Network routing. Routing

Or gateway, is a network node with several IP interfaces (containing its own MAC address and IP address) connected to different IP networks, which, based on solving the routing problem, redirects datagrams from one network to another for delivery from the sender to the recipient.

They are either specialized computers or computers with several IP interfaces, the operation of which is controlled by special software.

Routing in IP networks

Routing is used to receive a packet from one device and forward it across the network to another device via other networks. If there are no routers on the network, then routing is not supported. Routers route (forward) traffic to all networks that make up the internetwork.

To route a packet, the router must have the following information:

• Destination address
• A nearby router from which it can learn about remote networks
• Available paths to all remote networks
• The best path to each remote network
• Methods for maintaining and checking routing information

The router learns about remote networks from neighboring routers or from the network administrator. The router then builds a routing table that describes how to find remote networks.

If the network is connected directly to the router, it already knows how to route the packet to that network. If the network is not directly connected, the router must learn (learn) access paths to the remote network using static routing (the administrator manually enters the location of all networks into the routing table) or using dynamic routing.

Dynamic routing is a routing protocol process that determines how a device communicates with neighboring routers. The router will update information about each network it learns. If a change occurs in the network, the dynamic routing protocol automatically informs all routers of the change. If static routing is used, the system administrator will have to update the routing tables on all devices.

IP routing is a simple process that is the same on networks of any size. For example, the figure shows the process of step-by-step interaction between host A and host B on another network. In the example, the user of host A requests the IP address of host B by ping. Further operations are not so simple, so let’s look at them in more detail:

• IN command line the user enters ping 172.16.20.2. On host A, a packet is generated using network layer protocols and ICMP.

• IP calls ARP to find out the destination network for the packet by looking at the IP address and subnet mask of host A. This is a request to the remote host, i.e. the package is not intended for the host local network, so the packet must be forwarded to the router to forward to the desired remote network.
• In order for host A to send a packet to the router, the host must know the hardware address of the router interface connected to the local network. The network layer passes the packet and hardware destination address to the data link layer to be framed and forwarded to the local host. To obtain a hardware address, the host looks up the location of the destination in its own memory, called the ARP cache.
• If the IP address has not yet been reached and is not present in the ARP cache, the host sends an ARP broadcast to look up the hardware address at IP address 172.16.10.1. This is why the first Ping request will usually time out, but the other four requests will succeed. Once an address is cached, there is usually no timeout.
• The router responds and reports the hardware address of the Ethernet interface connected to the local network. Now the host has all the information to forward the packet to the router over the local network. The network layer passes the packet down to generate an ICMP echo request (Ping) to link level, appending the packet with the hardware address to which the host should send the packet. The packet has source and destination IP addresses along with an indication of the packet type (ICMP) in the network layer protocol field.
• The data link layer forms a frame that encapsulates the packet along with the control information necessary for forwarding over the local network. This information includes the source and destination hardware addresses, as well as the value in the type field set by the network layer protocol (this will be the type field since IP uses Ethernet_II frames by default). Figure 3 shows a frame generated at the link layer and forwarded over the local media. Figure 3 shows all the information necessary to communicate with the router: source and destination hardware addresses, source and destination IP addresses, data, and the frame CRC checksum located in the FCS (Frame Check Sequence) field.
• The link layer of host A forwards the frame to the physical layer. There, zeros and ones are encoded into a digital signal and then transmitted over a local physical network.

