Download Type of Networks (Continued)

CIS 4100 Systems Performance and Evaluation
Lecture 2
by
Zornitza Genova Prodanoff
Lect2..ppt - 08/11/04
Lecture Outline:
•
•
•
•
•
Types of networks
Network protocols
Client/Server Model
Peer-to-Peer Model
Web services protocols
ZGP002
Type of Networks
• Computer and Communications industries converge in the 70s
• The infrastructure underlying the Internet has evolved since
• Web is an overlay network on the Internet
• Web services offered trough Web sites are based on
− Client/Server model
− Peer-to-Peer model
ZGP003
Type of Networks
(Continued)
Wide Area Networks (WANs)
• The Internet is a WAN 
• High speed links are 45Mbps to Gbps-s
• Technologies: x25, ISDN, Frame Relay,SMDS, ATM
Internet
ZGP02
Type of Networks
(Continued)
• IP addresses: an ID unique for each computer
129.52.6.3
129
10000001
Octet
(8 bit)
ZGP02
52
6
3
00110100 00000110 00000011
Type of Networks
•
•
•
•
(Continued)
IP Addresses are written using dotted decimal notation:
4 groups of 8 bits
Each group can be 0 – 255
Example:
Source:
D. E. Comer, “Computer Networks and Internets”, 3rd edition,
Purdue University
ZGP02
Type of Networks
Client
(Continued)
Source and
Destination
address
Server
Ethernet
(cable, link)
Packets
(server to client)
• packets can get lost, duplicated, delayed, and corrupted
ZGP02
Type of Networks
(Continued)
Header
Source and
Destination
IP address
Data
10000000
00001010
…
Octet
(8 bit)
bit rate of link
packet rate (pkts/sec) 
packet length in bytes  8
ZGP02
00011110
Type of Networks
(Continued)
~22ms (=0.02sec)
• Electromagnetic signal speed ~ 300, 000km/sec
• Network links have capacity (data rate)
– dial-in link: 56-Kbps
– Ethernet: 10 or 100 (or 1000) Mbps
– “T1”:
1.544 Mbps
ZGP02
Type of Networks
(Continued)
• A router connects two or more physical networks
• A router is part of each network (has 2+ IP addresses)
• Forwarding packets to the right destination
• Glue smaller networks together
• Data travel packet by packet
ZGP02
Type of Networks
(Continued)
• Local Area Networks (LANs)
• Technologies:
− Ethernet (10 Mbps, 100 Mbps)
− Gigabit Ethernet
− Token Ring (4-16 Mbps)
− FDDI (100 Mbps)
• Ethernet
− No central node
− Access to a shared medium (called the ether – coaxial cable )
− Carrier Sense Multiple Access with Collision Detection
(CDMA/CD) – a distributed algorithm to determine which
station uses the shared medium next
ZGP0011
Type of Networks
(Continued)
• It is possible, however, for two NICs that are far apart in the
cable to attempt a transmission at about the same time, detect a
free medium, transmit their packets and interfere with each
other. This interference is called a collision.
• Collisions – As traffic on the Ethernet LAN increases the
probability
• Ethernet NICs are equipped to detect collisions and stop
transmitting a packet when collisions are detected
• NICs wait for a randomly selected time period before attempting
to retransmit their packets
• As traffic on an Ethernet network increases, the probability of a
collision increases and the network throughput decreases as more
of the bandwidth is spent on collisions and retransmissions
ZGP0012
Type of Networks
(Continued)
Token Ring
• Invented at IBM Research Labs and, as the name indicates, is
based on a ring topology as shown in Fig. 2.1b.
• A sender inserts the bits of its packet into the ring
• The packet goes around the ring and is copied by the NIC
specified in the destination address field of the packet
• The packet continues its flow around the ring back to the sender
which removes the packet and compares the received packet with
the packet sent for error control
• If two or more NICs attempt to transmit simultaneously
ZGP0013
Type of Networks
ZGP0014
(Continued)
Type of Networks
(Continued)
Fiber Distributed Data Interface (FDDI)
• a set of ANSI protocols for sending digital data over fiber optic
cable
• FDDI networks use token-passing
• support data rates of up to 100 Mbps (100 million bits) per
second
• used as backbones for WANs
• An improvement over token ring is the introduction of a second
ring – better fault tolerance
Type of Networks
(Continued)
Wireless LANs
• Use the Radio Frequency as a medium
• Use the data to be transmitted to modulate a carrier signal
(wave) transmitted by the RF transmitters
• Physical layer
− provides a carrier sense signal which indicates if there is a
transmission in progress
− data sent by one station can be received by all stations in its
area of coverage
− communication may suffer from the "hidden terminal
problem“:
 walls or other structures obstruct the RF signals
 station C receives signals from A and B, but for A and B
cannot communicate due to an obstacle
Type of Networks
ZGP0017
(Continued)
Type of Networks
(Continued)
• Figure 2.2 shows the architecture of IEEE 802.11 based LANs
• Stations communicate, within
− their cells or basic service set (BSS),
− with one another
− and with a base station called an access point (AP)
• AP is used to allow stations in different BSSs to communicate
with one another.
