Network Fundamentals Flashcards
What different transmission types exist
Broadcast links
Point to point links
Explain broadcast networks
Single communication channel shared by all machines on network. Packets sent are received by every machine and contain intended recipient.
What is multicasting?
Mode of operation that allows subset of machines to process given packet
Explain point to point links
Many connections between individual pairs of machines. Packets travelling between must visit intermediate machines. Various routes of different optimisation levels are available.
What is unicasting?
when point to point networks with single sender and receiver pair can share data
What does LAN stand for?
local area network
How can we distinguish LANs?
1) time: worst case transmission time can be determined in advanced
2) transmission technology: wired or wireless
3) topology: bus or ring
Explain bus in topology
Only single machine on network can transfer data at any time
Requires negotiation mechanism to resolve transmission conflicts
Ethernet is most common bus network
Explain ring in topology
Each transmission bit is propagated individually
Requires access control to resolve propagation queuing
Token ring (outdated), FDDI is most common ring network
What does WAN stand for?
Wide area network
Define link in the network context
Connection between 2 devices in network
What is bandwidth?
Max speed in which data can be transmitted on link
How is data transferred through the internet?
Circuit switching
Packet switching
Do links have the same bandwidth?
No
Explain circuit switching
End-to-end resources reserved for the session. Requires initial setup to reserve the resources. Dedicated resources with reserved bandwidth; no sharing
Explain packet switching
Sender divides data into packets, each of which contains a header (with source and destination address)
Network interface hardware transforms data for physical transmission then network delivers packets to destination (path may change!!!!). Receiver converts physical signal back into data packet. Receiver assembles packets back into data. Packets may be lost, corrupted or delivered out of order.
What are some advantages of packet switching?
Different packets can take different routes; resource sharing (packets from different users share resources)
Better utilisation of network resources
What are some disadvantages of packet switching?
No performance guarantees (hope it will get to destination but it may not)
Congestion: packets may be lost
What is a network protocol stack?
A stack of layers. Each layer provides a service to the layer above. Hierarchical approach.
What is http?
Network protocol. hypertext transfer protocol
What is a connection oriented service?
- connect, disconnect, use
- negotiation inherent in connection setup
- similar to telephone service
- packets travelling between destinations all use same route
- eg. Telco, guarantees reliability of subnet (QoS important)
What is a connectionless service?
- use
- message routed through intermediate nodes
- similar to postal service
- packets (datagrams) injected into subnet independently and packets are individually routed to destination
- eg. internet (QoS not easily implemented)
What is a service?
- set of primitives that a layer provides to a layer above it
- interfaces between layers
What is a protocol?
rules that govern the format and meaning of packets that are exchanged by peers within a layer
packets sent between peer entitites
What is the difference between a protocol and a service?
A service interfaces between layers, where protocol is packets sent between peer entities in same layer
Why do we need a network reference model?
Common baseline for development of many services and protocols by independent parties
What is the purpose of an API?
application programming interface (API) is a set of routines, protocols, and tools for building software and applications.
What is the OSI reference model?
Operation Systems Interconnection.
- layer should be created where a different abstraction is needed
- each layer should perform a well defined function
- function of each layer should be chosen with a view toward defining internationally standardised protocols
- layer boundaries should be chosen to minimise information flow across interfaces
- number of layers should be large enough that distinct functions need not be thrown together in same layer out of necessity and small enough that architecture doesn’t become too unwieldy
Explain the components of OSI model
Application: APDU Presentation: PPDU Session: SPDU Transport: TPDU Network: Packet Data link: Frame Physical: Bit
where first word after is the unit exchanged.
What is TCP/IP model?
Transmission control protocol/internet protocol
Does TCP/IP depend on infrastructure?
No
What layers are in TCP/IP model?
Application
Transport
Internet
Host to network
Explain host to network layers
This is in TCP/IP reference model.
It consists of:
Physical layer -
corresponds to signalling technology, done in hardware
Data link layer -
frame management: take packets from network layer and encapsulate them into frames (containing header, payload, trailer)
ethernet device address or MAC (media access control) address: 48 bit unique address
Explain purpose of network layer
Provide necessary functionality to combine networks and route data through network:
- creates internet address space(each host has 32 bit IP address)
- runs IP routing software
- implements packet routing across networks, defines a packet consisting of header and payload
- used to forward data among computer networks
- intermediate hosts are typically called gateways
What is contained within the header?
Packet size, source & destination address
What is contained within the payload?
contains data bits sent from source to host
What is a gateway?
Intermediate host
What do we call intermediate hosts?
Gateways
What is an IP address?
internet protocol. hierarchical, not portable. depends on IP subnet to which node is attached
What is a MAC address?
media access control. flat, portable, can move LAN card from one LAN to another
Distinguish between IP and MAC addresses?
