Process for transferring data packets between emulated LANs

A distinction is made between unicast frames and multicast/broadcast frames for the transmission of information packets between a source LEC of a first ELAN and a destination LEC of a second ELAN. After initiation of a connection setup, unicast information packets are transmitted between source LEC and destination LEC via a wide-area ATM network upon employment of the destination ATM address. Multicast/broadcast information packets are transmitted from the source LEC to the destination LECs via a CLS wide-area network offering a connectionless service. For the transmission of the multicast/broadcast information packets, a specific LEC in every ELAN of an exemplary embodiment is coupled to the CLS network via a bridge or a router. In one exemplary embodiment, the CLS network is employed for determining a destination ATM address of a destination LEC for the unicast transmission.

BACKGROUND OF THE INVENTION 
The invention is directed to a method for the transmission of information 
packets between a source LAN emulation client LEC of a first ELAN and an 
LAN emulation client of a second ELAN. 
ELAN stands for emulated LAN as described, in particular, in the 
specification 94-0035R9, "LAN Emulation Over ATM: Version 1.0" of the LAN 
Emulation SWG Drafting Group of the ATM Forum of Jan. 6, 1995, Bill 
Ellington, editor. This is thereby an approach of the ATM Forum to the 
migration of current LANs to ATM networks. ATM thereby means "Asynchronous 
Transfer Mode", i.e. asynchronous data or, respectively, information 
transmission methods. LAN is an abbreviation of "Local Area Network". LANs 
are datagram-oriented local networks that are described in, among other 
references, the article by David D. Clark, Kenneth D. Program and David P. 
Reed, "An Introduction to Local Area Networks" in Proceedings of the IEEE, 
Vol. 66, No. 11, November 1978, pages 1497 through 1517. LANs are also 
described in ISO/IEC TR 8802-1, "Overview of LAN-Standards". LANs offer a 
connectionless service, what is referred to as the MAC service. MAC 
thereby stands for "Media Access Control". By contrast to this 
connectionless service, ATM technology is connection-oriented. When the 
protocols of the higher layers developed for LANs are to be used in 
emulated LANs on the basis of an ATM network, the properties of the 
connectionless MAC service must be produced in this ATM network. The LAN 
emulation according to the aforementioned specification realizes the MAC 
service in the local ATM network and thus defines a single emulated LAN, 
called ELAN below. The standard LAN protocols such as LLC, TCP/IP, SPX/IPX 
or TP/CLNP can be used in this ELAN. 
The LAN emulation supports the two most frequently employed LAN standards, 
namely Ethernet according to IEEE 802.3 and Token Ring according to IEEE 
802.5, whereby three frame lengths are supported given token ring. The 
addressing of every LAN station ensues on the basis of a destination MAC 
address that is unambiguous worldwide. For the transmission of information 
between LANs, the addresses are handed over from a high layer are. For the 
description of the information path, token ring LANs employ what are 
referred to as route descriptors in the frame header in addition to MAC 
addresses. The frame can be conveyed to the destination within token ring 
LANs on the basis of such a descriptor. 
Only MAC addresses shall be mentioned below. 
For emulation of an LAN in an ATM network, the LAN emulation must, among 
other things, resolve destination MAC address into destination ATM 
addresses, realize multicast and broadcast, i.e. a distribution of 
information to as plurality of or to all subscribers, as well as assure 
the transmission of LAN emulation frames in the proper sequence. The LAN 
emulation has a client-server configuration. The client side is called LAN 
emulation client LEC and the server side is called LAN emulation service. 
The LAN emulation service is composed of LAN emulation server LES, 
broadcast-and-unknown server BUS and LAN emulation configuration server 
LECS. The LAN emulation client receives the destination MAC address from a 
higher-ranking layer, for example the LLC layer, and must find the 
corresponding ATM address, in order to subsequently initiate the setup of 
a direct ATM connection to the destination by signaling. The signaling can 
thereby ensue, for example, according to the ITU-T Recommendation 
Q.2831/Q.2971. An LAN emulation client can be realized in the software or 
in the hardware of the stations that participate in the LAN emulation. 
