1 Abstract Keywords: Wireless, wired, network, router, packet switching, circuit switching, protection, MPLS

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2 1 Abstract The growth number of broadband user connections in the world, the wide use of mobile devices and other appliances to get information through the Internet always requires some level of availability to support customer needs. This necessity made infrastructure high available for being used to be used on large scale and has then been migrated to service providers which offer solutions and they ensure short time to repair. In this seminar we present the structure of wired and wireless networks and the structure of computer networks with Internet. We overview the common point of wired and wireless networks, router, different network topologies, describe packet and circuit switch networks and point out major protection methods for high availability. Keywords: Wireless, wired, network, router, packet switching, circuit switching, protection, MPLS 2

3 2 Table of Contents 1 Abstract Table of Contents Introduction OSI Layer Wireless networks Wired Networks Protection on layer OSI Layer Circuit-switching networks ATM Packet switching network Token Ring CSMA OSI Layer Routing OSI Layer MPLS Suggestions for future work Non Protected Hot Standby Ring Protection Space Diversity Frequency Diversity Tributary Protection Tributary Always On IDU Hot Standby Protected Tributary IDU Hot Standby Tributary Always On IDU 1+1 Dual ODU Conclusion Works Cited

4 3 Introduction Increase in data transfer over computer networks requires a protection mechanism. With protection we intend to protect data due to network failure. Our goal is to make network parts redundant to achieve higher data transmit reliability. [1] [2]These network failures can happen as a result of broken links, equipment failures, traffic jams, etc. In practice protection can be done in two ways: with hardware and/or software. Hardware protection is done with redundant hardware element in the network system. This redundant element has to be ready all the time and at the point of failure it needs to take over all the responsibilities from failed one. The redundant element is the same in function and purpose as failing one. Both of them must control status of them self and among each other. This communication is done in software and controls relevant information, and switches to redundant element when failure occurs. Software protection can be done with redundant path, this means that between transmitter and receiver exist at least two independent paths (not necessarily same network technology). When failure occurs, software reroutes data to go through redundant path. Customers, who use this connection for transmitting data, must not notice the difference. We also need to have in mind that some protocols, like for voice call, must not exceed 50 milliseconds of failure time, so these systems must be fast in responding. Because these redundancy systems are very expensive, only important backbone routers use it. Protection can be done on multiple layers of ISO OSI layer scheme. OSI is divided into seven layers, within each, one or more entities implement its functionality. OSI layers are: 1. Physical; Media, signal and binary transmission 2. Data link; Physical addressing 3. Network; Path determination and logical addressing 4. Transport; End-to-end connections, reliability and flow control 5. Session; Inter host communication, managing sessions between applications 6. Presentation; Data representation, encryption and decryption, convert machine dependent data to machine independent data 7. Application; Network process to application For our seminar first three layers are important and later we will review them in details. Our goal in further research work will be to implement different protection scenarios in a real network, to measure time delay and data throughput. Based on these results we will try to propose new network protection scenarios. 4 OSI Layer Wireless networks Wireless networks have advantage comparing to wired networks mainly where a problem is terrain (mountains, swap, sea, jungle, etc.). Although term wireless network is loosely, there are three main types of network: wide area, local area and personal area networks. Wide area networks include the networks provided by telecoms. It is designed to transfer traffic across longer distances and can be used as part of backbone networks. A typical system contains access points, base station gateways and wireless bridging relays. The wireless connections between access points are usually point to point microwave links. In this type of network we have technologies like LTE, WiMAX, UMTS, GSM, etc. Wireless local area networks are set up to provide wireless connectivity within small place like house, airport, hotel, etc. This gives users ability to be connected to the Internet 4

