Service Providers & Data Link & Physical layers Week 4 Lecture 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 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
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
Floor 15 Floor 14 Floor 13 Machine room Router Servers WAN All wires would be 100mbps 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
TCP/IP Frame Relay/ATM ATM/Fibre 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 room Router Servers WAN All wires would be 100mbps UTP Cat 5 Optic fibre
Network Devices Application Transport Network Link Physical Link Physical Network Link Physical Application Transport Network Link Physical Host Bridge or Switch 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