Transcript 02. Network Hardware..

Technical issues in network design
IICT-BAS
Network Hardware
 Main Taxonomy Dimensions:
transmission technology
network range (scale, size)
 Transmission Technology
broadcast links
point-to point links
Broadcast Networks
• Single communication channel shared by all the
machines in the network
• Short messages (packets) with addressing field
– sent by any machine
– received by all others
• Target machine interprets current message; the rest
ignore it (“Peter, come here/stand up”)
• Special bits in the address field indicate the
transmission mode: broadcast (to all the machines);
multicast (to group of machines)
Point-to-point Networks
 Many connections between pairs of machines
 Packets visit 0, 1, 2 … intermediate machines reaching
the target one
 Alternative routes are possible - routing algorithms
 Basically for large networks, smaller, geographically
localized networks tend to use broadcasting (as a
general rule)
Network Range
• Physical Size
message passing sysfine grain parallel computers; many functional units tems; short and fast communication busses
perform any instruction
• Data Flow Machines & Multicomputers are Distributed
Systems but not Computer Networks
• Personal Area Network – a wireless network connecting a
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computer with its mouse, keyboard, and printer
Local Area Networks (LANs)
Metropolitan Area Networks
Wide Area Networks (WANs)
Internetworks (connection of more than one network - The
Internet)
Scale of interconnected processors
Local Area Networks (LANs)
 Up to 1-2 km physical range (room, building, campus)
 Private owned (companies, branches, laboratories, small
institutions)
 Connect PCs, workstations, disk stores, printers and other
peripherals
 Main characteristics:
size
transmission technology
topology
Size of the LANs
 Small, technologically restricted size
 Bounded and known transmission
time
 allows certain kinds of design
 Simple network management due to
the limited transmission time
Transmission Technology of the
LANs
 Usually based on a single cable attaching all the components
of the network
 Communication speed 100 Mb/S, 1 - 10 Gb/s
 Communication delay 10 mS (1 ms = 10-6 S), 1 ms, 100 ns
Topology of the LANs
 Topology is the graph of the connectivity of the
network components
 Typical topology of LANs is bus or ring
 Bus topology is based on linear cable
 Arbitration management - time-sharing control: 1
master machine at any instant is allowed to transmit;
 arbitration mechanism is needed to resolve conflicts
 Centralized or Distributed arbitration
 EthernetTM (IEEE 802.3) standard: bus-based,
distributed arbitration based on collision detection
and random delay for next attempt
Local Area Networks
• Two broadcast networks
• (a) Bus
• (b) Ring
Topology of the LANs - ring topology
• Network ring forms necklace of the workstations
• Bit-slice propagation of the packets - each bit propagates
around on its own, not waiting for the rest of the packet to
which it belongs
• A rule is needed for arbitrating simultaneous accesses to the
ring
• IBM Token Ring (IEEE 802.5) standard operates at 4-16
Mb/S
• Fibre Distributed Data Interface (FDDI) is also a ring
network – 100 Mbit/s optical standard
Local area networks
•Ethernet LAN technology (IEEE 802.3) has today the largest
installed base - types of cabling
•- thick coaxial (10BASE-5) with AUI connectors and
transceivers (not in use any more)
• - thin coaxial (10BASE-2) with BNC connectors (not in use)
• - unshielded twisted pair (UTP or 10-base-T) with RJ-45
jacks.
•The 10BASE-T standard introduced a collision-free full
duplex mode of operation that eliminated collisions. Modern
Ethernets are entirely collision-free
•Each station on an Ethernet has an Ethernet network
interface card (NIC), which has a special hardware address,
assigned to guarantee link layer uniqueness, even across
vendors
Metropolitan Area Networks
• A metropolitan area network (MAN), covers a city
• best-known example of a MAN, available in many
cities – the cable television network
• When Internet became popular, cable TV network
operators started to provide two-way Internet service
in the unused parts of the spectrum
• Another MAN – IEEE 802.16 standard(s) WirelessMAN - commercialized under the name
WiMAX (from Worldwide Interoperability for
Microwave Access)
Metropolitan Area Networks
 A metropolitan area network based on cable TV.
