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Spend between terminal system and intermediary system based on ISO8473
(ES-IS)
1. Introduction 2
2, application range 3
3. Reference 3
4, definition 4
4.1 Reference Model Definition 4
4.2 Network layer structure definition 4
4.3 Network layer address definition 4
4.4 LAN Definition 4
4.5 Supplement Definition 5
5. Code and abbreviation 5
5.1 Data Unit 5
5.2 Protocol Data Unit 5
5.3 Protocol Data Unit Part 5
5.4 parameter 6
5.5 Miscellaneous 6
6. Agreement Overview 6
6.1 Information provided by the agreement 6
6.2 Subsites 6
6.3 Address 6
6.4 Agreement assumes an existing service 7
6.5 Services available in local environment 7
6.6 Subnet Type 8
7. Agreement function 9
7.1 Protocol Timer 9
7.2 Configuration Report Function 10
7.3 Configuration Record Function 11
7.4 Old Configuration Clear Function 11
7.5 Configuring Query Function 11
7.6 Configuring Response Function 12
7.7 Redirection Request Function 12
7.8 Redirect Recording Function 13
7.9 Redirection Refresh Features 13
7.10 Old Redirection Clear Function 13
7.11 PDU Head Error Detection 13
7.12 Function Classification 14
8. The structure of the PDU and the encoding 14
8.1 Structure 14
8.2 Fixed part 15
8.3 Network Address Part 16
8.4 Subnet Address Section 17
8.5 optional part 18
8.6 end system Hello PDU 19
8.7 Mediation System Hello PDU 20
8.8 Redirect PDU 21
Appendix A Technical Support Material 23
A.1 Timer use 23
A.2 Refresh and timing 24 routing redirection information 24
A.3 System Initialization 25
A.4 Optimization of Redirection Clearance 25
1 Introduction
This Agreement is one of an international standard that is used to facilitate the interconnection of the open system. This set of standards contains reaching
The services and protocols required for this purpose are.
This Agreement has fully considered the relevant layers defined in an open system interconnect reference model and international network organizations.
The defined network structure. In particular, this agreement is a network layer protocol. It allows end systems and intermediaries
Exchange configuration and routing information between the system to facilitate the route and relay operation of the network layer.
Communication between network layers between network layers and intermediary systems is separately considered. This Agreement is special
The former discussions. If an agreement is attached to the agreement between the intermediary system, the functionality of the network layer will be greatly enhanced. But
This Agreement is also very useful without this additional agreement.
The ES-IS protocol provides a way to address the following issues:
1. How does the end system are not directly connected to another end system, this terminal system finds an intermediary system
The existence and reachability and pass it to transfer NPDUs to another.
2. Since the NSAP address does not provide the destination address in the subnet, how to find the same subnet
Another end system.
3, how the intermediary system finds the existence of end systems in each subnet thereof directly connected.
The ES-IS protocol assumes the presence of the following:
1. The subnet itself can smoothly complete the job to send information to the subnet connection point in this website.
2, the subnet itself cannot rely on the NSAP address to communicate with the destination address within the entire network.
Note: Due to the above reasons, application layer communications cannot directly utilize the functions provided by this protocol.
The ES-IS protocol is not connected, it is designed to use:
1. Reduce status information needed before communication between terminal systems.
2. Reduce the memory space required to store routing information on the end system.
3. Reduce the complexity of the routing algorithm. This Agreement is designed to provide a close relationship with a protocol that provides connectionless network services. Due to routes and communication
The species are closely related, so when the network layer is not using the ISO protocol, this agreement may not provide a letter to the routing needs.
interest.
2, application range
International standards provide an agreement to maintain the road for end systems and intermediary system for network layers using ISO8473.
By information. The protocols mentioned here are services that require no connection.
This standard indicated:
A) Configuration between the network entity of the terminal system and the intermediary system and the transfer process of routing information;
b) Coding of protocol data units used in configuration and routing information;
c) The correct explanation process of the protocol control information, and
d) Function requirements with the standard consistency.
These processes are defined as follows:
A) The interaction process of the exchange protocol data unit between terminal systems and intermediaries;
b) The interaction process of exchanging subnet service primitives between network entities and next service providers.
This Agreement does not transmit the protocol element and algorithm for the passage of routing and information in the intermediary system. These features are this
The agreement cannot be affected.
3. reference
ISO7489 Information Processing System ------ Open System Interconnection ------ Basic reference.
DIS7489 / DAD1 Information Processing System ------ Open System Interconnection ------ ISO7489 Standard Supplement (About
Connection).
ISO8348 information processing system ------ Inter-system telecommunications and information exchange ------ Supplement for network service definitions
(About connection transmission).
ISO8348 / AD2 information processing system ------ Inter-system telecommunications and information exchange ------ Supplement for network service definitions
(About the network layer address).
ISO8473 information processing system ------ Inter-system telecommunications and information exchange ------ Provide connectionless network services
protocol.
