The Architecture of a Gb/ s
`Multimedia Protocol Adapte r
`
`Erich Rutsch e
`IBM Research Division ,
`Zurich Research Laboratory
`Saumerstrasse 4, 8803 Ri schlikon, Switzerlan d
`
`Abstract
`In this paper a new multiprocessor-based communication adapter is presented. The adapter architec-
`ture supports isochronous multimedia traffic and asynchronous data traffic by handling them separate-
`ly . The adapter architecture and its components are explained and the protocol processing performance
`for TCP/IP and for ST-II is evaluated . The architecture supports the processing of ST II at the network
`speed of 622 Mb/s . The calculated performance for TCP/IP is more than 30000 segments/sec . The ar-
`chitecture can be extended to protocol processing at one Gb/s .
`
`Keywords : Multimedia Communication Subsystems ; Network Protocols ; Parallel Protoco l
`Processin g
`
`1. Introduction
`As data transmission speeds have increased dramatically in recent years, the processing of protocols ha s
`become one of the major bottlenecks in data communications . Current experimental networks provide a
`bandwidth in the Gb/s range . New multimedia applications require that networks guarantee the qualit y
`of service of bulk data streams for video or HDTV . The protocol processing bottleneck has been over -
`come by dedicated communication subsystems which off-load protocol processing from the worksta-
`tion. Many of such communication subsystems proposed in the literature are multiprocessor architec-
`tures [Braun 92, Jain 90, Steenkiste 92, Wicki 90] . In this paper we present a new multiprocesso r
`communication subsystem architecture, the Multimedia Protocol Adapter (MPA), which is based o n
`the experience with the Parallel Protocol Engine (PPE) [Kaiserswerth 92] and is designed to connect t o
`a 622 Mb/s ATM network . The MPA architecture exploits the inherent parallelism between the trans-
`mitter and receiver parts of a protocol and provides support for the handling of new multimedia proto -
`cols.
`The goal of this architecture is to speed up the handling of multiple protocol stacks and of multimedi a
`protocols such as the Internet Stream Protocol (ST II) [Topolcic 90] . Multimedia traffic often require s
`isochronous transmission in contrast to conventional asynchronous traffic for file transfer or for remot e
`procedure call . To guarantee the isochronous processing of multimedia data streams, the asynchronou s
`and isochronous traffic are handled separately . A Header Parser scans incoming packets, detects th e
`header fields and extracts the header information . This information is used to separate isochronous an d
`asynchronous traffic and to split the header and the data portions of a packet . Dedicated header and data
`memories are used to store the header and data portions of a packet . The separation of receiver, trans -
`mitter and the dedicated memories decreases memory contention .
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`In Section 2 the concepts of the MPA architecture are presented . Section 3 explains protocol processin g
`on the MPA. In Section 4 the performance of the MPA is evaluated by adapting the measurements of ou r
`TCP/IP implementation on the PPE to the MPA architecture . The last section gives the conclusions .
`
`2. Architectur e
`The architecture of the MPA is based on our experiments with the PPE [Kaiserswerth 92],[Rutsche 92] .
`The PPE is a four-processor system based on the transputer T425 with a network interface running a t
`120 Mb/s . On the separate transmit and receive side two processors, the host system and the networ k
`interface use a shared memory for storing and processing protocol data . Transmit and receive side are
`only connected via serial transputer links .
`
`2.1 Concep t
`The protocol processing requirements of multimedia protocols are very different from the requirement s
`of traditional transport protocols . Isochronous multimedia traffic may require the processing of bul k
`data streams with low delay and low jitter but may accept bit errors or packet loss . Asynchronous traffic ,
`such as file transfer or remote procedure call, requires more moderate throughput but tolerates no er-
`rors. In a file transfer between a file server and a client the throughput is limited by the I/O bus and th e
`disk speed. Errors in the data are not acceptable, whereas a bit-error in uncompressed video is not vis -
`ible.
`
`To guarantee the requirements of multimedia connections the processing of multimedia data must b e
`separated from the processing of asynchronous data . A Header Parser detects the connection to whic h
`an incoming packet belongs . Multimedia packets are then forwarded to dedicated multimedia device s
`while other packets go through normal protocol processing .
