ABSTRACT
An ISP (Internet service provider) is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and virtual hosting. ISPs employ a range of technologies to enable consumers to connect to their network. Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. Internet Service Provider (ISP) peering and transit has emerged as one of the most important and effective ways for ISPs to improve the efficiency of operation. Peering is defined as “an interconnection business relationship whereby ISPs provide connectivity to each others’ transit customers.” ISPs seek peering relationships primarily for two reasons. First, peering decreases the cost and reliance on purchased Internet transit. As the single greatest operating expense, ISPs seek to minimize these telecommunications costs. Second, peering lowers inter-Autonomous System (AS) traffic latency. By avoiding a transit provider hop in between ISPs traffic between peering ISPs has lower latency. BGP is a multi-vendor “open” protocol with multiple implementations, all mostly interoperable. It is the only actively used EGP on the Internet. The main design feature of BGP was to allow ISPs to richly express their routing policy, both in selecting outbound paths and in announcing internal routes. Thus ISP play an important role in providing Internet access to its customers.
1. INTRODUCTION
An ISP (Internet service provider) is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and virtual hosting. An ISP has the equipment and the telecommunication line access required to have a point-of-presence on the Internet for the geographic area served. The larger ISPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. Among the largest national and regional ISPs are AT&T WorldNet, IBM Global Network, MCI, Netcom, UUNet, and PSINet.
The larger ISPs interconnect with each other through MAE (ISP switching centers run by MCI WorldCom) or similar centers. The arrangements they make to exchange traffic are known as peering agreement. There are several very comprehensive lists of ISPs worldwide available on the Web. In the past, most ISPs were run by the phone companies. Now, ISPs can be started by just about any individual or group with sufficient money and expertise. In addition to Internet access via various technologies such as dial-up and DSL, they may provide a combination of services including Internet transit, domain name registration and hosting, web hosting, and colocation.
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2. ISP CONNECTION OPTIONS
ISPs employ a range of technologies to enable consumers to connect to their network. For "home users", the most popular options include dial-up, DSL (typically ADSL), Broadband wireless access, Cable modem, and ISDN (typically BRI). For customers who have more demanding requirements, such as medium-to-large businesses, or other ISPs, DSL (often SHDSL or ADSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN (BRI or PRI), ATM, satellite Internet access and SONET are more likely. With the increasing popularity of downloading music and online video and the general demand for faster page loads, higher bandwidth connections are becoming more popular.
Typical Home User connection:
Dial-up DSL Broadband wireless access Cable modem ISDN
Typical Business connection:
DSL SHDSL Ethernet technologies
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2.1. Dial-up access:
Dial-up access is a form of Internet access via telephone line. The client uses a modem connected to a computer and a telephone line to dial into an Internet service provider's (ISP) node to establish a modem-to-modem link, which is then routed to the Internet Dialup requires time to establish a telephone connection (several seconds, depending on the location) and perform handshaking before data transfers can take place. In locales with telephone connection charges, each connection incurs an incremental cost. If calls are timecharged, the duration of the connection incurs costs. Dial-up access is a transient connection, because either the user or the ISP terminates the connection. Internet service providers will often set a limit on connection durations to prevent hogging of access, and will disconnect the user — requiring reconnection and the costs and delays associated with it.
2.2. T-1 carrier or DS1 lines:
A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24 individual channels (a transmission path), each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access. T-1 lines are a popular leased line (a permanent telephone connection between two points set up by a telecommunications common carrier. Typically, leased lines are used by businesses to connect geographically distant offices. Unlike normal dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality) option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet
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backbone itself consists of faster T-3 connections. T-1 lines are sometimes referred to as DS1 lines.
2.3. T-3 line or DS3 lines:
A dedicated phone connection supporting data rates of about 43 Mbps. A T-3 line actually consists of 672 individual channels, each of which supports 64 Kbps. T-3 lines are used mainly by Internet Service Providers (ISPs) connecting to the Internet backbone and for the backbone itself. T-3 lines are sometimes referred to as DS3 lines.
2.4. xDSL:
Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Very high DSL (VDSL). DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations. xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream traffic, and from 32 Kbps to over 1 Mbps for downstream traffic. ADSL: Short for asymmetric digital subscriber line, a new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).ADSL requires a special ADSL modem. ADSL is growing in popularity as more areas around the world gain access. SDSL: Short for symmetric digital subscriber line, a technology that allows more data to be sent over existing copper telephone lines (POTS). SDSL supports data rates up to 3 5
Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires and can not operate simultaneously with voice connections over the same wires. SDSL requires a special SDSL modem. SDSL is called symmetric because it supports the same data rates for upstream and downstream traffic. A similar technology that supports different data rates for upstream and downstream data is called asymmetric digital subscriber line (ADSL). ADSL is more popular in North America, whereas SDSL is being developed primarily in Europe.
