Method and apparatus for providing connection identifier by concatenating CAM's addresses at which containing matched protocol information extracted from multiple protocol header

The present application concerns a method and an apparatus, in a communication network, for processing the various fields of a protocol header preceding a data stream to provide a unique connection identifier for processing the data stream. All relevant protocol information is extracted from the protocol header for look up in a Content-Addressable Memory (CAM) (80). Each time an entry in the CAM (80) matches protocol information applied to the CAM's input (84), the CAM address of this storage section, i.e. the address of a row of the CAM (80), is provided at the output (82) thereof. The CAM addresses obtained from the protocol header are concatenated by means of a Connection Number Builder (CNB, 95) resulting in a unique connection identifier provided at the Protocol Filter's output (96) to be used for the processing of the data stream.

TECHNICAL FIELD 
The present invention concerns a method and an apparatus for scanning data 
streams in a communication network and extracting connection information 
to provide for unique protocol connection identifiers. 
BACKGROUND OF THE INVENTION 
The technological convergence of computer and communication networks, as 
well as the fast development in either one of these two areas, has led to 
such an intimate mixture of information processing and communication that 
the transmission and exchange of data, voice, images etc. becomes more and 
more complex. Each transmission or exchange of information--information 
used as synonym for various kinds of data, services, and 
communications--has necessarily to be governed by rules of procedure. 
When different units, e.g. two remote computer terminals, or two procedures 
are interacting via an interface, which is not necessarily a hardware 
interface, respective protocols are employed. Depending on the network, 
various protocols are hierarchically ordered, resulting in a vertical 
stack of protocols, each of these protocols interacting with the adjacent 
ones. Basic transport protocols are known to organize the information 
exchange and transmission between remote systems, such as host computers. 
A typical example is the ARPA (Advanced Research Projects Agency) 
host-to-host protocol. Such a basic protocol enables the higher-level 
protocols of the vertical protocol stack to base all their operations on 
the basic protocol mechanisms. 
Depending on the network environment, there are several higher-level 
protocols set up on the basic protocol. A schematic representation of a 
typical vertical protocol stack, known as OSI (Open Systems 
Interconnection) reference model for CCITT (Consultative Committee on 
International Telephone and Telegraph) applications is defined in the 
CCITT Recommendation X.200, "Reference Model of Open Systems 
Interconnection for CCITT Applications", Blue Book, Fascicle VIII.4, 
Geneva, 1989. Said OSI reference model uses seven levels, referred to as 
layers. Each layer has its own specific function and offers a defined 
service to the layer above using the services provided by the layer below. 
If an application program, for example, which runs on a first system 
requires the use of data held in a second, remote system, an exchange of 
information takes place. When said second system receives a request to 
send a specific data packet, this data packet has to be transmitted from 
the highest protocol level, e.g. the application layer, down through all 
lower protocol levels, prior to be sent along the physical link. Each of 
these protocol layers adds its layer-specific connection information to 
the data packet received from the higher layer. Therefore, a communication 
connection between two systems is defined in a packet header, hereinafter 
referred to as protocol header, by the aggregate of fields carrying 
connection information of the vertical protocol stack. 
When receiving a data stream made up of data packets at a receiver site, 
prior to routing, multiplexing or compressing it, said protocol header has 
to be scanned to extract the respective words comprising connection 
information for further processing 
To date, most of the protocol connections are identified by sequentially 
processing the protocol headers in software. This operation consumes a 
considerable amount of time in the protocol processing, in particular when 
dealing with many connections, e.g. in a server, or when processing 
multimedia data streams. 
A microprogrammed controller, used to recognize the protocol type of a 
protocol header and to extract protocol specific data fields, has been 
described in "Implementing PE-1000 Based Internetworking Nodes", H. W. 
Chin et al., Part 3 of 3, Transfer, Vol. 5, No. 3, May/June 1992, pp. 5-8. 