An LAN emulation server LES maintains a table with all MAC addresses that 
are reported in the emulated LAN, for example in the framework of a 
configuration, and with the corresponding ATM addresses. The communication 
between the LAN emulation clients and the LAN emulation client ensues 
according to an LAN emulation address resolution protocol that, conforming 
to the English designation LAN Emulation Address Resolution Protocol, is 
referred to as LE.sub.-- ARP. When an LAN emulation client does not know 
the destination ATM address of a destination MAC address, then it sends an 
inquiry with the destination MAC address to the LAN emulation server. Such 
an inquiry for address resolution is referenced LE.sub.-- ARP request. 
When the LES can resolve the destination ATM address, it replies with 
LE.sub.-- ARP response. When it cannot, it sends the request to further 
LAN emulation clients. 
When an LAN emulation client receives an address resolution response 
LE.sub.-- ARP response, then it sets up an ATM-UBR connection to the ATM 
address contained therein and sends a unicast frame. UBR thereby denotes 
"Unspecified Bit Rate", i.e. indicates that the bit rate is not specified. 
A unicast frame is an information or, respectively, data packet with a 
single addressee. In the transmission of frames within an ELAN, a 
distinction is made between unicast frame to one receiver and multicast or 
broadcast frame to several or all receivers. An ATM-UBR connection is 
maintained for 20 minutes from the last transmitted frame so that further 
frames can be sent to the same receiver in a simple way. To this end, the 
variable C12 is referenced in point 5.1.1 of the LAN emulation 
specification. The destination ATM addresses of destination MAC addresses 
is stored for a certain length of time in the LAN emulation client with 
the assistance of a cache mechanism. When there is no connection to a 
destination LAN emulation client but the destination ATM address is known 
in the sender LAN emulation client, a sender LAN emulation client LEC can 
set up a connection without address resolution request and send a unicast 
frame. 
Multicast frames to a group of subscribers or, respectively, LAN emulation 
clients and broadcast frames to all subscribers or, respectively, LAN 
emulation client LECen are sent to the aforementioned BUS. Within an ELAN, 
the BUS maintains connections to all LEC for the arrived frames to the 
addressees. 
Every LAN can be reported as what is referred to as proxi-LEC. A proxi-LAN 
emulation client receives all address resolution requests LE.sub.-- ARP 
request that an LES cannot resolve. A proxi-LEC also receives all 
multicast and all broadcast frames. 
The advantage of ATM technology is to be seen, among other things, therein 
that direct connections with flexible bandwidth can be set up between the 
communication parties. Such direct connections guarantee minimum time 
delays and a high information transmission rate. This advantage of ATM 
technology is utilized in the LAN emulation for unicast frames. Various 
concepts for connecting local ATM networks such as, for example, ELANs via 
a wide-area ATM network are known in the article, "Interconnect Emulated 
LANs with Wide Area ATM networks" by Peter T. P. Chang and Bill Ellington, 
ATM Forum Technical Committee of Nov. 29 through Dec. 2, 1994. In a first 
concept, a plurality of ELANs are thereby connected to a wide-area ATM 
network, whereby the address resolution and the data transmission are 
undertaken via a single LAN emulation server and a single BUS. This 
concept leads to an enormous traffic volume for the realization of the 
broadcast function. The address resolution delay times in such a network 
are extremely high. 
A further concept provides that ELANs be respectively connected to a 
wide-area ATM network via remote bridges. Either all remote bridges are 
thereby connected to one another via permanent virtual circuits PVC or the 
remote bridges are dynamically connected to one another with the 
assistance of an ATM signaling upon employment of an address resolution 
server. The transmission possibilities are thereby limited by the 
transmission possibilities of the remote bridges and the bandwidth of the 
permanent virtual circuits between two remote bridges. The remote bridges 
are flooded with broadcast and unknown servers of remote ELANs insofar as 
the remote bridge thereof does not respectively know the address of the 
remote bridges allocated to the destination MAC addresses. 
A further concept provides that, instead of remote bridges, routers be 
provided, a mixture of bridge and router. In this case, these routers 
fulfill the function of an LAN emulation bridge at the ELAN side and 
fulfill the functions of a router at the side of the ATM wide-area 
network. As a result thereof, the broadcast problems are reduced; however, 
a limitation of the transmission possibilities via the ATM wide-area 
network due to the transmission possibilities of the routers and of the 
permanent virtual circuits continues to exist. 