DIS8648 Information Processing System ------ Inter-system telecommunications and information exchange ------ internal organization of the network layer.
SC21 / N965 OSI Framework Management ------ No.7 Work.
DIS8802 LAN.
First part review
4, definition
4.1 Reference Model Definition
This article uses the following concept (defined by ISO7489):
a) Network layer
b) Network Service Access Point
c) Network Service Access Point Address
d) Network entity
e) route
f) Network Agreement
g) Network delay
h) Network protocol unit
4.2 Network layer structure definition
This article uses the following concept (defined by DIS8648):
a) subnet
b) end system
c) intermediary system
d) Subnet Service
e) Subnet access protocol
f) Subnet Independent Convergence Agreement
4.3 Network layer address definition
This article uses the following concept (supplemented by DIS8348 / DAD2, network service (about network layer address)
Righteous):
a) subnet address
b) Subnet access point
4.4 LAN Definition
This article uses the following concept (defined by the DIS8802 LAN):
a) multicast address
b) Broadcast address
4.5 Supplemental Definition
In this article, the following definitions apply:
Configuration: The end system and intermediary system belonging to the same subnet (defined by the term "system type", involving network service
A collection of communication between the access point address, network entity, system, and sub-network connection points.
Network entity title: Network entity identifier, which has the same syntax structure as the network service access point, it can be accurate
Define end systems or intermediaries in a network entity.
5. Code and abbreviation
5.1 data unit
PDU protocol data unit
SNSDU subnet service data unit
5.2 protocol data unit
ESH PDU end system Hello protocol data unit
ISH PDU Mediation System Hello Protocol Data Unit RD PDU Redirection Protocol Data Unit
5.3 Protocol Data Unit
NPID network layer protocol identifier
LI length indication
V / P version / protocol extension identifier
TP type
CS check
NETL network entity title length
NET network entity title
DAL destination address length
DA destination address
SAL source address length
SA source address
Best route of BSnpal destination
Best route subnet address for BSnpa destination
HT keep timer
5.4 parameters
CT configuration timer
RT redirection timer
5.5 miscellaneous
ES end system
IS mediation system
SN subnet
SNACP subnet access protocol
SNICP subnet independent convergence protocol
6. Overview of the protocol
6.1 Information provided by the protocol
This Agreement provides two information to network entities to support its operation:
a) configuration information;
b) Routing redirection information
The configuration information allows the end system to find the existence and accessibility of the intermediary system, and allow the intermediary system to discover the storage of the end system.
Ins and reachability. This discovery is dynamic, except for the establishment of a network entity identifier (this is the network protocol data.
The artificial interference in the process of unit routing is required).
The configuration information also allows the terminal system to obtain the other party's information without the intervention of the intermediary system.
Note: The term "configuration information" is not broad configuration (such as the same as the OSI system management), but only refers to
The features specifically defined here.
Routing Redirection Information is used by the intermediary system to notify the terminal system to pass NPDU to a flash.
ground. This better route may be another IS in the same subnet, or it may be the destination system itself (if
The destination system is in the same subnet in the same subnet and the source system). It also makes the intermediary system simplifies the route decision of the end system.
And improve the efficiency of the routing decision because ESS can use a better IS and subnet during transmission.
6.2 Subcommitte
A network entity can choose to support configuration information or routing redirection information, or both support, or not.
If you support configuration information, you don't need the entire subnet to which the network entity belongs is configured.
6.3 Address
The parameters involved in the source address and destination address of this international standard are the OSI network service access point address. Phrase
And semantics are described in dedicated ISO8348 / DAD2.
6.4 Agreement assumes that the existing service
The services required by this Agreement are defined by the primitives in the form:
SN_UNITDATA .REQUEST
. Indication
SN_DESTINATION_ADDRESS,
Sn_Source_Address,
SN_QUALITY_OF_SERVICE,
SN_USERDATA
Note: These service primitives are used to describe the protocol mechanism and the following solid network (or rely on convergence)
Abstract interfaces between the subnets on the solid network or the real data link to provide the required service).
6.4.1 subnet address
The source address and destination address indicate the access point of the public or private subnet (called subnet access points). Subnet address
Definitions are made in each subnet. This Agreement is designed to take into account the subnets should support broadcast, multicast, or other forms.
Address mode. As a complementary address of the single, parameter SN_DESTINATION_ADDRESS may be the following many more items
One of the address of the address:
All end system network entities
All intermediary system network entities
When a solid net does not support a broadcast mode or other multi-purpose address transmission mode, the network can use convergence to support multiple transmissions to these destinations.
When the sn_destination_address parameter in the SN_UNITDATA.REQUEST primitive indicates the multi-destination address,
The value of the same parameter in its corresponding SN_UNITDATA.Indication primitive should not change.
In addition to the features mentioned above, the syntonym and semantics of subnet addresses are not defined in this Agreement.
6.4.2 Subnet User Data
Sn_userdata is a plurality of bytes placed in a certain order, these bytes are transparent between the specified subnet access points.
lost.
