Computer Network Technology Wide Area Network (WAN) Technology TK3133 Computer Network Technology Wide Area Network (WAN) Technology

Introduction Needs to cover long distance Company workers have to access their network when they are out of office Networking among branches of an organization Share information with another organization that is far away Government agencies, private companies, educationist and other individuals have to access to the information on the Internet This technology called WAN - Wide Area Network

WAN Needs a set of technology and implementation regulations differs from LAN. Discuss long distance network concept and typical technology that used to connect computers in various locations (state, country and continent)

Network switching types Data can be sent to long distance through various types of channels by using either circuit switching or packet switching

Taxonomy of switched networks

Circuit-switched network A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link.Each link is normally divided into n channels by using FDM or TDM. Old technology that suitable for sending real-time data such as telephone conversation. Physical connection between two stations is needed before sending the data. connection oriented type because there is a connection created before starting data transmission

Packet switching Data is divided into several smaller units called packet and send to one host to another by going through different links ( if there is no direct link) to reach the destination and finally the units are combined to get the original form.

Switching (a) Circuit Switching (b) Packet Switching

Switching Circuit Switching (b) Message Switching (c) Packet switching

Comparing switching network

Packet switching Two approaches :- Datagram (without connection) Make sure that each packet has sufficient information to enable any switch to send packet to a destination Virtual Circuit (connection oriented) Needs to create virtual connection from source host to destination Whether switched virtual circuit or permanent virtual circuit

Comparing virtual circuit and datagram

Examples of WAN communication system PSTN ISDN xDSL Arpanet X.25 Frame Relay ATM

PSTN PSTN – Public Switched Telephone Network Originally to transmit voice public dial-up telephone network normally use PSTN Available worldwide cheap Connection to various switching centre and connection to client Circuit-switched networks type

Dial-up and leased line 2 methods : use dial-up and leased line Modem is used in available telephone infrastructure for dial-up connection (temporary connection in overall session) For leased line, high speed fixed connection without involving dial-up from a point to another (such as from office to ISP)

ISDN ISDN – Integrated Services Digital Network Enhancement from IDN Support voice, data and video by using medium digital transmission through a higher bandwidth channel Combination of circuit and packet switching techniques

ISDN Basic service is 2B + D (BRI) in which B = a data channel of 64kbps D = a sekunder channel (signalling) of 16kbps ISDN Primary Access - 23B+D (64kbps) (PRI) B-ISDN – Broadband ISDN More bandwidth than ISDN use fiber optic and bandwidth 600Mbps

Other circuit switching technologies xDSL – Digital Subscriber Line Collection of technology for sending data in high speed on normal line Exp : ASDL (Asymmetric DSL) To optimize user that receive more information compared to the sent information (high-bit downstream and low-bit upstream) Speed between 16 – 640 kbps (upstream) and 1.544 Mbps to 6 Mbps (downstream)

Teknologi Pensuisan Litar yang lain DSL SDSL (Symmetric DSL) Symmetric bit rate on both ways HDSL (High Data Rate DSL) Bit rate 1.544 Mbps on both ways VDSL (Very HDSL) Bit rate from 12.96 Mbps to 55.2 Mbps but for short distance needs Optical Network Unit (ONU)

Packet switching technology ARPANET developed by ARPA for Defense Department in USA It is the first WAN that used packet switching Formed Internet

X.25 packet switching It is the first commercial packet switching network with CCITT reference X.25 – It is a standard protocol how WAN communicate using X.25 packet switch which is connected by leased line Provide interface between a DTE (host) and DCE (network switch) Sharing lines through multiplexing A connection between sender and receiver called virtual circuit (or logical connection) Slow and more management tasks

X.25 architecture mhmh

Comparison between X.25 and TCP/IP protocol Messages have boundaries Messages have no boundaries Urgent data may overtake ordinary data in the data streams With TCP, urgent data cannot preceed ordinary data that has been sent The X.25 packet layer depends upon the datalink level for reliable delivery of data TCP/IP requires very little reliance on the lower layers X.25 protects data against errors on the data link by CRC code TCP protects data against errors with checksum X.25's CRCs are computed separately for each transmission link, hence protection is end-to-end TCP's checksums are computed once by the sender and checked once by the receiver, hence protection is not end-to-end The packet layer depends on the data link layer to tell it when delivery is not possible TCP/IP retransmit data if acknowledge-ment is not received. If this happens after a certain number of times, it decides that the network's reliability is too poor to continue data transmission The maximum number of virtual circuits that can be "open" at any time is limited by the amount of free buffer memory on the X.25 interface In contrast, TCP's buffering is taken from a pool on the host, hence there is no limit on the number of open connections mhmh