• The signal reaches Ethernet interface 0 of the router, which is synchronized by the preamble digital signal to extract the frame. After constructing the frame, the router interface checks the CRC, and at the end of receiving the frame, compares the received value with the contents of the FCS field. In addition, it checks the transfer process for media fragmentation and conflicts.
• The destination hardware address is checked. Since it matches the router's address, the frame type field is analyzed to determine what to do next with this data packet. The type field specifies the IP protocol, so the router passes the packet to the IP protocol process running on the router. The frame is deleted. The original packet (generated by host A) is placed in the router's buffer.
• The IP protocol looks at the destination IP address in the packet to determine whether the packet is destined for the router itself. Since the destination IP address is 172.16.20.2, the router determines from its routing table that network 172.16.20.0 is directly connected to Ethernet interface 1.
• The router forwards the packet from the buffer to Ethernet interface 1. The router needs to frame it to forward the packet to the destination host. The router first checks its ARP cache to determine whether the hardware address has already been resolved during previous interactions with the given network. If the address is not in the ARP cache, the router sends an ARP broadcast request to Ethernet interface 1 to look up the hardware address for IP address 172.16.20.2.
• Host B responds with the hardware address of its network adapter to an ARP request. The router's Ethernet 1 interface now has everything it needs to forward the packet to its final destination. The figure shows a frame generated by the router and transmitted over the local physical network.

The frame generated by the router's Ethernet 1 interface has a source hardware address from Ethernet interface 1 and a destination hardware address for the host B network adapter. It is important to note that, despite changes in the source and destination hardware addresses, on each router interface that sent the packet, the IP addresses source and destination never change. The package is not modified in any way, but the frames are changed.

• Host B receives the frame and checks the CRC. If the check is successful, the frame is discarded and the packet is transferred to the IP protocol. It analyzes the destination IP address. Since the destination IP address is the same as the address set in Host B, the IP protocol examines the protocol field to determine the destination of the packet.
• Our packet contains an ICMP echo request, so host B generates a new ICMP echo reply with a source IP address equal to host B and a destination IP address equal to host A. The process starts again, but in opposite direction. However, the hardware addresses of all devices along the packet's path are already known, so all devices will be able to obtain the hardware addresses of the interfaces from their own ARP caches.

In large networks, the process is similar, but the packet will have to travel more hops on the way to the destination host.

Routing tables

In the TCP/IP stack, routers and end nodes make decisions about who to pass a packet to in order to successfully deliver it to the destination node, based on so-called routing tables.

The table is a typical example of a route table using network IP addresses for the network shown in the figure.

Routing table for Router 2

The table shows a multi-route routing table, since it contains two routes to network 116.0.0.0. In the case of constructing a single-route routing table, it is necessary to specify only one path to network 116.0.0.0 based on the lowest metric value.

As you can easily see, several routes with different parameters are defined in the table. You need to read each such entry in the routing table as follows:

To deliver a packet to the network with an address from the Network Address field and a mask from the Network Mask field, you need to send a packet from the interface with the IP address from the Interface field to the IP address from the Gateway Address field, and the “cost” of such delivery will be equal to the number from the field Metrics.

In this table, the "Destination Network Address" column indicates the addresses of all networks to which this router can transmit packets. The TCP/IP stack adopts the so-called one-hop approach to optimizing the packet forwarding route (next-hop routing) - each router and end node takes part in choosing only one packet transmission step. Therefore, each line of the routing table does not indicate the entire route as a sequence of IP addresses of the routers through which the packet must pass, but only one IP address - the address of the next router to which the packet must be transmitted. Along with the packet, responsibility for choosing the next routing hop is transferred to the next router. The one-hop approach to routing means a distributed solution to the route selection problem. This removes the restriction on the maximum number of transit routers along the packet's path.

To send a packet to the next router, knowledge of its local address is required, but in the TCP/IP stack, it is customary to use only IP addresses in routing tables to preserve their universal format, independent of the type of networks on the Internet. To find a local address from a known IP address, you must use the ARP protocol.

One-hop routing has another advantage - it allows you to reduce the size of routing tables in end nodes and routers by using the so-called default route (0.0.0.0), which usually occupies the last line in the routing table, as the destination network number. If there is such an entry in the routing table, then all packets with network numbers that are not in the routing table are sent to the router specified in the default line. Therefore, routers often store limited information about Internet networks in their tables, forwarding packets for other networks to the default port and router. The default router is assumed to forward the packet to backbone network, and routers connected to the backbone have complete information about the composition of the Internet.

In addition to the default route, there may be two types of special entries in the routing table - an entry about a host-specific route and an entry about the addresses of networks directly connected to the router ports.