The hardware implementation of a routing table for the translation of 
packet identifiers into an appropriate physical output link is described 
in "Putting Routing Tables in Silicon", T.-B. Pei and C. Zukowski, IEEE 
Network Magazine, January 1992, pp. 42-50. This approach is mainly 
characterized in that a Content-Addressable Memory (CAM) is employed to 
match connection information in the header of a single protocol. In 
addition, the advantages and disadvantages of CAMs versus conventional 
Random-Access-Memories (RAM), used to store routing information, have been 
evaluated by Pei and Zukowski. 
Neither of the two systems above, both of them relating to the solution of 
sub-problems, nor the known software approaches allow fast processing of 
multiple transport protocols such as TCP (Transmission Control 
Protocol)--"Transmission Control Protocol; DARPA Internet Program Protocol 
Specification", RFC 793, DARPA, September 1981--and XTP (Express Transport 
Protocol)--"XTP Protocol Definition", Protocol Engines Incorporated, 
Revision 3.6., edited by Protocol Engines, Mountain View, Calif., 11 Jan. 
1992--which build on the Internet Protocol (IP)--"Internet Protocol; DARPA 
Internet Program Protocol Specification", RFC 791, DARPA (Defense Advanced 
Research Projects Agency), September 1981--or TP4 (Transport Protocol, 
Type 4)--"Connection Oriented Transport Protocol Specification", ISO/IEC 
JTC1 Draft International Standard ISO/IEC DIS 8073--which builds on CLNP 
(Connectionless Network Protocol)--"Protocol for Providing the 
Connectionless-Mode Network Service", ISO ISO/IEC 8473. The abbreviation 
RFC, as herein used, is an acronym of the term Request for Comments. In 
addition, the present invention is well suited for processing multimedia 
traffic as for example ST-II (Stream protocol, version 2)--"Experimental 
Internet Stream Protocol; Version 2 (ST-II)", RFC 1190, October 1990, 
edited by C. Topolcic. The processing of protocol headers and the 
recognition of different protocol types in real time is a very complicated 
and difficult undertaking. In almost all network systems, header 
processing is still a major CPU-cycle (Central Processor Unit) consuming 
activity. The claimed invention does not only extract protocol data 
fields, see H. W. Chin et al., but uses these fields to extract a unique 
connection identifier. This operation is performed in real-time. 
Additionally, the present method and apparatus are designed for processing 
protocol stacks. 
It is an object of the present invention to provide a method for improved 
header processing in networks carrying traffic of various protocols. 
It is a further object of the present invention to provide a method for 
fast and reliable processing of addressing, i.e. connection, information 
of multiprotocol data streams. 
It is another object of the present invention to provide a method for fast 
and reliable processing of multiprotocol data streams comprising 
multimedia data. 
It is an object of the present invention to provide a method which allows 
real-time processing of addressing, i.e. connection, information of 
complex protocol headers. 
It is another object of the present invention to provide a hardware 
implementation of said methods. 
SUMMARY OF THE INVENTION 
The above objects have been accomplished by providing a method in 
accordance with claim 9 and a hardware implementation, referred to as 
Protocol Filter, of said method in accordance with claim 1. This method 
and apparatus are characterized in that the protocol-type information of a 
first protocol is extracted and the protocol information of protocols 
built on said first protocol are read, sequentially. The protocol-type 
information and said protocol information are applied to the input of a 
CAM to provide an address at the CAM's output each time the information 
applied to this input matches information stored in said CAM. The 
addresses provided at the output are concatenated to a unique connection 
identifier.

GENERAL DESCRIPTION 
When exchanging or transmitting information, e.g. data packets or 
multimedia data streams, in or along a network, the transmission or 
exchange builds on multiple protocol types. The protocol information of 
the different protocol types is inserted into a protocol header of a data 
packet or data stream to be transmitted. 
This protocol header has to be received and processed prior to routing the 
attached data stream through a switch or a network, prior to compressing 
incoming traffic, or prior to multiplexing it. The processing of headers, 
in particular the processing of the protocol related words therein, 
typically takes place in network nodes, adapters, bridges, multiplexers, 
compressors, protocol analyzers, switches and servers, just to name some 
of the conceivable environments. 
