Network Architectures
ITEC 370
George Vaughan
1
Sources for Slides
• Material in these slides comes primarily
from course text, Guide to Networking
Essentials,Tomsho, Tittel, Johnson (2007).
• Other sources are cited in line and listed in
reference section.
2
TCP/IP and OSI Models
TCP/IP and OSI Models (OSI-Model, n.d.) and (Tomsho, 2007)
TCP/IP
Layers
Application
PDU
Data
OSI Layers
7 Application
6
5
Transport
Segments 4
Network
Packets
3
Link
Frames
2
Function
Network process to application,
Initiates or accepts a request to transfer
data
Presentation Adds formatting, display, and
encryption of information
Session
Adds communication session control
information, Login/Logout
Transport
Adds End-to-end connections and
reliability, re-sequencing, flow control
Network
Path determination and logical
addressing (IP), translates MAC
address to logical address
LLC
Data
Adds error checking and physical
Link
addressing (MAC & LLC)
Devices - Apps
Standards
Browsers,
servers,
Gateways
Gateways
HTTP, SNMP,
FTP, Telnet
DNS,
Gateways
Gateways
NetBIOS
Routers
IP, ICMP,
ARP, NetBEUI
Switches,
Bridges, NICs
802.3, 802.11,
FDDI
ASCII, MPEG
TCP, UDP
MAC
Bits
1 Physical
Media, signal and binary transmission, Hubs,
sends data as a bit stream
Repeaters
10Base-T, T1,
E1
3
Major Access Methods
• Channel access is handled at the MAC
sublayer of the Data Link layer in the OSI
model
• Five major types of channel access
– Contention
– Switching
– Token passing
– Demand priority
– Polling
4
Contention
•
Carrier Sense Multiple Access Collision Detection
(CSMA/CD)
–
–
–
–
•
Used by Ethernet
Computer listens – if quiet then transmit
If collision occurs, wait and then retry
Server doesn’t have priority over workstation
Carrier Sense Multiple Access with Collision Avoidance
(CSMA/CA)
–
–
–
Used by wireless LANs because not all wireless devices can
hear each other
When network is quiet, device sends ‘intent-to-transmit’ signal
Slower than CSMA/CD
5
Carrier Sense Multiple Access with Collision Detection
(CSMA/CD)
Tomsho, Tittel, Johnson (2007)
6
Switching
•
•
•
•
•
•
Contention only occurs when 2 or more
senders try to access the same receiver
More fair than contention based technologies
Supports multiple, simultaneous transmissions.
Priorities can be assigned for Quality of
Service (QoS)
Different ports can operate at different speeds.
Can emulate all common topologies
7
Token Passing
•
•
•
•
All devices have equal guaranteed
access
Good for time sensitive applications
If only computer is sending it must share
token periodically with other non-sending
devices
Requires more expensive hardware
8
Token Passing
Tomsho, Tittel, Johnson (2007)
9
Demand Priority
•
•
•
Used only by 100VG-AnyLAN (IEEE
802.12)
Smart hubs use ‘round-robin’ to control
access.
Not common, therefore expensive
10
Polling
•
•
•
•
•
One of oldest access methods
Uses centralized controller to control
access
Supports priorities
Not efficient use of network media
Used in IBM’s Systems Network
Architecture (SNA)
11
Polling
Tomsho, Tittel, Johnson (2007)
12
Ethernet Architecture
• Most popular network architecture
• Ranges from 10Mbps – 10 Gbps
• Uses NIC’s MAC address to address frames.
• Access handled at MAC sub-layer of Data Link
layer (layer 2)
• MAC – Media Access Control address
– 48 bits in length
– Unique physical address defined in NIC
• What differs is cable/speed – Frame format is
common – backward compatibility.
13
Ethernet Architecture
• Best effort transmission – no guarantee of frame
delivery.
• Upper layers must ensure reliable delivery.
• Access method is
– CSMA/CD (logical bus – Half Duplex)
– Switching
•
•
•
•
Relies on CRC at frame for error detection.
Bad frames are just dropped at destination
Collisions can occur in Half-Duplex
In Switched topology (Full Duplex), collisions do not
occur.