A host-specific route contains a full IP address instead of a network number, that is, an address that has non-zero information not only in the network number field, but also in the host number field. It is assumed that for such an end node the route should be chosen differently from all other nodes in the network to which it belongs. In the case when the table contains different records about the progress of packets for the entire network N and its individual node, which has address N,D, upon arrival of a packet addressed to node N,D, the router will give preference to the entry for N,D.

Entries in the routing table related to networks directly connected to the router contain zeros (“connected”) in the “Metrics” field.

Routing Algorithms

Basic requirements for routing algorithms:

• accuracy;
• simplicity;
• reliability;
• stability;
• justice;
• optimality.

There are various algorithms for constructing tables for one-hop routing. They can be divided into three classes:

• simple routing algorithms;
• fixed routing algorithms;
• adaptive routing algorithms.

Regardless of the algorithm used to build the routing table, the result of their work has a single format. Due to this, in the same network, different nodes can build routing tables according to their own algorithms, and then exchange missing data with each other, since the formats of these tables are fixed. Therefore, a router using an adaptive routing algorithm can provide an end node using a fixed routing algorithm with path information to a network that the end node knows nothing about.

Easy routing

This is a routing method that does not change when the topology and state of the data transmission network (DTN) changes.

Simple routing is provided by various algorithms, typical of which are the following:

• Random routing is the transmission of a message from a node in any randomly selected direction, with the exception of the directions in which the message was received by the node.
• Flooding routing is the transmission of a message from a node in all directions except the direction in which the message arrived at the node. This routing guarantees short packet delivery time, at the expense of throughput degradation.
• Routing based on previous experience - each packet has a counter for the number of nodes passed, in each communication node the counter is analyzed and the route that corresponds to the minimum value of the counter is remembered. This algorithm allows you to adapt to changes in network topology, but the adaptation process is slow and ineffective.

In general, simple routing does not provide directional packet transmission and has low efficiency. Its main advantage is to ensure stable operation of the network in the event of failure of various parts of the network.

Fixed Routing

This algorithm is used in networks with a simple connection topology and is based on the manual compilation of a routing table by the network administrator. The algorithm often works effectively also for backbones of large networks, since the backbone itself may have simple structure with obvious the best ways The following algorithms distinguish packets in subnets connected to the backbone:

• Single-path fixed routing is when a single path is established between two subscribers. A network with such routing is unstable to failures and overloads.
• Multi-path fixed routing - several can be installed possible ways and a path selection rule is introduced. The efficiency of such routing decreases as the load increases. If any communication line fails, it is necessary to change the routing table; for this, several tables are stored in each communication node.

Adaptive Routing

This is the main type of routing algorithm used by routers in modern networks with complex topology. Adaptive routing is based on the fact that routers periodically exchange special topological information about the networks available on the Internet, as well as about the connections between routers. Usually, not only the topology of links is taken into account, but also their capacity and condition.

Adaptive protocols allow all routers to collect information about the topology of connections in the network, quickly processing all changes in the connection configuration. These protocols are distributed in nature, which is expressed in the fact that there are no dedicated routers in the network that would collect and summarize topological information: this work is distributed among all routers, the following algorithms are distinguished:

• Local adaptive routing - each node contains information about the link state, queue length and routing table.
• Global adaptive routing is based on the use of information received from neighboring nodes. To do this, each node contains a routing table, which indicates the transit time of messages. Based on information received from neighboring nodes, the table value is recalculated taking into account the queue length in the node itself.
• Centralized adaptive routing - there is some central node that collects information about the state of the network. This center generates control packets containing routing tables and sends them to communication nodes.
• Hybrid adaptive routing is based on the use of a table periodically sent by the center and on analyzing the queue length from the node itself.

Algorithm indicators (metrics)

Routing tables contain information that switching programs use to select the best route. What characterizes the construction of routing tables? What is the nature of the information they contain? This section on algorithm metrics attempts to answer the question of how an algorithm determines whether one route is preferable to another.

Routing algorithms use many different metrics. Complex routing algorithms can rely on multiple metrics when selecting a route, combining them in such a way that the result is one hybrid metric. The following are the metrics used in routing algorithms:

• Route length.
• Reliability.
• Delay.
• Bandwidth.