In connection with the first embodiment, the basic concept of the present 
invention will be described. The inventive Protocol Filter (PF) 10 is 
shown in FIG. 1. By means of the PF 10, processing of protocols is much 
simpler, since connection identification of layered protocol headers--in 
accordance with the inventive method--when being implemented in hardware, 
is much faster. The function of the Protocol Filter 10 is to extract the 
relevant information from the protocol header of a received data stream or 
packet, to compare this information with stored connection information and 
to provide the associated connection identifier if both data are equal. In 
the present embodiment, PF 10 is employed in a Token-Ring network adapter 
14 to extract all relevant words from the fields 22-27 of a protocol 
header 20 preceding a data stream 21, received via bus 11, as 
schematically illustrated in FIG. 2. At an output port 12, a connection 
identifier is provided which can be used for further processing. This 
further processing depends on the environment in which the Protocol Filter 
10 is used. 
As schematically illustrated in FIG. 2, the data stream 21 is preceded by 
said protocol header 20. In this simplified Figure, the header 20 
comprises fields 22, 23, and 24 which belong to a first protocol and 
fields 25 through 27 belonging to a second protocol which builds on said 
first protocol. In this Figure, fields comprising protocol information 
relevant for the processing of the respective data stream 21 are hatched. 
The Protocol Filter 10 of the first embodiment, as part of said Token-Ring 
adapter 14, is employed in a Token-Ring network carrying TCP/IP, ST-II, 
and ISO CLNP/TP4 traffic. Details of said network are described in "IBM 
Token-Ring Network: Architecture Reference", SC30-3374-02, third edition, 
September 1989. The Token-Ring adapter 14 handles the Medium Access 
Control (MAC) in its finite state machines. The LLC (Logical Link Control) 
frames, in LPDU (Link Protocol Data Unit) format, received by the adapter 
14 and to be processed by the Protocol Filter 10, are shown in FIG. 3. The 
DSAP (Destination Service Access Point) field 30 identifies the access 
point for which said LPDU is intended. Typical values of the DSAP field 30 
are given in the above mentioned "IBM Token-Ring Network: Architecture 
Reference", SC30-3374-02. The DSAP value, i.e. the protocol-type 
information, is used as starting point by the Protocol Filter 10 in the 
search through the different protocol addresses. These protocol addresses 
are arranged in trees, in accordance with the present invention. In the 
first embodiment, the TCP/IP and ST-II addresses are part of a first tree 
shown in FIG. 4, and the addresses corresponding to the CLNP/TP4 protocol 
are arranged in a second tree, which is illustrated in FIG. 5. 
The addresses and protocol specific information used in the various layers 
of the Internet Protocol (IP) form the tree shown in FIG. 4. The first 
protocol which builds on the Internet Protocol, i.e. the TCP/IP, is 
arranged on the left hand side of FIG. 4 and consists of four tree levels. 
A TCP/IP connection is defined by the path through said tree 
(short-dashed) starting at the root 40 of the tree characterizing the 
Protocol Type (=Internet) on which the TCP builds. The first level defines 
the protocol version (Ver. Prot.) 41, the second level the source address 
(S.Addr.) 43, followed by the destination address (D.Addr.) 44 and, at the 
fourth level, the source/destination port (S.D.P.) 45. This first path 
defining the TCP/IP connection is stored in a Content-Addressable Memory 
of the Protocol Filter 10, as will be described later. A second path 
(dashed) defines a ST-II connection. This second path starts at the root 
40 of the same tree and ends at the first level at 42. This second 
connection is solely defined by the protocol type (=Internet) and the 
protocol version (=#0052HID) in the present example. This second path is 
stored in the PF 10, too. In the present application, the # sign is used 
in connection with hexadecimal notation. 
FIG. 6A illustrates a TCP/IP header. The uppermost part of FIG. 6A shows 
the Internet Protocol header. The meaning of the abbreviations used in the 
IP header fields are listed in the below given Table 1. The abbreviations 
of the header fields 60-65 required for processing in the present Protocol 
Filter 10, i.e. carrying words comprising protocol information, are 
printed bold. 
