networks introduction Flashcards
hosts
millions of connected computing devices, hosts = end systems running on network applications
communication links
physical infrastructure - fibre, copper, radio, satelite
what is bandwidth
transmission rate
what do packet switches do?
forward packets
what do protocols generally do
control sending and receiving of messages
name 2 internet standards
RFC - request for comments
IETF - internet engineering task force
RFC
REQUEST FOR COMMENTS
IETC
INTERNET ENGINEERING TASK FORCE
what is a protocol
define format and order of messages sent and received amongst network entities and actions taken on message transmission receipt
name some pieces that make up a network
hosts, routers, links of various media, applications, protocols, hardware, software
what does a network layer do in general
each layer implements a service via its own internal-layer actions, relying on services provided by the layer below
why is layering used?
Because we’re dealing with complex systems
- explicit structure allows identification relationship of complex system pieces
- modularization eases maintenance and updating of system
how does modularization ease maintenance and make updating a system easier?
change of implementation of a layer’s service is transparent to the rest of the system - e.g change in gate procedure doesnt affect how the rest of the system operates
List the 7 layers in the ISO/OSI reference model
application presentation session transport network link physical
purpose of application layer
supporting network application. Focused on end-to-end, App-App and device-device
presentation layer purpose
allows applications to interpret the meanings of data - how data/info is presented to the user
What is the session layer
devices - src and dest need to synchronize and be at the same point to ensure that data is not missed - synchronization, checkpointing, recovery of data
Transport layer purpose
process to process data transfer
network layer purpose
routing of datagrams from src to dest
link layer purpose
transfer between neighboring network elements
physical layer purpose
encoded bits on the physical architecture
which layers can be embeded into the application layer?
app, pres, session
Which layers occur in the Internet protocol stack and TCP/IP suite? give examples of some protocols that exist in these layers
Application - ftp, http, smtp transport - tcp, udp network - ip, routing protocols link - ethernet, wifi (802.111) physical
Explain the process of encapsulating in a network
message - gets new header at each layer (encoded). Fro m src travels down layers and get put into layer packet each time, then passed back up layers moving along physical and link layers
LAN
Local area network - interconnect hosts up to a few or maybe a few tens of km apart
MAN
metropolitan area network - connects devices up to a few hundred km apart
WAN
wide area network - interconnect hosts that are all over the world
Unicast
info sent from one sender to one receiver
Anycast
Info delivered to any one receiver that is part of a particular set
Multicast
info sent to set of receipients
broadcast
info sent to all nodes that are part of a particular network
network edge
hosts: client-server - where end devices reside in
Where are servers located
often in data centers
access networks/physical media
wired, wireless communication links, allow edge to connect to the internet
what is the network core
inter connected routers - network of networks
allows movement of traffic between the src and dest
how does the network core work?
through packet switching: hosts break application layer messesages into packets
packets are then forwarded from one router to the next, across links on path from source to destination
routing
determines src-dest path
forwarding
move packets from router input to router output
Describe the internet’s structure
network of networks
End systems connect to internet via access ISPs
Access ISPs are inter connected
how not to connect ISPs. Why?
have each ISP link to every other ISP in the world- doesnt scale - O(N^2) connections
Discuss connecting each ISP to one global ISP - drawbacks
monopoly
not possible - others will see what a viable business it is and join in - will never just have 1 global isp
problem with multiple global isp that are not connected
fragmented internet
What is an IXP
Internet exchange point - ISPs come together - physical inter connection point because there is traffic that needs to be transfered between ISPs
Purpose of a regional network
connect access networks to ISPs
what if there was no regional network?
unnecessary hops - e.g.) cape town to global to jhb instead of just cpt to jhb
what is the purpose of content provider networks
not aimed at providing internet access - instead, they run their own networks to bring their content closer to where the end users are - e..g google will push content to different servers in different parts of the world - content nodes
Tier 1 ISP
have global reach - nodes in major cities - connect to them and be able to access everyhting
What are content provider networks and what do they do? part2
private network that connects data centers to internet - often bypassing tier 1 and regional ISPs
