COMP1321 Digital Infrastructure Richard Henson February 2018

Week 15: Specifics of LANs Objectives Explain functions of client-server networks and network services Define networking standards Relate Lower OSI layers to technologies and naming systems

The Client-Server Model Centralisation of organisational resources client can still hold resources a lot (fat client) not much (thin client) peer-peer network needs processing and storage on each device (!) Microsoft LAN model: a domain

Advantages & disadvantages Client-Server v Peer-peer In groups… don’t look at next slides… yet!

Advantages of a client-server network v workgroup Centralised: security access to resources network administration With more than about 10 users, much easier to manage than a workgroup. Can handle up to thousands of users

Disadvantages of client-server, compared to a workgroup Expensive: dedicated computer(s) not accessible to users server operating system needed network management required Reduces user autonomy If one server, and it goes down, the network ceases to function!!!

Request and response All network users use client devices/machines Client requests information… 2. Server processes the request, sends a response back to the client

Requirements of organisational networks The server would be expected to offer: Network Access Access to “restricted” files held on servers only users with permission get access Applications Printing Access to email & The Internet

Servers in Larger Networks To fulfill multiple requirements, larger networks have MANY servers University ITS network: at least 50 Functions can be distributed servers e.g: Login Server(s) File and Print server Applications Server Internet Gateway

Login Servers (the most crucial!) Dedicated to logging on users database of usernames/passwords Only allows a potential user to access the network if both username and password exactly correspond with entries in the database Windows networks… called Domain Controllers

Windows LANs Client-server networks: Enterprise networks domains access to domain via domain controller(s) Enterprise networks multiple domains logically linked in a hierarchy of LANs

Local (client) and Cloud (server) Networks Cloud-based server Extension of client-server model… client-end less resource intensive most of resources & processing at server end Clients less CPU & maintenance therefore lower cost… Cloud (somewhere in Internet) client

Local Client/Cloud v conventional Local LAN Advantages and disadvantages? 3 minutes….

What makes up a LAN (1)? Hardware: computers and other network end devices e.g. printers, web cameras transmission media, e.g. cable, radio waves network cards, and intermediate devices which link the network devices to the transmission media

What makes up a LAN (2)? Software to (e.g. …) manage naming and routing send/receive data provide an even flow of data between devices make sure sent data goes to the right place provide a path for data through the network make sure data is checked for corruption as it passes through the network anything else that may need to be done to the data e.g. formatting, compression, encryption

Transfer of data through LANs (1) All done through electrical signals Medium/media transport(s) the signals insulated copper wire (cheap but effective) fibre optic cable (expensive, high volume) wireless (microwaves that are sent out a specific frequency)

Transfer of data through LANs (2) Cables designed from the start to transmit high volumes of digital data Network cards provide the computer-medium interface: control flow rate and error checking of data send/receive data at high, and even higher… speeds

Network Media 3 main types: If a cabled LAN connection exceeds: standardised copper cabling standardised optical fibre cabling “wifi” (wireless: e/m radiation of a standardised frequency) If a cabled LAN connection exceeds: 100 metres (twisted pair cabling) 185 metres (coaxial cabling – rarely used now) then a repeater (booster) is needed

Twisted Pair Cabling Consists of: RJ45 wiring four pairs of colour coded copper wires in a plastic sheath connectors for device at each end (RJ45) RJ45 wiring could be “straight through” could be “cross over”

Cross-Over and Straight Through “Cross over” when wires are “crossed” between RJ45 connectors essential for direct communication between end (point) devices “Straight through” for end-point connections to switches, routers, etc.

Network Adaptors Generally fit inside the computer: either as a separate card or on the motherboard… have their own unique “MAC address” connect externally via RJ45 socket use own software (firmware) work with other connectivity software to control sending & receiving of data

Network Software On a peer-peer network, connectivity software is all that is needed… If network is client-server… complex “server” software is needed at the server end “client” software as peer-peer at the client end

Servers High-powered computers high storage capacity a lot of memory Provide network services which are access by users through clients requires highly specialized software collectively called a Network Operating System (NOS)

Servers in small networks Scenario: a single server (or cluster of servers) is the central controlling point… The server also looks after security on the network: only allows valid users to log on only allows access to resources for users that have logged on stores appropriate “user rights” for access to its files and directories

