Advanced Computer Networks

Bits

Shannon and information theory lecture

Measure of information

Information

Shannon and information theory lecture

Resolution of uncertainty

Shannon information

Shannon and information theory lecture

Proposed a measure of that contains a discrete random variable and asks how much information is received when we observe a specific value for this variable

• The “degree of surprise”

Shannon entropy

Shannon and information theory lecture

Where p(x) is the probability of x

h(x) = log 2 p(x)

Shannon information

Shannon and information theory lecture

Less likely a value, the more information is imported by revealing its value

If learn two independent facts, information is additive - so can sum the h values

p(x,y) = P(x)p(y)

h(x,y) = h(x) + h(y)

Information/Shannon entropy

Shannon and information theory lecture

For a series of values. The average amount of information transmitted is given by

h(x) = -∑p(x) log2 p(x)

Solutions to IPv4 address exhausation

IPv6 lecture

• Address conservation

• NAT

• Proposed address release eg 0/8, 127/8, 240/4

• Address recovery

• CGNAT

Carrier grade NAT (CGNAT)

IPv6 lecture

• ISP subnet becomes a large private network

• Home routers are assigned private IP’s

• The amount of required public addresses is reduced as wall as the cost

• One bad actor could mean lots of people are blocked

Carrier grade NAT (CGNAT) problems

IPv6 lecture

• Breaks end to end IP connectivity

• Limits or removes ability to port forward

• Stateful: ISP network has to keep state of all connections

• Everyone gets punished by public IP abuse

• Security and privacy implications

• Does not solve IPv4 address exhausation

IPv6

IPv6 lecture

• 128 bit addresses

• 3.4×10³8 addresses

• Addresses represented in colon hexadecimal format

• Multicast replaces broadcast

IPv6 address formatting

IPv6 lecture

• Leading 0’s in a block can be omitted

• A single set of repeated 0 blocks can be replaced by ::

• Subnets represented in CIDR notation

Changing to IPv6 challenges

IPv6 lecture

• It isn’t ‘needed’

• Those who want it can work around it

• Some ISPs are being stubborn

• Money

• Training

• New infrastructure

• New issues

• No urgency

Motivation for IPv6

IPv6 lecture

• IPv4 address exhaustion

• Direct addressability - End to end addressing

• Less complex networks

Why not deploy IPv6

IPv6 lecture

• ‘I have enough global IPv4 addresses’

• ‘I like NAT, it adds security’ (It does not)

• ‘I have little time/money; it’s not a priority’

• ‘Application x does not support it’

IPv6 common misconceptions

IPv6 lecture

• Puts the current infrastructure at risk - they can co-exist

• Insecure

• Cost - Cost savings and long-term investment

• ‘ISP doesn’t offer it, so we can’t’ - Are transition mechanisms

• Don’t break it if it’s not broken

IPv6 challenges

IPv6 lecture

Support

• Network operators

• Content providers

• Software developers

• Hardware developers

Chicken and the egg problem

Urgency - Killer application is not here yet

Need for IPv6 deployment

IPv6 lecture

• Address space

• Routing

• Firewalling

• DNS that serves it

• Address allocation mechanism

IPv6 address allocation

IPv6 lecture

• SLAAC

• DHCPv6

DHCPv6

IPv6 lecture

A mix of multicast and unicast traffic, link local and global addresses

• Client sends a SOLICIT over multicast

• Server responds with and ADVERTISEment of an address directly to the client

• Client sends a request for the advertised address over multicast

• Server sends a REPLY confirming the address allocation

DHCPv6 Unique Identifier (DUID)

IPv6 lecture

Used to identify a host to the DHCPv6 server

Four different types in RFC 8415

Dual stack deployment

IPv6 lecture

Run both protocols on the same equipment so device have two addresses

IPv6 deployment stratergy

IPv6 lecture

Optimal deployment strategy could be

• Start with it from ISP to your firewall

• Roll out some test nets

• Enable public facing services

• Enable client devices

Tunnelling

IPv6 lecture

Encapsulation of IPv6 packets in IPv4 packets between two destinations

Three main approaches

• 6 in 4

• VPN

• Teredo

6 in 4

IPv6 lecture

IPv6 packet with an IPv4 header bolted in front

Teredo

IPv6 lecture

Encapsulates IPv6 in IPv4 UDP packets

NAT64 (RFC 6146)

