slides for week 5 - lec 1
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Service Providers &Data Link & Physical layers
Week 4 Lecture 1
Internet Architecture
Application layer – HTTP, SMTP etc
Transport layer – TCP, UDP
Network layer - IP
Data link & Physical layers – the territory of the Lan & Telcos
W3C
IETF
ITUIEEE
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
WAN
Workstations
Router &Firewall
File server
Application & Database Servers
Printers
Main characteristics
• 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
Floor 14
Floor 13
Machine roomRouter
Servers
WAN
All wires would be100mbps UTP Cat 5
Backbone could be Optic fibre
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 re-transmits
• 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
• Ethernet - 10mb
• Fast Ethernet - 100mb
• Gigabit Ethernet - 1000mb
• 10 Gigabit Ethernet - 10000mb
TCP/IP
Frame Relay/ATM
ATM/Fibre
CSMA/CD CSMA/CD
Routers
Local ISP POP
City carrier hubs
Devices in the network
• 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
Floor 14
Floor 13
Machine roomRouter
Servers
WAN
All wires would be100mbps UTP Cat 5
Optic fibre
Network Devices
Application
Transport
Network
Link
Physical
Link
Physical
Network
Link
Physical
Application
Transport
Network
Link
Physical
Host Bridge orSwitch
Router Host
Physical
Hub
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 ApplicationProcess
Application layer
Message
Application ApplicationProcess
Transport layer
Message
Transport TransportSegmentHost
Application ApplicationProcess
Network layer
Message
Transport TransportSegmentHost
Network Network NetworkHost & Router
Datagram Datagram
Application ApplicationProcess
Link layer
Message
Transport TransportSegmentHost
Network NetworkHost & Router
Datagram Datagram
Link Link
Host, router& switch
Frame Frame
LinkLink LinkLink
LinkNetwork