Wide Area Networks (WANs)
 WAN covers large geographic area (country, continent)
 Connects different types of machines (for
user/application programs) - “hosts” via
communication subnet
 Separation of the services: hosts run application
programs and subnet performs the connection tasks
 Subnet consists of transmission lines and switching
elements (“routers”: specialized in connecting 2 or
more switching lines)
Wide Area Networks (WANs)
• WAN covers large geographic area (country, continent)
• Connects different types of machines - “hosts” via
communication subnet
• Separation of the services: hosts (owned by customers)
run application programs and subnet (owned by
telephone company or ISP) performs the connection
tasks
• Subnet consists of transmission lines and switching
elements (“routers”: specialized in connecting 2 or
more switching lines)
WANs & Routers
 Router is specialized switching element in the WAN subnet
 Switching is the process of:
1) receiving data on the incoming channel[s];
2) interpreting it;
3) choosing an outgoing line and
4) forwarding the data on it
 Typical structure of WAN: hosts connected by LANs; LANs
connected by the subnet
Wide Area Networks
 Relation between hosts on LANs and the subnet.
WANs & Subnets
• Subnet consists of routers and connection lines
• The subnet lines are based on cables (telephone lines)
that connects pairs of routers (point-to-point network)
in a connected graph. Exception: wireless/satellite
based subnets are of broadcast type (for WANs
specialized in broadcasting communication)
• Non connected routers communicate via intermediate
routers in store-and-forward (store until required output
line is free, then forward) mode (or packet-switch)
• Subnet topology - usually irregular
• Subnet acquired a second, rather different meaning in
conjunction with network addressing (discussed later)
WANs & Subnets
• a host process sending a message to a process on some
other host, first cuts the message into packets, each
one bearing its number in the sequence
• packets are then injected into the network one at a
time in quick succession
• packets are transported individually over the network
and deposited at the receiving host, where they are
reassembled into the original message and delivered to
the receiving process
A stream of packets sender receiver
Routing
 Routing decisions are made locally
 When a packet arrives at router A, A decides if this
packet should be sent on the line to B or the line to C
 The way A makes the decision - routing algorithm
 Many routing algorithm exist – shall study some of
them later
Satellite WANs
• Some WANs are not packet switched
• With satellite systems each router has an antenna through
which it can send and receive
• Routers can hear the output from the satellite, in some
cases they can also hear the upward transmissions of other
routers to the satellite
• Sometimes the routers are connected to a substantial
point-to-point subnet, with only some of them having a
satellite antenna
• Satellite networks are inherently broadcast and are most
useful when the broadcast property is important
Wireless Networks
Categories of wireless networks:
• System interconnection
• Wireless LANs
• Wireless WANs
System interconnection
• Interconnecting the components of a computer using
short-range radio
• Some computers connect their components (
keyboard, mouse, printer, etc) by short-range wireless
network called Bluetooth
• Bluetooth allows digital cameras, headsets, scanners,
and other devices to connect to a computer by merely
being brought within range
• No cables, no driver installation, just put them down,
turn them on, and they work - ease of operation
System interconnection
• Interconnection networks use the master-slave
paradigm
• The system unit is normally the “master”, talking to the
mouse, keyboard, etc. – they are “slaves”
• The master tells the slaves what addresses to use, when
they can broadcast, how long they can transmit, what
frequencies they can use, and so on
Wireless Networks
• (a) Bluetooth configuration
• (b) Wireless LAN
Wireless LANs
• Systems in which every computer has a radio modem and
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antenna with which the computer can communicate with
other systems
The antenna may be on the ceiling so that the machines
talk to it
If the systems are close enough, they can communicate
directly with one another in a peer-to-peer configuration
Wireless LANs - common in small offices and homes,
avoiding Ethernet installation
The standard for wireless LANs is called IEEE 802.11 - very
widespread
Wireless WANs
• Radio network used for cellular telephones is an
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example of a low-bandwidth wireless system – four
generations:
1G - first generation - analog and for voice only
2G - second generation - digital and for voice only
3G - third generation – digital for both voice and data
4G – fourth generation - provides mobile ultrabroadband Internet access; designed to deliver speed on average from four to ten times faster than 3G
Internetworks
• Internetwork (or internet) = communication
between LANs, MANs and WANs with different
internal standards (hardware, software)
• Compatibility requires gateways – machine/device
to make the connection and provide the necessary
translation, both in terms of hardware and software
• Typical architecture: collection of LANs connected
by a WAN: (WAN differs from the subnet just by
presence of hosts and not only routers)
• The Internet = biggest internetwork connecting
universities, public and private offices, persons etc. –
we always capitalize