Introduction Flashcards
Network Edge
Hosts (clients and servers), end of data route, sends packets of data, takes application message
Network Core
Route must pass through it.
Interconnected routers.
Network of Networks
Devices are connected using a hierarchy of networks
Host
Client and server. End system that provides user with information/data
Protocol
Define format and order of messages sent and received among network entities and actions taken on message transmission/receipt.
HTTP (web), TCP, IP, 4G, Ethernet.
ISP
Internet Service Provider, provides connection between host and network
Internet Structure
- Network edge
- Access networks, Physical media
- Network core
Access Networks/ISP
Residential, institutional, or mobile access networks. (within an organization). Smallest type of network
Types of Access Networks
- Cable-based Access
- Digital subscriber line
- Home networks
- Wireless network
- Enterprise network
- Data Center network
Cable-Based Access Network
Network of cable/fiber that connectes homes to ISP router.
Homes share connection from access network to cable headend.
Digital Subscriber Line Access Network
Uses existing telephone line to central office DSLAM. Voice and data transmitted at different frequencies.
Data over DSL phone line goes to Internet. Voice over DSL phone goes to telephone net.
Home Access Network
Wired: Headend/central office to modem to router to host
Wireless: Headend/central office to modem to router to Wifi access point to host
Wireless Access Network
Through access point.
Wireless LAN: 100ft
Wide-Area Cellular: provided by mobile/cellular network operator
Enterprise Access Network
Companies, universities, etc.
Mix of wired, wireless link technologies (mix of switches and routers)
Data Center Access Network
High-bandwidth links connects many servers together and to the Internet
Transmission Rate
Link capacity or bandwidth.
Time needed to transmit bit packet into link = L (bits) / R (bits/sec)
Radio Link Types
- Wireless LAN (wifi)
- Wide-area
- Bluetooth
- Terrestrial microwave
- Satellite
Packet Switching
Host breaks application-layer messages into packets
Forwarding
Move arriving packets from routers input link to appropriate output link.
LOCAL ACTION
Routing
Determine source-destination paths taken by packets (routing algorithms)
GLOBAL ACTION
Packet Transmission Delay
Takes L/R seconds to transmit L-bit packet into link at R bps.
Store and Forward
Entire packet must arrive at router before it can be transmitted on next link.
Parts of Packet Switching
Store and forward, queueing
Queueing and when does it occur
When router becomes overloaded with packets. Can cause data loss. Occurs when work arrives faster than it can be serviced.
Circuit Switching
Alternative to packet switching. End to end resouces allocated to, reserved for the ‘call’ (no sharing) between source and destination. Call gets dropped if max num of connection is reached.
Can use FDM or TDM
FDM
Frequency Division Multiplexing. Used in circuit switching. Optical, electromagnetic frequencies divided into narrow frequencies bands. Each call allocated its own band
TDM
Time Division Multiplexing. Used in circuit switching. Time divided into slots, each call allocated periodic slots
Packet Switching VS Circuit Switching
Circuit-switching can only serve up to 10 users at a time, while packet-switching can serve 10 or more users. However, packet switching can lead to data loss as resources are not reserved.
Regional ISP
Provides access to subscribers in a franchise area. Higher then Access ISP
IXP
Internet Exchange Point. Physical location through which ISP companies can exchange internet traffic. Higher then Regional ISP
Tier 1 ISP
Commercial ISPs, national and international coverage (Sprint, AT&T, NTT), Higher then IXP, same as Content Provider Network
Content Provider Network
Private network that connects data centers to internet, bypass Tier-1 and Regional ISPs. Same level as Tier-1
When does Packet Loss occur?
Occurs when memory to hold queued packets fills up
Packet Delay Calculation
Nodal processing + queueing delay + transmission delay + propagation delay = packet delay
Nodal Processing
Time it takes for router to process incoming packets (check bit errors, determine output link)
Queuing Delay
Time spent waiting for output link, depends on congestion level of router
Transmission Delay
Time it takes for packet to leave router through output link.
L/R, L is packet length (bits) and R is link transmission rate (bps)
Propagation Delay
Time it takes for packet to travel to next router or final destination.
d/s, d is length of physical link and s is propagation speed
Traceroute Program
Provides delay measurement from source to each router along end-end Internet path to destination. Sends three packets to each router on path, router then returns packets and time is calculated.
Throughput
Rate (bits/time unit) at which bits are being sent to receiver.
Instantaneous Throughput
Rate (bits/time unit) at given point in time
Average Throughput
Rate (bits/time unit) over longer period of time, uses minimum throughput of entire path
Bottleneck Link
Link on end-end path that constrains overall throughput
