Wan Protocols
Content
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Wan Technologies
Wan Protocols and Services
Gary Aitken
2010
Wan Technologies
Contents
What is a WAN ................................ ................................ ................................ ................................ .. 2 What is a WAN ................................ ................................ ................................ ................................ .. 3 Point to point ................................ ................................ ................................ ................................ .... 4 Circuit Switching ................................ ................................ ................................ ................................ 5 Packet Switching................................ ................................ ................................ ............................ 6 Message Switching ................................ ................................ ................................ ........................ 7 Cell Switching ................................ ................................ ................................ ................................ 7 DTE and DCE ................................ ................................ ................................ ................................ ...... 8 DTE ................................ ................................ ................................ ................................ ................ 8 DCE ................................ ................................ ................................ ................................ ................ 8 PTO Switched Services ................................ ................................ ................................ ....................... 9 PSTN ................................ ................................ ................................ ................................ .............. 9 ISDN ................................ ................................ ................................ ................................ .............. 9 Leased Lines ................................ ................................ ................................ ................................ .. 9 X.25 ................................ ................................ ................................ ................................ ............... 9 PTO Switched Services ................................ ................................ ................................ ..................... 10 Frame Relay................................ ................................ ................................ ................................ . 10 Routing ................................ ................................ ................................ ................................ ............ 11 Congestion control Algorithms................................ ................................ ................................ ......... 11 Congestion control Algorithms................................ ................................ ................................ ......... 12 Slow Start ................................ ................................ ................................ ................................ .... 12 Congestion Avoidance ................................ ................................ ................................ ................. 12 Fast Retransmit................................ ................................ ................................ ............................ 12 Fast Recovery ................................ ................................ ................................ .............................. 12 Mobile and Broadband Services................................ ................................ ................................ ....... 13 ATM................................ ................................ ................................ ................................ ............. 13 xDSL................................ ................................ ................................ ................................ ............. 13 GPRS ................................ ................................ ................................ ................................ ............ 13
Mobile and Broadband Services ................................ ................................ ................................ 14
3G Services ................................ ................................ ................................ ................................ ...... 14
Mobile and Broadband Services ................................ ................................ ................................ 15
H.32x ................................ ................................ ................................ ................................ ........... 15 VoIP ................................ ................................ ................................ ................................ ............. 15
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What is a WAN
A WAN is a network used for communication over a large geographical area. The acronym WAN stands for Wide Area Network, it uses the services of established carriers like telephone companies. The technologies used by a WAN mostly work at the lower levels of the O.S.I model. So they work on the Network Layer, Data-Link layer and the physical layer.Wans are basically interconnected LANs. The Main reason for a WAN is to allow people to communicate and move information between eachother over large areas, such as across nations or countries. The internet is considered a WAN. Users are connected to a central point where connections can be made between them. Creating these connections is known as switching. WANs use several different ways to create these connections, which will be described in more detail as we go through the report, these include:
y y y y y
Point to point links Circuit Switching Packet Switching Message Switching Cell Switching
Point to point Diagram
Circuit switching diagram
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Packet Switchin Diagram
essage Switching Diagram
Cell Switching Diagram
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Point to point
Point to point refers to Point to Point Protocol (PPP) which is a protocol suite. PPP is the link or interface between IP (internet Protocol) and a physical link such as a Serial line. The path goes from the customer through a carrier network like a phone company to a remote network. It is also known as a leased line.
The protocol works at layer 2 of the OSI model, the Data-link Layer. PPP takes higher layer messages, IP datagrams and encapsulates them for transmission over the physical layer. PPP can be used over many types of Physical media.
It delivers frames between two nodes by creating a logical connection called a Session. This connection has to be set up before any data is transferred. The two links agree on things like datagram size, error detection and if authentication will be used. Once the link is established, it will remain set for communication until a certain frame closes the link.
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Circuit Switchi g
Circuit Switching is probably the most familiar way of building a communication network. It allows the sender and user to use the full communication channel. The Channel that is set up is a dedicated channel between the two end users. The best e ample of this is PSTN (Public switched telephone network) When you make a phone call the phone company reserves a physical path to the number you have dialled, the e change at the other end then finds the person you called. Once the circuit is set up communication can take place. (The path is decided before Data transmission begins) The channel is dedicated for the duration of your call and no one else can use that line. The connection is fast and reliable. Once the call has ended the channel is cleared. This type of connection is called connection orientated because the path between the devices is set up before communication can take place. Circuit switching is often seen as the opposite of Packet Switching.
