TCOM 509

1
TCOM 509 Internet Protocols (TCP/IP)Lecture
02_a

• Instructor Dr. Li-Chuan ChenDate 09/08/2003

• Based in part upon slides of Prof. J. Kurose (U
  Mass), Prof. B. Yener (Rensselaer Polytechnic
  Institute)

2
Outline

• Chapter 2.1 2.6
• Packet switching, circuit-switching
• WAN, LAN
• LAN Technologies
• Ethernet
• FDDI
• ATM
• Chapter 4

3
What is Internet?

• The Internet is a technology of interconnecting
  computing devices via routers in the
  communication networks through out the world.
• Communication networks consist of nodes and
  communication links.
• Computing devices are nodes or end-systems (e.g.,
  PCs, workstations, servers, phones) running
  network applications.
• Communication links
• fiber, copper, radio, satellite
• Routers forward packets.

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
4
A closer look at network structure

• network edge applications and hosts
• network core
• routers
• network of networks
• access networks, physical media communication
  links

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
5
The network edge

• end systems (hosts)
• run application programs(e.g. Web, email) at
  theedge of network
• client/server model
• client host requests, receives service from
  always-on server(e.g. Web browser/server email
  client/server)
• peer-peer model
• minimal (or no) use of dedicated servers

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
6
Network Core

• Mesh of interconnected routers
• They are either packet switched or circuit
  switched

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
7
Network Core Circuit Switching

• Reserved bandwidth
• Call setup required
• Guaranteed performance

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
8
Packet Switching Routing

• Goals move packet from source to a router, and
  from one router to another until reaching the
  destination.
• Datagram network
• Destination address determines next hop
• Routing can change during the session
• Analogy driving, traffic, take another route

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
9
Access Network and Physical Media

• Residential Network
• Dial up (up to 56Kbps)
• ADSL (asymmetric digital subscriber line)
• 1.5M 9Mbps downstream traffic, 64K1.5M
  upstream
• typical 384K-768K for downstream, 128K-384K for
  upstream
• Cable Modem
• up to 40 Mbps.
• typical 1-3 Mbps downstream traffic, 250 Kpbs to
  2.5 Mpbs upstream.
• Wireless Access
• Institutional Access (school, company)

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
10
Physical Media

• Guided media
• Copper (twisted pair, co-axial cable)
• Fiber links
• Unguided media
• Radio (microwave, wireless LAN, satellite etc.)

SourceComputer Networking A Top Down Approach
Featuring the Internet, 2nd edition.
11
Network Communication

• Two switching mechanisms
• Circuit-switching
• Packet-switching
• Circuit-switching
• connection-oriented technology.
• dedicated communication connection between
  endpoints
• use synchronous TDM scheme and provides fixed
  rate (64 kbps for voice).
• designed for voice and used in telephone
  networks.
• pros provides guarantee bandwidth.
• cons inefficient bandwidth, i.e. you pay even
  when no one is talking.

12
Network Communications

• Packet Switching
• Computers use packet-switching networks to send
  data.
• Data are divided into packets.
• Each packet carries headers to identify the
  destination and is routed inside the network.
• Communication links are shared among computers.
• pros more efficient in utilization, flexibility
• cons longer network delay. As load increases,
  congestion occurs at the routers.

13
Circuit Switching vs. Packet Switching

• Circuit switching
• dedicated path, fixed bandwidth
• call setup, messages are not stored, data arrives
  same order as sent.
• no overhead once the path is setup.
• overload may block call
• good for sending large data.
• Packet switching
• no dedicated path, dynamic bandwidth
• no call setup, packets are stored and forward,
  and delay, data may arrive out of order.
• overhead needed for routing info
• overload increases packet delay
• good for sending small data.

14
Network Types

• WANs (Wide Area Networks)
• span large geographical distances, e.g.,
  continent
• operate at slower speed,1.5M - 155 Mbps
• greater delay, lt several tenths of sec
• e.g., X.25, Arpanet, ISDN, Frame Relay
• LANs (Local Area Network)
• spans a single building or campus
• provide highest speed connections among computers
  at 10M-2Gbps
• lower delay, lt 10 ms
• e.g., Ethernet, Token Ring, Gigabit Ethernet

15
WAN vs. LAN

• Scalability
• LANs are not scalable cannot connect many
  computers at arbitrary sites.
• A WAN is scalable - capable of connecting many
  sites spread across geographical distances with
  many computers at each site.
• Performance
• WANs are usually slower than LANs.
• Cost
• WANs are much more expensive than LANs.
• WANs are usually owned/operated by large public
  companies

16
Ethernet Technology

• Ethernet is the most popular local area network
  (LAN) technology.
• Standardized by Xerox, DEC and Intel in 1978
• Original Ethernet consists of a coaxial cable
  (ether).
• The ether is completely passive, all active
  electronic components that make up the network
  function are associated with computers that
  attach to the network.