This Agreement requires that the system supports providing the smallest service data unit that has no connection network service.
6.5 Services that should be provided by local environment
The agreement requires timetable events for timer service support protocol entities.
Three primitives related to the S-timer:
1.S-Timer Request;
2. S-TIMER RESPONSE; and
3. S-Timer Cancel.
S-Timer Reques primitive indicates a timer that initializes a specified name, record and keeps designation length
A period of time.
The S-Timer Response primitive is generated locally, and it indicates that the delay time has arrived.
S-Timer Cancel primitives Indicates the local environment to cancel the timer service. If the parameter is not explained, all specified names
The timer of the word will be canceled. If there is no timer to match the parameter, the primitive will not cause any action.
The parameters of the service primitive of the S-timer are shown in the following table:
S-Timer .Request
.RESPONSE
S-Time,
S-Name,
S-SUBScript
S-Name,
S-SUBScript
The Time parameter indicates the living cycle of the timer, and the Name parameter gives each timer a tag, Subscript
The number gave each timer to assign a value to make the timer of the same name can distinguish, the Name and Subscript parameters are constituted.
The timer is unique to the reference.
If the timer is combined with a certain protocol function, the timer will be defined in the protocol function.
Note: This international standard does not specify the value of the timer. Any inference related to this is not forced. select
Time device parameters should enable service quality to guarantee and meet all kinds of characteristics required by various services.
6.6 subnet type
In order to assess the applicability of the protocol under various configurations of the specific end system, intermediaries, and subnets, three are defined.
General subnet:
1. Point-to-point network;
2. Broadcast net;
3. General topology subnet.
These three types are discussed below:
6.6.1 point to point net
A point-to-site network supports two systems. These two systems can be two end systems or one end system and a single
Independent intermediary system. A data link connected to the two network entities is an example of a point-to-point network.
Point the configuration information of the idea net. In the point-to-point net, the configuration information of the protocol notifies the network entity being communicated.
Next:
1. Whether the topology is only composed of two end systems; or
2. Is there one of the system is an intermediary system
Note: In the point-to-point net, if the two systems are an intermediary system, the protocol is not applicable, replaced
Is the IS-IS protocol. But this is not to say that configuration information in IS-IS does not work.
The intermediary system receives the NSAP address of the end system, which makes the accessibility information and route of these NSAP addresses
The degree can be distributed into other intermediary systems, so that the routing calculation is possible.
6.6.2 Broadcast Net
A broadcast subnet supports any number of end systems and intermediaries, and can respond
Sn_Unitdata.Request, transmit SNPDU to all of these systems or some of its subsets. A typical broadcast
An example of the network is the first class of DIS8802.
The configuration information in the broadcast subsidiary. In the broadcast subnet, the configuration information of the protocol is used to notify the information of the network entity being communicated:
1. Notify the reachability of each intermediary system in the end system subnet, network entity title and SNPA
site.
2. Notify the intermediary system end system NSAP address and subnet address. Once the intermediary system gets these
Information, the accessibility information and routing metrics of the NSAP are spread to other intermediary systems to calculate the road
by.
3. If a mediation system is missing, the end system is inquiry in the broadcast network, see the specific NSAP in the loan network.
Whether it can be reached, if it can be reached, which SNPA address is used to connect.
Routing redirection in the broadcast network. The broadcast network uses routing to reach the intermediary system to notify the intermediary system to arrive.
A better route for a NSAP. This route may be another intermediary system in the subnet, or the destination system
Independent itself.
6.6.3 General Topology Subnet
A general topology subnet supports any of the number of end systems and intermediaries, but it is not as supported by the broadcast subnet.
Connected multi-address transfer. The X.25 and ISO8208 belong to this type.
Note: The key difference between the broadcast subsidiary and the general topological subnet is to reach a potential larger through multiple transmission.
The overhead used by the subnet set. In the general topological subnet, the overhead is assumed to be close to the transfer of a PDU to the subnet.
All SNPAs. Instead, in the broadcast subnet, the overhead is assumed to be close to one of the transfer of a PDU to the subnet.
SNPA. There is of course case where the extreme cases between these two is certain, at this time, it can be used as a broadcast subnet, also
It can be used as a general topology subnet.
General Topology of configuration information in the subnet. In the general topological subnet, configuration information is generally not used because it is very occupied.
Subnet resources.
The network of general topology subsets is redirected. General topological subnets use routing redirect to allow intermediaries to notify the terminal system
Unfair to a destination NSAP better route. This route may be another intermediary system, or the destination system
(If it is in the same subnet with the source system).
Second part agreement specification
7. Agreement function
This section describes some of the features in the protocol. Not all applications require all of these functional support. 7.21
The section pointed out which function should be ignored, and it is also pointed out that the correct behavior is in a certain function that does not work properly.
7.1 protocol timer
Many protocol functions are based on timer. This means that these functions can only be performed within the time of timer restrictions.