5 through access point and to move around within a local coverage. Main presenter of WLAN is standard also known as Wi-Fi. Personal area networks are networks that provide wireless connectivity over distances of few meters. The devices establish an ad-hoc network when they are within range, and the network is dissolved when the devices get out of range. These technologies are infrared (IR), Blue Tooth, ZigBee, etc. 4.2 Wired Networks Wired networks consist of cooper twisted pair, coaxial lines and fiber-optic lines. Cooper twisted pair is mainly used for telephone networks. One wire transmitting data is like an antenna, while twisted pair cancels out the waves from each other. Coaxial line has better shielding than twisted pairs, so it can span longer distances at higher speeds. It is used mainly in cable television. Fiber optic is the most advanced technology, used for all kinds of services: telephone, television and internet. 4.3 Protection on layer 1 There are several ways how to achieve protection on Layer 1 and some researches have been made [3]. If we have a case where an excavator cuts the bundle of cables and we have a primary and redundant cable in this bundle, we are not able to reestablish a connection and the problem remains. We have two solutions; first is that we have wireless redundant link; second is that redundant cable goes in totally different way. The less primary and redundant connection have in common, the better is the protection. 5 OSI Layer 2 Today s networking is combination of different sub networks [4]. This sub networks are circuit switched or packet switched networks. For quality assurance it is important to understand how packets of data are created and how are they directed across different networks. 5.1 Circuit-switching networks The term circuit switching refers to a communication protocol where two network nodes establish dedicated channel. Instead of having each channel correspondent to physical path, paths are virtual. Three general properties define the circuit switched path: point-topoint connection; steps for establish connection, using it and to destroy It; equivalent to physical path. Point-to-point connection means that connection is made between two end points; transmitter and receiver. Second property describes that each connection is done in three steps. In first step circuit is established, in second step data is exchanged and in third step the path is terminated. Third property describes that although it is virtual path, for a user it is the same as isolated physical path. For explaining circuit switching network parallelism with phone call can be made. When we are trying to call someone we need to dial his number and then wait for the connection before we can talk. All the words follow the same path through network. After the conversation is over the connection is terminated. And if something is wrong on the way- if failure occurs - the connection is terminated. This is one of the main reasons what telecoms do not like about it. But it has some good sites like Quality of service (QoS) and billing. Despite having technologies like TDM, X.25 and Frame relay, Asynchronous Transfer Mode (ATM) is far more important. 5

6 5.1.1 ATM ATM [5] [6] uses asynchronous time-division multiplex. It is core protocol over SONET/SDH backbone of the public telephone network. At first it was designed for telephone circuit switched networks, but then it was adapted for small packet switched networks as well. It is constructed for high-throughput data traffic and real time, low latency content like voice and video. The ATM cell consists of a 5-byte header and a 48-byte payload. (For comparison, Ethernet packets can be up to 1500-byte). ATM technology gives the impression that multiple data is transmitted along at the same time, but it actually divides time slots among more strings, so only one data string at a time is being transmitted over the path. Time slots are determined based on type of data. It operates as a channel-based transport layer, using virtual circuits. Virtual circuits are divided in two levels as shown on Figure [1], virtual path (VPI) and virtual channel (VCI). On each physical line there is 8 or 12-bit VPI identifier and 16-bit VCI identifier. Figure 1: ATM path 5.2 Packet switching network The main alternative for circuit switching is packet switching, which form the basis for internet. A packet switching uses statistical multiplexing in which multiple packets compete for the use of shared media [7]. The big difference arises because a packet switching requires from a transmitter to divide the message into blocks of data, called packets. The size of packets varies depending on used technology. There are three main properties: arbitrary, asynchronous communication; no set-up required before communication begins; performance varies due to statistical multiplexing among blocks. The first property means that the transmitter can communicate with one or multiple recipients, and one receiver can receive packets from one or many transmitters. Between two successive communications an arbitrary long delay can occur and this connection can happen at any time. A second property means that packets can be transmitted directly, no need to perform initialization and after transfer is done, no need to notify for terminating a connection. Third property means that statistical multiplexing is rather done among blocks (packets) than bits or bytes. That is, the transmitter transmits entire packet, and then allows other transmitters to transmit packets. Only when no other transmitters are ready to transmit a packet, one can transmit repeatedly. A data packet on Ethernet link is called Ethernet frame. It can be up to 1500-byte in size in some cases even bigger. Packet size depends on data size. As shown on Figure[2] in the head of a packet are 6-byte Media Access Control (MAC) source address and 6-byte MAC destination address. Based on these two addresses switch can determine from which physical interface the packet came and which physical interface to transmit it. Switch builds its own database and each MAC address is in a combination with a particular physical interface. So when packet is traveling around network, each time it comes to switch, it checks source and destination MAC address, it changes the header with new source and destination MAC address and transmits it to the destination. 6

