Download Lec 1

Service Providers &
Data Link & Physical layers
Week 4 Lecture 1
Internet Architecture
Application layer – HTTP, SMTP etc
W3C
Transport layer – TCP, UDP
IETF
Network layer - IP
Data link & Physical layers –
the territory of the Lan & Telcos
ITU
IEEE
Local Area Networks (LAN)
• Nearly all organisation have a LAN in each
office
• All devices are connected to the LAN
• LANs are then connected to the WAN via a
router and firewall
• LANs provide file and print services, and
application and database servers
Workstations
Router &
Firewall
WAN
File server
Printers
Application &
Database Servers
Main characteristics
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Owned & Operated by the Organisation
Single geographic area, usually a building
Relatively fast media
Most common protocol is Ethernet using
CSMA-CD
Bus topology using Co-axial cable
Hub topology using UTP
Floor 15
All wires would be
100mbps UTP Cat 5
Floor 14
Backbone could be
Optic fibre
Floor 13
Machine room
Servers
Router
WAN
LAN Protocols
• Most likely to be CSMA/CD at the data link layer
• Carrier Sense Multiple Access/Collision Detection
• Adaptor listens to see if other devices are transmitting – if
not, it sends
• Adaptors looks for own packets and accepts
• If a collision occurs (propagation delay), the sending
adaptors back-off for a random amount of time and then retransmits
• CSMA/CD is a connectionless, unreliable service
• The IP address is converted to the adaptor address by the
Address Resolution Protocol module on each Internet host
and Router
Ethernet speeds
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Ethernet
- 10mb
Fast Ethernet
- 100mb
Gigabit Ethernet
- 1000mb
10 Gigabit Ethernet - 10000mb
TCP/IP
CSMA/CD
Frame Relay/ATM
Routers
Local ISP POP
ATM/Fibre
City carrier hubs
CSMA/CD
Devices in the network
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Network Adaptors
Hubs
Bridges
Switches
Routers
Firewalls
Network adaptors
• Adaptor, NIC or PCMCIA card
– connects the device to the network
– Implements the data link layer and physical
layer in hardware
– Chip set makes adaptors relatively cheap
– It is semi-autonomous - accepts and hands over
IP packets – full responsibility for transmission
& error control
– Each adaptor has a unique 6 byte address. IEEE
allocates address ranges to manufacturers
Hubs
• Essentially a repeater – when it receives a bit it sends it
down the other links to other adaptors and hubs – thus
includes all devices in the one collision zone
• Physical layer devices
• Carries out some network management functions – if an
adaptor malfunctions and floods the Ethernet it can
internally disconnect the link – collects some statistics
• Extends the length of the LAN as each link has a discrete
limit - 200 metres
Bridges &
Switches
• They operate on Ethernet frames and are layer 2 devices
– they are store and forward devices but use LAN addresses – LAN
devices
• Acts as a switch and only sends frames down a link on which
the destination address is. Thus it can break a LAN into
discrete collision zones – single tree
• Uses MAC addresses
• It also connects links at different bandwidths i.e. 10mbps and
100mbps
• They are plug & play devices and self learn what devices are
on what links.
• But if there are multiple paths they could generate duplicate
packets, so they disable duplicate paths.
Floor 15
All wires would be
100mbps UTP Cat 5
Floor 14
Floor 13
Machine room
Optic fibre
Servers
Router
WAN
Network Devices
Application
Application
Transport
Transport
Network
Link
Physical
Host
Physical
Hub
Network
Network
Link
Link
Link
Physical
Physical
Physical
Router
Host
Bridge or
Switch
Routers
• Routers send packets on best path to the destination. This
is necessary for path redundancy
• Because they operate at layer 3 they are inherently slower
than bridges but more complex technologies are
compensating – Route on IP addresses can use different
paths
• They maintain separate network segments
• LAN or WAN devices
• Can be used as simple firewalls by filtering out packets
within an organisation
• Vary between core trunk routers to SOHO routers for less
that $1500.
Router design
• Bus with CPU software switching
• Bus with intelligent line cards
• Non blocking cross bar switching with up to
5 TBPS switching. Cisco 12000 series is an
example. Juniper Networks, Avici and
Lucent have similar capacity routers
• Switching decisions on 100m packets per
second
Application layer
Process
Application
Message
Application
Transport layer
Process
Host
Application
Transport
Message
Segment
Application
Transport
Network layer
Process
Host
Host &
Router
Application
Transport
Network
Message
Application
Segment
Datagram
Network
Transport
Datagram
Network
Link layer
Process
Host
Host &
Router
Message
Application
Segment
Transport
Network
Datagram
Frame
Link
Host, router
& switch
Link
Application
Link
Transport
Datagram
Network
Link
Network
Frame
Link
Link
Link