Route length.

Route length is the most common routing metric. Some routing protocols allow network administrators to assign arbitrary prices to each network link. In this case, the path length is the sum of the costs associated with each channel that was traversed. Other routing protocols define a "hop count," a metric that describes the number of trips a packet must make on its way from its source to its destination through network aggregation elements (such as routers).

Reliability.

Reliability, in the context of routing algorithms, refers to the reliability of each link in the network (usually described in terms of bit-to-error ratio). Some network links may fail more often than others. Failures of some network links can be resolved more easily or quickly than failures of other links. When assigning reliability ratings, any reliability factors can be taken into account. Reliability ratings are typically assigned to network channels by administrators. As a rule, these are arbitrary digital values.

Delay.

Routing latency typically refers to the length of time it takes for a packet to travel from its source to its destination across an internetwork. Latency depends on many factors, including the bandwidth of the intermediate links in the network, the queues at the port of each router along the packet's path, network congestion on all intermediate links in the network, and the physical distance over which the packet must travel. Because there is a conglomeration of several important variables, latency is the most common and useful metric.

Bandwidth.

Bandwidth refers to the available traffic capacity of any link. All other things being equal, a 10 Mbps Ethernet channel is preferable to any leased line with a 64 KB/s bandwidth. Although bandwidth is an estimate of the maximum achievable capacity of a link, routes passing through higher-bandwidth links are not necessarily better than routes passing through slower links.

Magnitude (and in calculations the following can be accepted:

■ for automated and mechanized hump sorting
stations 1.5-2.2 hours;

■ for non-mechanized stations 2.1-2.8 hours; „|____________ ;:_,___ , t ________ „„..

■ for humpless stations 4.0-5.0 hours.

In addition, when passing jets without processing, it must be taken into account that recycling carriages at stations and pass them without processing The costs are far from the same. Recycling requires sorting tracks, humps, hoods, locomotives, and a large staff of station workers.

Therefore, in order to take into account the economic costs of the options, the concept of the equivalent of car recycling was introduced. Savings from railcar recycling are expressed by the equivalent h in= 1.5-2.5, savings in locomotive hours and crew hours are expressed by h = 0.4-1.5.

Thus, the final formula for calculating the reduced car-hour savings per car is:

All calculations by definition T are conducted at the Ministry of Railways of Russia using electronic computer technology.

3.2. Organization of car flows from loading points

Types of routes, basic routing indicators

On railway networks are allocated several hundred main, decisive stations, at which 70 % loading, and about the same number of stations - 70 % unloading. At loading stations, powerful cargo flows are formed, which are included in the top ten most important cargoes: oil, forestry, coal, ore, construction, chemical and mineral fertilizers, grain, etc. The most effective way organization of car flows is transportation routing. It allows you to speed up the delivery of goods, reduce the need for a working fleet of cars, free passing stations from expensive work on processing cars, and therefore reduce operating costs in the transportation process.

The routes are distinguished:

According to the terms of the organization from the loading points;
■ for its intended purpose;

According to the terms of the application.

According to the conditions of the organization, the following routes are distinguished from the loading points:

Routes are distinguished by destination:

According to the terms of application, the routes are:

A high percentage of coverage by sender routing has such cargo as ore (more than 90%), coal and oil (about 70%), chemical and mineral fertilizers (more than 50%). Grain cargo is poorly routed (about 3 %).

If we analyze the distance traveled, then more than 57% of routes follow short distances(up to 400 km). And routes traveling over distances of more than 1,500 km make up only 10%. The indicated percentages cannot fully characterize the level of routing on the network, because one third of the routes go only to route bases, i.e. into spraying, which is less efficient compared to pure sender routing to the unloading station.

The quality of routing organization is assessed by the following indicator:

as routing level ^, where () m is the mass of goods sent on routes; 0, - total weight of shipped goods.

But it is much more expedient to take the ratio ^-p as the main indicator of the routing level, where 1 M is the average route distance

volume of cargo on shipping routes, km; I is the average distance of cargo, km.

