Local Area Network Interconnection

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In this way the filtering database contains information about the only stations which are actually within the network, getting rid of information about old stations. Data-link-layer networks natively support mobility : if the station is moved, remaining within the same LAN, so as to be reachable through another port, the bridge has to be 'notified' of the movement by sending any broadcast frame e.

ARP Request , so that the backward learning algorithm can fix the filtering database. Windows systems tend to be more 'loquacious' than UNIX systems. Bridges have scalability issues because they are not able to organize traffic, and therefore they are not suitable for complex networks such as Wide Area Network :. From Wikibooks, open books for an open world. Category : Book:Local Area Network design. Namespaces Book Discussion. Views Read Edit View history.

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Edraw Infographic. Visio alternative. Electrical symbols. Flowchart symbols. Find reseller. Edraw Max. How it works. Within this technology model, the bilateral settlement becomes easier, as the model simplifies to the case where the terminating provider charges the originating provider a per-call minute cost within an accounting rate that has been bilaterally agreed between the two parties.

As both parties can charge each other using the same accounting currency, the ultimate financial settlement is based on the net outcome of the two sets of call minute transactions with the two call minute termination accounting rates applied to these calls. There is no requirement for the termination rates for the two parties to be set at the same level. Each provider invoices the originating end user for the entire call duration, and the financial settlements provide the accounting balance intended to ensure equity of cost distribution in supporting the costs of the calls made between the two providers.

Where there is equity of call accounting rates between the two providers, the bilateral inter-provider financial settlements are used in accordance with originating call minute imbalance, in which the provider hosting the greater number of originating call minutes pays the other party according to a bilaterally negotiated rate as the mechanism of cost distribution between the two providers.

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This accounting settlement issue is one of the drivers behind the increasing interest in Voice-over IP solutions, because typically no accounting rate settlement component exists in such solutions, and the call termination charges are cost-based, without bilateral price setting. In those cases where accounting rates have come to dominate the provider's call costs, Voice-over IP is perceived as an effective lever to bypass the accounting rate structure and introduce a new price point for call termination in the market concerned.

The second model, rarely used in telephony interconnection, is that of Sender Keep All SKA , in which each service provider invoices their originating client's user for the end-to-end services, but no financial settlement is made across the bilateral interconnection structure. Within the bilateral settlement model, SKA can be regarded as a boundary case of bilateral settlements, where both parties simply deem the outcome of the call accounting process to be absolutely equal, and consequently no financial settlement is payable by either party as an outcome of the interconnection.

The third model is that of transit fees, in which the one party invoices the other party for services provided. For example, this arrangement is commonly used as the basis of the long-distance provider local access provider interconnection arrangements. Again, this can be viewed as a boundary case of a general bilateral settlement model , where in this case the parties agree to apply call accounting in only one direction, rather than bilaterally. The international telephony settlement model is by no means stable, and currently significant pressure is being placed on the international accounting arrangements to move away from bilaterally negotiated uniform call accounting rates to rates separately negotiated for calls in each direction of a bilateral interconnection.

Simultaneously, communications deregulation within many national environments is changing the transit fee model, as local providers extend their network into the long-distance area and commence interconnection arrangements with similar entities. Criticism also has been directed at the bilaterally negotiated settlement rates, because of the observation that in many cases the accounting rates are not cost-based rates but are based on a desire to create a revenue stream from accounting settlements.

A number of critical differences exist between the telephony models of interconnection and the Internet environment, which have confounded all attempts to cleanly map telephony interconnection models into the Internet environment.

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The downstream ISP resells this service to its clients. However, given two ISPs that interconnect, the decision as to which party should assume the upstream provider role and which party should assume the downstream customer role is not always immediately obvious to either party, or even to an outside observer. However, this factor is not the only possible one within the scope of the discussion. One ISP may host significant content and may observe that access to this content adds value to the other party's network, which may be used as an offset against a more uniform customer relationship.

In a similar vein, an ISP with a very large client population within a limited geographic locality may see this large client base as an offset against a more uniform customer relationship with the other provider. In many ways, the outcome of these discussions can be likened to two animals meeting in the jungle at night. Each animal sees only the eyes of the other, and from this limited input, the two animals must determine which animal should attempt to eat the other! An objective and stable determination of which ISP should be the provider and which should be the client is not always possible.

In many contexts, the question is inappropriate, given that for some traffic classes the respective roles of provider and client may swap over. The question often is rephrased along the lines of, "Can two providers interconnect without the implicit requirement to cast one as the provider and the other as the client?

Local Interconnect Network (LIN) Overview and Training

One potential accounting model is based on the observation that a packet incurs cost as it is passed through the network. For a small interval of time, the packet occupies the entire transmission capacity of each circuit over which it passes. Similarly, for a brief interval of time, the packet is exclusively occupying the switching fabric of the router.