A further concept provides that the LAN emulation servers of the individual 
ELANs as well as the BUS of the individual ELANs be connected to one 
another by direct connections. This, however, leads to a great plurality 
of direct connections and to a high traffic volume between the LAN 
emulation servers and the BUS of the individual ELANs. The traffic volume 
thereby increases linearly with the plurality of connected ELANs. 
A further concept provides that the LAN emulation servers of the individual 
ELANs as well as the BUS of the individual ELANs be connected to a 
higher-ranking LAN emulation server or, respectively, to a higher-ranking 
BUS via direct connections. This, however, likewise leads to a great 
plurality of direct connections and to a high traffic volume. The 
multilayer nature of BUS and higher-ranking BUS or, respectively, LES and 
higher-ranking LES also leads to time delays. 
SUMMARY OF THE INVENTION 
When, within an ELAN, information is to be transmitted from one LAN 
emulation client to another LAN emulation client, the source LEC usually 
initiates an ATM connection setup to the destination LEC. The destination 
ATM address is required therefor. The source LEC knows a destination MAC 
address from higher layers. Moreover, a destination ATM address for the 
destination MAC address can be deposited in its memory. When no 
destination ATM address is deposited, the source LEC normally forwards an 
address resolution request LE.sub.-- ARP.sub.-- Request to an LAN 
emulation server of the ELAN. When the client allocated to the destination 
MAC address does not belong to the ELAN of this LAN emulation server, this 
LAN emulation server cannot resolve the ATM address, i.e. cannot answer 
the address resolution request. 
Inventively, the first and the second ELAN are connected to a wide-area 
network (regionally and/or globally) that offers a connectionless service 
such as, for example, SMDS (Switched Multi-megabit Data Service) or CBDS 
(Connectionless Broadband Data Service). Insofar as no explanations to the 
contrary are provided, what is always meant for the sake of simplicity 
below and in the patent claims by wide-area network is a wide-area network 
offering a connectionless service, i.e. a CLS wide-area network (regional 
and/or global). 
When, given unicast mode, the destination MAC address is allocated to an 
LAN emulation client of a second ELAN, then the information transmission 
is inventively enabled with the following method steps: 
initiation of a connection setup between source LEC and destination LEC via 
a wide-area ATM network upon employment of the destination ATM address; 
transmission of the information packets via the wide-area ATM network. 
In one embodiment of the invention, the destination ATM address can be 
determined therefor by transmission of an address resolution request of 
the source LEC to the second ELAN via a CLS wide-area network offering a 
connectionless service and resolution of the destination MAC address in 
the second ELAN into the appertaining ATM address. Subsequently, a 
connection setup between source LEC and destination LEC can be initiated 
via an ATM network ranking higher than the first ELAN and the second ELAN 
upon employment of the identified destination ATM address. 
In one exemplary embodiment, the identified ATM address is transmitted via 
the CLS wide-area network as address resolution response to the first ELAN 
and is transmitted thereat to the source LEG, and the source LEC initiates 
a connection setup to the destination LEC. 
Preferably, the destination ATM address is thereby resolved with the 
following method steps: 
encapsulation of the address resolution request present in the first ELAN 
as ELAN frame in a frame format of the CLS wide-area network with an E-164 
address allocated to the destination MAC address in the frame header part; 
handing over this encapsulated address resolution request to the CLS 
wide-area network and transmission to the second ELAN; 
de-encapsulation of the encapsulated address resolution request and 
handover to an LAN emulation server of the second ELAN in the ELAN frame 
format; 
resolution of the destination MAC address into an appertaining ATM address 
by this server of the second ELAN and output of an address resolution 
response; 
encapsulation of this address resolution response into the frame format of 
the CLS wide-area network and transmission to the first ELAN; 
de-encapsulation of the encapsulated address resolution response and 
handover to the source LEC. 
When the transmission of unicast frames is planned, then, according to the 
aforementioned "LAN-Emulation over ATM-Specification", an address 
resolution request is sent from the source LEC to the LAN emulation server 
of the local ELAN. Since the LAN emulation server only knows the local ATM 
addresses, it cannot resolve the destination ATM address. The local LAN 
emulation server therefore hands over the address resolution request of 
the source LRC to all proxy-LEC signed on in the local ELAN. In a 
beneficial development of the invention, the individual ELANs are 
therefore respectively connected via a specific LAN emulation client to 
the wide-area network offering a connectionless service. This access LEC 
is respectively preferably signed on as proxy-LEC in its ELAN. 