• Access points may be connected through a wired LAN, as shown in
Figure 2.2, or through a wireless LAN
• Similar to transmission in an Ethernet, wireless stations may
interfere with one another if they transmit at the same time
Type of Networks
(Continued)
• The IEEE 802.11 protocol uses a Carrier Sense Multiple Access/
Collision Avoidance (CSMA/CA) protocol
• If the channel is sensed idle for an amount of time equal to the
Distributed Inter Frame Space (DIFS), a station may transmit
• The receiver of a correct frame sends an acknowledgement
frame to the sender after a short period of time called the Short
Inter Frame Spacing (SIFS)
• Acknowledgements (ACK) in IEEE 802.11 LANs are required, but
not in Ethernet LANs since the sender can hear its own
transmission
Type of Networks
(Continued)
• The IEEE 802.11 protocol does not use collision detection, as
Ethernet does and aims at avoiding collisions
• Any transmitted frame contains the duration of the transmission,
so that other stations can avoid transmitting collision at that
time.
Type of Networks
(Continued)
• Collisions can occur because of the hidden terminal problem.
• It is possible for two stations hidden from one another to collide
when transmitting to the same destination at about the same time
• To avoid this problem, IEEE 802.11 provides for the optional use
of a Request To Send (RTS) and Clear To Send (CTS) exchange of
frames before the data transmission
− Before a sender transmits its data frame, it sends a RTS
frame to the receiver indicating the entire duration of the
transmission including the time to send the ACK
− If the RTS is received correctly a short CTS is sent by
the intended receiver to the sender, which may proceed
with the actual transmission
− All other stations hear this exchange and avoid interfering
with the data transmission.
Type of Networks
(Continued)
Ad hoc wireless networks
• Stations organize themselves into networks without an access
point
Type of Networks
ZGP0023
(Continued)
Type of Networks
(Continued)
• The LAN to WAN Connection
• LANs usually connect to WANs through dedicated leased lines at
T1 (1.5 Mbps) or T3 (45 Mbps) speeds.
• The adequate sizing of the LAN-to-Wan link will be discussed in
Chapters 9 and 10
Type of Networks
(Continued)
Figure 2.4 shows the networking topology for a company
headquarters in Los Angeles, with branches in Chicago and New
York:
• The three locations are connected through a Frame Relay
WAN
• The headquarters has a Ethernet and a Token Ring LAN
connected to a 100-Mbps FDDI ring backbone
• The backbone connects to the Frame Relay WAN through a
T1 line
• The Chicago branch has two LAN segments connected by a
bridge
• The router to the WAN is located in one of the LAN
segments
• The New York branch has a single 16-Mbps Token Ring LAN
connected to the WAN through a router
Type of Networks
ZGP0026
(Continued)
Type of Networks
(Continued)
Alternatives, when connecting a home PC (LANs) to a WAN:
• Dial-up analog modems at speeds ranging from 14.4 to 56 Kbps
• ISDN Basic Rate Interface (BRI): requires a dial-up digital
modem and provides speeds of 128 Kbps
• ISDN Primary Rate Interface (PRI) delivers 1.544 Mbps
• Leasing a T1 line: 1.544 Mbps
• T1-like speeds can also be obtained with High-Bit-Rate Digital
Subscriber Line (HDSL) but with more flexibility
• An asymmetric version of HDSL, Asymmetric Digital Subscriber
Line (ADSL), provides 640 Kbps outbound and 6 Mbps inbound
This asymmetry is advantageous for Web access, since the
bandwidth requirements for fast image and video downloads are
higher than for sending requests to Web servers
Type of Networks
ZGP0028
(Continued)