Network%20Architectures

1
Network Architectures

• ITEC 370
• George Vaughan

2
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.

3
TCP/IP and OSI Models
4
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

5
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 doesnt 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

6
Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) Tomsho, Tittel, Johnson
(2007)
7
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

8
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

9
Token PassingTomsho, Tittel, Johnson (2007)
10
Demand Priority

• Used only by 100VG-AnyLAN (IEEE 802.12)
• Smart hubs use round-robin to control access.
• Not common, therefore expensive

11
Polling

• One of oldest access methods
• Uses centralized controller to control access
• Supports priorities
• Not efficient use of network media
• Used in IBMs Systems Network Architecture (SNA)

12
PollingTomsho, Tittel, Johnson (2007)
13
Ethernet Architecture

• Most popular network architecture
• Ranges from 10Mbps 10 Gbps
• Uses NICs 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.

14
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.

15
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
  Xeroxs 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 Xeroxs Ethernet
  (10 Mbps)
• 1990 IEEE defined the 802.3 specification
• Defines how Ethernet networks operate at layers
  1-2

16
Accessing Network Media

• Ethernet uses CSMA/CD in a shared-media
  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

17
Collisions and Collision DomainsTomsho, Tittel,
Johnson (2007)
18
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 dont match, the data was corrupted
• Destination computer discards the frame
• No notice is given to the sender

19
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 arent possible
• Results in a considerable performance advantage

20
Ethernet Frame
21
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

22
TCPDUMP (Cont.)

• Example Ping (Internet Control Message Protocol)
• 162357.892354 0015f24d5219 gt
  0020ed73b71d, ethertype IPv4 (0x0800),
  length 74 IP (tos 0x0, ttl 128, id 8475, offset
  0, flags none, proto 1, length 60)
  192.168.1.101 gt 192.168.1.12 icmp 40 echo
  request seq 11520
• Timestamp 162357.892354
• Source (MAC Address) 0015f24d5219
• Destination (MAC Address) 0020ed73b71d
• Source IP 192.168.1.101
• Destination IP 192.168.1.12
• Protocol icmp

23
TCPDUMP (Cont.)

• Example arp (Address Resolution Protocol)
• 162237.497442 0015f24d5219 gt Broadcast,
  ethertype ARP (0x0806), length 60 arp who-has
  192.168.1.112 tell 192.168.1.101
• Timestamp 162237.497442
• Source (MAC Address) 0015f24d5219
• Destination (MAC Address) Broadcast
• Protocol arp who-has 192.168.1.112 tell
  192.168.1.101

24
TCPDUMP (Cont.)

• example Web Request
• 162243.383893 0020ed73b71d gt
  0016b62171d1, 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 gt www8.cnn.com.http S tcp
  sum ok 970586877970586877(0) win 5840 ltmss
  1460,sackOK,timestamp 5790847 0,nop,wscale 2gt
• Timestamp 162243.383893
• Source (MAC Address) 0020ed73b71d
• Destination (MAC Address) 0016b62171d1
• Source IP 192. 92.168.1.12
• Destination IP www8.cnn.com.http

25
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.

26
Ethereal (Cont.)
27
Data Link Protocols
28
The Token Ring ArchitectureTomsho, Tittel,
Johnson (2007)
29
Token Ring FunctionTomsho, Tittel, Johnson (2007)

• A token passes around the ring
• If an in use token is received from the Nearest
  Active Up-stream 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

30
BeaconingTomsho, Tittel, Johnson (2007)
31
Hardware ComponentsTomsho, Tittel, Johnson (2007)

• A hub can be a multistation access unit (MSAU) or
  smart multistation access unit (SMAU)
• IBMs 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

32
The Fiber Distributed Data Interface (FDDI)
Architecture Tomsho, Tittel, Johnson (2007)
33
The Fiber Distributed Data Interface (FDDI)
Architecture (continued)Tomsho, Tittel, Johnson
(2007)
34
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)

35
Broadband TechnologiesTomsho, 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

36
Cable Modem TechnologyTomsho, Tittel, Johnson
(2007)
37
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

38
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

39
ATM and SONET Signaling RatesTomsho, Tittel,
Johnson (2007)
40
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