The two most important timers are defined in the protocol: Configure Timer (CT) and Keep Timers (HT).
7.1.1 Configuring Timers
Configuring Timers is a local timer (the timer of each system remains independent) to perform configuration reporting work.
can. This timer determines what kind of frequency used to report its usability to other systems within the subnet. set
The shorter time, the more other systems in the subnet can know the availability of the system. The increase in responsiveness is in
The use of resources in the subnet and the resource within the receiving system.
7.1.2 Keep the timer
Keep the timer is applied to configuration information and routing redirection information. Keep the value of the timer set in the source of the information,
Transfer in the appropriate PDU. The recipient of the information maintains this information during timing. When timing timing, expire
Configuration or routing redirection information must be lost to ensure the correctness of the protocol.
More principles and applications about these timers can be found in Appendix 10.
7.2 Configuring Report Features
This feature is used to report our accessibility and the current subnet address. This feature
The timer time each time ES or IS is time is called. It is a query PDU when receiving the configuration of other end systems.
It will also be called.
7.2.1 End System Configuration Report
One end system creates an ESH PDU and transmits all NSAP it serves. It is still in the ESH PDU
Send a Sn_UnitData.Request as a subnet service data unit for the subnet.
Note: Send an ESH PDU separately to each NSAP is due to the lack of network entity headings and NSAP addresses.
contact. If all NSAP addresses are designated as subdomains of the domains represented by the network entity title representation of the local network entity, each ESH PDU can be converted to include an end system network entity title. The internet
The entity title suggests which NSAPs in the end system exist.
Keep the timer is set to be twice the configuration timer, and the value of this variable is large enough. Make even
The ESH PDU of his system is discarded (due to lack of resources), or in the subnet is lost, the configuration information can still be
save. This value must be small enough, so that the intermediary system can reply to a terminal that is going to be available or unavailable.
system.
The parameter SN_DESTINATION_ADDRESS is set to the group address, which means "all intermediary system network entities", which makes
Available in a wide range of broadcasts can be sent to all arrival intermediary systems.
Note: The actual value used to indicate the "all the intermediary network entities" Sn_Destination_Address is
The network is related and each subnet is different. It means the above meaning or "all end system" in some widely used subnets
Network entity. "Let these value standardization is of course a good thing.
7.2.2 Intermediary System Configuration Report
One intermediary system creates a ISH PDU containing the network entity title and sending one
Sn_unitdata.Request as Snsdu.
Keep the timer is set to approximate the intermediary system configuration timer parameters. This variable is set enough
Large, make even if all ISH PDUs are discarded (due to lack of resources), or in the subnet is lost, configuration information
It is still saved. This value must be sufficiently small, so that the end system can quickly terminate the use of failed intermediary systems to resist
The generation of "black hole" in the network.
The parameter SN_DESTINATION_ADDRESS is set to the group address, indicating "all end system network entities", which makes
One transmission on the broadcast subsidy can be sent to all accessible end systems.
7.3 Configuring Record Features
Configuration Record Function Receives ESH or ISH PDUs, extracts configuration information, routed by local network entities
The related configuration information is added or modified. If the storage space is insufficient, these PDUs will be lost and there will be no errors.
Information report.
Note: As described in the agreement, the end system receives and only records ISH PDU, and the intermediary system receives and only
Handling ESH PDU. If necessary, one end system can also handle the ESH PDU (in the broadcast network, adopting
When the group address can be easily implemented). Doing so allows some potential performance of the network to improve, but spending
More storage space on the end system also makes the processing cycle grow long. The end system records configuration information of other end systems.
It is possible to directly route NPDUs on the end system within the subnet without the redirection of the intermediary system.
Similarly, the intermediary system can also choose to accept ISH PDUs for other intermediaries, which makes the protocol as
A complete IS-IS routing protocol initialization and topology maintenance section.
The above two may be discussed in the future.
7.4 Old Configuration Clear
The old configuration clearance function is used to perform the configuration entry in the routing library that has expired. ES
Or the IS keep timer expires, this feature will clear the relevant portions of the routing library of local network entities.
7.5 Configuring Query Features
Configuring Query Functions Perform:
1, the end system is in the broadcast subnet;
2, there is no IS in the current subnet (for example, since the last old configuration clearance function, the old information is not cleared
Can receive any ISH);
3, the function of the network layer routing PDU needs to get the SNPA address to pass the PDU to a NSAP; and
4, the SNPA address cannot be obtained locally, and it cannot be found in the local table.
Note: There is a very common, some isolated local area networks have no intermediary systems to get routing information. If the intermediary system is temporarily unreachable, communication within the local area is impossible, unless each end system or subnet all NSAP
Artificially join the SNPA address.
When the end system needs to send an NPDU to a SNPA unknown destination NSAP, it will put one
Sn_unitdata.Request is sent to the NPDU in the NPDU when user data (Sn_UserData) is sent. one of them
The SN_DESTINATION_ADDRESS parameter is set to represent "all end system network entities" group addresses.
