ENGN2219/COMP6719 Computer Architecture & Simulation Ramesh Sankaranarayana Semester 1, 2020 (based on original material by Ben Swi�t and Uwe Zimmer) 1
Week 11: Networks 2
Outline basic concepts 7-layer OSI model Examples: standard protocols 3
Basic concepts 4
We want to communicate with others 5
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 6
7
Information theory information theory is a whole sub-�eld of maths/CS—you can take a course on it here at the ANU data requires di�ference! 9
talk on a wire carrying electrical signals, what might di�ference look like? 10
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 11
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 12
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 13
Copper wires 14
Fibre-optic cables 15
Waves in some other medium… 16
Physics refresher In case you haven’t studied physics… a voltage is a relative measurement, it’s a voltage di�ference 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) 17
remember, we’re still talking about digital information ( 0 and 1 ) 18
Communication protocol an agreed-upon set of rules about what to “say” and how to understand the responses this is where heaps of the di�ferences between di�ferent 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 19
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 20
Bell System international switchboard in 1943 21
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 di�ferent nodes to share the same physical connections (multiplexing) 22
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 23
Topology topology is the way that the nodes are connected to one another (both physically and logically) there are several di�ferent ways to connect the nodes together, each with pros and cons 24
Sending a message how about sending a message to a speci�c node? circuit-switched vs packet-switched? 25
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 need to keep all the connections in sync simpler 26
Timing & synchronisation There are two main approaches: synchronous asynchronous transitions on a clock line allow (independent) timers at each end are used both ends to co-ordinate (e.g. to determine when to do things (e.g. RS232) SPI ) no clock skew issues, but no extra connections required, but more requires an extra connection vulnerable to synchronisation issues 27
so far we’ve been building our vocabulary now, let’s get a bit more formal 28
7 layer OSI model 29
What’s the OSI model? “ 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 ) 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 30
it’s an abstract model the layers are the key point 31
32
Layer 1: physical layer Service: Transmission of a raw bit stream over a communication channel Functions: Conversion of bits into electrical or optical signals 33
Layer 2: data link layer Service: Reliable transfer of frames over a link Functions: Synchronization, error correction, �low control 34
Layer 3: network layer Service: Transfer of packets inside the network Functions: Routing, addressing, switching, congestion control 35
Layer 4: transport layer Service: Transfer of data between hosts Functions: Connection establishment, management, termination, �low-control, multiplexing, error detection 36
Layer 5: session layer Service: Coordination of the dialogue between application programs Functions: Session establishment, management, termination 37
Layer 6: presentation layer Service: Provision of platform independent coding and encryption Functions: Code conversion, encryption, virtual devices 38
Layer 7: application layer Service: Network access for application programs Functions: Application/OS speci�c 39
talk where does the most interesting stu�f happen? which layer? 40
Examples: standard protocols 41
TCP/IP 42
TCP/IP layers 43
TCP/IP protocols 44
Host-to-host communication in TCP/IP 45
Layered communication at the source host 46
The OSI network model revisited 47
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 48
SPI connections full duplex, 4-wire, �lexible clock rate 49
SPI timing & data representation 50
SPI full-duplex with one slave 51
SPI concurrent simplex with multi-slave 52
SPI daisy-chaining (all slaves) 53
Ethernet / IEEE 802.3 Local area network (LAN) developed by Xerox in the 70’s 10 Mbps speci�cation 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) 54
Analyzing actual Ethernet encoding | Networking tutorial (4 of 13) Analyzing actual Ethernet encoding | Networking tutorial (4 of 13) Watch later Watch later Share Share 55
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 56
remember the basic concepts 57
Further study this was a really high-level overview; a whirlwind tour to go deeper, you could take COMP3310 58
Questions 59
Recommend
More recommend