Routing shipments from loading points is a highly efficient way to organize freight transportation.

Routing is the subject of a contract for the organization of cargo transportation by rail, therefore only the parties to the contract have the right to determine its content. It may provide for departure routes formed on a railway access track or on railway station, groups of cars for organizing stepped station or section routes, etc.

Below the origin route means a train composition of a specified weight or length, formed by the shipper on the railway access track of the organization or under an agreement with the railway at the railway station with the mandatory exemption of at least one technical station from processing such a train, provided for by the current plan for the formation of freight trains.

Departure routes pass through one or more sorting stations without processing, therefore, the delivery of cargo is accelerated, the work on reforming trains is reduced, the cost of transportation is reduced, the turnover of wagons is accelerated, the need for wagons is reduced, the safety of transported goods is better ensured, and the competitiveness of manufacturers of goods and railway transport increases.

Stepped routes are formed from wagons loaded by different shippers on the tracks of one or several stations of a section or junction. The rules for the transportation of goods along consignor routes by rail provide that in order to speed up the delivery of goods, reduce transport and operating costs, the transportation of goods can be carried out by consignor routes and be provided for in contracts for the organization of cargo transportation by rail. Sender routing is the basis for creating a network of logistics centers for Russian railways in the future.

The procedure for transporting goods along dispatch routes is established by the Rules for transporting goods along dispatch routes by rail.

Depending on the destination, departure routes are:

• direct - when transporting to one destination (transshipment) station to one or more consignees (freight cars addressed to each consignee must be part of a separate group);
• to spraying - when transporting by appointment to disbandment stations according to the plan for the formation of freight trains, or by appointment to points (stations) of route spraying announced by JSC Russian Railways, where carriages are addressed (indicating destination stations and consignee) at unloading stations to specific consignees, or by appointment to entry and distribution stations receiving fuel cargo, with further diverting of wagons to the unloading station.

The shipper agrees with the consignee on the possibility of accepting routes of a specified weight or length for unloading. If there is a change in the mass of the train (breaking point) in the direction of the station routes in the direction of decrease, the departure of the routes is organized from the core and the trailer part, which follows as part of the route to the turning point of the mass.

The core is the main part of the sending route of the established mass, which follows without reorganization to the destination railway station in the event of a change in the mass of the train along the route.

According to the conditions of circulation, sending routes are distinguished:

• circular trains with a constant train, which after unloading in the same train return to the same station or department for re-loading;
• circular trains with a variable composition, which, after unloading, return to the same station or department, while the number, type of cars and their purpose are maintained, but if necessary, some cars can be replaced by other similar cars.

The organization of circular routes significantly reduces the cost of preparing cars for loading, while reducing downtime of cars at loading points, since cars require minimal preparation for loading.

Transportation routing

1) by method of organization

2) as intended

3) by following distance

Organization of cargo transportation by routes

The development of sustainable loaded car flows through route transportation is taken into account when developing a train formation plan.

The shipper with an application for the transportation of goods submits to the Railway Directorate an application for the transportation of goods by routes in 3 copies in the prescribed form.

When considering an application, the compliance of the volumes of cargo presented for transportation with the established norms of weight and route length is checked.

1 copy accepted application for the transportation of goods by route is sent to the shipper

2 copies departure station manager

3 copies remains in DUD Railway

At the loading station of the route, in the transportation documents for wagons traveling as part of a route or core to one unloading station, a stamp is made with the stamp “Departure route No. ... direct.”

And the appointment at the spraying station with the stamp “Departure route No.... with spraying at the station...”

The procedure for supplying cars for loading and unloading routes, their formation, return of empty cars after unloading, technological standards for loading/unloading are established in contracts for the operation of non-public tracks and for the supply/removal of cars.

When organizing route transportation, one should take into account the technical equipment of cargo loading/unloading areas, weight standards, length of route trains, and other factors.

The shipper must agree with the consignee on the technological feasibility of accepting routes of the established weight and length for unloading; thanks to the development of transportation according to the direct option scheme, the mass length of the time of departure and arrival at the consignee's warehouses is agreed upon departure routes, which turns them into logistics trains.

