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ZL50130 数据表(PDF) 18 Page - Zarlink Semiconductor Inc |
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ZL50130 数据表(HTML) 18 Page - Zarlink Semiconductor Inc |
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18 / 60 page  ZL50130 Data Sheet 18 Zarlink Semiconductor Inc. Features include: • Up to 24 bytes of higher layer protocol headers (layers 2 to 5) • Specific support for the following protocols: • UDP (RFC 768) • L2TP versions 2 and 3 (RFC 2661, draft-ietf-l2tpext-l2tp-base-02) • Ethernet PW (draft-ietf-pwe3-ethernet-encap) • Support for the following dynamic fields: • 16 bit checksum over header and data • 16 bit datagram length field • 8 and 16 bit sequence numbers 3.3 Packet Transmit The Packet Transmit block serves two main functions. Firstly, it directs the packets to the appropriate Ethernet MAC. Four separate queues are directed at each MAC, allowing different classes of service to be established. For instance, packets from the host can be given lower priority service than normal transmission packets. The queues can be managed either on a strict priority basis, or using Weighted Fair Queuing (WFQ). There is also a limit on the maximum number of packets in an individual queue. Beyond the limit packets are dropped, avoiding a large build-up in packet delay variation, and preventing the memory becoming full and thereby "crashing" the device. Secondly, the Packet Transmit block adds a header to the packet before it is sent out for transmission. Typically this contains the data-link and network layer headers (layers 2 and 3), such as Ethernet, IP and MPLS. While the main contents of this header are static and programmed by the user in a block of memory reserved for each context, certain fields can be dynamically adjusted by the block. These are the Ethernet, IPv4 and IPv6 length fields and the IPv4 identification field (effectively a sequence number). Once the packet header has been appended, any packets that are still smaller than the minimum Ethernet packet size (64 bytes) are padded. Features include: • Four separate queues to each Ethernet MAC, with different classes of service • Queue disciplines on packet interface are: • Weighted Fair Queuing with programmable weights • Strict Priority • Programmable drop threshold when queues get too big • Adds up to 64 bytes of layer 2 and layer 3 headers • Automatically adjusts Ethernet length, IP length and IP identification fields • Pads small packets to meet the 64 byte minimum Ethernet packet size • Packets can be directed to any of the four Ethernet MACs 3.4 Packet Receive The Packet Receive block handles two main functions: writing the packet into memory, and identifying the packet received. Packets are written into memory as they arrive at the device. A small buffer is used to cope with simultaneous requests for memory access. The device is capable of accepting packets on 3 ports in MII mode, either ports 0, 1 and 2, or ports 0, 1 and 3. |
类似零件编号 - ZL50130 |
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类似说明 - ZL50130 |
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