When a plurality of destination LECs are allocated to a destination MAC 
address, i.e. it is a matter of a multicast MAC address, then the 
information packets are inventively transmitted from the source LEC to the 
destination LECs via a CLS wide-area network offering a connectionless 
service. 
transmission of the information packets to a specific LAN emulation client 
with access to a wide-area network offering a connectionless service; 
handover of the individual information packets to a conversion function 
with an address memory for group addresses of the ELAM and E.164 addresses 
of the CLS wide-area network allocated to one another and with a memory 
for an E.164 address allocation to the transfer from the CLS wide-area 
network to this conversion function; 
handover of the information packets in common with the E.164 address 
(potentially, global E.164 group address of all ELANs) belonging to the 
destination MAC address to the CLS wide-area network; 
encapsulation of the information packets in a frame format of the CLS 
wide-are network; 
communication of the information packets to the ELAN of the destination LAN 
emulation client via the wide-area network offering a connectionless 
service; 
de-encapsulation of the encapsulated information packets and handover of 
the de-encapsulated information packets by a conversion function to a 
specific LAN emulation client of the second ELAN with access to the 
wide-ware network offering a connectionless service; and 
communication of the information packets to the destination LAN emulation 
client. 
When the individual ELANs are respectively connected via an access LEC to 
the network offering a connectionless service, then the transition between 
an ELAN and the CLS wide-area network is preferably formed by an 
interworking function IWF that is arranged between the CLS wide-area 
network (T-reference point) and an access LEC of the respective ELAN. Such 
an interworking function can be a bridge or a router. 
A bridge as interworking function has, for example, an address memory for 
MAC addresses or group addresses of the ELAN and E.164 addresses of the 
CLS wide-area network allocated to one another and a memory for an E.164 
address allocated to the transition from the CLS wide-area network to the 
bridge. 
A simple embodiment of such a bridge can provide that multicast data frames 
with the E.165 address of a group address agent GM of the CLS wide-area 
network are forwarded to the CLS wide-area network. Preferably, the 
conversion function also hands over the E.164 address allocated to the 
source MAC address. Frames coming from the CLS wide-area network are 
handed over to the interface (layer LEC) to the ELAN.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The connectionless service or CLS service can be realized with various 
technologies (for example, DQDB, ATM, FR). The service is described in the 
ITU-T Recommendation F.812. Known realizations are the switched 
multi-megabit data service (SMDS) described in specifications of Bellcore, 
SMDS Interest Group (SIG) and European SMDS Interest Group (ESIG), as well 
as the connectionless broadband data service (CBDS) defined in ETSI 
Standard 300 217 and ITU-T Recommendation 1.364. CLS has become widespread 
worldwide due to these realizations. Systems that offer this service are 
built by many manufacturers in the field of telecommunication. 
The service is envisioned for worldwide data communication. At every access 
to the CLS network, one or more CLNAP addresses according to E.164 (E.164 
address) are assigned (CLNAP=connection network access protocol). 
A destination CLNAP address (E.164 address) is attached (encapsulation) to 
an incoming unicast frame with static or dynamic allocation tables on the 
basis of its destination MAC address and the encapsulated frame (also 
called CLS packet) is conducted to this CLNAP address. 
For better understanding, the addresses in the ELAN are called unicast or, 
respectively, multicast/broadcast MAC addresses, but individual and group 
addresses shall be referred to in the CLS network. 
Each CLS packet is transmitted independently of the others in the CLS 
network. The networks sees to the proper sequence of the CLS packets. 
Under certain conditions (see prETS 300 478, 300 479), the CLNAP PDUs are 
encapsulated in CLNIP PDUs (CLNIP=connectionless network interface 
protocol). 
The handling of multicast traffic in the CLS network is realized in the 
following way. What are referred to as group address agents (GAAs) contain 
tables with the individual CLNAP addresses that belong to a CLNAP group 
address. Each CLS packet that has a group address as destination address 
is conducted to the corresponding group address agent. When encapsulation 
was carried out, the same group address resides in the fields "CLNAP 
destination address" and "CLNIP destination address". 
