in a limited time period. The professor may want to change the sequence of questions for every student. The problem that a student has is whenever a date for the exam is declared the student has to take it and there is no way he can take it at some other time. This project will create an interface for the examiner to create and store questions in a repository. It will also create an interface for the student to take examinations at his convenience and the questions and/or exams may be timed. Thereby creating an application which can be used by examiners and examinee’s simultaneously.
Examination System is very useful for Teachers/Professors. As in the teaching profession, you are responsible for writing question papers. In the conventional method, you write the question paper on paper, keep question papers separate from answers and all this information you have to keep in a locker to avoid unauthorized access. Using the Examination System you can create a question paper and everything will be written to a single exam file in encrypted format. You can set the General and Administrator password to avoid unauthorized access to your question paper. Every time you start the examination, the program shuffles all the questions and selects them randomly from the database, which reduces the chances of memorizing the questions.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
We have compiled the most important slides from each speaker's presentation. This year’s compilation, available for free, captures the key insights and contributions shared during the DfMAy 2024 conference.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Using recycled concrete aggregates (RCA) for pavements is crucial to achieving sustainability. Implementing RCA for new pavement can minimize carbon footprint, conserve natural resources, reduce harmful emissions, and lower life cycle costs. Compared to natural aggregate (NA), RCA pavement has fewer comprehensive studies and sustainability assessments.
2. Agenda
• Sharing resources
• Medium Access Control
• Congestion Control
• Internet applications
3. ALOHA
N=1;
while ( N<= max) do
send frame;
wait for ack on return channel or timeout:
if ack on return channel
exit while;
else
/* timeout */
/* retransmission is needed */
wait for random time;
N=N+1;
end do
/* too many attempts */
4. CSMA
N=1;
while ( N<= max) do
wait until channel becomes free;
send frame immediately;
wait for ack or timeout:
if ack received
exit while;
else
/* timeout */
/* retransmission is needed */
N=N+1;
end do
/* too many attempts */
5. CSMA/CD
• Basic solution
N=1;
while ( N<= max) do
wait until channel becomes free;
send frame and listen;
wait until (end of frame) or (collision)
if collision detected
stop transmitting;
/* after a special jam signal */
else
/* no collision detected */
wait for interframe delay;
exit while;
N=N+1;
end do
/* too many attempts */
6. Example
A B
Start of frame
1
Frame is propagated on LAN (5 microsecond per kilometer)
2
Frame stops at left side and first bit reaches B
3
4
Frame leaves the LAN
7. Collisions
A B
Frame starts at A and B almost at the same time
1
2
Collision : at this point on the
shared medium, it is impossible
to decode the signal
A detects the collision and
stops transmitting its frame
3
8. Can we detect all
collisions ?
A B
A and B send a small frame almost at the same time
1
The two frame collide in the middle of the medium
2
A did not notice any collision
B did not notice any collision
They both consider that their frames were received correctly
3
9. Worst case
A B
Start of 1 the frame sent by A
3
After t seconds, A’s frame reaches B
A time t-e, B starts to transmit its own frame
B notices the collision immediately and stops transmitting
A detects collision at time t+t-e
2
10. How to detect all
collisions ?
• All nodes must always transmit during at
least the two way delay (2∗τ)
• If bandwidth is fixed => minimum frame
size
11. How to react after
collision ?
• Exponential backoff
• Wait random time after collision
• Divide time in slots Backoff (slot = (2∗τ))
• 1st collision : wait 0 or 1 slot
• 2nd collision :wait 0, 1,2 or 3 slots
• ith collision : wait 0..2i-1 slots
12. CSMA/CD
• Final solution
N=1;
while ( N<= max) do
wait until channel becomes free;
send frame and listen;
wait until (end of frame) or (collision)
if collision detected
stop transmitting;
/* after a special jam signal */
k = min (10, N);
r = random(0, 2k – 1);
wait for r time slots;
else
/* no collision detected */
wait for interframe delay;
exit while;
N=N+1;
end do
/* too many attempts */
13. CSMA/CA
• A MAC for wireless networks
• Cannot always detect collisions
• Improvements to CSMA
• Initial delay to transmit (EIFS)
• Min. delay between frames (DIFS)
• Delay between frame and ack (SIFS)
14. CSMA/CA : receiver
While (true)
{
Wait for data frame;
if not(duplicate)
{ deliver (frame) }
wait during SIFS;
send ack (frame) ;
}
15. CSMA/CA : sender
N=1;
while ( N<= max) do
if (previous frame corrupted)
{ wait until channel free during t>=EIFS; }
else
{ wait until endofframe;
wait until channel free during t>=DIFS; }
send data frame ;
wait for ack or timeout:
if ack received
exit while;
else
/* timeout retransmission is needed */
N=N+1;
end do
/* too many attempts */
16. Example
A B C
DIFS
Data frame
Busy
SIFS
ACK frame
DIFS
Data frame
17. Collisions
A B C
DIFS
DIFS
Data frame
Busy
Busy Data frame
Timeout Timeout
Data frame
Busy
Data frame
18. CSMA/CA : sender
N=1;
while ( N<= max) do
if (previous frame corruped)
{ wait until channel free during t>=EIFS; }
else
{ wait until endofframe;
wait until channel free during t>=DIFS; }
backoff_time = int(random[0,min(255,7*2N-1)])*T
wait(channel free during backoff_time)
send data frame ;
wait for ack or timeout:
if ack received
exit while;
else /* timeout retransmission is needed */
N=N+1; }
end do
19. Backoff
A B C
DIFS
DIFS
Backoff[0,7]
Backoff[0,7]
Channel busy!
