Would you like to inspect the original subtitles? These are the user uploaded subtitles that are being translated:
1
1
00:00:00,000 --> 00:00:04,000
And in this section we gonna look at TCP/IP transport layer or layer 4 of the OSI model.
2
2
00:00:07,000 --> 00:00:13,000
We are specifically gonna concentrate on the TCP and UDP protocol that reside at this layer.
3
3
00:00:14,000 --> 00:00:17,000
I’d like to start up with the comparison of UDP and TCP
4
4
00:00:18,000 --> 00:00:20,000
and show you the differences between those 2 protocols
5
5
00:00:21,000 --> 00:00:25,000
we need to have a discussion of port numbers and explain how ports numbers are used.
6
6
00:00:26,000 --> 00:00:29,000
We look at the details of UDP and the details of TCP
6
7
00:00:30,000 --> 00:00:33,000
and we look at some of the mechanisms that TCP uses including the TCP 3 way handshake.
7
8
00:00:34,000 --> 00:00:37,000
We gonna look at windowing and we're gonna look at sequence numbers.
8
9
00:00:38,000 --> 00:00:39,000
So there's quite a bit to cover on these 2 protocols.
9
10
00:00:40,000 --> 00:00:43,000
Before discussing TCP and UDP I'd like to remind you
10
11
00:00:44,000 --> 00:00:48,000
that IP or internet protocol is connectionless.
11
12
00:00:49,000 --> 00:00:53,000
Every packet it’s treated individually and separately by routers or routers in the network.
12
13
00:00:54,000 --> 00:00:59,000
So this PC on the left hand side send is sending traffic to this server on the right hand side.
13
14
00:01:00,000 --> 00:10:03,000
Individual packets from the PC could take the upper path
14
15
00:01:04,000 --> 00:01:07,000
or they could traverse the lower link.
15
16
00:01:08,000 --> 00:01:14,000
The internet consist of many, many devices and multiple parts to destinations
16
17
00:01:15,000 --> 00:01:18,000
and it’s important to realize that traffic from one host to another host
17
18
00:01:19,000 --> 00:01:22,000
could take different paths even though that traffic
18
19
00:01:23,000 --> 00:01:25,000
is part of the same conversation or same session.
19
20
00:01:26,000 --> 00:01:30,000
So if the PC is communicating to the server across the internet
20
21
00:01:31,000 --> 00:01:34,000
traffic from that PC could use multiple parts
21
22
00:01:36,000 --> 00:01:37,000
depending on how the traffic is routed through the internet.
22
23
00:01:38,000 --> 00:01:42,000
That means the traffic could arrive out of order.
23
24
00:01:43,000 --> 00:01:46,000
So for example if the PC sends packet 1
24
25
00:01:51,000 --> 00:01:54,000
Packet 2 could arrive before packet 1
25
26
00:01:55,000 --> 00:01:58,000
and does the packet arrive at the server in this order
26
27
00:01:59,000 --> 00:02:01,000
packet 2, packet 1, and packet 3
27
28
00:02:02,000 --> 00:02:07,000
that server requires a mechanism to reorder the packets into the original sequence.
28
29
00:02:08,000 --> 00:02:12,000
IP also does not guarantee the delivery of packets
30
30
00:02:13.000 --> 00:02:017.000
so there’s no guarantee that the packets actually arrived at the server
29
31
00:02:18,000 --> 00:02:21,000
or they arrived in the correct order or free from errors.
30
32
00:02:22,000 --> 00:02:26,000
Higher layer protocols need to ensure the reordering of packets
31
33
00:02:27,000 --> 00:02:31,000
and checking that the packets actually arrived successfully.
32
34
00:02:32,000 --> 00:02:39,000
The 2 protocols that we're gonna concentrate on this section, as mentioned are TCP and UDP.
33
35
00:02:40,000 --> 00:02:45,000
TCP and UDP reside at layer 4 the OSI model, in other words the transport layer.
34
36
00:02:46,000 --> 00:02:50,000
Just to recap at the physical layer we'll have Ethernet
37
37
00:02:51,000 --> 00:02:53,000
or another type of physical presentation.