`
`Protocol processing must be done in software to handle a multitude of protocols . Only functions that are
`common to all or most of the protocols are implemented in hardware . The MAC layer for ATM and the
`ATM Adaptation Layer (AAL) must be implemented in hardware or firmware to achieve the full net -
`work bandwidth of 622 Mb/s .
`
`Our measurements of TCP/IP on the PPE have shown that the processors were not equally loaded be -
`cause of the different processing requirements of the protocol layers and because of the very high cost s
`of the memory operations [Riitsche 92] . The loose coupling via serial links between the receive and a
`transmit part had only minor impact on the performance . An optimal speedup of 1 .7 was calculated fo r
`two processors . Therefore we chose a two-processor architecture for the MPA . One processor on the
`transmit side is connected via serial links to one processor on the receive side . The processors are sup -
`ported by an intelligent Direct Memory Access Unit and dedicated devices for header parsing an d
`checksumming . The memory of both parts is split into a header memory and a data memory to lowe r
`memory contention . The two halves of the MPA are only connected by serial message links .
`
`2.2 Main Building Blocks
`
`The MPA is split into two parts, a receiver and a transmitter, as shown in Figure 1 . The various compo -
`nents and their function are presented in the following .
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`Media Access Control Unit (MACU )
`
`Header Parser (HP)
`
`Checksum
`Generator (CG)
`+
`DMA Unit (DMAU )
`
`A
`
`cb
`
`hI cp
`
`1
`I Q
`I c
`
`cu
`
`(I)
`
`a0
`
`c~
`
`Media Access Control Unit (MACU )
`
`t Data
`•a- Control
`
`Bus (BC)
`Controller
`
`Direct
`Device
`ttachement
`
`Workstation Bus
`
`Workstation Bus
`
`Figure 1 . MPA Architecture
`Media Access Control Unit (MACU) : The MPA is designed to be connected to any high-speed net -
`work . The design of the MAC is beyond the scope of this paper . [Traw 91] for example describes an
`interface to the Aurora ATM network ,
`Header Parser (HP) : The HP is similar to the ProtoParser 1 [Chin 92] . The HP detects on the fly th e
`protocol type of an incoming packet and extracts the relevant header information . This information i s
`forwarded to the DMA Unit and the Checksum Generator .
`
`Checksum Generator (CG) : The CG is triggered by the HP to calculate the appropriate checksum o r
`Cyclic Redundancy Check (CRC) for the packet on the fly . The algorithms are implemented in hard -
`ware and selected by decoding the HP signal . On the sender side the CG is triggered by the DMA unit .
`[Birch 92], for example, describes a programmable CRC generator which is capable of processing 80 0
`Mb/s .
`The Protocol Processor T9000 : The selection of the inmos2 T9000 [inmos 91] is based on our good
`experience with the transputer family of processors in the PPE, The most significant improvements o f
`the T9000 over the T425 for protocol processing are faster programmable link interfaces, a faste r
`memory interface, and a cache . The serial message passing link provides a transmission speed of 10 0
`ProtoParser is a trademark of Protocol Engines, Inc .
`1.
`inmos is a trademark of INMOS Limited .
`2.
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`Mb/s plus a set of instructions to use the links for control purposes . The peek and poke instructions issue
`read and write operations in the address space of the second transputer connected to the other end of th e
`link. These commands allow distributed 'shared memory' between transputers . Two transputers ma y
`allocate a block of memory at identical physical addresses in their local memory . Whenever a value i s
`written into the local copy of the data structure, the address of the variable and its value are also sent via a
`control link to the second transputer .
`
`The Memories : The memory is split into dedicated parts for each flow of data through the MPA t o
`lower memory contention and to provide high bandwidth to those components that access the memor y
`most. The following memory split is used :
`Header memory : stores the protocol headers . Fast static memory operating at cache speed is used t o
`avoid wait cycles .
`Data memory : stores the data part of the packets . Inexpensive video memory (VRAM) is used . The seri -
`al port of the VRAM provides guaranteed access via the DMA Unit to the network . The parallel
`port of the VRAM is used in normal processing by the Bus Controller only . The processor ca n
`accesses the parallel port, e .g. for exception handling .