Next, the system will receive an ESH PDU containing the NSAP address and its corresponding SNPA address.
(See Section 7.6). In this case, the end system performs the configuration recording function on the NSAP. Use the specified SNPA,
You can send a PDU to this NSAP. If the ESH PDU is not received, the end system will consider that the NSAP is unreachable.
As for how many times to perform, how many times is to make, and how long to wait for how long it is waiting for it,
The discusses have not specified for this.
7.6 Configuring Response Function
When one end system in the broadcast subnet receives a Sn_Destination_address parameter is set to "all end
The NPDU representing the Sn_UnitData.Indication meaning of the network entity "and the NSAP carried in this NPDU
It is exactly the system all, the configuration response function begins. This feature is the configuration query function described in 7.5.
The execution occurs.
This system generates a similar ESH PDU generated by the configuration report function (see 7.2.1), and its content is
Offs the system. The end system generates a Sn_UnitData.Request, and the destination address is indicated as it received.
The source address of the NPDU is sent out.
7.7 Redirection request function
This feature only exists in the intermediary system and is closely related to its routing function and relay function relationship, and "PDU routing)
Function "is also related. This feature starts execution after the" PDU Routing Function "calculates the next hoot of the data PDU.
When the intermediary system is preparing to forward an NPDU, it first checks Sn_Source_Address in the NPDU. Such as
If this parameter is not an end system address of a local subnet (judgment by querying the configuration information obtained by querying the configuration record function
The NPDU is not further processed.
If the NPDU is obtained directly from one end system, the route of the intermediary system and the output of the relay function need
Be checked. The output information contains the following information:
1. A local subnet identifier, the transmission of the NPDU is passed by this subnet;
2, a intermediary system network entity title and subnet address, the NPDU is sent through this intermediary system; or
3, the subnet address of the destination system.
The redirection request function should be able to determine that the NPDU that you are about to forward can be sent directly from the source system.
Network entity. If any of the following conditions are true, the source system will be inform with a better route (by sending one
RD PDU to this system):
1. Next Jump point to the destination system and the destination in the source system subnet is directly up; or
2, the next hop pointing to a mediation system and the system is in the same subnet in the same subnet with the source system.
If there is a better routing, the intermediary system will first do general processing and forward it for the received NPDU. Course
After it generates an RD PDU and writes an NPDU destination address in the next, the subnet address where the next hop is
ES redirected IS network entity title (if this information can be omitted when redirected directly to destination system),
Keep time, quality, priority, security parameters (these are simply copied from NPDU). maintain
Time is set to the time of the local redirect timer. How to choose time for the redirect timer is described in Appendix A.
If there is not enough resource to generate and send an RD PDU while forwarding NPDUs, then NPDU should be forwarded. The intermediary system then sends a RD PDU to the source system with the address information in the NPDU.
7.8 Redirect Recording Function
The redirect recording function exists only on the end system, which is called when receiving the RD PDU. It extracts redirection
Information is added or modified for relevant redirection information in the local network entity routing library. Among them
One is to map the destination address to the redirect mapping information of the subnet address, which also illustrates priority, security, service
Parameters necessary for mapping of quality and holding time. Of course, if the redirection is to another intermediary system, then the network
The entity title is also essential.
Note: If there is not enough space to store heavy-oriented information, the RD PDU will be released safely. Send
The intermediary system of RD PDU will also continue to work for the previous work on behalf of this network entity.
7.9 Redirect Refresh Features
The redirect refresh function is only performed in the end system. This feature receives an NPDU as a destination in one end system
Time called. This feature is functioning with the NPDU received in the destination network entity (called in ISO8473
Related to "PDU Decomposition")). The purpose of this feature is to extend the time of redirection and the wrong letter in the routing as soon as possible.
interest. Parameters such as source address, priority, security, and service quality are extracted and with routing information libraries (this information
Save is compared by the redirected recording function. You can find this PDU from the Sn_Source_Address parameter
The upper hop address. Keep the value of the timer if this address is consistent with the next hop address stored in redirection information.
The initial value of the holding timer will be reset to the RD PDU.
Note: When the network entity sends data to a destination address, the data may be forwarded back. The purpose of this function
It is to avoid the entry of expired redirection information at this time. Given that only one redirect is redirected in communication in the end system to the end system
There is no need to intermediaries, this feature is especially suitable for situations where the source and destination are in the same subnet.
In order to prevent the production of black holes, this function must be carried out in a very conservative mode, keeping the remaining time of the timer only
In the above case, it can be modified. For information on this, please refer to Appendix 10.
7.10 Old Redirection Clear
The purpose of this feature is to clear the configuration information in the route information library. End system and intermediary system
When the timer time arrives, the relevant entry in the local network entity routing the information library is cleared.
7.11 PDU head error detection
The PDU head error detection function is used to protect when the intermediary system and end system processes the PDU header error. This
The implementation of the function is done by the Checksum area of the PDU header. Each node for processing PDU
Verify Checksum. If Checksum is wrong, the PDU must be discarded.