The GAA resolves the group address of the incoming CLS packet into 
individual CLNIP addresses, generates copies of the original packet and 
attaches to corresponding individual address to each copy as CLNIP 
address. The "CLNAP destination address" field remains unmodified, so that 
the receiver can learn about the original group address. 
The LAN emulation describes an individual emulated LAN. No solutions are 
currently known for the coupling of ELANs. For performance reasons, the 
mechanisms described in the LAN emulation for address resolution and for 
the realization of multicast/broadcast in the WAN region cannot simply be 
transferred. 
Methods for coupling ELANs upon application of the invention are described 
below: 
A first example handles the transmission of multicast frames given at least 
one destination LEC LEC B, LEC C located outside the ELAN of the source 
LEC LEC A and provides the transmission of multicast frames by a network 
offering a connectionless service and, subsequently, an ATM connection 
setup from sender to receiver. Multicast frame thereby also always 
includes broadcast frames. 
An advantage of the LAN emulation is the setup of a direct Atm connection 
between sender and receiver, as referenced with data direct VCC in the LAN 
emulation specification. The improvement of the invention of this example 
therefore proposes that the destination MAC address for the unicast 
traffic be resolved into the ATM address upon employment of a network such 
as, for example, SMDS or CBDS that offers a connectionless service and 
that a direct ATM connection to the destination then be set up. 
In the same way, FIGS. 1 and 2 show three ELANs ELAN 1, ELAN2 and ELAN3 
respectively having an LAN emulation server LES, an ATM switching means 
ATMS, an LAN emulation client LEC A, LEC B, LEC and a specific LAN 
emulation client LEC Z1, LEC Z2, LEC Z3 that is referred to below as 
access LEC and that enables then respective ELAN ELAN1, ELAN2 or, 
respectively, ELAN3 to have access via a customer premises equipment CPE 
to a network CLSnet (also shown) that offers a connectionless service. 
Each customer premises equipment CPE thereby has an interworking function 
IWF allocated to it for the conversion of a destination MAC address into 
an E.164 address of the customer premises equipment CPE of the ELAN in 
which the LAN emulation client to whom the destination MAC address is 
allocated is located or for the conversion of an E.164 group address of 
all ELANs. In the exemplary embodiments of FIGS. 1 and 2, the network 
CLSnet offering a connectionless service is realized with the assistance 
of a higher-ranking (spatially higher-ranking, i.e. regional or global) 
ATM network with ATM switching equipment ATMS. The type of realization of 
the network CLSnet offering a connectionless service, however, has no 
influence on the invention. 
The broadcast and unknown server BUS1, BUS2, BUS3 of the ELAN1, ELAN2 and 
ELAN3 are also respectively shown in FIG. 1. As shown by an overlapping 
frame, access LEC LEC Z1, LEC Z2 or, respectively, LEC Z3, interworking 
function IWF and customer premises equipment CPE in the illustrated 
example respectively form a bridge whose bridge function is the 
interworking function IWF. 
The network CLSnet offering a connectionless service contains a server 
(connectionless server) CLS offering a connectionless service and a group 
address agent GAA. 
A simple coupling of ELANs with respect to the transmission of multicast 
or, respectively, broadcast frames can thus be realized when all multicast 
or, respectively, broadcast data frames that are to be delivered to LAN 
emulation clients outside the ELAN are transported via the CLS network 
(network offering a connectionless service). An LAN emulation client that 
has access to the CLS network (see LAN emulation clients LEC Z1, LEC Z2, 
LEC Z3 in FIG. 1) via an interworking function is required in every ELAN 
for this purpose. 
When, for example, LAN emulation client LEC A wishes to send a multicast 
frame, it sends this multicast frame to the BUS BUS1 that, dependent on 
the embodiment of the BUS, distributes the frame either to specific LECs 
(intelligent BUS) or to all LECs (non-intelligent BUS). In any case, the 
access LEC LEC Z1 must thereby receive a copy of the frame. 
The access LEC LEC Z1 hands the frame over to an interworking function IWF 
that is described in greater detail below. The interworking function IWF 
transforms every arrived multicast frame into the format of a CLS packet 
(CLNAP packet) and hands it over to the CLS network. The interworking 
function IWF takes the individual E.164 addresses (potentially, global 
E.164 group address) belonging to the group address from a table and 
attaches this to the frame. 