`Local memory : stores the program code of the processor and the control information of the connections .
`Multimedia FIFO : stores multimedia data and is the interface to a multimedia device . It can be con -
`trolled by the processor for synchronization with asynchronous data streams . Multiple multime-
`dia FIFOs can be arranged in parallel .
`The design does not employ physically shared memory between the transmitter and the receiver, be -
`cause the implementation costs are too high compared to a software implementation using transpute r
`links.
`
`Memory Access ; Processor to
`
`Data Memory
`Header Memory
`Local Memory
`Table 1 . Memory Access Tim e
`
`Memory Type
`Video RAM
`Static RAM
`Dynamic RAM
`
`Average Access Tim e
`60 ns
`30 ns
`60 ns
`
`Direct Memory Access Unit (DMAU) : The DMAU directs the in- and outgoing data streams to th e
`correct destination . The DMAU splits an incoming packet into its header and data part and moves th e
`parts to the respective memories . A pointer to the header structure is written to the receive queue . To
`send a packet the DMAU gathers the data from the data memory and the header from the heade r
`memory . For multimedia traffic the data are gathered from the multimedia FIFO . The memory buffer s
`are handled in a linked list format. The DMAU handles this linked list in hardware and thereby off -
`loads part of the memory management from the protocol processor .
`
`Bus Controller (BC) : The BC is a programmable busmaster DMA controller . It provides a small FIFO
`and a table for DMA requests . The FIFO contains a pointer to the linked list of source data and a connec -
`tion identifier . The BC determines the destination memory address through the connection identifier i n
`the table . The list format is the same for the BC and the DMAU . In the transmit BC the host writes to th e
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`FIFO and the protocol processor to the table . In the receive BC the protocol processor writes to the FIF O
`and the host to the table .
`
`2.3 Packet Processin g
`Packets are processed in a hardware pipeline which runs at network speed . The pipelined packet proces -
`sing is shown in Figure 2 .
`
`Receive r
`The MACU receives cells from the ATM network, processes the AAL, and triggers the receive pipelin e
`to start . The receive pipeline is run by the DMAU . The HP and the CG process the data as they are co -
`pied from the MACU to the destination address in the memories or to the multimedia FIFO . The HP
`extracts the relevant header information from the packet and forwards the information to the DMA U
`and the CG . The CG uses this information to detect which checksum or CRC it must calculate . The CG
`calculates the checksum on the fly as the packet is copied by the DMAU and forwards the result to th e
`DMAU. The DMAU uses the information generated by the HP to determine the format and the connec -
`tion of the packet . For a multimedia connection the DMAU removes the header from the packet an d
`writes the data part to the Multimedia FIFO .
`
`Transmit Pipeline
`
`MACU
`
`HP
`
`CG
`
`DMAU
`
`HP
`
`parse heade r
`-------------- -
`
`Multimedia
`- Header
`Data
`
`Receive Pipeline Header ~~
`
`DMAU
`
`CG
`
`MACU
`
`Data
`
`Multimedia
`
`DMAU
`
`CG
`
`write header
`
`o
`
`Figure 2. Pipelined Packet Processin g
`
`calculate , write checksum -
`
`For asynchronous traffic the DMAU writes a structure to the header memory which holds the header ,
`the header information extracted by the HP, the checksum calculated by the CG, and the pointer to th e
`data in data memory . The data part of the packet is written to the data memory . The DMAU writes a
`pointer to the header structure to the receive queue . The protocol processor is then responsible for pro-
`cessing of the header structure . The addresses of free buffers in header and data memory are obtaine d
`from a linked list of free buffers .
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`If the HP does not recognize a packet header the entire packet is written to the data memory . In this case ,
`the protocol processor performs the processing of the packet header in data memory . For a new connec -
`tion the protocol processor builds up the connection and programs the HP to recognize the header .