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Packet S itchin
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Packet Switching takes a Source message and breaks it up into smaller packets. The Message works its way down the OSI model to the Transport Layer which breaks the message up into manageable chunks called packets and sends it on to the network layer. At the network layer a router would open the packet and look at the packet header for IP address information, and then would choose the best network for delivering the packet. The packets are individually sent to the destination and can take many different routes to get there. Once they arrive they are put in the correct sequence to create the original message. Because the messages are sent in smaller chunks this makes delivery more efficient. Different types of media can be multiplexed across the network. Unlike circuit switching where a dedicated point to point connection is needed and messages have to arrive in the correct order, packets can arrive in any order from many paths which optimizes bandwidth by being more flexible. Because packets can get lost etc., circuit switching is better for real time data like audio and video.
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Message Switching, which is also known as store- and forward switching is a technique where messages are transmitted from node to node through a network. The messages are stored on each node until a forwarding path is made available, so data is not transferred in real time. There is no physical connection is set up in advance between sender andreceiver. Message switching was the pre-cursor to Packet Switching. An example of message switching would be Email where the mail is stored on a server until the receiver creates the connection and downloads the email.
Cell Switching is very similar to Packet Switching but the data is transported using fixed length cells. It combines the best of Circuit Switching by giving guaranteed delivery and the best of Packet Switching by being efficient. The most popular form of Cell Switching is ATM (Asynchronous Transfer Mode) which is used for LANs and WANs. It transmits data and real time voice and video. The data is transferred on fixed length cells of 53 bytes, is scalable and supports several transmission speeds. Having the cells fixed allows for very fast switches to be built, because known packet sizes are faster to process. ATM uses these switches to create logical circuits from end to end which guarantee Quality of Service (QoS) andunused bandwidth (in a video call for example) can be used to transfer data. The ATM service is connection orientated which means that the data uses the same predefined path and arrives in the correct order.
Cell S itchin
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DTE and DCE
DTE refers to Data Terminal Equipment which is part of a device that ends a line of communication. DCE refers to Data Communication Equipment. DCEProvides the path for communication. If you wanted to surf the internet for example, you could connect through a modem and a dial up connection. The modem dials the number of your internet service provider (ISP) and the ISPs modem replies, you will hear modem noise which is the noise your modem makes when it is communicating down the phone line to establish a connection. Once the connection is established the modem turns off the speaker so that the rest of the communication is done in silence. You will then see your login prompt. Now you have a connection with your ISPs server and wander the internet. In the above example your PC is a Data Terminal (DTE). Your modem and the ISPs modem are DCEs, which makes the communication between you and your ISP possible. The ISPs Server is also a DTEbecause it ends the communication line between your PC and the Server. If you want to go from your ISPs server to another server, the ISPs server uses another interface. So DTE and DCEis interface dependant.
DTE
DTE converts digital signals into analogue tones on a network and it also reconverts analogue tones back into a digital format that computers can understand. The hardware that makes up the DTE side of a network is the cabling and also end user devices such as a modem and a network card. The DTE runs the length of the network from one end user device to another end user device, mainly providing a connection where Packets of Data can be sent, received, encoded and decoded.
DCE
The main responsibility of the DCE is to make sure that the packets going through the DTE doesn t naturally fade out along the length of the DTE; it does this by giving a boost to the signal at hardware nodes like HUBs. The DCE also routes data to different computer hardware and different networks. The hardware that makes up a DCEincludes HUBs, Bridges, Switches, Routers and Gateways. The DCE is connected to the DTE at certain points to allow it control and boost Packets moving along the DTE.
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PTO S itched Services
PSTN
PSTN refers to Public Switched Telephone Network. It is the world-wide public telephone network, and is a circuit switched system. This system was originally a fixed line analogue system but has now become digital. It consists of Telephone lines, fibre optic cables, and cellular networks all connected through switching centres. These switching centres allow any telephone to communicate with any other telephone in the world.
ISDN
ISDN refers to Integrated Services Digital Network, which allows voice, Data and video to be transmitted simultaneously over the PSTN network. ISDN is the set of protocols that allow voice and data to be transported over a circuit switched system. The advantage of ISDN is that speech and Data are integrated on the same lines while the old system was considered a voice transport tool only. It also gives higher speeds and better quality than the 56 kbps dialup connection.
Leased Lines
A leased line is a permanent link between two points, it is referred to as a dedicated line. It is different from the PSTN because telephone numbers are not used. The leased line is a contract between a provider and a customer. They are mostly used by Business to connect Offices over long distances. Leased lines are always activated, and because it is dedicated, other peoples communications are not carried on the line which ensures a high level of quality. An Internet leased line is delivered over Fibre and is considered a premium Internet connection service.
