ENGN2219/COMP6719 Computer Architecture & Simulation Ramesh - - PowerPoint PPT Presentation

ENGN2219/COMP6719

Computer Architecture & Simulation Ramesh Sankaranarayana Semester 1, 2020 (based on original material by Ben Swit and Uwe Zimmer)

Week 11: Networks

Outline

basic concepts 7-layer OSI model Examples: standard protocols

Basic concepts

We want to communicate with others

What’s so hard about this?

communication is easy if both ends of the communication can share memory/registers e.g. function calls, shared global variables (in the .data section) but most of the time that’s not the case

Information theory

information theory is a whole sub-eld of maths/CS—you can data requires diference! take a course on it here at the ANU

talk

• n a wire carrying electrical signals, what might diference look like?

Aspects of network communication

there are a few fundamental “dimensions” to a given communications network transmission medium communications protocol(s) topology these are all (at least partially) orthogonal

What’s a node?

the term node is used a lot when talking about networks a node is anything which communicates on the network computers mobile phones IoT devices nanobots

Transmission medium

lots of options here: electrical voltages on a wire (or several wires) co-axial cable twisted-pair cable EM waves in the air light in an optic-ber cable

Copper wires

Fibre-optic cables

Waves in some other medium…

Physics refresher

In case you haven’t studied physics… a voltage is a relative measurement, it’s a voltage diference between two endpoints the ground pins are the reference point on your discoboard sometimes the values matter (low or high, 0 or 1) and sometimes the transitions are most important (rising/falling edge triggers)

remember, we’re still talking about digital information (0 and 1)

Communication protocol

an agreed-upon set of rules about what to “say” and how to understand the responses this is where heaps of the diferences between diferent communication networks are (and the creativity/innovation, too) how many wires? how big are the messages? lsb rst, or msb? both sides must agree! (somewhat) independent of the transmission medium

Circuit-switched networks

circuit-switched means nodes set up & use a dedicated connection (physical or logical) example: phone lines in ye olden dayse—to route the phone call to the right place, the switchboard operator would literally make a physical connection between the caller & the receiver

Bell System international switchboard in 1943

Packet-switched networks

packet-switched means data transmitted over the network is segmented into packets (or frames) these packets contain both: a payload (what you want to send) an address (who you want to send it to) these days, most network protocols are packet-switched this allows diferent nodes to share the same physical connections (multiplexing)

Directions of information low

simplex means information only lows one way: from sender to receiver half-duplex means information can low both ways, but not at the same time full-duplex means information can low both ways simultaneously

Topology

topology is the way that the nodes are connected to one another (both physically and logically) there are several diferent ways to connect the nodes together, each with pros and cons

Sending a message

how about sending a message to a specic node? circuit-switched vs packet-switched?

Serial vs parallel

serial parallel data is sent one-bit-at-a-time multiple bits sent simultaneously (e.g. multiple wires) fewer bits sent per signal, but simpler need to keep all the connections in sync

Timing & synchronisation

There are two main approaches: synchronous asynchronous transitions on a clock line allow both ends to co-ordinate (e.g. ) (independent) timers at each end are used to determine when to do things (e.g. RS232) no clock skew issues, but requires an extra connection no extra connections required, but more vulnerable to synchronisation issues SPI

so far we’ve been building our vocabulary now, let’s get a bit more formal

7 layer OSI model

What’s the OSI model?

standardised in 1977: 7 layer architecture, connection oriented hardy implemented anywhere in full… …but its concepts and terminology are widely used, when describing existing and designing new protocols

“

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology (from ) Wikipedia

it’s an abstract model the layers are the key point

Layer 1: physical layer

Service: Transmission of a raw bit stream over a communication channel Functions: Conversion of bits into electrical or optical signals

Layer 2: data link layer

Service: Reliable transfer of frames over a link Functions: Synchronization, error correction, low control

Layer 3: network layer

Service: Transfer of packets inside the network Functions: Routing, addressing, switching, congestion control

Layer 4: transport layer

Service: Transfer of data between hosts Functions: Connection establishment, management, termination, low-control, multiplexing, error detection

Layer 5: session layer

Service: Coordination of the dialogue between application programs Functions: Session establishment, management, termination

Layer 6: presentation layer

Service: Provision of platform independent coding and encryption Functions: Code conversion, encryption, virtual devices

Layer 7: application layer

Service: Network access for application programs Functions: Application/OS specic

talk

where does the most interesting stuf happen? which layer?

Examples: standard protocols

TCP/IP

TCP/IP layers

TCP/IP protocols

Host-to-host communication in TCP/IP

Layered communication at the source host

The OSI network model revisited

SPI: Serial Peripheral Interface

used by gazillions of devices… and it’s not even a formal standard! speed only limited by what both sides can survive usually push-pull drivers, i.e. fast and reliable, yet not friendly to wrong wiring/programming

SPI connections

full duplex, 4-wire, lexible clock rate

SPI timing & data representation

SPI full-duplex with one slave

SPI concurrent simplex with multi-slave

SPI daisy-chaining (all slaves)

Ethernet / IEEE 802.3

Local area network (LAN) developed by Xerox in the 70’s 10 Mbps specication 1.0 by DEC, Intel, & Xerox in 1980 First standardised as IEEE 802.3 in 1983 (10 Mbps over thick co-ax cables) currently 1 Gbps (802.3ab) copper cable ports used in most desktops and laptops currently standards up to 100 Gbps (IEEE 802.3ba 2010) more than 85% of current LAN lines worldwide (according to the International Data Corporation)

Wi / IEEE 802.11

Wireless local area network (WLAN) developed in the 90’s First standard as IEEE 802.11 in 1997 (1-2 Mbps over 2.4 GHz) Typical usage at 54 Mbps over 2.4 GHz carrier at 20 MHz bandwidth Current standards up to 780 Mbps (802.11ac) over 5 GHz carrier at 160 MHz bandwidth Future standards are designed for up to 100 Gbps over 60 GHz carrier Direct relation to IEEE 802.3 and similar OSI layer association

remember the basic concepts

Further study

this was a really high-level overview; a whirlwind tour to go deeper, you could take COMP3310

Questions