17
Ethernet Technology

• Thick Ethernet or 10Base5 (IEEE 802.3)
• max. distance is 500 meters (m) per segment, up
  to 200 transceivers, at least 2.5 m between
  transceivers.
• Thin Ethernet (thinnet) or 10Base2
• Cheaper, but max. distance is 200 m.
• Differ only in electrical connection
  characteristics, not protocol.
• Twisted-pair Ethernet or category 5
• Cheapest and easiest to install. Max distance is
  100 m.

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Ethernet
0.5 diameter
Thick Ethernet cable(10Base5)
transceiver
AUI cable
transceiver
mux
AUI cables
Time
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Thinnet Hubs
0.25 diameter
Thin Ethernet cable(10-Base2)
BNC connector
terminator
Twisted-pair Ethernet (10Base-T) Category 5 cable
hub
lt 100 meter
RJ45 connector
20
Variants of Ethernet

• Ethernet
• up to10 Mbps
• Fast Ethernet or 100Base-T
• up to 100 Mbps.
• Dual-speed Ethernet or 10/100 Ethernet
• either 10 or 100 Mbps (auto detects).
• Gigabit Ethernet or 1000Base-T
• up to 1 Gbps
• All of the above Ethernet technologies use the
  same packet format and maximum packet size.

21
Properties of Ethernet

• Broadcast bus technology with best-effort
  delivery.
• All stations in the network read each packet.
• Protocol carrier sense multiple access with
  collision detect (CSMA/CD)
• listen before sending packets (carrier sense),
  stops when someone is using.
• when both stations by chance transmit at the same
  time (collision occurs by comparing data), use an
  exponential random time delay before retransmit.

22
Ethernet Hardware Addresses

• Each host is assigned a 48-bit integer known as
  Ethernet address (hardware address, or physical
  address).
• Ethernet addresses are associated with the
  Ethernet interface card.
• IEEE distributes the unique Ethernet addresses to
  the manufacturers.
• Each interface receives a copy of every packet,
  the interface filters packets based on the
  destination address field.

23
Ethernet address

• 48-bit Ethernet address specify
• physical address of one network interface
• network broadcast address
• a multicast address
• When machine boots, the OS initializes the
  Ethernet interface giving it a set of addresses
  to recognize.
• A host interface usually accepts the following
  packets
• those addressed to the interfaces unicast
  physical address.
• network broadcast address (all 1s)
• multicast group address

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Ethernet Frame Format
4 bytes
8 bytes
6 bytes
6 bytes
2 bytes
46 - 1500 bytes
CRC
Frame type - identifies type of data being
carried. Also called self-identifying frames
Dest. address
Source address
Preamble alternating 0s and 1s to help
receiving nodes synchronize (not part of Ethernet
Frame)

• minimum frame size 64 octets
• maximum frame size 1518 octets
• header size 18 (6624) octets

Example B9.5C.01.88.FE.52
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Example of Ethernet Frame Type
Frame Type in Hex Description
0800 IPv4
0806 ARP
8035 RARP
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Repeaters and Bridges

• Repeater
• Operates at layer 1 (physical layer).
• Used to restore (amplify or regenerated if
  digital signal) the electrical signals and relay
  them from one cable to another with the same
  physical characteristics
• Works at layer 1 (physical)
• Connect segments of a LAN together. Extends
  Ethernet from 500 m to 1000 m. At most two
  repeaters can be placed between any two
  transceivers (host machines).
• Why not use repeaters to extend Ethernet
  indefinitely? CSMA/CD requires low delay and
  cant support long medium. A repeater also
  propagates noise.
• Bridge
• Operates on frames rather than signals.
• Works at layer 2 (data link)
• Performs frame filtering, i.e. forward only if
  necessary and does not forward noise, errors, or
  malformed frames.
• Make larger networks by connecting arbitrary
  number of Ethernets together with bridges.
• adaptive or learning bridges make intelligent
  decisions about which frames to forward.
• Multiple Ethernet segments connected by bridges
  repeaters act as single physical network system.

27
FDDI and ATM

• Fiber Distributed Data Interconnect (FDDI)
• Data rate of 100 Mbps, up to 100 km in length.
• Use optical fibers for backbone networks.
• Token ring technology
• Large frame size - up to 4500 octets.
• Efficient for large file transfer.

28
FDDI and ATM

• Asynchronous Transfer Mode (ATM)
• Data rate of Gbps at the ATM network, and 155
  Mbps between users PC and ATM network.
• Scalable Use optical fibers for both LANs and
  WANs.
• Designed for multimedia (data, audio, and video)
  transmission.
• Packet switching with connection-oriented
  service.
• Fixed packet size of 53 octets, called a cell,
  with 5 octets of header size.
• Efficient due to its fixed packet size, but
  expensive.