WAN technologies

LANs v. WANs LAN (Local Area Network) Limited geographical area (up to a few hundred metres) Fast connections Normally owned/ operated by a single organisation

LANs v. WANs WAN (Wide Area Network) Collection of LANs connected together Links between LANs are generally Slower than the LAN connections Provided by a 3rd party organisation

WAN example Key points Simplified – only shows servers Presence of VPN Devices (routers) between servers and VPN Link between LANs shown as a cloud Cloud represents network services provided by 3rd parties

Network Services Wired Wireless ISDN ADSL Packet (X.25) switched ATM GSM GPRS 3G/4G/5g? WAP Services offered by 3rd party companies to allow organisations to join LANs together into WANs

Circuit switching Dedicated channel between source and destination for duration of connection Circuit must be set up before communication can start Time delay Cost Circuit gives dedicated bandwidth (on the point to point section) => possibility of wasted capacity

Circuit switching The public telephone system, sometimes referred to as plain old telephone service (POTS), is a circuit-switched communications network. When a telephone call is placed in this type of network, only one physical path is used between the telephones for the duration of that call.

ISDN types Basic Rate Interface (BRI)2B+D Also known as ISDN2e 2 x Bearer channels (B) 64Kbps 1 x Delta channel (D) 16Kbps Multilink 2xB channels to give 128Kbps Primary Rate Interface (PRI) 30B+D Also known as ISDN30 30 x Bearer channels (B) 64Kbps 1 x Delta channel (D) 64Kbps

ISDN channel use Delta (D) channel Bearer channels Call setup & breakdown Control signalling Sometimes used for data Bearer channels Up to 8 devices per 2B+D line Max of 2 active at one time No distinction data / voice / fax

Packet switching Data moved in packets, cells or frames these can take different routes Network capacity shared => lower cost than circuit switching Possible drawbacks Delays (latency) Variable delays (jitter) Examples X.25 / Frame Relay ATM

X.25 Originally (1974 test network) designed for data transmission over unreliable analogue lines High level of resilience built-in Error-checking & retransmission logic Packet switching (up to 128 bytes per packet) Speed around 64 Kbps (i.e. only 1.5 x dial up) Now being replaced by IP at OSI layer 3 and Ethernet or ATM at lower layers

X.25 DTE = Data terminal equipment DCE = Data circuit-terminating equipment PSE = Packet-Switching Exchange Source: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/x25.htm

Frame relay X.25 with error correction removed Improved throughput Still packet switching Originally designed for use over ISDN interfaces OSI layers 1 & 2 (Physical & datalink) Virtual circuits (switched or permanent) Speed between 56Kbps and 1.544Mbps Variable size frames

Frame relay DTE = terminals, personal computers, routers, and bridges DCE = normally packet switches (clocking & switching)

ATM Asynchronous Transfer Mode Operates at OSI layer 2 Not routed Point-to-point connections Fixed-sized data cells 53 bytes (48 data, 5 header) Speed up to 622Mbps Improved utilisation (v. TDM) Performance measured in OC levels OC-1 = 51.8 Mbps (i.e. between 6-25 x average ADSL) e.g. OC-3 155Mbps , OC-12 622Mbps) Max OC-192 10Gbps