TABLE 1 
______________________________________ 
Internet Protocol header 
Bits No. 
______________________________________ 
Ver (Protocol) Version 
4 60 
IHL Internet Header Length 
4 61 
TOS Type of Service 8 62 
L Total length 16 
ID Identification 16 
F Flags 3 
FO Fragment Offset 13 
TTL Time to Live 8 
PROTO Protocol 8 63 
HC Header ChecKsum 16 
DA Destination Address 
32 65 
SA Source Address 32 64 
______________________________________ 
The TCP part of the protocol header is illustrated in FIG. 6A, too. The 
abbreviations used in the fields of this TCP header are listed in Table 2. 
The abbreviations of the relevant fields 66, 67 of the TCP header are 
printed bold. 
TABLE 2 
______________________________________ 
TCP header 
Bits No. 
______________________________________ 
SP Source Port 16 66 
DP Destination Port 
16 67 
SN Sequence Number 32 
AN Acknowledge Number 
32 
DO Data Offset 4 
RF Reserved/Flags 12 
W Window 16 
______________________________________ 
The content of the header fields of the IP header is defined in 
"Experimental Internet Stream Protocol; Version 2 (ST-II)", RFC 1190, 
October 1990, edited by C. Topolcic (in particular on page 75 thereof). 
The value of the IP Version number (Ver; 60) is #4, the normal header 
length of the Internet header (IHL; 61) is #5 and the value of the Type Of 
Service field (TOS; 62) is #00, these values being given in hexadecimal 
notation. The protocol field (PROTO; 63) in IP holds an 8-bit number which 
is defined in "Assigned Numbers", J. Postel, RFC 790, September 1981. This 
8-bit number of the protocol field (PROTO; 63) is #06. These four 
mentioned IP header fields 60-63 are concatenated and padded to get a 
32-bit word to be stored in the Protocol Filter 10, in accordance with the 
present invention. This results in a 32-bit word #00450006 in the present 
case defining the protocol version, herein referred to as Ver.Prot. field 
41, see first level of the tree given in FIG. 4. Source Address (SA; 64) 
and Destination Address (DA; 65) of said IP header are equal to the 
addresses at 43 (S.Addr.) and 44 (D.Addr.) of the tree. The format of the 
addresses being held in these two fields are also defined in "Assigned 
Numbers", J. Postel, RFC 790, September 1981. The source/destination port 
(S.D.P.) address 45 in the tree is derived from the Source Port (SP; 66) 
field and the Destination Port (DP; 67) field of the TCP header in FIG. 
6A. Details of TCP are given in the already mentioned protocol 
specification "Transmission Control Protocol; DARPA Internet Program 
Protocol Specification", RFC 793, DARPA, September 1981. How these four 
levels of the TCP/IP part of the tree, shown in FIG. 4, are stored in the 
Protocol Filter is shown in FIG. 8. 
The header of the second protocol, the ST-II protocol, derived from the 
Internet Protocol, is illustrated in FIG. 6B. The abbreviations are 
explained in Table 3. Fields 68-70 carry protocol information being 
relevant. 
TABLE 3 
______________________________________ 
ST-II header 
Bits No. 
______________________________________ 
ST IP Version numbdr = 5 4 68 
Ver ST-Version number = 2 in case of ST-II 
4 69 
Pri Priority of the packet 
3 
T Time Stamp 1 
L TotalBytes 16 
HID Hop Identifier 16 70 
HC Header Checksum 16 
______________________________________ 
ST is the IP Version number assigned to ST packets and the Ver field 69 
comprises the ST-Version number. The value for ST is #5 and the value for 
Ver is #2 in case of ST-II, as defined in "Experimental Internet Stream 
Protocol; Version 2 (ST-II)", RFC 1190, October 1990, edited by C. 
Topolcic. For ST-II, the content of the ST, Ver, and HID fields 68-70 is 
extracted from the header and concatenated to the 32-bit word #0052HID, 
which is stored in the present PF 10. 