2.5. Cable modem:
A modem designed to operate over cable TV lines. Because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, a cable modem can be used to achieve extremely fast access to the World Wide Web. This, combined with the fact that millions of homes are already wired for cable TV, has made the cable modem something of a holy grail for Internet and cable TV companies. There are a number of technical difficulties, however. One is that the cable TV infrastructure is designed to broadcast TV signals in just one direction - from the cable TV company to people's homes. The Internet, however, is a two-way system where data also needs to flow from the client to the server. In addition, it is still unknown whether the cable TV networks can handle the traffic that would ensue if millions of users began using the system for Internet access. Despite these problems, cable modems that offer speeds up to 2 Mbps are already available in many areas.
2.6. VPN:
(Pronounced as separate letters) Short for virtual private network, a network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.
2.7. ISDN:
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Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). There are two types of ISDN: • • Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one Dchannel for transmitting control information. Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe). The original version of ISDN employs baseband transmission. Another version, called BISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.
2.8. Ethernet Technology :
Ethernet : Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format. Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from the 1990s to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, is prevalent in home and small office networks and augmenting Ethernet in larger installations.
Gigabit Ethernet:
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Gigabit Ethernet (GbE or 1 GigE) is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2005 standard. Half duplex gigabit links connected through hubs are allowed by the specification but in the marketplace full duplex with switches is the norm.
Metro Ethernet: A Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan access network to connect subscribers and businesses to a Wide Area Network, such as the Internet. Large businesses can also use Metro Ethernet to connect branch offices to their Intranets.
3. HOW ISPS CONNECT TO THE INTERNET
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Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. In the simplest case, a single connection is established to an upstream ISP using one of the technologies described above, and the ISP uses this connection to send or receive any data to or from parts of the Internet beyond its own network; in turn, the upstream ISP uses its own upstream connection, or connections to its other customers (usually other ISPs) to allow the data to travel from source to destination. In reality, the situation is often more complicated. For example, ISPs with more than one Point of presence (PoP) may have separate connections to an upstream ISP at multiple PoPs, or they may be customers of multiple upstream ISPs and have connections to each one at one or more of their PoPs. ISPs may engage in peering, where multiple ISPs interconnect with one another at a peering point or Internet exchange point (IX), allowing the routing of data between their networks, without charging one another for that data - data that would otherwise have passed through their upstream ISPs, incurring charges from the upstream ISP. ISPs that require no upstream, and have only customers and/or peers, are called Tier 1 ISPs, indicating their status as ISPs at the top of the Internet hierarchy. Routers, switches, Internet routing protocols, and the expertise of network administrators all have a role to play in ensuring that data follows the best available route and that ISPs can "see" one another on the Internet.
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Upstream
Backbon e
Backbon e
Regional Internet Service Providers
Local Internet Service Providers
Downstream End Users & businesses
Figure :The Internet Hierarchy Peering point or Internet exchange point: An Internet exchange point (IX or IXP) is a physical infrastructure that allows different Internet Service Providers (ISPs) to exchange Internet traffic between their networks (autonomous systems) by means of mutual peering agreements, which allow traffic to be exchanged without cost. IXPs reduce the portion of an ISP's traffic which must be delivered via their upstream transit providers, thereby reducing the Average Per-Bit Delivery Cost of their service. Furthermore, the increased number of paths learned through the IXP improves routing efficiency and fault-tolerance.
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3.1 ISP to ISP interconnect: Peering
Peering is voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the customers of each network. The pure definition of peering is settlement-free or "sender keeps all," meaning that neither party pays the other for the exchanged traffic, instead, each derives revenue from its own customers. Marketing and commercial pressures have led to the word peering routinely being used when there is some settlement involved, even though that is not the accurate technical use of the word. The phrase "settlement-free peering" is sometimes used to reflect this reality and unambiguously describe the pure cost-free peering situation.Peering requires physical interconnection of the networks, an exchange of routing information through the Border Gateway Protocol (BGP) routing protocol and is often accompanied by peering agreements of varying formality, from "handshake" to thick contracts. To illustrate peering, consider figure 1 below showing a much simplified Internet: the Internet with only three ISPs: WestNet, USNet, and EastNet. WestNet has customers shown as green circles. USNet has customers of its own (beige circles) and EastNet has its customers shown as yellow circles.