14
Ethernet Architecture (History)
• 1960s and 1970s: many organizations worked on methods to
connect computers and share data
– E.g., the ALOHA network at the University of Hawaii
– 1972: Robert Metcalf and David Boggs, from Xerox’s
PARC, developed an early version of Ethernet
• 1975: PARC released first commercial version (3 Mbps,
up to 100 computers, max. 1 km of total cable)
• DIX developed standard based on Xerox’s Ethernet (10
Mbps)
• 1990: IEEE defined the 802.3 specification
– Defines how Ethernet networks operate at layers 1-2
15
Accessing Network Media
• Ethernet uses CSMA/CD in a sharedmedia environment (a logical bus)
– Ethernet device listens for a signal or carrier
(carrier sense) on the medium first
– If no signal is present, no other device is
using the medium, so a frame can be sent
– Ethernet devices have circuitry that detects
collisions and automatically resends the frame
that was involved in the collision
16
Collisions and Collision Domains
Tomsho, Tittel, Johnson (2007)
17
Ethernet Error Handling
• Collisions are the only type of error for which Ethernet
automatically attempts to resend the data
• Errors can occur when data is altered in medium
– Usually caused by noise or faulty media connections
– When the destination computer receives a frame, the
CRC is recalculated and compared against the CRC
value in the FCS
– If values match, the data is assumed to be okay
– If values don’t match, the data was corrupted
• Destination computer discards the frame
• No notice is given to the sender
18
Half-Duplex Versus Full-Duplex
Communications
• When half-duplex communication is used with
Ethernet, CSMA/CD must also be used
• When using a switched topology, a computer can send
and receive data simultaneously (full-duplex
communication)
– The collision detection circuitry is turned off because
collisions aren’t possible
– Results in a considerable performance advantage
19
Ethernet Frame
Ethernet Frame Styles (Odom, 2006)
DIX (Ethernet II) – Used in TCP/IP
Preamble
Destination
8
6
Source
6
Type
2
Data
46-1500
FCS
4
IEEE 802.3 (Original)
Preamble
SFD
Destination
7
1
6
Source
6
Length
2
Data
46-1500
FCS
4
IEEE 802.3 (Revised 1997)
Preamble
SFD
Destination
Source
Length
xor Type
2
Data
FCS
46-1500
4
7
1
Field
Preamble
Start Frame Delimiter (SFD)
Destination MAC address
Source MAC Address
Length
Type
Data and Pad
Frame Check Sequence (FCS)
6
6
Length
(Bytes)
7
1
6
6
2
2
46-1500
4
Purpose
Synchronization
Signifies that next byte begins Destination MAC field
Identifies recipient
Sender
Length of data field
Type of protocol of encapsulated data
Holds data from higher layer
Info for receiving NIC to check for errors
20
TCPDUMP
• Unix/Linux command line protocol analyzer
(packet sniffer) used for:
– Debugging networks
– Debugging applications that depend on networking.
– Monitoring traffic
• Available for Windows
• Supports user defined filters
• Command Line syntax:
tcpdump -v –e
• Check Man page for other options
21
TCPDUMP (Cont.)
• Example: Ping (Internet Control Message Protocol)
– 16:23:57.892354 00:15:f2:4d:52:19 > 00:20:ed:73:b7:1d,
ethertype IPv4 (0x0800), length 74: IP (tos 0x0, ttl 128, id 8475,
offset 0, flags [none], proto 1, length: 60) 192.168.1.101 >
192.168.1.12: icmp 40: echo request seq 11520
–
–
–
–
–
–
Timestamp = 16:23:57.892354
Source (MAC Address) = 00:15:f2:4d:52:19
Destination (MAC Address) = 00:20:ed:73:b7:1d
Source IP = 192.168.1.101
Destination IP = 192.168.1.12
Protocol = icmp
22
TCPDUMP (Cont.)
• Example: arp (Address Resolution Protocol)
– 16:22:37.497442 00:15:f2:4d:52:19 > Broadcast,
ethertype ARP (0x0806), length 60: arp who-has
192.168.1.112 tell 192.168.1.101
–
–
–
–
Timestamp = 16:22:37.497442
Source (MAC Address) = 00:15:f2:4d:52:19
Destination (MAC Address) = Broadcast
Protocol = arp who-has 192.168.1.112 tell
192.168.1.101
23
TCPDUMP (Cont.)
• example: Web Request
– 16:22:43.383893 00:20:ed:73:b7:1d > 00:16:b6:21:71:d1,
ethertype IPv4 (0x0800), length 74: IP (tos 0x0, ttl 64, id 42626,
offset 0, flags [DF], proto 6, length: 60) 192.168.1.12.56478 >
www8.cnn.com.http: S [tcp sum ok] 970586877:970586877(0)
win 5840 <mss 1460,sackOK,timestamp 5790847 0,nop,wscale
2>
–
–
–
–
–
Timestamp = 16:22:43.383893
Source (MAC Address) = 00:20:ed:73:b7:1d
Destination (MAC Address) = 00:16:b6:21:71:d1
Source IP = 192. 92.168.1.12
Destination IP = www8.cnn.com.http
24
Ethereal
•
•
•
•
•
GUI based protocol analyzer
Available for Unix, Linux, Windows
Open Source application
www.ethereal.com
Can be used to analyze raw data files from
TCPDUMP tool.
• Supports user-defined filters.
25
Ethereal (Cont.)