`
`Sende r
`On the transmit side the protocol processor builds the layered protocol header in the header memory . It
`builds a structure which holds the pointers to the header and to the data, the length of the header an d
`data, and the connection type . This structure is written to the send queue . The DMAU runs the sen d
`pipeline . It interprets the structure and forwards the connection type to the CG . The CG calculates the
`checksum on the fly as the packet is written to the MACU memory . In the MACU the packets are store d
`to process the AAL and to segment the AAL frame into ATM cells . Once the CG has finished, it write s
`the checksum to its position in the packet frame and triggers the MACU to send the packet . Once th e
`packet is sent, the DMAU appends the buffers to the corresponding free—lists .
`
`3. Protocol Processin g
`
`3.1 Transport Protocol Stack s
`
`Transport protocol processing on the MPA in the example of TCP/IP is shown in Figure 3 . The socke t
`layer is split into a lower half serving TCP and an upper half which interfaces to the application . A more
`detailed description of our parallel TCP/IP implementation can be found in [Riitsche 92] .
`
`Sending a packet : The send data are in a buffer allocated on the host . The application creates a socke t
`and establishes a TCP/IP connection . The socket send call triggers the write process which copies th e
`data to the MPA and gives the control over the data to xtask . The xtask process is then responsibl e
`for the transmission and possible retransmissions of the data . It builds the TCP packet and forwards th e
`pointer to the packet to ip_send . Here the IP header is placed in front of the TCP segment . Then th e
`pointer to the packet is written to the send queue and the DMAU sends the packet via the MACU to th e
`network.
`
`Receiving a packet : Upon receipt of a packet the DMAU writes the pointer to the packet to the receiv e
`queue . ip_demux reads the receive queue, checks the header and, if no error or exception occurred ,
`forwards the packet to tcp_recv, or else to icmp_demux . The tcp_recv process analyzes th e
`TCP header and calls the appropriate handler function for a given protocol state . To send an acknowl -
`edgement or a control packet tcp_recv uses a Remote Procedure Call (RPC) to the transmit side .
`Correctly received packets are appended to the receive list . rtask forwards the received segments t o
`the application process which is blocked in the socket receive procedure . This procedure then fills th e
`user buffer with data from the receive list .
`
`3.2 Multimedia Protocols
`
`For multimedia traffic often real—time data and continuous data streams are required . ST—II is a good
`example of a protocol that supports this type of traffic . After a connection has been set up, the receptio n
`of data packets requires only the detection of the connection and the calculation of the header checksum .
`For sending, the header can be built only once in the header memory and then used for all the data pack -
`ets of the connection . These functions are done in a hardware pipeline by the HP and the CG (see Figur e
`2) . The DMAU scatters and gathers the header and the data without any interaction of the protocol pro -
`
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`Applicatio n
`
`Transmission
`Control
`Protocol
`
`TCB
`
`DMAU out
`Transmit Side
`
`Receive Sid e
`
`rVitual Shared Memory
`
`I
`
`.
`rciceiaced .`,
`~bI.IaCdIwIare.:in.tlle, MP.
`
`Figure 3. Parallel TCP/IP Implementatio n
`cessor. Therefore real-time processing of ST-II at the network speed of 622 Mb/s is possible . The inter-
`(SCMP), which
`action of the processor is only required to handle the Stream Control Message Protocol
`is responsible for creating and keeping most of the state in a ST-II protocol connection .
`
`4. Performance Estimatio n
`4.1 The Method
`The measurements of the TCP/IP implementation on the PPE were used and adapted to the MPA archi-
`tecture [Rutsche 92] . The execution times of program segments accessing local memory Tiocaimem and
`data memory Tdatame,n are calculated from the execution times on the PPE minus the time saved by th e
`hardware devices replacing software functions . These execution times are multiplied by a speedup fac-
`tor S, which is determined by the memory timing and the faster processor, and summed to get the execu -
`tion time TMPA on the MPA.
`TMPA = Tlocai,nem * Slocabnem + Tdatamem * Ssharedmem
`(1)
`
`This approach is valid for protocol processing because most operations are memory operations to buil d
`a header or to compare header data with expected data in a control block . The control information i s
`built with simple arithmetical and logical operations such as add, multiply, and, or etc .