Busy
Data frame
Data frame
SIFS
Ack frame
Remaining
backoff
21. Hidden station
• How to solve it ?
• Sender reserves time slot
• Receiver confirms the time reservation
22. RTS/CTS
A B C
DIFS+Backoff
Busy[
100microsec+
SIFS+
CTS+
SIFS+
ACK
]
RTS [100 microsec]
SIFS
CTS[100microsec]
Data [100 microsec]
SIFS
ACK frame
SIFS
23. Agenda
• Sharing resources
• Medium Access Control
• Congestion Control
• Internet applications
24. Max-min fairness
• Fairness definition for networks
• a max-min allocation of bandwidth is an
allocation of bandwidth which maximises the
allocation of bandwidth to the sources
receiving the smallest allocation
• Property
• a max-min fair allocation is such that in
order to increase the bandwidth allocated to
one source, it is necessary to decrease the
bandwidth allocated to another source
which already receives a lower allocation
25. Max-min fairness
• a max-min allocation maximises the
allocation of bandwidth to the sources
receiving the smallest allocation
• Property
• to increase the bandwidth allocated to
one source, it is necessary to decrease
the bandwidth allocated to another
source which already receives a lower
allocation
26. Example
R
R
D1 D3 D5
R
R
R
1000 Mbps
100 Mbps
S1
S2
S3 S4 S5 S6 S7 S8
• Max-min fair bandwidth allocation
D2
D4
D6
D7
D8
Link1
Link2
Link3
Link4
27. Router output port
Q[1]
Q[2]
Q[3]
Q[N]
Flow identification
Input links
Output link
Flow identification
Identifies the TCP/UDP flow
to which the arriving packet
belongs
Buffer acceptance
accepts or rejects
incoming packets
Queuing strategy
Logical organization of the
router's buffers
Scheduler
Chooses the packet to
be transmitted first on
the output link
28. Round robin
Flow 1
Flow 2
Flow 3
Flow 4
Flow 5
Flow 1
Flow 2
Flow 3
Flow N
Scheduler :
F1
F2
FN
F4 F3
29. Example
F1
F2
F3
Flow1(L=1)
Flow2 (L=2)
Flow3 (L=1) F1
F3 F2
Flow1 and Flow3 send packets of size 1
Flow 2 sends packets of size 2
33. How to detect
congestion ?
• Packet losses
• Routers add information to packets
• Forward binary feedback
• Backward binary feedback
• Rate feedback
34. Congestion control
• Additive Increase / Multiplicative Decrease
# Additive Increase Multiplicative Decrease
if congestion :
rate=rate*betaC # MD, betaC<1
else
rate=rate+alphaN # AI
35. Window-based
Congestion control
# Initialisation
cwin = 1 # congestion window measured in segments
# Ack arrival
if newack : # new ack, no congestion
# increase cwin by one every rtt
cwin = cwin+ (1/cwin)
else:
# no increase
Congestion detected:
cwnd=cwin/2 # only once per rtt
36. Agenda
• Sharing resources
• Internet applications
• DNS
• Email
• Web
• Remote Procedure Calls
37. Internet
Transport services
• Service provided by UDP
• Connectionless, unreliable
• Service provided by TCP
• Connection-oriented
• reliable bytestream
38. Internet addresses
• IPv4
• 32 bits, written as a.b.c.d, e.g.
130.104.1.1
• IPv6
• 128 bits, written in hexadecimal notation,
e.g. 2001:6a8:3080:1::3
39. UDP service
UDP service
Applic.
2
Applic.
1
Identification
IP address : 2001:4860:a005::68
Protocol : UDP
Port : 53
Identification:
IP address :
2001:6a8:3080:2:217:f2ff:fed6:65c0
Protocol : UDP
Port : 1234
• Identification of an application
• IP address + port number
40. TCP service
TCP service
• Identification of an application
• IP address + TCP + port number
Applic.
2
Applic.
