Introduction	Behind every successful service organisation there needs to be an efficient infrastructure that can deliver products to the correct destinations, at the correct time and at a competitive price. For a technology driven organisation this infrastructure is both complex and vast. Below, an attempt is made to present this infrastructure without getting into the more technical details. CytaNet is one of the largest and most experienced Internet Service Providers (ISPs) in Cyprus and the Eastern Mediterranean region, providing both dial-up access (PSTN, ISDN and GSM) and leased line access along with a vast portfolio of Internet Services and customised solutions. The topology of CytaNet has been designed with the aim to achieve the following: 1. High Performance and Top Quality of Service. 2. Reliability and Security 3. Flexibility 4. Expandability To this end, CytaNet has been laid out using state-of-the-art technology at all levels of the network: access, backbone and services.
Network Overview	CytaNet spans across the whole island with Points of Presence (PoPs) in all major towns, as shown below: [INLINE] Each PoP provides access with local calling rates for the whole District. The PoPs are connected with high-speed links to a Central Node in Nicosia where all the major servers are located. The Central Node is served by a 100 Mbps backbone Fast-Ethernet network that ensures fast access to the local servers as well as the rest of the Internet. The CytaNet backbone network comprises of CISCO top-of-the-range routers, such as the CISCO 7500 and CISCO 4500M. The access network comprises CISCO routers AS5300, AS5200 and 2500 series.
Access Network - Points of Presence	Each PoP provides access to CytaNet through a multitude of ways: 1. PSTN - This is the ordinary telephone network which allows users with standard modems to connect onto CytaNet with a maximum speed of 56000 bits per second (bps). CytaNet modems support the following standards: ITU(T) V.90 - Up to 56000 bps Rockwell/Lucent K56flex - Up to 56000 bps ITU(T) V.34 Annex 12 - Up to 33600 bps ITU(T) V.34        - Up to 28800 bps ITU(T) V.32bis    - Up to 14400 bps ITU(T) V.32        - Up to 9600 bps ITU(T) V.22bis    - Up to 2400 bps All CytaNet modems are equipped to use ITU(T) V.42 and MNP error control and V.42bis and MNP data compression. In order to fully benefit from the high-speed capabilities of these modems the user's computer should be equipped with a fast serial port using, for example, the 16550 UART chip. The connection protocol is PPP (Point-to-Point Protocol). 2. ISDN - This new digital telephone network allows for a much better connection quality reaching speeds upto 64000 bps. To be able to connect to CytaNet through ISDN the personal computer or router must be equipped with an ISDN interface following the EuroISDN - NET3 standard. 3. GSM - Users "on the move" can always connect to CytaNet using their GSM mobile telephone. To do this they require an apropriate PCMCIA card inserted in their portable PC and connected to the mobile phone. Alternatively, Nokia 9000 owners can use their mobile phone to connect and browse the Internet without any additional hardware required. One should keep in mind that the speed of connection using a GSM phone is 9600 bps. This limit is imposed by the GSM air-interface standard and not by CytaNet. 4. Leased Lines - These allow continuous Internet connectivity and come in a variety of speeds. For speeds above 64 kbps a Network Termination Unit (NTU) is installed by CYTA at the customer's premises which provides a V.35 connection straight to the customer's networking equipment. In order to support all the above every PoP consists of a 10 Mbps Local Area Network (LAN), served through a switching hub for optimum performance. This LAN interconnects all the access servers (CISCO 2500, AS5300 and AS5200), routers and other servers, as shown in the schematic below. Each PoP is equipped also with a Web Proxy Server for the sole use of the local users. [INLINE] To date the CytaNet PoPs are connected to the Central Node with the following speeds: PoP Speed Lemesos 6Mbps Larnaka 2Mbps Pafos 2Mbps Ammochostos 2Mbps To access CytaNet users may dial the following numbers: PSTN / ISDN / GSM Lefkosia 0991600 Lemesos 0991600 Larnaka 0991600 Pafos 0991600 Ammochostos 0991600 Cytanet for all 0992626
Central Node and Backbone Network	Our Central node is located in Nicosia and its function is threefold: To provide Global Internet connectivity. To provide Internet Services to our customers (e.g. e-mail, ftp, www etc). To manage the CytaNet network. To accomplish these we employ a number of Internet Servers all connected with each other through a 100 Mbps Fast Ethernet Backbone Network operating in full-duplex mode, thereby delivering an aggregate throughput of 200 Mbps. The routers handling the international links and the links to the Regional PoPs are also connected on the same backbone for optimum performance, as shown below. [INLINE] The routers handling the international links are high performance CISCO 7500 routers equipped with dual CPUs and dual power supplies for reliability and high-availability. They run industry standard BGP4 routing protocol in order to manage effectively the routing of the traffic through multiple international links.