X.25
X.25 is a protocol standard for WAN communications. It defines how User devices and network devices establish and maintain connections. It is mostly used in packet switched networks owned by telephone companies. It was designed to allow different types of public networks like CompuServe , tymenet or TCP/IP to communicate through an intermediary computer at the layer three, network layer. Subscribers were charged on how much they used the network. It was used by financial and telecommunication Companies. It has been mostly replaced by the IP (Internet Protocol) which is a less complicated protocol.
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PTO S itched Services
Frame Relay
Initially Frame Relay was created to use ISDN equipment, to access packet switched services on a B channel, but is now seen as a Data service on its own right. Frame Relay is a technique for the efficient transmission of digital data cheaply and quickly on a relay of frames from one or many end points to another end point or many endpoints. Frame relay is a packet switched version of ISDN. It is implemented as an encapsulation technique for voice and data, and is used between LANS over a WAN. Each end user gets access to a leased line to a frame relay node. It is similar to X.25 but costs less and is more efficient.
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Routin
BGP (Border Gateway Protocol) IS-IS (Intermediate System - Intermediate System) OSPF (Open Shortest Path First) RIP (Routing Information Protocol)
Routing is the way of selecting paths along a network on which to send network traffic. Routing directs packets from their source to their final destination through intermediate nodes. These nodes are hardware devices like Routers,Switches, firewalls and Gateways. When an IP packet is to be forwarded a router looks up its forwarding table, sometimes called a routing table to determinethe next hop for the packets destination based on the destination IP address in the IP header. It then forwards the packet appropriately. The next router then does the same using its own routing table and this carry s on until the packet reaches its destination. The IP destination address in the IP header is all that is needed to find the next hop. Routers are enabled to create these forwarding tables by Routing Protocols. Some of these are:
y y y y
For each IP address in the routing table IPv4 performs a logical and operation between the destination IP address and the subnet mask and the result is compared with the destination field of the entry for a match. The list of matching routes is compiled and IPv4 selects the longest match. The longest matching route is the most specific route to the destination address. If the router finds multiple longest match routes it uses the lowest metric to pick the best route.
Con estion control Al orithms
Congestion means that intermediate devices such as Routers are overloaded and if they are overloaded they start to drop datagrams. If datagrams contain TCP segments, then the segments will not be acknowledged because they have not reached the destination. They would then have to be ir retransmitted. When TCP segments have not been acknowledged, it is mostly assumed that they have been dropped by intermediate devices because of congestion. By detecting the rate at which segments are being sent and they are not being acknowledged a device can tell the level of congestion between itself and its TCP connection Peer. Using this information, four techniques were developed to handle congestion.
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Con estion control Al orithms
Each sender is initially restricted to sending an amount of data equal to the MSS value for the connection. Every time there is an acknowledgement, the amount of data the sender can send is increased by the size of another full segment. It then increases until it reaches the full window size or if congestion is discovered on the link then the congestion avoidance technique comes into play.
Con estion Avoidance
When congestion is detected, the device starts to throttle back the speed that it is sending the segments. It uses a special algorithm, which allows it to slow the speed down quickly when congestion is found. The device would gradually increase the speed back up by using theSlow Startalgorithm.
Fast Retransmit
This allows missing segments to be transmitted immediately without having to go through the whole retransmission queue process, after three acknowledgements asking for a segment starting with byte #N it would say that the byte #N is lost due to congestion.
Fast Recovery
When using Fast Retransmit to send a lost segment, the device using it performs Congestion Avoidance but it does not use Slow Startto speed the rate back up. Since several ACKS were received showing out of sequence segments these have been removed from the flow between the devices and for efficiency transmission speeds can be increased more quickly than when congestion happens in other ways.
Slo
Start
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Mobile and Broadband Services
ATM
ATMrefers toAsynchronous Transfer Modewhich has been designed for transferring Voice, Data and Video at high speeds over public as well as private networks. It is connection oriented. It uses fixed size cells of 53 bytes, is scalable and supports several transmission speeds. ATM is a cell switching and multiplexing technology. ATM combines the best features of circuit switching (constant transmission delay and guaranteed capacity) and the best of packet switching (flexibility, efficiency for intermittent traffic).
xDSL
xDSL is the collective title for all types of Digital Subscriber Lines. The two main categories are ADSL and SDSL. Other types include HDSL (High Data Rate)DSLand VDSL (Very High) DSL. They are known as last mile connections because they are used for connections from a telephone switching station to a home or office, but not between telephone switching stations. xDSL is very similar to ISDN because they run over the existing copper telephone lines. But xDSL offers far higher speeds, up to 32 Mbps for upstream traffic and from 32 Kbps to over 1Mbps.for downstream traffic. The maximum length of the wire is 1,820 m or 6000 feet from the service providers central office to home or office. These services are delivered with normal telephone services at the same time on the same telephone line. This is achievable because xDSL runs at a higher frequency and the different frequencies are filtered to keep them separate. With SDSL the upstream and downstream Data rates are the same, withADSL the Data rates are faster going to the customer (downstream) and slower coming from the customer (upstream).