The respective frames of TP4 which builds on CLNP, as well as the frames 
corresponding to CLNP are illustrated in FIG. 7. The abbreviations 
assigned to the respective frames of the CLNP packet header are explained 
in Table 4. 
TABLE 4 
______________________________________ 
CLNP header 
Bits No. 
______________________________________ 
NLPI Network Layer Protocol lndicator 
8 71 
LI Length Indicator 8 
V/PIE Version/Protocol ld Extension 
8 72 
LT Life Time 8 
F Flag 3 73 
Type Type: DT PDU 5 74 
SL Segment Length 16 
Chs Checksum 16 
______________________________________ 
Next, some typical values of fields 71-74 of the CLNP header are given. 
NLPI=#81 indicates that Version 1 of the respective protocol is used. The 
value of V/PIE is #01. The value 11100 is assigned to the Type frame 74 in 
case of DT PDU. The following fields of the CLNP header, NLPI=#81, 
V/PIE=#01, F=X, and Type=Y are concatenated and padded to a 32-bit word 
#008101XY. This word is herein referred to as CLNP Hdr 51, see FIG. 5. The 
meaning of the abbreviations used in the TP4 header fields is shown in 
Table 5. 
TABLE 5 
______________________________________ 
TP4 header 
Bits No. 
______________________________________ 
LI Length Indicator 16 
DT Data 8 75 
DR Destinationreference 
16 76 
TN TPDU Number and EOT Flags 
8 
______________________________________ 
The value of the Data field (DT; 75) of said TP4 header is 1111 0000 which 
is equal to #F0 using hexadecimal notation. The Destination reference (DR; 
76) is XXXX resulting in a 32-bit word #F000XXXX, referred to as TP4 
header (TP4 Hdr; 52). The characteristic 32-bit words CLNP Hdr 51 and TP4 
Hdr 52 are stored in the present Protocol Filter 10, as described below. 
Referring now to FIG. 8, a Content-Addressable Memory (CAM) 80 is shown, 
which is part of the Protocol Filter 10. This CAM 80 is characterized in 
that an address of a row which comprises a word is presented at the output 
82 each time a protocol information at its input 84, e.g. the word 83, 
matches the word stored in a row. If for example the word #1000450006 is 
applied to the CAM's input 84, the CAM provides the CAM address of the 
respective row at its output 82 as soon as the word at the input 84 
matches a stored word. Since the CAM 80 of the present embodiment is a CAM 
having 256 rows, CAM addresses with 2.sup.8 bits or two-digit hexadecimal 
addresses are needed. In the given example the two digit-address #01, 
corresponding to row 81, would be sent to the output 82. CAMs are 
described in "Content-Addressable and Associative Memory", L. Chisvim et 
al., IEEE Computer, July 1989, pp. 51-63. 
As shown in FIG. 8, the different paths are stored in the CAM, where a row 
contains the information of a tree level (Tag), the protocol-type 
information (PType) and the address information (HId). There are two 
possibilities in a protocol filter to compare the protocol information 
with the CAM content. The simplest way is to concatenate the header 
information to a concatenated information word of width w, the width of a 
row of this CAM, and compare it in one operation with the rows of a CAM. 
This approach has the advantage that it is easy to implement. The width of 
the CAM is determined by the number of bits required when the maximum 
possible number of header information are concatenated. 
The tagged CAM 80, presented in the first embodiment, consumes less memory 
space than a conventional CAM. The number of header words to be scanned is 
1, if for example a protocol such as XTP, directly builds on the Media 
Access Control (MAC), or at most 5 for the example on the left hand side 
of FIG. 4. Using the tagged CAM one takes advantage of the hierarchical 
structure of the protocols and the protocol addresses. In FIG. 8, an 
exemplary row 83 of the CAM is illustrated. The first section of this row 
83 comprises a tag, also referred to as level number, being equal to the 
respective level of one of the protocol trees of FIGS. 4 and 5. In the 
next field, to the right of the tag field, the respective protocol-type 
information (PType) is stored, followed by an address such as for example 
the 32-bit words Ver. Prot, D.Addr. and so on. 