26
Data Link Protocols
(Tomsho, 2007)
Standard
Advantages
DisMin
advantages Cable
10BaseT
802.3
Cheap
Cat 3
Star
CSMA/CD 100m
1024
100BaseT
(Fast
Ethernet)
1000BaseT
802.3u
Fast, Easy
Small
segments
Cost,
distance
Cat 5
Star
CSMA/CD 100m
1024
802.3ab
Fast, Full
duplex
Cost,
distance
Cat 5
Star
1024
2
1024
1000
Mbps
Fast, Full
duplex
Fast, Full
duplex
Fast,
Reliable
High cost,
complex
Cost,
complex
Cost and
debugging
Fiber
Star
CSMA/CD 100m
or
Switching
Switching 5000m
1024
2
1024
Fiber
Star
Switching
550m
1024
2
1024
Cable Star
- fiber
Token
Passing
45m
33 hubs
Depends
on hub
72 UTP
260 STP
Very fast,
reliable,
distance
X-fast, Qos
Cost,
complex
Fiber
Ring
Token
Passing
100 km
1000
Mbps
1000
Mbps
4 and
16
Mbps
100
Mbps
Fiber
Dedicated
Circuit
Type
1000BaseLX 802.3z
1000BaseSX 802.3z
Token Ring
802.5
FDDI
X3T9.1
ATM/Sonet
Physical
Topology
Access
Max
Max
Segment Segments
Length
Max
Max
Trans
Devices Devices Speed
per
per
Segment Network
2
1024
10
Mbps
1
1024
100
Mbps
500
>100
Gps
27
The Token Ring Architecture
Tomsho, Tittel, Johnson (2007)
28
Token Ring Function
Tomsho, Tittel, Johnson (2007)
• A token passes around the ring
– If an “in use” token is received from the Nearest Active Upstream Neighbor (NAUN), and the computer has data to
send, it attaches its data to the token and sends it to its
Nearest Active Down-stream Neighbor (NADN)
– If received token is in use, NIC verifies if it is the
destination station
• If not, the computer re-creates the token and the data
exactly and sends them to its NADN
• If it is, data is sent to the upper-layer protocols
– Two bits in data packet are toggled and token is
sent to NADN; when original sender receives it, it
frees the token and then passes it along
29
Beaconing
Tomsho, Tittel, Johnson (2007)
30
Hardware Components
Tomsho, Tittel, Johnson (2007)
• A hub can be a multistation access unit (MSAU) or
smart multistation access unit (SMAU)
• IBM’s token ring implementation is the most popular
adaptation of the IEEE 802.5 standard
– Minor variations but very similar to IEEE specs
• IBM equipment is most often used
– 8228 MSAU has 10 connection ports, eight of which
can be used for connecting computers
– The RO port on one hub connects to RI port on the
next hub, and so on, to form a ring among the hubs
• IBM allows connecting 33 hubs
31
The Fiber Distributed Data Interface (FDDI)
Architecture Tomsho, Tittel, Johnson (2007)
32
The Fiber Distributed Data Interface (FDDI)
Architecture (continued)
Tomsho, Tittel, Johnson (2007)
33
Networking Alternatives
• Many other network architectures are available
• Some are good for specialized applications, and others
are emerging as new standards
• Topics
– Broadband technologies (cable modem and DSL)
– Broadcast technologies
– ATM
– ATM and SONET Signaling Rates
– High Performance Parallel Interface (HIPPI)
34
Broadband Technologies
Tomsho, Tittel, Johnson (2007)
• Baseband systems use a digital encoding scheme at a
single fixed frequency
• Broadband systems use analog techniques to encode
information across a continuous range of values
– Signals move across the medium in the form of
continuous electromagnetic or optical waves
– Data flows one way only, so two channels are
necessary for computers to send and receive data
– E.g., cable TV
35
Cable Modem Technology
Tomsho, Tittel, Johnson (2007)
36
Digital Subscriber Line (DSL)
Tomsho, Tittel, Johnson (2007)
• Competes with cable modem for Internet access
– Broadband technology that uses existing phone lines
to carry voice and data simultaneously
– Most prominent variation for home Internet access is
Asymmetric DSL (ADSL)
• Splits phone line in two ranges: Frequencies below
4 KHz are used for voice transmission, and
frequencies above 4 KHz are used to transmit data
• Typical connection speeds for downloading data
range from 256 Kbps to 8 Mbps; upload speeds
are in the range of 16 Kbps to 640 Kbps
37
Asynchronous Transfer Mode (ATM)
Tomsho, Tittel, Johnson (2007)
• High-speed network technology for LANs and WANs
– Connection-oriented switches
• Dedicated circuits are set up before communicating
– Data travels in fixed-size 53-byte cells (5 byte-header)
• Enables ATM to work at extremely high speeds
– Quick switching
– Predictable traffic flow
• Enables ATM to guarantee QoS
– Used quite heavily for the backbone and infrastructure in
large communications companies
– LAN emulation (LANE) required for LAN applications
38
ATM and SONET Signaling Rates
Tomsho, Tittel, Johnson (2007)
39
References
Tomsho, Tittel, Johnson (2007). Guide to Networking
Essentials. Boston: Thompson Course Technology.
Odom, Knott (2006). Networking Basics: CCNA 1
Companion Guide. Indianapolis: Cisco Press
Wikipedia (n.d.). OSI Model. Retrieved 09/12/2006 from
http://en.wikipedia.org/wiki/OSI_Model
40