Unit 5 Flashcards
Protocol to get own IP addr, first-hop router addr, and DNS server addr
DHCP
Binary Exponential Backoff
Time a host waits for before transmitting a packet to avoid collision
After mth collision, k is chosen from { 0,1,2, …. ,2^m-1 }
Waits for [k*512 bit] length before transmission
Self Learning Switch
Switch floods the network with frames / sends a frame with a specific destination
The host(s) respond to the frame with IP address and MAC address. The switch then enters the necessary details i.e { MAC address, Interface to reach host, TTL } into the switch table.Ethernet Broadcast
FF-FF-FF-FF-FF-FF
Day in the life of a web request
DHCP > ARP > DNS > TCP + HTTP > HTTP req/reply
OSI stack layers
Application - [Presentation - Session] - Transport -Network - Link Layer - Physical
Bit Time
Time taken by a bit to occupy the media
Bandwidth
Physical Layer: Total capacity of a medium to carry data at any given amount of time.
Depends on the properties of the medium and signaling methods
Throughput
PHYSICAL LAYER: Transfer rate of data over the medium
Factors that affect: Amount and type of traffic, number of devices
Goodput
PHYSICAL LAYER: Transfer rate of actual usable data bits
Throughput less the data protocol overhead, error corrections, and retransmissions
Optical Fibre (Indexing)
1) Multimode Step Index: Total Internal Reflection of light within cable, zig-zag path, path function of angle of incidence
2) Multimode Graded Index: Sinusoidal oscillations, better performance, 10-12kms
3) Single-mode Step Index: Propagation of one transverse EM mode (solution to Helmholtz equation (del^2)f = -(k^2)*f), high capacity
Access Point (AP)
An entity that has station functionality and provides access to the distribution system via the wireless medium for associated stations.
Basic Service Set (BSS)
A set of stations controlled by a single coordination function.
Coordination Function
The logical function that determines when a station operating within a BSS is permitted to transmit and receive PDUs
Distribution System
A system used to interconnect a set of BSSs and integrated LANs to create ESS (Extended Service Set)
Extended Service Set (ESS)
A set of interconnected BSSs and integrated LANs that appear as a single BSS at the LLC(Logical Link Control) layer at any given station associated with these BSSs
Station
Any system that contains an 802.11 conformant MAC and Physical Layer
MPDU & MSDU
MAC Protocol Data Unit
MAC Service Data Unit
CSMA in Ethernet and WiFi
Ethernet -> CSMA/CD
WiFi -> CSMA/CA
Sublayers of Data Link Layer
LLC (Logic Link Control) -> IEEE 802.1 (LAN, MAN, WAN, internetworking and security)
MAC (Media Access Control) -> PCF(Point coordination func), DCF (Distributed coordination functions)
SIFS, DIFS & PISF
SIFS (Shorter Inter-frame Space): time interval required by a wireless device in between receiving a frame and responding to the frame.
DISF (DCF inter-frame Space): Using the DCF technique, a station needs to sense the status of the wireless channel before it can place its request to transmit a frame. The time interval that a station should wait before it sends its request frame is known as DIFS. = SISF + 2*slot time
PISF (PCF Inter-frame Space): Access Point (AP) coordinating with the communications centrally, waits for PIFS duration to grasp the channel. Since PIFS is less than DIFS duration, the AP always has the priority to access the channel over the other stations. PISF = SISF + slot time.
RTS, CTS
Request To Send
Clear To Send -> handshake in CSMA/CA can avoid a collision from a hidden station.