Meaning, characteristics and classification of non-public railway tracks.

Railway PNP are intended to serve individual enterprises and institutions. They are related to common network railway Russia continuous rail gauge.

PNP. – this is a complex of devices, including track facilities, storage facilities, loading and unloading devices and mechanisms, weighing instruments, signaling and communication devices, etc.

The PNP must ensure, in accordance with the volume of work, uninterrupted loading and unloading, shunting work and rational use of cars and locomotives.

Here the process of transporting cargo, carried out by public transport, begins and ends; the main part of cargo operations is carried out on them. Also, the PNP carries out a large volume of in-plant transportation of finished products, raw materials and semi-finished products during the production process. These transportations are called technological. They are carried out, as a rule, at enterprises of ferrous and non-ferrous metallurgy and the chemical industry.

Another category of PNP includes PNP that is not related to technological intra-plant transportation. On such tracks, only cargo loading/unloading and shunting operations are performed.

The Charter provides that PNP not related to technological transportation may belong to the carrier or enterprises and organizations.

6. Basic requirements for railway PNP adjacent to public railway tracks

Railroad PNP and the structures and devices located on them must ensure shunting and sorting work in accordance with the volume of transportation.

Rhythmic loading and unloading, as well as rational use of railway transport and its safety.

The design and condition of structures and devices located at the POP must comply with building codes and regulations, ensure the passage of cars within the technical load standards permissible on railway tracks, as well as the passage of locomotives intended for servicing the railway POP.

The owner of the PNP ensures, at his own expense, their maintenance in compliance with the requirements of traffic safety and operation of railway transport, and also, together with the Civil Defense and State Enterprise, carry out the lighting of such tracks within the territory they occupy and in places where cargo is loaded and unloaded. The PNP is cleaned of debris and snow.

If a railway substation is supplied to the POP, the operation of which is also carried out on public railway tracks, the railway POP must comply with the requirements established for the railway POP and in certain cases are subject to mandatory certification.

Construction and reconstruction of the railway POP, devices intended for loading and unloading cargo, cleaning and washing of cars (containers), determination of the junction points of the railway POP to the railway POP is carried out in the manner established by the federal executive body in the field of railway transport (FAZhT) in agreement with the owner of the infrastructure to which the railway PNP is adjacent and the federal executive body in the field of transport (Ministry of Transport).

The construction of new railway stations is carried out in agreement with the executive authority of the constituent entity of the Russian Federation on the territory of which such railway tracks will be located.

The adjoining of public railway tracks under construction, new or restored railway PNP is carried out in the manner determined by the government of the Russian Federation.

Adjacent to the railway POP of the POP under construction in the manner determined by the federal executive body in the field of railway transport together with the federal executive body in the field of transport.

The contract for the operation of the railway PNP contains the following provisions:

1. Belonging to a non-public railway track;

2. Indication of the expanded length of the railway PNP in meters;

3. Description of the procedure for transmitting notification of the delivery of wagons;

4. Description of the procedure for the movement of trains on the railway PNP, including compliance with PTE, IDP, instructions for shunting work, ISI (signaling);

5. The number of cars to each group simultaneously handed over and the place of their transfer;

6. The procedure for exchanging information about the readiness of cars for assembly and the period for cleaning the cars by the carrier;

7. Standards for the technological period of wagon turnover (hours);

8. Unpaid technological time for performing initial/final operations included in the tariff, as well as unpaid time for delivering cars to loading (unloading) places, tender counterparty

9. Processing capacity for main types of cargo;

10. Distance for which the fee for supplying and cleaning wagons is charged

11. Measures for the development of transport facilities.

12. Types of fees paid by the owner for the supply and cleaning of wagons.

Container terminals

Container processing on the Russian railway network takes place at container terminals, which are part of the station territory, where: loading/unloading, sorting, storage, import/export, picking, technical and commercial inspection and maintenance, registration of cargo and transportation documents, forwarding documents, informing the consignee about the time of arrival of the container, as well as other operations ensuring the safety of the cargo.