The head error detection function is optional, and is selected by the homework network entity. If this feature is not selected,
Checksum will be set to 0.
If the function is started to select the network entity, Checksum meets the following formula:
All A (i) models 255 and = 0; (i = 1 → L)
All (L-I 1) * a (i) model 255 and = 0; (i = 1 → L)
L is the number of bytes of the PDU head, and A (i) is the value of the i-byte. The most in front of the byte is i = 0.
When the function is selected, the two bytes of Checksum are not 0.
7.12 classification
Do not need to use all the features in Section 7 in practical applications. These features are divided into four categories:
Category A: Such functions should be supported in all applications.
Class B: Such functions are supported in the system that handles configuration information.
Class C: Such functions are supported in systems that process redirection information.
Class D: Such functions are optional in any system.
If the system receives a call to an optional function that cannot be executed, the PDU should be discarded. The following table shows the classification of various functions and how they are applied.
Features
classification
System type
Configuration report
Configuration record
Configuration response
Old configuration clearance
Redirection request
Configuration query
Redirect record
Redirect refresh
Old redirection clearance
PDU head error detection
B
B
A
B
C
B
C
Di
C
A
ES, IS
ES, IS
ES
ES, IS
IS
ES
ES
ES
ES
ES, IS
8.PDU structure and encoding
Note: This Agreement is fully compliant with ISO8473 on the encoding of the PDU.
8.1 structure
The number of bytes of all protocol data units should be an integer. The bytes in the PDU are numbered from 1, this number is smooth
The order is also the order they are placed in the SNSDU. The number of the bit in each byte ranges from 1 to 8, 1, 8 is high
Bit. When the continuous byte is used to represent a binary number, the low bit is more meaningful than the high position.
Any subnet supporting this Agreement is required to use "Most Significant Bit" and "Least Significant Bit" instructions.
Its byte is transmitted. This information will be used to define the PDU.
Note: The chart used in the encoding process uses the following representation:
a) The number of numbered is placed on the left, and the big is placed on the right;
b) From the top 8 to the first bit in the byte from left to right.
The following sections are included in the following order in the PDU:
1. Fixed part;
2. Network address part;
3. Subnet address part (if needed);
4. Optional part, if needed;
8.2 fixed part
8.2.1 Overview
The fixed portion contains frequent parameters, including the type code (ESH, ISH, RD) of the protocol data unit. fixed
The length and structure of the part are defined by the PDU.
The fixed portion is the following form:
byte
Network layer protocol representation
Length indication
Version / Protocol Extension Identification
Reserved (must be 0)
0
0
0
Types of
Hold time
check
1
2
3
4
5
6,7
8,9
8.2.2 Network Layer Protocol Identifier
The value of this domain should be 1000 0010
Note: This value is temporary, not the final conclusion.
8.2.3 Long indication
This length is represented by a binary number, the maximum value is 254 (1111 1110). This value represents the entire PDU (including
The number of bytes of the entire head). 255 is the reserved value.
8.2.4 version / agreement extension identification
The value of this domain is a binary number 0000 0001. This value indicates that this is a standard version of ISO.
8.2.5 Type
The type code indicates the type of protocol data unit. Its value is one of the following:
Types of
Bit 5 4 3 2 1
ESH PDU
0 0 0 1 0
ISH PDU
0 0 1 0 0
RD PDU
0 0 1 1 0
8.2.6 Holding time
Maintaining Time Shi indicates how long the configuration / routing information in the PDU should be maintained as a recipient's network entity. Pick up
The closing network entity should discard any information obtained from the PDU when the timing time will be discarded. Holding time is two
The integer value of a week.
8.2.7pdu verification
This value is calculated from the entire head. If it is equal to 0, it indicates that the verification is not used. PDU head error detection function
The certificate 0 is not a legal verification value. A non-0 value indicates that this value is not negligible. If the verification error, the PDU should
thrown away.
8.3 Network Address Part
8.3.1 review
The address parameter is used to distinguish the location. The address parameters carried by different PDU types are also different. ESH PDU
Carry a source NSAP address; ISH PDU carries a intermediary system network entity title; an RD PDU carries a destination NSAP address, or it is possible to be a network test title.
8.3.2 Network Protocol Address Information (NPAI) Coding
The destination address and source address refers to the address of the network service access point, defined in ISO 8348 / AD2. Destination address,
The source address and network entity title are coded as the NPAI according to the binary sentence defined by ISO8348 / AD2.
of.
The address information is variable length. Each address parameter is encoded as follows:
Byte N
Address parameter length indication
Byte N 1 to N M
Address parameter value
8.3.3 ESH PDU source address parameters
This source address is an address of NSAP that sends an ESH PDU network entity. It encodes as follows:
byte
Source address length indication
source address
10
11
... ..