Peering W estNet USNet
Peering EastNet
Routing Tables
Figure - Peering and Transit relationships
In this example, WestNet has a peering relationship with USNet in which USNet announces reachability of its beige customers to WestNet, and WestNet announces reachability to its green customers to USNet. This is the essence of the peering relationship;
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each ISP reciprocally provides access to each others customers. EastNet also peers with USNet, announcing its yellow customers to USNet while USNet announces its blue customers to EastNet. It is important to note that WestNet and EastNet cannot access each other’s customers in this configuration. (The boxes below the ISPs show their respective routing tables.) WestNet only knows how to get to blue and green customers, and EastNet knows how to reach only blue and yellow customers. The fact that they both peer with USNet is inconsequential; peering is a non-transitive relationship. Since peering is a reciprocal non-transitive relationship, EastNet and WestNet must peer with every other ISP or find another way of accessing every other ISP. 3.1.2 Physical interconnections for peering: The physical interconnections used for peering are categorized into two types: • • Public peering - Interconnection utilizing a multi-party shared switch fabric such as an Ethernet switch. Private peering - Interconnection utilizing a point-to-point interconnection such as a patch-cable or dark fiber between two parties Public peering: Interconnection utilizing a multi-party shared switch fabric such as an Ethernet switch.At these locations, multiple carriers interconnect with one or more other carriers across a single physical port. Historically public peering locations were known as network access points (NAPs), today they are most often called exchange points or Internet exchanges ("IXP" or "IX").public peering allows networks interested in peering to interconnect with many other networks through a single port.it is often considered to offer "less capacity" than private peering,but to a larger number of networks.
Private peering:
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Private peering is the direct interconnection between only two networks, across a Layer 1 or 2 media that offers dedicated capacity that is not shared by any other parties. Early in the history of the Internet, many private peers occurred across 'telco' provisioned SONET circuits between individual carrier-owned facilities. Today, most private interconnections occur at carrier hotels or carrier neutral colocation facilities, where a direct crossconnect can be provisioned between participants within the same building, usually for a much lower cost than telco circuits. Most of the traffic on the Internet, especially traffic between the largest networks, occurs via private peering. However, because of the resources required to provision each private peer, many networks are unwilling to provide private peering to "small" networks, or to "new" networks who have not yet proven that they will provide a mutual benefit. ISP Physical Interconnection Methods
Interconnection Method
Direct-Circuit Interconnection
Exchange-Based Interconnection
For direct-circuit interconnects, key issues center upon interconnection location(s) and who pays for and manages the interconnection. This becomes a material cost issue as traffic grows and circuits increase in size and cost. In either case, ISPs generally have the following goals for establishing peering: 1. Get peering set up as soon as possible, 2. Minimize the cost of the interconnection and transit costs, 3. Maximize the benefits of a systematic approach to peering. 4. Execute the regional operations plan as strategy dictates (may be architecture/network development group goal), and 5. Fulfill obligations of larger business agreement.
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3.2 ISP to ISP interconnect: Transit
ISP 1 needs to deliver its customers’ traffic to the rest of the internet, and the rest of the internet needs to know how to get to ISP 1’s customers. So, • • ISP 2 announces all the routes on the internet to ISP 1 ISP 1 announces just its customer routes to ISP 2
ISP 1 is a customer of ISP 2 Definition: Transit is the business relationship whereby one ISP provides (usually sells) access to all destinations in its routing table. Consider a simplistic Internet model below in figure 2. In this picture, EastNet purchases transit from USNet, and in return gets connectivity to all networks in USNet’s routing table. As a customer of USNet, USNet announces EastNet routes across all of its peering and transit interconnections.
Transit Relationship - selling access to entire routing table
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4. BORDER GATEWAY PROTOCOL
The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It works by maintaining a table of IP networks or 'prefixes' which designate network reachability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional IGP metrics, but makes routing decisions based on path, network policies and/or rulesets. BGP is a multi-vendor “open” protocol with multiple implementations, all mostly interoperable. It is the only actively used EGP on the Internet. The main design feature of BGP was to allow ISPs to richly express their routing policy, both in selecting outbound paths and in announcing internal routes.
Purpose of BGP:
• • • • To allow networks to tell other networks about routes (parts of the IP address space) that they are “responsible” for. Using “route advertisements”, or “promises” - also called “NLRI” or “networklayer reachability information”. Networks are “Autonomous Systems”. Identified in BGP by a number, called the ASN (“Autonomous System Number”) iBGP: When BGP speakers in the same AS form a BGP connection for the purpose of exchanging routing information, they are said to be running IBGP or internalBGP. IBGP speakers are usually fully-meshed. eBGP : eBGP sessions are established when peering with the different AS.