GPRS
GPRS refers to General Packet Radio Service which is based on Global System for Mobile communications (GSM). It is used for SMS (Short Message Service) and WAP (Wireless Application Protocol). GPRS uses packet based connections rather than circuit switched for Mobile Networks which makes it a best effort service. It is also used for access to the Web and Email. Unlike circuit switching Data which is billed for per minute connection time, GPRS is billed on how much Data you transfer. GPRSextends the capabilities of the GSM circuit switched Data capabilities and is described as 2.5G, i.e. between 2G and 3G mobile technology.
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Mobile and Broadband Services
3G Services
3G refers to 3rd Generation which is a generation of standards for mobile phones and mobile communications. It also refers to pending improvements in wireless data and voice communications through a range of proposed standards. The main goal is to achieve transmission spe from 9.5k eds to2M bit/sec. 3Gservice, offers high speed access to Data and Voice services, by using a 3G network which is a mobile broadband network is offering speeds of at least 144 Kbps. The standard developed by the International Telecommunications Union, known as the IMT-2000 criteria. It has similarities with WiFiwhich allows high bandwidth transfer of data over a short range transmission. 3G connects to a system of telecommunication towers using satellite driven connections which means that the range is far greater than other technologies. This makes it ideal for connecting to large networks. The key part of 3G service is mobile to mobile voice transfer. Applications that were not available to mobile phones before are becoming available, these include:
3G Wireless Combines a mobile phone, laptop PC and TV Features includes: - Phone calls/fax - Global roaming - Send/receive large email messages - High-speed Web Navigation/maps Videoconferencing - TV streaming - Electronic agenda meeting reminder. Speed: 144kb/sec-2mb/sec Time to download a 3min MP3 song: 11sec-1.5min
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Mobile and Broadband Services
H.32x
H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) and it defines the protocols that provide audio visual communication sessions on any packet network. Widely used by video conferencing manufacturers and is used with real time applications like GnuGK and NetMeeting. The H.323 standard deals with call signalling and control, multimedia transport and control and bandwidth control for point to point and multipoint conferences. It is part of theTU-T H.32x group of protocols and is used worldwide by service providers and enterprises for video services over IP(Internet Protocol) networks.
VoIP
Refers to Voice over Internet Protocol is a general term for phone services over the net. It is another way of making phone calls over the internet, which are cheaper or even free. If you have a good enough internet connection and a computer with a microphone and speakers you can use VoIP for free. Voice, Fax and SMS are transported over the Internet instead of using the public switched telephone network (PSTN). Communication over the IP network is less reliable than the circuit switched public telephone network because it is a best effort network and does not have fundamentalQuality of Service (QoS) guarantees.
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Biblio raphy
http://communication.howstuffworks.com/convergence/router4.htm. (n.d.). http://en.allexperts.com/q/General-Networking-Lan-1049/network-switch.htm. (n.d.). http://en.wikipedia.org/wiki/3G. (n.d.). http://en.wikipedia.org/wiki/H323. (n.d.). http://en.wikipedia.org/wiki/Isdn. (n.d.). http://en.wikipedia.org/wiki/Message_switching. (n.d.). http://en.wikipedia.org/wiki/Pstn. (n.d.). http://en.wikipedia.org/wiki/Voice_over_IP. (n.d.). http://technet.microsoft.com/en-us/library/bb727001.aspx. (n.d.). http://www.cisco.com/en/US/docs/internetworking/technology/handbook/DSL_Dig_Subscr_Ln.htm l. (n.d.). http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Intro-to-Internet.html. (n.d.). http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm. (n.d.). http://www.ciscopress.com/articles/article.asp?p=31533. (n.d.). http://www.cs.bris.ac.uk/Teaching/Resources/COMS11200/pages/tour18/tsld004.htm. (n.d.). http://www.javvin.com/networkingterms/MessageSwitching.html. (n.d.). http://www.tcpipguide.com/free/t_NetworkingStandards.htm. (n.d.). http://www.tcpipguide.com/free/t_TCPCongestionHandlingandCongestionAvoidanceAlgorit 2.htm. (n.d.). http://www.tcpipguide.com/free/t_WhatIsNetworking.htm. (n.d.). http://www.tomshardware.co.uk/forum/29645-17-router-switch. (n.d.). http://www.beest-built.com/voip-technology.html
Wan Technologies
Wan Protocols and Services
Gary Aitken
2010
Wan Technologies
Contents
What is a WAN ................................ ................................ ................................ ................................ .. 2 What is a WAN ................................ ................................ ................................ ................................ .. 3 Point to point ................................ ................................ ................................ ................................ .... 4 Circuit Switching ................................ ................................ ................................ ................................ 5 Packet Switching................................ ................................ ................................ ............................ 6 Message Switching ................................ ................................ ................................ ........................ 7 Cell Switching ................................ ................................ ................................ ................................ 7 DTE and DCE ................................ ................................ ................................ ................................ ...... 8 DTE ................................ ................................ ................................ ................................ ................ 8 DCE ................................ ................................ ................................ ................................ ................ 8 PTO Switched Services ................................ ................................ ................................ ....................... 9 PSTN ................................ ................................ ................................ ................................ .............. 9 ISDN ................................ ................................ ................................ ................................ .............. 9 Leased Lines ................................ ................................ ................................ ................................ .. 9 X.25 ................................ ................................ ................................ ................................ ............... 9 PTO Switched Services ................................ ................................ ................................ ..................... 10 Frame Relay................................ ................................ ................................ ................................ . 10 Routing ................................ ................................ ................................ ................................ ............ 11 Congestion control Algorithms................................ ................................ ................................ ......... 11 Congestion control Algorithms................................ ................................ ................................ ......... 12 Slow Start ................................ ................................ ................................ ................................ .... 12 Congestion Avoidance ................................ ................................ ................................ ................. 12 Fast Retransmit................................ ................................ ................................ ............................ 12 Fast Recovery ................................ ................................ ................................ .............................. 12 Mobile and Broadband Services................................ ................................ ................................ ....... 13 ATM................................ ................................ ................................ ................................ ............. 13 xDSL................................ ................................ ................................ ................................ ............. 13 GPRS ................................ ................................ ................................ ................................ ............ 13
Mobile and Broadband Services ................................ ................................ ................................ 14
3G Services ................................ ................................ ................................ ................................ ...... 14
Mobile and Broadband Services ................................ ................................ ................................ 15
H.32x ................................ ................................ ................................ ................................ ........... 15 VoIP ................................ ................................ ................................ ................................ ............. 15
Wan Technologies
What is a WAN
A WAN is a network used for communication over a large geographical area. The acronym WAN stands for Wide Area Network, it uses the services of established carriers like telephone companies. The technologies used by a WAN mostly work at the lower levels of the O.S.I model. So they work on the Network Layer, Data-Link layer and the physical layer.Wans are basically interconnected LANs. The Main reason for a WAN is to allow people to communicate and move information between eachother over large areas, such as across nations or countries. The internet is considered a WAN. Users are connected to a central point where connections can be made between them. Creating these connections is known as switching. WANs use several different ways to create these connections, which will be described in more detail as we go through the report, these include:
y y y y y
Point to point links Circuit Switching Packet Switching Message Switching Cell Switching
Point to point Diagram
Circuit switching diagram
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Packet Switchin Diagram
essage Switching Diagram
Cell Switching Diagram
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Point to point
Point to point refers to Point to Point Protocol (PPP) which is a protocol suite. PPP is the link or interface between IP (internet Protocol) and a physical link such as a Serial line. The path goes from the customer through a carrier network like a phone company to a remote network. It is also known as a leased line.
The protocol works at layer 2 of the OSI model, the Data-link Layer. PPP takes higher layer messages, IP datagrams and encapsulates them for transmission over the physical layer. PPP can be used over many types of Physical media.
It delivers frames between two nodes by creating a logical connection called a Session. This connection has to be set up before any data is transferred. The two links agree on things like datagram size, error detection and if authentication will be used. Once the link is established, it will remain set for communication until a certain frame closes the link.
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Circuit Switchi g
Circuit Switching is probably the most familiar way of building a communication network. It allows the sender and user to use the full communication channel. The Channel that is set up is a dedicated channel between the two end users. The best e ample of this is PSTN (Public switched telephone network) When you make a phone call the phone company reserves a physical path to the number you have dialled, the e change at the other end then finds the person you called. Once the circuit is set up communication can take place. (The path is decided before Data transmission begins) The channel is dedicated for the duration of your call and no one else can use that line. The connection is fast and reliable. Once the call has ended the channel is cleared. This type of connection is called connection orientated because the path between the devices is set up before communication can take place. Circuit switching is often seen as the opposite of Packet Switching.