The CLS network transports the packet to the destination CPE of the ELAN2, 
which unpacks the original data frame and forwards it to the access LEC 
(LEC Z2) via the interworking function. This LAN emulation client LEC Z2 
transmits the multicast data frame to the BUS BUS2, which forwards it to 
the destination LEC LEC B. The CLS network also transports the packet to 
the destination CPE of the ELAN3, which unpacks the original data frame 
and forwards it to the access LEC (LEC Z3) via the interworking function 
IWF. This LAN emulation client LEC Z3 transmits the multicast data frame 
to the BUS BUS3 and this to the destination LEC LEC C. 
When the IWF does not know the corresponding E.164 addresses, the CLS 
packets containing the multicast/broadcast frames are handed over to the 
CLS network with the global E.164 group address. 
It can be seen in FIG. 1 that multicast frames are transmitted from the LAN 
emulation client LEC A of the ELAN1 via the ATM switching equipment ATMS 
of this ELAN1 to the BUS BUS1 and then to the access LEC LEC Z1. The 
multicast frames proceed from the access LEC LECZ1 to the customer 
premises equipment CPE, are respectively converted into a different form 
therein and communicated to the customer premises equipment CPE of the 
ELAN3 via connectionless servers CLS as well as to the customer premises 
equipment CPE of the ELAN2 via a further ATM switching equipment ATMS and 
a further connectionless server CLS. In each of the ELANs ELAN2 and ELAN3, 
the multicast frames are then transmitted to the BUS of the ELAN via an 
access LEC LEC Z2, LEC Z3 and the ATM switching equipment ATMS of the 
ELAN. The BUS of the ELAN2 can communicate the multicast frames to the 
destination LAN emulation client LEC B via the ATM switching equipment 
ATMS, and the BUS of the ELAN3 can communicate the multicast frames to the 
destination LAN emulation client LEC C via the ATM switching equipment 
ATMS. 
When the LAN emulation client LEC A knows the destination ATM address for 
the transmission of unicast frames to the LEC LEC B of the ELAN ELAN2, it 
can set up a direct connection to the destination LAN emulation client LEC 
B in the ELAN2 via an ATM network illustrated in FIG. 2 by a plurality of 
ATM switching equipment ATMS, as shown in FIG. 2 by bold face lines 
between the LAN emulation client LEC A and the LAN emulation client LEC B 
as well as intervening ATM switching equipment ATMS. 
The following example according to FIG. 2 handles the transmission of 
unicast frames given an unknown destination ATM address and provides the 
transmission of address resolution requests or, respectively, address 
resolution responses LE.sub.-- ARP Request/Response by a network offering 
a connectionless service and, subsequently, an ATM connection setup from 
sender to receiver. 
An LAN emulation client LEC Z1, LEC Z2 or, respectively, LEC Z3 of each 
emulated LAN ELAN1, ELAN2, ELAN3 has access (via a CPE) to a network 
CLSnet offering a connectionless service. When the LAN emulation client 
LEC A of the ELAN1 would like to send a unicast frame to the LAN emulation 
client LEC B of the ELAN2 but does not know the destination ATM address, 
it sends an address resolution request LE.sub.-- ARP Request to the LAN 
emulation server LES of the ELAN1. When the LAN emulation server LES of 
the ELAN1 has no entry for the destination MAC address in its table, it 
must forward this address resolution request LE.sub.-- ARP Request to the 
access LEC LEC Z1 of the ELAN1. For example, this can be realized by 
signing the access LEC LEC Z1 on as proxy at the LAN emulation server LES 
of the ELAN1. 
Like the other access LECs LEC Z2, LEC Z3 of the other emulated ELANs ELAN2 
and ELAN3, the access LEC LEC Z1 of the ELAN1 is respectively connected to 
a customer premises equipment of a network CLSnet offering a 
connectionless service. The transition from the access LEC LEC Z1, LEC Z2, 
LEC Z3 to a network CLSnet offering a connectionless service is thereby 
realized with the assistance of an aforementioned interworking function 
IWF described in greater detail later that encapsulates every address 
resolution request LE.sub.-- ARP Request or, respectively, address 
resolution response LE.sub.-- ARP Response that arrives at an access LEC 
LEC Z1, LEC Z2, LEC Z3 and for which it has an entry (E.164 address) for 
the destination MAC address into the format of a packet (CLNAP packet) of 
the network CLSnet offering a connectionless service and hands this 
request or, respectively, response over to the network CLSnet offering a 
connectionless service. 