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Local network interconnection schemes and their availability analysis - IEEE Conference Publication

The more routers the packet passes through, and the greater the number and distance of transmission hops the packet traverses, the greater the incurred cost in carrying the packet. A potential settlement model could be constructed from this observation. The strawman model is that whenever a packet is passed across a network boundary, the packet is effectively sold to the next provider.

The sale price increases as the packet transits through the network, accumulating value in direct proportion to the distance the packet traverses within the network. Each boundary packet sale price reflects the previous sale price, plus the value added in transiting the ISP's infrastructure.

Ultimately, the packet is sold to the destination client. This model is indicated in Figure Financial inter-provider settlement via packet cost accounting.

As with all strawman models, this one has a number of critical weaknesses, but let's look at the strengths first. An ISP gains revenue from a packet only when delivered on egress from the network, rather than in network ingress. Accordingly, a strong economic incentive exists to accept packets that will not be dropped in transit within the ISP, given that the transmission of the packet only generates revenue to the ISP on successful delivery of the packet to the next hop ISP or to the destination client.

This factor places strong pressure on the ISP to maintain quality in the network, because dropped packets imply foregone revenue on local transmission. Because the packet was already purchased from the previous provider in the path, packet loss also implies financial loss.

Strong pressure also is exerted to price the local transit function at a commodity price level, rather than attempt to undertake opportunistic pricing. If the chosen transit price is too great, the downstream provider has the opportunity to extend its network to reach the next upstream provider in the path, resulting in bypassing the original upstream ISP and purchasing the packets directly from the next hop upstream source. Accordingly, this model of per-packet pricing, using a settlement model of egress packet accounting, and locally applied value increments to a cumulative per-packet price, based on incremental per hop transmission costs, does allow for some level of reasonable stability and cost distribution in the inter-provider settlement environment.

However, weaknesses of this potential model cannot be ignored. First, some level of packet drop is inevitable irrespective of traffic load. Generally, the more remote the sender from the destination, the less able the sender is to ascertain that the destination address is a valid IP address, and the destination host is available.

Interconnection, Peering, and Settlements

To minimize the liability from such potential packet loss, the ISP should maintain a relatively complete routing table and only accept packets in which a specific route is maintained for the network. More critical is the issue that the mechanism is open to abuse. Packets, which are generated by the upstream ISP, can be transmitted across the interface, which in turn results in revenue being generated for the ISP. Of course, per-packet accounting within the core of the network is a significant refinement of existing technology.

Within a strict implementation of this model, packets require the concept of an attached value that ISPs augment on an ingress-to-egress basis, which could be simplified to a hop-by-hop value increment. Implementations feasibly can use a level of averaging to simplify this by using a tariff for domestic transit and a second for international transit. These traffic-based metrics do exhibit some weaknesses because of their inability to resist abuse and likelihood of exacting an inter-provider payment even when the traffic is not delivered to an ultimate destination.

Of more concern is that this settlement regime has a strong implication in the retail pricing domain, where the method of payment on delivered volume and distance is then one of the more robust ways that a retail provider can ensure that there is an effective match between the inter-provider payments and the retail revenue. Given that there is no intrinsic match of distance, and therefore cost, to any particular end-to-end network transaction, such a retail tariff mechanism would meet with strong consumer resistance.

Does an alternative settlement structure that can address these weaknesses exist?


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One approach is to perform significantly greater levels of analysis of the traffic as it transits a boundary between a client and the provider, or between two providers, and to adopt financial settlement measures that match the type of traffic being observed. Such detailed accounting of traffic passed across a provider boundary could allow for a potential settlement structure based on duration call minutes , or volume call volumes.


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  6. Although such settlement schemes are perhaps limited more by imagination in the abstract, very real technical considerations must be borne to bear on this speculation. For a client-facing access router to detect a TCP flow and correctly identify the TCP session initiator requires the router to correctly identify the initial SYN handshake, the opening packet, and then record all in-sequence subsequent packets within this TCP flow against this accounting element.

    This identification process may be completely impossible within the network at an inter-provider boundary. The outcome of the routing configuration may be an asymmetric traffic path, so that a single inter-provider boundary may see only traffic passing in a single direction. However, the greatest problem with this, or any other traffic accounting settlement model, is the diversity of retail pricing structures that exist within the Internet today. Some ISPs use pricing based on received volume, some on sent volume, some on a mix of sent and received volume, and some use pricing based on the access capacity irrespective of volume.

    This discussion leads to the critical question when considering financial settlements: Considering that the end client is paying the local ISP for comprehensive Internet connectivity, when a client's packet is passed from one ISP to another at an interconnection point, where is the revenue for the packet? Is the revenue model one where the packet sender pays or one the packet receiver pays?