updated computer networking

hosts/end systems

refers to all connected devices

each end systems are interconnected by a network of communication links and packet switches

packet switches

routers and link layer switches, forward packets to their destination

route (path) through the network

the sequence of links and switches a packet traverses

packet switched networks

comparative to transportation networks, with packets → trucks
communication links → highways and roads

Internet Service Providers (ISPs)

how end systems access the internet, including residential, corporate, university, WiFi, and cellular data

internet protocols

TCP and IP, govern data transmission within the internet

internet applications

distributed and run on end systems, not within packet switches

socket interface

used by end systems to instructs the internet to deliver to other end systems

network edge

where the end systems are found, including computers smartphones and other devices

Home Access: DSL

one of the most common broadband residential access type
often provided by local telephone company
offers varying transmission rates, both downstream and upstream with potential for high speed access
best suited for short distance within central office

Home Access: Cable

uses existing cable TV infrastructure
fiber optics connect cable head end to neighborhood junctions, then coaxial cable reaches individual homes
often referred to as hybrid fiber coax (HFC) because both fiber and coaxial cable are has downstream and upstream channels, downstream typically has higher transmission rates

home access: FTTH (fiber to the home)

provides high speed residential boradband access via optical fiber
can offer gigabit per second internet speeds
shared fiber networks use two architectures: active optical networks (AON) and passive optical networks (PON)

guided media (physical media)

signals propagate in solid media: copper, fiber, coax

unguided media (physical media)

signals propagate freely,
e.g., radio

packet switching

use store and forward transmission
host breaks application-layer messages into packets
must receive the entire packet before transmission

queueing delay and packet loss

packet switches have output buffers (output queues)
queueing delay occurs when the link is busy
packet loss can happen when the buffer is full due to congestion

client-side architecture

there is a dedicated service that services requests from multiple client hosts
clients do not directly communicate with each other but interact with the server
the server has a fixed well-known IP address
ex: web, FTP, telnet, email

peer-to-peer (P2P) architecture

there is minimal reliance on dedicated servers in data centers
considered intermittently connected hosts, communicate directly with eachother without a dedicated server intermediary

communications between processes

on different end systems they exchange messages across the computer network

socket

analogous to door through which a process send and receives messages
messages sent between processes must pass through the network using this software interface

Socket Communication

serve as the interface between application layer and transport layer within a host
they are the Application Programming Interface (API) for building network applications

reliable data transfer

ensures that data sent by one end is delivered correctly and completely to the other end.
Some applications require this service to prevent data loss, while others like multimedia apps can tolerate some loss.

Throughput

the rate at which bits are delivered from the sender to the receiver in a communication session. Bandwidth sensitive applications need guaranteed throughput.

multiplexing and demultiplexing

objective is to extend host-to-host delivery to process-to-process delivery for applications

demultiplexing

directs the segment to the corresponding socket, ensuring data is delivered to the correct process.
Transport layer delivers data to an intermediary socket, not directly to a process.
In the household analogy, this is similar to handing out mail to the right person based on the address.

multiplexing

involves gathering data from different sockets, encapsulating it with header information to create segments, and passing the segments to the network layer.

UDP (User Datagram Protocol)

unreliable data transfer
“best effort” service
does not provide:
- internet as it is
- reliablility, flow control, congestion control, timing, throughput guarantee, security, or connection setup

connectionless

UDP - No handshaking between sender and receiver. each UDP segment handled independently
Often used for real time, low delay, and low overhead applications. 

forwarding

refers to the router-local action of transferring a packet from an input link interface to the appropriate output link interface
1. Moves packets from a router's input link to the appropriate output link.
2. The primary function in the data plane.

routing

refers to the network-wide process that determines end-to-end paths that packets take from source to destinaton
1. Determines the route or path packets take from sender to receiver.
2. Implemented in the control plane.
3. Routing algorithms calculate these paths.

components of a generic router

1. input ports

2. switching fabric

3. output ports

4. routing processor

input ports

Terminate incoming physical links.
Perform link-layer functions for interoperability.
Conduct a lookup function to determine the output port using the forwarding table.
Forward control packets (e.g., carrying routing protocol information) to the routing processor.

switching fabric

Connects input ports to output ports.
Completely contained within the router.
a network inside of a network router

Output Ports:

Store and transmit packets received from the switching fabric
Conduct link-layer and physical-layer functions
Paired with input ports for bidirectional links.

routing processor

Performs control-plane functions.

protocols

define the format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

host sending function (sending packets of data)

1. takes application message

2. breaks into smaller chunks, known as packets, of length L bits

3. transmits packets into access network at transmission rate R (link bandwidth)

packet transmission delay

equals the time needed to transmit L-bit packet into link 
= L (bits) / R (bits/sec)

network core

mesh of interconnected routers

store and forward

entire packet must arrive at router before it can be transmitted on next link

packet queuing and loss

if arrival rate (in bps) to link exceeds transmission rate (bps) of link for some period of time:
- packets will queue, waiting to be transmitted on output link
- packets can be dropped (lost) if memory (buffer) in router fills up

circuit switching

end-end resources allocated to, reserved for “call” between source and destination

process

program running within a host

identifier

needed from the process to receive messages in order to communicate using a socket
includes both: IP address and port numbers associated with process on host

TCP

• internet transport layer offered service, providing

  • reliable data transport

  • flow control

  • congestion control

  • connection-oriented, handshaking is required

  • doesn’t provide throughput guarantees, security, timing

network layer

logical communication between hosts

transport layer

logical communication between processes, relying on enhances, network layer services