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5. VIRTUAL ISP
A Virtual ISP (vISP) purchases services from another ISP (sometimes called a wholesale ISP or similar within this context) that allow the vISP's customers to access the Internet via one or more Points of Presence (PoPs) that are owned and operated by the wholesale ISP. There are various models for the delivery of this type of service, for example, the wholesale ISP could provide network access to end users via its dial-up modem PoPs or DSLAMs installed in telephone exchanges, and route, switch, and/or tunnel the end user traffic to the vISP's network, whereupon they may route the traffic toward its destination. In another model, the vISP does not route any end user traffic, and needs only provide AAA (Authentication, Authorization and Accounting) functions, as well as any "value-add" services like email or web hosting. Any given ISP may use their own PoPs to deliver one service, and use a vISP model to deliver another service, or, use a combination to deliver a service in different areas. The service provided by a wholesale ISP in a vISP model is distinct from that of an upstream ISP, even though in some cases, they may both be one and the same company. The former provides connectivity from the end user's premises to the Internet or to the end user's ISP, the latter provides connectivity from the end user's ISP to all or parts of the rest of the Internet. A vISP can also refer to a completely automated white label service offered to anyone at no cost or for a minimal set-up fee. The actual ISP providing the service generates revenue from the calls and may also share a percentage of that revenue with the owner of the vISP. All technical aspects are dealt with leaving the owner of vISP with the task of promoting the service. This sort of service is however declining due to the popularity of unmetered internet access also known as flatrate.
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6. MULTIHOMING
It is a technique to increase the reliability of the Internet connection for an IP network. As an adjective, it is typically used to describe a customer, rather than an Internet service provider (ISP) network. There are several ways to multihome, separate from the actual protocols used to do so, amongst which the most important are: • Single Link, Multiple IP address (Spaces)
The host has multiple IP addresses (e.g. 2001:db8::1 and 2001:db8::2 in IPv6), but you only have one physical upstream link. When the single link fails, connectivity is down for all addresses. • Multiple Interfaces, Single IP address per interface
The host has multiple interfaces and each interface has one, or more, IP addresses. If one of the links fail that IP address is unreachable, the other will still work. Hosts that have multiple AAAA or A records enabled can then still be reachable at the penalty of having the client program time out and retry on the broken address. Existing connections can't be taken over by the other interface, as TCP does not support this. To remedy this, one could use SCTP which does allow this situation. However SCTP is not used very much in practice. • Multiple Links, Single IP address (Space)
This is what in general is meant with Multihoming. With the use of a routing protocol, in most cases BGP, the end-site announces this address space to its upstream links. When one of the links fails, the protocol notices this on both sides and traffic is not sent over the failing link any more. Usually this method is used to multihome a site and not for single hosts.
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•
Multiple Links, Multiple IP address (Spaces), no routing protocol like BGP
This approach uses a specialized Link Load Balancer (or WAN Load Balancer) appliance between the firewall and the link routers. No special configuration is required in the ISP’s routers. It allows to use all links at the same time to increase the total available bandwidth and detects link saturation and failures in real time to redirect traffic. Algorithms allow traffic management. Incoming balancing is usually performed with a real time DNS resolution.
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7.CONCLUSION
Today many new ISPs are coming up and thus there is a huge competition among them in providing good services at low cost to its customers. For this they are continuously upgrading their technology. The basic peering game does a good job of highlighting the issues ISPs face when peering. Several comments from ISPs offering enhancements add reality to the game at the cost of complexity. For example, ISPs capture market share in order to be an attractive acquisition target. Adding merger rules adds a real complexity, somewhat tangentially related to peering and transit. Adding rules for ISPs to buy/sell transit to each other similarly adds complexity but adds a negotiating dynamic that ISPs face today. Balancing the desire to explain and explore against the desire for the simulation to match reality has proven to be a challenge.
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8.REFERENCES
[1] “Maturation in a Free Market: The Changing Dynamics of Peering in the ISP Market“ by Jennifer DePalma [2] www.wikipedia.org [3] www.webopedia.com [4] ISP Survival Guide, Geoff Huston, Wiley Publishers
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doc_687989551.doc
An ISP (Internet service provider) is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and virtual hosting. ISPs employ a range of technologies to enable consumers to connect to their network. Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. Internet Service Provider (ISP) peering and transit has emerged as one of the most important and effective ways for ISPs to improve the efficiency of operation. Peering is defined as “an interconnection business relationship whereby ISPs provide connectivity to each others’ transit customers.” ISPs seek peering relationships primarily for two reasons. First, peering decreases the cost and reliance on purchased Internet transit. As the single greatest operating expense, ISPs seek to minimize these telecommunications costs. Second, peering lowers inter-Autonomous System (AS) traffic latency. By avoiding a transit provider hop in between ISPs traffic between peering ISPs has lower latency. BGP is a multi-vendor “open” protocol with multiple implementations, all mostly interoperable. It is the only actively used EGP on the Internet. The main design feature of BGP was to allow ISPs to richly express their routing policy, both in selecting outbound paths and in announcing internal routes. Thus ISP play an important role in providing Internet access to its customers.