Proxy Hierarchy	The function of a Proxy Server is to speed up user access to internet data, such as web pages. This is achieved in a twofold manner: First, the Proxy Server accepts requests from Internet users that want to access web pages (or any other internet data) and fetches the data in their place. Since the Proxy is physically and logically connected directly on the backbone of the network it can fetch the data at the maximum possible speed, much faster than a dialup user can achieve. It, then, streams transparently the received data to the user, again at maximum user speed. Second, the Proxy server maintains an active cache of internet data. This means that it keeps a local copy of the data before it sends them to the user. The next time someone wants to access the same web page, the proxy simply checks if the data has been modified and if not, it reads them off the disk and transfers the data to the client machine immediately, thereby avoiding the delay of transferring the same data through the global Internet mesh. CytaNet employs a number of Proxy Servers to speed up surfing though the net as much as possible. These servers are setup in a hierarchical manner, as shown below, in order to make their operation even more efficient. Communication between the servers is established through "parent" and "sibling" relationships based on the Internet Cache Protocol ICPv2. In this way, stored web pages or other internet data on one server can be used by all other servers. In essence, the interconnection of the Proxy servers in this way realises a large distributed virtual cache across the network. [INLINE] The following addresses identify current and future Proxy Server farms (i.e. may be more than one machine) located at the various CytaNet nodes: address port Lefkosia www-proxy-ni.cytanet.com.cy 8080 Lemesos www-proxy-li.cytanet.com.cy 8080 Larnaka www-proxy-la.cytanet.com.cy 8080 Pafos www-proxy-pa.cytanet.com.cy 8080 Ammochostos www-proxy-fm.cytanet.com.cy 8080
Reliability, Availability and Security	A high quality network is not just a fast network; it is also a reliable one. As the Internet is being used more and more by professionals for business, the need for reliability becomes essential. People generally perceive Internet as an unreliable means to communicate, suffering from message losses, link failures etc. CytaNet has put extra effort in establishing a reliable and highly available network so as to allow users, business or otherwise, to get on with their work without interruptions. To this end, CytaNet employs duplicate (redundant) equipment configurations in most core network elements, and eliminates most single points of failure: It connects to the global Internet through more than 2 International Links. The core routers are duplicated and have dual power supplies and dual CPU's (Route Switch Processors). The Central Node and every Regional PoP utilises a UPS which is attached on an Electric Power Generator. All essential Servers employ disk mirroring technology (RAID). Incoming mail is served by multiple Mail-Servers (relays). Multiple proxy servers are employed in a hierarchical fashion. Additional network reliability enhancements are planned for the future. Security is an issue closely related to reliability. CytaNet implements security through a firewall at the first point of contact with the Global Internet. Moreover, all CytaNet servers make use of appropriate software to monitor and block unwanted traffic and other malicious attacks.
Network Management	Coupled with the advanced networking technologies CytaNet employs excellent Network Management facilities. All network elements (routers, switches, servers, links) are centrally monitored and managed on a 24-hour basis. Our Network Management tools make use of the standard SNMP protocol to collect and analyse alarms and performance statistics. In addition, "heart-beat" tests are performed on all the server applications (e.g. Mail servers, Usenet News, Proxies etc) as well as links in order to safeguard the continuous operation. To facilitate easy access and remote monitoring and control, our suite of Management tools are accessible also from the Web through a controlled interface. Alarms and other notifications are signalled by audible sounds and logged in appropriate files for analysis. They are also forwarded to the network administrators by e-mail and by automated calls to their mobile phones.

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