IPv6 lecture

IPv4 addresses embedded in a specific IPv6 prefix

Allows IPv6 clients to communicate with IPv4 servers

DNS64 (RFC 6147)

IPv6 lecture

DNS server synthesis a AAAA record for a domain that only has A records

Combine with NAT 64 for a whole solution

Breaks

• DNSSEC

• Does nothing for IPv4 literals

• Does nothing for IPv4 sockets

Without it, a query for an IPv4 only service will yield an IPv4 destination address in response and an IPv6 only service cannot communicate with it

IPv6 mostly

IPv6 lecture

Devices that can operate IPv6 only do so, other devices are dual stack or IPv4 only

MAP-T (RFC 7599)

IPv6 lecture

Translates IPv4 packets into IPv6

• MAP-E (RFC 7597) encapsulates, so has at least 40 bytes of overhead

• MAP-T reduces this to 20 bytes but does not maintain the IPv4 header

Dual stack lite (DS-lite)

IPv6 lecture

Native IPv4, tunnelled and NATed IPv4 (RFC 6333)

Higher bandwidth

IPv6 lecture

Higher the data rate achievable

Higher frequency

IPv6 lecture

Easier it is to use more bandwidth

Centre frequency

Radio fundamentals lecture

Also called carrier frequency

Bandwidth

Radio fundamentals lecture

How wide the signal is

Propagation

Radio fundamentals lecture

How radio waves bounce around an environment

Link budget

Radio fundamentals lecture

Summary of the gains/losses in a radio system

Prx

Radio fundamentals lecture

Received power

Ptx

Radio fundamentals lecture

Transmitter output power

Gtx

Radio fundamentals lecture

Transmitted antenna gain

Grx

Radio fundamentals lecture

Receiver antenna gain

Ltx

Radio fundamentals lecture

Transmit feeder and associated losses (Feeder, connectors, etc)

Lfs

Radio fundamentals lecture

Free space loss or path loss (Inverse square law, atmosphere absorption etc)

Lp

Radio fundamentals lecture

Miscellaneous losses

Modulation

Radio fundamentals lecture

Have a carrier frequency and then change a number of things

• Amplitude

• Frequency

• Phase

Quadrature phase shift keying

Radio fundamentals lecture

Can send multiple bits simultaneously by extending multiple phase shifts

Quadrature amplitude modulation

Radio fundamentals lecture

Combining different modulation schemes

Application of modulation schemes

Radio fundamentals lecture

• Bluetooth

• Wi-Fi

• GSM

• UMTS - Universal Mobile Telecommunications system

• LORA

Frequency Division Multiple Access (FDMA)

Radio fundamentals lecture

Divide frequency band into channels and assign each user a different channel (Uplink and downlink may be on different channel)

Time Division Multiple Access (TDMA)

Radio fundamentals lecture

Divide access to the frequency band into a number of distinct time slots

Code Division Multiple Access (CDMA)

Radio fundamentals lecture

Same carrier frequency but are assigned a mutually orthogonal signal composed of ‘chips’

802.15.4

802.15.4 & 6LoWPAN lecture

Standard that covers physical specifications (PHY) and MAC for LR-WPANs (Low rate wireless personal area network)

Sits in the network access layer of TCP/IP model and layer 1 and 2 of OSI model

802.15.4 applications

802.15.4 & 6LoWPAN lecture

• Wireless/Environmental sensor networks

• Industrial communications and control

• Home automation

• Health monitoring

• Smart metering

• Asset and inventory tracking

• Intelligent agriculture

PAN coordinator

802.15.4 & 6LoWPAN lecture

The networks overall coordinator

Coordinator

802.15.4 & 6LoWPAN lecture

Provides synchronisation services to other devices eg router

Full function device

802.15.4 & 6LoWPAN lecture

• Can function as a PAN coordinator or coordinator

• Can associate with multiple other devices at once

Reduced function device

802.15.4 & 6LoWPAN lecture

• Cannot function as a PAN coordinator or coordinator

• For very simple applications eg light switch or PIR sensor

• Can only associate with one FFD at a time

Star topology

802.15.4 & 6LoWPAN lecture

All communications are to/from the PAN coordinator

Peer to peer

802.15.4 & 6LoWPAN lecture

All devices in range of each other can communicate directly. Is the basis of mesh networking