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Packet S itchin
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Packet Switching takes a Source message and breaks it up into smaller packets. The Message works its way down the OSI model to the Transport Layer which breaks the message up into manageable chunks called packets and sends it on to the network layer. At the network layer a router would open the packet and look at the packet header for IP address information, and then would choose the best network for delivering the packet. The packets are individually sent to the destination and can take many different routes to get there. Once they arrive they are put in the correct sequence to create the original message. Because the messages are sent in smaller chunks this makes delivery more efficient. Different types of media can be multiplexed across the network. Unlike circuit switching where a dedicated point to point connection is needed and messages have to arrive in the correct order, packets can arrive in any order from many paths which optimizes bandwidth by being more flexible. Because packets can get lost etc., circuit switching is better for real time data like audio and video.
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Messa e S itchin
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Message Switching, which is also known as store- and forward switching is a technique where messages are transmitted from node to node through a network. The messages are stored on each node until a forwarding path is made available, so data is not transferred in real time. There is no physical connection is set up in advance between sender andreceiver. Message switching was the pre-cursor to Packet Switching. An example of message switching would be Email where the mail is stored on a server until the receiver creates the connection and downloads the email.
Cell Switching is very similar to Packet Switching but the data is transported using fixed length cells. It combines the best of Circuit Switching by giving guaranteed delivery and the best of Packet Switching by being efficient. The most popular form of Cell Switching is ATM (Asynchronous Transfer Mode) which is used for LANs and WANs. It transmits data and real time voice and video. The data is transferred on fixed length cells of 53 bytes, is scalable and supports several transmission speeds. Having the cells fixed allows for very fast switches to be built, because known packet sizes are faster to process. ATM uses these switches to create logical circuits from end to end which guarantee Quality of Service (QoS) andunused bandwidth (in a video call for example) can be used to transfer data. The ATM service is connection orientated which means that the data uses the same predefined path and arrives in the correct order.
Cell S itchin
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DTE and DCE
DTE refers to Data Terminal Equipment which is part of a device that ends a line of communication. DCE refers to Data Communication Equipment. DCEProvides the path for communication. If you wanted to surf the internet for example, you could connect through a modem and a dial up connection. The modem dials the number of your internet service provider (ISP) and the ISPs modem replies, you will hear modem noise which is the noise your modem makes when it is communicating down the phone line to establish a connection. Once the connection is established the modem turns off the speaker so that the rest of the communication is done in silence. You will then see your login prompt. Now you have a connection with your ISPs server and wander the internet. In the above example your PC is a Data Terminal (DTE). Your modem and the ISPs modem are DCEs, which makes the communication between you and your ISP possible. The ISPs Server is also a DTEbecause it ends the communication line between your PC and the Server. If you want to go from your ISPs server to another server, the ISPs server uses another interface. So DTE and DCEis interface dependant.
DTE
DTE converts digital signals into analogue tones on a network and it also reconverts analogue tones back into a digital format that computers can understand. The hardware that makes up the DTE side of a network is the cabling and also end user devices such as a modem and a network card. The DTE runs the length of the network from one end user device to another end user device, mainly providing a connection where Packets of Data can be sent, received, encoded and decoded.
DCE
The main responsibility of the DCE is to make sure that the packets going through the DTE doesn t naturally fade out along the length of the DTE; it does this by giving a boost to the signal at hardware nodes like HUBs. The DCE also routes data to different computer hardware and different networks. The hardware that makes up a DCEincludes HUBs, Bridges, Switches, Routers and Gateways. The DCE is connected to the DTE at certain points to allow it control and boost Packets moving along the DTE.
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PTO S itched Services
PSTN
PSTN refers to Public Switched Telephone Network. It is the world-wide public telephone network, and is a circuit switched system. This system was originally a fixed line analogue system but has now become digital. It consists of Telephone lines, fibre optic cables, and cellular networks all connected through switching centres. These switching centres allow any telephone to communicate with any other telephone in the world.
ISDN
ISDN refers to Integrated Services Digital Network, which allows voice, Data and video to be transmitted simultaneously over the PSTN network. ISDN is the set of protocols that allow voice and data to be transported over a circuit switched system. The advantage of ISDN is that speech and Data are integrated on the same lines while the old system was considered a voice transport tool only. It also gives higher speeds and better quality than the 56 kbps dialup connection.
Leased Lines
A leased line is a permanent link between two points, it is referred to as a dedicated line. It is different from the PSTN because telephone numbers are not used. The leased line is a contract between a provider and a customer. They are mostly used by Business to connect Offices over long distances. Leased lines are always activated, and because it is dedicated, other peoples communications are not carried on the line which ensures a high level of quality. An Internet leased line is delivered over Fibre and is considered a premium Internet connection service.
