Transcript ppt for Chapters 1-5 - Computer and Information Sciences

Welcome
to
CS 334/534
1
Network of networks
BHM
CHL
NO
ATL
“Fig 1.5” – An internet
4 Ethernet LANs linked by a WAN
2
Comer Figure 1.1 – Growth of the Internet
3
WORLD TOTALS
► Population 2010:
6,845,609,960
►Internet Users Dec 31 2000:
360,985,492
►Internet Users June 30 2010:
1,966,514,816 (+444.8 %)
►Penetration of population:
28.7 %
August 2010: “ Sometime this month, the 5 billionth device will
plug into the Internet”
“Today, there are over 1 billion computers that regularly connect
to the Internet.”
“But cellular devices, such as Internet-connected smartphones,
have outstripped that total and are growing at a much faster rate.” 4
2.2 Two Approaches to Network Communication
* circuit-switched networks (telephone)
3 phases:
establish connection between end points
use connection
relinquish connection
disadvantage: cost independent of use
* packet-switched networks (post office)
at source, data divided into packets
packets individually sent from source to destination
data reassembled at destination
advantage: can share transport facilities
disadvantage: traffic spike may overload
5
2.4 Ethernet Technology
Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)
6
7
2.4.5 Properties of an Ethernet
Ethernet was “designed to be”
i.e. “classical” or “original” Ethernet
■ shared bus
- shared bandwidth
- only one station transmitting at a time
- “half duplex”
(station transmits XOR receives)
■ broadcast technology
- all stations receive all messages
■ best-effort delivery
- Like Post Office
■ distributed access control
- CSMA/CD
8
2.4.8 Ethernet Hardware Addresses
6 bytes total - globally unique
High-Order 3 bytes: assigned to manufacturer by IEEE
Low-Order 3 bytes: serial number assigned by
manufacturer
Destination address as filter
An Ethernet station receiving packet
checks destination address
ignores packet if not intended for this station
9
Ethernet Addresses – continued
Types of Destination address
An address can be used to specify
■ a single, specific station
on this network
(“unicast address”)
■ all stations on this network
(“broadcast address”)
■ a subset of stations on this network
(“multicast address”)
Interface Modes of Operation
■ normal mode
Interface processes only packets with destination
* its own unicast address
* the network broadcast address
■ promiscuous mode
Interface process all received packets
(including those addressed to other stations)
10
11
Figure 2.1 (with hub)
Figure 2.2 Format of an Ethernet frame (packet)
12
13
► Bridge is “store and Forward” device, operating at frame level
►2 interfaces operting in promiscous mode,
frame buffer for each interface
►receives frame, checks for validity before forwarding –
no “runts”
14
►” An (almost) arbitrary number of Ethernets can be connected
together with bridges”
►”A set of bridged segments acts like a single Ethernet”
(“transparent”)
► “Most bridges . . . Make intelligent decisions about which
frames to forward” -- No “runts”
► Special case when bridge first powered up -- “flooding”
15
switch
16
► No waiting to transmit
► not CSMA/CD
► If we upgrade switch with fast backplane, we can
have multiple transmissions at same time
► Special case – station can be transmitting and
receiving at same time - Full Duplex
17
2.4.5 Properties of an Ethernet
Ethernet was “designed to be”
i.e. “classical” or “original” Ethernet
■ shared bus
- shared bandwidth
- only one station transmitting at a time
- “half duplex”
(station transmits XOR receives)
■ broadcast technology
- all stations receive all messages
■ best-effort delivery
■ distributed access control
- CSMA/CD
18
Properties of a “switched” Ethernet
■ not shared bus
- point-to-point connections
- not shared bandwidth
- “full duplex”
(station can be transmitting and
receiving)
■ not broadcast technology
- stations receive only their own messages
■ best-effort delivery
■ no access control needed
- private frame buffer
- no entrance collisions
- not CSMA/CD
- exit port collision
Most new wired Ethernet installations are switched
19
Return to section 2.4.7 Wireless Networks and Ethernet
IEEE 802.11 standards for wireless LANs
Speed
Range
Radio Frequency
802.11b
11 Mbits/sec
100 meters
2.4 GHz
802.11a
54 Mbits/sec
80 meters
802.11g
54 Mbits/sec
150 meters
2.4 GHz
802.11n
248
Mbits/sec
70 meters
2.4 and 5 GHz
5 Ghz
We have 802.11g in the lab
20
(Independent) Basic Service Set
(ad-hoc network)
Figure 1
Extended
Service Set
(infrastructure
network)
New components: Distribution System
each BSS has an Access Point
Figure 2
21
Figure 3 – Hidden Station Problem
22
Figure 4 – CSMA/Collision Avoidance
23
Independent Basic Service Set (IBSS)
Station Service (SS)
must be provided by all stations:
(a) Authentication
(b) Deauthentication
(c) Privacy
(d) Data Unit Delivery
Extended Service Set (ESS)
Additional services that must be provided by the access
point/distribution system:
(a) Association
(b) Distribution
(c) Disassociation
(d) Reassociation
24
Figure 5
AP acts like a bridge
25
Figure 6
26
Network, BSS, and Station Identification
In the Network Lab:
BSSID is 00:06:25:49:B3:B2
(MAC address of Access Point)
Each station identification is its MAC address
ESSID is netlab_w
27
Wired Ethernet Frame Format
Wired: All frames are data frames
Wireless: Management, Control, and Data frames
Figure 6 - 802.11 frame format
28
Usage of Address Fields in 802.11
Address 1 identifies the immediate receiver
(the unit that will process the frame)
Address 2 identifies the transmitter
(the unit that transmits the frame and will receive the acknowledgment)
Usage of other addresses is situation-dependent.