PPDU

802.15.4 & 6LoWPAN lecture

PHY protocol data unit

PSDU

802.15.4 & 6LoWPAN lecture

PHY Service Data Unit

Wireless HART

802.15.4 & 6LoWPAN lecture

Wireless Highway Addressable Remote Transducer Protocol

Intended for industrial wireless sensing applications

6LoWPAN

802.15.4 & 6LoWPAN lecture

IPv6 over low power wireless personal area networks

RPL

802.15.4 & 6LoWPAN lecture

Routing protocol for low power and lossy networks, RFC 6550

Work out routing over mesh networks and allows for multi hop networks

TSCH

802.15.4 & 6LoWPAN lecture

Time {slotted | synchronised} channel hopping

Essentially combines TDMA and FDMA

Each node gets a timeslot to talk to other nodes

Thread

802.15.4 & 6LoWPAN lecture

A royalty free open industry standard designed for connected home appliances

Matter

802.15.4 & 6LoWPAN lecture

A royalty free, open source protocol standard for IoT and smart home

MQTT

MQTT and CoAP lecture

Message Querying Telemetry Transport

Messages are published to a broker

Clients subscribe to data streams

CoAP

MQTT and CoAP lecture

Constrained Application Protocol

Efficient for low power IoT systems

RESTful

CoAP key features

MQTT and CoAP lecture

• More modern and lightweight design the MQTT

• Prefers UDP

• Binary format for protocol

• DTLS security option

• Block transfers

• Resource discovery

• Push notifications

• Cache model

• Multicast support

Thread and CoAP

MQTT and CoAP lecture

Thread (which uses 6LoWPAN/Ble/Wi-Fi) uses CoAP to

• Configure

• Management messages

LPWAN

LPWAN lecture

Low Power Wide Area Network

Characteristics of LORA

LPWAN lecture

• High immunity to interference

• Long range due to high sensitivity

• Doppler resistant - good for fast moving things

• Multipath resistant - Better in urban environments with lots of reflecting surfaces

• Scalability - To lots of nodes transmitting on the same frequency

LoraWAN architecture

LPWAN lecture

Each gateway makes a star network to nodes

Multiple gateways can overlap coverage and packet copies are managed

LoraWAN classes

LPWAN lecture

• Class A - End device transmits a message and receives a response (or confirmation of receipt) in one of two downlink receive windows

• Class B - Adds scheduled receive for downlinks, meaning the end device dies not have to transmit first to get a response

• Class C - End device always listening, apart from during transmission

Frame counter

LPWAN lecture

• Increments each time a packet is sent

• Network and device reject counters that are lower than expected

• Helps to prevent reply attacks

The things network

LPWAN lecture

Acts as a broker for LoraWAN base station control and data transfer and has a variety of integrations avaliable

NB-IoT

LPWAN lecture

• Narrowband IoT

• Uses LTE frequencies and GSM towers

• 700MHz, 800Mhz, 900MHz with slightly better coverage than ‘normal’ GSM

• Standardised in 2016

• Low cost per sim card

LTE-M

LPWAN lecture

GSM low bandwidth network - Uses 4G infrastructure

Roughly 1Mbit/s each way and ~23dBm power

Can roam between base stations

Uses more power than NB-IoT

Internet of things

IoT lecture

Ubiquitous computing with a focus on objects

Computing is distributed into the environment, and onto physical objects

A happy convergence

• Networking devices, sensors, actuators, becoming prevalent, small and cheap

• Internet connectivity becoming integrated into everyday life

• Cloud platforms for storage; API’s for data collection

• Smaller, lower cost, computing devices

IoT product categories

IoT lecture

• Personal

• Home

• Urban

• Industry

• Ambient devices

IoT communication categories

IoT lecture

• Wi-Fi

• Bluetooth

• Zigbee

• 6LowPAN over 802.15.4 radios

• NB-IoT and cat-M (mobile phone networks)