Frame Relay New high-speed packet switching technology (fast-packet) used on digital line for bigger block data that changing its size Enhancement from X.25 – high performance, high reliability, cost-effective Use PVC (connection oriented)

ATM Asynchronous Transfer Mode (ATM) Similar to packet switching network but the most popular Support high-speed application (data, streaming audio and video) Data rate are 25Mbps, 155Mbps, 622Mbps, 1Gbps Fragment data into smaller fragment with fixed size of 53 byte (48 byte data and 5 byte overhead)

ATM Connection oriented type Connection between two points called virtual circuit – (either PVC or SVC) use pre-defined circuit

Wireless Network Example of cellular network using GSM (Global System for Mobiles) for sending mobile voice and digital data services Teknologi GSM : 2G GPRS 3G

Routing in WAN

Introduction To connect long distance computer, network needs to use packet switch connecting medium Packet Switches is also knows as router Each switch transport overall packet from a connection to another A special computer with network interface, memory and programs are used as packet processor

Connection to router Router is connected to computer or another router

Connection to router Router can be connected together in forming WAN Each router can be connected to one or more switches and to one or more computers

Connection to router Exp : 4 router connection and 8 computers form WAN

Store and Forward WAN allows many computers to send packet at once Basic feature in packet switching WAN is store and forward Require buffer to store arriving packet, to process packet to determine interface output to forward the packet

Addressing in WAN Similar to LAN Data is transmitted in packet (similar to frame) Each packet has format with head Packet head include source and destination address

Information on Router Router must choose exit connection to send the delivery (either to local or another router (next-hop) Selection is based on destination address in the packet Information on router (table) contain only the information about the next-hop So, in each packet, router see the destination in the routing table and send it to next hop Subsequent sending process is called ‘routing’ Information is stored in routing table

Routing technique To determine path to certain host or router , routing table required A technique to reduce the content of routing table is next-hop routing

Figure 19.28 Next-hop routing

Figure 19.29 Network-specific routing

Routing strategy Accurate: packet arrive to the destination safely Simple : easy to perform and to update resilient : Failure in network but communication still allowed Stable : small changes in adding connection is not going to disrupt overall paths just : each host has the same chance Optimum : use all available tracks and bandwidth

Routing Table 2 types Static Dynamic Routing is counted earlier and wont change Shortest Path Routing Flooding Dynamic Routing selection changes depend on the network situation Distance vector routing Link state routing

Shortest Path Routing static algorithm Find “shortest path” in path from source host to destination host Popular algorithm to count is Dijkstra Algorithm using graphical representation

Figure 21.12 Example of an internet Example of internetwork with 7 networks (N1, N2, .. N5) + 2 point to point network A, B, .., F are routers

Figure 21.13 Graphical representation of an internet

Dijkstra Algorithm 1. Start with the local node (router): the root of the tree. 2. Assign a cost of 0 to this node and make it the first permanent node. 3. Examine each neighbor node of the node that was the last permanent node. 4. Assign a cumulative cost to each node and make it tentative. 5. Among the list of tentative nodes 1. Find the node with the smallest cumulative cost and make it permanent. 2. If a node can be reached from more than one direction 1. Select the direction with the shortest cumulative cost. 6. Repeat steps 3 to 5 until every node becomes permanent.

Each router use Dijkstra algorithm to find shortest path between 2 points in the network

Figure 21.20 Shortest-path calculation for Router A

Table 21.2 Link state routing table for router A Network Cost Next Router Other Information N1 5 C N2   7 D N3 10 B N4 11 N5 15

Shortest Path Routing Find shortest path between two nodes Each node is labeled with its distance from source node throughout the best known path mhmh

Flooding Each packet will be sent to all immediate nodes except to sending node Problem when there is overlapping To avoid the problem Count the nodes Trace the packet Selective flooding – select only the path that moving in right direction

Distance Vector Routing Algorithm to resolve dynamic routing Also known as Bellman-Ford routing or Ford-Fulkerson algorithm Used in the Internet Each router maintain routing table from time to time Each router will provide routing table to its neighbor at certain time 2 parts – the chosen exit path and destination distance

Distance Vector Routing (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J.

Link State Routing Also known as Shortest Path First (SPF) routing Router send message through network by bringing path status between two router, and the mesage spread to all routers Each router receive message status and use it to build network graph Then Router use Dijkstra algorithm to generate routing table with itself as source

Link State Routing A subnet status packet connection for subnet