35
38
00:02:54,000 --> 00:02:56,000
At layer 2 on Ethernet, we use MAC addresses
36
39
00:02:57,000 --> 00:03:02,000
on WAN interfaces, we would use another type of encapsulation such as frame relay or PPP
37
40
00:03:03,000 --> 00:03:08,000
At layer 3 were using IP and devices are represented by IP addresses
38
41
00:03:09,000 --> 00:03:11,000
and at layer 4 we have TCP and UDP.
39
42
00:03:12,000 --> 00:03:15,000
Here’s a quick analogy explaining the difference between
40
43
00:03:16,000 --> 00:03:23,000
UDP or User Datagram Protocol and TCP or Transmission Control Protocol.
41
44
00:03:24,000 --> 00:03:30,000
UDP like IP is connectionless, it does not guarantee the delivery of packets.
42
45
00:03:31,000 --> 00:03:34,000
It requires high layer protocols for instance
43
46
00:03:35,000 --> 00:03:38,000
at the application layer to ensure the successful delivery of packets
44
47
00:03:39,000 --> 00:03:45,000
as an analogy UDP services are similar to using regular mail offered by the Post Office
48
48
00:03:46,000 --> 00:03:50,000
you would write your letter and enclose it in an envelope
45
49
00:03:51,000 --> 00:03:55,000
by the same token, you would take your data and encapsulate it in UDP
46
50
00:03:56,000 --> 00:04:01,000
you would then post your letter and hopefully the postal service
47
51
00:04:02,000 --> 00:04:03,000
will deliver the letter to the recipient
48
52
00:04:04,000 --> 00:04:06,000
there’s is however no guarantee that the letter
49
53
00:04:07,000 --> 00:04:11,000
will be collected, transported, delivered
50
54
00:04:12,000 --> 00:04:16,000
and opened by the recipient as this is regular mail.
51
55
00:04:17,000 --> 00:04:20,000
You as the sender do not get an acknowledgement
52
56
00:04:21,000 --> 00:04:22,000
or proof of delivery of that letter.
57
57
00:04:23,000 --> 00:04:29,000
The postal service once again, does not guarantee delivery and is not responsible
53
58
00:04:30,000 --> 00:04:33,000
for letting you know that the delivery was successful or unsuccessful.
54
59
00:04:38,000 --> 00:04:41,000
but has the inherent disadvantage of unreliability.
55
60
00:04:42,000 --> 00:04:46,000
In a UDP environment, UDP at layer 4 does not guarantee delivery
62
61
00:04:47,000 --> 00:04:50,000
higher layer protocols at the application layer
56
62
00:04:51,000 --> 00:04:54,000
will need to ensure reliability and delivery acknowledgement if required.
57
63
00:04:55,000 --> 00:05:01,000
TCP on the other hand, does provide delivery acknowledgement and reliability
58
64
00:05:02,000 --> 00:05:05,000
but with the disadvantage of the additional overhead
59
65
00:05:06,000 --> 00:05:10,000
as an analogy, a TCP session could be seen as the telephone call
60
66
00:05:11,000 --> 00:05:14,000
TCP is connection orientated in the same way that a telephone call is.
61
67
00:05:15,000 --> 00:05:18,000
The person on the left makes a call to the person on the right.
62
68
00:05:19,000 --> 00:05:23,000
The person on the right is notified of the incoming connection
63
69
00:05:24,000 --> 00:05:26,000
or incoming call by the phone ringing.
71
70
00:05:27,000 --> 00:05:29,000
When the person on the right hand side answers the call
64
71
00:05:30,000 --> 00:05:31,000
they will acknowledge that by saying like
65
72
00:05:32,000 --> 00:05:35,000
"hello, it's David speaking"
66
73
00:05:36,000 --> 00:05:38,000
the person on the left hand side or the caller is does notify
67
74
00:05:39,000 --> 00:05:41,000
that the telephone call has been answered.
68
75
00:05:42,000 --> 00:05:43,000
The caller can then say
69
76
00:05:44,000 --> 00:05:45,000
"hello David, it's Peter speaking".