The interaction of the various units of the inventive Protocol Filter 10 
with said tagged CAM 80 will now be described in connection with FIG. 9. 
The Protocol Filter 10 comprises the following four units: the already 
mentioned Content-Addressable Memory (CAM) 80, a Protocol-Type Detector 
(PTD) 90, a Mask Generator (MG) 91, and a Connection Number Builder (CNB) 
95. 
The Protocol-Type Detector (PTD) 90 is a state machine which reads the 
header protocol-type information on a bus 97, e.g. a Token-Ring, and 
extracts the protocol-type information from an incoming protocol header. 
Next, the PTD 90 forwards this protocol-type information to the Mask 
Generator (MG) 91. In case of a LLC header, illustrated in FIG. 3, the PTD 
90 extracts the protocol-type information from the Destination Service 
Access Point (DSAP) field 30 by looking up the DSAP in a table. This table 
is a memory, not shown, of the size 256 times t, with t being equal to the 
size of the protocol type field 99 in the Mask Register (MR) 93 of the 
Mask Generator 91. The DSAP is used as the address to read the 
protocol-type information in this table. 
The Mask Generator (MG) 91 consists of a Header State Machine (HSM) 94 and 
a Tag Counter (TC) 92. The HSM 94 is started by the PTD protocol-type 
information and the HSM 94 sequentially reads the header fields provided 
via bus 97. If a header field is reached which comprises information 
relevant for the connection detection, i.e. for the processing of a data 
stream, it is written to the field 100 of the Mask Register (MR) 93. As 
described above, the tag determines the tree level for which a header word 
is valid. The Tag Counter (TC) 92 is a c-bit counter which is incremented 
for each relevant field to be compared and reset by the PTD 90. For TCP/IP 
and most other transport protocol stacks a 2-bit counter is sufficient. In 
case of the IP header, see FIG. 6A, the protocol information 60-63 is 
concatenated in one 32-bit word (#00450006), called concatenated 
information word, and is compared with the rows of the CAM 80 in one 
operation. The tag counter and the PTD type are concatenated with the 
protocol information in the mask register 93. The tag counter is stored in 
the tag field 98 of the MR 93. The size t of the protocol type field 99 in 
said MR 93 depends on the number of different protocols which must be 
processed. With 6 bits most of today's protocols can be covered. With the 
PF 10 according to the first embodiment, processing of two different 
protocol types, illustrated in FIGS. 4 and 5, is possible. In this 
particular example, the length t of the protocol type field 99 is only 1 
bit. 
The CAM 80, has the same width (w=c+t+32 Bits) as the MR 93. For a match, 
the CAM address of the data is given out. In cases where the word 
#100052HID is situated in said MR 93, the content of the MR 93 matches 
with the content of the row stored under CAM address A=#05 (=0000 0101) 
and the CAM address A=#05 will be provided at the CAM's output 82. Because 
the protocol-type information and the tag is included in the mask register 
93, the CAM output at port 82 is unique for the specific protocol 
information, protocol-type information and tree level. The CAM 80 can be 
written from outside. 
The Connection Number Builder (CNB) 95 reads the CAM addresses at the 
output of CAM 80 and generates a unique connection identifier by 
concatenating the CAM addresses of the present path through one of the 
protocol trees. The CNB 95 is triggered by the Mask Generator 91 to read 
the CAM output 82. If the CAM 80 does not find a match, the CNB 95 is 
reset and the protocol information is unknown to the present PF 10, and 
must be dealt with in software. This CNB 95 generates a unique connection 
identifier, i.e. a unique number, out of the stacked protocol header of 
LLC/IP/TCP, see short-dashed path in the IP tree of FIG. 4, as set out in 
context with FIGS. 10A and B. The 8-bit CAM addresses, referred to as 
Ver.Prot. 101, S.Addr. 102, D.Addr. 103, and S.D.P. 104, are concatenated 
to form one concatenated information word 105. In case of the LLC/IP/TCP 
path the value of this word is #01020304 in hexadecimal notation, as 
illustrated in FIG. 10B. When preceding this word by the protocol-type 
information, e.g. PType=#00 in the present case, a unique connection 
identifier #0001020304 is assigned to the present protocol stack. 
