1. WAN technologies

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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.

8. 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

9. 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

10. 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

11. 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

12. X.25 DTE = Data terminal equipment
DCE = Data circuit-terminating equipment
PSE = Packet-Switching Exchange
Source:

13. 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

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

15. 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 Mbps)
Max OC Gbps