1. INTRODUCTION
An ISP (Internet service provider) is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and virtual hosting. An ISP has the equipment and the telecommunication line access required to have a point-of-presence on the Internet for the geographic area served. The larger ISPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. Among the largest national and regional ISPs are AT&T WorldNet, IBM Global Network, MCI, Netcom, UUNet, and PSINet.
The larger ISPs interconnect with each other through MAE (ISP switching centers run by MCI WorldCom) or similar centers. The arrangements they make to exchange traffic are known as peering agreement. There are several very comprehensive lists of ISPs worldwide available on the Web. In the past, most ISPs were run by the phone companies. Now, ISPs can be started by just about any individual or group with sufficient money and expertise. In addition to Internet access via various technologies such as dial-up and DSL, they may provide a combination of services including Internet transit, domain name registration and hosting, web hosting, and colocation.
2
2. ISP CONNECTION OPTIONS
ISPs employ a range of technologies to enable consumers to connect to their network. For "home users", the most popular options include dial-up, DSL (typically ADSL), Broadband wireless access, Cable modem, and ISDN (typically BRI). For customers who have more demanding requirements, such as medium-to-large businesses, or other ISPs, DSL (often SHDSL or ADSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN (BRI or PRI), ATM, satellite Internet access and SONET are more likely. With the increasing popularity of downloading music and online video and the general demand for faster page loads, higher bandwidth connections are becoming more popular.
Typical Home User connection:
Dial-up DSL Broadband wireless access Cable modem ISDN
Typical Business connection:
DSL SHDSL Ethernet technologies
3
2.1. Dial-up access:
Dial-up access is a form of Internet access via telephone line. The client uses a modem connected to a computer and a telephone line to dial into an Internet service provider's (ISP) node to establish a modem-to-modem link, which is then routed to the Internet Dialup requires time to establish a telephone connection (several seconds, depending on the location) and perform handshaking before data transfers can take place. In locales with telephone connection charges, each connection incurs an incremental cost. If calls are timecharged, the duration of the connection incurs costs. Dial-up access is a transient connection, because either the user or the ISP terminates the connection. Internet service providers will often set a limit on connection durations to prevent hogging of access, and will disconnect the user — requiring reconnection and the costs and delays associated with it.
2.2. T-1 carrier or DS1 lines:
A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24 individual channels (a transmission path), each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access. T-1 lines are a popular leased line (a permanent telephone connection between two points set up by a telecommunications common carrier. Typically, leased lines are used by businesses to connect geographically distant offices. Unlike normal dial-up connections, a leased line is always active. The fee for the connection is a fixed monthly rate. The primary factors affecting the monthly fee are distance between end points and the speed of the circuit. Because the connection doesn't carry anybody else's communications, the carrier can assure a given level of quality) option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet
4
backbone itself consists of faster T-3 connections. T-1 lines are sometimes referred to as DS1 lines.
2.3. T-3 line or DS3 lines:
A dedicated phone connection supporting data rates of about 43 Mbps. A T-3 line actually consists of 672 individual channels, each of which supports 64 Kbps. T-3 lines are used mainly by Internet Service Providers (ISPs) connecting to the Internet backbone and for the backbone itself. T-3 lines are sometimes referred to as DS3 lines.
2.4. xDSL:
Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Very high DSL (VDSL). DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations. xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for upstream traffic, and from 32 Kbps to over 1 Mbps for downstream traffic. ADSL: Short for asymmetric digital subscriber line, a new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate).ADSL requires a special ADSL modem. ADSL is growing in popularity as more areas around the world gain access. SDSL: Short for symmetric digital subscriber line, a technology that allows more data to be sent over existing copper telephone lines (POTS). SDSL supports data rates up to 3 5
Mbps. SDSL works by sending digital pulses in the high-frequency area of telephone wires and can not operate simultaneously with voice connections over the same wires. SDSL requires a special SDSL modem. SDSL is called symmetric because it supports the same data rates for upstream and downstream traffic. A similar technology that supports different data rates for upstream and downstream data is called asymmetric digital subscriber line (ADSL). ADSL is more popular in North America, whereas SDSL is being developed primarily in Europe.