1
Identification
IP address: 2001:6a8:3080:1::3
Protocol : TCP
Port : 80
Identification:
IP address :
2a02:2788:2c4:16f:226:bbff:fe09:266e
Protocol : TCP
Port : 9876
41. Agenda
• Sharing resources
• Internet applications
• DNS
• Email
• Web
• Remote Procedure Calls
42. The Domain Name
System
• Hierarchy of domain names
• Domain Name servers
• DNS resolvers
43. DNS messages
Each DNS request contains a number that will be returned in the
response by the server to allow the client to match the request.
32 bits
Identification Flags
12 bytes Number of questions
Number of answers
Number of authority Number of additional
Questions
(variable number of resource records)
Answers
(variable number of resource records)
Authority
(variable number of resource records)
Additional information
(variable number of resource records)
lQuestion/Response
lRecursive question or not
lAuthoritative answer or not
lPossible error
44. DNS Resource Records
• A
• IPv4 address
• AAAA
• IPv6 address
• NS
• Name server
45. Agenda
• Sharing resources
• Internet applications
• DNS
• Email
• Web
• Remote Procedure Calls
46. Simplified architecture
Alice’s
email server
b.net ‘s
email server
Alice@a.net Bob@b.net
Alice sends her email
to local mail forwarder
Alice’s server sends email
to b.net’s MX
Bob retrieves message
from his server
47. Message format
Exp: ABC S.A.
Rue de Fer 10
5000 Namur
DEF Corp.
Steel street 9
WA78 AX London
Grande Bretagne
From: president@abc.be
To: ceo@def.com
Subject: Hello
Date : 27 Sept. 1999 0901
Dear Sir,
Bla Bla Bla...
Header
Message
body
48. Header format
• At least three lines that end with <CRLF>
• From: sender@domain
• To:recipient@domain
• Date: <creation date of message>
• Optional fields
• Subject: , cc: ,Message-ID:, Received: In-
Reply-To: , ...
• Header ends with empty line (<CRLF>)
49. Email protocols
SMTP
SMTP Email
a.net’s
SMTP server
b.net’s SMTP
server
retrieval
Alice@a.net Bob@b.net
50. Agenda
• Sharing resources
• Internet applications
• DNS
• Email
• Web
• Remote Procedure Calls
52. Key elements of the
web
• URL : An addressing scheme that allows to
identify any document stored on a server
• HTML : An hypertext language to easily
write documents with hypertext links
• HTTP : An efficient and lightweight
protocol to exchange documents
• Servers
• Clients (browsers)
53. URL
• syntax : <protocol>://<document>
• http is the most common
• document indicates the server and the
location of the document
• <user>:<password>@<server>:<port>/
<path>
54. HTML
<HTML>
<HEAD>
<TITLE>HTML test page</TITLE>
</HEAD>
<BODY>
<IMG SRC="http://www.images.be/logo.gif">
<H1>Web servers from UCL UCL<P></H1>
<HR>
<UL>
<LI><A HREF="http://www.uclouvain.be">UCL</A>
<LI><A HREF="http://www.info.ucl.ac.be">CSE Dept.</A>
<LI><A HREF="http://www.math.ucl.ac.be">Math</A>
</UL>
</BODY>
</HTML>
Header
Body
Image on remote server
First level title
External hypertext link
55. HTTP
Client
Server
Request
Method
Header
CRLF
MIME Document
Method
GET
lPOST
l...
Header contains additional information
about request sent by client
Response
Status line
Header
CRLF
MIME Document
Header contains information about server
and optional parameters specific to response
Success or failure
HTTP is a stateless protocol, server does not maintain any state from
one request to another
57. Agenda
• Sharing resources
• Internet applications
• DNS
• Email
• Web
• Remote Procedure Calls
Editor's Notes
The value T is defined in the standard, but a detailed discussion of this value is outside the scope of this presentation.
How to determine a max-min fair bandwidth allocation for a given network ?
Algorithm [Bertsekas & Gallager, Data Networks, 2nd edition, Prentice Hall 1992]
First start with an allocation of 0 Mbps for each source
Then equally increment the allocation to each source until one link becomes saturated. At this point, each source which uses the saturated link receives an allocation equal to the bandwidth of this saturated link divided by the number of sources using this bottleneck link.
Next, the allocation of all the sources which do not use a saturated link is equally incremented until another link becomes saturated.
The algorithm continues from step to step, always incrementing the allocation of the sources which do not use a saturated link, until all sources use at least one of the saturated links.
UDP is defined in
J. Postel, User Datagram Protocol. RFC768, August 1980
It will be described in more details later
TCP is defined in
J. Postel, Transmission Control Protocol, RFC793, September 1981
It will be described in more details later
The RR MX were proposed in
C. Partridge. Mail routing and the domain system. Request for Comments 974, Internet Engineering Task Force, January 1986.
A complete list of DNS RR may be found at
http://www.its.uq.edu.au/tn-0011