70
77
00:05:46,000 --> 00:05:51,000
So the called party or the person on the right hand side, knows you've made the call.
71
78
00:05:51,000 --> 00:05:55,000
So there sort of a three-way handshake that takes place here
72
79
00:05:56,000 --> 00:05:58,000
with the person on the right hand side initiates the call
73
80
00:05:59,000 --> 00:06:01,000
the person on the right hand side acknowledges the call.
74
81
00:06:02,000 --> 00:06:06,000
and the person on the left hand side then indicates who's speaking
75
82
00:06:07,000 --> 00:06:11,000
Once the three-way handshake has taking place, and please note once again
84
83
00:06:12,000 --> 00:06:14,000
that this is just an analogy and in a telephone environment
76
84
00:06:15,000 --> 00:06:16,000
there are many more steps that take place
77
85
00:06:17,000 --> 00:06:22,000
but once as an analogy that has taken place, there’s communication between the 2 parties.
78
86
00:06:23,000 --> 00:06:26,000
If the party on the left hand side, wanted to provide some information
79
87
00:06:27,000 --> 00:06:30,000
to the party on the right hand side, let’s say for instance a telephone number.
80
88
00:06:31,000 --> 00:06:33,000
The party on the left hand side would read out the number
81
89
00:06:34,000 --> 00:06:36,000
and in this example I’m just keeping it simple
82
90
00:06:37,000 --> 00:06:40,000
and imagine for the moment that this is very long and complicated number
83
91
00:06:41,000 --> 00:06:44,000
the party on the left hand side would say the number is 555
84
92
00:06:45,000 --> 00:06:49,000
and then the party on the right hand side would acknowledge receipt of that number
85
93
00:06:50,000 --> 00:06:53,000
by reading back the number received which is 555.
86
94
00:06:54,000 --> 00:06:59,000
The party on the left hand side, can check that the number received is the correct number
87
95
00:07:00,000 --> 00:07:04,000
and then can continue with the subsequent digits like 1234.
88
96
00:07:05,000 --> 00:07:08,000
The party on the right hand side would read those number back
89
97
00:07:09,000 --> 00:07:11,000
to ensure correct receipt of the number.
90
98
00:07:12,000 --> 00:07:15,000
Now in TCP environment the information is not echoed
91
99
00:07:16,000 --> 00:07:20,000
but there is the use of sequence numbers to ensure successful delivery
92
100
00:07:21,000 --> 00:07:23,000
or successful receive of information
93
101
00:07:24,000 --> 00:07:26,000
Before continuing I'd like to explain what a socket is
94
102
00:07:27,000 --> 00:07:31,000
as this term is often used in networking and I'm going to mention it in the upcoming slides
95
103
00:07:32,000 --> 00:07:36,000
A socket is the combination of the IP Address of the host
96
104
00:07:37,000 --> 00:07:42,000
in other words the location of a computer for example and the port number used.
97
105
00:07:43,000 --> 00:07:46,000
Port numbers are used to identify applications
98
106
00:07:47,000 --> 00:07:51,000
for instance port 80, identified http and the transport protocol used
99
107
00:07:52,000 --> 00:07:58,000
108
7:52 --> 7:58
in other words TCP or UDP, these 3 are then combined into a single entity
100
109
00:07:59,000 --> 00:08:06,000
in the same way like a telephone connection is the combination of the phone number and a particular extension
101
110
00:08:07,000 --> 00:08:12,000
We'll be discussing TCP and UDP protocols in more detail in a moment
102
111
00:08:13,000 --> 00:08:17,000
We'll also be looking at various port numbers and how they are used to identify applications
103
112
00:08:18,000 --> 00:08:21,000
and in the previous section we've discussed IP addressing
104
113
00:08:22,000 --> 00:08:24,000
A socket is a combination of these 3 things
105
114
00:08:25,000 --> 00:08:28,000
used to identify connection between hosts
106
115
00:08:29,000 --> 00:08:32,000
TCP and UDP allow for session multiplexing
116
116
00:08:33,000 --> 00:08:39,000
which is when a single computer or host with the single IP address is able to communicate
117
117
00:08:40,000 --> 00:08:43,000
with multiple servers or multiple devices
107
118
00:08:44,000 --> 00:08:46,000
and have multiple sessions occurs simultaneously.