X.25
X.25 is a protocol standard for WAN communications. It defines how User devices and network devices establish and maintain connections. It is mostly used in packet switched networks owned by telephone companies. It was designed to allow different types of public networks like CompuServe , tymenet or TCP/IP to communicate through an intermediary computer at the layer three, network layer. Subscribers were charged on how much they used the network. It was used by financial and telecommunication Companies. It has been mostly replaced by the IP (Internet Protocol) which is a less complicated protocol.
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PTO S itched Services
Frame Relay
Initially Frame Relay was created to use ISDN equipment, to access packet switched services on a B channel, but is now seen as a Data service on its own right. Frame Relay is a technique for the efficient transmission of digital data cheaply and quickly on a relay of frames from one or many end points to another end point or many endpoints. Frame relay is a packet switched version of ISDN. It is implemented as an encapsulation technique for voice and data, and is used between LANS over a WAN. Each end user gets access to a leased line to a frame relay node. It is similar to X.25 but costs less and is more efficient.
Wan Technologies
Routin
BGP (Border Gateway Protocol) IS-IS (Intermediate System - Intermediate System) OSPF (Open Shortest Path First) RIP (Routing Information Protocol)
Routing is the way of selecting paths along a network on which to send network traffic. Routing directs packets from their source to their final destination through intermediate nodes. These nodes are hardware devices like Routers,Switches, firewalls and Gateways. When an IP packet is to be forwarded a router looks up its forwarding table, sometimes called a routing table to determinethe next hop for the packets destination based on the destination IP address in the IP header. It then forwards the packet appropriately. The next router then does the same using its own routing table and this carry s on until the packet reaches its destination. The IP destination address in the IP header is all that is needed to find the next hop. Routers are enabled to create these forwarding tables by Routing Protocols. Some of these are:
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For each IP address in the routing table IPv4 performs a logical and operation between the destination IP address and the subnet mask and the result is compared with the destination field of the entry for a match. The list of matching routes is compiled and IPv4 selects the longest match. The longest matching route is the most specific route to the destination address. If the router finds multiple longest match routes it uses the lowest metric to pick the best route.
Con estion control Al orithms
Congestion means that intermediate devices such as Routers are overloaded and if they are overloaded they start to drop datagrams. If datagrams contain TCP segments, then the segments will not be acknowledged because they have not reached the destination. They would then have to be ir retransmitted. When TCP segments have not been acknowledged, it is mostly assumed that they have been dropped by intermediate devices because of congestion. By detecting the rate at which segments are being sent and they are not being acknowledged a device can tell the level of congestion between itself and its TCP connection Peer. Using this information, four techniques were developed to handle congestion.
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Con estion control Al orithms
Each sender is initially restricted to sending an amount of data equal to the MSS value for the connection. Every time there is an acknowledgement, the amount of data the sender can send is increased by the size of another full segment. It then increases until it reaches the full window size or if congestion is discovered on the link then the congestion avoidance technique comes into play.
Con estion Avoidance
When congestion is detected, the device starts to throttle back the speed that it is sending the segments. It uses a special algorithm, which allows it to slow the speed down quickly when congestion is found. The device would gradually increase the speed back up by using theSlow Startalgorithm.
Fast Retransmit
This allows missing segments to be transmitted immediately without having to go through the whole retransmission queue process, after three acknowledgements asking for a segment starting with byte #N it would say that the byte #N is lost due to congestion.
Fast Recovery
When using Fast Retransmit to send a lost segment, the device using it performs Congestion Avoidance but it does not use Slow Startto speed the rate back up. Since several ACKS were received showing out of sequence segments these have been removed from the flow between the devices and for efficiency transmission speeds can be increased more quickly than when congestion happens in other ways.
Slo
Start
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Mobile and Broadband Services
ATM
ATMrefers toAsynchronous Transfer Modewhich has been designed for transferring Voice, Data and Video at high speeds over public as well as private networks. It is connection oriented. It uses fixed size cells of 53 bytes, is scalable and supports several transmission speeds. ATM is a cell switching and multiplexing technology. ATM combines the best features of circuit switching (constant transmission delay and guaranteed capacity) and the best of packet switching (flexibility, efficiency for intermittent traffic).
xDSL
xDSL is the collective title for all types of Digital Subscriber Lines. The two main categories are ADSL and SDSL. Other types include HDSL (High Data Rate)DSLand VDSL (Very High) DSL. They are known as last mile connections because they are used for connections from a telephone switching station to a home or office, but not between telephone switching stations. xDSL is very similar to ISDN because they run over the existing copper telephone lines. But xDSL offers far higher speeds, up to 32 Mbps for upstream traffic and from 32 Kbps to over 1Mbps.for downstream traffic. The maximum length of the wire is 1,820 m or 6000 feet from the service providers central office to home or office. These services are delivered with normal telephone services at the same time on the same telephone line. This is achievable because xDSL runs at a higher frequency and the different frequencies are filtered to keep them separate. With SDSL the upstream and downstream Data rates are the same, withADSL the Data rates are faster going to the customer (downstream) and slower coming from the customer (upstream).