Architecture of Small Networks Server(s) still need connecting to clients Need IP addressing function (DHCP) set of addresses set through router or server itself Normal to use Ethernet switch (es) to connect to clients structure called a VLAN

VLANs Segment of a LAN controlled by a switch Router (sets IP Addresses) Segment of a LAN controlled by a switch addressing of data to/from VLAN using IP address packets need routing addressing between switch and its connected devices using MAC addresses frames not packets… more efficient… no routing needed IP packets switch MAC frames

Network Layer Transport Layer Network Layer User Specifies Service Transport Layer Network Service Network Layer Network provides Service Diagram shows the all important communication between transport layer (user oriented service) and network layer (network oriented service) Network layer service definitions

Data Link Layer Responsible for error free transmission, using data frames A frame is a basic unit for network traffic, and has a highly structured format Mechanism: Down: data from the upper layers (ie the network layer) is converted by the data link layer into frames Up: groups raw data bits received via the physical layer into frames, for passing on to the upper layers may include an error recovery mechanism and flow control mechanism, but this could be done at the transport layer Bridges & Ethernet Switches operate at this level

Physical Layer Responsible for communicating with the network media Bits are converted into electrical signals and vice versa Issues include modulation of signals and timing Manages the interface between a computer and the network medium, but cable type and speeds of transmission are deliberately omitted to allow future technology to be easily included Repeaters work only at this level

Network Hardware Nodes: computers/ other intelligent devices with MAC addresses Repeaters: boost weak digital signals Hubs: link devices through a cabling or wireless system most hubs are also repeaters Switches/Bridges OSI level 2 devices that can process and filter the data in various ways, whilst hubs just send it on

More Network Hardware Switches Routers Gateways/Firewalls OSI level 2/3 devices also used to set up virtual LANs Routers Level 3 devices with routing protocols for network/Internet packet routing Gateways/Firewalls Level 4-7 devices with software allowing conversion between protocols & control of services

IEEE 802 Specifications and Layers 1&2 of the OSI model Emerged from IEEE/OSI meeting: February ‘80 applied mainly to lower level OSI layers (1/2) found it necessary to extend the data link layer into two parts Essential for development of LANs Definitions used by manufacturers for hardware and software of network interface cards origin of the MAC address…

Effect of IEEE 802 on the OSI model To cover engineering issues, IEEE divided the Data Link Layer into two sub-layers: Layer 2 (upper): Logical Link Control – IEE 802.1 & 802.2 Layer 2 (lower): Media Access Control – IEEE 802.3, 4, 5, 11, 12, etc.

Layer 2 (upper) Logical Link Control Focuses on IEEE 802.1 & 802.2 Controls transfer of data to the network layer Uses logical interface points called SAPs (service access points)

Layer 2 (lower) Media Access Control Direct communication with the network card provides packets with MAC address Focuses on IEEE 802.3, 4, 5, 11, 12… Provides shared access for multiple network interface cards to the physical layer Responsible for ensuring error-free communication across the network

OSI layer software and Network cards Layer 1 and 2 software supplied with the network card card itself should contain software (on ROM) that conforms to one of the sixteen IEEE 802 specifications Cards for wired connections have connectors for cables: usually IEEE 802.3 more rarely… IEEE 802.5 Wireless Cards usually based on IEEE802.11

“Binding” Network Card Software Data received by the network card needs to be passed on to level 3 software Normally held on the computer hard disk Configuration: level 2 software needs to combine with level 3 achieved through “binding” OSI Level 3 software binding OSI Level 1/2 software Shows how OSI level 3 software must link in with level 2 software. Process known as binding.

IP addresses For packets to move between devices, each device must have an IP address e.g. 192.168.2.22 Three ways to allocate an IP address to a Windows PC: manually… just type it into client interface from DHCP server/router (between fixed range) through autoconfig (randomly allocated from a range of IP addresses)

Switches and IP addresses Switches (and routers) link devices together By default, a switch will create a virtual LAN (VLAN) allows communication between devices on allocated IP address (e.g. 192.168.1.0-63) fine for small networks regular cause of lack of connectivity!

Configuring Switches Come with default configurations for VLANs May need changing… IP address needs to be consistent with devices being connected need IP addresses on the same subnet

Check your PC’s IP address Access the Windows CLI Type ipconfig Where has IP address come from? What is the IP address that it connects to? Is it on the same subnet?

Practical… VLANs connectivity with Switches Simulation MORE Packet Tracer (after the break…)