M-1
8.3.4 ISH PDU Network Entity Title Parameters
This network entity title parameter is a network entity title of the intermediary system that sends ISH PDU. It encodes as follows:
byte
Network entity title length indication
Network entity title
10
11
... ..
M-1
8.3.5 RD PDU destination address parameters
This destination address is the associated address of the NPDU forwarded the NPDU forwarding the RD PDU of the RD PDU. It is as follows
French code:
byte
Destination address length indication
Destination address
10
11
... ..
M-1
8.4 subnet address part
The subnet address part is only in the RD PDU. It is used to indicate another end system or intermediary system in the same subnet.
A network entity (they may be a subnet address of better route) to the destination indicated by the network address section). child
The encoding of the network address parameters is similar to the network address parameters.
8.4.1 RD PDU subnet address parameters
Subnet address parameters are encoded as follows:
byte
Subnet address length indication
Subnet address
M
M 1
... ..
N-1
8.5 optional part
8.5.1 review
Optional part is used to transmit optional parameters. An optional part of the PDU head is described below:
byte
Option
p
Qi
If the optional part exists, it may contain one or more parameters. The number of parameters is based on the length and limit of the optional part,
The length of the optional section has the following formula decision:
PDU head length - (fixed part length address portion length segment portion length)
It is also determined by the length of individual optional parameters.
The order in which the parameters defined in the optional section is uncertain, and the options are not allowed to be reproducible. Received options
PDU is a mistake for the agreement.
The encoding form of the parameters in the optional section describes the following:
byte
content
n
Parameter encoding
N 1
Parameter length
N 2 to N m 1
Parameter value
The parameter coding domain uses binary encoding and cannot be extended, and the different parameter encoding in 255 can be represented. thing
In fact, no value of the 8th and 7th bit of the parameter encoded is 00, so the maximum number of available can be provided.
Wherein, encoding 255 (binary 1111 1111) is retained.
The parameter length domain indicates the number of bytes of parameter values. This length is binary positive integer M, in theoretical maximum value is
254, but the actual value is small. For example, when only one parameter is only one parameter, the length of the parameter is each occupied.
One byte. In this way, M is limited to:
M = 252- (fixed part length address portion length segment portion length)
The larger the next few parameters, the smaller M. The parameter value indicates the value of the parameters specified in the parameter coding domain.
8.5.2 Security
Safety parameters Transfer the security information required by the data PDU, which causes the RD PDU. This
The encoding and semantics of a parameter are similar to the security parameters defined by ISO8473.
Parameter code: 1100 0101
Parameter length: variable parameter value: see 7.5.3 in ISO8473
8.5.3 Service Quality Keep
Service quality transmits data PDU requirements, this data PDU causes RD PDUs.
The encoding and semantics of this parameter are similar to the service quality defined service quality defined by ISO8473.
Parameters encoding: 1100 0011
Parameter length: variable
Parameter value: See 7.5.6 in ISO8473
8.5.4 Priority
The priority parameter transmits the priority information required by the data PDU, which causes the RD PDU.
This parameter is similar to the priority parameter defined by ISO8473.
Parameters code: 1100 1101
Parameter length: variable
Parameter value: See 7.5.7 in ISO8473
8.6 end system Hello PDU
8.6.1 Structure
The ESH PDU has the following form:
byte
Network protocol identifier
Length indication
Version / Protocol Extension Identification
Reserved (must be 0)
0
0
0
Types of
Hold time
check
Source address length indication
source address
Option
1
2
3
4
5
6,7
8,9
10
11
M-1
M
P-1
8.7 Mediation System Hello PDU
8.7.1 Structure
ISH PDU has the following form:
byte
Network protocol identifier
Length indication
Version / Protocol Extension Identification
Reserved (must be 0)
0
0
0
Types of
Hold time
check
Network entity title length indication
Network entity title
Option
1
2
3
4
5
6,7
8,9
10
11
M-1
M
P-1
8.8 Redirect PDU
8.8.1 Structure
When the PRD PDU is sent to the intermediary system, it has the following form:
byte
Network protocol identifier
Length indication
Version / Protocol Extension Identification
Reserved (must be 0)
0
0
0
Types of
Hold time
check
Destination address length indication
Destination address
Subnet address length indication
Subnet address
Network entity title indication
Network entity title
Option
1
2
3
4
5
6,7
8,9
10
11
M-1
M
M 1
N-1
n
N 1
P-1
p
Q-1
Has the following form when the PRD PDU is sent to the end system:
byte
Network protocol identifier
Length indication
Version / Protocol Extension Identification
Reserved (must be 0)
0
0
0
Types of
Hold time
check
Destination address length indication
Destination address
Subnet address length indication
Subnet address
Network entity title length indication (= 0)
Option
service quality
1
2
3
4
5
6,7
8,9
10
11
M-1
M
M 1
N-1
n
N 1
P-1
N 1
Appendix A Technical Support Materials
A.1 Timer
In order to be configured and redirected features, this agreement is widely used in this agreement. this
The section discusses how these timers are used and give the background using them.
