w1

K = 10^3 M = 10^6 G = 10^9

Internet is a collection of devices connected to each other; or network of networks -> ISPs (???)

Host == end systems == device

Types of devices

1. Packet Switches

• Forwards packets of data to other devices

• Routers, Switches

1. Communication links

• Medium of transmission

• Fiber, Copper, Radio, Satellite

• Measured in Bandwidth, or transmission rate

1. Networks

• Collection of devices, routers, and link managed by an organisation

• Types:

  • Area-wise:

    • LAN/WAN

  • Transmission media

    • Wired/Wireless network

  • By speed -> Broadband speed

  • By standard -> Proprietary, open network

  • By business function domain -> intranet, extranet

Protocols

• Are in charge of control of sending, receiving and streaming of messages

  • Ie. HTTP, TCP, IP, Ethernet..etc

• Are like rules that define the format, order of data and actions taken on a piece of data.

Common Protocols

1. DHCP

2. NAT

3. DNS

4. BGP

5. HTTP

6. IEEE 802.3 - Ethernet

7. IEEE 802.11 - Wifi

not WPA, as WPA is a security protocol used within the 802 series.

Infrastructure

• Provides services to applications

• Provides programming interface to distributed applications -> A programming interface is a set of functions/tools that allow software programs to communicate with each other. Ie. APIs -> hooks allow connection/sending/receiving of data through the Internet

Network Edge

• Literal edge, contains hosts and servers

• Also contains access networks that can be wired or wireless communication links

Network Core

• Contains the interconnections of routers and networks, or a mesh of interconnected routers

Functions of Network Cores

1. Forwarding

• Switching, in which packets that arrive are checked on the forwarding table to output to the correct route link

• local action ??

• tells direction, but not specific to location

1. Routing

• Predetermined source to destination path that everyone agrees on based on a common routing algorithm.

• global action ??

• specific to location

Differences: Routing is more specific, Forwarding only points in the correct direction

In dept of a transmission:

1. Host breaks application message into small packets of length L

2. Host then transmits the packets into access networks at a transmission rate of R. => Also known as link capacity/link bandwidth

Packet transmission delay in seconds (ms) = time need to transmit L-bit packet into link = L bits (bits) / R (bps - bits/sec)

Packet Switching

• A method in which the host will break the messages into packages, and sends the packets through different routes to reach the same destination. The receiving device will need to reassemble the data first before being able to read it.

• Dynamic sharing of resources: Data is broken into packets and sent independently through the network.

• Efficient for bursty traffic: Ideal for data communication like internet traffic, where data is sent intermittently rather than continuously.

• Too much data at once can overflow router buffers, causing packet loss and delays.

• Needs congestion control: Special protocols must manage traffic to avoid network overload.

Circuit Switching

• End-to-end resources are reserved: A fixed path with dedicated bandwidth is established for the entire duration of a communication session (called a “call”) between source and destination.

• No resource sharing: Once a circuit is assigned, no one else can use that part of the network, even if it's idle. This causes the reserved circuit stays unused, wasting resources.

• ???? (slide 31-32)

Store and Forward

• Once packet arrives at the router, the router saves it into memory and checks the validity of the packet. If invalid, or packet is a bad packet, then the packet is dropped.

• Makes network more reliable and clean, less overhead.

Queueing

• Occurs when packets arrives faster than it can be serviced

• ie. Router has input links of 100Mb/s, and output transmission rate of 1.5Mb/s, leading to queue of packets waiting t be transmitted on output link

• packets can be dropped if memory (buffer) in router fills up

Delays and Loss Delays happen when there is a wait occurring Loss occurs when memory to hold queued packets is full and packets are dropped when there is no free buffers.

d nodal = d1 + d2 + d3 + d4

Delays

1. Nodal Processing

• Checks bit errors + determines output link

1. Queueing delay

• Time waiting at output link for transmission

• Depends on congestion level of router

(refer to slide 44??)

1. Transmission delay

• = L/R !!(Careful of the sign)

1. Propagation delay

• Length of physical link/propagation speed (~ 3 * 10^8 m/sec)

• = d/s

a -> 8.00001 b -> Link 2: 800.0001667 Link 3: Same as Link 1 Total Delay = 816.0001867

Careful of the M!

Loss

1. Packet Loss

Performance Metrics

• Throughput

• Rate at which bits are being sent from sender to receiver

• bits/time unit

2 Types:

1. Instantaneous - rate at specific moment.

2. Average - averate rate over a period of tim

Bottleneck Link

• The slowest link on the path, the limiting factor of throughput.

• Bottleneck determines the throughput

  • Ie. when sender can send at 1Mbps, and link can handle 5 Mbps, the limiting factor here to throughput is the sender, and thus the sender is the bottleneck.

Throughput = min(Rc, Rs, R/10), where 10 is the insert slide 47 R client, R server "In practice: Rc or Rs is often smaller than R/N"

End to End Delay

• total time it takes for data to travel from sender to receiver

1. Single Hop

• Processing delay (Nodal processing)

• Queueing delay

• Transmission delay

• Propagation delay

1. Multi Hop

• Add up delays across each hop

• Transmission is pipelined

Protocol Layers Application - HTTP, DNS - contains Message Transport - TCP/UDP - Encapsulates message with transport layer header to create a segment Network - IP, routing protocols - Encapsulates segment with network layer header to create datagram Link - Ethernet, 802.11 - Encapsulates datagram with link-layer header to create frame Physical - Bits