2.5. Cable modem:
A modem designed to operate over cable TV lines. Because the coaxial cable used by cable TV provides much greater bandwidth than telephone lines, a cable modem can be used to achieve extremely fast access to the World Wide Web. This, combined with the fact that millions of homes are already wired for cable TV, has made the cable modem something of a holy grail for Internet and cable TV companies. There are a number of technical difficulties, however. One is that the cable TV infrastructure is designed to broadcast TV signals in just one direction - from the cable TV company to people's homes. The Internet, however, is a two-way system where data also needs to flow from the client to the server. In addition, it is still unknown whether the cable TV networks can handle the traffic that would ensue if millions of users began using the system for Internet access. Despite these problems, cable modems that offer speeds up to 2 Mbps are already available in many areas.
2.6. VPN:
(Pronounced as separate letters) Short for virtual private network, a network that is constructed by using public wires to connect nodes. For example, there are a number of systems that enable you to create networks using the Internet as the medium for transporting data. These systems use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted.
2.7. ISDN:
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Abbreviation of integrated services digital network, an international communications standard for sending voice, video, and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64,000 bits per second). There are two types of ISDN: • • Basic Rate Interface (BRI) -- consists of two 64-Kbps B-channels and one Dchannel for transmitting control information. Primary Rate Interface (PRI) -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe). The original version of ISDN employs baseband transmission. Another version, called BISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.
2.8. Ethernet Technology :
Ethernet : Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media Access Control (MAC)/Data Link Layer, and a common addressing format. Ethernet is standardized as IEEE 802.3. The combination of the twisted pair versions of Ethernet for connecting end systems to the network, along with the fiber optic versions for site backbones, is the most widespread wired LAN technology. It has been in use from the 1990s to the present, largely replacing competing LAN standards such as token ring, FDDI, and ARCNET. In recent years, Wi-Fi, the wireless LAN standardized by IEEE 802.11, is prevalent in home and small office networks and augmenting Ethernet in larger installations.
Gigabit Ethernet:
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Gigabit Ethernet (GbE or 1 GigE) is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2005 standard. Half duplex gigabit links connected through hubs are allowed by the specification but in the marketplace full duplex with switches is the norm.
Metro Ethernet: A Metro Ethernet is a computer network based on the Ethernet standard and which covers a metropolitan area. It is commonly used as a metropolitan access network to connect subscribers and businesses to a Wide Area Network, such as the Internet. Large businesses can also use Metro Ethernet to connect branch offices to their Intranets.
3. HOW ISPS CONNECT TO THE INTERNET
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Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. In the simplest case, a single connection is established to an upstream ISP using one of the technologies described above, and the ISP uses this connection to send or receive any data to or from parts of the Internet beyond its own network; in turn, the upstream ISP uses its own upstream connection, or connections to its other customers (usually other ISPs) to allow the data to travel from source to destination. In reality, the situation is often more complicated. For example, ISPs with more than one Point of presence (PoP) may have separate connections to an upstream ISP at multiple PoPs, or they may be customers of multiple upstream ISPs and have connections to each one at one or more of their PoPs. ISPs may engage in peering, where multiple ISPs interconnect with one another at a peering point or Internet exchange point (IX), allowing the routing of data between their networks, without charging one another for that data - data that would otherwise have passed through their upstream ISPs, incurring charges from the upstream ISP. ISPs that require no upstream, and have only customers and/or peers, are called Tier 1 ISPs, indicating their status as ISPs at the top of the Internet hierarchy. Routers, switches, Internet routing protocols, and the expertise of network administrators all have a role to play in ensuring that data follows the best available route and that ISPs can "see" one another on the Internet.
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Upstream
Backbon e
Backbon e
Regional Internet Service Providers
Local Internet Service Providers
Downstream End Users & businesses
Figure :The Internet Hierarchy Peering point or Internet exchange point: An Internet exchange point (IX or IXP) is a physical infrastructure that allows different Internet Service Providers (ISPs) to exchange Internet traffic between their networks (autonomous systems) by means of mutual peering agreements, which allow traffic to be exchanged without cost. IXPs reduce the portion of an ISP's traffic which must be delivered via their upstream transit providers, thereby reducing the Average Per-Bit Delivery Cost of their service. Furthermore, the increased number of paths learned through the IXP improves routing efficiency and fault-tolerance.
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3.1 ISP to ISP interconnect: Peering
Peering is voluntary interconnection of administratively separate Internet networks for the purpose of exchanging traffic between the customers of each network. The pure definition of peering is settlement-free or "sender keeps all," meaning that neither party pays the other for the exchanged traffic, instead, each derives revenue from its own customers. Marketing and commercial pressures have led to the word peering routinely being used when there is some settlement involved, even though that is not the accurate technical use of the word. The phrase "settlement-free peering" is sometimes used to reflect this reality and unambiguously describe the pure cost-free peering situation.Peering requires physical interconnection of the networks, an exchange of routing information through the Border Gateway Protocol (BGP) routing protocol and is often accompanied by peering agreements of varying formality, from "handshake" to thick contracts. To illustrate peering, consider figure 1 below showing a much simplified Internet: the Internet with only three ISPs: WestNet, USNet, and EastNet. WestNet has customers shown as green circles. USNet has customers of its own (beige circles) and EastNet has its customers shown as yellow circles.
