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Interworking Between Public Data Networks and the Internet A numbering perspective. ITU “IP and Telecoms Interworking” Workshop 25-27January 2000 Submitted by Peter Hicks Rapporteur ITU-T SG 7 Q3: Data Network Numbering Tel: + 613 9253 6308, Fax: + 613 9253 6777

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Interworking between public data networks and the internet a numbering perspective
Interworking Between Public Data Networks and the Internet A numbering perspective

ITU “IP and Telecoms Interworking” Workshop

25-27January 2000

Submitted by Peter Hicks

Rapporteur ITU-T SG 7 Q3: Data Network Numbering

Tel: + 613 9253 6308, Fax: + 613 9253 6777

email: [email protected]


Summary
Summary

  • This presentation examines numbering and addressing issues associated with the interworking of Public Data Networks and the Internet.

  • Interworking largely depends on being able to signal the “called” terminal’s number or address

  • This presentation does not attempt to solve all the technical or implementation problems but highlights the key issues that will either allow or prevent interworking to occur in the future.


Some issues
Some Issues

  • Key requirement:

    • Seamless interworking between terminals (DTEs) on Public Data Networks (X.25, FR or ATM) & terminals (also known as hosts) on IP routed networks or the Internet

  • PDN Protocols (X.25, Frame Relay, ATM) are connection oriented

    • PVC or SVC is established between the originating terminal and the destination terminal before protocol data units (user data) are transferred.

  • IP connectionless

    • no call set up phase exists

  • Is single-stage “dialling” possible or is two stage “call setup” required?


Some issues cont
Some Issues (cont)

  • Can PDN terminals be identified by mnemonic address such as [email protected]

  • How will PDN terminals be identified

    • X.121 or E.164 number only

    • X.121 or E.164 number plus an IP address

    • IP address only

    • is dual numbering/addressing required?

  • What functionality is required in the gateway between PDNs and the Internet

  • Where is the gateway located

  • What QoS does the “end-to-end” connection achieve (This is not a numbering issue)


Numbering of public data networks
Numbering of Public Data Networks

  • Frame Relay networks numberedunder either X.121 or E.164 - identifies DTE point of attachment.

  • ATM networks numbered under E.164

    - also can use NSAP formats for ATM end system addresses

  • The leading digits of an X.121 and an E.164 number identify the country where the network is located

  • Network Identification

    • within an X.121 number, the Data Network Identification Code (DNIC) uniquely identifies a specific network

    • E.164 numbers generally do not have a network ID code built in to the number; (flat number structure)

    • for networks numbered under E.164, a network ID code as per Rec X.125 may be carried in a specific field of the signalling protocol (not currently used for call set up)


Call set up for frame relay atm
Call Set-up for Frame Relay & ATM

  • Call Setup message identifies the called terminal

  • Called terminal’s point of attachment carried in the called party information element (as per X.36, X.76 or Q.2931 signalling)

  • For Frame Relay the called terminal identified by:

    • X.121 or E.164 number or NSAP address

  • For ATM the called terminal may be identified by:

    • E.164 number or NSAP address

    • only certain NSAP formats supported (embedded E.164, ICD, DCC)

  • X.25 allows the called terminal to be identified by an “alternative address” which can be an IP address, a mnemonic address or an NSAP


Use of nsap to identify called terminal
Use of NSAP to identify called terminal

  • NSAP Formats (see Rec X.213 Annex A) include:

    • embedded X.121 number

    • embedded E.164 number

    • ICD (International Code Designator) Format

    • DCC (Data Country Code) Format

    • embedded IP address

  • Hence capability exists to signal an IP address

  • However use of NSAPs to identify the called terminal requires additional intelligence in the switch to which the calling terminal is connected

    • address resolution entity required

    • requires a “large” data base


General interworking scenario
General Interworking Scenario

Point of attachment to public data network

defined by X.121 or E.164 number

Term A

Public Data Network

(X.25, FR, ATM)

IWF

INTERNET

Term B

Terminal identified by IP address


Notes on

General Interworking Scenario

  • Requirement is for Terminal A to be able to send data to Terminal B and for Terminal B to be able to send data to Terminal A at any time

  • initiated by either party

  • Terminal A identified by X.121 or E.164 number

  • Terminal B identified by an IP address

  • Does Terminal A need to have an IP Address?

  • What protocol stack does Terminal A use?

  • What functionality is required in the IWF

    • address resolution or protocol translation


Interworking via an

Internet Service Provider

Point of attachment to public data network

defined by X.121 or E.164 number

Term A

Public Data Network

( X.25, FR or ATM)

FR or ATM

Connection

Edge

Router

INTERNET

Edge

Router

FR, ATM or leased line

Connection to

Internet Backbone

Internet

Service

Provider

Term B

Edge

Router

Terminal B identified

only by IP address


Notes on interworking via an internet service provider 1
Notes on Interworking via an Internet Service Provider (#1)

Case A: Terminal A sending data to Terminal B

  • Terminal A must subscribe to the service provided by an Internet Service Provider

  • Terminal A sets up SVC or PVC connection to Internet Service Provider.