29
Another IBSS!
Example 1 – IBSS
For frames traveling within an IBSS:
Address 1 is the destination address
Address 2 is the source address
Address 3 is the BSSID
(used as a filter, since IBSSs may overlap)
30
31
Example 2 – ESS with 802.3 (wired) DS, client-server transaction
On 802.11 segment
Client request
Server reply
Addr 1 - immediate destination - AP
Addr 1 – client
Addr 2 – client address
Addr2 – immediate source (AP)
Addr 3 – ultimate destination (DA)
Addr3 – original source (server)
32
33
Example 3 – ESS with 802.11 (wireless) DS
AP1
AP2
Addr 1 – AP2
Addr 2 – AP1
Addr 3 – ultimate dest
Addr 4 – original source
34
35
“Fig 1.5” – An internet
4 Ethernet LANs linked by a WAN
36
Net 1
Net 2
B?
C1
C2
Figure 3.1
Net 1
Net 3
B1 ?
Net 2
C1
B2 ?
C2
Figure 3.2
37
Comer figure 3.3 (a) user’s view
(b) structure of physical
networks and routers
38
“Fig 1.5” – An internet
4 Ethernet LANs linked by a WAN
Comer section 3.8: All Networks are Equal
We regard each of the links
in the WAN as a network
39
0
31
|
|
|
0
|
|
|
10
|
|
|
B
110
|
|
|
C
A
40
IPv4
Figure 4.1 The original classful IP addressing scheme
IP addresses specify network connections
A router must have at least two IP addresses,
with different network parts
41
Figure 4.4 Special forms of IP addresses
42
4.11 Dotted Decimal Notation
10001010
138
00011010
.
26
01000010
.
66
00000110
.
6
43
4.14 Internet Addressing Authority
44
Figure 4.5 Logical connection of
Two networks to the Internet backbone
45
128.10.0.0
128.210.0.0
9.0.0.0
Figure 4.6 Example IP address assignment
46
BHM
CHL
NO
ATL
“Fig 1.5” – An internet
Final router has to deliver packet to final destination
over Ethernet network.
47
Final Router has to deliver packet over Ethernet network.
The ONLY way data can move over an Ethernet
is in the payload of an Ethernet frame.
0800
IP Packet
Destination
Ethernet
Address
Figure 2.2 Format of an Ethernet Frame
From the incoming packet final router knows the
destination IP address.
We have to find the Ethernet address
corresponding to the destination IP address.
48
Ch 5: Mapping Internet Addresses to Physical Addresses
Incoming
IP Packet
router
destination
49
Comer Section 5.10 ARP Implementation
■ action when sending an ARP request
detain outgoing data message in queue
until ARP reply received
■ action when receiving an ARP message
either request or reply contain mapping(s)
in either case
look in ARP cache to see if receiver already has an
entry for the sender.
if yes, overwrite physical address (quickest way) and reset timer
if no, make new entry and start timer
further action depends on two sub-cases:
* incoming ARP message was a request
look at target IP address; if it’s for this
machine, generate ARP reply
* incoming ARP message was a reply
since reply is unicast, this machine earlier sent an ARP request
for the IP address in the reply
so release outgoing data message from
50
queue, incorporate packet into outgoing frame and transmit.
5.11 ARP Encapsulation and Identification
0806
ARP MESSAGE
Figure 2.2 Ethernet Frame Format
51
Figure 5.3 ARP Message Format
52
5.12 ARP Protocol Format
ARP Message
0806
53
54