GPRS
GPRS refers to General Packet Radio Service which is based on Global System for Mobile communications (GSM). It is used for SMS (Short Message Service) and WAP (Wireless Application Protocol). GPRS uses packet based connections rather than circuit switched for Mobile Networks which makes it a best effort service. It is also used for access to the Web and Email. Unlike circuit switching Data which is billed for per minute connection time, GPRS is billed on how much Data you transfer. GPRSextends the capabilities of the GSM circuit switched Data capabilities and is described as 2.5G, i.e. between 2G and 3G mobile technology.
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Mobile and Broadband Services
3G Services
3G refers to 3rd Generation which is a generation of standards for mobile phones and mobile communications. It also refers to pending improvements in wireless data and voice communications through a range of proposed standards. The main goal is to achieve transmission spe from 9.5k eds to2M bit/sec. 3Gservice, offers high speed access to Data and Voice services, by using a 3G network which is a mobile broadband network is offering speeds of at least 144 Kbps. The standard developed by the International Telecommunications Union, known as the IMT-2000 criteria. It has similarities with WiFiwhich allows high bandwidth transfer of data over a short range transmission. 3G connects to a system of telecommunication towers using satellite driven connections which means that the range is far greater than other technologies. This makes it ideal for connecting to large networks. The key part of 3G service is mobile to mobile voice transfer. Applications that were not available to mobile phones before are becoming available, these include:
3G Wireless Combines a mobile phone, laptop PC and TV Features includes: - Phone calls/fax - Global roaming - Send/receive large email messages - High-speed Web Navigation/maps Videoconferencing - TV streaming - Electronic agenda meeting reminder. Speed: 144kb/sec-2mb/sec Time to download a 3min MP3 song: 11sec-1.5min
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Mobile and Broadband Services
H.32x
H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) and it defines the protocols that provide audio visual communication sessions on any packet network. Widely used by video conferencing manufacturers and is used with real time applications like GnuGK and NetMeeting. The H.323 standard deals with call signalling and control, multimedia transport and control and bandwidth control for point to point and multipoint conferences. It is part of theTU-T H.32x group of protocols and is used worldwide by service providers and enterprises for video services over IP(Internet Protocol) networks.
VoIP
Refers to Voice over Internet Protocol is a general term for phone services over the net. It is another way of making phone calls over the internet, which are cheaper or even free. If you have a good enough internet connection and a computer with a microphone and speakers you can use VoIP for free. Voice, Fax and SMS are transported over the Internet instead of using the public switched telephone network (PSTN). Communication over the IP network is less reliable than the circuit switched public telephone network because it is a best effort network and does not have fundamentalQuality of Service (QoS) guarantees.
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Biblio raphy
http://communication.howstuffworks.com/convergence/router4.htm. (n.d.). http://en.allexperts.com/q/General-Networking-Lan-1049/network-switch.htm. (n.d.). http://en.wikipedia.org/wiki/3G. (n.d.). http://en.wikipedia.org/wiki/H323. (n.d.). http://en.wikipedia.org/wiki/Isdn. (n.d.). http://en.wikipedia.org/wiki/Message_switching. (n.d.). http://en.wikipedia.org/wiki/Pstn. (n.d.). http://en.wikipedia.org/wiki/Voice_over_IP. (n.d.). http://technet.microsoft.com/en-us/library/bb727001.aspx. (n.d.). http://www.cisco.com/en/US/docs/internetworking/technology/handbook/DSL_Dig_Subscr_Ln.htm l. (n.d.). http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Intro-to-Internet.html. (n.d.). http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/frame.htm. (n.d.). http://www.ciscopress.com/articles/article.asp?p=31533. (n.d.). http://www.cs.bris.ac.uk/Teaching/Resources/COMS11200/pages/tour18/tsld004.htm. (n.d.). http://www.javvin.com/networkingterms/MessageSwitching.html. (n.d.). http://www.tcpipguide.com/free/t_NetworkingStandards.htm. (n.d.). http://www.tcpipguide.com/free/t_TCPCongestionHandlingandCongestionAvoidanceAlgorit 2.htm. (n.d.). http://www.tcpipguide.com/free/t_WhatIsNetworking.htm. (n.d.). http://www.tomshardware.co.uk/forum/29645-17-router-switch. (n.d.). http://www.beest-built.com/voip-technology.html