`4.2 Cost of Basic Operations
`The transputer T9000 is downwards compatible with the T425 used in the PPE . The main difference s
`are a higher link speed of 100 Mb/s, a sustained performance of more than 70 MIPS and a peak rate o f
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`200 MIPS . A function call or process switch costs less than 1 Rs . The sustained MIPS rate improves the
`performance at least seven times for the simple protocol processing operations . The memory function s
`are determined by the memory access time shown in Table 1 . The access time to the header memor y
`decreases by a factor of 19, the access time to the data memory by a factor of 9 .5. Therefore the full
`power of the processor can be utilized, and the typical speedup factor 1/10 [inmos 91] can be assumed fo r
`Sdaramem • The speedup factor to the local memory is determined by the processor speedup, because th e
`local memory and the cache provide an optimal memory interface to the processor . We assume a conser -
`vative speedup factor of Slocatmem = 1 /7 for the local memory .
`The costs of basic operations for protocol handling are listed in Table 2 . The connection detection an d
`the calculation of a CRC or a checksum are implemented in hardware . These operations run at networ k
`speed as the data is clocked in from the MACU . The T9000 improves the implementation of the distrib -
`uted shared memory, because the peek and poke calls are already implemented in the microcode . There-
`fore the costs of the distributed 'shared memory' are only the issuing of a peek or poke instruction .
`
`Number of Processor Instructions Estimated Time in n s
`3
`180
`4
`240
`3
`300 + size[word] * 46 0
`
`Processor Operation
`Queue read / write
`Linked List add/remove
`Distributed shared memory
`read/write
`0 (implemented in hardware)
`Connection detection
`0 (implemented in hardware)
`Checksum/CRC calculation
`Table 2. Cost of Basic Operation s
`
`network spee d
`network speed
`
`4.3 TCP/IP Performance
`The performance of TCP/IP is evaluated using the measurements of our TCP/IP implementation on th e
`PPE. The TCP stack, the socket layer and a test application run on the MPA . The cost of the single pro -
`cesses of TCP/IP is calculated using (1) . Table 3 lists the execution times on the PPE and the calculate d
`execution times on the MPA . In the PPE implementation of the IP processes 60% of the accesses go t o
`the shared memory, in tcp_send 47% and in tcp_recv 10% . In the MPA architecture all of thes e
`accesses are replaced by accesses to the header memory . In the user_task and the ip_intrsv c
`most processing is replaced by the list handling in the DMAU and the BC . However the write process i s
`still needed to control the send queue . All copy operations are implemented in the BC . The ip_demux
`process is supported by the HP, which extracts the header information .
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`Process (Procedure) on Receiver
`tcp_recv
`user_task (socket_recv/copy)
`ip_intrsvc
`ip_demux
`Process (Procedure) on Transmitter
`write
`tcp_snd_data
`ip_send
`driver_send
`Access to Shared Memory (poke call)
`Table 3 . Process Execution Time s
`
`PPE
`µs/Packet
`235
`31+ 0 .545µs/word
`9
`23
`µs/Packet
`30+ 0 .545µs/word
`147
`23
`17+ 0.27µs/word
`18 .6+2,4µs/word
`
`MPA
`µs/Packet
`25
`1
`-
`1 .7
`µs/Packe t
`4. 3
`9 .8
`1
`0.7
`0.3 + 0.46µs/word
`
`The TCP/IP process pipeline for bidirectional traffic is shown in Figure 4 . The throughput is deter -
`mined by tcp_recv and ip_demux, which add up to 26 .7 µs. The transmitter is less costly than i n
`the PPE implementation because of the faster network speed .
`. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
`user_task
`ip_send driver_sen d
`1 o7
`
`tcp_recv
`25
`
`Receiver
`
`ip_demu x
`1 .7
`
`Transmitter
`
`-
`
`DMAU
`
`writ e
`4 .3
`
`tcp_snd_dat a
`9 .8
`
`writ e
`4 .3
`copy
`15,4
`Figure 4 . TCP/IP Processin g
`
`tcp_snd_data
`9 .8
`
`The throughput calculated for unidirectional TCP/IP traffic between two MPA systems is 35720 TC P
`segments/s . For bidirectional traffic, the throughput is 20290 segments/s, if for every eight packets a n
`acknowledgment packet is sent . The throughput numbers are independent of the packet size because al l
`data copying is done in hardware overlapped to protocol processing . However for large packets, th e
`network becomes the bottleneck (4 kByte segments would result in more than 1 Gb/s)
`. If we assume a
`segment size of 1024 bytes, the throughput is 292 Mb/s which is more than most current workstation ca n
`handle.