When the interworking function has no entry, it can either discard the 
corresponding address resolution request frame or, respectively, address 
resolution response frame or provide this frame with an E.164 group 
address with which all emulated LANs that have an access to the network 
CLSnet offering a connectionless service can be reached. In the latter 
instance, a group address agent GM resolves this group address into the 
individual E.164 addresses of the individual customer premises equipment 
CPE of the individual ELANs ELAN1, ELAN2, ELAN3. 
It is thereby especially beneficial when the E.164 group address that an 
interworking function attaches to an address resolution request or, 
respectively, address resolution response respectively contains the E.164 
addresses of the customer premises equipment CPE of all emulated LANs 
ELAN2, ELAN3 that are connected to the network CLSnet offering a 
connectionless service, with the exception of the E.164 address of the 
customer premises equipment of its own ELAN ELAN1. 
The group address agent GM resolves the E.164 group address and sends 
copies of the packet with the address resolution request LE.sub.-- ARP 
Request to said group of customer premises equipment CPE of the individual 
ELANs ELAN2, ELAN3. As a result thereof, all access LECs LEC Z2, LEC Z3 
receive the address resolution request LE.sub.-- ARP Request via the 
interworking function. Each access LEC LEC Z2, LEC Z3 recognizes the frame 
type as address resolution request and therefore sends the frame to the 
LAN emulation server LES of its emulated LAN ELAN2 or, respectively, 
ELAN3. Usually, any LAN emulation server LES can resolve the unicast 
destination MAC address of the destination LAN emulation client LEC B into 
the ATM address. 
The return of an address resolution response is especially beneficially 
configured when the address resolution request LE.sub.-- ARP Request has 
the E.164 address of the customer premises equipment CPE of the output 
ELAN ELAN1 attached to it upon encapsulation by the interworking function, 
when, upon de-encapsulation of the address resolution request, the output 
E.164 address of the address resolution request is stored in the customer 
premises equipment CPE of the ELAN2, and this output E.164 address, upon 
encapsulation of the address resolution response handed over by the LAN 
emulation server LES of the ELAN2 to the customer premises equipment CPE 
of the ELAN2 via the access LEC LEC Z, is attached to the header part of 
the packet to be transmitted via the network CLSnet offering a 
connectionless service. As a result thereof, an immediate transmission of 
the address resolution response LE.sub.-- ARP Response in encapsulated 
form to the customer premises equipment CPE of the ELAN1 is enabled by the 
network CLSnet offering a connectionless service. 
The access LEC LEC Z1 in the output ELAN ELAN1 forwards the address 
resolution response LE.sub.-- ARP Response to the output LEC LEC A after 
this has been encapsulated by the interworking function. After the output 
LEC LEC A has received the address resolution response LE.sub.-- ARP 
Response with the destination ATM address, it sets up a direct ATM 
connection to the destination LEC LEC B via a regional or, respectively, 
global ATM network. 
No modifications in the existing LAN emulation specification are required 
for the realization of the disclosed method for the coupling of ELANs. An 
access LEC must merely be signed on as proxy at the LAN emulation server 
LES and be connected via a customer premises equipment CPE to a network 
CLSnet offering a connectionless service. This access LEC then receives 
all unanswered address resolution requests LE.sub.-- ARP Request from the 
LAN emulation server LAN of the corresponding, emulated LANs ELAN1, ELAN2, 
ELAN3. 
The existing networks such as, for example, SMDS or CBDS offering a 
connectionless service also need not be modified either in terms of their 
standards or in terms of their specifications. An E.164 group address with 
all individual CPE addresses with which emulated LANs can be reached must 
merely be defined within this network. A mechanism can thereby be 
potentially provided that precludes an addressing of the sending customer 
premises equipment CPE. 
The interworking function IWF is commented on in general below: 
The IWF realizes the connection between the "access LEC" on the one hand 
and the CLS network on the other hand. The IWF for the coupling of ELANs 
by the CLS network handles MAC and E.164 addresses and is to be allocated 
to layer 2 according to the OSI reference model. I.e., the IWF is an 
ELAN-CLS bridge. 