    • Edge router of the ISP identified by X.121 number

    • IP address is allocated to terminal A by the ISP

      • Can this address be “permanent” or use made of DHCP?

  • IP packets encapsulated as Frame Relay or ATM user Data and sent to the Internet Service Provider

  • Internet Service Provider routes IP packets into the Internet for forwarding to Terminal B


Notes on interworking via an internet service provider 2
Notes on Interworking via an Internet Service Provider (#2)

Case B: Terminal B sending data to Terminal A

  • What happens if Terminal A’s connection to the Internet Service Provider is “inactive”

  • What is the IP address for Terminal A

  • How does Terminal B know what Terminal A’s IP address is - can use be made of Inverse ARP?

  • How does the Internet “know” the location of terminal A

    • if Terminal B receives an IP packet from Terminal A, does this imply that the reverse path and IP Address for Terminal A is known


What s required for efficient routing from the ip network to a terminal on the pdn
What’s required for efficient routing from the IP network to a terminal on the PDN?

  • How is the PDN terminal identified

    • Does the terminal have a dual address ie, X.121 or E.164 number plus an IP address

    • what mechanisms are there available for carrying an X.121 or E.164 number within the address block of an IP packet

    • what extensions in IP addressing are needed to “signal” an X.121 or E.164 number

  • What additional functionality is required in gateway or border routers that allows identification of the PDN


Example showing interworking via gateway routers if the IP terminal could signal an X.121 Address

IPv6

Network Layer

IPv6

Network Layer

PDN - X.25 or Frame Relay

Interworking

Gateway

Routers

X.121= 3134 908 949 5369

Edge or Border Routers

X.121=3134 908080136

Network DNIC

3134

X.121=3134 908087788

I

N

T

E

R

N

E

T

X.121=22889089495369

Network DNIC

2288

X.121= 2288 914 308 3270

IP Terminals

Network DNIC

5052

X.121=505292536308

Network DNIC

3139

X.121= 505291556144

X.121= 313991556144

In order that IP data packets can be efficiently routed to end system terminals connected to public data networks, the Gateway Routers connected to the various public data networks could advertise the DNIC to the border routers on the Internet: e.g. DNIC = 2288, The gateway routers would then need to establish the necessary connections to the PDN terminals based on the full X.121 number.


Is there a requirement for service interworking

IWF terminal could signal an X.121 Address

Is there a requirement for service Interworking ?

PDN / IP Service Interworking

PDN

DTE

IP

Terminal

PDN

IP

PDU on PDN

encapsulation

PDU on IP

encapsulation

The PDN Terminal has no

knowledge that it is

talking to a IP Terminal

The IP Terminal has no

knowledge that it is

talking to a PDN DTE.


Typical scenario for service interworking

Video terminal could signal an X.121 Address

R

LAN

R

LAN

Typical Scenario for Service Interworking

Central

Host

IWF

FR / ATM

IP

Video

Conference

Server

IP

terminal

Private

Network

FR /ATM

terminal

FR /ATM

terminal


Service Interworking via a Gateway terminal could signal an X.121 Address

Point of attachment to public data network

defined by X.121 or E.164 number

Term A

Public Data Network

( X.25, FR or ATM)

FR or ATM

Connection

Edge

Router

INTERNET

Protocol translation

&

encapsulation

FR, ATM or leased line

Connection to

Internet Backbone

Term B

Edge

Router

Terminal B identified

only by IP address

Service Interworking

Gateway


Fr or atm ip interworking protocol stacks
FR or ATM / IP Interworking terminal could signal an X.121 AddressProtocol Stacks

Payload

Application

Application

Data PDU

Voice PDU

RFC Encap

Data PDU

Voice PDU

RFC Encap

IP

IP

FR

or

ATM

FR

or

ATM

? Implemtdepend

? Implemtdepend

Physical

Physical

Physical

Physical

FR

or ATM

UNI

Interworking

Gateway

FR/ATM DTE

IP Terminal


Conclusions
Conclusions terminal could signal an X.121 Address

  • The necessary code points within the FR signalling protocols enable a calling terminal on the PDN to identify an IP terminal (by use of an NSAP) in the call setup message.

    • extensions required in ATM signalling (Rec Q.2931) to allow NSAP (embedded IP format ) to be supported

    • features such as X.25 “alternative addressing” would enable the called party to be identified by a mnemonic address such [email protected]

      • extensions required to FR and ATM signalling protocols

      • required to facilitate interworking as demonstrated in the use email today

  • Two stage interworking from the PDN into the Internet is achievable today


Conclusions cont
Conclusions (cont) terminal could signal an X.121 Address

  • Interworking from the IP world to the PDN appears to be constrained by the fact that an IP packet can not readily carry an X.121 or E.164 number to identify the destination terminal on the PDN

  • will require extensions in IP addressing or functionality to “signal” an X.121 or E.164 number

    • No such functionality in IPv4

    • May be able to use IPV6 address extensions options to carry an OSI NSAP which contained the embedded X.121 or E.164 number


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