The system using this Agreement is only available from other systems from the PDU issued by other systems. In no connection
In the middle, the system must use updated information to determine if the information you have mastered is correct. For example, if a system becomes
With the only way to be known by other systems, it should be lost by the information it issued. And the maintenance defined in this Agreement
Time to ensure that outdated information will not always be saved.
There is a very effective way to update configuration information and redirection information, that is, the system keeps a slow
Save. This cache is periodically refreshed, ensuring that only timely information can be saved. Unlike general caches, this
The save time of information in the cache is not fully available. Instead, there is a source of information decisions. Some examples can clearly illustrate this.
A.1.1 Routing Redirection Keep Timer Example
Routing redirection information is that the end system is reached and saved by the redirected function. The intermediary system is very likely to end
Dressing to another intermediary system, and this intermediary system suddenly becomes unreachable (when the routing algorithm is in configuration
This situation is likely to occur during the convergence process. If there is no timer, or its value is set
Very large, the end system will be redirected to a black hole. And the time of this timer is set to the black hole allows the existence
Maximum time.
In addition, if the value of this routing is set too short, it will cause another other we don't want to see it.
s consequence. First, each of the redirected PDUs will cause additional PDUs to be generated and transmitted, which will increase overhead.
In addition, each time the timer time is maintained, the redirected end system is used to send a PDU using at least the wrong route.
A.1.2 Conservation Timer Example for Configuration Information
There are also similar problems that have also occurred on configuration information. If the maintenance timer of an ISH PDU is set, it is very long.
And ISH PDU's IS suddenly becomes unachable, it will form a black hole. During this time, the end system assumes that
The intermediary system will continue to forward the PDU for it, which cannot communicate normally with other systems. And when the timer time arrives,
The end system finds an unavailable intermediary system.
Whether the problem occurs, the response of the error message is required to find the source correctly. In order to achieve
This, the configuration information and routing redirection information are calculated in the source and accurately transmitted to the receiving end.
A.2 Refresh and timing of routing redirection information
This Agreement allows the end system to keep the timer has not been time to, and to the path to receive new redirection information.
Refresh by redirection information. This process is often used in connection with the connection network, it is called "reversal path information",
"Front hop" and so on.
Refreshing redirection information has a significant benefit, but if it is dealing with it, it is very likely to have serious consequences. In order to be heavy
Directional information security refresh, must ensure the following points:
1. The source address of the received PDU must be consistent with the destination address of the previous RD PDU. Cannot
The short address, group address, or similar address is consistent.
2. The quality of service parameters in the received PDU must be consistent with the corresponding redirection information. Cannot guarantee
The PDU of the same service quality parameter is sent through the same path. Very likely to quality for certain service
The parameter is in a black hole.
3. The front hop of the PDU received must be consistent with the next hop in the redirection information. Special, send PDU
Sn_suRCE_ADDRESS parameters must be refactored in Sn_UnitData.indication primitives
The Sn_Destination_Address in the middle is consistent. The IS that accepts redirection information is the original
First sender.
Note that the above conditions still allow redirection to refresh in the most advantageous case. For example, the destination is another
ES.
A.3 System Initialization
This Agreement is designed to be two systems that can communicate freely as much as possible. Therefore, the end system requires all the net online.
The intermediary system reports configuration information, or the intermediary system requires all end system report configuration information.
In a certain operating environment, the system is greatly limited. Before the network reaches the normal operation, the end system must first
I found a mediation system as soon as possible. In turn, do the intermediary systems also have to discover the end system? This basically has a configuration timer
Decide. We must have a trade-off on the applicability of overhead and configuration information. Reduce the value of the configuration timer means the availability of information,
It also means an increase in overhead.
We recommend the following methods to solve the above conflicts. When the recording configuration function is referenced in any system
When this feature must determine if this information is not known. If yes, then configure timer time in the system
This feature is to be referenced. Then the configuration report feature generates the Hello PDU and sent to the original unknown network entity.
Thus, when ES or IS becomes operable, it will immediately issue a configuration report. Once a system discovers this new network entity, they will make them know their existence.
The overhead brought about this method is much smaller. In addition, since the new configuration information is found, the timer is time
It is periodically extended to reduce overhead. There is also an advice: Since the first Hello is likely to be lost,
The initialization phase should issue a Hello package in a very short interval.
Note that this method may only be executed in all systems only in IS or ES. This process is just a book
The ground process and may be changed by the local system.
A.4 Redirection Clear Optimization
An ES will send an NPDU to an IS specified by the redirected information, only to the main timer time, ie
The IS has become unreachable. In some cases, it is possible to discover the presence of black holes faster. Special, if
ES wants to get the Hello package it is redirected, and keep the timer has arrived, all about this IS
The information will be discarded, including redirection information, even if the time is redirected.
Route information between end systems and intermediary systems based on RFCXXX - ISO8473 (ES-IS)
2
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