7 Figure 2: Ethernet and IP Packet We know different protocols for statistical multiplexing in packet switching: ALOHA, MACA, MACAW, CSMA, Token ring, Token bus, etc. Two dominant protocols we will present in details: Token ring and CSMA. To understand different packet switched network topologies we prepared an overview. Topology is the layout pattern of different network components, computers, switches, hubs, routers, etc. Its physical design of a network includes the devices, location and connections among them. We have six basic topologies and several combinations. Basic topologies are: Point-to-point; the simplest topology, where two devices are connected with one link Star, Figure[3.1]; special point-to-point connection, where multiple nodes are connected to central device. With N nodes, we have N point-to-point connections. Ring, Figure[3.2]; this topology got name after the circular fashion in which nodes transmit data in one direction around the ring. Each node has two neighbors, one on its left and the other on its right, because data are traveling in only one way, each node acts like repeater. Mash, Figure[3.3]; this is the most protected, fault proof network. Here each node is directly connected with all other nodes. The number of connections can be calculated with this formula: (N(N - 1) / 2), where the N is the number of nodes. Bus, Figure[3.4]; basic topology for Ethernet, where each node is connected with a single cable to bus cable. Bus cable is like backbone and connects all the nodes. It works based on device address. Data is sent to all nodes on the bus but only the node with right address keeps it, other nodes discard the data. Figure 3: Network topologies: 2.1-Star topology; 2.2- Ring topology; 2.3- Mash topology; 2.4- Bus topology 7

8 5.2.1 Token Ring [8]Physically, a token ring network is connected as a star, with hub in the center, and other communication equipment as arms. Because only one transmitter can transmit at the time, special 3-byte frame is sent around stations- called token. Only the station carrying token, can transmit data. Duration for transmitting depends on predetermined importance of station. When the permitted data is sent from one station, token moves to the next station, which can then start to transmit data. This protocol is good to send distributed data, but has speed issue. It can only operate up to 100 Mbps and this is main reason why CSMA dominates CSMA CSMA is algorithms for allocating MAC. Its purpose is to transmit packets among bus without collision [9]. When a transmitter has data to transmit, it first listens to the channel to see if anyone else is transmitting at that time. If the channel is busy, the transmitter waits until it becomes idle. When the transmitter detects an idle channel, it transmits a frame. If a collision occurs, the transmitter waits a random amount of time and starts all over again. This random delay in case of collision detection has an important effect on the performance. There is a small chance that two transmitters will wait exact same time and then start with protocol from beginning, but in case this happens the delay gets more and more important and protocols performance gets worse. Many protocols arising from CSMA have been proposed: CSMA With Collision Detection (CSMA/CD) [10], CSMA With Collision Avoidance (CSMA/CA), CSMA With Collision Avoidance and Resolution using Priorities (CSMA/CARP). 6 OSI Layer Routing Routing, on 3th OSI layer, is a process of selecting paths, where network traffic will be sent. It is performed for different kind of networks, for circuit switching and packet switching. In packet switching networks, each packet is routed individually. Packets are forwarded as logically addressed packets from their source towards their destination through intermediate nodes, typically hardware devices called routers. Between source and destination device is usually more than just one path. Two successive packets sent from source towards destination do not have to go through the same path. Reasons for not going the same path are different; link failure, rout congestion, hardware problem, etc. This routing is done based on routing tables. Each router device builds and maintains its own table for routes to various network destinations. Devices communicate with each other through protocols Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) [11]. These protocols bases on different variables, for example; vector distance determination to the destination device and cost of a path, which provider can determine for each path. Protocol calculates all variables and determines the shortest path to destination. These protocols are also ready for network failure, as they have mechanism that checks the connectivity with other routers. If they sense router failure, they update routing tables with bypass of failed router if possible. The structure of IP packet is shown on Figure[4] and is similar to Ethernet packet without MAC addresses [12]. IP packet is transmitted across networks with Internet Protocol (IP) source and IP destination, each having 4-byte. Important information for routing is also the subnet mask which is a logically visible subdivision of an IP network. All computers that belong to a subnet are addressed with a same most-significant bit-group in their IP address. This results in the logical division of an 8

