Protocol is Hi to be replied by Hi Protocol is not Hi, Get lost : well until at least you are dealing with a nut Talk about packet transports, introduce packet headers, packet payload etc.
Talk about major hubs where you land and then take off. Point out similarity with networks
Give egs using services such as 1-800, call-waiting.
Explain distinction with the telco network here. Explain that you have services at end points. Though we now have mechanisms inside the network for QoS etc.
Routing implemented in network (eg for the second interpretation)
Give eg of voice, where the end users adjust for error correction.
If you want to ensure survivability then need to maintain state; this can be done either inside the network or at the end-hosts. If inside the network then we need to ensure replication of state to ensure survivability against routers or gateways. So this might not be a better option as compared to maintaining state at the end points. So if the end point dies then nothing lost.
At issue is the conventional understanding of the`Internet philosophy’ freedom of action user empowerment end-user responsibility for actions taken lack of control “in” the net that limit or regulate what users can do The end-end argument fostered that philosophy because they enable the freedom to innovate, install new software at will, and run applications of the users choice ” Bluementhal and Clark 2001
A technique to organize a system into a succession of logically distinct entities, such that the service provided by one entity is solely based on the service provided by the previous (lower level) entity
Decomposition of a complex system into an ordered series of distinct abstractions
Service: what a layer does (e.g. message delivery)
Interface: how to use the service
Protocol: how the service is implemented
Protocol stack: collection of protocols implementing a series of layers
Divide and conquer Analogy: Organization of air travel
Protocols: a series of functions performed at different locations
Layered air travel: services Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane airplane routing from source to destination Similarly, we organize computer systems into a bunch of layers! Each layer has a protocol to talk to its peer
adds header information to create new data unit (“encapsulation”)
passes new data unit to layer below
source destination message segment datagram frame application transport network link physical application transport network link physical M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l
add addressing, reliability check info to form “datagram”
send datagram to peer
wait for peer to ack receipt
analogy: post office
transport transport (Source: Kurose & Ross) application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data data data ack
Example: Transport Protocol (Physical Communication) (Source: Kurose & Ross) application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data data
network: routing of datagrams from source to destination
ip, routing protocols
link: data transfer between neighboring network elements
physical: bits “on the wire”
application transport network link physical
Reference Models for Layering Application Transport Internetwork Host to Network FTP TCP IP Ether net Telnet HTTP UDP Packet Radio Point-to- Point TCP/IP Model OSI Ref Model TCP/IP Protocols Application Presentation Session Transport Network Datalink Physical
as more and more value depends on network services, can't afford random downtimes
Textbook Internet vs. real Internet dominance of Ethernet, but also L2’s not designed for networks ( 1394 Firewire, Fibre Channel, MPEG2, …) multitude of L2 protocols (ATM, ARCnet, Ethernet, FDDI, modems, …) network address translation (NAT) globally unique and routable time-varying (DHCP) permanent interface identifier (IP address) middle boxes (proxies, ALGs, …) end-to-end (application only in 2 places)
Textbook Internet vs. real Internet layer splits 4 layers (link, network, transport, application) firewalls, L7 filters, “transparent proxies” transparent network grandma, frustrated if email doesn’t work technical users, excited about new technology Linksys, Dlink, Netgear, …, available at Radio Shack small number of manufacturers, making expensive boxes hackers, spammers, con artists, pornographers, … mostly trusted end users