`
`5. Conclusion
`The separation of isochronous and asynchronous traffic permits processing of isochronous multimedi a
`traffic at the network speed . The separate header and data memories provide optimized access to th e
`critical components . The parallelism between the transmitter and receiver is the most suitable form o f
`moderate parallelism to speed up protocol processing and to lower hardware contention .
`The hardware components such as the HP, CG and DMAU can be built to process one Gb/s . The MPA
`could then process multimedia streams at one Gb/s . A multimedia application could for example look a s
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`follows. The multimedia interface handles 700 Mb/s in hardware . The protocol processors perfor m
`transport protocol processing at a throughput of 300 Mb/s and forward the data to the workstation . This
`split of the bandwidth would make sense, because applications which require reliable transport connec-
`tions in the Gb/s range do not seem feasible in the near future because of the I/O bottleneck of th e
`workstations . However transport protocol processing at one Gb/s is already possible with an architec-
`ture based on the MPA .
`
`The efficient attachment of the subsystem to the workstation is yet unsolved . To take advantage of the
`high bandwidth available on the network and on the MPA, the current workstation hardware and soft -
`ware interfaces must be changed . Designing these interfaces especially for multimedia will be one o f
`the goals of future work.
`
`6. Reference s
`[Birch 92]
`
`Birch, J ., Christensen, L . G ., Skov, M ., "A programmable 800Mbit/s CRC check / gen-
`erator unit for LANs and MANs", Computer Networks and ISDN Systems, Nr . 24,
`North—Holland 1992 .
`Chin, H. W., Edholm, Ph., Schwaderer, D . W., "Implementing PE—1000 Based Inter -
`networking Nodes, Part 2 of 3", Transfer, Volume 5, Nr 3, March/April 1992 .
`Braun, T., Zitterbart, M ., "Parallel Transport System Design", IFIP Conference o n
`High Performance Networking, Liege (Belgium), 1992 .
`"The T9000 Transputer Products Overview Manual", inmos 1991 .
`Jain, N., Schwartz, M ., Bashkow, T. R., "Transport Protocol Processing at GBP S
`Rates", Proceedings of the SIGCOMM '90 Symposium , Sept . 1990.
`[Kaiserswerth 92] Kaiserswerth, M ., 'The Parallel Protocol Engine", IBM Research Report, RZ 229 8
`(#77818), March 1992 .
`Rutsche, E ., Kaiserswerth, M ., "TCP/IP on the Parallel Protocol Engine", Proceedings ,
`IFIP Conference on High Performance Networking, Liege (Belgium), Dec . 1992.
`Topolcic, C. (Editor), "Experimental Internet Stream Protocol, Version 2 (ST—II)" ,
`RFC 1190, Oct . 1990.
`Traw . B., Smith, J., "A High—Performance Host Interface for ATM Networks", Pro -
`ceedings ACM SIGCOMM '91, Zurich, Switzerland, Sept . 1991 .
`Stennkiste, P., et al ., "A Host Interface Architecture for High—Speed Network s", Pro -
`ceedings IFIP Conference on High Performance Networking, Liege (Belgium), Dec .
`1992.
`Wicki, T., "A Multiprocessor —Based Controller Architecture for High—Speed Commu-
`nication Protocol Processing", Doctoral Thesis, IBM Research Report, RZ 205 3
`(#72078), Vol 6, 1990 .
`
`[Chin 92]
`
`[Braun 92]
`
`[inmos 91]
`[Jain 90]
`
`[Rutsche 92 ]
`
`[Topolcic 90 ]
`
`[Traw 91 ]
`
`[Steenkiste 92 ]
`
`[Wicki 90]
`
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