9 IP address into two fields, a routing prefix and the rest for host identifier. The rest field is an identifier for each computer. 7 OSI Layer MPLS [13] [14] Multiprotocol label switching (MPLS) was originally designed to improve speed of routers but now it is merging as a new important standard technology that offers new capabilities for IP networks. MPLS takes the best of ATM and Ethernet at same time. Instead of IP source and destination it uses short labels, similar like ATM. In MPLS there are two types of routers; edge and label switched routers. Edge router where packet enters the MPLS network encapsulates the IP packet and adds the label in the header. Edge router prepares label switched path for packets and notice, over OSPF protocol, all the routers on the path which label to use. Label switched routers forward MPLS packet based on label, they also have possibility to change, drop or add labels. Finally before labeled packet leaves the MPLS network another edge router removes the label. The same can be done for ATM network except that MPLS packet is first divided to fit ATM cells size (48-byte). These labels can also be dynamically changed due to forwarding or network failure. MPLS besides OSPF and RIP protocols support manually updating the forwarding tables. This benefit in traffic engineering where we can control the data flow, predict and prevent congestions, etc. MPLS packet is shown on Figure[4], where we see that MPLS header is between Ethernet (OSI layer 2) and IP header (OSI layer 3) so we say that MPLS is in 2.5 in OSI layer. Header size is 4-bytes it can have multiple labels in one packet, but last label must have s bit set to 1and all prior labels must have s bit set to 0. Figure 4 MPLS packet 8 Suggestions for future work Till now we discovered different networks and protocols they use to direct data packets across network. The goal for the future work is to implement different scenarios containing these networks in real environment and measure throughput and time delay. Based on results we will get we will try to optimize protection scenarios and provide better solutions to the existing ones. We prepared several scenarios that will be explained in this chapter. We will presume that our router can handle these technologies: wireless microwave point to point and wired; fiber and twisted pair cooper. Microwave hardware consists of three parts as shown on Figure[5]: Outdoor Unit (ODU), Radio access card (RAC) and Indoor unit (IDU), wired hardware consist of Data Accessed Card (DAC). 9

10 Figure 5: Router with IDU, RAC, ODU and DAC Protection scenarios are: 8.1 Non Protected A non-protected terminal, also known as 1+0, is a configuration in which there is a single transmission path without redundancy of any kind. A terminal has a single ODU and a single RAC. In this configuration any traffic-affecting fault in either of these units will result in a loss of traffic over the link. 8.2 Hot Standby A protected terminal, also known as 1+1, provides two redundant transmission paths, but only one is active at any one time [15]. A hot standby terminal consists of two ODUs and RACs. Each ODU operates on the same frequency, with the online transmitter connected to the antenna, while the offline ODU is muted. In the receive path, the incoming signal is split between the two receivers. Once again the RAC automatically selects a corrected frame over an uncorrectable frame. 8.3 Ring Protection The architecture enables a self-restoring ring construction, where the traffic enters and leaves the ring from a single point. The traffic is carried in one direction around the ring and the alternate direction is used to provide a protection path when the primary direction fails [16] [17]. 8.4 Space Diversity Space Diversity is a special equipment configuration used to combat the adverse effects caused by multipath fading (which occurs only at lower frequencies). The diversity operation is realized by receiving the same signal using two antennas, spatially separated (vertically). Each antenna is connected to a receiver. Once again the RAC automatically selects a corrected frame over an uncorrectable frame. 8.5 Frequency Diversity Frequency diversity is a dual-frequency protected configuration, which provides protection against multi-path fading (although less than that provided by space diversity), but requires the use of a single antenna. In FF configuration, the main and redundant radio links 10