119
119
00:08:47,000 --> 00:08:53,000
The session is created when a source host needs to send data or information to a destination host.
108
120
00:08:54,000 --> 00:08:57,000
Replies are often received but aren't mandatory
121
121
00:08:58,000 --> 00:09:02,000
the session is created and controlled within the network application
109
122
00:09:03,000 --> 00:09:06,000
which contains the functionality of OSI layers 5 through 7.
123
123
00:09:07,000 --> 00:09:10,000
In a best effort environment the settings are very simple
110
124
00:09:11,000 --> 00:09:15,000
sessions parameters are sent to UDP, which as we know now as a best effort protocol.
111
125
00:09:16,000 --> 00:09:20,000
Information is just sent to a destination IP address and destination port number.
126
126
00:09:21,000 --> 00:09:25,000
It’s important to remember that each transmission is a totally separate event
112
127
00:09:26,000 --> 00:09:31,000
with no memory or association between various transmissions retain.
113
128
00:09:32,000 --> 00:09:38,000
When using a reliable service like TCP, as discussed a connection must first be established
114
129
00:09:39,000 --> 00:09:41,000
between the sender and receiver before any data can be transmitted.
115
130
00:09:42,000 --> 00:09:46,000
TCP will open a connection and negotiate various connection parameters
116
131
00:09:47,000 --> 00:09:51,000
which I'll discuss in more detail in a moment before actually transmitting any data.
117
132
00:09:52,000 --> 00:09:56,000
Sharing data flow, TCP will maintain reliable delivery of the data
133
133
00:09:57,000 --> 00:09:59,000
and will close the connection once complete.
118
134
00:10:00,000 --> 00:10:05,000
An example of this, is that on my machine, I can’t open up multiple connections
119
135
00:10:06,000 --> 00:10:08,000
to different servers at the same time.
120
136
00:10:09,000 --> 00:10:15,000
So I could open a connection to Gmail, I could open up connection to yahoo
121
137
00:10:16,000 --> 00:10:23,000
I could open up a connection to Google and so forth and so on.
122
138
00:10:24,000 --> 00:10:27,000
On this individual machine that has 1 IP address
123
139
00:10:28,000 --> 00:10:35,000
I’m connecting to multiple servers simultaneously, therefore using session multiplexing.
15119
Can't find what you're looking for?
Get subtitles in any language from opensubtitles.com, and translate them here.
Afrikaans
Akan
Albanian
Amharic
Arabic
Armenian
Azerbaijani
Basque
Belarusian
Bemba
Bengali
Bihari
Bosnian
Breton
Bulgarian
Cambodian
Catalan
Cebuano
Cherokee
Chichewa
Chinese (Simplified)
Chinese (Traditional)
Corsican
Croatian
Czech
Danish
Dutch
English
Esperanto
Estonian
Faroese
Finnish
Galician
Georgian
German
Greek
Guarani
Haitian Creole
Hausa
Hawaiian
Hebrew
Hmong
Hungarian
Icelandic
Indonesian
Irish
Italian
Japanese
Kazakh
Kinyarwanda
Kirundi
Kongo
Korean
Krio (Sierra Leone)
Kurdish
Kyrgyz
Laothian
Latin
Latvian
Lithuanian
Luganda
Luo
Luxembourgish
Macedonian
Malagasy
Malay
Maltese
Maori
Mauritian Creole
Moldavian
Mongolian
Myanmar (Burmese)
Montenegrin
Nepali
Norwegian
Pashto
Persian
Polish
Portuguese (Brazil)
Quechua
Romanian
Romansh
Russian
Samoan
Scots Gaelic
Serbian
Sesotho
Setswana
Seychellois Creole
Shona
Sindhi
Sinhalese
Slovak
Slovenian
Somali
Spanish
Swedish
Tajik
Thai
Tigrinya
Tonga
Turkish
Turkmen
Ukrainian
Uzbek
Vietnamese
Welsh
Wolof