When concatenating the CAM address of the CAM row in which the value 
#0052HID, characterizing the ST-II protocol stack, is stored, the 
connection number #0005 is obtained (A=#05 preceded by PType=#00). 
The 32-bit word #008101XY, characterizing the CLNP, header and the 32-bit 
word assigned to the TP4 header are stored at addresses #07 and #08 of the 
CAM 80. A unique connection identifier is generated by the CNB 95 when 
concatenating these two 8-bit wide hexadecimal numbers preceded by a 
number characterizing the protocol type (PType). This number 
characterizing the protocol type, referred to as protocol-type 
information, is #01 in the present case. The value of the connection 
identifier is #010708. 
In case of the TCP/IP protocol stack, the value of the Ver.Prot. field 
identifies the respective protocol stack. The source addresses (S.Addr.), 
destination addresses (D.Addr.) and the source/destination ports (S.D.P.) 
can each identify up to 256 addresses. To use the connection identifier as 
a pointer in an array of connection control blocks, the 32-bit connection 
identifier must be converted to a connection index. This can be done in 
the following, exemplary way: The first byte, given in the Ver.Prot. field 
101, is used as a pointer to the array of control blocks of the specific 
protocol version, in this example the TCP/IP control block. The 8-bit 
addresses are different, because each address codes an identifier in 
another tree level. Therefore only b.sub.i bits of the 8 bits are needed 
to distinguish 2.sup.b.sbsp.i addresses in a tree level i. The connection 
index is generated by extracting the b.sub.i bits in each address and 
concatenating them. The CAM must be written such that all addresses of the 
same protocol type and tree level i are different in the least significant 
bits b.sub.i. 
If, for example, 8 source IP addresses, 4 destination addresses, and 8 
source/destination addresses are reserved to generate a connection index, 
they can be coded in 3, 2, and 3 bits, respectively. The 2- and 3-bit 
identifiers of the 8 bit wide words 110-112 are concatenated to an 8-bit 
connection index 113, shown in FIG. 11. In this example, 20 entries in CAM 
80 are used for TCP/IP, the remaining 236 are free for other protocols. If 
the maximal number of address entries at level i is allowed to dynamically 
increase and 2.sup.b.sbsp.i+1 addresses of level i must be distinguished, 
then all addresses used for tree level i must be examined to guarantee 
that they are different in the least significant b.sub.i+1 bits. The size 
of the connection index 113 is increased by one bit. Therefor a table, 
called routing table, must be built, which holds the pointers to the 
control blocks, and the connection index is used as a pointer to this 
table. The generation of a connection index and the management of the CAM 
is performed by a protocol processor to keep the architecture flexible. 
Many protocol connections use less than four tree levels. The ST-II for 
example uses only the protocol type and stream identifier given in the 
fields 40 and 42 of the tree in FIG. 4. The resulting connection 
identifier has 16 significant bits and can be used directly by the 
Token-Ring adapter 14 to detect multimedia data and to handle these data 
in dedicated devices. 
Prior to describing other embodiments of the present invention, the 
advantage of a tagged CAM in view of conventional CAMs is addressed. There 
are three possibilities in a Protocol Filter to compare the necessary 
protocol information with the CAM content. The simplest way is to 
concatenate the protocol information, the words comprising protocol-type 
information and a tag (level number) to a concatenated information word of 
width w, as described in connection with the first embodiment. This 
approach makes use of the hierarchical structure of the `protocol trees`. 
The second approach, which is easy to implement, is characterized in that 
all relevant protocol information of a protocol header is concatenated to 
form one word of the width k. The width k of the CAM is determined by 
number of bits required when the maximal possible number of header 
information is concatenated. The number of bits required, for example, for 
TCP/IP over LLC-Type 1, as illustrated in FIG. 6A, is 128, as shown in 
Table 6. 