11 operate on different frequencies, with path selection made again between the two received signals. There is no transmitter switch. 8.6 Tributary Protection In this construction two data access cards are used to provide protection against card failure. Cables connect the two cards to the customer s equipment. Both cards receive data from the customer s equipment. One of the cards puts this data onto the back plane. In the transmit direction one of the cards supplies data to the customers equipment, the other mutes its interface. 8.7 Tributary Always On This configuration is the same as the Tributary protection operation, except that in the transmit direction both of the cards supply data to the customers equipment. The customer s equipment switches between these two always on tributaries. 8.8 IDU Hot Standby Protected Tributary In this configuration two protectable IDUs are used to provide protection against equipment failure. It is similar to Hot Standby in the radio link, and Tributary Protection in the customers interface. Cables connect the two IDUs to the customer s equipment. Both IDUs receive Ethernet packets from the customer s equipment. The active IDU transmits the packets onto the radio link. In the transmit direction the active IDU supplies packets to the customers equipment, while the inactive IDU mutes its transmitter interface. 8.9 IDU Hot Standby Tributary Always On In this configuration two protectable IDUs are used to provide protection against equipment failure. It is similar to Hot Standby in the radio link, and Tributary Always On, on the customer s interface (the customers equipment switches between these two always on tributaries) IDU 1+1 Dual ODU In this configuration a single IDU connects to two ODU s to provide protection for the ODU s and the radio link. Hitless Rx diversity is supported in this configuration. 11

12 9 Conclusion The principle of high availability architectures is reviewed. We have also described the structure of computer networks which are basic for Internet. We presented different approaches how to upgrade network to be protected for case of hardware and software failure. For further research we will investigate optimization for different network topologies. The main goal in these researches will be to find optimal protection, hardware or software with the minimum cost for customer. All of these considerations can make a protection topology more complicated. 12

13 10 Works Cited [1] - v l b l ty ut t tw k Reliability and Maintainability Symposium (RAMS), 2011 Proceedings - Annual, pp. 1-6, [2] S I R uc Detection and recovery of the blocked ports defect for the reliable Ethernet R t ct Sw tc OptoeElectronics and Communications Conference (OECC), th, pp , [3] J d D B db d cc N tw k w t l R du d cy Design of Reliable Communication Networks, [4] A. S. Tanenbaum, Computer Networks, Fourth Edition, 2003, pp [5] R Hu t M - t c l d c t ctu Computer Communications, pp , [6] o. T. D. E. &. T. Woo-Y u v d l x bl du d cy M cc w tc y t ATM (ICATM 2001) and High Speed Intelligent Internet Symposium, Joint 4th IEEE International Conference on, pp , [7] B R l bl d t l c u c t y t u u l bl tw k t d Communications Systems, IEEE Transactions on, zv 12 št 1 1-9, [8] S yt IS0 8802/5 token ring local- tw k Electronics & Communication Engineering Journal, zv 11 št , [9] B N d ll Ex t l Ev lu t O t l SM IEEE Infocom, pp , [10] Z Adaptively Switching between CSMA and SD-CSMA in Multi-Antenna Based Ad Hoc N tw k IEEE Military Communications Conference, pp. 1-6, [11] J M y OS F V 2 Network Working Group, [12] J R J t l St d d t I D t v IEEE 802 N tw k : Information Sciences Institute, [13] E R Mult t c l L b l Sw tc c t ctu Network Working Group, [14] M. A.-L B cc N tw k v l b l ty t t v c u I /M LS tw k Communications Magazine, IEEE, zv 46 št , [15] S S v t v R du d cy M t N tw k D v c IEEE CONFERENCES, pp ,

14 [16] D. L. K. L. June-K K v R Et t R t ct N tw k Optical Internet (COIN), pp. 1-3, [17] L B F G R - t ct c : l t d c t l t t Computers and Digital Techniques, zv 132 št ,