The terminal may have one or more container areas, which include loading and unloading and crane tracks, a short-term storage area, lifting devices and machines, parking for trailers and semi-trailers.

There are 700 terminals in the network, 298 of which are open for processing large-capacity containers.

Depending on the type of work performed, containers can be classified as cargo, sorting or mixed. Freight containers process only local containers, sorting containers only transit containers, mixed containers of both.

Placement of containers in compliance with the rules for the design and safe operation of cranes, fire safety rules, dimensions and requirements related to the organization of routine repairs of containers and maintenance of cranes.

Medium-tonnage containers are installed on the site, as a rule, in one tier; large-tonnage containers, depending on the loading and unloading machines used and the strength of the area's coverage, can be installed in no more than 6 tiers. (most often 1-2).

The number of loading and unloading tracks, quantity, and linear dimensions of the platforms are determined by the volume of work, the nature of the operations and the means of mechanization.

The area of ​​container sites is calculated, but the norms established by the instructions on the design of stations and nodes. Container terminals should be adjacent to the station tracks on the side where the sorting devices are located or to the neck in parallel with the connecting track; it is advisable to have an exhibition track about 220 meters long, accommodating 50% of the container train.

It is necessary that the movement of vehicles at the terminal be continuous, and that vehicles do not cross the railway tracks at the same level.

Oversized cargo index

Oversized cargo index To indicate in transportation documents as well as in train documents data issued from a computer about zones and degrees of oversized cargo transported, the concept of oversized cargo index is introduced, which consists of 5 characters. Each sign of the oversize index (except for the first) indicates the degree of oversize. Oversized in any zone is indicated by the number 8.

Designation in the oversize index.

First character: always the letter H

Second character: degree of lower oversize (from 1 to 6)

Third character: degree of lateral oversize (from 1 to 6)

Fourth character: degree of upper oversize (from 1 to 3)

Fifth character: vertical oversized (8)

The absence of oversize in any zone, including the absence of vertical oversize, is marked with the number 0 in the corresponding sign of the oversize index.

For example, the oversize index H8480 means that the oversized cargo has lower and upper oversize, lateral oversize of the 4th degree, and there is no vertical oversize. In the full-scale sheet and telegram on the full-scale sheet, next to the train number, the train's oversize index is indicated. That is, the letter H and the codes of the greatest degrees of lower, lateral and upper oversize (taking into account the calculated) as well as the code for the vertical oversize (0 or 8) of cargo available on the train.

Definition and classification of routes

Transportation routing– is a highly effective way to optimize freight transportation. It ensures the fastest movement of goods from points of production to points of consumption. Reduces the work of technical stations to reorganize trains, wagon turnover, reduces the cost of transportation, and ensures the safety of transportation. On routes, wagons as part of full-fledged trains transit without reorganization all or part of the district and marshalling stations located between loading and destination stations.

In accordance with Article 13, a route is a train of a specified weight or length, formed in accordance with the rules technical operation Railway PTE and a plan for the formation of cars for a specific purpose, subject to passing through at least 1 technical station without processing.

Routes from loading points are classified according to the following criteria:

1) by method of organization

a) consignors, loaded and formed at 1 station or on 1 non-public route, by one or more shippers.

b) stepped, loaded by several GOs on non-public tracks with the merging of groups of cars at the junction station, or loaded at several stations of a node or section with merging at the reference station.

c) circular (turntables), train sets circulating between 1 loading and unloading station on the principle of shuttle movement.

2) as intended

a) straight lines, made up of cars traveling to 1 destination station

b) in a spray, consisting of cars traveling to several destination stations subject to disbandment at the nearest unloading area of ​​the technical station.

3) by following distance

a) network – following from the formation station to the destination station within two or more railway lines.

b) intraroad - within one railway.

The weight and length of network routes are established by JSC RZh/D, and internal roads by the head of the directorate, respectively, or his deputy. The weight and length of the route are determined by the shipper. The route can transport homogeneous cargo or cargo of several types.