TABLE 6 
______________________________________ 
TCP/IP/LLC 
Bits 
______________________________________ 
S.Addr. 32 
D.Addr. 32 
S.D.P. 32 
Version/Type 8 
Protocol 8 
LLC DSAP 8 
LLC SSAP 8 
total bits per row (k) 
128 
______________________________________ 
To support 256 connections 256 CAM rows with a total of 32768 bits are 
required. The header information is extracted in a similar fashion as in 
the Protocol Type Detector (PTD) and the Mask Generator (MG). 
The third approach is to sequentially apply word by word, each carrying 
address information, read from the protocol header to the input of a CAM. 
According to this approach it is neither necessary to concatenate header 
words prior to applying them to the CAM nor to store information in said 
CAM in reflecting the hierarchical structure of the `protocol trees`. 
The tagged CAM 80, presented in connection with the first embodiment, 
consumes less memory space than the two other approaches. The number of 
header fields which have to be scanned is 1 if, for example, XTP directly 
builds on the MAC (Media Access Control), or at most 5 for the example in 
FIG. 4. By using the tagged approach one takes advantage of the 
hierarchical structure of the protocols and the protocol addresses. 
Because of the integration of the tag information into the Mask Register 
(MR) 93, up to four levels are compared. The memory space consumed for the 
256 TCP/IP connections in the example is 800 bits, i.e. 20 times the CAM 
width of 40 bits. For 256 XTP connections 256 rows with a total of 10240 
bits are consumed. 
In connection with the second embodiment of the present invention a 
Protocol Filter 120, being part of a Multiprotocol Router 124, is 
described. This Multiprotocol Router 124 comprises a Routing Table (RT) 
125 and a Routing Engine (RE) 127, as illustrated in FIG. 12. For 
simplicity reasons, the second embodiment is restricted to four different 
protocols; Internet Protocol (IP), System Network Architecture (SNA), 
Netbios (Local Area Network Basic Input/Output System), and OSI (Open 
Systems Interconnection). In case that a data stream is received via input 
121, said Protocol Filter 120 scans this data stream and extracts the 
protocol-type information thereof. Next, all relevant protocol header 
fields are scanned and read. The information of these fields is preceded 
by said protocol-type information and tagged using a level number 
generated by a Tag Counter. Then, identical entries in a tagged CAM are 
looked for, and the respective CAM addresses provided at the CAM's output 
are concatenated to form a unique connection identifier. Either this 
unique connection identifier, or a connection index distinguished thereof, 
is forwarded via link 122 to a Routing Table 125. With aid of the routing 
information of this table 125, a Routing Engine (RE, 127) starts 
processing of the data stream whose protocol header has been scanned and 
processed by the Protocol Filter 120 in the meanwhile. 
The use of the present method and apparatus is not limited to the two 
embodiments described above. Further applications are schematically 
illustrated in FIGS. 13 and 14. In FIG. 13, the Protocol Filter 130 is 
shown as part of a multimedia protocol adapter used to separate audio, 
video and traditional data received. The unique connection identifier is 
forwarded to a Stream Demultiplexer (SD) 131 for separation of the 
different data streams. In FIG. 14, a Protocol Filter 140 is shown being 
connected to a server 142. The data stream received, as well as the unique 
connection identifier, is forwarded to a Protocol Processor (PP) 141 for 
further processing. 
The Protocol Filter can also be used in a light-weight Multimedia Adapter 
to separate isochronous and asynchronous data streams and to trigger units 
for checksumming, decryption and decompression of data. Such a Multimedia 
Adapter at least comprises a Medium-Access Control (MAC) Unit, a Checksumm 
Unit, a Direct-Memory Access (DMA) Unit and the Protocol Filter. 
In addition to the embodiments and applications mentioned, it is 
advantageous to employ a Protocol Filter, in accordance with the present 
invention, in a Protocol Analyzer, also referred to as Protocol Sniffer, 
which can be plugged to a network, wherever a problem occurs, for 
monitoring reasons. 
Typical environments for the present Protocol Filter are FDDI (Fiber 
Distributed Data Interface), ATM (Asyncronous Transfer Mode), and FCS 
(Fiber Channel Standard) networks.