• Lorawan

Bluetooth low energy

IoT lecture

• Short range, not IP

• Available on phones/tablets/laptops

• Some existing devices like speakers

Zigbee

IoT lecture

• Protocol over 802.15.4 layer at 2.4Ghz/868/915MHz

• 64 bit addressing

• Payload up to 104 bytes

• Being replaced by thread

6LowPAN over 802.15.4

IoT lecture

• Low power radios (typically 10mw)

• Excellent integration with internet

• Gains IPv6 characteristics

• Mesh networking (RPL)

• But need gateway/hub to LAN/WAN

• Can use 2.4GHz or 868/900MHz

• Can be used by Thread/Matter

LoraWAN

IoT lecture

• Wide area low power network using gateway

• Based on starts - gateways link together

• Up to 50 kbps, uses ISM 868/915MHz boards

• Security mechanisms

• Proprietary physical layer (semtech)

• SS chrip modulation - very robust

MQTT

IoT lecture

• Publish/subscribe

• Light weight

• Tend to use a message broker like mosquito

• 'Topics’ published to broker which other can publish/subscribe

Hypercat

IoT lecture

Consortium is developing a new standard for secure IoT interoperability and creating commercial demonstrators

Wireless sensor networks applications

Wireless sensor networks lecture

• Environmental monitoring

• Security and surveillance

• Health monitoring (Personal area networks)

• Rapid response/disaster

Power aware routing

Wireless sensor networks lecture

Wireless sensor networks can often route to prevent overloading one node or cope with breakdowns

Listen-sleep media access protocol

Wireless sensor networks lecture

• Typically MAC protocol

• May need synchronisation

• Can sometimes use a low power preamble listen

Low energy adaptive clustering hierarchy (LEACH)

Wireless sensor networks lecture

Forms clusters of sensors, around a local temporary cluster head

Environmental sensor network

Wireless sensor networks lecture

Comprises an array of sensor nodes and a communications system which allows their data to reach a server

• Enable data that would previously be impossible to collect to be gathered

• Typically wireless

• Battery powered

Personal area network (PAN)

Bluetooth lecture

• Short range

• Body area networks (Network of things connected around body eg heart rate monitor, headphones and phone)

• Personal devices

• Some standards (Bluetooth, Zigbee)

Bluetooth

Bluetooth lecture

Open specification to enable short range wireless voice and data communications

Cable replacement between small mobile devices

2.4Ghz spectrum band

Bluetooth lecture

Globally unlicensed (regulated) part of the spectrum

Interference must be anticipated and appropriately handled - competes with 802.11 Wi-Fi

Aims to maximise bandwidth and minimise RF interference while operating at very low power

Bluetooth radio

Bluetooth lecture

Divides 2.4GHz band in to 79 channels

1MHz per channel

Maximum rate about 1Mbit/s

Uses PSK modulation

Frequency hopping

Bluetooth lecture

To reduce interference transmission frequently hop between channels

• Communication divided into slots

• Each slot uses a different channel

• Reduced RF interference

• Security enhances

Adaptive frequency hopping (AFH)

Bluetooth lecture

Bad (Marked unused) channels within hopping sequence are replaced by random good channels used in hopping sequence (Version 1.2)

Reduces interference with Wi-Fi competing for the same spectrum band

Controller and Responder

Bluetooth lecture

Controller may connect up to seven slaves

No difference in hardware between controller and responder

No responder can communicate directly with another responder

Other responders can be parked (255 of them)

Controller determines frequency hopping pattern and timing

Also called master and slave

IEEE 802.11

Wi-Fi lecture

Set of standards that cover physical specifications (PHY) and MAC for wireless local area networks (WLANs)