Peering W estNet USNet
Peering EastNet
Routing Tables
Figure - Peering and Transit relationships
In this example, WestNet has a peering relationship with USNet in which USNet announces reachability of its beige customers to WestNet, and WestNet announces reachability to its green customers to USNet. This is the essence of the peering relationship;
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each ISP reciprocally provides access to each others customers. EastNet also peers with USNet, announcing its yellow customers to USNet while USNet announces its blue customers to EastNet. It is important to note that WestNet and EastNet cannot access each other’s customers in this configuration. (The boxes below the ISPs show their respective routing tables.) WestNet only knows how to get to blue and green customers, and EastNet knows how to reach only blue and yellow customers. The fact that they both peer with USNet is inconsequential; peering is a non-transitive relationship. Since peering is a reciprocal non-transitive relationship, EastNet and WestNet must peer with every other ISP or find another way of accessing every other ISP. 3.1.2 Physical interconnections for peering: The physical interconnections used for peering are categorized into two types: • • Public peering - Interconnection utilizing a multi-party shared switch fabric such as an Ethernet switch. Private peering - Interconnection utilizing a point-to-point interconnection such as a patch-cable or dark fiber between two parties Public peering: Interconnection utilizing a multi-party shared switch fabric such as an Ethernet switch.At these locations, multiple carriers interconnect with one or more other carriers across a single physical port. Historically public peering locations were known as network access points (NAPs), today they are most often called exchange points or Internet exchanges ("IXP" or "IX").public peering allows networks interested in peering to interconnect with many other networks through a single port.it is often considered to offer "less capacity" than private peering,but to a larger number of networks.
Private peering:
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Private peering is the direct interconnection between only two networks, across a Layer 1 or 2 media that offers dedicated capacity that is not shared by any other parties. Early in the history of the Internet, many private peers occurred across 'telco' provisioned SONET circuits between individual carrier-owned facilities. Today, most private interconnections occur at carrier hotels or carrier neutral colocation facilities, where a direct crossconnect can be provisioned between participants within the same building, usually for a much lower cost than telco circuits. Most of the traffic on the Internet, especially traffic between the largest networks, occurs via private peering. However, because of the resources required to provision each private peer, many networks are unwilling to provide private peering to "small" networks, or to "new" networks who have not yet proven that they will provide a mutual benefit. ISP Physical Interconnection Methods
Interconnection Method
Direct-Circuit Interconnection
Exchange-Based Interconnection
For direct-circuit interconnects, key issues center upon interconnection location(s) and who pays for and manages the interconnection. This becomes a material cost issue as traffic grows and circuits increase in size and cost. In either case, ISPs generally have the following goals for establishing peering: 1. Get peering set up as soon as possible, 2. Minimize the cost of the interconnection and transit costs, 3. Maximize the benefits of a systematic approach to peering. 4. Execute the regional operations plan as strategy dictates (may be architecture/network development group goal), and 5. Fulfill obligations of larger business agreement.
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3.2 ISP to ISP interconnect: Transit
ISP 1 needs to deliver its customers’ traffic to the rest of the internet, and the rest of the internet needs to know how to get to ISP 1’s customers. So, • • ISP 2 announces all the routes on the internet to ISP 1 ISP 1 announces just its customer routes to ISP 2
ISP 1 is a customer of ISP 2 Definition: Transit is the business relationship whereby one ISP provides (usually sells) access to all destinations in its routing table. Consider a simplistic Internet model below in figure 2. In this picture, EastNet purchases transit from USNet, and in return gets connectivity to all networks in USNet’s routing table. As a customer of USNet, USNet announces EastNet routes across all of its peering and transit interconnections.
Transit Relationship - selling access to entire routing table
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4. BORDER GATEWAY PROTOCOL
The Border Gateway Protocol (BGP) is the core routing protocol of the Internet. It works by maintaining a table of IP networks or 'prefixes' which designate network reachability among autonomous systems (AS). It is described as a path vector protocol. BGP does not use traditional IGP metrics, but makes routing decisions based on path, network policies and/or rulesets. BGP is a multi-vendor “open” protocol with multiple implementations, all mostly interoperable. It is the only actively used EGP on the Internet. The main design feature of BGP was to allow ISPs to richly express their routing policy, both in selecting outbound paths and in announcing internal routes.
