Advanced Computer Networks

Bits

Measure of information

Information

Resolution of uncertainty

Shannon information

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

Where p(x) is the probability of x

h(x) = log 2 p(x)

Shannon information

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

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

• Address conservation

• NAT

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

• Address recovery

• CGNAT

Carrier grade NAT (CGNAT)

• 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

• 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

• 128 bit addresses

• 3.4×10³8 addresses

• Addresses represented in colon hexadecimal format

• Multicast replaces broadcast

IPv6 address formatting

• 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

• 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

• IPv4 address exhaustion

• Direct addressability - End to end addressing

• Less complex networks

Why not deploy IPv6

• ‘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

• 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

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

• Address space

• Routing

• Firewalling

• DNS that serves it

• Address allocation mechanism

IPv6 address allocation

• SLAAC

• DHCPv6

DHCPv6

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)

Used to identify a host to the DHCPv6 server

Four different types in RFC 8415

Dual stack deployment

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

IPv6 deployment stratergy

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

Encapsulation of IPv6 packets in IPv4 packets between two destinations

Three main approaches

• 6 in 4

• VPN

• Teredo

6 in 4

IPv6 packet with an IPv4 header bolted in front

Teredo

Encapsulates IPv6 in IPv4 UDP packets

NAT64 (RFC 6146)

IPv4 addresses embedded in a specific Ipv6 prefix

DNS64 (RFC 6147)

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

Combine with NAT 64 for a whole solution

IPv6 mostly

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

MAP - T (RFC 7599)

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)

Native IPv4, tunnelled and NATed IPv4 (RFC 6333)

Higher bandwidth

Higher the data rate achievable

Higher frequency

Easier it is to use more bandwidth

Centre frequency

Also called carrier frequency

Bandwidth

How wide the signal is

Propagation

How radio waves bounce around an environment

Link budget

Summary of the gains/losses in a radio system

Prx

Received power

Ptx

Transmitter output power

Gtx

Transmitted antenna gain

Grx

Receiver antenna gain

Ltx

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

Lfs

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

Lp

Miscellaneous losses

Modulation

Have a carrier frequency and then change a number of things

• Amplitude

• Frequency

• Phase

Quadrature phase shift keying

Can send multiple bits simultaneously by extending multiple phase shifts

Quadrature amplitude modulation

Combining different modulation schemes

Application of modulation schemes

• Bluetooth

• Wi-Fi

• GSM

• UMTS - Universal Mobile Telecommunications system

• LORA

Frequency Division Multiple Access (FDMA)

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)

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

Code Division Multiple Access (CDMA)

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

802.15.4

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

• Wireless/Environmental sensor networks

• Industrial communications and control

• Home automation

• Health monitoring

• Smart metering

• Asset and inventory tracking

• Intelligent agriculture

PAN coordinator

The networks overall coordinator

Coordinator

Provides synchronisation services to other devices eg router

Full function device

• Can function as a PAN coordinator or coordinator

• Can associate with multiple other devices at once

Reduced function device

• 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

All communications are to/from the PAN coordinator

Peer to peer

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

PPDU

PHY protocol data unit

PSDU

PHY Service Data Unit

Wireless HART

Wireless Highway Addressable Remote Transducer Protocol

Intended for industrial wireless sensing applications

6LoWPAN

IPv6 over low power wireless personal area networks

RPL

Routing protocol for low power and lossy networks, RFC 6550

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

TSCH

Time {slotted | synchronised} channel hopping

Essentially combines TDMA and FDMA

Each node gets a timeslot to talk to other nodes

Thread

A royalty free open industry standard designed foe connected home appliances

Matter

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

MQTT

Message Querying Telemetry Transport

Messages are published to a broker

Clients subscribe to data streams

CoAP

Constrained Application Protocol

Efficient for low power IoT systems

RESTful

CoAP key features

• 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

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

• Configure

• Management messages

LPWAN

Low Power Wide Area Network