When the IWF is also to fulfill routing functions, it can also handle layer 
3 addresses (for example, IP, IPX, etc.). This, however, is not required 
for the realization of the methods of the invention. 
A first realized example for the incorporation of an above-described 
interworking function between an ELAN and a wide-area network offering a 
connectionless service for that case wherein the connectionless service is 
a "switched multi-megabit data service" SMDS and the wide-area network for 
the realization of this service is a "distributed queue dual bus" DQDB can 
provide that--at the wide-area network side--the protocol layers 
SMDS interface protocol layer 1, SIP.sub.--1, 
SMDS interface protocol layer 2, SIP.sub.-- 2, and 
SMDS interface protocol layer 3, SIP.sub.-- 3 
are provided and that the interworking function communicates at the 
wide-area network side with the SMDS interface protocol layer 3, 
SIP.sub.-- 3. 
At, for example, the ELAN side, the protocol layers 
physical layer, PHY, 
asynchronous transfer mode layer, ATM, 
asynchronous transfer mode adaption layer-5, AAL5, and 
LAN emulation client layer, LEC, are provided, whereby the interworking 
function communicates at the ELAN side with the LAN emulation client 
layer, LEC. 
In another example, the connectionless service can be a "switched 
multi-megabit data service" (SMDS) and the wide-area network for the 
realization of this service can be an ATM network, whereby the protocol 
layers physical layer, PHY, asynchronous transfer mode layer, ATM, 
segmentation and assembling sub-layer of the asynchronous adaption 
layer-3/4, ML3/4SAR, and SMDS interface protocol layer 3, SIP.sub.-- 3 are 
provided at the wide-area network side, and whereby the interworking 
function communicates at the wide-area network side with the SMDS 
interface protocol layer 3, SIP.sub.-- 3. 
In a further example, the connectionless service can be a "connectionless 
broadband data service" CBDS, and the wide-area network for the 
realization of this service can be an ATM network, whereby--at the 
wide-area network side--the protocol layers 
physical layer, PHY, 
asynchronous transfer mode layer, ATM, 
asynchronous transfer mode adaption layer-3/4, AAL3/4, and 
connectionless network access protocol layer, CLNAP, 
are provided, and whereby the interworking function communicates at the 
wide-area network side with the connectionless network access protocol 
layer, CLNAP. 
The meanings of the abbreviations employed are recited below in the form of 
the technical terms according to the applicable standards: 
______________________________________ 
AAL ATM adaptation layer 
ATM asynchronous transfer mode 
BUS broadcast and unknown server 
CBDS connectionless broadband data service 
CLNAP connectionless network access protocol 
CLNIP connectionless network interface protocol 
CLNP connectionless network protocol 
CLS connectionless service/server 
CPE customer premises equipment 
CRC cyclic redundancy check 
DQDB distributed queue dual bus 
DS1 digital signal 1 
DS3 digital signal 3 
E1 European transmission level 1 
E3 European transmission level 3 
ELAN emulated local area network 
ESIG European SMDS Interest Group 
ETSI European Telecommunications Standards Institute 
FR frame relay 
GAA group address agent 
IEEE Institute of Electrical and Electronics Engineers 
IP Internet protocol 
IPX internetwork packet exchange 
ITU-T International Telecommunications Union- 
Telecommunications 
IWF interworking function 
L3.sub.-- PDU 
Level 3 protocol data unit 
LAN local area network 
LE.sub.-- ARP 
LAN emulation address resolution protocol 
LEC LAN emulation client 
LECS LAN emulation configuration server 
LES LAN emulation server 
LLC logical link control 
MAC media access control 
OSI open systems interconnection 
PDU protocol data unit 
PHY physical layer 
SIG SMDS Interest Group 
SIP.sub.-- 3 
SMDS interface protocol layer 3 
SMDS switched multi-megabit data service 
SPX sequenced packet exchange 
TCP transmission control protocol 
TP transport protocol 
UBR unspecified bit rate 
WAN wide area network 
______________________________________ 
The invention is not limited to the particular details of the method 
depicted and other modifications and applications are contemplated. 
Certain other changes may be made in the above described method without 
departing from the true spirit and scope of the invention herein involved. 
It is intended, therefore, that the subject matter in the above depiction 
shall be interpreted as illustrated and not in a limiting sense.