Purpose of BGP:
• • • • To allow networks to tell other networks about routes (parts of the IP address space) that they are “responsible” for. Using “route advertisements”, or “promises” - also called “NLRI” or “networklayer reachability information”. Networks are “Autonomous Systems”. Identified in BGP by a number, called the ASN (“Autonomous System Number”) iBGP: When BGP speakers in the same AS form a BGP connection for the purpose of exchanging routing information, they are said to be running IBGP or internalBGP. IBGP speakers are usually fully-meshed. eBGP : eBGP sessions are established when peering with the different AS.
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5. VIRTUAL ISP
A Virtual ISP (vISP) purchases services from another ISP (sometimes called a wholesale ISP or similar within this context) that allow the vISP's customers to access the Internet via one or more Points of Presence (PoPs) that are owned and operated by the wholesale ISP. There are various models for the delivery of this type of service, for example, the wholesale ISP could provide network access to end users via its dial-up modem PoPs or DSLAMs installed in telephone exchanges, and route, switch, and/or tunnel the end user traffic to the vISP's network, whereupon they may route the traffic toward its destination. In another model, the vISP does not route any end user traffic, and needs only provide AAA (Authentication, Authorization and Accounting) functions, as well as any "value-add" services like email or web hosting. Any given ISP may use their own PoPs to deliver one service, and use a vISP model to deliver another service, or, use a combination to deliver a service in different areas. The service provided by a wholesale ISP in a vISP model is distinct from that of an upstream ISP, even though in some cases, they may both be one and the same company. The former provides connectivity from the end user's premises to the Internet or to the end user's ISP, the latter provides connectivity from the end user's ISP to all or parts of the rest of the Internet. A vISP can also refer to a completely automated white label service offered to anyone at no cost or for a minimal set-up fee. The actual ISP providing the service generates revenue from the calls and may also share a percentage of that revenue with the owner of the vISP. All technical aspects are dealt with leaving the owner of vISP with the task of promoting the service. This sort of service is however declining due to the popularity of unmetered internet access also known as flatrate.
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6. MULTIHOMING
It is a technique to increase the reliability of the Internet connection for an IP network. As an adjective, it is typically used to describe a customer, rather than an Internet service provider (ISP) network. There are several ways to multihome, separate from the actual protocols used to do so, amongst which the most important are: • Single Link, Multiple IP address (Spaces)
The host has multiple IP addresses (e.g. 2001:db8::1 and 2001:db8::2 in IPv6), but you only have one physical upstream link. When the single link fails, connectivity is down for all addresses. • Multiple Interfaces, Single IP address per interface
The host has multiple interfaces and each interface has one, or more, IP addresses. If one of the links fail that IP address is unreachable, the other will still work. Hosts that have multiple AAAA or A records enabled can then still be reachable at the penalty of having the client program time out and retry on the broken address. Existing connections can't be taken over by the other interface, as TCP does not support this. To remedy this, one could use SCTP which does allow this situation. However SCTP is not used very much in practice. • Multiple Links, Single IP address (Space)
This is what in general is meant with Multihoming. With the use of a routing protocol, in most cases BGP, the end-site announces this address space to its upstream links. When one of the links fails, the protocol notices this on both sides and traffic is not sent over the failing link any more. Usually this method is used to multihome a site and not for single hosts.
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Multiple Links, Multiple IP address (Spaces), no routing protocol like BGP
This approach uses a specialized Link Load Balancer (or WAN Load Balancer) appliance between the firewall and the link routers. No special configuration is required in the ISP’s routers. It allows to use all links at the same time to increase the total available bandwidth and detects link saturation and failures in real time to redirect traffic. Algorithms allow traffic management. Incoming balancing is usually performed with a real time DNS resolution.
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7.CONCLUSION
Today many new ISPs are coming up and thus there is a huge competition among them in providing good services at low cost to its customers. For this they are continuously upgrading their technology. The basic peering game does a good job of highlighting the issues ISPs face when peering. Several comments from ISPs offering enhancements add reality to the game at the cost of complexity. For example, ISPs capture market share in order to be an attractive acquisition target. Adding merger rules adds a real complexity, somewhat tangentially related to peering and transit. Adding rules for ISPs to buy/sell transit to each other similarly adds complexity but adds a negotiating dynamic that ISPs face today. Balancing the desire to explain and explore against the desire for the simulation to match reality has proven to be a challenge.
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8.REFERENCES
[1] “Maturation in a Free Market: The Changing Dynamics of Peering in the ISP Market“ by Jennifer DePalma [2] www.wikipedia.org [3] www.webopedia.com [4] ISP Survival Guide, Geoff Huston, Wiley Publishers
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