Routing is the process of determining the path of information in communication networks. Routing is used to receive a packet from one device and transmit it to another device through other networks. A router or gateway is a network node with several interfaces, each of which has its own MAC address and IP address.

Another important concept is the routing table. A routing table is a database stored on a router that describes the mapping between destination addresses and the interfaces through which a data packet should be sent to the next hop. The routing table contains: the address of the destination node, the destination network mask, the gateway address (indicating the address of the router on the network to which the packet must be sent to the specified destination address), interface (the physical port through which the packet is transmitted), metric (a numerical indicator that specifies the priority route).

Entries in the routing table can be placed in three different ways. The first method involves using a direct connection in which the router itself determines the connected subnet. A direct route is a route that is local to the router. If one of the router's interfaces is connected directly to a network, then when it receives a packet addressed to such a subnet, the router immediately sends the packet to the interface to which it is connected. Direct connection is the most reliable routing method.

The second method involves entering routes manually. In this case, static routing takes place. A static route specifies the IP address of the next neighbor router or local egress interface that is used to route traffic to a specific destination subnet. Static routes must be set at both ends of the communication channel between routers, otherwise the remote router will not know the route along which to send response packets and only one-way communication will be organized.

And the third method involves automatic placement of records using routing protocols. This method is called dynamic routing. Dynamic routing protocols can automatically track changes in network topology. The successful operation of dynamic routing depends on the router performing two main functions:

1. Keeping your routing tables up to date
2. Timely dissemination of information about networks and routes known to them among other routers

The parameters for calculating metrics can be:

1. Bandwidth
2. Latency (time for a packet to travel from source to destination)
3. Loading (channel load per unit of time)
4. Reliability (relative number of errors in the channel)
5. Number of hops (transitions between routers)

If the router knows more than one route to the destination network, then it compares the metrics of these routes and transmits the route with the lowest metric (cost) to the routing table.

There are quite a lot of routing protocols - they are all divided according to the following criteria:

1. According to the algorithm used (distance vector protocols, communication channel state protocols)
2. By area of ​​application (for intra-domain routing, for inter-domain routing)

The channel state protocol is based on Dijkstra’s algorithm, I’ve already talked about it. I’ll tell you briefly about the distance vector algorithm.

So, in distance vector protocols, routers:

• Determine the direction (vector) and distance to the desired network node
• Periodically forward routing tables to each other
• In regular updates, routers learn about changes in network topology

Without going into too much detail, the link-state routing protocol is better for several reasons:

• Accurate understanding of network topology. Link-state routing protocols create a tree of shortest paths in a network. Thus, each router knows exactly where its “brother” is located. There is no such topology in distance vector protocols.
• Fast convergence. When routers receive an LSP link state packet, they immediately forward the packet further in an avalanche manner. In distance vector protocols, a router must first update its routing table before flooding it to other interfaces.
• Event-driven updates. LSPs are sent only when a change occurs in the topology and only information related to that change.
• Division into zones. Link state protocols use the concept of zone - the area within which routing information is distributed. This separation helps reduce the router's CPU load and structure the network.

Examples of link state protocols: OSPF, IS-IS.

Examples of distance vector protocols: RIP, IGRP.

Another global division of protocols by scope: for intra-domain IGP routing, for inter-domain EGP routing. Let's go through the definitions.

IGP (Interior Gateway Protocol) – internal gateway protocol. These include any routing protocols used within an autonomous system (RIP, OSPF, IGRP, EIGRP, IS-IS). Each IGP protocol represents one routing domain within an autonomous system.

EGP (Exterior Gateway Protocol) – internal gateway protocol. Provides routing between different autonomous systems. EGP protocols provide the connection of individual autonomous systems and the transit of transmitted data between these autonomous systems. Example protocol: BGP.

Let us also explain the concept of an autonomous system.

An autonomous system (AS) is a set of networks that are under a single administrative management and which use a single routing strategy and rules.

The autonomous system for external networks acts as a single object.

A routing domain is a collection of networks and routers that use the same routing protocol.

Finally, a picture explaining the structure of dynamic routing protocols.

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