IP: like a postal address, internet protocol. hierarchical, not portable. depends on IP subnet to which node is attached
MAC: like social security number, media access control. flat, portable, can move LAN card from one LAN to another
What do switches do?
Link layer device
Maintain switch table
Implement filtering algorithms
Plug-and-play; self learning
What do routers do?
Network layer device
Maintain forwarding table
Implementing routing algorithms
Must be configured by admin
Explain the transport layer
This has 2 primary protocols.
TCP (transmission control protocol): connection oriented, reliable delivery, provides stream-oriented access to network
UDP (user datagram protocol): connectionless (no guarantee packets will be delivered), more efficient relative to TCP
This layer has 16 bit port number as interface for applications
Provide reliable cost-effective data transport from source to destination independent of physical or data networks
What are the 2 primary protocols of the transport layer? Which is more efficient?
TCP (transmission control protocol): connection oriented, reliable delivery, provides stream-oriented access to network
UDP (user datagram protocol): connectionless (no guarantee packets will be delivered), more efficient relative to TCP
What is the difference in reliability between network and transport layers?
Network layer is unreliable. Transport layer is reliable.
Explain the application layer and give examples
Examples: HTTP, FTP, SMTP, DNS
Treats transport layer and lower protocols as black boxes
What does transport layer provide application layer?
application layer relies on network layer to help provide a service
service is between processes (eg. sockets)
What does network layer provide application layer?
services between nodes (eg. routers and hosts)
hides details of link technology (eg. IP)
What is a key function of the network layer?
Forward packets from source to destination
What is QoS?
Quality of service
What issues should be considered when connecting networks?
different network types and protocols
different motivations for network choices
different technologies at both hardware and software levels
What does a packet contain?
A header (with source and destination address)
Explain how packets travel within a network
The sender puts data into packets
Network interface hardware transforms data for physical transmission
Network delivers packets to variable destination
Receiver converts physical signal back into data packet
Receiver assembles packets back into data
What is IP?
Internet protocol. Provides best effort service to route datagrams from source host to destination host. Connectionless model (path taken can be different)
Does IP use connection oriented or connectionless model?
Connectionless
What are IP design goals?
Services should be independent of router technologies (remember path taken can be different)
Transport layer should be shielded from number, type and topology of routers
Network addressing should use a uniform numbering pattern
How many bits is IP?
32 bits
Describe structure of IPv4
Consists of header and some text
Header is 20 bit fixed part + variable length optional part
Version: IPv4 or IPv6
IHL: internet header length is variable
Type: differentiates different classes of service
Total length: header and payload, max length 65535 bytes
Identification: allows host to determine which datagram new fragment belongs to
DF: don’t fragment byte
MF: more fragment byte - is this last frag? are there more?
Fragment offset: where in datagram current fragment belongs
TTL: limits packet lifetimes (time to live)
Protocol: TCP, UDP, others
Header checksum: verifies header only
Source address: IP - host/network
Destination address: IP - host/network
Options: dw about these
Explain time to live
we give packets of data a certain time to jump between nodes to get to their destination. if they don’t make it in that time frame, the packet is deleted. This is part of the IPv4 frame structure
What is the purpose of fragmentation?
allows network gateways to meet size constraints
Explain IP addresses
32 bit number that encodes network and host number
0.0.0.0 is lowest and 255.255.255.255 is highest
What does 127.0.0.1 mean?
127.0.0.0 has all zeros for the host bits, so it is a network address. 127.0.0.1 is a loopback address.
What is subnetting?
Allows networks to be split into several parts for internal uses while acting like a single network for external use
What 2 types of notation can subnet masks be written in?
Dotted decimal or slash
What is a NAT box?
Network address translation: in this local area, everyone has same address. NAT determines which internal device sent out a request (remember all machines on home network have same IP)
What different classes of IP are available?
Class A: 128 networks, 16m hosts each, , 8/24
Class B: 16,384 networks, 64k hosts each, 16/16
Class C: 2m networks, 256 hosts each, 24/8
Class D: multicast
(host vals should be -2)
Recall that class a uses 1 bit (0) to identify it as being class a, class b uses 2 bits (10) and class c uses 3 (110)
What is the network ID?
First address (all 0s in host portion)
What is the broadcast address of subnet?
Last address with all 1s in host portion
What is a subnet mask?
32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all “1”s and setting host bits to all “0”s.
What is a network?
Interconnected or intersecting system of components
Is the internet a single network?
No, it’s a network of networks with a single point of control
What is the WWW?
Distributed system that runs on top of internet
What is responsible for error detection/correction in packet switching?
Higher-level protocol
Does IP depend on router technology?
No, these should be independent
What is fragmentation?
This allows data to fit through smaller gateways.
What’s the difference between ipv4 and ipv6?
ipv6 is 128 bits instead of 32
